C (part 2)

The following figure and description will explain the construction of the three-ply imperial Scotch and two-ply Kidderminster carpet loom, which is merely a modification of the Jacquard métier. The Brussels carpet-loom, on the contrary, is a draw-boy loom on the damask plan, and requires the weaver to have an assistant. Fig. 270. A A A, is the frame of the loom, consisting of four upright posts, with caps and cross rails to bind them together. The posts are about six feet high. C C, the cloth-beam, is a wooden cylinder, six inches or thereby in diameter, of sufficient length to traverse the loom, with iron gudgeons in the two ends, which work in bushes in the side frame. On one end of this beam is a ratchet wheel, with a tooth to keep it from turning round backwards by the tension of the web. D, the lay, with its reed, its under and upper shell, its two lateral rulers or swords, and rocking-tree above. There are grooves in the upper and under shell, into which the reed is fitted. E, the heddles, or harness, with a double neck attached to each of the tower or card mechanisms F F, of the Jacquard loom. The heddles are connected and work with the treddles B B, by means of cords, as shown in the figure. G G are wooden boxes for the cards. H, the yarn, or warp beam.

In draw-looms of every kind, there is no sinking of any portion of the warp, as in plain cloth-weaving; but the plane of the warp is placed low, and the threads under which the shuttle is to pass are raised, while all the rest remains stationary. The harness part of this carpet loom is moved by an assistant boy or girl, who thus allows the weft to be properly decussated, while the weaver attends to working the front mounting or heddles. Fig. 271., A represents the frame of a carpet draw-loom; B is a box or frame of pulleys, over which the cords of the harness pass, and are then made fast to a piece of wood, seen at E, which the weavers call a table. From the tail of the harness the simples descend, and to the end of each is attached a small handle G, called a bob. These handles being disposed in pairs, and their regularity preserved by means of a perforated board C, it is merely necessary to pull every handle in succession; the weaver, at the same time, working his treddles with his feet, as in any other loom. The treddles are four in number, the fabric being that of plain or alternate cloth, and two treddles allotted for each web. The harness part of the carpet draw-loom is furnished with mails, or metallic eyes, to save friction; two threads being drawn through each eye. The design or pattern of a carpet is drawn upon cross-rule paper, exactly in the same way as every other kind of fancy-loom work, and is transferred from the paper to the mounting by the rules for damask weaving. Suppose that a double web is so mounted that every alternate thread of the one may be raised, so as to form a sufficient shed-way for the shuttle, without depressing the other in the least. Then suppose another web placed above the former, at such a distance that it will exactly touch the convexity of those threads of the former, which are raised. Then, if the threads of the latter web are sunk while the others are raised, the two would be entirely incorporated. But if this be only partially done, that is, at particular places, only those parts immediately operated upon will be affected by the action of the apparatus. If the carpet is a two-coloured pattern, as black and red, and if upon the upper surface, as extended in the loom, red flowers are to be represented upon a black ground, then all those species of design paper which are coloured may be supposed to represent the red, and those which are vacant the black. Then counting the spaces upon the paper, omit those which are vacant, and cord those which are coloured, and the effect will be produced. But as the two webs are to be raised alternately, whatever is corded for the first handle must be passed by for the second, and vice versâ; so that the one will form the flower, and the other the ground.

The board by which the simples are regulated appears at F. D shows the weights.

CARTHAMUS, or safflower (carthamus tinctorius), (Carthame, Fr.; Färber distel, Germ.), the flower of which alone is used in dyeing, is an annual plant cultivated in Spain, Egypt, and the Levant. There are two varieties of it—one which has large leaves, and the other smaller ones. It is the last which is cultivated in Egypt, where it forms a considerable article of commerce.

Carthamus contains two colouring matters, one yellow and the other red. The first alone is soluble in water; its solution is always turbid: with re-agents it exhibits the characters usually remarked in yellow colouring matters. The acids render it lighter, the alkalies deepen it, giving it more of an orange hue: both produce a small dun precipitate, in consequence of which it becomes clearer. Alum forms a precipitate of a deep yellow, in small quantity. The solution of tin and the other metallic solutions cause precipitates which have nothing remarkable in them.

The yellow matter of carthamus is not employed; but in order to extract this portion, the carthamus is put into a bag, which is trodden under water, till no more colour can be pressed out. The flowers, which were yellow, become reddish, and lose in this operation nearly one half of their weight. In this state they are used.

For extracting the red part of carthamus, and thereafter applying it to stuff, the property which alkalies possess of dissolving it is had recourse to, and it is afterwards precipitated by an acid.

The process of dyeing consists, therefore, in extracting the colouring matter by means of an alkali, and precipitating it on the stuff by means of an acid. It is this fecula which serves for making the rouge employed by ladies.

As to this rouge, the solution of carthamus is prepared with crystallised carbonate of soda, and it is precipitated by lemon juice. It has been remarked that lemons, beginning to spoil, were fitter for this operation than those which were less ripe, whose juice retained much mucilage. After squeezing out the lemon juice, it is left to settle for some days. The precipitate of carthamus is dried at a gentle heat upon plates of stone-ware; from which it is detached and very carefully ground with talc, which has been reduced to a very subtile powder, by means of the leaves of shave-grass (presle), and successively passed through sieves of increasing fineness. It is the fineness of the talc, and the greater or less proportion which it bears to the carthamus precipitate, which constitute the difference between the high and low priced rouges.

Carthamus is used for dyeing silk, poppy, nacarat (a bright orange-red), cherry, rose colour, and flesh colour. The process differs according to the intensity of the colour, and the greater or less tendency to flame colour that is wanted. But the carthamus bath, whose application may be varied, is prepared as follows:

The carthamus, from which the yellow matter has been extracted, and whose lumps have been broken down, is put into a trough. It is repeatedly sprinkled with cendres gravelées (crude pearl ashes), or soda (barilla) well powdered and sifted at the rate of 6 pounds for 120 lbs. of carthamus; but soda is preferred, mixing carefully as the alkali is introduced. This operation is called amestrer. The amestred carthamus is put into a small trough with a grated bottom, first lining this trough with a closely woven cloth. When it is about half filled, it is placed over the large trough, and cold water is poured into the upper one, till the lower becomes full. The carthamus is then set over another trough, till the water comes from it almost colourless. A little more alkali is now mixed with it, and fresh water is passed through it. These operations are repeated till the carthamus be exhausted, when it turns yellow.

After distributing the silk in hanks upon the rods, lemon juice, brought in casks from Provence, is poured into the bath till it becomes of a fine cherry colour; this is called turning the bath (virer le bain). It is well stirred, and the silk is immersed and turned round the skein-sticks in the bath, as long as it is perceived to take up the colour. For ponceau (poppy colour), it is withdrawn, the liquor is run out of it upon the peg, and it is turned through a new bath, where it is treated as in the first. After this it is dried and passed through fresh baths, continuing to wash and dry it between each operation, till it has acquired the depth of colour that is desired. When it has reached the proper point, a brightening is given it by turning it round the sticks seven or eight times in a bath of hot water, to which about half a pint of lemon juice for each pailful of water has been added.

When silk is to be dyed ponceau or flame colour, it must be previously boiled as for white; it must then receive a slight foundation of annotto, as explained in treating of this substance. The silk should not be alumed.

The nacarats, and the deep cherry colours, are given precisely like the ponceaux, only they receive no annotto ground; and baths may be employed which have served for the ponceau, so as to complete their exhaustion. Fresh baths are not made for the latter colours, unless there be no occasion for the poppy.

With regard to the lighter cherry-reds, rose colour of all shades and flesh colours, they are made with the second and last runnings of the carthamus, which are weaker. The deepest shades are passed through first.

The lightest of all these shades, which is an extremely delicate flesh colour, requires a little soap to be put into the bath. This soap lightens the colour, and prevents it from taking too speedily, and becoming unevenly. The silk is then washed, and a little brightening is given it, in a bath which has served for the deeper colours.

All these baths are employed the moment they are made, or as speedily as possible, because they lose much of their colour upon keeping, by which they are even entirely destroyed at the end of a certain time. They are, moreover, used cold, to prevent the colour from being injured. It must have been remarked in the experiments just described, that the caustic alkalies attack the extremely delicate colour of carthamus, making it pass to yellow. This is the reason why crystals of soda are preferred to the other alkaline matters.

In order to diminish the expense of the carthamus, it is the practice in preparing the deeper shades to mingle with the first and the second bath about one fifth of the bath of archil.

Dobereiner regards the red colouring matter of carthamus as an acid, and the yellow as a base. His carthamic acid forms, with the alkalies, colourless salts, decomposed by the tartaric and acetic acids, which precipitate the acid of a bright rose-red. Heat has a remarkable influence upon carthamus, rendering its red colour yellow and dull. Hence, the colder the water is by which it is extracted, the finer is the colour. Light destroys the colour very rapidly, and hitherto no means have been found of counteracting this effect. For this reason this brilliant colour must be dried in the shade, its dye must be given in a shady place, and the silk stuffs dyed with it must be preserved as much as possible from the light. Age is nearly as injurious as light, especially upon the dye in a damp state. The colour is very dear, because a thousand parts of carthamus contain only five of it.

In preparing the finest rouge, the yellow colouring matter being separated by washing with water, the red is then dissolved by the aid of alkali, and is thrown down on linen or cotton rags by saturating the solution with vegetable acid. The colour is rinsed out of these rags, dissolved anew in alkalis, and once more precipitated by lemon juice. The best and freshest carthamus must be selected. It is put into linen bags, which are placed in a stream of water, and kneaded till the water runs off colourless. The bags are then put into water soured with a little vinegar, kneaded till the colour is all expelled, and finally rinsed in running water. By this treatment the carthamus loses nearly half its weight. 6633 cwts. of safflower were imported into the United Kingdom in 1835, of which 2930 cwts. were retained for internal consumption.

CASE-HARDENING, is the name of the process by which iron tools, keys, &c., have their surfaces converted into steel.

Steel when very hard is brittle, and iron alone is for many purposes, as for fine keys, far too soft. It is therefore an important desideratum to combine the hardness of a steely surface with the toughness of an iron body. These requisites are united by the process of case-hardening, which does not differ from the making of steel, except in the shorter duration of the process. Tools, utensils, or ornaments, intended to be polished, are first manufactured in iron and nearly finished, after which they are put into an iron box, together with vegetable or animal charcoal in powder, and cemented for a certain time. This treatment converts the external part into a coating of steel, which is usually very thin, because the time allowed for the cementation is much shorter than when the whole substance is intended to be converted. Immersion of the heated pieces into water hardens the surface, which is afterwards polished by the usual methods. Moxon in his Mechanic Exercises, p. 56., gives the following receipt for case-hardening:—“Cow’s horn or hoof is to be baked or thoroughly dried and pulverised. To this add an equal quantity of bay salt; mix them with stale chamber-lye or white wine vinegar: cover the iron with this mixture, and bed it with the same in loam, or enclose it in an iron box: lay it on the hearth of the forge to dry and harden: then put it into the fire, and blow till the lump have a blood-red heat, and no higher, lest the mixture be burnt too much. Take the iron out, and immerse it in water to harden.” I consider the vinegar to be quite superfluous.

I shall now describe the recent application of prussiate (ferrocyanate) of potash to this purpose. The piece of iron, after being polished, is to be made brightly red-hot, and then rubbed or sprinkled over with the above salt in fine powder, upon the part intended to be hardened. The prussiate being decomposed, and apparently dissipated, the iron is to be quenched in cold water. If the process has been well managed, the surface of the metal will have become so hard as to resist the file. Others propose to smear over the surface of the iron with loam made into a thin paste with a strong solution of the prussiate, to dry it slowly, then expose the whole to a nearly white heat, and finally plunge the iron into cold water, when the heat has fallen to dull redness. See Steel.

CASHMERE or CACHEMERE, a peculiar textile fabric first imported from the kingdom of Cashmere, and now well imitated in France and Great Britain. The material of the Cashmere shawls is the downy wool found about the roots of the hair of the Thibet goat. The year 1819 is remarkable in the history of French husbandry for the acquisition of this breed of goats, imported from the East under the auspices of their government, by the indefatigable courage and zeal of M. Jaubert, who encountered every fatigue and danger to enrich his country with these valuable animals, aided by the patriotism of M. Ternaux, who first planned this importation, and furnished funds for executing it at his own expence and responsibility. He placed a portion of the flock brought by M. Jaubert, at his villa of Saint Ouen, near Paris, where the climate seemed to be very favourable to them, since for several successive years after their introduction M. Ternaux was enabled to sell a great number of both male and female goats. The quantity of fine fleece or down afforded by each animal annually, is from a pound and a half to two pounds.

The wool imported into Europe comes by the way of Casan, the capital of a government of the Russian empire upon the eastern bank of the Wolga; it has naturally a grayish colour, but is easily bleached. Its price a few years back at Paris was 17 francs per kilogramme; that is, about 6 shillings the pound avoirdupois. The waste in picking, carding, and spinning, amounts to about one third of its weight.

The mills for spinning Cachemere wool have multiplied very much of late years in France, as appears from the premiums distributed at the exposition of 1834, and the prices of the yarn have fallen from 25 to 30 per cent. notwithstanding their improved fineness and quality. There is a fabric made with a mixture of Cachemere down and spun silk, which is becoming very general. One of the manufacturers, M. Hindenlang, exhibited samples of Cachemere cloth woven with yarn so fine as No. 130 for warp, and No. 228 for weft.

Messrs. Pollino, brothers, of Paris, produced an assortment of Cachemere pieces from 22 to 100 francs the yard, dyed of every fancy shade. Their establishment at Ferté-Bernard occupies 700 operatives, with an hydraulic wheel of 60 horse power.

The oriental Cashmere shawls are woven by processes extremely slow and consequently costly; whence their prices are very high. They are still sold in Paris at from 4,000 to 10,000 francs a piece; and from 100 to 400 pounds sterling in London. It became necessary therefore either to rest satisfied with work which should have merely a surface appearance, or contrive economical methods of weaving, to produce the real Cachemere style with much less labour. By the aid of the draw-loom and still better of the Jacquard loom, M. Ternaux first succeeded in weaving Cachemere shawls perfectly similar to the oriental in external aspect, which became fashionable under the name of French Cachemere. But to construct shawls altogether identical on both sides with the eastern, was a more difficult task, which was accomplished only at a later period by M. Bauson of Paris.

In both modes of manufacture, the piece is mounted by reading-in the warp for the different leaves of the heddles, as is commonly practised for warps in the Jacquard looms. The weaving of imitation shawls is executed, as usual, by as many shuttles as there are colours in the design, and which are thrown across the warp in the order established by the reader. The greater number of these weft yarns being introduced only at intervals into the web, when the composition of the pattern requires it, they remain floating loose at the back of the piece, and are cut afterwards, without affecting in the least the quality of the texture; but there is a considerable waste of stuff in the weaving, which is worked up into carpets.

The weaving of the imitation of real Cachemere shawls is different from the above. The yarns intended to form the weft are not only equal in number to that of the colours of the pattern to be imitated, but besides this, as many little shuttles or pirns (like those used by embroiderers) are filled with these yarns, as there are to be colours repeated in the breadth of the piece; which renders their number considerable when the pattern is somewhat complicated and loaded with colours. Each of these small bobbins or shuttles passes through only that portion of the flower in which the colour of its yarn is to appear, and stops at the one side and the other of the cloth exactly at its limit; it then returns upon itself after having crossed the thread of the adjoining shuttle. From this reciprocal intertexture of all the yarns of the shuttles, it results, that although the weft is composed of a great many different threads, they no less constitute a continuous line in the whole breadth of the web, upon which the lay or batten acts in the ordinary way We see therefore that the whole art of manufacturing this Cachemere cloth consists in avoiding the confusion of the shuttles, and in not striking up the lay till all have fulfilled their function. The labour does not exceed the strength of a woman, even though she has to direct the loom and work the treddles. Seated on her bench at the end opposite to the middle of the beam, she has for aids in weaving shawls from 45 to 52 inches wide, two girl apprentices, whom she directs and instructs in their tasks. About four hundred days of work are required for a Cachemere shawl of that breadth. For the construction of the loom, see Jacquard.

In the oriental process all the figures in relief are made simply with a slender pirn without the shuttle used in European weaving. By the Indians the flower and its ground are made with the pirn, by means of an intertwisting, which renders them in some measure independent of the warp. In the Lyons imitation of this style, the leaves of the heddles lift the yarns of the warp, the needles embroider as in lappett weaving, and the flower is united to the warp by the weft thrown across the piece. Thus a great deal of labour is saved, the eye is pleased with an illusion of the loom, and the shawls cost little more than those made by the common fly shuttle.

Considered in reference to their materials, the French shawls present three distinct classes, which characterise the three fabrics of Paris, Lyons, and Nimes.

Paris manufactures the French Cachemere, properly so called, of which both the warp and the weft are the yarn of pure Cachemere down. This web represents with fidelity the figures and the shades of colour of the Indian shawl, which it copies; the deception would be complete if the reverse of the piece did not show the cut ends. The Hindoo shawl, also woven at Paris, has its warp in spun silk, which reduces its price without impairing its beauty much.

Lyons however has made the greatest progress in the manufacture of shawls. It excels particularly in the texture of its Thibet shawls, the weft of which is yarn spun with a mixture of wool and spun silk.

Nimes is remarkable for the low price of its shawls, in which spun silk, Thibet down, and cotton, are all worked up together.

The value of shawls exported from France in the following years was:—

1831. 1832. 1833.

Francs. Francs. Francs.

Woollen 1,863,147 2,070,926 4,319,601

Cachemere down 433,410 655,200 609,900

Spun silk 401,856 351,152 408,824

It appears that M. J. Girard at Sèvres, near Paris, has succeeded best in producing Cachemere shawls equal in stuff and style of work to the oriental, and at a lower price. They have this advantage over the Indian shawls, that they are woven without seams, in a single piece, and exhibit all the variety and the raised effect of the eastern colours. Women and children alone are employed in his factory.

CASK, (Tonneau, Fr.; Fass, Germ.) manufacture of by mechanical power. Mr. Samuel Brown obtained a patent in Nov., 1825, for certain improvements in machinery for making casks, which seems to be ingenious and worthy of record. His mechanism consists in the first place of a circular saw attached to a bench, with a sliding rest, upon which rest each piece of wood intended to form a stave of a cask is fixed; and the rest being then slidden forward in a curved direction, by the assistance of an adjustable guide, brings the piece of wood against the edge of the rotatory saw, and causes it to be cut into the curved shape required for the edge of the stave. The second feature is an apparatus with cutters attached to a standard, and traversing round with their carrier upon a centre, by means of which the upper and lower edges of the cask are cut round and grooved, called chining, for the purpose of receiving the heads. Thirdly, an apparatus not very dissimilar to the last, by which the straight pieces of wood designed for the heads of the cask are held together, and cut to the circular figure required, and also the bevelled edges produced. And fourthly, a machine in which the cask is made to revolve upon an axis, and a cutting tool to traverse for the purpose of shaving the external part of the cask, and bringing it to a smooth surface.

The pieces of wood intended to form the staves of the cask, having been cut to their required length and breadth, are placed upon the slide-rest of the first mentioned machine, and confined by cramps; and the guide, which is a flexible bar, having been previously bent to the intended curve of the stave and fixed in that form, the rest is then slidden forward upon the bench by the hand of the workman, which as it advances (moving in a curved direction) brings the piece of wood against the edge of the revolving circular saw, by which it is cut to the curved shape desired.

The guide is a long bar held by a series of movable blocks fitted to the bench by screws, and is bent to any desired curve by shifting the screws: the edge of the slide-rests which holds the piece of wood about to be cut, runs against the long guide bar, and of consequence is conducted in a corresponding curved course. The circular saw receives a rapid rotatory motion by means of a band or rigger from any first mover; and the piece of wood may be shifted laterally by means of racks and pinions on the side-rest, by the workman turning a handle, which is occasionally necessary in order to bring the piece of wood up to, or away from, the saw.

The necessary number of staves being provided, they are then set round within a confining hoop at bottom, and brought into the form of a cask in the usual way, and braced by temporary hoops. The barrel part of the cask being thus prepared, in order to effect the chining, it is placed in a frame upon a platform, which is raised up by a treddle lever, that the end of the barrel may meet the cutters in a sort of lathe above: the cutters are then made to traverse round within the head of the barrel, and, as they proceed, occasionally to expand, by which means the bevels and grooves are cut on the upper edge of the barrel, which is called chining. The barrel being now reversed, the same apparatus is brought to act against the other end, which becomes chined in like manner.

The pieces of wood intended to form the heads of the cask are now to be cut straight by a circular saw in a machine, similar to the first described; but in the present instance the slide-rest is to move forward in a straight course. After their straight edges are thus produced, they are to be placed side by side, and confined, when a scribing cutter is made to traverse round, and cut the pieces collectively into the circular form desired for heading the cask.

The cask having now been made up, and headed by hand as usual, it is placed between centres, or upon an axle in a machine, and turned round by a rigger or band with a shaving cutter, sliding along a bar above it, which cutter being made to advance, and recede as it slides along, shaves the outer part of the cask to a smooth surface.

CASSAVA. Cassava bread, conaque, &c., are different names given to the starch of the root of the Manioc (Jatropha Manihot, Linn.), prepared in the following manner in the West Indies, the tropical regions of America, and upon the African coast. The tree belongs to the natural family of the euphorbiaceæ.

The roots are washed, and reduced to a pulp by means of a rasp or grater. The pulp is put into coarse strong canvas bags, and thus submitted to the action of a powerful press, by which it parts with most of its noxious juice (used by the Indians for poisoning the barbs of their arrows). As the active principle of this juice is volatile, it is easily dissipated by baking the squeezed cakes of pulp upon a plate of hot iron. Fifty pounds of the fresh juice, when distilled, afford, at first, three ounces of a poisonous water, possessing an intolerably offensive smell; of which, 35 drops being administered to a slave convicted of the crime of poisoning, caused his death in the course of six minutes, amid horrible convulsions.

The pulp dried in the manner above described concretes into lumps, which become hard and friable as they cool. They are then broken into pieces, and laid out in the sun to dry. In this state they afford a wholesome nutriment, and are habitually used as such by the negroes, as also by many white people. These cakes constitute the only provisions laid in by the natives, in their voyages upon the Amazons. Boiled in water with a little beef or mutton they form a kind of soup similar to that of rice.

The Cassava cakes sent to Europe (which I have eaten with pleasure) are composed almost entirely of starch, along with a few fibres of the ligneous matter. It may be purified by diffusion through warm water, passing the milky mixture through a linen cloth, evaporating the strained liquid over the fire, with constant agitation. The starch dissolved by the heat, thickens as the water evaporates, but on being stirred, it becomes granulated, and must be finally dried in a proper stove. Its specific gravity is 1·530—that of the other species of starch.

The product obtained by this treatment is known in commerce under the name of tapioca; and being starch very nearly pure, is often prescribed by physicians as an aliment of easy digestion. A tolerably good imitation of it is made by heating, stirring, and drying potato starch in a similar way.

The expressed juice of the root of manioc contains in suspension a very fine fecula, which it deposits slowly upon the bottom of the vessels. When freed by decantation from the supernatant liquor, washed several times and dried, it forms a beautiful starch, which creaks on pressure with the fingers. It is called cipipa, in French Guyana; it is employed for many delicate articles of cookery, especially pastry, as also for hair powder, starching linen, &c.

Cassava flour, as imported, may be distinguished from arrow-root and other kinds of starch, by the appearance of its particles viewed in a microscope. They are spherical, all about 1-1000th of an inch in diameter, and associated in groups; those of potato starch are irregular ellipsoids, varying in size from 1-300th to 1-3000th of an inch; those of arrow-root have the same shape nearly, but vary in size from 1-500th to 1-800th of an inch; those of wheat are separate spheres 1-1000th of an inch.

CASSIS, the black currant (ribes nigra, Linn.), which was formerly celebrated for its medicinal properties with very little reason.

The only technical use to which it is now applied is in preparing the agreeable liqueur called ratafia, by the following French recipe:—Stone, and crush three pounds of black currants, adding to the magma one drachm of cloves, two of cinnamon, four quarts of spirit of wine, at 18° Baumé (see Aréomètre of Baumé), and 2⁄2 pounds of sugar. Put the mixture into a bottle which is to be well corked; let it digest for a fortnight, shaking the bottle once daily during the first eight days; then strain through a linen cloth, and finally pass through filtering paper.

CASTING OF METALS. (See Founding.) Casts from elastic moulds.—Being much engaged in taking casts from anatomical preparations, Mr. Douglas Fox, Surgeon, Derby, found great difficulty, principally with hard bodies, which, when undercut, or having considerable overlaps, did not admit of the removal of moulds of the ordinary kind, except with injury. These difficulties suggested to him the use of elastic moulds, which, giving way as they were withdrawn from complicated parts, would return to their proper shape; and he ultimately succeeded in making such moulds of glue, which not only relieved him from all his difficulties, but were attended with great advantages, in consequence of the small number of pieces into which it was necessary to divide the mould.

The body to be moulded, previously oiled, must be secured one inch above the surface of a board, and then surrounded by a wall of clay, about an inch distant from its sides. The clay must also extend rather higher than the contained body: into this, warm melted glue, as thick as possible so that it will run, is to be poured, so as to completely cover the body to be moulded; the glue is to remain till cold, when it will have set into an elastic mass, just such as is required.

Having removed the clay, the glue is to be cut into as many pieces as may be necessary for its removal, either by a sharp-pointed knife, or by having placed threads in the requisite situations of the body to be moulded, which may be drawn away when the glue is set, so as to cut it out in any direction.

The portions of the glue mould having been removed from the original, are to be placed together and bound round by tape.

In some instances it is well to run small wooden pegs through the portions of glue, so as to keep them exactly in their proper positions. If the mould be of considerable size, it is better to let it be bound with moderate tightness upon a board to prevent it bending whilst in use; having done as above described, the plaster of Paris, as in common casting, is to be poured into the mould, and left to set.

In many instances wax may also be cast in glue, if it is not poured in whilst too hot; as the wax cools so rapidly when applied to the cold glue, that the sharpness of the impression is not injured.

Glue has been described as succeeding well where an elastic mould is alone applicable; but many modifications are admissible. When the moulds are not used soon after being made, treacle should be previously mixed with the glue (as employed by printers) to prevent it becoming hard.

The description thus given is with reference to moulding those bodies which cannot be so done by any other than an elastic mould; but glue moulds will be found greatly to facilitate casting in many departments, as a mould may be frequently taken by this method in two or three pieces, which would, on any other principle, require many.

CASTOR. (Eng. and Fr.; Biber, Germ.) The castor is an amphibious quadruped, inhabiting North America; also found in small numbers in the islands of the Rhone. In the arts, the skin of this animal is employed either as a fur or as affording the silky hair called beaver, with which the best hats are covered. Beaver skins, which form a very considerable article of trade, are divided into 3 sorts: 1. The fresh beaver skins from castors, killed in winter before shedding their hair; these are most in request among the furriers, as being the most beautiful. 2. The dry or lean beavers are the skins of the animals killed during the moulting season; they are not much esteemed, as the skin is rather bare. 3. The fat castors: these are the skins of the first sort, which have been worn for some time upon the persons of the savages and have got imbued with their sweat. The last are principally used in the hat manufacture. In France, the marine otter has been for many years substituted in the place of the castor or beaver.

CASTOR or CASTOREUM. This name is given to a secretion of the castors, contained in pear-shaped cellular organic sacs, placed near the genital organs of both the male and female animals. It is a substance analogous to civet and musk, of a consistence similar to thick honey. It has a bitter acrid taste; a powerful, penetrating, fetid, and very volatile smell; but, when dried, it becomes inodorous. Several chemists, and in particular Bouillon Lagrange, Laugier, and Hildebrandt have examined castor; and found it to be composed of a resin, a fatty substance, a volatile oil, an extractive matter, benzoic acid, and some salts.

The mode of preparing it is very simple. The sacs are cut off from the castors when they are killed, and are dried to prevent the skin being affected by the weather. In this state, the interior substance is solid, of a dark colour, and a faint smell; it softens with heat, and becomes brittle by cold. Its fracture betrays fragments of membranes, indicating its organic structure. When chewed, it adheres to the teeth somewhat like wax; it has a bitter, slightly acrid, and nauseous taste.

The castor bags, as imported, are often joined in pairs by a kind of ligature. Sometimes the substance which constitutes their value is sophisticated; a portion of the castoreum being extracted, and replaced by lead, clay, gums, or some other foreign matters. This fraud may be easily detected, even when it exists in a small degree, by the absence of the membranous partitions in the interior of the bags, as well as by the altered smell and taste.

The use of castoreum in medicine is considerable, especially in nervous and spasmodic diseases, and it is often advantageously combined with opium.

CASTORINE. A chemical principle lately discovered to the amount of a few parts per cent. in Castoreum.

CASTOR OIL. The expressed oil of the seeds of the Palma Christi, or Ricinus communis, a native tree of the West Indies and South America; but which has been cultivated in France, Italy, and Spain. Bussy and Lecanu discovered in it 3 species of fatty matters, obtained partly by saponification, and partly by dry distillation—the margaritic, ricinic, and elaiodic acids. None of these has been separately applied to any use in the arts.

The quantity of castor oil imported in 1835 into the United Kingdom, was 1,109,307 libs.; retained for home consumption, 670,205 libs. See Oils.

CATECHU, absurdly called Terra Japonica, is an extract made from the wood of the tree mimosa catechu, which grows in Bombay, Bengal, and other parts of India. It is prepared by boiling the chips of the interior of the trunk in water, evaporating the solution to the consistence of syrup over the fire, and then exposing it in the sun to harden. It occurs in flat rough cakes, and under two forms. The first, or the Bombay, is of uniform texture, of a dark red colour, and of specific gravity 1·39. The second is more friable and less solid. It has a chocolate colour, and is marked inside with red streaks. Its specific gravity is 1·28.

According to Sir H. Davy, these two species are composed as follows:—

Bombay. Bengal.

Tannin 54 ·5 48 ·5

Extractive 34 ·0 36 ·5

Mucilage 6 ·5 8

Insoluble matters, sand and lime 5 7

100 ·0 100 ·0

Areka nuts are also found to yield catechu; for which purpose they are cut into pieces watered in an earthen pot with solution of nitre, and have a little of the bark of a species of mimosa added to them. The liquor is then boiled with the nuts, and affords an inspissated decoction.

Good catechu is a brittle, compact solid, of a dull fracture. It has no smell, but a very astringent taste. Water dissolves the whole of it, except the earthy matter, which is probably added during its preparation. Alcohol dissolves its tannin and extractive. The latter may be oxidized, and thus rendered insoluble in alcohol, by dissolving the catechu in water, exposing it for some time to a boiling heat, and evaporating to dryness.

The tannin of catechu differs from that of galls, in being soluble in alcohol, and more soluble in water. It precipitates iron of an olive colour, and gelatine in a mass which gradually becomes brown.

It has been long employed in India for tanning skins, where it is said to effect this object in five days. I have seen a piece of sole leather completely tanned by it in this country in ten days, the ox-hide having been made into a bag, with the hair outside, and kept filled with the solution of catechu. In India it has also been used to give a brown dye to cotton goods, and of late years it has been extensively introduced into the calico print-works of Europe. The salts of copper with sal ammoniac cause it to give a bronze colour, which is very fast; the proto-muriate of tin, a brownish yellow; the per-chloride of tin, with the addition of nitrate of copper, a deep bronze hue; acetate of alumina alone, a reddish brown, and, with nitrate of copper, a reddish olive gray; nitrate of iron, a dark brown gray. For dyeing a golden coffee brown, it has entirely superseded madder; one pound of it being equivalent to six pounds of this root.

A solution of one part of catechu in ten parts of water, which is reddish brown, exhibits the following results with—

Acids A brightened shade.

Alkalis A darkened shade.

Proto-sulphate of iron Olive brown precipitate.

Per-sulphate of iron Olive green do.

Sulphate of copper Yellowish brown.

Alum A brightening of the liquor.

Per-nitrate of iron Olive green precipitate.

Nitrate of copper Yellowish brown do.

Nitrate of lead Salmondo.

Proto-nitrate of mercury Milk-coffee do.

Muriate of alumina Brown yellow.

Muriate of tin Do. do.

Per-chloride of tin Do.darker.

Corrosive sublimate Light chocolate do.

Acetate of alumina Brightening of the liquor.

Acetate of copper Copious brown precipitate.

Acetate of lead Salmon coloureddo.

Bichromate of potash Copious browndo.

Pure tannin may be obtained from catechu, by treating it with sulphuric acid and carbonate of lead; but this process has no manufacturing application.

CATGUT, (Corde à boyau, Fr.; Darmsaite, Germ.) the name absurdly enough given to cords made of the twisted intestines of the sheep. The guts being taken while warm out of the body of the animal, are to be cleared of feculent matter, freed from any adhering fat, and washed in a tub of water. The small ends of all the intestines are next to be tied together, and laid on the edge of the tub, while the body of them is left to steep in some water, frequently changed, during two days, in order to loosen the peritoneal and mucous membranes. The bundle of intestines is then laid upon a sloping table which overhangs the tub, and their surface is scraped with the back of a knife, to try if the external membrane will come away freely in breadths of about half the circumference. This substance is called by the French manufacturers filandre, and the process filer. If we attempt to remove it by beginning at the large end of the intestine, we shall not succeed. This filandre is employed as thread to sew intestines, and to make the cords of rackets and battledores. The flayed guts are put again into fresh water, and after steeping a night, are taken out and scraped clean next day, on the wooden bench with the rounded back of a knife. This is called curing the gut. The large ends are now cut off, and sold to the pork-butchers. The intestines are again steeped for a night in fresh water, and the following day in an alkaline lixivium made by adding 4 ounces of potash, and as much pearlash, to a pail of water containing about 3 or 4 imperial gallons. This lye is poured in successive quantities upon the intestines, and poured off again, after 2 or 3 hours, till they be purified. They are now drawn several times through an open brass thimble, and pressed against it with the nail, in order to smooth and equalize their surface. They are lastly sorted, according to their sizes, to suit different purposes.

Whip-cord is made from the above intestines, which are sewed together endwise by the filandre, each junction being cut aslant, so as to make it strong and smooth. The cord is put into the frame, and each end is twisted separately; for whip-cord is seldom made out of two guts twisted together. When twisted it is to be sulphured (see Sulphuring) once or twice. It may also be dyed black with common ink, pink with red ink, which the sulphurous acid changes to pink, and green with a green dye which the colour dealers sell for the purpose. The guts take the dyes readily. After being well smoothed, the cord is to be dried, and coiled up for sale.

Hatter’s cords for bowstrings.—The longest and largest intestines of sheep, after being properly treated with the potash, are to be twisted 4, 6, 8, 10, or 12 together, according to the intended size of the cord, which is usually made from 15 to 25 feet long. This cord must be free from seams and knots. When half dry, it must be exposed twice to the fumes of burning sulphur; and, after each operation, it is to be well stretched and smoothed; it should be finally dried in a state of tension.

Clockmaker’s cord.—This cord should be extremely thin, and be therefore made from very small intestines, or from intestines slit up in their length by a knife fitted for the purpose; being a kind of lancet surmounted with a ball of lead or wood. The wet gut is strained over the ball which guides the knife, and the two sections fall down into a vessel placed beneath. Each hand pulls a section. Clockmakers also make use of stronger cords made of 2 or more guts twisted together.

Fiddle and harp strings.—These require the greatest care and dexterity on the part of the workmen. The treble strings are peculiarly difficult to make, and are best made at Naples, probably because their sheep, from their small size and leanness, afford the best raw material.

The first scraping of the guts intended for fiddle-strings must be very carefully performed; and the alkaline lyes being clarified with a little alum, are added, in a progressively stronger state from day to day, during 4 or 5 days, till the guts be well bleached and swollen. They must then be passed through the thimble, and again cleansed with the lixivium; after which they are washed, spun, or twisted and sulphured during two hours. They are finally polished by friction, and dried. Sometimes they are sulphured twice or thrice before being dried, and are polished between horse-hair cords.

It has been long a subject of complaint, as well as a serious inconvenience to musicians, that catgut strings cannot be made in England of the same goodness and strength as those imported from Italy. These are made of the peritoneal covering of the intestines of the sheep; and, in this country, they are manufactured at Whitechapel, and probably elsewhere in considerable quantity; the consumption of them for harps, as well as for the instruments of the violin family, being very great. Their chief fault is weakness; whence it is difficult to bring the smaller ones, required for the higher notes, to concert pitch; maintaining at the same time, in their form and construction, that tenuity or smallness of diameter, which is required to produce a brilliant and clear tone.

The inconvenience arising from their breaking when in use, and the expense in the case of harps, where so many are required, are such as to render it highly desirable to improve a manufacture which, to many individuals may, however, appear sufficiently contemptible.

It is well known to physiologists, that the membranes of lean animals are far more tough than of those animals which are fat or in high condition; and there is no reason to doubt that the superiority of the Italian strings arises from the state of the sheep in that country. In London, where no lean animals are slaughtered, and where, indeed, an extravagant and useless degree of fattening, at least for the purpose of food, is given to sheep in particular, it is easy to comprehend why their membranes can never afford a material of the requisite tenacity. It is less easy to suggest an adequate remedy; but a knowledge of the general principle, should this notice meet the eyes of those interested in the subject, may at least serve the purpose of diminishing the evil and improving the manufacture, by inducing them to choose in the market the offal of such carcases as appear least overburthened with fat. It is probable that such a manufacture might be advantageously established in those parts of the country where the fashion has not, as in London, led to the use of meat so much overfed; and it is equally likely, that in the choice of sheep for this purpose, advantage would arise from using the Welch, the Highland, or the Southdown breeds, in preference to those which, like the Lincoln, are prone to excessive accumulations of fat. It is equally probable, that sheep dying of some of the diseases accompanied by emaciation, would be peculiarly adapted to this purpose.

That these suggestions are not merely speculative is proved by comparing the strength of the membranes in question, or that of the other membranous parts, in the unfattened Highland sheep, with that of those found in the London markets.

CATHARTINE. The name proposed by MM. Feneulle and Lassaigne for a chemical principle, which they suppose to be the active constituent of senna.

CAUSTIC. Any chemical substance corrosive of the skin and flesh; as potash, called common caustic, and nitrate of silver, called lunar caustic, by surgeons.

CAVIAR. The salted roe of certain species of fish, especially the sturgeon. This product forms a considerable article of trade, being exported annually from the town of Astrachan alone, upon the shores of the Caspian sea, to the amount of several hundred tons. The Italians first introduced it into Eastern Europe from Constantinople, under the name of caviale. Russia has now monopolized this branch of commerce. It is prepared in the following manner:—

The female sturgeon is gutted; the roe is separated from the other parts, and cleaned by passing it through a very fine searce, by rubbing it into a pulp between the hands: this is afterwards thrown into tubs, with the addition of a considerable quantity of salt; the whole is then well stirred, and set aside in a warm apartment. There is another sort of caviar, the compressed, in which the roe, after having been cured in strong brine, is dried in the sun, then put into a cask, and subjected to strong pressure.

CAWK. The English miner’s name for sulphate of baryta, or heavy spar.

CEDRA, (Cedrat, Fr.) is the fruit of a species of orange, citron, or lemon, a tree which bears the same name. Its peel is very thick, and covered with an epidermis which encloses a very fragrant and highly prized essential oil. The preserves flavoured with it are very agreeable. The citrons are cut into quarters for the dry comfits, but are put whole into the liquid ones. The liquorist-perfumer makes with the peel of the cedra an excellent liqueur; for which purpose, he plucks them before they are quite ripe; grates down the peel into a little brandy, or cuts them into slices, and infuses these in the spirits. This infusion is distilled for making perfume; but the flavour is better when the infusion itself is used. See Essences, Liquorist, Perfumery.

CELESTINE. Native sulphate of strontia, found abundantly near Bristol, in the red marl formation. It is decomposed, by ignition with charcoal, into sulphuret of strontia, which is converted into nitrate by saturation with nitric acid, evaporation, and crystallization. This nitrate is employed for the production of the red light in theatrical fire-works.

CEMENTATION. A chemical process, which consists in imbedding a solid body, in a pulverulent matter, and exposing both to ignition in an earthen or metallic case. In this way, iron is cemented with charcoal to form steel, and bottle glass with gypsum powder, or sand, to form Reaumur’s porcelain.

CEMENTS. (Ciments, Fr.; Cämente, Kitte, Germ.) Substances capable of taking the liquid form, and of being in that state applied between the surfaces of two bodies, so as to unite them by solidifying. They may be divided into two classes, those which are applied through the agency of a liquid menstruum, such as water, alcohol, or oil, and those which are applied by fusion with heat.

The diamond cement for uniting broken pieces of china, glass, &c. which is sold as a secret at an absurdly dear price, is composed of isinglass soaked in water till it becomes soft, and then dissolved in proof spirit, to which a little gum resin, ammoniac, or galbanum, and resin mastic are added, each previously dissolved in a minimum of alcohol. When to be applied, it must be gently heated to liquefy it; and it should be kept for use in a well-corked phial. A glass stopper would be apt to fix so as not to be removable. This is the cement employed by the Armenian jewellers in Turkey for glueing the ornamental stones to trinkets of various kinds. When well made it resists moisture.

Shell-lac dissolved in alcohol, or in a solution of borax, forms a pretty good cement. White of egg alone, or mixed with finely sifted quick lime, will answer for uniting objects which are not exposed to moisture. The latter combination is very strong, and is much employed for joining pieces of spar and marble ornaments. A similar composition is used by copper-smiths to secure the edges and rivets of boilers; only bullock’s blood is the albuminous matter used instead of white of egg. Another cement in which an analogous substance, the curd or caseum of milk is employed, is made by boiling slices of skim-milk cheeses into a gluey consistence in a great quantity of water, and then incorporating it with quicklime on a slab with a muller, or in a marble mortar. When this compound is applied warm to broken edges of stoneware, it unites them very firmly after it is cold.

A cement which gradually indurates to a stony consistence may be made by mixing 20 parts of clean river sand, two of litharge, and one of quicklime, into a thin putty with linseed oil. The quicklime may be replaced with litharge. When this cement is applied to mend broken pieces of stone, as steps of stairs, it acquires after some time a stony hardness. A similar composition has been applied to coat over brick walls, under the name of mastic.

The iron-rust cement is made of from 50 to 100 parts of iron borings, pounded and sifted, mixed with one part of sal-ammoniac, and when it is to be applied moistened with as much water as will give it a pasty consistency. Formerly flowers of sulphur were used, and much more sal-ammoniac in making this cement, but with decided disadvantage, as the union is effected by the oxidizement, consequent expansion and solidification of the iron powder, and any heterogeneous matter obstructs the effect. The best proportion of sal-ammoniac is, I believe, one per cent. of the iron borings. Another composition of the same kind is made by mixing 4 parts of fine borings or filings of iron, 2 parts of potter’s clay, and 1 part of pounded potsherds, and making them into a paste with salt and water. When this cement is allowed to concrete slowly on iron joints, it becomes very hard.

For making architectural ornaments in relief, a moulding composition is formed of chalk, glue, and paper paste. Even statues have been made with it, the paper aiding the cohesion of the mass.

Mastics of a resinous or bituminous nature which must be softened or fused by heat are the following:—

Mr. S. Varley’s consists of sixteen parts of whiting sifted and thoroughly dried by a red heat, adding when cold a melted mixture of 16 parts of black rosin and 1 of bees’-wax, and stirring well during the cooling.

Mr. Singer’s electrical and chemical apparatus cement consists of 5 lbs. of rosin, 1 of bees’-wax, 1 of red ochre, and two table-spoonsful of Paris-plaster, all melted together. A cheaper one for cementing voltaic plates into wooden troughs is made with 6 pounds of rosin, 1 pound of red ochre, ⁄2 of a pound of plaster of Paris, and ⁄4 of a pound of linseed oil. The ochre and the plaster of Paris should be calcined beforehand, and added to the other ingredients in their melted state. The thinner the stratum of cement that is interposed, the stronger generally speaking is the junction.

Boiled linseed oil and red lead mixed together into a putty are often used by coppersmiths and engineers, to secure joints. The washers of leather or cloth are smeared with this mixture in a pasty state.

The resin mastic alone is sometimes used by jewellers to cement by heat cameos of white enamel or coloured glass to a real stone, as a ground to produce the appearance of an onyx. Mastic is likewise used to cement false backs or doublets to stones to alter their hue.

Melted brimstone either alone, or mixed with rosin and brick dust, forms a tolerably good and very cheap cement.

Plumber’s cement consists of black rosin one part, brick dust two parts, well incorporated by a melting heat.

The cement of dihl for coating the fronts of buildings consists of linseed oil, rendered dry by boiling with litharge, and mixed with porcelain clay in fine powder, to give it the consistence of stiff mortar. Pipe-clay would answer equally well if well dried, and any colour might be given with ground bricks, or pottery. A little oil of turpentine to thin this cement aids its cohesion upon stone, brick, or wood. It has been applied to sheets of wire cloth, and in this state laid upon terraces, in order to make them water tight; but it is little less expensive than lead.

The bituminous or black cement for bottle corks consists of pitch hardened by the addition of rosin and brick-dust.

In certain localities where a limestone impregnated with bitumen occurs, it is dried, ground, sifted, and then mixed with about its own weight of melted pitch, either mineral, vegetable, or that of coal tar. When this mixture is getting semifluid, it may be moulded into large slabs or tiles in wooden frames lined with sheet iron, previously smeared over with common lime mortar, in order to prevent adhesion to the moulds, which, being in movable pieces, are easily dismounted so as to turn out the cake of artificial bituminous stone. This cement is manufactured upon a great scale in many places, and used for making Italian terraces, covering the floors of balconies, flat roofs, water reservoirs, water conduits, &c. When laid down, the joints must be well run together with hot irons. The floor of the terrace should be previously covered with a layer of Paris plaster or common mortar, nearly an inch thick, with a regular slope of one inch to the yard. Such bituminous cement weighs 144 pounds the cubic foot; or a foot of square surface, one inch thick, weighs 12 pounds. Sometimes a second layer of these slabs or tiles is applied over the first, with the precaution of making the seams or joints of the upper correspond with the middle of the under ones. Occasionally a bottom bed, of coarse cloth or gray paper, is applied. The larger the slabs are made, as far as they can be conveniently transported and laid down, so much the better. For hydraulic cements, see Mortar.

CERASIN. The name given by Dr. John to those gums which swell, but do not dissolve in water; such as gum tragacanth. It is synonymous with Bassorine, which see.

CERATE from cera, wax. An unguent, of rather a stiff consistence, made of oil, or lard and wax, thickened occasionally with pulverulent matters.

CERINE. A substance which forms from 70 to 80 per cent. of bees’-wax. It may be obtained by digesting wax, for some time, in spirit of wine, at a boiling temperature. The myricine separates, while the cerine remains dissolved, and may be obtained from the decanted liquor by evaporation. Cerine is white, analogous to wax, fusible at 134° F., hardly acted upon by hot nitric acid, but is readily carbonized by hot sulphuric acid. When treated with caustic alkaline lye, it is converted into margaric acid and ceraïne.

CERIUM. A peculiar metal discovered in the rare mineral, called cerite, found only in the copper mine of Bastnaes, near Riddarhytta, in Sweden. Cerium, extracted from its chloride by potassium, appears as a dark red or chocolate powder, which assumes a metallic lustre by friction. It does not conduct electricity well, like other metals; it is infusible; its specific gravity is unknown. It has been applied to no use in the arts.

CERUSE. A name of white lead. See Lead.

CETINE. The name given by Chevreul to spermaceti.

CHAINWORK is a peculiar style of textile fabric, to which hosiery and tambouring belong. See Hosiery.

CHALK. (Craie, Fr.; Kreide, Germ.) A friable carbonate of lime, white, opaque, soft, dull, or without any appearance of polish in its fracture. Its specific gravity varies from 2·4 to 2·6. It usually contains a little silica, alumina, and oxide of iron. It may be purified by trituration, and elutriation. The siliceous and ferruginous matters subside first, and the finer chalky particles floating in the supernatant liquid, may be decanted with it, and obtained by subsidence. When thus purified, it is called whitening and Spanish white, in England; schlemmkreide, in Germany; blanc de Troyes, and blanc de Meudon, in France. Pure chalk should dissolve readily in dilute muriatic acid, and the solution should afford no precipitate with water of ammonia.

CHALK—Black. A mineral, called also drawing-slate.

CHALK—French. Steatite, or soap stone; a soft magnesian mineral.

CHALK—Red. A clay coloured with the peroxide of iron, of which it contains about 17 per cent.

CHARCOAL. The fixed residuum of vegetables exposed to ignition out of contact of air. In the article Carbon, I have described the general properties of charcoal and the simplest mode of making it. I shall here detail the best systems of manufacturing this product upon the continent of Europe.

To carbonize wood under a movable covering, the plan of meiler, or heaps, is employed very much in Germany. The wood is arranged either in horizontal layers, or in nearly vertical ones, with a slight slope, so as to form conical rounded heaps of different sizes. The former are called lying meiler, fig. 272.; the latter standing meiler, figs. 273. and 274. Both are distributed in much the same way.

In districts where the wood can be transported into one place by means of rivers, or mountain slides, a dry flat space must be pitched upon, screened from storms and floods, which may be walled round, having a slight declivity made in the ground, towards the centre. See fig. 275. Into this space the tarry acid will partially fall, and may be conducted outwards, through a covered gutter beneath, into a covered tank. The mouth of the tank must be shut, during the coaking, with an iron or stone slab, luted with clay. A square iron plate is placed over the inner orifice of the gutter, to prevent it being choked with coal ashes. Fig. 275. represents a walled meiler station; a, the station; b, the gutter; c, the tank, which is covered with the slab d; e, a slab which serves to keep the gutter clear of coals. The cover of the heaps is formed of earth, sand, ashes, or such other matter as may be most readily found in the woods. They should be kindled in the centre. From 6 days to 4 weeks may be required for charring a heap, according to its size; hard wood requiring most time; and the slower the process, the better and greater is the product, generally speaking.

Charring of wood in mounds (Haufe or liegende werke) figs. 276. and 277. differs from that in the meiler, because the wood in the haufe is successively charred, and the charcoal is raked out by little and little. The product is said to be greater in this way, and also better. Uncleft billets, 6 or 8 feet long, being laid over each other, are covered with ashes, and then carbonized. The station is sometimes horizontal, and sometimes made to slope. The length may be 24 feet, the breadth 8 feet; and the wood is laid crosswise. Piles are set perpendicularly to support the roof, made of boughs and leaves, covered with ashes. Pipes are occasionally laid within the upper part of the mounds, which serve to catch and carry off some of the liquid products into proper tanks.

Fig. 278. is a vertical section, and fig. 279. a half bird’s-eye view, and half cross section, at the height of the pit-bottom, of Chabeaussière’s kiln for making wood charcoal. a is the oven; b, vertical air-pipes; c c, horizontal flues for admitting air to the kiln; d d, small pits which communicate by short horizontal pipes e e, with the vertical ones; f, the sole of the kiln, a circle of brickwork, upon which the cover or hood h reposes; i, a pipe which leads to the cistern k; l, the pipe destined for carrying off the gaseous matter; m m, holes in the iron cover or lid.

The distribution of the wood is like that in the horizontal meilers, or heaps; it is kindled in the central vertical canal with burning fuel, and the lid is covered with a few inches of earth. At the beginning of the operation all the draught flues are left open, but they are progressively closed, as occasion requires. In eight kilns of this kind, 500 decasters of oak wood are carbonized, from which 16,000 hectolitres of charcoal are obtained, equal to 64,000 pounds French, being about 25 per cent.; besides tar and 3000 velts of wood vinegar, of from 2° to 3°. Baumé.

At Crouy upon the Ourcq, near Meaux, there is a well constructed kiln for making turf-charcoal. It resembles most nearly a tar-kiln. In fig. 280. a is the cylindrical coaking place, whose surrounding walls are heated by the flame which passes through the intermediate space b. The place itself is divided by partitions of fire tiles into three stages, through the apertures in which the flames of the fire c c, rise, and heat the exterior of the coaking apartment. In order to confine the heat, there is in the enclosing walls of the outer kiln a cylindrical hollow space d, where the air is kept stagnant. Through the apertures left in the upper end at e, the turf is introduced; they are then shut with an iron plate f, which is covered with ashes or sand. The fire-place opens above this aperture, and its outlet is provided with a moveable iron cover g, in which there is a small hole for the issue of the gases. The sole of the kiln consists of a cast iron slab h, which may be raised by means of a hook i upon it. This is drawn back after the carbonization is completed, whereby the charcoal falls from the coaking space into a subjacent vault. The volatile products are carried off by the pipe k, and led into the condensing cistern; the gases escaping to the fire-place where they are burned. The iron slab is protected from the corrosion of the acid vapours by a layer of coal ashes.

CHICA is a red colouring principle made use of in America by some Indian tribes to stain their skins. It is extracted from the bignonia chica by boiling its leaves in water, decanting the decoction, and allowing it to settle and cool, when a red matter falls down, which is formed into cakes and dried. This substance is not fusible, and, when burned, diffuses the same odour as animal bodies do. It is insoluble in cold water, very soluble in alcohol and ether, but, after the evaporation of these liquids, it is recovered unchanged. Fats and unctuous oils both dissolve it. It is soluble in carbonated and caustic alkaline lyes, from which it is precipitated by the acids without alteration. An excess of alkali, however, speedily decomposes it. Nitric acid transforms it into oxalic acid, and a bitter matter. Chlorine makes it white.

The savages mix this pigment with the fat of the cayman or alligator, and rub their skins with the mixture. It may probably be turned to account in the arts of civilized nations.

CHIMNEY. (Cheminée, Fr.; Schornstein, Germ.) Chimney is a modern invention for promoting the draught of fires and carrying off the smoke, introduced into England so late as the age of Elizabeth, though it seems to have been employed in Italy 100 years before. The Romans, with all their luxurious refinements, must have had their epicurean cookery placed in perpetual jeopardy from their kitchen fires, which, having no vent by a vertical tunnel in the walls, discharged their smoke and frequently their flames at the windows, to the no small alarm of their neighbours, and annoyance of even the street passengers.

Chimneys in dwelling houses serve also the valuable purpose of promoting salubrious circulation of air in the apartments, when not foolishly sealed with anti-ventilating stove-chests.

The first person who sought to investigate the general principles of chimney draughts, in subserviency to manufacturing establishments, was the celebrated Montgolfier. As the ascent of heated air in a conduit depends upon the diminution of its specific gravity, or, in other words, upon the increase of its volume by the heat, the ascensional force may be deduced from the difference between the density of the elastic fluid in the interior of the chimney, and of the external air; that is, between the different heights of the internal and external columns of elastic fluid supposed to be reduced to the same density. In the latter case, the velocity of the gaseous products of combustion in the interior of the chimney is equal to that of a heavy body let fall from a height equal to the difference in height of the two aerial columns.

To illustrate this position by an example, let us consider the simple case of a chimney of ventilation for carrying off foul air from a factory of any kind; and suppose that the tunnel of iron be incased throughout with steam at 212 degrees Fahr. Suppose this tunnel to be 100 yards high, then the weight of the column of air in it will be to that of a column of external air 100 yards high, assumed at 32° F. inversely as its expansion by 180°; that is, as 1000 is to 1·375; or as 72·727 is to 100. The column of external air at 32° being 100 yards, the internal column will be represented by 72·727; and the difference = 27·27, will be the amount of unbalanced weight or pressure, which is the effective cause of the ventilation. Calculating the velocity of current due to this difference of weight by the well-known formula for the fall of heavy bodies, that is to say, multiplying the above difference, which is 27·27, by the constant factor 19·62, and extracting the square root of the product; thus, √19·62 × 27·27 = 23·13 will be the velocity in yards per second, which, multiplied by 3, gives 69·39 feet. The quantity of air which passes in a second is obtained of course by multiplying the area or cross section of the tunnel by this velocity. If that section is half a yard, that is = a quadrangle 2⁄4 feet by 2, we shall have 23·13 × 0·5 = 11·565 cubic yards, = 312⁄4 cubic feet.

The problem becomes a little more complicated in calculating the velocity of air which has served for combustion, because it has changed its nature, a variable proportion of its oxygen gas of specific gravity 1·111, being converted into carbonic acid gas of specific gravity 1·524. The quantity of air passed through well-constructed furnaces may, in general, be regarded as double of what is rigorously necessary for combustion, and the proportion of carbonic acid generated, therefore, not one half of what it would be were all the oxygen so combined. The increase of weight in such burned air of the temperature of 212°, over that of pure air equally heated, being taken into account in the preceding calculation, will give us about 19 yards or 57 feet per second for the velocity in a chimney 100 yards high incased in steam.

Such are the deductions of theory; but they differ considerably from practical results, in consequence of the friction of the air upon the sides of the chimneys, which varies likewise with its form, length, and quality. The direction and force of the winds also exercise a variable influence upon chimney furnaces differently situated. In chimnies made of wrought iron, like those of steam boats, the refrigeration is considerable, and causes a diminution of velocity far greater than what occurs in a factory stalk of well-built brick work. In comparing the numbers resulting from the trials made on chimneys of different materials and of different forms, it has been concluded that the obstruction to the draught of the air, or the deduction to be made from the theoretical velocity of efflux, is directly proportional to the length of the chimneys and to the square of the velocity, and inversely to their diameter. With an ordinary wrought-iron pipe, of from 4 inches to 5 inches diameter, attached to an ordinary stove, burning good charcoal, the difference is prodigious between the velocity calculated by the above theoretical rule, and that observed by means of a stop-watch, and the ascent of a puff of smoke from a little tow, dipped in oil of turpentine thrust quickly into the fire. The chimney being 45 feet high, the temperature of the atmosphere 68° Fahr., the velocity per second was,—

Trials. By
theory. By
experiment. Mean temperature
of chimney.

1 26·4 feet 5 feet 190 ° Fahr.

2 29·4 5 ·76 214

3 34·5 6 ·3 270

To obtain congruity between calculation and experiment, several circumstances must be introduced into our formulæ. In the first place, the theoretical velocity must be multiplied by a factor, which is different according as the chimney is made of bricks, pottery, sheet iron, or cast iron. This factor must be multiplied by the square root of the diameter of the chimney (supposed to be round), divided by its length, increased by four times its diameter. Thus, for pottery, its expression is 2·06 √DL + D; D being the diameter, and L the length of the chimney.

A pottery chimney, 33 feet high, and 7 inches in diameter, when the excess of its mean temperature above that of the atmosphere was 205° Fahr., had a pressure of hot air equal to 11·7 feet, and a velocity of 7·2 feet per second. By calculating from the last formula, the same number very nearly is obtained. In none of the experiments did the velocity exceed 12 feet per second, when the difference of temperature was more than 410° Fahr.

Every different form of chimney would require a special set of experiments to be made for determining the proper factor to be used.

This troublesome operation may be saved by the judicious application of a delicate differential barometer, such as that invented by Dr. Wollaston; though this instrument does not seem to have been applied by its very ingenious author in measuring the draughts or ventilating powers of furnaces.

If into one leg of this differential syphon, water be put, and fine spermaceti oil into the other, we shall have two liquids, which are to each other in density as the numbers 8 and 7. If proof spirit be employed instead of water, we shall then have the relation of very nearly 20 to 19. I have made experiments on furnace draughts with the instrument in each of these states, and find the water and oil syphon to be sufficiently sensible: for the weaker draughts of common fire-places the spirits and oil will be preferable barometric fluids.

To the lateral projecting tube of the instrument, as described by Dr. Wollaston, I found it necessary to attach a stop-cock, in order to cut off the action of the chimney, while placing the syphon, to allow of its being fixed in a proper state of adjustment, with its junction line of the oil and water at the zero of the scale. Since a slight deviation of the legs of the syphon from the perpendicular, changes very considerably the line of the level, this adjustment should be made secure by fixing the horizontal pipe tightly into a round hole, bored into the chimney stalk, or drilled through the furnace door. On gently turning the stop-cock, the difference of atmospherical pressure corresponding to the chimney draught, will be immediately indicated by the ascent of the junction-line of the liquids in the syphon. This modification of apparatus permits the experiment to be readily rectified by again shutting off the draught, when the air will slowly re-enter the syphon; because the projecting tube of the barometer is thrust into the stop-cock, but not hermetically joined; whereby its junction line is allowed to return to the zero of the scale in the course of a few seconds.

Out of many experiments made with this instrument, I shall content myself with describing a few, very carefully performed at the breweries of Messrs. Trueman, Hanbury, and Buxton, and of Sir H. Meux, Bart., and at the machine factory of Messrs. Braithwaite; in the latter of which I was assisted by Captain Ericsson. In the first trials at the breweries, the end of the stop-cock attached to the differential barometer was lapped round with hemp, and made fast into the circular peep-hole of the furnace door of a wort copper, communicating with two upright parallel chimneys, each 18 inches square, and 50 feet high. The fire was burning with fully its average intensity at the time. The adjustment of the level being perfect, the stop-cock orifice was opened, and the junction level of the oil and water rose steadily, and stood at 1⁄4 inches, corresponding to 1·258 = 0·156 of 1 inch of water, or a column of air 10·7 feet high. This difference of pressure indicates a velocity of 26 feet per second. In a second set of experiments, the extremity of the stop-cock was inserted into a hole, bored through the chimney stalk of the boiler of a Boulton and Watt steam-engine of twenty-horse power. The area of this chimney was exactly 18 inches square at the level of the bored hole, and its summit rose 50 feet above it. The fire-grate was about 10 feet below that level. On opening the stop-cock, the junction line rose 2⁄4 inches. This experiment was verified by repetition upon different days, with fires burning at their average intensity, and consuming fully 12 lbs. of the best coals hourly for each horse’s power, or nearly one ton and a third in twelve hours. If we divide the number 2⁄4 by 8, the quotient 0·28 will represent the fractional part of 1 inch of water, supported in the syphon by the unbalanced pressure of the atmosphere in the said chimney; which corresponds to 19⁄4 feet of air, and indicates a velocity in the chimney current of 35 feet per second. The consumption of fuel was much more considerable in the immense grate under the wort copper, than it was under the steam-engine boiler.

In my experiments at Messrs. Braithwaite’s factory, the maximum displacement of the junction line was 1 inch, when the differential oil and water barometer was placed in direct communication with a chimney 15 inches square, belonging to a steam boiler, and when the fire was made to burn so fiercely, that, on opening the safety-valve of the boiler, the excess of steam beyond the consumption of the engine, rushed out with such violence as to fill the whole premises. The pressure of one-eighth of an inch of water denotes a velocity of draught of 23·4 feet per second.

In building chimneys, we should be careful to make their area rather too large than too small; because we can readily reduce it to any desired size, by means of a sliding register plate near its bottom, or a damper plate applied to its top, adjustable by wires or chains, passing over pulleys. Wide chimneys are not so liable as narrow ones to have their draught affected by strong winds. In a factory, many furnace flues are often conducted into one vertical chimney stalk, with great economy in the first erection, and increased power of draught in the several fires.

Vast improvements have been made in this country, of late years, in building stalks for steam boilers and chemical furnaces. Instead of constructing an expensive, lofty scaffolding of timber round the chimney, for the bricklayers to stand upon, and to place their materials, pigeon-holes, or recesses, are left at regular intervals, a few feet apart, within the chimney, for receiving the ends of stout wooden bars, which are laid across, so as to form a species of temporary ladder in the interior of the tunnel. By means of these bars, with the aid of ropes and pulleys, every thing may be progressively hoisted, for the building of the highest engine or other stalks. An expert bricklayer, with a handy labourer, can in this way raise, in a few weeks, a considerable chimney, 40 feet high, 5 feet 8 inches square outside, 2 feet 8 inches inside at the base, 28 inches outside, and 20 inches inside at the top. To facilitate the erection, and at the same time increase the solidity of an insulated stalk of this kind, it is built with three or more successive plinths, or recedures, as shown in fig. 281. It is necessary to make such chimneys thick and substantial near the base, in order that they may sustain the first violence of the fire, and prevent the sudden dissipation of the heat. When many flues are conducted into one chimney stalk, the area of the latter should be nearly equal to the sum of the areas of the former, or at least of as many of them as shall be going simultaneously. When the products of combustion from any furnace must be conducted downwards, in order to enter near the bottom of the main stalk, they will not flow off until the lowest part of the channel be heated by burning some wood shavings or straw in it, whereby the air syphon is set agoing. Immediately after kindling this transient fire at that spot, the orifice must be shut by which it was introduced; otherwise the draught of the furnace would be seriously impeded. But this precaution is seldom necessary in great factories, where a certain degree of heat is always maintained in the flues, or, at least, should be preserved, by shutting the damper plate of each separate flue, whenever its own furnace ceases to act. Such chimneys are finished at top with a coping of stone-slabs, to secure their brickwork against the infiltration of rains, and they should be furnished with metallic conducting rods, to protect them from explosions of lightning.

When small domestic stoves are used, with very slow combustion, as has been recently proposed, upon the score of a misjudged economy, there is great danger of the inmates being suffocated or asphyxied, by the regurgitation of the noxious burned air. The smoke doctors who recommend such a vicious plan, from their ignorance of chemical science, are not aware that the carbonic acid gas, of coke or coal, must be heated 250° F. above the atmospheric air, to acquire the same low specific gravity with it. In other words, unless so rarefied by heat, that gaseous poison will descend through the orifice of the ash-pit, and be replaced by the lighter air of the apartment. Drs. Priestley and Dalton have long ago shown the co-existence of these two-fold crossing currents of air, even through the substance of stone-ware tubes. True economy of heat, and salubrity, alike require vivid combustion of the fuel, with a somewhat brisk draught inside of the chimney, and a corresponding abstraction of air from the apartment. Wholesome continuous ventilation, under the ordinary circumstances of dwelling houses, cannot be secured in any other way. Were these mephitic stoves, which have been of late so ridiculously puffed in the public prints, generally introduced, the faculty would need to be immediately quadrupled to supply the demand for medical advice; for headaches, sickness, nervous ailments, and apoplexy, would become the constant inmates of every inhabited mansion. The phenomena of the grotto of Pausilippo might then be daily realised at home, among those who ventured to recline upon sofas in such carbonated apartments; only instead of a puppy being suffocated pro tempore, human beings would be sacrificed, to save two-penny worth of fuel per diem.

The figures upon the preceding page represent one of the two chimneys, recently erected at the Camden Town station, for the steam boilers of the two engines of 60 horse-power each, belonging to the London and Birmingham Railway Company. These engines draw their train of carriages up the inclined plane of Hampstead Hill. The chimneys were designed by Robert Stephenson, Esq., engineer to the Company, executed by William Cubitt, Esq., of Gray’s Inn Road,—and do equal honour to both gentlemen, being probably the most elegant and substantial specimens of this style of architecture in the world. In the section, fig. 281.,

A represents a bed of concrete, 6 feet thick, and 24 feet square.

B, brick footings set in cement; the lower course 19 feet square.

C, Bramley-fall stone base, with a chain of wrought iron let into it.

D, a portion, 15 feet high, curved to a radius of 113 feet, built entirely of Malm paviours, (a peculiarly good kind of bricks.)

E, shaft built of Malm paviours in mortar.

F, ditto, built from the inside, without exterior scaffolding.

G, the cap ornamented, (as shown in the plan alongside,) with Portland stone, the dressings being tied together with copper cramps and an iron bond.

Fig. 282. represents the mouldings of the top, upon an enlarged scale.

Fig. 283., a plan of the foundation, ditto.

Fig. 284., ditto, at the level of the entrance of the flue, as seen in

Fig. 285., the elevation of the chimney.

Fig. 286., plan at the ground level I, in fig. 281. and 285.

K, fig. 281., the lightning conducting rod.

CHINTZ is a peculiar style of fast-printed calico, in which figures of at least five different colours are impressed upon a white or light coloured ground.

CHLORATE OF POTASH, commonly called oxymuriate of potash. This interesting saline compound has become the object of a pretty extensive manufacture, in consequence of its application to make matches for procuring instantaneous light, and a detonating powder for fire-arms. It may be prepared both in the humid and dry way.

Having made a strong solution of purified potash, or carbonate of potash, with from two to three parts of water, we pass through it in a Woulfe’s apparatus a current of chlorine gas, till it ceases to absorb any more. Chloride of potash and chloride of potassium alone are formed as long as there is an excess of alkali in the solution; but afterwards in the further reaction of the materials, the chloride passes into the state of a chlorate, and, as such, precipitates from the solution. During the first half of the operation, that is, till the potash be about one half saturated with chlorine, as indicated by litmus paper ceasing to be darkened and beginning to be blanched, only the chloride of potassium or muriate of potash falls. The process should be interrupted at this point in order to remove the salt, to wash it, to add the washings to the liquor, and then to transmit the gas freely through the solution. As the operation advances, less muriate of potash is formed, and at length nothing but the pure chlorate is separated in crystals. When finally the bubbles of gas pass through without being sensibly absorbed, the process is known to be completed; the liquid may then be allowed to settle, and be poured off from the crystals of chlorate of potash, which are purified from the muriate by dissolving them in three times their weight of boiling water, and filtering the solution while hot. On its cooling, the chlorate will separate in pearly-looking crystalline plates. It may be rendered quite pure by a second crystallization, in which state it does not affect solution of nitrate of silver.

The above potash lye usually gets a reddish tint in the course of the process in consequence of a little manganesic acid coming over with the chlorine, but it gradually loses this colour as the saturation becomes complete, when the solution turns yellow. The tubes for conveying the gas should be of large diameter, if they be plunged into the saline solution, because the crystallization which takes place in it is apt to choke them up. This inconvenience may however be obviated by attaching to the end of the glass tube, a tube of caoutchouc terminated in a small glass funnel, or simply the neck of a caoutchouc bottle with a part of its body, whose width will not be readily closed with a saline crust. The residuary lixivium may be used against another operation, or it may be evaporated down to half its bulk and set aside to crystallize, whereby some more chlorate will be obtained, mixed indeed with muriate and carbonate, from which however it may be separated by a second crystallization. In general the pure chlorate obtained does not exceed one tenth the weight of the potash employed; because in thus treating potash with chlorine, five-sixths of it are converted into muriate of potash and only one sixth into chlorate, and a part of the latter adheres to the muriate, or is lost in the mother waters of the crystallizations.

The chlorate of potash may be more conveniently manufactured, like that of lime, in the dry way. St. Romer patented at Vienna the following method for that purpose in 1821:—Ten pounds of crystallised peroxide of manganese are to be finely pulverised, mixed with ten pounds of plumbago, and thirty pounds of common salt, and put into the leaden retort represented in fig. 287. p. 287. From the middle of the helmet-shaped lid of this vessel, a lead tube, two feet long and two inches wide, conducts to the receiver, which is a square earthen pan, hard glazed both within and without, of the same capacity with the retort. The end of the tube must be made fast to a frame at the height of six inches above the bottom of the receiver. Upon its inner sides four inches apart, brackets are to be fixed for supporting a series of laths or shelves of white wood, on which a number of little paper or paste-board boxes are to be laid. In these boxes ten pounds of the purest carbonate of potash, prepared from tartar, are to be spread. The receiver must now be covered with a lid made tight by a water lute. Twenty pounds of concentrated sulphuric acid previously diluted with sixteen pounds of water, and then cooled, are to be poured upon the mixed materials in the retort, the lid immediately secured, with the tube adjusted in the receiver. The whole must be allowed to operate spontaneously without heat for twelve hours. At the end of this time the retort is to be surrounded with a water bath and steadily heated during twelve hours, and then left to cool for six hours. The apparatus must now be opened, the cakes of chlorate of potash removed, and freed from muriate by solution and crystallization.

M. Liebig proposes the following process for obtaining chlorate of potash:—

Heat chloride of lime in water till it ceases to destroy vegetable colours. In this case a mixture of chloride of calcium and chlorate of potash is obtained. This is to be dissolved in hot water, and to the solution concentrated by evaporation, chloride of potassium is to be added, and then suffered to cool. After cooling, a quantity of crystals of chlorate of potash is obtained, which are to be redissolved and crystallized again to purify them. M. Liebig considers that this will be a cheap process for obtaining chlorate of potash. From 12 ounces of chloride of lime, of so bad a quality that it left 65 per cent. of insoluble matter, he obtained an ounce of chlorate of potash.

The only difficulty to overcome in this process is, from the chloride of lime not being so easily decomposed by heat as is generally supposed; a solution of it may be kept boiling for an hour without losing its bleaching power. The best method is to form a thin paste with chloride of lime and water, and then to evaporate it to dryness. If it be required to prepare it by passing chlorine into cream of lime, it is advantageous to keep it very hot.

The chlorate of potash which separates from the solution by crystallization, has not the form of scales which it usually possesses, but is prismatic: whether this is occasioned by some admixture has not been ascertained; but on re-crystallizing, it is obtained in the usual form.

The solution ought not merely to be left to cool, in order to procure crystals, for the crystallization is far from being terminated even after complete cooling; crystals continue to be deposited for 3 or 4 days.

The following modification of the process for making chlorate of potash is that of M. Vée. A solution of chloride of lime marking 18° or 20° Baumé, is to be set upon the fire in a lead or cast iron pot, and when it begins to get hot, there is to be dissolved in it, a quantity of chloride of potassium sufficient to raise the hydrometer 3 or 4 degrees. It must be then concentrated as quickly as possible till it marks 30° or 31°, taking care that it does not boil over by the sudden extrication of oxygen. The concentrated liquor is set aside to crystallize in a cool place; where a deposit of chlorate of potash forms, mixed with chloride of potassium. The mother waters being evaporated to the density of 36°, afford another crop of crystals, after which they may be thrown away.

The salts obtained at the first crystallization are to be re-dissolved, and the solution being brought to 15° or 16° is to be filtered, when it will afford upon cooling pure chlorate of potash.

Chlorate or oxymuriate of potash has a cooling, somewhat unpleasant and nitrous taste. It does not bleach. At 60° F. 100 parts of water dissolve six parts of it, and at its boiling point or 220°, sixty parts. When heated to dull ignition in a glass retort it gives out 39·15 per cent. of its weight of oxygen, and becomes thereby chloride of potassium. When strongly triturated in a mortar it crackles, throws out sparks, and becomes luminous. It deflagrates upon red-hot cinders like nitre: when triturated along with sulphur, or phosphorus, it detonates with great violence, not without danger to the hands of the operator, if they be not protected by a thick glove. Similar detonations may be produced with cinnabar or vermillion, sulphuret of potassium, sugar, volatile oils, &c.; but they can be effected only by the smart blow of a heated hammer and anvil. A mixture of sugar or starch with chlorate of potash is readily inflamed by a drop of sulphuric acid, and this experiment is the basis of the preparation of the oxygenated matches, as they have been commonly called. The following formula forms a good paste for tipping the said matches, made of narrow slips of either wood or card. Thirty parts of the chlorate in fine powder are to be mixed gently with a spatula upon paper with ten parts of flowers of sulphur well levigated, eight of sugar, five of gum arabic, and enough of vermillion to give the whole a rose tint. We begin by mixing tenderly together the sugar, the gum, and the salt previously pulverised; we then add as much water as shall reduce the mixture to a thin paste, and lastly introduce the sulphur; after which all must be well incorporated. The points of the matches, either previously tipped with sulphur or not, are to be dipped in that paste, so as to get coated with a little of it, and are lastly laid in a warm place till they become thoroughly dry. To kindle one of them, it must be touched with strong sulphuric acid, which for this purpose is usually kept in a small well-stoppered phial, and thickened with amianthus. Aspen is reckoned the best wood for matches.

Of late years a detonating priming for fire-arms has been much used with the percussion locks. The simplest formula for making it is to take ten parts of gunpowder, to lixiviate it with water, and to mix the residuum, while moist, with five parts and a quarter of chlorate of potash, reduced to an extremely fine powder. The paste may be made pretty thin, for the salt is sparingly soluble in the cold water, and it mixes best when tolerably fluid. This powder when dry is dangerous to handle, being very apt to explode. But this danger is guarded against by letting fall a drop of the paste into each copper percussion cap, and leaving it to dry there. In the detonation of this powder, besides muriate of potash, there are generated a little sulphate of potash and chlorine gas, which rust the metal very fast. For which reason fulminate of mercury is now preferred by many sportsmen as a detonating powder. See Fulminate.

CHLORATES, compounds of chloric acid with the salifiable bases. The only acid belonging to this class of any manufacturing importance is the following:

CHLORIC ACID; the acid constituent of the preceding salt; it consists of one equivalent prime of chlorine = 35·476, + 5 of oxygen, = 40·065; of which the sum 75·535 is the prime equivalent of the acid.

CHLORINE; the most energetic of the undecompounded bodies, or chemical elements as they are usually called, exists, under ordinary circumstances, as a greenish yellow gas, but, when exposed to a pressure of 4 atmospheres, it becomes a yellow transparent liquid. In the first state, its density compared to air, reckoned 1·000, is 2·47; in the second, its density compared to water, 1·000, is 1·33. No degree of cold, hitherto tried, has liquefied the gas when dry. It is obtained by putting into a glass retort a mixture of 3 parts of common salt, with 2 parts of peroxide of manganese, and pouring upon it 2 parts of sulphuric acid diluted with its own weight of water; or, more conveniently, by pouring moderately strong muriatic acid upon peroxide of manganese in a retort; and in either case applying the gentle heat of a spirit lamp or a water bath, while the beak of the retort is plunged under brine upon the shelf of the pneumatic trough. The gas issues, and may be received in the usual way into inverted glass jars, or phials; but the first which comes over being mixed with the air of the retort, must be rejected. It has a peculiar smell, and irritates the nostrils most violently when inhaled, as also the windpipe and lungs. It is eminently noxious to animal life, and, if breathed in its undiluted state, would prove instantly fatal. It supports the combustion of many bodies, and indeed spontaneously burns several without their being previously kindled. The resulting combinations are called chlorides, and act most important parts in many manufacturing processes.

Water absorbs, at the ordinary temperature of the atmosphere, about double its volume of chlorine, and acquires the colour, smell, and taste of the gas, as well as its power of destroying or bleaching vegetable colours. When this aqueous chlorine is cooled to 36° F. dark yellow crystalline plates appear in it of the hydrate of chlorine, which are composed in 100 parts of 27·7 chlorine, and 72·3 water. If these crystals be heated to about 45° they liquefy, and the gas flies off.

Chlorine has a powerful affinity for hydrogen, not only combining with it rapidly in the gaseous, but seizing it in many of its liquid and solid combinations, as in volatile oils, which it inflames, and in yellow wax, cotton, and flax, which it whitens. The compound of chlorine and hydrogen gases is muriatic acid gas. Manganese, when mixed with liquid muriatic acid, as in the above process, abstracts the hydrogen, and lets the chlorine gas go free. When chlorine is passed into water, it decomposes some of it, seizes its hydrogen to form a little muriatic acid, and enables its oxygen to unite either with the chlorine, into chlorous acid, or with the remaining water, and to constitute oxygenated water. Hence, aqueous chlorine, exposed to the sunbeam, continually evolves oxygen, and, ere long, becomes muriatic acid.

This watery compound acts in a powerful way upon coloured vegetable fibres, extracting their hydrogen or colouring element by the twofold affinities of the chlorine and oxygen for it.

Hence chlorine, as a bleaching agent, requires to be tempered by the quiescent affinity of some alkaline base, potash or lime. Malaria, or morbific and putrescent miasmata, consist chiefly of hydrogenous matter as their basis, and are best counteracted by chlorine, where it can be conveniently applied.

Chlorides of Potash, Soda, and Lime.—These are the most important preparations through which chlorine exercises its peculiar powers upon the objects of manufactures. When a weak solution of caustic potash or soda is saturated with chlorine, it affords a bleaching liquor which is still used by some bleachers and calico-printers for their most delicate processes; but the price of the alkalis has led to the disuse of these chlorides as a general means, and has occasioned an extensive employment of chloride of lime. Upon the manufacture of this interesting compound I made an elaborate series of experiments several years ago, and published the results in the 13th volume of Brande’s Journal, for April 1822. I have no reason to suppose, from any thing that has been published since, that the processes there described have been essentially improved, or that any errors, either theoretical or practical, of any moment, exist in that memoir. I shall therefore first present my readers with a brief abstract of it, and then make such observations as subsequent inquiries suggest.

In the researches which I made, at many different times, upon the nature of the chloride of lime, I generally sought to combine the information flowing from both synthesis and analysis; that is, I first converted a known portion of hydrate of lime into bleaching-powder, and then subjected this chloride to analysis.

Two hundred grains of the atomic proto-hydrate of pure lime were put into a glass globe, which was kept cold by immersion in a body of water at 50°. A stream of chlorine, after being washed in water of the same temperature in another glass globe, connected to the former by a long narrow glass tube, was passed over the calcareous hydrate. The globe with the lime was detached from the rest of the apparatus from time to time, that the process might be suspended as soon as the augmentation of weight ceased. This happened when the 200 grains of hydrate, containing 151·9 of lime, had absorbed 130 grains of chlorine. By one analytical experiment it was found, that dilute muriatic acid expelled from 50 grains of the chloride, 20 grains of chlorine, or 40 per cent.; and by another, from 40 grains, 16·25 of gas, which is 40·6 per cent. From the residuum of the first 39·7 grains of carbonate of lime were obtained by carbonate of ammonia; from that of the second, 36·6 of ignited muriate of lime. The whole results are therefore as follows:—

Synthesis. 1st
Analysis. 2d
Analysis. Mean.

Chlorine 39·39 40·00 40·62 40·31

Lime 46·00 44·74 46·07 45·50

Water 14·60 15·26 13·31 14·28

100·00 100·00 100·00 100·00

Though the heat generated by the action of the dilute acid had carried off in the analytical experiments a small portion of moisture with the chlorine, yet their accordance with the synthetic experiment is sufficiently good to confirm the general results. The above powder appears to have been a pure chloride, without any mixture of muriate. But it exhibits no atomic constitution in its proportions.

To 200 grains of that hydrate of lime 30 grains of water being added, the powder was subjected to a stream of chlorine in the above way, till saturation took place. Its increase of weight was 150 grains.

It ought to be remarked, that in this and the preceding experiment, there was no appreciable pneumatic pressure employed to aid the condensation of the chlorine. In the last case, we see that the addition of 30 grains of water has enabled the lime to absorb 20 grains more of chlorine, being altogether a quantity of gas nearly equal to that of the dry lime. Thus, an atom of lime seems associated with ⁄9 of an atom of chlorine. Analysis by muriatic acid confirmed this composition. It gave

Chlorine 39·5 = 51·8 cubic inches.

Lime 39·9

Water 20·6

100·0

A great variety of apparatus has been at different times contrived for favouring the combination of chlorine with the slacked lime for the purposes of commerce. One of the most ingenious forms, is that of a cylinder, or barrel, furnished with narrow wooden shelves within, and suspended on a hollow axis by which the chlorine was admitted, and round which the barrel was made to revolve. By this mode of agitation, the lime-dust being exposed on the most extensive surface, was speedily impregnated with the gas to the requisite degree. Such a mechanism I saw at MM. Oberkampf and Widmer’s celebrated fabrique de toiles peintes, at Jouy, in 1816. But this is a costly refinement, inadmissible on the largest scale of British manufacture. The simplest, and, in my opinion, the best construction for subjecting lime-powder to chlorine, is a large chamber 8 or 9 feet high, built of siliceous sandstone, having the joints of the masonry secured with a cement composed of pitch, resin, and dry gypsum in equal parts. A door is fitted into it at one end, which can be made air-tight by strips of cloth and clay lute. A window on each side enables the operator to judge how the impregnation goes on by the colour of the air, and also gives light for making the arrangements within at the commencement of the process. As water lutes are incomparably superior to all others where the pneumatic pressure is small, I would recommend a large valve or door on this principle to be made in the roof, and two tunnels of considerable width at the bottom of each side wall. The three covers could be simultaneously lifted off by cords passing over a pulley, without the necessity of the workman approaching the deleterious gas, when the apartment is to be opened. A great number of wooden shelves, or rather trays, 8 or 10 feet long, 2 feet broad, and 1 inch deep, are provided to receive the riddled slacked lime, containing generally about 2 atoms of lime to 3 of water. These shelves are piled one over another in the chamber, to the height of 5 or 6 feet, cross bars below each keeping them about an inch asunder, that the gas may have free room to circulate over the surface of the calcareous hydrate.

The alembics for generating the chlorine, which are usually nearly spherical, are in some cases made entirely of lead, in others of two hemispheres, joined together in the middle, the upper hemisphere being lead, the under one cast-iron. The first kind of alembic is enclosed for two-thirds from its bottom, in a leaden or iron case, the interval of two inches between the two being destined to receive steam from an adjoining boiler. Those which consist below of cast-iron, have their bottom directly exposed to a very gentle fire; round the outer edge of the iron hemisphere a groove is cast, into which the under edge of the leaden hemisphere fits, the joint being rendered air-tight by Roman or patent cement. In this leaden dome there are four apertures, each secured by a water-lute. The first opening is about 10 or 12 inches square, and is shut with a leaden valve, with incurvated edges, that fit into the water channel at the margin of the hole. It is destined for the admission of a workman to rectify any derangement in the apparatus of rotation, or to detach hard concretions of salt from the bottom.

The second aperture is in the centre of the top. Here a tube of lead is fixed, which descends nearly to the bottom, and down through which the vertical axis passes. To its lower end the cross bars of iron, or of wood, sheathed with lead, are attached, by whose revolution the materials receive the proper agitation for mixing the dense manganese with the sulphuric acid and salt. The motion is communicated either by the hand of a workman applied from time to time to a winch at top, or it is given by connecting the axis with wheel work, impelled by a stream of water or a steam-engine. The third opening admits the syphon-formed funnel, through which the sulphuric acid is introduced; and the fourth is the orifice of the eduction-pipe.

Manufacturers differ much from each other in the proportion of their materials for generating chlorine. In general, 10 cwt. of salt are mixed with from 10 to 14 cwt. of manganese, to which mixture, after its introduction into the alembic, from 12 to 14 cwt. of sulphuric acid are added in successive portions. That quantity of oil of vitriol must, however, be previously diluted with water, till its specific gravity becomes about 1·6. But, indeed, this dilution is seldom actually made, for the manufacturer of bleaching-powder almost always prepares his own sulphuric acid for the purpose, and therefore carries its concentration no higher in the leaden boilers than the density of 1·65, which from my table of sulphuric acid, indicates ⁄4th of its weight of water, and therefore ⁄3d more of such acid must be used.

The fourth aperture, I have said, admits the eduction pipe. This pipe is afterwards conveyed into a leaden chest or cylinder, in which all the other eduction pipes also terminate. They are connected with it simply by water-lutes, having a hydrostatic pressure of 2 or 3 inches. In this general diversorium the chlorine is washed from adhering muriatic acid, by passing through a little water, in which each tube is immersed, and from this the gas is let off by a pretty large leaden tube, into the combination room. It usually enters in the top of the ceiling, whence it diffuses its heavy gas equally round.

Four days are required, at the ordinary rate of working, for making good marketable bleaching-powder. A more rapid formation would merely endanger an elevation of temperature, productive of muriate of lime, at the expense of the bleaching quality. But skilful manufacturers use here an alternating process. They pile up, first of all, the wooden trays only in alternate shelves in each column. At the end of two days the distillation is intermitted, and the chamber is laid open. After two hours the workman enters, to introduce the alternate trays covered with fresh hydrate of lime, and at the same time rakes up thoroughly the half-formed chloride in the others. The door is then secured, and the chamber, after being filled for two days more with chlorine, is again opened, to allow the first set of trays to be removed, and to be replaced by others, containing fresh hydrate, as before. Thus the process is conducted in regular alternation; thus, to my knowledge, very superior bleaching-powder is manufactured, and thus the chlorine may be suffered to enter in a pretty uniform stream. But for this judicious plan, as the hydrate advances in impregnation, its faculty of absorption becoming diminished, it would be requisite to diminish proportionately the evolution of chlorine, or to allow the excess to escape to the great loss of the proprietor, and, what is of more consequence, to the great detriment of the health of the workmen.

The manufacturer generally reckons on obtaining from one ton of rock-salt, employed as above, a ton and a half of good bleaching-powder. But the following analysis of the operation will show that he ought to obtain two tons.

When a mixture of sulphuric acid, common salt, and black oxide of manganese are the ingredients used, as by the manufacturer of bleaching-powder, the absolute proportions are, upon the oxygen scale of equivalents:—

1 atom muriate of soda 7 ·5 29·70 100·0

1 atom peroxide of manganese 5 ·5 21·78 73·3

2 atoms oil of vitriol 1·846 12 ·25 48·52 163·3

25 ·25 100·00

And the products ought to be:—

Chlorine disengaged 1 atom. 4 ·5 17·82

Sulphate of soda 1 — 9 ·0 35·64

Proto-sulphate of manganese 1 — 9 ·5 37·62

Water 2 — 2 ·25 8·92

25 ·25 100·00

These proportions are, however, very different from those employed, by many, nay I believe by all manufacturers; and they ought to be so, on account of the impurity of their oxide of manganese. Yet making allowance for this, I am afraid that many of them commit great errors in the relative quantities of their materials.

From the preceding computation, it is evident that 1 ton of salt with 1 ton of the above native oxide of manganese properly treated, would yield 0·59 of a ton of chlorine, which would impregnate 1·41 tons of slaked lime, producing 2 tons of bleaching-powder, stronger than the average of the commercial specimens; or allowing for a little loss, which is unavoidable, would afford 2 tons of ordinary powder, with a little more slaked lime.

Fig. 287. represents a retort of lead, well adapted to the evolution of chlorine from the mixture of salt, manganese, and sulphuric acid, or from manganese and muriatic acid. The interior vessel is cast in lead, and it has round its bottom part a cast-iron steam case. The salt and manganese are introduced by the aperture C, and the sulphuric acid by the syphon funnel F. The contact of these three substances is continually renewed by the agitator or stirrer B, which consists of wrought or cast iron sheathed with lead. e is the gas discharge pipe. The residuums are drawn off by the bottom discharge pipe G. The heating case receives its steam by the pipe h.

The chlorine gas fig. 288. is conveyed from the retort B into the chamber I, by the tube E E E. This chamber is divided into four compartments, to receive the gas disengaged from four retorts, like the above. The bottom of it is covered with a stratum three or four inches thick of quicklime, newly slaked and sifted, which is stirred about from time to time, by the rakes L L L L. When the saturation is sufficient, the chloride of lime is taken out by the doors K K K K. The size of this apparatus allows 2 cwt. of manganese, and its equivalent quantity of salt and sulphuric acid, or of muriatic acid, to be introduced at once into the retort. D is the handle of the agitator.

The same form of retort will suit perfectly well to prepare chlorine for making liquid chloride of lime, which is preferred by many bleachers and calico-printers who have conveniences for preparing it themselves. The most concentrated solutions of the dry chloride of lime do not mark more than 6° B. (sp. grav. 1·04), and discolour only 50 volumes of Gay Lussac’s solution of indigo, whilst the chloride made in the humid way marks from 8° to 9° B. (about 1·060), and discolours 80 volumes of the same solution.

In the chloride of lime apparatus, most generally used by the skilful calico-printers of Mulhausen, the mixture of muriatic acid and manganese is put into glass globes, with long necks, heated upon a sand-bath. The chlorine is conveyed by glass tubes into a cylindrical stone cistern, containing milk of lime. The furnace of the sand baths is made of cast iron, and has brick partitions, to give each retort its own fire. The smoke of all these fires goes off by a flue into sheet iron pipes. The cistern is made of siliceous sandstone. Its cover is of wood, coated with a resinous cement; and it fits at its edges into grooves cut in the stone. A wheel serves to agitate the liquid continually; its paddles being kept at two inches distance from the sides of the cistern. The milk of lime is introduced by a funnel, and the chloride is drawn off by a discharge pipe. I think the lead retort and agitator used in this country greatly preferable to the experimental laboratory plan described above. In all such apparatus we should avoid giving any pressure to the tubes or vessels, and should not therefore dip the extremities of the gas pipes beneath the surface of the liquid, but rather facilitate the combination of the chlorine and the lime, by enlarging the surfaces of contact and by agitating. Intermediate vessels containing water, or the chemical cascade of M. Clement, are very useful for absorbing any muriatic acid which may be disengaged along with the chlorine, and thereby preventing the needless formation of muriate of lime in the chambers or cisterns of impregnation.

When the solution of the chloride of lime is mixed with hydrate of lime, it bears, without decomposing, a pretty high temperature, provided it be not too long continued; it may even, in certain cases, be raised to near the boiling point without suffering a marked loss of its discolouring power; but when the chloride is deprived of that excess of lime, it is decomposed in a short time, even at a heat of 110° F.

When chlorine is admitted to milk of lime, it infallibly produces some muriate of lime; but the quantity is kept at a minimum by constantly presenting an excess of lime to the gas with the agitator, and by keeping the temperature as low as possible. Hence the influx of gas should not be so rapid as to generate much heat. An automatic agitator, moved by steam or water power, is therefore much better than one driven by the hand of the operator, who is apt to intermit his labours. If the liquor becomes hot at the end of the process, it should be immediately drawn off into large stone bottles, and cooled. The rose-colour, which sometimes supervenes, is due to a minute quantity of manganese. The strongest liquid chloride of lime that can be prepared will not discolour more than 80 times its volume of Gay Lussac’s indigo test.

On acting upon cotton cloth with a concentrated solution of chloride of lime, at from 110° to 120° F., pure carbonic acid gas is disengaged, and the texture of the cloth is injured. Here the hydrogen of the water and the cotton being seized by the chlorine, the liberated oxygen combines with the carbon to form carbonic acid. In the discharge troughs where printed calicoes are passed through strong solutions of chloride of lime, stalactitic crusts of carbonate of lime come to be formed in this way.

The chlorometre of Gay Lussac consists of a test solution of indigo and a graduated tube. One part of the best indigo, passed through a silk sieve, is to be dissolved in nine parts of concentrated sulphuric acid, by the aid of a water-bath heat applied for six hours. The sulphate of indigo is now to be diffused through such a body of water that one volume of chlorine gas shall discolour exactly ten times its volume of this dilute solution. The test liquor should be protected from the agency of light.

Mr. Crum, of Thorniebank, near Glasgow, has lately modified Dr. Dalton’s copperas test for chloride of lime, and made it convenient to the practical man. The Doctor justly considered that the more chlorine any bleaching powder contains, the more of the green sulphate of iron will it convert into the red sulphate, so that we have only to add successive portions of the chloride to a given weight of the dissolved copperas, and note the point at which all the iron gets peroxidized. See Bleaching.

Besides the method of analysis already quoted from my memoir on the manufacture of the chloride of lime, another occurred to me long ago, which I often practised as an easy and expeditious test. Chlorine decomposes ammonia. If therefore water of ammonia, faintly tinged with litmus, be added slowly to a solution of a given weight of chloride of lime, the colour will continue to disappear till the chlorine be all neutralized by the reaction of the hydrogen of the ammonia. The quantity of liquid ammonia of a certain strength requisite to neutralize in this way, a certain volume, say, one cubic inch, or a thousand grain measures of chlorine gas, may be assumed as the standard of such a chlorometer. As chlorine or chloride of lime, when mixed with water of ammonia, causes the disengagement of azote, the quantity of this gas evolved may also be made the foundation of an accurate and convenient chlorometer. The two substances should be mixed over mercury, in a graduated syphon tube. The shut end A and the open end B are both graduated to one scale; for example, to hundredths of a cubic inch, or to grain or 10 grain measures. The tube is to be filled with mercury, and then 10 measures of it are to be displaced at the open end, by inserting a wooden plug. This space, being filled with the solution of chloride of lime, is to be turned up into the shut end by covering the open end with the finger, and inverting the tube; a few drops of water may be sent through to wash the mercury. The ammonia being now let up, will cause a reaction, and evolve a quantity of azote, equivalent to the chlorine present. The action may be quickened by holding the sealed end of the tube obliquely over a lamp heat. The mercury is protected from the chlorine by the ammonia; and should any notion be entertained of such an action, the ammonia may be let up first. I have made innumerable researches over mercury with a detached apparatus of that kind, which combines precision with rapidity of result. It was by a similar mercurial syphon that I analyzed the carbonates, as described in the first edition of my Dictionary of Chemistry, twenty-one years ago.

M. Gay Lussac takes, as the basis of his indigo chlorometer, the fact, that one pound of pure crystallized peroxide of manganese is capable of affording, with muriatic acid, 0·7964 parts of a pound of chlorine; or one kilogramme yields 251⁄4 litres; that is, one pound yields 251⁄4 pound measures. Hence 3·98 grammes of that manganese are capable of affording 1000 gramme measures, or 1 litre of chlorine; or, in round numbers, 4 grains will yield 1000 grain measures. This quantity of gas, being received into that volume of milk of lime, constitutes therefore Gay Lussac’s primary standard. The small retort in which the manganese and muriatic acid are put, ought to be heated to ebullition, to discharge every particle of chlorine. To prevent the manganese, in this experiment, from sticking to the bottom in a cake, it has been proposed to mix it previously with a little plumbago. See Chlorometry.

For preparing the chlorides of potash and soda, the same apparatus may be employed as for the liquid chloride of lime. The alkaline solutions should be weak, containing not more than a pound to the gallon of water. Potash liquor saturated with chlorine, is much employed at Paris for whitening linen, under the name of the water of Javelle, the place where it was first made as a manufacture. One hundred parts of chlorine are said to saturate 133 parts of pure potash, and 195 of the carbonate; but the latter should not be used for preparing the bleaching fluid, as the carbonic acid resists the combination of the chlorine. A chloride of carbonate of soda has been lately recommended as a disinfecting substance against contagious miasmata or fomites. One hundred parts of chlorine will saturate 150 of the dry carbonate, and 405 of the crystallized. M. Payen prepares this medicinal chloride by adding 138 parts of carbonate of soda to a liquid, consisting of water 1800, chloride of lime 100, at 98° of strength, by Gay Lussac’s standard. The chloride of lime is to be dissolved, and the sediment well washed; the carbonate of soda, dissolved by heat, is to be poured into the solution, the precipitate allowed to subside, the clear fluid decanted, and the solid matter washed upon a filter. The collected solutions are neutral chloride of soda. Sixty-two parts of the carbonate of soda are then to be dissolved in the remainder of the water, and added to the preparation; the whole being thus filtered, a limpid liquor is obtained, indicating 5° by the hydrometer of Baumé.

The chloride of magnesia was long ago proposed by Sir H. Davy for bleaching linen, as being preferable to chloride of lime, because the resulting muriate of magnesia was not injurious to the fibre of cloth, as muriate of lime may be, under certain circumstances. I prepared a quantity of chloride of magnesia, by exposing a hydrate of that earth in the chlorine chamber of a large manufactory of chloride of lime at Glasgow, and obtained a compound possessed of considerable discolouring powers; but I found that the chlorine was so feebly saturated by the base, that it destroyed the colours of fast-dyed calicoes as readily as chlorine gas or chlorine water did, and was therefore dangerous for common bleaching, and destructive in clearing the grounds of printed goods, which is one of the most valuable applications of the calcareous and alkaline chlorides. The occasion of my making these experiments was the importation of a considerable quantity of magnesite, or native atomic carbonate of magnesia, from the district of Madras, by an enterprising friend of mine. Encouraged by the encomiums bestowed on the chloride of magnesia by many chemical writers, he expected to have benefited both the country and himself, by bringing home the earthy base of that compound, at a moderate price; but was disappointed to his cost.

Dr. Thomson is of opinion that the bleaching compound of lime and chlorine is not a chloride of lime, but a combination of chlorous acid with lime and of chlorine with calcium; consisting in its most concentrated state of

3 atoms of chloride of calcium = 21

1 atom of chlorite of lime = 11

32

So that about one third of the weight is chlorite of lime, to which alone the bleaching powers of the substance are owing. He admits a fact, rather inconsistent with this opinion, that bleaching powder does not attract moisture from the atmosphere with nearly so much rapidity as might be expected from a mixture containing two thirds of its weight of so deliquescent a salt as muriate of lime; unless this indeed be prevented by the chloride and chlorite being united into a double salt, which is a mere conjecture without either proof or analogy. And further, when dilute sulphuric or muriatic acid is poured upon bleaching powder, a profusion of chlorine is given out immediately, which he also admits to be inconsistent with the notion of its being a mixture of chloride of calcium and chlorite of lime, for no such evolution takes place when the above acids are mixed with solutions of chloride of calcium and chlorate of potash. Though I am of opinion that bleaching powder is simply a chloride of lime, in which the lime corresponds to the water in the aqueous chlorine, yet I cannot see the truth or appositeness of his last reason, because chlorine is certainly given out when chlorate of potash is acted upon by dilute muriatic acid, as any man may prove by adding to a mixture of these two substances a vegetable colour; for it will be speedily blanched. Dr. Thomson considers the chloride which is at present made in Mr. Tennant’s great factory, as containing one atom of chlorine associated with one atom of lime, or, taking his numbers, as consisting of

Hydrate of lime 4 ·625

Chlorine 4 ·5

Or nearly equal weights of the chlorine and the base; indicating a surprising degree of excellence in the preparation. The average commercial samples of bleaching powder from different factories which I examined some years ago, did not possess nearly that strength; but varied in their quantity of chlorine from 20 to 28 per cent. In my synthetic experiments related above, the greatest quantity of chlorine that would combine with the atomic hydrate of lime, was in the proportion of 130 to 200; but there is no doubt that if the lime contains additional water, it will condense more gas. I have never seen a chloride of lime of the strength mentioned by Dr. Thomson, and I should think there must be some fallacy in his statements. I have recorded in the paper above quoted an experiment which proves that with additional moisture, a chloride of lime may be obtained of the following composition:—

Chlorine 39·5

Lime 39·9

Water 20·6

100·0

In the article Bleaching, of the Encyclopædia Britannica, Dr. Thomson deduces from a test trial of Mr. Crum, that the best bleaching powder is a compound of 1 atom chlorite of lime = 11, 3 atoms chloride of calcium = 21, and 8 atoms of water = 9. “But,” adds he, “in general the whole lime is not accurately saturated with chlorine. Accordingly, when the bleaching powder is dissolved in water a small residue almost always remains undissolved. Unless the powder be fresh made, a portion of chlorite is always converted into chloride of calcium. It is probable therefore that the best bleaching powder, as it comes into the hands of the bleachers, consists of

1 atom chlorite of lime 11

3 atoms chloride of calcium 21

6 atoms water 6 ·75

Impurity 2 ·25

41 ·00

“If we consider the bleaching powder as a compound of chlorine and lime, our mode of calculating will not be altered. Instead of 1 atom chlorite of lime, and 3 atoms chloride of calcium, we shall have 4 atoms chloride of lime, 6 atoms water, and 2·25 of impurity as before.” In such ambiguity does this able chemist place this interesting compound, for theoretical reasons, of which I cannot see the value. Surely there is no difficulty in conceiving chlorine to exercise a direct attractive force towards the hydrate of lime, as it is known to do towards each of its elementary constituents, the oxygen and the calcium. Such refinements as the preceding tend merely to mystify a plain matter. Even the chlorous acid here brought into play to form the ideal chlorite, is by his own admission a hypothetical being. “When chlorate of potash” says Dr. Thomson, “is mixed with sulphuric acid, and made into small balls the size of a pea, if we expose these balls to a heat somewhat lower than that of boiling water, a bright yellowish green gas separates, which may be received over mercury. Its smell is peculiar and aromatic. Water absorbs at least seven times its volume of it. It destroys vegetable blues. Its constituents are,

1 volume chlorine 2 ·5 or 4 ·5

2 volumes oxygen 2 ·222 or 4 .

Thus this compound consists in weight of chlorine 4·5, oxygen 4 = 8·5. It has been called quarteroxide of chlorine, but it is more probably a teroxide. It has been supposed by some to possess acid properties, and has therefore been called chlorous acid. But this is only as yet a hypothesis.”

Surely this by the Doctor’s own showing is very slender authority for renouncing our long-received doctrines concerning the constitution of bleaching powder. I shall conclude by remarking that the ultra-atomists are now in a dilemma about this substance; M. Welter, and many French chemists calling it a sub-chloride, of 1 atom of chlorine to 2 atoms of lime, and Dr. Thomson showing that Mr. Tennant, the greatest and best manufacturer of it, has produced it in the state of a chloride, or 1 atom of each. The fact is, in chloride of lime, as in water of ammonia, alcohol, and muriatic acid, there is no sufficient reason for definite proportion in any term short of saturation, and therefore we shall find that chloride in every gradation of strength from 1 per cent. of chlorine up to 40 per cent.—the strongest which I succeeded in preparing, though I passed a constant stream of chlorine in great excess over a pure hydrate of lime for upwards of 24 hours, with frequent renewal of the surface; indeed, till it refused to absorb any more gas, as indicated by its remaining stationary in weight.

CHLOROMETRY; Chlorometrie, is the name given by the French to the process for testing the decolouring power of any combination of chlorine, but especially of the commercial articles, the chlorides of lime, potash, and soda. M. Gay Lussac proposed many years ago the following graduated method of applying indigo to this purpose. As indigo varies much in its dyeing quality, and of consequence in the proportion of chlorine required for its decoloration, he assumes as the unity of blanching power, one litre of chlorine gas, measured at the mean pressure of 29·6 inches, and at the temperature of melting ice. This volume of gas, when combined with a determinate quantity of water, is employed to test the standard solution of indigo. For this purpose a solution in sulphuric acid of any sample of indigo is taken, and diluted with water to such a degree that 10 measures of it, in a graduated tube, are decoloured by that one measure of combined chlorine gas. Each measure of indigo solution so destroyed is called a degree, and this measure being divided into five parts, the real test of chlorine is given to fiftieths, which is sufficiently nice. For the standard of the assays, a chloride of lime as pure and fully saturated as possible is taken, and dissolved in such a quantity of water, that the solution shall contain, or be equivalent to, one volume of chlorine gas. Calculation proves that this condition is exactly fulfilled by dissolving 4938 grammes of the said chloride in half a litre of water; or in English measures, 5 gr. very nearly in 500 grain measures of water. This solution, which serves for a type, indicates 10° in the assay, or proof; that is to say, each single volume destroys the colour of 10 volumes of the dilute indigo solution. It may be remarked, that a greater degree of precision is in general attainable with a weak solution of chlorine or a chloride, for example at 4° or 5°, than with one much stronger; consequently if, after a preliminary trial, the standard considerably exceeds 10°, a given volume of water must be added to the solution, and then the above proof must be taken. If the volume of water added was double, the number of degrees afterwards found must be tripled, to obtain the true title of the chloride. It is, however, to be observed that the degree of decoloration varies with the time taken in making the mixture; the more slowly the chlorine is added to the indigo, the less of it escapes into the atmosphere, and the more effective it becomes in destroying the colour. The best mode of obtaining comparable results, is to pour suddenly into the test quantity of chlorine the whole volume of the indigo solution likely to be decoloured; but it is requisite to find approximately beforehand, what quantity of indigo-blue will probably be destroyed. When it comes to the verge of destruction, it is green; but yellowish-brown when entirely decomposed.

I have tried the indigo test in many ways, but never could confide in it. The sulphuric solution of indigo is very liable to change by keeping, and thus to lead to erroneous results. The method of testing the chlorides by green sulphate of iron, described under bleaching, is in my opinion preferable to the above.

M. Gay Lussac has recently proposed another proof of chlorine, founded on the same principle as that by green vitriol, namely, the quantity of it requisite to raise a metallic substance from a lower to a higher stage of oxidizement. He now prescribes as the preferable plan of chlorometry, to pour very slowly from a graduated glass tube, a standard solution of the chloride, to be tested upon a determinate quantity of arsenious acid dissolved in muriatic acid, till the whole arsenious be converted into the arsenic acid. The value of the chloride is greater the less of it is required to produce this effect. It is easy to recognize, by a few drops of solution of indigo, the instant when all the arsenious acid has disappeared; for then the blue tint is immediately effaced, and cannot be restored by the addition of a fresh drop of the indigo solution.

In graduating the arsenical chlorometer, M. Gay Lussac takes for his unity the decolouring power of one volume of chlorine at 32° Fahr., and divides it into 100 parts. Suppose that we prepare a solution of chlorine containing its own volume of the gas, and an arsenious solution, such, that under a like volume, the two solutions shall reciprocally destroy each other. Let us call the first, the normal solution of chlorine, and the second, the normal arsenious solution. We shall fix at 10 grammes the weight of chloride of lime subjected to trial; and dissolve it in water, so that the total volume of the solution shall be a litre (1000 grammes measure), including the sediment. If we take a constant volume of this solution, 10 centimetres cube (10 gramme measures), for example, divided into 100 equal parts, and pour into it gradually the arsenious solution (measured by like portions), till the chlorine be destroyed, the bleaching power will be proportional to the number of portions of the arsenious solution, which the chloride shall have required. If the chloride has destroyed 100 portions of the arsenious solution, its title will be 100; if it has destroyed 80 portions, its title will be 80, &c. and so forth.

On pouring the acidulous arsenious solution into the chloride of lime, this will become very acid; the chlorine will be emitted abundantly, and the proof will be quite incorrect. If, on the contrary, we pour the solution of the chloride of lime into the arsenious solution, this evil will not occur, since the chlorine will always find plenty of arsenious acid to act upon, whatever be the dilution of the one or the other; but in this case, the standard of the chlorine is not given directly, as it is in the inverse ratio of the number of portions which are required to destroy the measures of the arsenious solution. If 50 portions of the chloride have been required, the proof will be 100 × 10050 = 200°; if 200 have been required, the proof will be 100 × 100200 = 50°, &c. This evil is not, however, very serious, since we have merely to consult a table, in which we can find the proof corresponding to each volume of the chloride employed for destroying the constant measure of the arsenious solution. The arsenious solution should be slightly tinged with sulphate of indigo, so as to show, by the disappearance of the colour, the precise point or instant of its saturation with chlorine, that is, its conversion into arsenic acid. If the arsenious acid be pure, the normal solution may be made directly by dissolving 4·439 grammes of it in muriatic acid (free from sulphurous acid), and diluting the solution till it occupies one litre, or 1000 grammes measure. Annales de Chimie et Physique, LX. 225.

CHOCOLATE. Is an alimentary preparation of very ancient use in Mexico, from which country it was introduced into Europe by the Spaniards in the year 1520, and by them long kept a secret from the rest of the world. Linnæus was so fond of it, that he gave the specific name, theobroma, food of the gods, to the cacao tree which produced it. The cacao-beans lie in a fruit somewhat like a cucumber, about 5 inches long and 3⁄2 thick, which contains from 20 to 30 beans, arranged in 5 regular rows with partitions between, and which are surrounded with a rose-coloured spongy substance, like that of water-melons. There are fruits, however, so large as to contain from 40 to 50 beans. Those grown in the West India islands, Berbice and Demerara, are much smaller, and have only from 6 to 15; their development being less perfect than in South America. After the maturation of the fruit, when their green colour has changed to a dark yellow, they are plucked, opened, their beans cleared of the marrowy substance, and spread out to dry in the air. Like almonds, they are covered with a thin skin or husk. In the West Indies they are immediately packed up for the market when they are dried; but in the Caraccas they are subjected to a species of slight fermentation, by putting them into tubs or chests, covering them with boards or stones, and turning them over every morning, to equalize the operation. They emit a good deal of moisture, lose the natural bitterness and acrimony of their taste by this process, as well as some of their weight. Instead of wooden tubs, pits or trenches dug in the ground are sometimes had recourse to for curing the beans; an operation called earthing (terrer). They are lastly exposed to the sun, and dried. The latter kind are reckoned the best; being larger, rougher, of a darker brown colour, and, when roasted, throw off their husk readily, and split into several irregular fragments; they have an agreeable mild bitterish taste, without acrimony. The Guiana and West India sorts are smaller, flatter, smoother-skinned, lighter coloured, more sharp and bitter to the taste. They answer best for the extraction of the butter of cacao, but afford a less aromatic and agreeable chocolate. According to Lampadius, the kernels of the West India cacao beans contain, in 100 parts, besides water, 53·1 of fat or oil, 16·7 of an albuminous brown matter, which contains all the aroma of the bean, 10·91 of starch, 7⁄4 of gum or mucilage, 0·9 of lignine, and 2·01 of a reddish dye stuff somewhat akin to the pigment of cochineal. The husks form 12 per cent. of the weight of the beans; they contain no fat, but, besides lignine, or woody fibre, which constitutes half their weight, they yield a light brown mucilaginous extract by boiling in water. The fatty matter is of the consistence of tallow, white, of a mild agreeable taste, called butter of cacao, and not apt to turn rancid by keeping. It melts only at 122° Fahr., and should, therefore, make tolerable candles. It is soluble in boiling alcohol, but precipitates in the cold. It is obtained by exposing the beans to strong pressure in canvass bags, after they have been steamed or soaked in boiling water for some time. From 5 to 6 ounces of butter may be thus obtained from a pound of cacao. It has a reddish tinge when first expressed, but it becomes white by boiling with water.

The beans, being freed from all spoiled and mouldy portions, are to be gently roasted over a fire in an iron cylinder, with holes in its ends for allowing the vapours to escape; the apparatus being similar to a coffee-roaster. When the aroma begins to be well developed, the roasting is known to be finished; and the beans must be turned out, cooled, and freed by fanning and sifting from their husks. The kernels are then to be converted into a paste, either by trituration in a mortar heated to 130° F., or by the following ingenious and powerful machine. The chocolate paste has usually in France a little vanilla incorporated with it, and a considerable quantity of sugar, which varies from one third of its weight to equal parts. For a pound and a half of cacao, one pod of vanilla is sufficient. Chocolate paste improves in its flavour by keeping, and should therefore be made in large quantities at a time. But the roasted beans soon lose their aroma, if exposed to the air.

Fig. 290. represents the chocolate mill. Upon the sole A, made of marble, six conical rollers B B, are made to run by the revolution of the upright axis or shaft q, driven by the agency of the fly wheel E and bevel wheels I K. The sole A rests upon a strong iron plate, which is heated by a small stove, introduced at the door H. The wooden frame work F, forms a ledge, a few inches high, round the marble slab, to confine the cocoa in the act of trituration. C is the hopper of the mill through which the roasted beans are introduced to the action of the rollers, passing first into the flat vessel D to be thence evenly distributed. After the cacao has received the first trituration, the paste is returned upon the slab, in order to be mixed with the proper quantity of sugar, and vanilla, previously sliced and ground up with a little hard sugar. When the chocolate is sufficiently worked, and while it is thin with the heat and trituration, it must be put carefully into the proper moulds. If introduced too warm, it will be apt to become damp and dull on the surface; and, if too cold, it will not take the proper form. It must be previously well kneaded with the hands to ensure the expulsion of every air bubble.

In Barcelona, chocolate mills on this construction are very common, but they are turned by a horse-gin set to work in the under story, corresponding to H in the above figure. The shaft G is, in this case, extended down through the marble slab, and is surrounded at its centre with a hoop to prevent the paste coming into contact with it. Each of these horse-mills turns out about ten pounds of fine chocolate in the hour, from a slab two feet seven inches in diameter.

Chocolate is flavoured with cinnamon and cloves, in several countries, instead of the more expensive vanilla. In roasting the beans the heat should be at first very slow, to give time to the humidity to escape; a quick fire hardens the surface, and injures the process. In putting the paste into the tin plate, or other moulds, it must be well shaken down to insure its filling up all the cavities, and giving the sharp and polished impression so much admired by connoisseurs. Chocolate is sometimes adulterated with starch; in which case it will form a pasty consistenced mass when treated with boiling water. The harder the slab upon which the beans are triturated, the better; and hence porphyry is far preferable to marble. The grinding rollers of the mill should be made of iron, and kept very clean.

CHROMATES, saline compounds of chromic acid with the bases. See Chromium.

CHROMIC ACID; see Chromium.

CHROMIUM. The only ore of this metal, which occurs in sufficient abundance for the purposes of art, is the octohedral chrome-ore, commonly called chromate of iron, though it is rather a compound of the oxides of chromium and iron. The fracture of this mineral is uneven; its lustre imperfect metallic; its colour between iron-black and brownish-black, and its streak brown. Its specific gravity, in the purest state, rises to 4·5; but the usual chrome-ore found in the market varies from 3 to 4. According to Klaproth, this ore consists of oxide of chromium, 43; protoxide of iron, 34·7; alumina, 20·3; and silica, 2; but Vauquelin’s analysis of another specimen gave as above, respectively, 55·5, 33, 6, and 2. It is infusible before the blowpipe; but it acts upon the magnetic needle, after having been exposed to the reducing smoky flame. It is entirely soluble in borax, at a high blowpipe heat, and imparts to it a beautiful green colour.

Chrome-ore is found at the Bare Hills, near Baltimore, in Maryland; in the Shetland isles, Unst and Fetlar; the department of Var, in France, in small quantity; and near Portsoy, in Banffshire; as also in Silesia and Bohemia.

The chief application of this ore is to the production of chromate of potash, from which salt the various other preparations of this metal used in the arts are obtained. The ore, freed, as well as possible, from its gangue, is reduced to a fine powder, by being ground in a mill under ponderous edge-wheels, and sifted. It is then mixed with one third or one half its weight of coarsely bruised nitre, and exposed to a powerful heat, for several hours, on a reverberatory hearth, where it is stirred about occasionally. In the large manufactories of this country, the ignition of the above mixture in pots is laid aside, as too operose and expensive. The calcined matter is raked out, and lixiviated with water. The bright yellow solution is then evaporated briskly, and the chromate of potash falls down in the form of a granular salt, which is lifted out from time to time from the bottom with a large ladle, perforated with small holes, and thrown into a draining-box. This saline powder may be formed into regular crystals of neutral chromate of potash, by solution in water and slow evaporation; or it may be converted into a more beautiful crystalline body, the bichromate of potash, by treating its concentrated solution with nitric, muriatic, sulphuric, or acetic acid, or, indeed, any acid exercising a stronger affinity for the second atom of the potash than the chromic acid does.

Bichromate of potash, by evaporation of the above solution, and slow cooling, may be obtained in the form of square tables, with bevelled edges, or flat four-sided prisms. They are permanent in the air, have a metallic and bitter taste, and dissolve in about one tenth of their weight of water, at 60° F.; but in one half of their weight of boiling water. They consist of chromic acid 13, potash 6; or, in 100 parts, 68·4 + 31·6. This salt is much employed in calico-printing and in dyeing; which see.

Chromate of lead, the chrome-yellow of the painter, is a rich pigment of various shades, from deep orange to the palest canary yellow. It is made by adding a limpid solution of the neutral chromate (the above granular salt), to a solution, equally limpid, of acetate or nitrate of lead. A precipitate falls, which must be well washed, and carefully dried out of the reach of any sulphuretted vapours. A lighter shade of yellow is obtained by mixing some solution of alum, or sulphuric acid, with the chromate, before pouring it into the solution of lead; and an orange tint is to be procured by the addition of subacetate of lead, in any desired proportion.

For the production of chromate of potash from chrome ore, various other processes have been recommended. The following formulæ, which have been verified in practice, will prove useful to the manufacturers of this important article:—

I. Two parts of chrome ore, containing about 50 per cent. of protoxide of chromium:

One part of saltpetre.

II. Four parts of chrome ore, containing 34 per cent. of protoxide of chromium.

Two parts of potashes.

One part of saltpetre.

III. Four parts of chrome ore,cont—ining34per cent. of pro—

Two of potashes.

Four tenths of a part of peroxide of manganese.

IV. Three parts of chrome ore.

Four parts of saltpetre.

Two parts of argal.

Some manufacturers have contrived to effect the conversion of the oxide into an acid, and of course to form the chromate of potash, by the agency of potash alone, in a calcining furnace, or in earthen pots fired in a pottery kiln.

After lixiviating the calcined mixtures with water, if the solution be a tolerably pure chromate of potash, its value may be inferred, from its specific gravity, by the following table:—

At specific gravity 1·28 it contains about 50 per cent. of the salt.

1·21 33

1·18 25

1·15 20

1·12 16

1·11 14

1·10 12

In making the red bichromate of potash from these solutions of the yellow salt, nitric acid was at first chiefly used; but, in consequence of its relatively high price, sulphuric, muriatic or acetic acid has been frequently substituted upon the great scale.

There is another application of chrome which merits some notice here; that of its green oxide to dyeing and painting on porcelain. This oxide may be prepared by decomposing, with heat, the chromate of mercury, a salt made by adding to nitrate of protoxide of mercury, chromate of potash, in equivalent proportions. This chromate has a fine cinnabar red, when pure; and, at a dull red heat, parts with a portion of its oxygen and its mercurial oxide. From M. Dulong’s experiments it would appear, that the purest chromate of mercury is not the best adapted for preparing the oxide of chrome to be used in porcelain painting. He thinks it ought to contain a little oxide of manganese and chromate of potash, to afford a green colour of a fine tint, especially for pieces that are to receive a powerful heat. Pure oxide of chrome preserves its colour well enough in a muffle furnace; but, under a stronger fire, it takes a dead-leaf colour.

The green oxide of chrome has come so extensively into use as an enamel colour for porcelain, that a fuller account of the best modes of manufacturing it must prove acceptable to many of my readers.

That oxide, in combination with water, called the hydrate, may be economically prepared by boiling chromate of potash, dissolved in water, with half its weight of flowers of sulphur, till the resulting green precipitate ceases to increase, which may be easily ascertained by filtering a little of the mixture. The addition of some potash accelerates the operation. This consists in combining the sulphur with the oxygen of the chromic acid, so as to form sulphuric acid, which unites with the potash of the chromate into sulphate of potash, while the chrome oxide becomes a hydrate. An extra quantity of potash facilitates the deoxidizement of the chromic acid by the formation of hyposulphite and sulphuret of potash, both of which have a strong attraction for oxygen. For this purpose the clear lixivium of the chromate of potash is sufficiently pure, though it should hold some alumina and silica in solution, as it generally does. The hydrate may be freed from particles of sulphur by heating dilute sulphuric acid upon it, which dissolves it; after which it may be precipitated, in the state of a carbonate, by carbonate of potash, not added in excess.

By calcining a mixture of bichromate of potash and sulphur in a crucible, chromic acid is also decomposed, and a hydrated oxide may be obtained; the sulphur being partly converted into sulphuret of potassium, and partly into sulphuric acid (at the expense of the chromic acid), which combines with the rest of the potash into a sulphate. By careful lixiviation, these two new compounds may be washed away, and the chrome green may be freed from the remaining sulphur, by a slight heat.

Liebig and Wöhler have lately contrived a process for producing a subchromate of lead of a beautiful vermillion hue. Into saltpetre, brought to fusion in a crucible at a gentle heat, pure chrome yellow is to be thrown by small portions at a time. A strong ebullition takes place at each addition, and the mass becomes black, and continues so while it is hot. The chrome yellow is to be added till little of the saltpetre remains undecomposed, care being taken not to overheat the crucible, lest the colour of the mixture should become brown. Having allowed it to settle for a few minutes, during which the dense basic salt falls to the bottom, the fluid part, consisting of chromate of potash and saltpetre, is to be poured off, and it can be employed again in preparing chrome yellow. The mass remaining in the crucible is to be washed with water, and the chrome red being separated from the other matters, is to be dried after proper edulcoration. It is essential for the beauty of the colour, that the saline solution should not stand long over the red powder, because the colour is thus apt to become of a dull orange hue. The fine crystalline powder subsides so quickly to the bottom after every ablution, that the above precaution may be easily observed.

As Chromic Acid will probably ere long become an object of interest to the calico printer, I shall describe here the best method of preparing it. To 100 parts of yellow chromate of potash, add 136 of nitrate of barytes, each in solution. A precipitate of the yellow chromate of barytes falls, which being washed and dried would amount to 130 parts. But while still moist it is to be dissolved in water by the intervention of a little nitric acid, and then decomposed by the addition of the requisite quantity of sulphuric acid, whereby the barytes is separated, and the chromic acid remains associated with the nitric acid, from which it can be freed by evaporation to dryness. On re-dissolving the chromic acid residuum in water, filtering and evaporating to a proper degree, 50 parts of chromic acid may be obtained in crystals.

This acid may also be obtained from chromate of lime, formed by mixing chromate of potash and muriate of lime; washing the insoluble chromate of lime which precipitates, and decomposing it by the equivalent quantity of oxalic acid, or for ordinary purposes even sulphuric acid may be employed.

Chromic acid is obtained in quadrangular crystals, of a deep red colour; it has a very acrid and styptic taste. It reddens powerfully litmus paper. It is deliquescent in the air. When heated to redness, it emits oxygen and passes into the deutoxide. When a little of it is fused along with vitreous borax, the compound assumes an emerald green colour.

As chromic acid parts with its last dose of oxygen very easily, it is capable in certain styles of calico printing of becoming a valuable substitute for chlorine where this more powerful substance would not from peculiar circumstances be admissible. For this ingenious application, the arts are indebted to that truly scientific manufacturer, M. Daniel Kœchlin, of Mulhouse. He discovered that whenever chromate of potash has its acid set free by its being mixed with tartaric or oxalic acid, or a neutral vegetable substance, (starch or sugar for example), and a mineral acid, a very lively action is produced, with disengagement of heat, and of several gases. The result of this decomposition is the active reagent, chromic acid, possessing valuable properties to the printer. Watery solutions of chromate of potash and tartaric acid being mixed, an effervescence is produced which has the power of destroying vegetable colours. But this power lasts no longer than the effervescence. The mineral acids react upon the chromate of potash only when vegetable colouring matter, gum, starch, or a vegetable acid are present, to determine the disengagement of gas. During this curious change carbonic acid is evolved; and when it takes place in a retort, there is condensed in the receiver a colourless liquid, slightly acid, exhaling somewhat of the smell of vinegar, and containing a little empyreumatic oil. This liquid heated with the nitrates of mercury or silver reduces these metals. On these principles M. Kœchlin discharged indigo blue by passing the cloth through a solution of chromate of potash, and printing nitric acid thickened with gum upon certain spots. It is probable that the employment of chromic acid would supersede the necessity of having recourse in many cases to the more corrosive chlorine.

The following directions have been given for the preparation of a blue oxide of chrome. The concentrated alkaline solution of chromate of potash is to be saturated with weak sulphuric acid, and then to every 8 lbs. is to be added 1 lb. of common salt, and half-a-pound of concentrated sulphuric acid; the liquid will now acquire a green colour. To be certain that the yellow colour is totally destroyed, a small quantity of the liquor is to have potash added to it, and filtered; if the fluid is still yellow, a fresh portion of salt and of sulphuric acid is to be added: the fluid is then to be evaporated to dryness, redissolved, and filtered; the oxide of chrome is finally to be precipitated by caustic potash. It will be of a greenish-blue colour, and being washed, must be collected upon a filter.

Chromate of Potash, adulteration of, to detect. The chromate of potash has the power of combining with other salts up to a certain extent without any very sensible change in its form and appearance; and hence it has been sent into the market falsified by very considerable quantities of sulphate and muriate of potash, the presence of which has often escaped observation, to the great loss of the dyers who use it so extensively. The following test process has been devised by M. Zuber, of Mulhouse. Add a large excess of tartaric acid to the chromate in question, which will decompose it, and produce in a few minutes a deep amethyst colour. The supernatant liquor will, if the chromate be pure, afford now no precipitate with the nitrates of barytes or silver; whence the absence of the sulphates and muriates may be inferred. We must, however, use dilute solutions of the chromate and acid, lest bitartrate of potash be precipitated, which will take place if less than 60 parts of water be employed. Nor must we test the liquid till the decomposition be complete, and till the colour verge rather towards the green than the yellow. Eight parts of tartaric acid should be added to one of chromate to obtain a sure and rapid result. If nitrate of potash (saltpetre) is the adulterating ingredient, it may be detected by throwing it on burning coals, when deflagration will ensue. The green colour is a certain mark of the transformation of the chromic acid partially into the chrome oxide; which is effected equally by the sulphurous acid and sulphuretted hydrogen. Here this metallic acid is disoxygenated by the tartaric, as has been long known. The tests which I should prefer, are the nitrates of silver and baryta, having previously added so much nitric acid to the solution of the suspected chromate, as to prevent the precipitation of the chromate of silver or baryta. The smallest adulteration by sulphates or muriates will thus be detected.

CINNABAR; the native red sulphuret of mercury. It occurs sometimes crystallized in rhomboids; has a specific gravity varying from 6·7 to 8·2; a flat conchoidal fracture; is fine grained; opaque; has an adamantine lustre, and a colour passing from cochineal to ruby red. The fibrous and earthy cinnabar has a scarlet hue. It is met with disseminated in smaller or larger lumps in veins, which are surrounded by a black clay, and is associated with native quicksilver, amalgam with iron-ore, lead-glance, blende, copper-ore, gold, &c. Its principal localities are Almaden in Spain, Idria in the Schiefergebirge, Kremnitz and Schemnitz in Hungary; in Saxony, Bavaria, Bohemia, Nassau, China, Japan, Mexico, Columbia, Peru. It consists of two primes of sulphur, = 32·240, combined with one of mercury, = 202,863; or in 100 parts of 12·7 sulphur + 87·3 mercury. It is the most prolific ore of this metal; and is easily smelted by exposing a mixture of it with iron or lime to a red heat in retorts. Factitious cinnabar is called in commerce Vermillion, which see, as also Mercury.

CINNAMON. (Cannelle, Fr.; Zimmt, Germ.) Is the inner bark of the laurus cinnamomum, a handsome-looking tree, which grows naturally to the height of 18 or 20 feet, in Java, Sumatra, Ceylon, and other islands in the East Indian seas. It has been transplanted to the Antilles, particularly Guadaloupe and Martinique, as well as Cayenne, but there it produces a bark of very inferior value to the Oriental.

Cinnamon is gathered twice a year, but not till after the tree has attained to a certain age and maturity. The young twigs yield a bark of better quality than the larger branches. The first and chief harvest takes place from April to August; the second, from November to January. After having selected the proper trees, all the branches more than three years old are cut off; the epidermis is first removed with a two-edged pruning knife, then a longitudinal incision is made through the whole extent of the bark, and lastly, with the bluntest part of the knife, the true bark is carefully stripped off in one piece. All these pieces of bark are collected, the smaller ones are laid within the larger, and in this state they are exposed to the sun, whereby in the progress of drying, they become rolled into the shape of a quill. These convoluted pieces are formed into oblong bundles of 20 or 30 lbs. weight, which are placed in warehouses, sorted and covered with mats. Good cinnamon should be as thin as paper, have its peculiar aromatic taste, without burning the tongue, and leave a sweetish flavour in the mouth. The broken bits of cinnamon are used in Ceylon for procuring the essential oil by distillation. 445,367 lbs. of cinnamon were imported into this kingdom in 1835, of which 16,604 only were retained for internal consumption.

CITRIC ACID. (Acide citrique, Fr.; Citronensäure, Germ.) Scheele first procured this acid in its pure state from lemon juice, by the following process. The juice put into a large tub, is to be saturated with dry chalk in fine powder, noting carefully the quantity employed. The citrate of lime which precipitates being freed from the supernatant foul liquor, is to be well washed with repeated affusion and decantation of water. For every 10 pounds of chalk employed, nine and a half pounds of sulphuric acid, diluted with six times its weight of water, are to be poured while warm upon the citrate of lime, and well mixed with it. At the end of twelve hours, or even sooner, the citrate will be all decomposed, dilute citric acid will float above, and sulphate of lime will be found at the bottom. The acid being drawn off, the calcareous sulphate must be thrown on a canvass filter, drained, and then washed with water to abstract the whole acid.

The citric acid thus obtained may be evaporated in leaden pans, over a naked fire till it acquires the specific gravity 1·13; after which it must be transferred into another vessel, evaporated by a steam or water bath till it assumes a syrupy aspect, when a pellicle appears first in patches, and then over the whole surface. This point must be watched with great circumspection, for if it be passed, the whole acid runs a risk of being spoiled by carbonization. The steam or hot water must be instantly withdrawn, and the concentrated acid put into a crystallizing vessel in a dry, but not very cold apartment. At the end of four days, the crystallization will be complete. The crystals must be drained, re-dissolved in a small portion of water, the solution set aside to settle its impurities, then decanted, re-evaporated, and re-crystallized. A third or fourth crystallization may be necessary to obtain a colourless acid.

If any citrate of lime be left undecomposed by the sulphuric acid, it will dissolve in the citric acid, and obstruct its crystallization, and hence it will be safer to use the slightest excess of sulphuric acid, than to leave any citrate undecomposed. There should not however be any great excess of sulphuric acid. If there be, it is easily detected by nitrate of barytes, but not by the acetate of lead as prescribed by some chemical authors; because the citrate of lead is not very soluble in the nitric acid, and might thus be confounded with the sulphate, whereas citrate of barytes is perfectly soluble in that test acid. Sometimes a little nitric acid is added with advantage to the solution of the coloured crystals, with the effect of whitening them.

Twenty gallons of good lemon juice will afford fully ten pounds of white crystals of citric acid.

Attempts were made both in the West Indies and Sicily, to convert the lime and lemon juice into citrate of lime, but they seem to have failed through the difficulty of drying the citrate for shipment.

The crystals of citric acid are oblique prisms with four faces, terminated by dihedral summits, inclined at acute angles. Their specific gravity is 1·617. They are unalterable in the air. When heated, they melt in their water of crystallization; and at a higher heat, they are decomposed. They contain 18 per cent. of water, of which one half may be separated in a dry atmosphere, at about 100° F., when the crystals fall into a white powder.

Citric acid in crystals is composed by my analysis of carbon, 35·8, oxygen 59·7, and hydrogen 45; results which differ very little from those of Dr. Prout, subsequently obtained. I found its atomic weight to be 8·375, compared to oxygen 1,000. I cannot account for Berzelius’s statements relative to the composition of this acid.

Citric acid in somewhat crude crystals is employed with much advantage in calico-printing. If adulterated with tartaric acid, the fraud may be detected by adding potash to the solution of the acid, which will occasion a precipitate of cream of tartar.

CIVET. (Civette, Fr.; Zibeth, Germ.) This substance approaches in smell to musk and ambergris; it has a pale yellow colour, a somewhat acrid taste, a consistence like that of honey, and a very strong aromatic odour. It is the product of two small quadrupeds of the genus viverra (v. zibetha and v. civetta), of which the one inhabits Africa, the other Asia. They are reared with tenderness, especially in Abyssinia. The civet is contained in a sac, situated between the anus and the parts of generation, in either sex. The animal frees itself from an excess of this secretion by a contractile movement which it exercises upon the sac, when the civet issues in a vermicular form, and is carefully collected. The negroes are accustomed to increase the secretion by irritating the animal; and likewise introduce a little butter, or other grease, by the natural slit in the bag, which mixes with the odoriferous substance, and increases its weight. It is employed only in perfumery.

According to M. Boutron-Chalard, it contains a volatile oil, to which it owes its smell, some free ammonia, resin, fat, an extractiform matter, and mucus. It affords, by calcination, an ash, in which there are some carbonate and sulphate of potash, phosphate of lime, and oxide of iron.

CLAY (Argile, Fr.; Thon, Germ.) is a mixture of the two simple earths, alumina and silica, generally tinged with iron. Lime, magnesia, with some other colouring metallic oxides, are occasionally present in small quantities in certain natural clays.

The different varieties of clay possess the following common characters:—

1. They are readily diffusible through water, and are capable of forming with it a plastic ductile mass, which may be kneaded by hand into any shape. This plasticity exists, however, in very different degrees in the different clays.

2. They concrete into a hard mass upon being dried, and assume, upon exposure to the heat of ignition, a degree of hardness sometimes so great as to give sparks by collision with hardened steel. In this state they are no longer plastic with water, even when pulverised. Tolerably pure clays, though infusible in the furnace, become readily so by the admixture of lime, iron, manganese, &c.

3. All clays, even when previously freed from moisture, shrink in the fire in virtue of the reciprocal affinity of their particles; they are very absorbent of water in their dry state, and adhere strongly to the tongue.

4. Ochrey, impure clays emit a disagreeable earthy smell when breathed upon.

Brongniart distributes the clays into:—

1. Fire-clays, (argiles apyres, Fr.; feuerfeste, Germ.)

2. Fusible, (schmelzbare, Germ.)

3. Effervescing (brausende, Germ.), from the presence of chalk.

4. Ochrey (ocreuses, Fr.; ockrige, Germ.)

Fire-clay is found in the greatest abundance and perfection for manufacturing purposes in,

1. Slate-clay. (Thon-schiefer, Germ.) Its colour is gray or grayish-yellow. Massive, dull, or glimmering from admixture of particles of mica. Fracture slaty, approaching sometimes to earthy. Fragments tabular. Soft, sectile, and easily broken. Sp. gr. = 2·6. Adheres to the tongue, and breaks down in water. It occurs along with pit coal; which see. Slate-clay is ground, and reduced into a paste with water, for making fire-bricks; for which purpose it should be as free as possible from lime and iron.

2. Common clay or loam.—This is an impure coarse pottery clay, mixed with iron ochre, and occasionally with mica. It has many of the external characters of plastic clay. It is soft to the touch, and forms, with water, a somewhat tenacious paste; but is in general less compact, more friable, than the plastic clays, which are more readily diffusible in water. It does not possess the property of acquiring in water that commencement of translucency which the purer clays exhibit. Although soft to the touch, the common clay wants unctuosity, properly so called. The best example of this argillaceous substance is afforded in the London clay formation, which consists chiefly of bluish or blackish clay, mostly very tough. Those of its strata which effervesce with acids partake of the nature of marl. This clay is fusible at a strong heat, in consequence of the iron and lime which it contains. It is employed in the manufacture of bricks, tiles, and coarse pottery ware.

3. Potter’s clay, or Plastic clay.—This species is compact, soft, or even unctuous to the touch, and polishes with the pressure of the finger; it forms, with water, a tenacious, very ductile, and somewhat translucent paste. It is infusible in a porcelain kiln, but assumes in it a great degree of hardness. Werner calls it pipe-clay. Good plastic clay remains white, or if gray before, becomes white in the porcelain kiln.

The geological position of the plastic clay is beneath the London clay, and above the sand which covers the chalk formation. The plastic clay of the Paris basin is described as consisting of two beds separated by a bed of sand. The lower bed is the proper plastic clay. The plastic clay of Abondant, near the forest of Dreux, analysed by Vauquelin, gave—

Silica, 43·5; alumina, 33·2; lime, 0·35; iron, 1; water, 18.

This clay is employed as a fire clay for making the bungs or seggars, or coarse earthenware cases, in which china ware is fired.

The plastic clay of Dorsetshire and Devonshire supplies the great Staffordshire potteries. It is gray coloured, less unctuous than that of Dreux, and consequently more friable. It becomes white in the pottery kiln, and is infusible at that heat. It causes no effervescence with nitric acid, but falls down quickly in it, and becomes higher coloured. Its refractoriness allows of a harder glaze being applied to the ware formed from it without risk of the heat requisite for making the glaze flow, affecting the biscuit either in shape or colour. “Most of the plastic clays of France,” says M. Brongniart, “employed for the same ware, have the disadvantage of reddening a little in a somewhat strong heat; and hence it becomes necessary to coat them with a soft glaze, fusible by means of excess of lead at a low heat, in order to preserve the white appearance of the biscuit. Such a glaze has a dull aspect, and cracks readily into innumerable fissures by alternations of hot and cold water.” Hence one reason of the vast inferiority of the French stone-ware to the English.

4. Porcelain clay or Kaolin earth.—The Kaolins possess very characteristic properties. They are friable in the hand, meagre to the touch, and difficultly form a paste with water. When freed from the coarse and evidently foreign particles interspersed through them, they are absolutely infusible in the porcelain kiln, and retain their white colour unaltered. They harden with heat like other clays, and perhaps in a greater degree; but they do not acquire an equal condensation or solidity, at least when they are perfectly pure. The Kaolins in general appear to consist of alumina and silica in nearly equal proportions. Most of the Kaolin clays contain some spangles of mica which betray their origin from disintegrated granite.

This origin may be regarded as one of their most distinctive features. Almost all the porcelain clays are evidently derived from the decomposition of the felspars, granites, and principally those rocks of felspar and quartz, called graphic granite. Hence, they are to be found only in primitive mountain districts, among banks or blocks of granite, forming thin seams or partings between them. In the same partings, quartz and mica occur, being relics of the granite; while some seams of Kaolin retain the external form of felspar.

The most valuable Kaolins have been found:—

In China and Japan. The specimens imported from these countries appear pretty white; but are more unctuous to the touch, and more micaceous than the porcelain clays of France.

In Saxony. The Kaolin employed in the porcelain manufactories of that country has a slight yellow or flesh colour, which disappears in the kiln, proving as Wallerius observed, that this tint is not owing to any metallic matter.

In France, at Saint-Yriex-la-Perche, about 10 leagues from Limoges. The Kaolin occurs there in a bed, or perhaps a vein of beds of granite, or rather of that felspar rock called Pe-tun-tse, which exists here in every stage of decomposition. This Kaolin is generally white, but sometimes a little yellowish with hardly any mica. It is meagre to the touch, and some beds include large grains of quartz, called pebbly by the China manufacturers. This variety, when ground, affords, without the addition of any fusible ingredient, a very transparent porcelain.

Near Bayonne. A Kaolin possessing the lamellated structure of felspar, in many places. The rock containing it is a graphic granite in every stage of decomposition.

In England, in the county of Cornwall. This Kaolin or China clay is very white, and more unctuous to the touch than those upon the continent of Europe mentioned above. Like them it results from the decomposition of the felspars and granites, occurring in the middle of these rocks. Mr. Wedgewood found it to contain 60 of alumina or pure clay, and 40 of silica, in 100 parts.

Pure clay, the alumina of the chemist, is absolutely infusible; but when subjected to the fire of a porcelain kiln, it contracts into about one half of its total bulk. It must, however, be heated very cautiously, otherwise it will decrepitate and fly in pieces, owing to the sudden expansion into steam of the water combined with its particles, which is retained with a considerable attractive force. It possesses little plasticity, and consequently affords a very short paste, which is apt to crack when kneaded into a cake.

It is not only infusible by itself, but it will not dissolve in the fusible glasses; making them merely opaque. If either lime or silica be added separately to pure clay, in any proportion, the mixture will not melt in the most violent furnace; but if alumina, lime, and silica be mixed together, the whole melts, and the more readily, the nearer the mixture approaches to the following proportions:—1 of alumina, 1 of lime, and 3 of sand. If the sand be increased to five parts, the compound becomes infusible. These interesting facts show the reciprocal action of those earths which are mixed most commonly in nature with alumina.

Iron in small quantity, but in a state not precisely determined, though probably of protoxide, does not colour the clays till they are subjected to a powerful heat. There are very white clays, such as those of Montereau, which do not become red till calcined in the porcelain kiln; the oxide of iron contained in them, which colours them in that case, was previously imperceptible. It appears from this circumstance, that the clays fit for making fine white stone ware, as also the Kaolins adapted to the manufacture of porcelain, are very rare.

Iron, in larger proportion, usually colours the clays green or slate-blue, before they have been heated. Such clays, exposed to the action of fire, become yellow or red according to the quantity of iron which they contain. When the iron is very abundant, it renders the clays fusible; but a little lime and silica must also be present for this effect. The earthenware made with these ferruginous clays, can bear but a moderate baking heat; it is thick, porous, and possesses the advantage merely of cheapness, and of bearing considerable alternations of temperature without breaking.

Alumina and the very aluminous natural clays which possess most plasticity, are apt to crack in drying, or to lose their shape. This very serious defect for the purposes of pottery is rectified, in some measure, by adding to that earth a certain quantity of sand or silica. Thus, a compound is formed which possesses less attraction for water, and dries more equably from the openness of its body. The principal causes of the distortion of earthenware vessels, are the unequal thickness of their parts, and quicker desiccation upon one side than another. Hard burnt stone-ware ground to powder, and incorporated with clay, answers still better than sand for counteracting the great and irregular contraction which natural pottery paste is apt to experience. Such ground biscuit is called cement; and its grains interspersed through the ware, may be regarded as so many solutions of continuity, which arrest the fissures.

The preceding observations point out the principles of those arts which employ clay for moulding by the wheel, and baking in a kiln. See Porcelain and Pottery.

CLOTH, MANUFACTURE OF. See Textile Fabrics, Weaving, Wool.

CLOTH-BINDING. Nothing places in so striking a point of view the superior taste, judgment, and resources of London tradesmen over those of the rest of the world, than the extensive substitution which they have recently made of embossed silks and calicoes for leather in the binding of books. In old libraries, cloth-covered boards indeed may occasionally be seen, but they have the meanest aspect, and are no more to be compared with our modern cloth-binding, than the jupon of a trull, with the ballet dress of Taglioni. The silk or calico may be dyed of any shade which use or fancy may require, impressed with gold or silver foil in every form, and variegated by ornaments in relief, copied from the most beautiful productions in nature. This new style of binding is distinguished not more for its durability, elegance, and variety, than for the economy and dispatch with which it ushers the offspring of intellect into the world. For example, should a house eminent in this line, such as that of Westleys, Friar-street, Doctors’-commons, receive 5000 volumes from Messrs. Longman & Co. upon Monday morning, they can have them all ready for publication, within the incredibly short period of two days; being far sooner than they could have rudely boarded them upon the former plan. The reduction of price is not the least advantage incident to the new method, amounting to fully 50 per cent. upon that with leather.

The dyed cloth being cut by a pattern to the size suited to the volume, is passed rapidly through a roller press, between engraved cylinders of hard steel, whereby it receives at once the impress characteristic of the back, and the sides, along with embossed designs over the surface in sharp relief. The cover thus rapidly fashioned, is as rapidly applied by paste to the stitched and pressed volume; no time being lost in mutual adjustments; since the steel rollers turn off the former, of a shape precisely adapted to the latter. Hard glazed and varnished calico is moreover much less an object of depredation to moths, and other insects, than ordinary leather has been found to be.

COBALT. This metal being difficult to reduce from its ores, is therefore very little known, and has not hitherto been employed in its simple state in any of the arts; but its oxide has been extensively used on account of the rich blue colour which it imparts to glass, and the glaze of porcelain and stone-ware. The principal ores of cobalt are those designated by mineralogists under the names of arsenical cobalt and gray cobalt. The first contains, in addition to cobalt, some arsenic, iron, nickel, and occasionally silver, &c. The other is a compound of cobalt with iron, arsenic, sulphur, and nickel. Among the gray cobalts, the ore most esteemed for its purity is that of Tunaberg in Sweden. It is often in regular crystals which possess the lustre and colour of polished steel. The specific gravity of cobalt pyrites is 6·36 to 4·66. The Tunaberg variety afforded to Klaproth, cobalt, 44; arsenic, 55·5; sulphur, 0·5: so that it is an arseniuret. Others, however, contain much sulphur as well as iron. It imparts at the blowpipe a blue colour to borax and other fluxes, and gives out arsenical fumes.

The ore being picked to separate its concomitant stony matters, is pounded fine and passed through a sieve; and is also occasionally washed. The powder is then spread on the sole of a reverberatory furnace, the flue of which leads into a long horizontal chimney. Here it is exposed to calcination for several hours, to expel the sulphur and arsenic that may be present; the former burning away in sulphurous acid gas, the latter being condensed into the white oxide or arsenious acid, whence chiefly the market is supplied with this article. This calcining process can never disengage the whole of these volatile ingredients, and there is therefore a point beyond which it is useless to push it; but the small quantities that remain are not injurious to the subsequent operations. The roasted ore is sifted anew; reduced to a very fine powder, and then mixed with 2 or 3 parts of very pure siliceous sand, to be converted into what is called zaffre. With this product glasses are generally coloured blue, as well as enamels and pottery glaze. In the works where cobalt ores are treated, a blue glass is prepared with the zaffre, which is well known under the name of smalt or azure blue. This azure is made by adding to the zaffre 2 or 3 parts of potash, according to its richness in cobalt, and melting the mixture in earthen crucibles. The fused mass is thrown out while hot into water; and is afterwards triturated and levigated in mills mounted for the purpose. There remains at the bottom of the earthen pot a metallic lump, which contains a little cobalt, much nickel, arsenic, iron, &c. This is called speiss.

As it is the oxide of cobalt which has the colouring quality, the calcination serves the purpose of oxidizement, as well as of expelling the foreign matters.

A finer cobalt-oxide is procured for painting upon hard porcelain, by boiling the cobalt ore in nitric acid, which converts the arsenic into an acid, and combines it with the different metals present in the mineral. These arseniates being unequally soluble in nitric acid, may be separated in succession by a cautious addition of carbonate of soda or potash; and the arseniate of cobalt as the most soluble remains unaffected. It has a rose colour; and is easily distinguishable, whence the precipitation may be stopped at the proper point. The above solution should be much diluted, and the alkali should be cautiously added with frequent agitation.

The cobalt ores, rich in nickel, are exposed to slow oxidizement in the air, whereby the iron, cobalt, arsenic, and sulphur get oxygenated by the atmospheric moisture, but the nickel continues in the metallic state. This action of the weather must not be extended beyond a year, otherwise the nickel becomes affected, and injures the cobalt blue. The ore hereby increases in weight, from 8 to 10 per cent. Fig. 291. is a longitudinal section of the furnace: fig. 292., a horizontal section upon a level with the sole of the hearth. It is constructed for wood fuel, and the hearth is composed of fire-bricks or tiles. The vapours and gases disengaged in the roasting, pass off through the flues a a, into the channels b b, and thence by c into the common vent, or poison chamber. See the representation of the poison tower of Altenberg, under the article Arsenic. The flues are cleared out by means of openings left at suitable situations in the brick-work of the chimneys.

The azure manufacture is carried on chiefly in winter, in order that the external cold may favour the more complete condensation of the acids of arsenic. From 3 to 5 cwt. of Schlich (pasty ore), are roasted at one operation, and its bed is laid from 5 to 6 inches thick. After two hours, it must be turned over; and the stirring must be repeated every half hour, till no more arsenic is observed to exhale. The process being then finished, the ore must be raked out of the furnace, and another charge introduced.

The duration of the roasting is regulated partly by the proportion of sulphur and arsenic present, and partly by the amount of nickel; which must not be suffered to become oxidized, lest it should spoil the colour of the smalt. The latter ores should be but slightly roasted, so as to convert the nickel into speiss. The roasted ore must be sifted in a safety apparatus. The loss of weight in the roasting amounts, upon the average, to 36 per cent. The roasted ore has a brownish gray hue, and is called safflor in German, and is distributed into different sorts. F F S is the finest safre; F S, fine; O S, ordinary; and M S, middling. These varieties proceed from various mixtures of the calcined ores. The roasted ore is ground up along with sand, elatriated, and, when dry, is called zaffre. It is then mixed with a sufficient quantity of potash for converting the mixture into a glass.

Figs. 293. and 294. represent a round smalt furnace, in two vertical sections, at right angles to each other. The fire-place is vaulted or arched; the flame orifice a, is in the middle of the furnace; b is the feed hole; c, a tunnel which serves as an ash-pit, and to supply air; d, openings through which the air arrives at the fuel, the wood being placed upon the vault; e, knee holes for taking out the scoriæ from the pot bottoms; f, working orifices, with cast-iron plates g, in front of them. Under these are the additional outlets h. The smoke and flame pass off through the orifices i, which terminate in expanded flues, where the sand may be calcined or the wood may be baked. Eight hours are sufficient for one vitrifying operation, during which the glass is stirred about several times in the earthen melting pots.

The preparation of the different shades of blue glass are considered as secrets in the smelting works; and marked with the following letters:—F F F C, the finest; F C, fine; M C, middling; O C, ordinary. A melting furnace, containing 8 pots of glass; produces in 24 hours, from 24 cwts. of the mixture, 19 cwts. of blue glass; and from ⁄2 to ⁄4 cwt. of scoriæ or speiss (speise). The composition speise, according to Berthier, is,—nickel, 49·0; arsenic, 37·8; sulphur, 7·8; copper, 1·6; cobalt, 3·2 in 100. Nickel, arsenic, and sulphur, are its essential constituents; the rest are accidental, and often absent. The freer the cobalt ore is from foreign metals, the finer is the colour, and the deeper is the shade; paler tints are easily obtained by dilution with more glass. The presence of nickel gives a violet tone.

The production of smalt in the Prussian states amounted, in 1830, to 7452⁄2 cwts.; and, in Saxony, to 9697 cwts.; in 1825, to 12,310 cwts.

One process for making fine smalt has been given under the title Azure; I shall introduce another somewhat different here.

The ore of cobalt is to be reduced to very fine powder, and then roasted with much care. One part, by weight, is next to be introduced, in successive small portions, into an iron vessel, in which three parts of acid sulphate of potassa has been previously fused, at a moderate temperature. The mixture, at first fluid, soon becomes thick and firm, when the fire is to be increased, until the mass is in perfect fusion, and all white vapours have ceased. It is then to be taken out of the crucible with an iron ladle, the crucible is to be recharged with acid sulphate of potash, and the operation continued as before, until the vessel is useless. The fused mass contains sulphate of cobalt, neutral sulphate of potassa, and arseniate of iron, with a little cobalt. It is to be pulverized, and boiled in an iron vessel, with water, as long as the powder continues rough to the touch. The white, or yellowish white residue, may be allowed to separate from the solution, either by deposition or filtration. Carbonate of potassa, free from silica, is then to be added to the solution, and the carbonate of cobalt thrown down is to be separated and well washed, if possible, with warm water; the same water may be used to wash other portions of the fused mass. The filtered liquid which first passes, is a saturated solution of sulphate of potassa: being evaporated to dryness in an iron vessel, it may be reconverted into acid sulphate by fusing it with one half its weight of sulphuric acid: this salt is then as useful as at first.

The oxide of cobalt thus obtained, contains no nickel; so little oxide of iron is present, that infusion of galls does not show its presence; it may contain a little copper, if that metal exists in the ore, but it is easily separated by the known methods. Sometimes sulphuretted hydrogen will produce a yellow brown precipitate in the solution of the fused mass; this, however, contains no arsenic, but is either sulphuret of antimony or bismuth, or a mixture of both.

It has been found advantageous to add to the fused mass, sulphate of iron, calcined to redness, and one tenth of nitre when the residue is arseniate of iron, and contains no arseniate of cobalt. There is then no occasion to act upon the residue a second time for the cobalt in it.

This process is founded on the circumstances that the sulphate of cobalt is not decomposed by a red heat, and that the arseniates of iron and cobalt are insoluble in all neutral liquids. It is quite evident that to obtain a perfect result, the excess of acid in the bisulphate of potassa must be completely driven off by the red heat applied.

110,646 lbs. of smalts were imported into the United Kingdom in 1835, and 96,949 were retained for home consumption. In 1834, only 16,223 lbs. were retained.

In 1835, 322,562 lbs. of zaffres were imported, and 336,824 are stated to have been retained, which is obviously an error. 284,000 lbs. were retained in 1834.

COCCULUS INDICUS, or Indian berry, is the fruit of the Menispermum Cocculus, a large tree, which grows upon the coasts of Malabar, Ceylon, &c. The fruit is blackish, and of the size of a large pea. It owes its narcotic and poisonous qualities to the vegeto-alkaline chemical principle called picrotoxia, of which it contains about one-fiftieth part of its weight. It is sometimes thrown into waters to intoxicate or kill fishes; and it is said to have been employed to increase the inebriating qualities of ale or beer. Its use for this purpose is prohibited by act of parliament, under a penalty of 200l. upon the brewer, and 500l. upon the seller of the drug.

COCHINEAL was taken in Europe at first for a seed, but was proved by the observations of Lewenhoeck to be an insect, being the female of that species of shield-louse, or coccus, discovered in Mexico, so long ago as 1518. It is brought to us from Mexico, where the animal lives upon the cactus opuntia or nopal. Two sorts of cochineal are gathered—the wild, from the woods, called by the Spanish name grana silvestra; and the cultivated, or the grana fina, termed also mesteque, from the name of a Mexican province. The first is smaller, and covered with a cottony down, which increases its bulk with a matter useless in dyeing; it yields, therefore, in equal weight, much less colour, and is of inferior price to that of the fine cochineal. But these disadvantages are compensated in some measure to the growers by its being reared more easily, and less expensively; partly by the effect of its down, which enables it better to resist rains and storms.

The wild cochineal, when it is bred upon the field nopal, loses in part the tenacity and quantity of its cotton, and acquires a size double of what it has on the wild opuntias. It may therefore be hoped, that it will be improved by persevering care in the rearing of it, when it will approach more and more to fine cochineal.

The fine cochineal, when well dried and well preserved, should have a gray colour, bordering on purple. The gray is owing to the powder, which naturally covers it, and of which a little adheres; as also to a waxy fat. The purple shade arises from the colour extracted by the water in which they were killed. It is wrinkled with parallel furrows across its back, which are intersected in the middle by a longitudinal one; hence, when viewed by a magnifier, or even a sharp naked eye, especially after being swollen by soaking for a little in water, it is easily distinguished from the factitious, smooth, glistening, black grains, of no value, called East India cochineal, with which it is often shamefully adulterated by certain London merchants. The genuine cochineal has the shape of an egg, bisected through its long axis, or of a tortoise, being rounded like a shield upon the back, flat upon the belly, and without wings.

These female insects are gathered off the leaves of the nopal plant, after it has ripened its fruit, a few only being left for brood, and are killed, either by a momentary immersion in boiling water, by drying upon heated plates, or in ovens: the last become of an ash-gray colour, constituting the silver cochineal, or jaspeada; the second are blackish, called negra, and are most esteemed, being probably driest; the first are reddish brown, and reckoned inferior to the other two. The dry cochineal being sifted, the dust, with the imperfect insects and fragments which pass through, are sold under the name of granillo.

Cochineal keeps for a long time in a dry place. Hellot says that he has tried some 130 years old, which produced the same effect as new cochineal.

We are indebted to MM. Pelletier and Caventou for a chemical investigation of cochineal, in which its colouring matter was skilfully eliminated.

Purified sulphuric ether acquired by digestion with it a golden yellow colour, amounting by Dr. John to one tenth of the weight of the insect. This infusion left, on evaporation, a fatty wax of the same colour.

Cochineal, exhausted by ether, was treated with alcohol at 40° B. After 30 infusions in the digester of M. Chevreul, the cochineal continued to retain colour, although the alcohol had ceased to have any effect on it. The first alcoholic liquors were of a red verging on yellow. On cooling, they let fall a granular matter. By spontaneous evaporation, this matter, of a fine red colour, separated, assuming more of the crystalline appearance. These species of crystals dissolved entirely in water, which they tinged of a yellowish-red.

This matter has a very brilliant purple-red colour; it adheres strongly to the sides of the vessels; it has a granular and somewhat crystalline aspect, very different, however, from those compound crystals alluded to above; it is not altered by the air, nor does it sensibly attract moisture. Exposed to the action of heat, it melts at about the fiftieth degree centigrade (122° Fahr.). At a higher temperature it swells up, and is decomposed with the production of carburetted hydrogen, much oil, and a small quantity of water, very slightly acidulous. No trace of ammonia was found in these products.

The colouring principle of cochineal is very soluble in water. By evaporation, the liquid assumes the appearance of syrup, but never yields crystals. It requires of this matter a portion almost imponderable to give a perceptible tinge of bright purplish red to a large body of water. Alcohol dissolves this colouring substance, but, as we have already stated, the more highly it is rectified the less of it does it dissolve. Sulphuric ether does not dissolve the colouring principle of cochineal; but weak acids do, possibly owing to their water of dilution. No acid precipitates it in its pure state. This colouring principle, however, appears to be precipitable by all the acids, when it is accompanied by the animal matter of the cochineal.

The affinity of alumina for the colouring matter is very remarkable. When that earth, newly precipitated, is put into a watery solution of the colouring principle, this is immediately seized by the alumina. The water becomes colourless, and a fine red lake is obtained, if we operate at the temperature of the atmosphere; but if the liquor has been hot, the colour passes to crimson, and the shade becomes more and more violet, according to the elevation of the temperature, and the continuance of the ebullition.

The salts of tin exercise upon the colouring matter of cochineal a remarkable action. The muriatic protoxide of tin forms a very abundant violet precipitate in the liquid. This precipitate verges on crimson, if the salt contains an excess of acid. The muriatic deutoxide of tin produces no precipitate, but changes the colour to scarlet-red. If gelatinous alumina be now added, we obtain a fine red precipitate, which does not pass to crimson by boiling.

To this colouring principle the name carminium has been given, because it forms the basis of the pigment called carmine.

The process followed in Germany for making carmine, which consists in pouring a certain quantity of solution of alum into a decoction of cochineal, is the most simple of all, and affords an explanation of the formation of carmine, which is merely the carminium and the animal matter precipitated by the excess of acid in the salt, which has taken down with it a small quantity of alumina; though it appears that alumina ought not to be regarded as essential to the formation of carmine. In fact, by another process, called by the name of Madame Cenette of Amsterdam, the carmine is thrown down, by pouring into the decoction of cochineal a certain quantity of the binoxalate of potash. When carbonate of soda is added, then carminated lake also falls down. That carmine is a triple compound of animal matter, carminium, and an acid appears from the circumstance, that liquors which have afforded their carmine, when a somewhat strong acid is poured into them, yield a new formation of carmine by the precipitation of the last portions of the animal matter. But whenever the whole animal matter is thrown down, the decoctions, although still much charged with the colouring principle, can afford no more carmine. Such decoctions may be usefully employed to make carminated lakes, saturating the acid with a slight excess of alkali, and adding gelatinous alumina. The precipitates obtained, on adding acids to the alkaline decoctions of cochineal, are therefore true carmines, since they do not contain alumina; but the small quantity of alumina which is thrown down by alum in the manufacture of carmine, augments its bulk and weight. It gives, besides, a greater lustre to the colour, even though diluting and weakening it a little.

The carmines found in the shops of Paris were analysed, and yielded the same products. They are decomposed by the action of heat, with the diffusion at first of a very strong smell of burning animal matter, and then of sulphur. A white powder remained, amounting to about one-tenth of the matter employed, and which was found to be alumina. Other quantities of carmine were treated with a solution of caustic potash, which completely dissolved them, with the exception of a beautiful red powder, not acted on by potash and concentrated acids, and which was recognized to be red sulphuret of mercury or vermillion. This matter, evidently foreign to the carmine, appears to have been added, in order to increase its weight.

The preceding observations and experiments seem calculated to throw some light on the art of dyeing scarlet and crimson. The former is effected by employing a cochineal bath, to which there have been added, in determinate proportions, acidulous tartrate of potash, and nitro-muriatic deutoxide of tin. The effect of these two salts is now well known. The former, in consequence of its excess of acid, tends to redden the colour, and to precipitate it along with the animal matter: the latter acts in the same manner, at first by its excess of acid, then by the oxide of tin which falls down also with the carmine and animal matter, and is fixed on the wool, with which it has of itself a strong tendency to combine. MM. Pelletier and Caventou remark, that “to obtain a beautiful shade, the muriate of tin ought to be entirely at the maximum of oxidizement; and it is in reality in this state that it must exist in the solution of tin prepared according to the proportions prescribed in M. Berthollet’s treatise on dyeing.”

We hence see why, in dyeing scarlet, the employment of alum is carefully avoided, as this salt tends to convert the shade to a crimson. The presence of an alkali would seem less to be feared. The alkali would occasion, no doubt, a crimson-coloured bath; but it would be easy in this case to restore the colour, by using a large quantity of tartar. We should, therefore, procure the advantage of having a bath better charged with colouring matter and animal substance. It is for experience on the large scale to determine this point. As to the earthy salts, they must be carefully avoided; and if the waters be selenitish, it would be a reason for adding a little alkali.

To obtain crimson, it is sufficient, as we know, to add alum to the cochineal bath, or to boil the scarlet cloth in alum water. It is also proper to diminish the dose of the salt of tin, since it is found to counteract the action of the alum.

The alkalies ought to be rejected as a means of changing scarlet to crimson. In fact, crimsons by this process cannot be permanent colours, as they pass into reds by the action of acids.

According to M. Von Grotthuss, carmine may be deprived of its golden shade by ammonia, and subsequent treatment with acetic acid and alcohol. Since this fact was made known, M. Herschel, colour maker at Halle, has prepared a most beautiful carmine.

The officers of Her Majesty’s Customs have lately detected a system of adulterating cochineal, which has been practised for many years upon a prodigious scale by a mercantile house in London. I have analyzed about 100 samples of such cochineal, from which it appears that the genuine article is moistened with gum-water, agitated in a box or leather bag, first, with sulphate of baryta in fine powder, afterwards with bone or ivory black, to give it the appearance of negra cochineal, and then dried. By this means about 12 per cent. of the worthless heavy spar is sold at the price of cochineal, to the enrichment of the sophisticators, and the disgrace and injury of British trade and manufactures.

The specific gravity of genuine cochineal is 1·25; that of the cochineal loaded with the barytic sulphate 1·35. It was taken in oil of turpentine and reduced to water as unity, because the waxy fat of the insects prevents the intimate contact of the latter liquid with them, and the ready expulsion of air from their wrinkled surface. They are not at all acted upon by the oil, but are rapidly altered by water, especially when they have been gummed and barytified.

The quantities of cochineal imported into the United Kingdom in the following years, were:—

1827. 1828. 1829. 1830. 1831. 1832. 1833. 1834. 1835.

Libs. 320,722 258,032 288,456 316,589 244,371 388,478 359,381 410,387 418,320

The quantities re-exported were:—

Libs. 145,756 158,109 153,738 100,059 168,329 138,270 130,732 265,490 352,023

Humboldt states that so long ago as the year 1736, there was imported into Europe from South America cochineal to the value of 15 millions of francs. Its high price had for a long time induced dyers to look out for cheaper substitutes in dyeing red, and since science has introduced so many improvements in tinctorial processes, both madder and lac have been made to supersede cochineal to a very great extent. Its price has, in consequence of this substitution, as well as from more successful modes of cultivation, fallen very greatly of late years. At present it is only 7s. per lib. in London. See Scarlet Dyeing.

COCOA, STEARINE, AND ELAINE. Mr. Soames obtained a patent in September 1829, for making these useful articles, by the following process:

He takes the substance called cocoa-nut oil, in the state of lard, in which it is imported into this country, and submits it to a strong hydraulic pressure, having made it up in small packages, 3 or 4 inches wide, 2 feet long, and 1 or 1⁄2 inches thick. These packages are formed by first wrapping up the said substance in a strong linen cloth, of close texture, and then in an outward wrapper of strong sail cloth. The packages are to be placed side by side, in single rows, between the plates of the press, allowing a small space between the packages for the escape of the elaine.

The temperature at which the pressure is begun, should be from about 50 to 55 degrees, or in summer as nearly at this pitch as can be obtained, and the packages of the said substance intended for pressure, should be exposed for several hours previously to about the same temperature. When the packages will no longer yield their oil or elaine freely at this temperature, it is to be gradually raised; but it must at no time exceed 65 degrees, and the lower the temperature at which the separation can be effected, the better will be the quality of the oil expressed.

When the packages are sufficiently pressed, that is, when they will give out no more oil, or yield it only in drops at long intervals, the residuum in them is to be taken out and cleansed and purified, which is done by melting it in a well-tinned copper vessel, which is fixed in an outer vessel, having a vacant space between, closed at the top, into which steam is admitted, and the heat is kept up moderately for a sufficient time to allow the impurities to subside; but if a still higher degree of purity is required, it is necessary to pass it through filters of thick flannel lined with blotting paper.

Having been thus cleansed or purified, it is fit for the manufacture of candles, which are made by the ordinary process used in making mould tallow candles. Having thus disposed of the stearine, or what is called the first product, he proceeds with the elaine or oil expressed from it, and which he calls the second product, as follows: that is to say, he purifies it by an admixture, according to the degree of its apparent foulness, of from 1 to 2 per cent. by weight of the sulphuric acid of commerce, of about 1·80 specific gravity, diluted with six times its weight of water. The whole is then to be violently agitated by mechanical means, and he prefers for this purpose the use of a vessel constructed on the principle of a common barrel churn. When sufficiently agitated, it will have a dirty whitish appearance, and is then to be drawn off into another vessel, in which it is to be allowed to settle, and any scum that rises is to be carefully taken off. In a day or two the impurities will be deposited at the bottom of the oil, which will then become clear, or nearly so, and it is to be filtered through a thick woollen cloth, after which it will be fit for burning in ordinary lamps and for other uses.

The process of separating the elaine from the stearine, by pressure, in manner aforesaid, had never before been applied to the substance called cocoa-nut oil, and consequently no product had heretofore been obtained thereby from that substance, fit for being manufactured into candles in the ordinary way, or for being refined by any of the usual modes, so as to burn in ordinary lamps, both which objects are obtained by this method of preparing or manufacturing the said substance.

Candles well made from the above material are a very superior article. The light produced is more brilliant than from the same sized candle made of tallow; the flame is perfectly colourless, and the wick remains free from cinder, or any degree of foulness during combustion.

COFFEE. The coffee is the seed of a tree of the family rubiaceæ, and belongs to the Pentandria monogynia of Linnæus. There are several species of the genus, but the only one cultivated is the Coffæa Arabica, a native of Upper Ethiopia and Arabia Felix. It rises to the height of 15 or 20 feet; its trunk sends forth opposite branches in pairs above and at right angles to each other; the leaves resemble those of the common laurel, although not so dry and thick. From the angle of the leaf-stalks small groups of white flowers issue, which are like those of the Spanish jasmine. These flowers fade very soon, and are replaced by a kind of fruit not unlike a cherry, which contains a yellow glairy fluid, enveloping two small seeds or berries convex upon one side, flat and furrowed upon the other in the direction of the long axis. These seeds are of a horny or cartilaginous nature; they are glued together, each being surrounded with a peculiar coriaceous membrane. They constitute the coffee of commerce.

It was not till towards the end of the 15th century that the coffee tree began to be cultivated in Arabia. Historians usually ascribe the discovery of the use of coffee as a beverage to the superior of a monastery there, who, desirous of preventing the monks from sleeping at their nocturnal services, made them drink the infusion of coffee upon the report of shepherds, who pretended that their flocks were more lively after browsing on the fruit of that plant. The use of coffee was soon rapidly spread, but it encountered much opposition on the part of the Turkish government, and became the occasion of public assemblies. Under the reign of Amurath III. the mufti procured a law to shut all the coffee-houses, and this act of suppression was renewed under the minority of Mahomet IV. It was not till 1554 under Solyman the Great that the drinking of coffee was accredited in Constantinople; and a century elapsed before it was known in London and Paris. Solyman Aga introduced its use into the latter city in 1669, and in 1672 an Armenian established the first café at the fair of Saint Germain.

When coffee became somewhat of a necessary of life from the influence of habit among the people, all the European powers who had colonies between the tropics, projected to form plantations of coffee trees in them. The Dutch were the first who transported the coffee plant from Moka to Batavia, and from Batavia to Amsterdam. In 1714 the magistrates of that city sent a root to Louis XIV. which he caused to be planted in the Jardin du Roi. This became the parent stock of all the French coffee plantations in Martinique.

The most extensive culture of coffee is still in Arabia Felix, and principally in the kingdom of Yemen, towards the cantons of Aden and Moka. Although these countries are very hot in the plains, they possess mountains where the air is mild. The coffee is generally grown halfway up on their slopes. When cultivated on the lower grounds it is always surrounded by large trees which shelter it from the torrid sun, and prevent its fruit from withering before their maturity. The harvest is gathered at three periods, the most considerable occurs in May, when the reapers begin by spreading cloths under the trees, then shaking the branches strongly, so as to make the fruit drop, which they collect, and expose upon mats to dry. They then pass over the dried berries a very heavy roller, to break the envelopes, which are afterwards winnowed away with a fan. The interior bean is again dried before being laid up in store.

In Demerara, Berbice, and some of our West India islands, where much good coffee is now raised, a different mode of treating the pulpy fruit and curing the beans is adopted. When the cherry-looking berry has assumed a deep-red colour it is gathered, and immediately subjected to the operations of a mill composed of two wooden rollers, furnished with iron plates, which revolve near a third fixed roller called the chops. The berries are fed into a hopper above the rollers, and falling down between them and the chops, they are stripped of their outer skins and pulp, while the twin beans are separated from each other. These beans then fall upon a sieve, which allows the skin and the pulp to pass through, while the hard beans accumulate and are progressively slid over the edge into baskets. They are next steeped for a night in water, thoroughly washed in the morning, and afterwards dried in the sun. They are now ready for the peeling mill, a wooden edge wheel turned vertically by a horse yoked to the extremity of its horizontal axis. In travelling over the coffee, it bursts and detaches the coriaceous or parchment-like skin which surrounds each hemispherical bean. It is then freed from the membranes by a winnowing machine, in which four pieces of tin made fast to an axle are caused to revolve with great velocity. Corn fanners would answer better than this rude instrument of negro invention. The coffee is finally spread upon mats or tables, picked clean, and packed up for shipment.

The most highly esteemed coffee is that of Moka. It has a smaller and a rounder bean; a more agreeable taste and smell than any other. Its colour is yellow. Next to it in European reputation is the Martinique and Bourbon coffees; the former is larger than the Arabian and more oblong; it is rounded at the ends; its colour is greenish, and it preserves almost always a silver gray pellicle, which comes off in the roasting. The Bourbon coffee approaches nearest to the Moka from which it originally sprung. The Saint Domingo coffee has its two extremities pointed, and is much less esteemed than the preceding.

The coffee tree flourishes in hilly districts where its root can be kept dry, while its leaves are refreshed with frequent showers. Rocky ground, with rich decomposed mould in the fissures, agrees best with it. Though it would grow, as we have said, to the height of 15 or 20 feet, yet it is usually kept down by pruning to that of five feet for increasing the production of the fruit, as well as for the convenience of cropping. It begins to yield fruit the third year, but is not in full bearing till the fifth, does not thrive beyond the twenty-fifth, and is useless in general at the thirtieth. In the coffee husbandry, the plants should be placed eight feet apart, as the trees throw out extensive horizontal branches, and in holes ten or twelve feet deep to secure a constant supply of moisture.

Coffee has been analysed by a great many chemists, with considerable diversity of results. The best analysis perhaps is that of Schrader. He found that the raw beans distilled with water in a retort communicated to it their flavour and rendered it turbid, whence they seem to contain some volatile oil. On reboiling the beans, filtering, and evaporating the liquor to a syrup, adding a little alcohol till no more matter was precipitated, and then evaporating to dryness, he obtained 17·58 per cent. of a yellowish-brown transparent extract, which constitutes the characteristic part of coffee, though it is not in that state the pure proximate principle, called cafeine. Its most remarkable reaction is its producing, with both the protoxide and the peroxide salts of iron, a fine grass green colour, while a dark green precipitate falls, which re-dissolves when an acid is poured into the liquor. It produces on the solution of the salts of copper scarcely any effect, till an alkali be added, when a very beautiful green colour is produced which may be employed in painting. Coffee beans contain also a resin, and a fatty substance somewhat like suet. According to Robiquet, ether extracts from coffee beans nearly 10 per cent. of resin and fat, but he probably exaggerates the amount. The peculiar substance cafeine contained in the above extract is crystallizable. It is remarkable in regard to composition, that after urea and the uric acid, it is among organic products the richest in azote. It was discovered and described in 1820 by Runge. It does not possess alkaline properties. Pfaff obtained only 90 grains of cafeine from six pounds of coffee beans. There is also an acid in raw coffee to which the name of cafeic acid has been given. When distilled to dryness and decomposed, it has the smell of roasted coffee.

Coffee undergoes important changes in the process of roasting. When it is roasted to a yellowish brown it loses, according to Cadet, 12⁄2 per cent. of its weight, and is in this state difficult to grind. When roasted to a chestnut brown it loses 18 per cent., and when it becomes entirely black, though not at all carbonised, it has lost 23 per cent. Schrader has analyzed roasted coffee comparatively with raw coffee, and he found in the first 12⁄2 per cent. of an extract of coffee, soluble in water and alcohol, which possesses nearly the properties of the extract of the raw coffee, although it has a deeper brown colour, and softens more readily in the air. He found also 10·4 of a blackish brown gum; 5·7 of an oxygenated extract or rather apothème soluble in alcohol, insoluble in water; 2 of a fatty substance and resin; 69 of burnt vegetable fibre, insoluble. On distilling roasted coffee with water, Schrader obtained a product which contained the aromatic principle of coffee; it reddened litmus paper, and exhaled a strong and agreeable odour of roasted coffee. If we roast coffee in a retort, the first portions of the aromatic principle of coffee condense into a yellow liquid in the receiver; and these may be added to the coffee roasted in the common way, from which this matter has been expelled and dissipated in the air.

Chenevix affirmed that by the roasting of coffee a certain quantity of tannin possessing the property of precipitating gelatine is generated. Cadet made the same observation, and found, moreover, that the tannin was most abundant in the lightly roasted coffee, and that there was nearly none of it in coffee highly roasted. Payssé and Schrader, on the contrary, state that solution of gelatine does not precipitate either the decoction of roasted coffee or the alcoholic extract of this coffee. Runge likewise asserts that he could obtain no precipitate with gelatine; but he says that albumen precipitates from the decoction of roasted coffee the same kind of tannin as is precipitated from raw coffee by the acetate of lead, and set free from the lead by sulphuretted hydrogen. With these results my own experiments agree. Gelatine certainly does not disturb clear infusion of roasted coffee, but the salts of iron blacken it.

Schrader endeavoured to roast separately the different principles of coffee, but none of them exhaled the aromatic odour of roasted coffee except the horny fibrous matter. He therefore concludes that this substance contributes mainly to the characteristic taste of roasted coffee, which cannot be imitated by any other vegetable matter, and which, as we have seen, should be ascribed chiefly to the altered cafeic acid. According to Garot we may extract the cafeine without alteration from roasted coffee by precipitating its decoction by subacetate of lead, treating the washed precipitate with sulphuretted hydrogen, and evaporating the liquid product to dryness.

Of late years, much ingenuity has been expended in contriving various forms of apparatus for making infusions of coffee for the table. I have tried most of them, and find, after all, none so good as a cafetière à la Belloy, the coffee biggin, with the perforated tin plate strainer, especially when the filtered liquor is kept simmering in a close vessel, set over a lamp or steam pan. The useful and agreeable matter in coffee is very soluble: it comes off with the first waters of infusion, and needs no boiling.

To roast coffee rightly we should keep in view the proper objects of this process, which are to develop its aroma, and destroy its toughness, so that it may be readily ground to powder. Too much heat destroys those principles which we should wish to preserve, and substitutes new ones which have nothing in common with the first, but add a disagreeable empyreumatic taste and smell. If, on the other hand, the rawness or greenness is not removed by an adequate heat, it masks the flavour of the bean, and injures the beverage made with it. When well roasted in the sheet iron cylinders set to revolve over a fire, it should have a uniform chocolate colour, a point readily hit by experienced roasters, who now manage the business very well for the principal coffee dealers both of London and Paris, so far as my judgment can determine. The development of the proper aroma is a criterion by which coffee roasters frequently regulate their operations. When it loses more than 20 per cent. of its weight, coffee is sure to be injured. It should never be ground till immediately before infusion.

COKE, is carbonized pitcoal. See Charcoal; and Pitcoal at the end.

COLCOTHAR OF VITRIOL, (Rouge d’Angleterre, Fr.; Rothes Eisenoxyd, Germ.) is the brown-red peroxide of iron, produced by calcining sulphate of iron with a strong heat, levigating the resulting mass, and elutriating it into an impalpable powder. A better way of making it so as to complete the separation of the acid, is to mix 100 parts of the green sulphate of iron with 42 of common salt, to calcine the mixture, wash away the resulting sulphate of soda, and levigate the residuum. The sulphuric acid in this case expels the chlorine of the salt in the form of muriatic acid gas, and saturates its alkaline base produced by the chemical reaction; whence an oxide will be obtained free from acid, much superior to what is commonly found in the shops. The best sort of polishing powder called jewellers’ red rouge or plate powder is the precipitated oxide of iron prepared by adding solution of soda to solution of copperas, washing, drying, and calcining the powder in shallow vessels with a gentle heat, till it assumes a deep brown red colour. See Iron.

COLOPHANY, black rosin, the solid residuum of the distillation of turpentine, when all the oil has been worked off.

COLOURING MATTER. (Matière colorante, Fr.; Farbstoff, Germ.) See Dyeing, the several dye-stuffs and pigments.

COLUMBIUM, a peculiar metal extracted from a rare mineral brought from Haddam in Connecticut. It is also called Tantalium from the mineral tantalite and yttrotantalite, found in Sweden. It has hitherto no application to the arts. It combines with two successive doses of oxygen; by the second it becomes an acid.

COLZA, is a variety of cabbage, the brassica oleracea, whose seeds afford, by pressure, an oil much employed in France and Belgium for burning in lamps, and for many other purposes. This plant requires a rich but light soil; it does not succeed upon either sandy or clayey lands. The ground for it must be deeply ploughed and well dunged. It should be sown in July, and be afterwards replanted in a richly manured field. In October it is to be planted out in beds, 15 or 18 inches apart. Colza may also be sowed in furrows 8 or 10 inches asunder.

Land which has been just cropped for wheat is that usually destined to colza; it may be fresh dunged with advantage. The harvest takes place in July, with the sickle, a little before the seeds are completely ripe, lest they should drop off. As the seed is productive of oil, however, only in proportion to its ripeness, the cut plants are allowed to complete their maturation, by laying them in heaps under airy sheds, or placing them in a stack, and thatching it with straw.

The cabbage stalks are thrashed with flails, the seeds are winnowed, sifted, spread out in the air to dry; then packed away in sacks, in order to be subjected to the oil mill at the beginning of winter. The oil-cake is a very agreeable food to cattle, and serves to fatten them. It is reckoned to defray the cost of the mill.

Colza impoverishes the soil very much, as do, indeed, all the plants cultivated for the sake of their oleaginous seeds. It must not, therefore, be come back upon again for six years, if fine crops be desired. The double ploughing which it requires, effectually cleans the ground. See Oils, Unctuous.

COMB, the name of an instrument made of a thin plate either plane or curved of wood, horn, tortoise-shell, ivory, bone, or metal, cut out upon one or both of its sides or edges, into a series of somewhat long teeth, not far apart; which is employed for disentangling, laying parallel and smooth the hairs of man, horses, or other animals.

A thin steel saw bow, mounted in an iron or wooden handle, is the implement used by the comb-maker to cut the bone, ivory, and wood into slices of from a twelfth to a quarter of an inch thick, and of a size suitable to that of the comb. The pieces of tortoise-shell as found in commerce are never flat, or, indeed, of any regular curvature, such as the comb must have. They are therefore steeped in boiling water sufficiently long to soften them, and set to cool in a press between iron or brass moulds, which impart to them the desired form which they preserve after cooling. After receiving their outline shape, and curvature, by proper flat files or fine rasps, the place of the teeth is marked with a triangular file, and then the teeth themselves are cut out with a double saw, composed of two thin slips of tempered steel, such as the main-spring of a watch, notched with very fine sharp teeth. These slips are mounted in a wooden or iron stock or handle, in which they may be placed at different distances to suit the width of the comb teeth. A comb-maker, however, well provided in tools, has an assortment of double saws set at every ordinary width. The two slips of this saw have their teeth in different planes, so that when it begins to cut, the most prominent slip alone acts, and when the teeth of this one have fairly entered into the comb, the other parallel blade begins to saw. The workman, meanwhile, has fixed the plate of tortoise-shell or ivory between the flat jaws of two pieces of wood, like a vice made fast to a bench, so that the comb intended to be cut is placed at an angle of 45° with the horizon. He now saws perpendicularly, forming two teeth at a time, proceeding truly in the direction of the first tracing.

A much better mode of making combs is to fix upon a shaft or arbour in a lathe a series of circular saws, with intervening brass washers or discs to keep them at suitable distances; to set in a frame like a vice, in front of these saws, the piece of ivory or horn to be cut; and to press it forward upon the saws at an angle of 45 degrees, by means of a regulated screw motion. When the teeth are thus cut, they are smoothed and polished with files, and by rubbing with pumice stone and tripoli.

Mr. Bundy, of Camden Town, obtained a patent so long ago as 1796, for an apparatus of that kind, which had an additional arbour fitted with a series of circular saws, or rather files, for sharpening the points of the comb teeth.

More recently, Mr. Lyne has invented a machine in which, by means of pressure, two combs are cut out at once with chisels from any tough material, such as horn or tortoise-shell, somewhat softened at the moment by the application of a heated iron to it. The piece of horn is made fast to a carriage, which is moved forwards by means of a screw until it comes under the action of a ratchet-wheel, toothed upon a part of its circumference. The teeth of this wheel bring a lever into action, furnished with a chisel or knife, which cuts out a double comb from the flat piece, the teeth of which combs are opposite to each other. By this means no part of the substance is lost, as in sawing out combs. The same carriage may be used, also, to bear a piece of ivory in the hard state towards a circular saw, on the principles above explained, with such precision, that from 80 to 100 teeth can be formed in the space of one inch by a proper disposition of the tool.

Bullocks’ horns, after the tips are sawed off, are roasted in the flame of a wood fire, till they are sufficiently softened; when they are slit up, pressed in a machine between two iron plates, and then plunged into a trough of cold water, whereby they are hardened. A paste of quicklime, litharge, and water is used to stain the horn to resemble tortoise-shell. See Horn.

COMBINATION (Combinaison, Fr.; Verbindung, Germ.); a chemical term which denotes the intimate union of dissimilar particles of matter, into a homogeneous looking compound, possessed of properties generally different from those of the separate constituents.

COMBUSTIBLE (Eng. and Fr.; Brennstoff, Germ.); any substance which exposed in the air to a certain temperature, consumes spontaneously with the emission of heat and light. All such combustibles as are cheap enough for common use go under the name of Fuel; which see. Every combustible requires a peculiar pitch of temperature to be kindled, called its accendible point. Thus phosphorus, sulphur, hydrogen, carburetted hydrogen, carbon, each takes fire at successively higher heats.

COMBUSTION (Eng. and Fr.; Verbrennung, Germ.) results in common cases from the mutual chemical reaction of the combustible, and the oxygen of the atmosphere, whereby a new compound is formed; the heat and light evolved being most probably produced by the rapid motions of the particles during the progress of this combination.

COMPOUND COLOURS. If the effects of the colouring particles did not vary according to the combinations which they form, and the actions exercised upon them by the different substances present in a dyeing bath, we might determine with precision the shade which ought to result from the mixture of any two colours, or of the ingredients affording these colours separately. Though the chemical action of the mordants, and of the liquor in the dye-bath often changes the results, yet theory may always predict them within a certain degree. It is not the colour appropriate to the dye-stuffs which is to be considered as the constituent part of compound colours, but that which they must assume with a certain mordant and dye-bath. Our attention ought therefore to be directed principally to the operation of the chemical agents employed.

1. The mixture of blue and yellow dyes produces green. D’Ambourney, indeed, says that he has extracted a fast green from the fermented juice of the berries of the buckthorn (rhamnus frangula), but no dyer would trust to such a colour.

2. The mixture of red and blue produces violet, purple, columbine (dove-colour), pansy, amaranth, lilac, mallow, and a great many other shades, determined by the nature and tone of the red and blue dye-stuffs, as well as their relative proportions in the bath.

3. The mixture of red and yellow produces orange, mordoré, cinnamon, coquelicot, brick, capuchin; with the addition of blue, olives of various shades; and with duns instead of yellows, chestnut, snuff, musk, and other tints.

4. Blacks of the lighter kinds constitute grays; and, mixed with other colours, produce marrone (marroons), coffees, damascenes. For further details upon this subject, see Calico Printing, Dyeing, as also the individual colours in their alphabetical places.

CONCRETE. The name given by architects to a compact mass of pebbles, sand and lime cemented together, in order to form the foundations of buildings. Semple says that the best proportions are 80 parts of pebbles, each about 7 or 8 ounces in weight, 40 parts sharp river sand, and 10 of good lime; the last is to be mixed with water to a thinnish consistence, and grouted in. It has been found that Thames ballast, as taken from the bed of the river, consists nearly of 2 parts of pebbles to 1 of sand, and therefore answers exceedingly well for making concrete; with from one-seventh to one-eighth part of lime. The best mode of making concrete, according to Mr. Godwin, is to mix the lime, previously ground, with the ballast in a dry state; sufficient water is now thrown over it to effect a perfect mixture, after which it should be turned over at least twice with shovels, or oftener; then put into barrows, and wheeled away for use instantly. It is generally found advisable to employ two sets of men to perform this operation, with three in each set; one man to fetch the water, &c., while the other two turn over the mixture to the second set, and they, repeating the process, turn over the concrete to the barrow-men. After being put into the barrows, it should at once be wheeled up planks, so raised as to give it a fall of some yards, and thrown into the foundation, by which means the particles are driven closer together, and greater solidity is given to the whole mass. Soon after being thrown in, the mixture is observed usually to be in commotion, and much heat is evolved with a copious emission of vapour. The barrow-load of concrete in the fall spreading over the ground, will form generally a stratum of from 7 to 9 inches thick, which should be allowed to set before throwing in a second.

Another method of making concrete, is first to cover the foundation with a certain quantity of water, and then to throw in the dry mixture of ballast and lime. It is next turned and levelled with shovels; after which more water is pumped in, and the operation is repeated. The former method is undoubtedly preferable.

In some cases it has been found necessary to mix the ingredients in a pug-mill, as in mixing clay, &c. for bricks. For the preparation of a concrete foundation, as the hardening should be rapid, no more water should be used than is absolutely necessary to effect a perfect mixture of the ingredients. Hot water accelerates the induration. There is about one-fifth of contraction in volume in the concrete, in reference to the bulk of its ingredients. To form a cubical yard of concrete, about 30 feet cube of ballast and 3⁄2 feet cube of ground lime must be employed, with a sufficient quantity of water.

CONGELATION (Eng. and Fr.; Gefrierung, Germ.); the act of freezing liquids. Many means are supplied by chemistry of effecting or promoting this process, but they do not constitute any peculiar art or manufacture. See Ice-House.

COOLING OF FLUIDS. In Mr. Derosnes’s method, the cooling agents employed are a current of atmospheric air, and warm water of the same or nearly the same temperature as that of the vapours which are to be operated upon.

Fig. 295. represents merely a diagram of the general features of an apparatus constructed upon the principles proposed to be employed, which will serve to explain the nature of this improvement.

Let A be the source of the vapours, or the vessel, boiler, alembic, or closed pan that contains the liquid or syrup to be evaporated or concentrated. The pipe B, through which the vapour passes as it rises in the boiler, is surrounded by another tube C, of larger diameter, closed at both ends. A pump D, draws from the reservoir E, warm water, which water has been heated by its previous and continual passage through the apparatus in contact with the surface of the vapour pipes. This pump forces the water by the pipe F, into the annular space or chamber between the pipes B and C, in which chamber, by its immediate contact with the pipe B, it acquires the temperature of the vapours intended to be refrigerated. The pipe G conveys the water from the pipe C, into the annular colander or sieve H, which has a multitude of small holes pierced through its under part, and from whence the warm water descends in the form of a continued shower of rain. To the end of the pipe B, a distiller’s worm I I, is connected, which is placed beneath the colander H. The entire length of the worm-pipe should be bound round with linen or cotton cloth, as a conductor of the heat, which cloth will be continually moistened by the rain in its descent from the colander. As this water has been heated in passing along the tube C, the shower of rain descending from the colander will be at a higher temperature than that of the atmosphere, and, consequently, by heating the surrounding air as it descends, a considerable upward draft will be produced through the coils of the worm-pipe.

If the colander and the worm-pipe are enclosed within a chimney or upright tube, as K K, open at top and bottom, a current of ascending air will be produced within it by the descending shower of hot water, similar in effect to that which would be produced in a chimney communicating with a furnace, or to that of the burner of an argand lamp. Consequently, it will be perceived that in opposition to the descending rain, a strong upward current of air will blow through that part of the cylinder K K, which is beneath the colander. When the air first enters the lower aperture of the chimney or tube K, it is of the same temperature and moisture as the external atmosphere; but in its passage up the tube it meets with a warmer and damper atmosphere, caused by the heat given out from the hot fluid continually passing through the pipes, and by the hot shower of rain, and also by the steam evolved from the surfaces of the coils of the worm, which are continually wetted by the descending rain, the evaporation being considerably augmented by the cloth bound round the worm-pipe, retaining the water as it descends in drops from coil to coil.

The atmosphere within the tube being of a higher temperature than without, a current of air constantly ascends and escapes at the upper aperture K, and its place is supplied by fresh air from the surrounding atmosphere, entering the tube below. The fresh air thus admitted at the bottom of the tube being cold and dry, will be suited to take up the heat and moisture within, because the water within the tube being in a state of dispersion as rain, presents to the air many points, or a very extended surface, and also because it is of a higher temperature than the air; and, besides, cold dry air is continually renewed, and a source of warmth is furnished by the latent caloric to the steam, as fast as it is evolved. Thus a portion of the descending rain, or water, is evaporated, and the effect of this evaporation is to subtract caloric not only from the water held in contact with the coils of the worm-pipe by the cloth enveloping it, but also from the hot vapours which pass through the worm. This process of evaporation has, therefore, a cooling power, which is but slight in the lower part of the chimney or tube K; because the temperature of the water, or rain, and of the worm, at this part, are of a lower temperature; but its refrigerating power increases as it rises towards the colander, and there it acquires its maximum of intensity, so that at any point between the lower aperture of the cylinder and the colander, the current of air is always a little cooler than the atmosphere of the region through which it passes (that is, at its maximum); and in passing this region of higher temperature, it is not only put in equilibrium of temperature, but also made to take up an additional quantity of aqueous vapours, which equalises the new temperature it acquires with its capacity of saturation. The cooling caused by the evaporation acts in an incessant and progressive manner from the lower aperture of the cylinder to the under side of the colander; and this cooling not only acts as an agent of the evaporation which the current of air cools, but it refrigerates also, because it becomes warmed in abstracting caloric from the vapours or liquids passing through the worm; and this refrigeration acts also incessantly and progressively from the lower part of the tube or chimney to the colander.

The patentee states, in conclusion, that “the velocity or force of the current of air that passes through the chimney or tube K, can be accelerated by artificial means, either by conducting the air and vapour passing from the upper aperture of the cylinder into the chimney or flues of a furnace, or by means of a revolving, forcing, or exhausting fan, or ventilator, or any other contrivance which will produce an increased current of air, but which it is not necessary to be particularly described, as I only wish to explain the principles of a simple apparatus, constructed in any convenient form; and I would remark, that the area of the lower aperture through which the air is introduced into the chimney or tube K, and also the area of the upper aperture, or that through which it passes to the atmosphere, should be in accordance with the effect intended to be obtained.

“It is further to be remarked, that in order to obtain from this apparatus the best effect, the velocity of the current of air must be itself a maximum; and as the speed or velocity of the current of air is owing to and determined by the excess of the temperature of the descending water, or rain, and of the coils of the worm to that of the exterior atmosphere, it ensues that the temperature of the water, or rain, must be a maximum. But this excess of temperature is a maximum only when the source of the rain is at the same temperature as the vapours to be condensed: if less warm, it would attract less air; or, if warmer, it would augment the temperature of the vapours intended to be condensed. Consequently, the shower of water employed in the tube K, as the agent for cooling, bestows its maximum of effect when it is as warm as the vapours to be condensed; therefore, I may express this proposition, viz., ‘That in refrigerating with water, less of it may be expended when it is warm than when it is cold, and that the least quantity of water will be evaporated when it is as warm as the aqueous or spirituous vapours upon which it is to operate.’

“This proposition may appear strange, nevertheless it is conformable to the laws of nature; and appears only strange, because until now warm water has not been employed with currents of air for refrigerating.

“Hence it is necessary to raise the temperature of the water in the colander to the temperature of the vapours to be condensed: therefore, I cause the lukewarm water, pumped from the reservoir E, to circulate in the chamber C. In this circulation it also begins to act as a refrigerating medium, taking up a portion of heat from the vapours that pass through the pipe B, and afterwards it acts as a further condenser in the cylinder, in the way described. Finally, the portion of this water that is still in the fluid state, after having fallen down from coil to coil, arrives lukewarm to the inclined surface L, which conducts it into the reservoir E, from whence it is pumped up into the chamber C, as before described.

“The tube or chimney K, may have more or less altitude; the higher it is the greater is the current produced. The force or velocity of the current of air can be governed by the areas of the introduction and exit apertures. If the cylinder rises only to the height of the sieve, the effect is much less than when it is prolonged beyond this height. I would further remark, that if the cylinder was removed, a slight effect might be produced, provided that a current of air be preserved in the cylindrical space limited by the coils of the worm, and also if the current was produced between the coils; or a central passage might be formed in an apparatus of another shape than that above described.

“I have only shown the application of the worm, because intending only to explain the principles of this method of condensing and refrigerating.

“The small quantity of water wasted in this manner of condensation, (that is, that portion passed off to the atmosphere in the form of vapours, at the upper aperture of the cylinder K,) may be replaced by a small stream of cold water, which may be brought to the apparatus, and perhaps most conveniently introduced into the reservoir E, or into the chamber between the pipes B and C. When operating upon aqueous vapours, the waste of water is always less in weight than that of the vapours liquefied. When this apparatus is applied to the purposes of distillation, the end of the worm should terminate in a vessel M, which is to receive the produce of the condensation. It will be seen that this improved process is applicable to various purposes, where condensation or refrigeration is required; for instance, in the boiling or concentration of sugar; to condensing and refrigerating distilled vapours, or steam, or saline liquids, either in vacuum or not; to cooling brewers’ worts; and to the refrigeration of other liquors, or any other processes, when it may be required.”

I have inserted the specification of this patent verbatim. M. Derosne has busied himself during a long life with a prodigious number of ingenious little contrivances for clarifying and boiling syrups, distillation, &c., but he has in this invention taken a bolder flight, having secured the exclusive privilege of condensing vapours, and cooling liquors, with hot water, in preference to cold. No man at all versant in the scientific doctrines, or the practical applications of caloric, will ever seek to meddle with his monopoly of such a scheme. He may find, perhaps, some needy coppersmith ready to espouse that or any other equally foolish project, provided a productive job can be made of it, against credulous customers.

For some rational methods of cooling liquors, and condensing vapours, see Refrigeration, Still, and Sugar.

COPAL, a resin which exudes spontaneously from two trees, the Rhus copallinum, and the Elæocarpus copalifer, the first of which grows in America, and the second in the East Indies. A third species of copal tree grows on the coasts of Guinea, especially on the banks of some rivers, among whose sands the resin is found. It occurs in lumps of various sizes and of various shades of colour, from the palest greenish yellow to darkish brown. I found its specific gravity to vary in different specimens from 1·059 to 1·071, being intermediate in density between its two kindred resins, animé and amber. Some rate its specific gravity so high as 1·139, which I should think one of the errors with which chemical compilations teem. Copal is too hard to be scratched by the nail, whence the excellence of its varnish. It has a conchoidal fracture, and is without smell or taste. When exposed to heat in a glass retort over a spirit lamp it readily melts into a liquid, which being further heated boils with explosive jets. A viscid oily-looking matter then distils over. After continuing the process for some time, no succinic acid is found in the receiver, but the copal blackens in the retort. Anhydrous alcohol boiled upon it, causes it to swell, and transforms it by degrees into an elastic viscid substance. It is not soluble in alcohol of 0·825 at the boiling point, as I have ascertained. Copal dissolves in ether, and this ethereous solution may be mixed with alcohol without decomposition. Caoutchoucine acts very slightly upon it by my experiments, even at the boiling temperature of this very volatile fluid; but a mixture of it with alcohol of 0·825 in equal parts dissolves it very rapidly in the cold into a perfectly liquid varnish. Alcohol holding camphor in solution also dissolves it, but not nearly so well as the last solvent. According to Unverdorben, copal may be completely dissolved by digesting one part of it for 24 hours with one part and a half of alcohol (probably anhydrous), because that portion of copal which is insoluble in alcohol, dissolves in a very concentrated solution of the soluble portion. Oil of petroleum and turpentine dissolve only 1 or 2 per cent. of raw copal. By particular management, indeed, oil of turpentine may be combined with copal, as we shall describe under the article Varnish.

Fused copal possesses different properties from the substance in its solid state; for it then may be made to combine both with alcohol and oil of turpentine.

Unverdorben has extracted from the copal of Africa, five different kinds of resin, none of which has however been applied to any use in the arts.

The ultimate constituents of copal by my analysis are, carbon 79·87, hydrogen 9·00, oxygen 11·1; being of hydrogen 7·6 in excess above the quantity necessary to form water with the oxygen. Of copal and animé, 551,166 libs. were imported in 1835.

COPPER is one of the metals most anciently known. It was named from the island of Cyprus, where it was extensively mined and smelted by the Greeks. It has a reddish brown colour inclining to yellow; a faint but nauseous and rather disagreeable taste; and when rubbed between the fingers it imparts a smell somewhat analogous to its taste. Its specific gravity is from 8·8 to 8·9. It is much more malleable than it is ductile; so that far finer leaves may be obtained from it than wire. It melts at the 27th degree of Wedgewood’s pyrometer, and at a higher temperature it evaporates in fumes which tinge the fire of a bluish green. By exposure to heat with access of air, it is rapidly converted into black scales of peroxide. In tenacity it yields to iron; but surpasses gold, silver, and platinum, considerably in this respect.

In mineralogy, the genus copper includes about 13 different species, and each of these contains a great many varieties. These ores do not possess any one general exterior character by which they can be recognized; but they are readily distinguished by chemical re-agents. Water of ammonia digested upon any of the cupreous ores in a pulverized state, after they have been calcined either alone or with nitre, assumes an intense blue colour, indicative of copper. The richest of the ordinary ores appear under two aspects; the first class has a metallic lustre, a copper red, brass yellow, iron gray, or blackish gray colour, sometimes inclining to blue; the second is without metallic appearance, has a red colour, verging upon purple, blue, or green, the last tint being the most usual. Few copper ores are to be met with, indeed, which do not betray the presence of this metal by more or less of a greenish film.

1. Native copper, occurs in crystals, branches and filaments, its most common locality being in primitive rocks. It is found abundantly in Siberia, at the mines of Tourinski, in those of Hungary, of Fundo-Moldavi in Gallicia, of Fahlun in Sweden, of Cornwall, &c. The gangues of native copper are granite, gneiss, mica-slate, clay-slate, quartz, carbonate or fluate of lime, sulphate of barytes, &c. The most remarkable masses of native copper hitherto observed were; first, one in Brazil, 14 leagues from Basa, which weighed 2616 pounds; and secondly, another which Dr. Francis-le-Baron discovered in America to the south of Lake Superior. It was nearly 15 feet in circumference.

2. Sulphuret of Copper, the vitreous ore of Brochant. The texture of this ore is compact: its fracture, conchoidal, surface sometimes dull; colour, iron black or lead gray, often bluish, iridescent, or reddish from a mixture of protoxide. It is easily melted even by the heat of a candle; but more difficult of reduction than protoxide. This ore yields to the knife, assuming a metallic lustre when cut. Its density varies from 4·8 to 5·34. Its composition according to Klaproth is 78·5 copper, 18·5 sulphur, with a little iron and silica. Its equivalent constitution by theory is 80 copper + 20 sulphur = 100; whence 78·5 of metal should be associated with 19·6 of sulphur. This ore is therefore one of the richest ores, and forms very powerful veins, which likewise contain some orange protoxide. It is to be found in all considerable copper districts; in Siberia, Saxony, Sweden, and especially Cornwall, where the finest crystals occur.

3. Copper Pyrites, resembles in its metallic yellow hue, sulphuret of iron; but the latter is less pale, harder, and strikes fire more easily with steel. It presents the most lively rainbow colours. Its specific gravity is 4·3. It contains generally a good deal of iron; as the following analysis will show; copper 30, sulphur 37, iron 33, in 100 parts. According to Hisinger, the Swedish pyrites contains 63 of copper, 12 of iron, and 25 of sulphur. These ores occur in primitive and transition districts in vast masses and powerful veins; and are commonly accompanied with gray copper, sulphuret of iron, sparry iron, sulphurets of lead, and zinc.

4. Gray Copper, has a steel gray colour, more or less deep, either shining or dull; fracture uneven; a distinct metallic lustre; difficult of fusion at the blowpipe; it communicates to glass of borax a yellowish-red colour. Its density in crystals is 4·86. Its composition is very variable; consisting essentially of copper, iron, antimony, and sulphur. The exploration of this ore is profitable, in consequence of the silver which it frequently contains. It occurs in primitive mountains; and is often accompanied with red silver ore, copper pyrites, and crystallized quartz.

5. Protoxide of Copper, or red oxide of Copper: its colour is a deep red, sometimes very lively, especially when bruised. It is friable, difficult of fusion at the blowpipe, reducible on burning charcoal, soluble with effervescence in nitric acid, forming a green liquid. Its constitution when pure, is 88·9 copper + 11·1 oxygen = 100.

6. Black oxide of Copper, is of a velvet black, inclining sometimes to brown or blue; and it acquires the metallic lustre on being rubbed. It is infusible at the blowpipe. Its composition is, copper 80 + oxygen 20; being a true peroxide.

7. Hydrosilicate of Copper, consists essentially of oxide of copper, silica, and water. Its colour is green; and its fracture is conchoidal with a resinous lustre, like most minerals which contain water. Its specific gravity is 2·73. It is infusible at the blowpipe alone, but it melts easily with borax.

8. Dioptase Copper, or Emerald Malachite; a beautiful but rare cupreous mineral, consisting of oxide of copper, carbonate of lime, silica, and water in varying proportions.

9. Carbonate of Copper, Malachite; is of a blue or green colour. It occurs often in beautiful crystals.

10. Sulphate of Copper, Blue Vitriol, similar to the artificial salt of the laboratory. The blue water which flows from certain copper mines, is a solution of this salt. The copper is easily procured in the metallic state by plunging pieces of iron into it.

11. Phosphate of Copper, is of an emerald green, or verdigris colour with some spots of black. It presents fibrous or tuberculous masses with a silky lustre in the fracture. It dissolves in nitric acid without effervescence, forming a blue liquid; melts at the blowpipe, and is reducible upon charcoal, with the aid of a little grease, into a metallic globule. Its powder does not colour flame green, like the powder of muriate of copper.

12. Muriate of Copper, is green of various shades; its powder imparts to flame a remarkable blue and green colour. It dissolves in nitric acid without effervescence; and is easily reduced before the blowpipe. Its density is 3·5. By Klaproth’s analysis it consists of oxide of copper 73, muriatic acid 10, water 17.

13. Arseniate of Copper. It occurs in beautiful blue crystals. Before the blowpipe it melts exhaling fumes of a garlic odour, and it affords metallic globules when in contact with charcoal. See more upon the ores at the end of this article.

In the article Metallurgy, I have described the mode of working certain copper mines; and shall content myself here with giving a brief account of two cupreous formations, interesting in a geological point of view; that of the copper slate of Mansfeldt, and of the copper veins of Cornwall.

The curious strata of bituminous schist in the first of these localities, are among the most ancient of any which contain the exuviæ of organised bodies not testaceous. From among their tabular slabs the vast multitudes of fossil fish were extracted, which have rendered the cantons of Mansfeldt, Eisleben, Ilmenau, and other places in Thuringia and Voigtland so celebrated. Many of the fish are transformed into copper pyrites. Here, also, have been found the fossil remains of the lizard family, called Monitors.

Such is the influence of a wise administration upon the prosperity of mines, that the thin layer of slate in this formation, of which 100 pounds commonly contain but one pound and a half of copper, occasionally argentiferous, has been for several centuries the object of smelting works of the greatest importance to the territory of Mansfeldt and the adjoining country.

The frequent derangements which this metallic deposit experiences, led skilful directors of the under-ground operations at an early period to study the order of superposition of the accompanying rocks. From their observations, there resulted a system of facts which have served to guide miners, not only in the country of Mansfeldt, but over a great portion of Germany, and in several other countries where the same series of rocks, forming the immediate envelope of the cupreous schists, were found to occur in the same order of superposition.

Of the English copper works.—The deposits of copper in Cornwall occur always as veins in granite, or in the schistose rocks which surround and cover it; and hence, the Cornish miners work mostly in the granite or greenish clay slate; the former of which they call growan, the latter killas. But tin is sometimes disseminated in small veins in porphyry or elvan, which itself forms great veins in the above rocks. No stratification has been observed in Cornwall.

The copper veins are abundant in the killas and rare in the granite; but most numerous near the line of junction of the two rocks. The different kinds of mineral veins in Cornwall may be classed as follows:—

1. Veins of elvan; elvan courses, or elvan channels.

2. Tin veins, or tin lodes; the latter word being used by the Cornish miners to signify a vein rich in ore, and the word course, to signify a barren vein.

3. Copper veins running east and west; east and west copper lodes.

4. Second system of copper veins, or contra copper lodes.

5. Crossing veins; cross courses.

6. Modern copper veins; more recent copper lodes.

7. Clay veins; of which there are two sets, the more ancient, called Cross-Fluckans; and the more modern, called Slides.

There are therefore three systems of copper veins in Cornwall; of which the first is considered to be the most ancient, because it is always traversed by the two others, and because, on the contrary, it never cuts them off. The width of these veins does not exceed 6 feet, though occasional enlargements to the extent of 12 feet sometimes take place. Their length is unknown, but the one explored in the United Mines has been traced over an extent of seven miles. The gangue of these veins is generally quartz, either pure, or mixed with green particles analogous to chlorite. They contain iron pyrites, blende, sulphuret, and several other compounds of copper, such as the carbonate, phosphate, arseniate, muriate, &c. The most part of the copper veins are accompanied with small argillaceous veins, called by the miners fluckan of the lode. These are often found upon both sides of the vein, so as to form cheeks or salebandes.

When two veins intersect each other, the direction of the one thrown out becomes an object of interest to the miner and geologist. In Saxony it is regarded as a general fact that the rejected portion is always to the side of the obtuse angle; this also holds generally in Cornwall, and the more obtuse the angle of incidence, the more considerable the out-throw.

The great copper vein of Carharack, in the parish of Gwenap, is a most instructive example of intersection. The power of this vein is 8 feet; it runs nearly from east to west, and dips towards the north at an inclination of 2 feet in a fathom. Its upper part is in the killas, its lower part in the granite. The vein has suffered two intersections; the first results from encountering the vein called Steven’s fluckan, which runs from north-east to south-west, throwing it out several fathoms. The second has been caused by another vein, almost at right angles to the first, and which has driven it 20 fathoms out to the right side. The fall of the vein occurs, therefore, in one case to the right, and in the other to the left; but in both instances, it is to the side of the obtuse angle. This disposition is very singular; for one portion of the vein appears to have ascended, while another has sunk.

The mining works in the copper veins are carried on by reverse steps; see Mines. The grand shafts for drainage and extraction are vertical, and open upon the roof side of the vein, traversing it to a certain depth. These pits are sunk to the lowest point of the exploration; and, in proportion as the workings descend, by means of excavations in the vein, the pits are deepened and put into communication towards their bottom with each new gallery of elongation, by means of transverse galleries. At present, the main shafts are fully 160 fathoms deep. Their horizontal section is oblong, and is divided into two compartments; the one destined for extraction, the other for the pumps. Their timbering has nothing remarkable, but is executed with every attention to economy, the whole wood employed in these mines being brought from Norway.

The descent of the workmen is effected by inclined shafts scooped out of the vein; the ladders are slightly inclined; they are interrupted every 10 fathoms by floors; the steps are made of iron, and, to prevent them from turning under the foot, the form of a miner’s punch or jumper has been given them, the one end being round, and the other being wedge-shaped.

The ore is raised either by means of horse-gins, or by steam-engine power most frequently of high pressure. I shall take the Consolidated Mines as an example.

The draining, which is one of the most considerable sources of expense, both from the quantity of water, and from the depth of the mine, is executed by means of sucking and forcing pumps, the whole piston-rods of which, 120 feet long, are attached to a main-rod suspended at the extremity of the working beam of a steam-engine.

On this mine three steam-engines are erected of very great power, for the purpose of drainage; the one called the Maria engine is of the first-rate force, and most improved construction. The cylinder is 90 inches in internal diameter, and the length of the stroke is 9 feet 11 inches. It works single stroke, and is encased in a coating of bricks to prevent dissipation of the heat. The vapour is admitted at the upper end of the cylinder during the commencement of the fall of the piston, at a pressure capable of forming an equilibrium with a column of 60 inches of mercury. The introduction of the steam ceases whenever the piston has descended through a certain space, which may be increased or diminished at pleasure. During the remainder of the descent the piston is pressed merely by this vapour in its progressive expansion, while the under side of the piston communicates with the condenser. It ascends by the counterweight at the pump end of the working beam. Hence, it is only during the descent of the piston, that the effective stroke is exerted. Frequently the steam is admitted only during the sixth part of the course of the piston, or 18 inches. In this way the power of the engine is proportioned to the work to be done; that is, to the body of water to be raised. The maximum force of the above engine is about 310 horses; though it is often made to act with only one third of this power.

The copper mines of the isle of Anglesey, those of North Wales, of Westmoreland, the adjacent parts of Lancashire and Cumberland, of the south west of Scotland, of the Isle of Man, and of the south east of Ireland, occur also in primitive or transition rocks. The ores lie sometimes in masses, but more frequently in veins. The mine of Ecton in Staffordshire, and that of Cross-gill-burn, near Alston-moor in Cumberland, occur in transition or metalliferous limestone.

The copper ores extracted both from the granitic and schistose localities, as well as from the calcareous, are uniformly copper pyrites more or less mixed with iron pyrites; the red oxide, carbonate, arseniate, phosphate, and muriate of copper, are very rare in these districts.

The working of copper in the isle of Anglesey may be traced to a very remote era. It appears that the Romans were acquainted with the Hamlet mine near Holyhead; but it was worked with little activity till about 70 years ago. This metalliferous deposit lies in a greenish clay slate, passing into talc slate; a rock associated with serpentine and euphotide (gabbro of Von Buch). The veins of copper are from one to two yards thick; and they converge towards a point where their union forms a considerable mass of ore. On this mass the mine was first pierced by an open excavation, which is now upwards of 300 feet deep, and appears from above like a vast funnel. Galleries are formed at different levels upon the flank of the excavation to follow the several small veins, which run in all directions, and diverge from a common centre like so many radii. The ore receives in these galleries a kind of sorting, and is raised by means of hand windlasses, to the summit of a hill, where it is cleaned by breaking and riddling.

The water is so scanty in this mine that it is pumped up by a six-horse steam-engine. A great proportion of it is charged with sulphate of copper. It is conveyed into reservoirs containing pieces of old iron; the sulphate is thus decomposed into copper of cementation. The Anglesea ore is poor, yielding only from 2 to 3 per cent. of copper: a portion of its sulphur is collected in roasting the ore.

Mechanical preparation of the copper ores in Cornwall.—The ore receives a first sorting, either within the mine itself, or at its mouth, the object of which is to separate all the pieces larger than a walnut. These are then reduced by the hammer to a smaller size; after which the whole are sorted into four lots, according to their relative richness. The fragments of poor ore are pounded in the stamps so that the metallic portion may be separated by washing.

The rich ore is broken into small bits, of the size of a nut, with a flat beater, formed of a piece of iron 6 inches square and 1 inch thick, adapted to a wooden handle. The ore to be broken is placed upon plates of cast-iron; each about 16 inches square and 1⁄2 inch thick. These iron plates are set towards the edge of a small mound about a yard high, constructed with dry stones rammed with earth. The upper surface of this mound is a little inclined from behind forwards. The work is performed by women, each furnished with a beater; the ore is placed in front of them beyond the plates; they break it, and strew it at their feet, whence it is lifted and disposed of to the smelting-houses.

Inferior ores, containing a notable proportion of stony matters, are also broken with the beater, and the rich parts are separated by riddling and washing from the useless matters.

The smaller ore is washed on a sieve by shaking it in a stream of water, which carries away the lighter stony pieces, and leaves the denser metalliferous. They are then sorted by hand. Thus by beating, stamping, and riddling in water, the stony substances are in a great measure separated. The finer ground matter is washed on a plane table, over which a current of water is made to flow. Finally, the ore nearly fine is put into a large tub with water, and briskly stirred about with a shovel, after which it settles in the order of richness, the pure metallic ore being nearest the bottom. The stamps used for copper ore in Cornwall are the same as those used for tin ores, of which we shall speak in treating of the latter metal, as well as of the boxes for washing the fine powder or slime. These in fact do not differ essentially from the stamping mills and washing apparatus described in the article Metallurgy. Crushing rolls are of late years much employed. See Lead and Tin.

Cornwall being destitute of coal, the whole copper ore which this county produces is sent for smelting to South Wales. Here are 15 copper works upon the Swansea and Neath, which pursue a nearly uniform and much improved process, consisting in a series of calcinations, fusions, and roastings, executed upon the ores and the matters resulting from them.

The furnaces are of the reverberatory construction; they vary in their dimensions and in the number of their openings, according to the operations for which they were intended. There are 5 of them:—1. The calcining furnace or calciner; 2. The melting furnace; 3. The roasting furnace or roaster; 4. The refining furnace; 5. The heating or igniting furnace.

1. The calcining furnace rests upon a vault, C, into which the ore is raked down after being calcined; it is built of bricks, and bound with iron bars, as shown in the elevation, fig. 296. The hearth, B B, figs. 296. and 298. is placed upon a level with the lower horizontal binding bar, and has nearly the form of an ellipse, truncated at the two extremities of its great axis. It is horizontal, bedded with fire-bricks set on edge, so that it may be removed and repaired without disturbing the arch upon which it reposes. Holes, not visible in the figure, are left in the shelves before each door, c c, through which the roasted ore is let fall into the subjacent vault. The dimensions of the hearth B B are immense, being from 17 to 19 feet in length, and from 14 to 16 in breadth. The fire-place, A, fig. 298., is from 4⁄2 to 5 feet long, and 3 feet wide. The bridge or low wall, b, fig. 302., which separates the fire-place from the hearth, is 2 feet thick; and in Mr. Vivian’s smelting-works is hollow, as shown in the figure, and communicates at its two ends with the atmosphere, in order to conduct a supply of fresh air to the hearth of the furnace. This judicious contrivance will be described in explaining the roasting operation. The arched roof of the furnace slopes down from the bridge to the beginning of the chimney, f, fig. 296, 298., its height above the hearth being at the first point about 26 inches, and from 8 to 12 at the second.

Such great calcining furnaces have 4 or 5 doors, c c c c, fig. 298., one for the fire-place, as shown at the right hand in fig. 297., and 3 or 4 others for working the ore upon the reverberatory hearth. If there be 3, 2 of them are placed between the vertical binding bars upon one side, and a third upon the opposite side of the furnace; if there be 4, 2 are placed upon each side, facing one another. These openings are 12 inches square, and are bound with iron frames. The chimney is about 22 feet high, and is placed at one angle of the hearth, as at f, fig. 298., being joined by an inclined flue to the furnace.

For charging it with ore there is usually placed above the upper part of the vault 2 hoppers, E E, in a line with the doors; they are formed of 4 plates of iron, supported in an iron frame. Beneath each of them there is an orifice for letting the ore down into the hearth.

These furnaces serve for calcining the ore, and the matts or crude coppers: for the latter purpose, indeed, furnaces of two stories are sometimes employed, as represented in fig. 301. The dimensions of each floor in this case are a little less than the preceding. Two doors, c c, correspond to each hearth, and the workmen, while employed at the upper story, stand upon a raised movable platform.

2. Melting furnace, figs. 299 and 300.—The form of the hearth is also elliptical, but the dimensions are smaller than in the calcining furnace. The length does not exceed 11 or 11⁄2 feet, and the breadth varies from 7 to 8. The fire-place is however larger in proportion, its length being from 3⁄2 feet to 4, and its breadth from 3 to 3⁄2; this size being requisite to produce the higher temperature of this furnace. It has fewer openings, there being commonly three; one to the fire-place at D, a second one, O, in the side, kept generally shut, and used only when incrustations need to be scraped off the hearth, or when the furnace is to be entered for repairs; and the third or working-door, G, placed on the front of the furnace beneath the chimney. Through it the scoriæ are raked out, and the melted matters are stirred and puddled, &c.

The hearth is bedded with infusible sand, and slopes slightly towards the side door, to facilitate the discharge of the metal. Above this door there is a hole in the wall of the chimney (fig. 300.) for letting the metal escape. An iron gutter, O, leads it into a pit, K, bottomed with an iron receiving-pot, which may be lifted out by a crane. The pit M is filled with water, and the metal becomes granulated as it falls into the receiver. The melting furnaces are surmounted by a hopper, L, as shown in fig. 299.

Melting furnaces are sometimes used also for calcination. There are some such near Swansea, which serve this double purpose; they are composed of 3 floors (fig. 301.) The floor A is destined for melting the calcined ore; the other two, B C, serve for calcination. The heat being less powerful, upon the upper sole C, the ore gets dried upon it, and begins to be calcined—a process completed on the next floor. Square holes, d, left in the hearths B and C, put them in communication with each other, and with the lower one A; these perforations are shut during the operation by a sheet of iron, removable at pleasure.

The hearths b and c are made of bricks; they are horizontal at top and slightly vaulted beneath; they are 2 bricks thick, and their dimensions are larger than those of the inferior hearths, as they extend above the fire-place. On the floors destined for calcination the furnace has two doors on one of its sides: on the lower story there are also two; but they are differently collocated. The first, being in the front of the furnace, serves for drawing off the scoriæ, for working the metal, &c.; and the second, upon the side, admits workmen to make necessary repairs. Below this door the discharge or tap-hole A is placed, which communicates by a cast-iron gutter with a pit filled with water. The dimensions of this furnace in length and breadth are nearly the same as those of the melting furnace above described; the total height is nearly 12 feet. It is charged by means of one or two hoppers.

3. Roasting furnace.—The furnaces employed for this purpose are in general analogous to the calcining ones; but in the smelting works of Hafod, the property of Messrs. Vivian, these furnaces, alluded to above, present a peculiar construction, for the purpose of introducing a continuous current of air upon the metal, in order to facilitate its oxidizement. This process was originally invented by Mr. Sheffield, who disposed of his patent right to Messrs. Vivian.

The air is admitted by a channel, c c, through the middle of the fire-bridge, fig. 302, and extending all its length; it communicates with the atmosphere at its two ends c c; square holes, b b, left at right angles to this channel, conduct the air into the furnace. This very simple construction produces a powerful effect in the roasting operation. It not only promotes the oxidizement of the metals, but burns the smoke, and assists in the vaporisation of the sulphur; while by keeping the bridge cool it preserves it from wasting, and secures uniformity of temperature to the hearth.

4. Refining furnace.—In this, as in the melting furnace, the sole slopes towards the door in front, instead of towards the side doors, because in the refining furnace the copper collects into a cavity formed in the hearth towards the front door, from which it is lifted out by ladles; whereas, in the melting furnaces, the metal is run out by a tap-hole in the side. The hearth sole is laid with sand; but the roof is higher than in the melting furnace, being from 32 to 36 inches. If the top arch were too much depressed, there might be produced upon the surface of the metal a layer of oxide very prejudicial to the quality of the copper. When the metal in that case is run out, its surface solidifies and cracks, while the melted copper beneath breaks through and spreads irregularly over the cake. This accident, called the rising of the copper, hinders it from being laminated, and requires it to be exposed to a fresh refining process, when lead must be added to dissolve the oxide of copper. This is the only occasion upon which the addition of lead is proper in refining copper. When the metal to be refined is mixed with others, particularly with tin, as in extracting copper from old bells, then very wide furnaces must be employed, to expose the metallic bath upon a great surface, and in a thin stratum, to the oxidizing action of the air.

The door G, fig. 300., upon the side of the refining furnace, is very large, and is shut with a framed brick door, balanced by a counter-weight. This door being open during the refining process, the heat is stronger at B than at A (figs. 299, 300.)

5. Heating furnaces, being destined to heat the pigs or bars of copper to be laminated, as well as the copper sheets themselves, are made much longer in proportion to their breadth. Their hearth is horizontal, the vault not much depressed; they have only one door, placed upon the side, but which extends nearly the whole length of the furnace: this door may be raised by means of a counter-weight, in the same way as in the furnaces for the fabrication of sheet-iron and brass.

Series of operations to which the ore is subjected.—The ores which are smelted in the Swansea works are cupreous pyrites, more or less mingled with gangue (vein-stone). The pyrites is composed of nearly equal proportions of sulphuret of copper and sulphuret of iron.

The earthy matters which accompany the pyrites are usually siliceous, though in some mines the metalliferous deposit is mixed with clay or fluate of lime. Along with these substances, pretty uniformly distributed, tin and arsenical pyrites occur occasionally with the copper; and though these two metals are not chemically combined, yet they cannot be separated entirely in the mechanical preparations. The constituent parts of the ore prepared for smelting are, therefore, copper, iron, sulphur, with tin, arsenic, and earthy matters in some cases. The different ores are mixed in such proportions that the average metallic contents may amount to 8⁄2 per cent. The smelting process consists in alternate roastings and fusions. The following description of it is chiefly taken from an excellent paper, published by John Vivian, esq., in the Annals of Philosophy for 1823.

In the roasting operation the volatile substances are disengaged mostly in the gaseous state, while the metals that possess a strong affinity for oxygen become oxidized. In the fusion the earthy substances combine with these oxides, and form glassy scoriæ or slags, which float upon the surface of the melted metal.

These calcinations and fusions take place in the following order:—

1. Calcination of the ore. 2. Melting of the calcined ore. 3. Calcination of the coarse metal. 4. Melting of the calcined coarse metal. 5. Calcination of the fine metal (second matt). 6. Melting of the calcined fine metal. 7. Roasting of the coarse copper. In some smelting works, this roasting is repeated four times; in which case a calcination and a melting are omitted. In the Havod works, however, the same saving is made without increasing the number of roastings. 8. Refining or toughening the copper.

Besides these operations, which constitute the treatment of copper properly speaking, two others are sometimes performed, in which only the scoriæ are melted. These may be designated by the letters a and b. a is the re-melting of the portion of the scoriæ of the second process, which contain some metallic granulations. b is a particular melting of the scoriæ of the fourth operation. This fusion is intended to concentrate the particles of copper in the scoriæ, and is not practised in all smelting works.

First operation. Calcination of the ore.—The different ores, on arriving from Cornwall and other districts where they are mined, are discharged in continuous cargoes at the smelting works, in such a way, that by taking out a portion from several heaps at a time, a tolerably uniform mixture of ores is obtained; which is very essential in a foundry, because, the ores being different in qualities and contents, they act as fluxes upon each other. The ore thus mixed is transported to the works in wooden measures that hold a hundred-weight. The workmen entrusted with the calcination convey the ore into the hoppers of the calcining furnace, whence it falls into the hearth; other workmen spread it uniformly on the surface by iron rakes. The charge of a furnace is from three tons to three tons and a half. Fire is applied and gradually increased, till, towards the end of the operation, the temperature be as high as the ore can support without melting or agglutinating. To prevent this running together, and to aid the extrication of the sulphur, the surfaces are renewed, by stirring up the ore at the end of every hour. The calcination is usually completed at the end of 12 hours, when the ore is tumbled into the arch under the sole of the furnace. Whenever the ore is cold enough to be moved, it is taken out of the arch, and conveyed to the calcined heap.

The ore in this process hardly changes weight, having gained in oxidizement nearly as much as it has lost in sulphur and arsenic; and if the roasting has been rightly managed, the ore is in a black powder, owing to the oxide of iron present.

Second operation. Fusion of the calcined ore.—The calcined ore is likewise given to the melters in measures containing a hundred-weight. They toss it into hoppers, and after it has fallen on the hearth, they spread it uniformly. They then let down the door, and lute it tightly. In this fusion there are added about 2 cwt. of scoriæ proceeding from the melting of the calcined matt, to be afterwards described. The object of this addition is not only to extract the copper that these scoriæ may contain, but especially to increase the fusibility of the mixture. Sometimes also, when the composition of the ore requires it, lime, sand, or fluor spar is added; and particularly the last fluxing article.

The furnace being charged, fire is applied, and the sole care of the founder is to keep up the heat so as to have a perfect fusion; the workman then opens the door, and stirs about the liquid mass to complete the separation of the metal (or rather of the matt) from the scoriæ, as well as to hinder the melted matter from sticking to the sole. The furnace being ready, that is, the fusion being perfect, the founder takes out the scoriæ by the front door, by means of a rake. When the matt is thus freed from the scoriæ, a second charge of calcined ore is then introduced to increase the metallic bath; which second fusion is executed like the first. In this way, new charges of roasted ore are put in till the matt collected on the hearth rises to a level with the door-way, which happens commonly after the third charge. The tap hole is now opened; the matt flows out into the pit filled with water, where it is granulated during its immersion; and it collects in the pan placed at the bottom. The granulated matt is next conveyed into the matt warehouse. The oxidation with which the grains get covered by the action of the water, does not allow the proper colour of the matt or coarse metal to be distinguished; but in the bits which stick in the gutter, it is seen to be of a steel gray. Its fracture is compact, and its lustre metallic. The scoriæ often contain metallic grains; they are broken and picked with care. All the portions which include some metallic particles are re-melted in an accessory process. The rejected scoriæ have been found to be composed of siliceous matter 59, oxide of copper 1, oxide of tin 0·7.

In this operation, the copper is concentrated by the separation of a great part of the matters with which it was mixed or combined. The granulated matt produced, contains in general 33 per cent. of copper; it is therefore four times richer than the ore; and its mass is consequently diminished in that proportion. The constituent parts are principally copper, iron, and sulphur.

The most important point to hit in the fusion just described, is to make a fusible mixture of the earths and the oxides, so that the matt of copper may, in virtue of its greater specific gravity, fall to the under-part, and separate exactly from the slag. This point is attained by means of the metallic oxides contained in the scoriæ of the fourth operation, of which 2 cwt. were added to the charge. These consist almost entirely of black oxide of iron. When the ores are very difficult to melt, a measure of about half a hundred-weight of fluor spar is added; but this must be done with precaution, for fear of increasing the scoriæ too much.

The business goes on day and night. Five charges are commonly put through hands in the course of 24 hours; but when all circumstances are favourable, that is to say, when the ore is fusible, when the fuel is of the first quality, and when the furnace is in good condition, even six charges a day have been despatched.

The charge is a ton and a half of calcined ore, so that a melting furnace corresponds nearly to a calcining furnace; the latter turning out nearly 7 tons of calcined ore in 24 hours.

The workmen are paid by the ton.

Third operation. Calcination of the coarse metal, or the matt.—The object of this operation is principally to oxidize the iron, an oxidation easier to execute, than in the first calcining, because the metal is now disengaged from the earthy substances, which screened it from the action of the air.

This calcination is executed in the furnace already represented, fig. 296, , 298. page 318. exactly in the same way as the ore was calcined. The metal must be perpetually stirred about, to expose all its surfaces to the action of the hot air, and to hinder the clotting together. The operation lasts 24 hours; during the first six, the fire should be very moderate, and thereafter gradually increased to the end of the calcination. The charge is, like that of the first, 3 tons and a half.

Fourth operation. Melting of the calcined coarse metal, or calcined matt.—In the fusion of this first calcined matt, some scoriæ of the latter operations must be added, which are very rich in oxide of copper, and some crusts from the hearth, which are likewise impregnated with it. The proportion of these substances varies according to the quality of the calcined matt.

In this second fusion, the oxide of copper contained in the scoriæ, is reduced by the affinity of the sulphur, one portion of which passes to the state of acid, while the other forms a subsulphuret with the copper become free. The matt commonly contains a sufficient quantity of sulphur to reduce the oxide of copper completely; but if not, which may happen if the calcination of the matt has been pushed too far, a small quantity of uncalcined matt must be introduced, which, by furnishing sulphur, diminishes the richness of the scoriæ, and facilitates the fusion.

The scoriæ are taken out by the front door, by drawing them forward with a rake. They have a great specific gravity; are brilliant with metallic lustre, very crystalline, and present, in the cavities, crystals like those of pyroxene; they break easily into very sharp-edged fragments. They contain no granulated metal in the interior; but it sometimes occurs, on account of the small thicknesses of the stratum of scoriæ, that these carry off with them, when they are withdrawn, some metallic particles.

These scoriæ, as we have already stated, under the fusion of the roasted ore, are in general melted with it. In some cases, however, a special melting is assigned to them.

The matt obtained in this second fusion is either run out into water like the first, or moulded into pigs (ingots), according to the mode of treatment which it is to undergo. This matt, called by the smelters fine metal when it is granulated, and blue metal when it is in pigs, is of a light grey colour, compact, and bluish at the surface. It is collected in the first form when it is to be calcined anew; and in the second, when it must immediately undergo the operation of roasting. Its contents in copper are 60 per cent. This operation, which is but sometimes had recourse to, lasts 5 or 6 hours. The charge is 1 ton.

(b) Particular fusion of the scoriæ of the fourth operation.—In re-melting these scoriæ, the object is to procure the copper which they contain. To effect this fusion, the scoriæ are mixed with pulverized coal, or other carbonaceous matters. The copper and several other metals are deoxidized, and furnish a white and brittle alloy. The scoriæ resulting from this melting are in part employed in the first melting, and in part thrown away. They are crystalline, and present crystals often in the cavities, which appear to belong to bisilicate of iron. They have a metallic lustre, and break into very sharp-edged fragments. The white metal is melted again, and then united to the product of the second fusion.

Fifth operation. Calcination of the second matt, or fine metal of the smelter.—This is executed in precisely the same way as that of the first matt. It lasts 24 hours; and the charge is usually 3 tons.

Sixth operation. Melting of the calcined fine metal.—This fusion is conducted like that of the first matt. The black copper, or coarse copper, which it produces, contains from 70 to 80 per cent. of pure metal; it is run into ingots, in order to undergo the operation of roasting.

The scoriæ are rich in copper; they are added to the fusion of the calcined coarse metal of the fourth operation.

In the smelting houses of Messrs. Vivian, at Hafod, near Swansea, the fifth and sixth operations have been omitted of late years. The second matt is run into pigs, under the name of blue metal, to be immediately exposed to the roasting.

The disposition of the canal a a′, fig. 302., which introduces a continuous current of air to the hearth of the furnace, accelerates and facilitates the calcination of the matt; an advantage which has simplified the treatment, by diminishing the number of calculations.

Seventh operation. Roasting of the coarse copper, the product of the sixth operation. The chief object of this operation is oxidizement; it is performed either in an ordinary roasting furnace, or in the one belonging to fig. 302., which admits a constant current of air. The pigs of metal derived from the preceding melting are exposed, on the hearth of the furnace, to the action of the air, which oxidizes the iron and other foreign metals with which the copper is still contaminated. The duration of the roasting varies from 12 to 24 hours, according to the degree of purity of the crude copper. The temperature should be graduated, in order that the oxidizement may have time to complete, and that the volatile substances which the copper still retains may escape in the gaseous form. The fusion must take place only towards the end of the operation.

The charge varies from a ton and a quarter to a ton and a half. The metal obtained is run out into moulds of sand. It is covered with black blisters, like steel of cementation; whence it has got the name of blistered copper. In the interior of these pigs, the copper presents a porous texture, occasioned by the ebullition produced by the escape of the gases during the moulding. The copper being now almost entirely purged from the sulphur, iron, and the other substances with which it was combined, is in a fit state to be refined. This operation affords some scoriæ; they are very heavy, and contain a great deal of oxide of copper, sometimes even metallic copper.

These scoriæ, as well as those of the third melting and of the refining, are added to the second fusion, as we have already stated, in describing the fourth operation.