G. (part 1)

GABRONITE, is a yellowish stony substance, of a greasy lustre and spec. gr. = 2·74; affording no water by calcination; fusible at the blowpipe into an opaque glass; soluble in muriatic acid; solution affords hardly any precipitate by oxalate of ammonia. This mineral is distinguished by the large quantity of soda which it contains; its constituents being,—silica, 54; alumina, 24; soda, 17·25; magnesia, 1·5; oxide of iron, 1·25; water, 2. It belongs to the species Nepheline.

GADOLINITE; called also Yttrite and Ytterbite; is a mineral of a black, brownish, or yellowish colour, granular, or compactly vitreous, and conchoidal fracture; of spec. grav. 4·23? readily scratching glass; fusible at the blowpipe into an opaque glass, sometimes with intumescence. It affords, with acids, a solution that lets fall, with caustic soda, a precipitate partly re-soluble in carbonate of ammonia. It is remarkable for containing from 45 to 55 per cent. of the earth Yttria; its remaining constituents being silica, 25·8; oxide of cerium, 17·92; oxide of iron, 11·43. This mineral is very rare, having been hitherto found only in the neighbourhood of Fahlun and Ytterby, in Sweden; its peculiar constituent was discovered by Professor Gadolin.

GALACTOMETER, or LACTOMETER, is an instrument to ascertain the quality of milk; an article often sophisticated in various ways. Fresh milk, rich in cream, has a less specific gravity, than the same milk after it has been skimmed; and milk diluted with water becomes proportionably lighter. Hence, when our purpose is to determine the quantity of cream, the galactometer may consist merely of a long graduated glass tube standing upright upon a sole. Having filled 100 measures with the recent milk, we shall see, by the measures of cream thrown up, its value in this respect. A delicate long-ranged glass hydrometer, graduated from 1·000 up to 1·060, affords the most convenient means of detecting the degree of watery dilution, provided the absence of thickening materials has been previously ascertained by filtration. Good fresh milk indicates from 1·030 to 1·032; when the cream is removed, 1·035 to 1·037. When its density is less than 1·028, we may infer it has been thinned with water.

GALBANUM, is a gum-resin, which occurs sometimes in yellow, shining tears, easily agglutinated; of a strong durable smell; an acrid and bitter taste; at other times in lumps. It exudes either spontaneously or from incisions made into the stem of the bubon galbanum, a plant of the family of umbelliferæ, which grows in Africa, particularly in Ethiopia. It contains 67 of resin; 19·3 of gum; 6·4 of volatile oil and water; 7·5 of woody fibres and other impurities; with traces of acid malate of lime.

GALENA; (Plomb sulfuré, Fr.; Bleiglanz, Germ.;) is a metallic looking substance of a lead-gray colour, which crystallizes in the cubical system, and is susceptible of cleavages parallel to the faces of the cube; spec. gr. 7·7592; cannot be cut; fusible at the blowpipe with exhalation of sulphureous vapours; is easily reduced to metallic lead. Nitric acid first dissolves it, and then throws down sulphate of lead in a white precipitate; the solution affording with plates of zinc, brilliant laminæ of lead (arbor Saturni.) It consists of sulphur, 13; lead, 85; with a little iron, and sometimes a minute quantity of silver. This is the richest ore of lead, and it occurs in almost every geological formation, in veins, in masses, or in beds. It is almost always accompanied by sulphuret of zinc, different salts of lead, heavy spar, fluor spar, &c. Galena in powder, called Alquifoux, is employed as a glaze for coarse stoneware.

GALIPOT, is a name of a white semi-solid viscid rosin found on fir-trees; or an inferior sort of turpentine, poor in oil.

GALLATES; salts consisting of gallic acid combined with bases; the most important being that with oxide of iron, constituting a principal part of the black dye.

GALLIC ACID, is the peculiar acid extracted from gall-nuts; which see.

GALLIPOLI OIL, is a coarse olive oil, containing more or less mucilage; imported from a sea port so named, of the province of Otranto, in the kingdom of Naples.

GALL-NUTS, or GALLS; (Noix de Galle, Fr.; Galläpfel, Germ.;) are excrescences found upon the loaves and leaf-stalks of a species of oak, called Quercus infectoria, which grows in the Levant. They are produced in consequence of the puncture of the female of the gall wasp, (Cynips folii quercus), made in order to deposit her eggs; round which the juice of the tree exudes, and dries in concentric portions. When the insect gets fully formed, it eats through the nut, and flies off.

The Levant galls are of two different appearances and qualities; the first are heavy, compact, imperforated, the insect having not been sufficiently advanced to eat its way through the shell; prickly on the surface; of a blackish or bluish green hue; about the size of a musket ball. These are called black, blue, or Aleppo galls. The second are light, spongy, pierced with one or more holes; smooth upon the surface, of a pale grayish or reddish yellow colour, generally larger than the first, and are called white galls. Besides the galls of the Levant, others come from Dalmatia, Illyria, Calabria, &c.; but they are of inferior quality, being found upon the Quercus Cerris; they are smaller, of a brownish colour, and of inferior value. The further south the galls are grown, they are reckoned the better.

Galls consist principally of three substances; tannin or tannic acid; yellow extractive; and gallic acid. Their decoction has a very astringent and unpleasant bitter taste. The following are their habitudes with various reagents:—

Litmus paper is powerfully reddened.

Stannous chloride (protomuriate of tin), produces an isabel yellow precipitate.

Alum; a yellowish gray precipitate.

Acetate of lead; a thick yellowish white precipitate.

Acetate of copper; a chocolate brown precipitate.

Ferric sulphate (red sulphate of iron); a blue precipitate.

Sulphuric acid; a dirty yellowish precipitate.

Acetic acid brightens the muddy decoction.

The galls of the Quercus Cerris and common oak (Galles à l’épine, Fr.; Knoppern, Germ.) are of a dark-brown colour, prickly on the surface, and irregular in shape and size. They are used chiefly for tanning in Hungary, Dalmatia, and the southern provinces of the Austrian states, where they abound.

Tannin or tannic acid is prepared as follows: Into a long narrow glass adopter tube shut at its lower orifice with a cotton wick, a quantity of pounded galls are put, and slightly pressed down. The tapering end of the tube being inserted into a matrass or bottle, the vacant upper half of the tube is filled with sulphuric ether, and then closed with a ground-glass stopper. Next day there will be found in the bottle a liquid in two distinct strata; of which the more limpid occupies the upper part, and the other, of a syrupy consistence and amber colour, the lower. More ether must be filtered through the galls, till the thicker liquid ceases to augment. Both are now poured into a funnel, closed with the finger, and after the dense liquor is settled at the bottom, it is steadily run off into a capsule. This, after being washed repeatedly with ether, is to be transferred into a stove chamber, or placed under the receiver of an air pump to be evaporated. The residuary matter swells up in a spongy crystalline form of considerable brilliancy, sometimes colourless, but more frequently of a faintly yellowish hue.

This is pure tannin, which exists in galls to the amount of from 40 to 45 per cent. It is indispensable that the ether employed in the preceding process be previously agitated with water, or that it contain some water, because by using anhydrous ether, not a particle of tannin will be obtained.

Tannic acid is a white or yellowish solid, inodorous, extremely astringent, very soluble in water and alcohol, much less so in sulphuric ether, and uncrystallizable. Its watery solution, out of contact of air, undergoes no change; but if, in a very dilute state, it be left exposed to the atmosphere, it loses gradually its transparency, and lets fall a slightly grayish crystalline matter, consisting almost entirely of gallic acid. For procuring this acid in a perfectly pure state, it is merely necessary to treat that solution thus changed with animal charcoal, and to filter it in a boiling state, through paper previously washed with dilute muriatic acid. The gallic acid will fall down in crystals as the liquid cools.

If the preceding experiment be made in a graduated glass tube containing oxygen over mercury, this gas will be absorbed, and a corresponding volume of carbonic acid gas will be disengaged. In this case the liquor will appear in the course of a few weeks as if traversed with numerous crystalline colourless needles of gallic acid.

Tannin or tannic acid consists of carbon 51·56; hydrogen 4·20; oxygen 44·24.

From the above facts it is obvious that gallic acid does not exist ready formed in gall nuts, but that it is produced by the reaction of atmospheric oxygen upon the tannin of these concretions.

Gallic acid is a solid, feebly acidulous and styptic to the taste, inodorous, crystallizing in silky needles of the greatest whiteness; soluble in about 100 times its weight of cold, and in a much smaller quantity of boiling water; more soluble in alcohol than in water, but little so in sulphuric ether.

Gallic acid does not decompose the salts of protoxide of iron, but it forms, with the sulphate of the peroxide, a dark blue precipitate, much less insoluble than the tannate of iron. Gallic acid takes the oxide from the acetate and nitrate of lead, and throws down a white gallate unchangeable in the air, when it is mixed with that acetate and nitrate. It occasions no precipitate in solutions of gelatine (isinglass or glue), by which criterion its freedom from tannin is verified.

Gallic acid occurs but seldom in nature; and always united to brucine, veratrine, or lime. Its constituents are, carbon 49·89; hydrogen 3·49; oxygen 46·62. In the crystalline state it contains one atom of water, which it loses by drying.

Scheele obtained gallic acid by infusing pounded galls for 3 or 4 days in 8 times their weight of water, and exposing the infusion to the air, in a vessel covered loosely with paper. At the end of two months, the liquor had almost all evaporated, leaving some mouldiness mixed with a crystalline precipitate. The former being removed, the deposit was squeezed in a linen cloth, and then treated with boiling water. The solution being gradually evaporated, yielded crystals of gallic acid, granular or star-like, of a grayish colour. These crystals might be whitened by boiling their solution along with a little animal charcoal. About one fifth of gallic acid may be obtained by Scheele’s process from good gall-nuts.

From a decoction of 500 parts of galls, Sir H. Davy obtained 185 parts of solid extract; which consisted of 130 parts of tannin; 31 parts of gallic acid with extractive; 13 parts of mucilage; 12 parts of lime and salts. Hence gall-nuts would seem to contain, by this statement, more than two-thirds of their weight of tannin. This result is now seen, from the above experiments of Pelouze, to have been incorrect, in consequence of the admixture of yellow extractive in Davy’s tannin.

The uses of galls in many processes of dyeing, and in making black ink, are detailed under their respective heads.

GALL OF ANIMALS, or OX-GALL, purification of. Painters in water colours, scourers of clothes, and many others employ ox-gall or bile, but when it is not purified, it is apt to do harm from the greenness of its own tint. It becomes therefore an important object to clarify it, and to make it limpid and transparent like water. The following process has been given for that purpose. Take the gall of newly killed oxen, and after having allowed it to settle for 12 or 15 hours in a basin, pour the supernatant liquor off the sediment into an evaporating dish of stone ware, and expose it to a boiling heat in a water bath, till it is somewhat thick. Then spread it upon a dish, and place it before a fire till it becomes nearly dry. In this state it may be kept for years in jelly pots covered with paper, without undergoing any alteration. When it is to be used, a piece of it of the size of a pea is to be dissolved in a table spoonful of water.

Another and probably a better mode of purifying ox-gall is the following. To a pint of the gall boiled and skimmed, add one ounce of fine alum in powder, and leave the mixture on the fire till the alum be dissolved. When cooled, pour into a bottle, which is to be loosely corked. Now take a like quantity of gall also boiled and skimmed, add an ounce of common salt to it, and dissolve with heat; put it when cold into a bottle, which is likewise to be loosely corked. Either of these preparations may be kept for several years without their emitting a bad smell. After remaining three months, at a moderate temperature, they deposit a thick sediment, and become clearer, and fit for ordinary uses, but not for artists in water colours and miniatures, on account of their yellowish-green colour. To obviate this inconvenience, each of the above liquors is to be decanted apart, after they have become perfectly settled, and the clear portion of both mixed together in equal parts. The yellow colouring matter still retained by the mixture coagulates immediately and precipitates, leaving the ox-gall perfectly purified and colourless. If wished to be still finer, it may be passed through filtering paper; but it becomes clearer with age, and never acquires a disagreeable smell, nor loses any of its good qualities.

Clarified ox-gall combines readily with colouring matters or pigments, and gives them solidity either by being mixed with or passed over them upon paper. It increases the brilliancy and the durability of ultramarine, carmine, green, and in general of all delicate colours, whilst it contributes to make them spread more evenly upon the paper, ivory, &c. When mixed with gum Arabic, it thickens the colours without communicating to them a disagreeable glistering appearance; it prevents the gum from cracking, and fixes the colours so well that others may be applied over them without degradation. Along with lamp black and gum, it forms a good imitation of China ink. When a coat of ox-gall is put upon drawings made with black lead or crayons, the lines can no longer be effaced, but may be painted over safely with a variety of colours previously mixed up with the same ox-gall.

Miniature painters find a great advantage in employing it; by passing it over ivory, it removes completely the unctuous matter from its surface; and when ground with the colours, it makes them spread with the greatest ease, and renders them fast.

It serves also for transparencies. It is first passed over the varnished or oiled paper, and is allowed to dry. The colours mixed with the gall are then applied, and cannot afterwards be removed by any means.

It is adapted finally for taking out spots of grease and oil.

GALL OF GLASS, called also sandiver, is the neutral salt skimmed off the surface of melted crown glass; which, if allowed to remain too long, is apt to be reabsorbed in part, and to injure the quality of the metal, as the workmen call it.

GALVANIZED IRON, is the somewhat fantastic name newly given in France to iron tinned by a peculiar patent process, whereby it resists the rusting influence of damp air, and even moisture, much longer than ordinary tin plate. The following is the prescribed process. Clean the surface of the iron perfectly by the joint action of dilute acid and friction, plunge it into a bath of melted zinc, and stir it about till it be alloyed superficially with this metal; then take it out, and immerse it in a bath of tin, such as is used for making tin plate. The tin forms an exterior coat of alloy. When the metal thus prepared is exposed to humidity, the zinc is said to oxidize slowly by a galvanic action, and to protect the iron from rusting within it, whereby the outer tinned surface remains for a long period perfectly white, in circumstances under which iron tinned in the usual way would have been superficially browned and corroded with rust.

GAMBOGE; (Gomme Gutte, Fr.; Gutti, Germ.) is a gum resin, concreted in the air, from the milky juice which exudes from several trees. The gambogia gutta, a tree which grows wild upon the coasts of Ceylon and Malabar, produces the coarsest kind of gamboge; the guttaefera vera (Stalagmites cambogioides) of Ceylon and Siam affords the best. It comes to us in cylindrical lumps, which are outwardly brown yellow, but reddish yellow within, as also in cakes; it is opaque, easily reducible to powder, of specific gravity 1·207, scentless, and nearly devoid of taste, but leaves an acrid feeling in the throat. Its powder and watery emulsion are yellow. It consists of 80 parts of a hyacinth red resin, soluble in alcohol; and 20 parts of gum; but by another analysis, of 89 of resin, and 10·5 of gum. Gamboge is used as a pigment, and in miniature painting, to tinge gold varnish; in medicine as a powerful purge. It should never be employed by confectioners to colour their liqueurs, as they sometimes do.

GANGUE. A word derived from the German gang, a vein or channel. It signifies the mineral substance which either encloses or usually accompanies any metallic ore in the vein. Quartz, lamellar carbonate of lime, sulphate of baryta, sulphate and fluate of lime, generally form the gangues; but a great many other substances become such when they predominate in a vein. In metallurgic works the first thing is to break the mixed ore into small pieces, in order to separate the valuable from the useless parts, by processes called stamping, picking, sorting. See Metallurgy and Mines.

GARNET (Grenat, Fr.; Granat, Germ.); is a vitreous mineral of the cubic system, of which the predominating forms are the rhomboidal dodecahedron and the trapœzohedron; specific gravity varying from 3·35 to 4·24; fusible at the blowpipe. Its constituents are, silica, 42; alumina, 20·0; lime, 34·0; protoxide of iron, 4. Garnets are usually disseminated, and occur in all the primitive strata from gneiss to clay slate. The finer varieties, noble garnet or Almandine, and the reddish varieties of Grossulaire (Essonite), are employed in jewellery; the first are called the Syrian or oriental; the others, hyacinth. In some parts of Germany garnets are so abundant as to be used as fluxes to some iron ores; in others, the garnet gravel is washed, pounded, and employed as a substitute for emery. The garnets of Pegu are most highly valued. Factitious garnets may be made by the following composition:—Purest white glass, 2 ounces; glass of antimony, 1 ounce; powder of cassius, 1 grain; manganese, 1 grain.

GAS (Eng. and Fr.; Gaz, Germ.); is the generic name of all those elastic fluids which are permanent under a considerable pressure, and at the temperature of zero of Fahrenheit. In many of them, however, by the joint influence of excessive cold and pressure, the repulsive state of the particles may be balanced or subverted, so as to transform the elastic gas into a liquid or a solid. For this most interesting discovery, we are indebted to the fine genius of Mr. Faraday.

The following table exhibits the temperatures and pressures at which certain gases are liquefied.

Name of the gas. Becomes liquid Calculated
boiling point;
Barom. =
30 inches.

At Under a pressure of

Sulphurous acid 59 ° F. 3 atmospheres. - 4 ° Fahr.

Chlorine 60 4 - 22

Ammonia 50 6 ·5 - 64

Sulphuretted hydrogen 50 17 - 142

Carbonic acid 32 36 - 229

Hydrochloric or muriatic acid 50 50 - 249

Deutoxide of azote 45 50 - 254

Liquid carbonic acid becomes solidified, into a snowy-looking substance, by its own rapid evaporation. Oxygen, hydrogen, and azote, have hitherto resisted all attempts to divest them of their elastic form. For this purpose, it is probable that a condensing force equal to that of 650 atmospheres, will be required.

The volume of any gas is, generally speaking, inversely as the pressure to which it is exposed; thus, under a double pressure its bulk becomes one-half; under a triple pressure, one-third; and so on. For the change of volume in gaseous bodies by heat, see Expansion.

Ammonia, carbonic acid, carburetted hydrogen, chlorine, muriatic acid, sulphurous acid, sulphuretted hydrogen, are the gases of most direct interest in the arts and manufactures. Their detailed examination belongs to a work on chemistry.

GAS-LIGHT. (Eclairage par gas, Fr.; Gaslicht, Germ.) Dr. Clayton demonstrated, by numerous experiments in 1737 and 1738, that bituminous pit-coal, subjected to a red heat in close vessels, afforded a great deal of an air similar to the fire-damp of mines, but which burned with a brighter flame. It does not appear that this species of factitious air was ever produced from pit-coal for the purpose of artificial illumination till 1792, when Mr. William Murdoch, engineer to Messrs. Bolton and Watt, employed coal gas for lighting his house and offices, at Redruth in Cornwall. The gas was generated in an iron retort, whence it was received in a gasometer, distributed in different situations by pipes, and finally burned at small apertures which could be opened and stopped at pleasure. He moreover made this light movable, by confining the gas in portable tin-plate vessels, and burning it wherever he pleased. Between this period and 1802, Mr. Murdoch continued at intervals to make similar experiments; and upon occasion of the national illumination in the spring of the latter year, at the peace of Amiens, he lighted up part of the Soho manufactory with a public display of gas lights.

The earliest application of this artificial light, on a large systematic scale, was made at Manchester; where an apparatus for lighting the great cotton mills of Messrs. Philips and Lee, was fitted up in 1804 and 1805, under the direction of Mr. Murdoch. A quantity of light, nearly equal to 3000 candles, was produced and distributed in this building. This splendid pattern has been since followed very generally in Great Britain, and more or less in many parts of the continents of Europe and America. By the year 1822, gas-lighting in London had become the business of many public companies. At the Peter-street station, for example, 300 retorts had been erected, supplying 15 gasometers, having each an average capacity of 20·626 cubic feet, but, being never quite filled, their total contents in gas might be estimated at 309,385 cubic feet. The extent of main pipes of distribution belonging to this station was then about 57 miles, with two separate mains in some of the streets. The product of gas was from 10,000 to 12,000 cubic feet from a chaldron of coals. The annual consumption of coals was therefore altogether 9282 chaldrons, affording 11,384,000 cubic feet of gas, allowing 153 retorts to be in constant daily action, upon an average of the year; and illuminating 10,660 private lamps, 2248 street lamps, and 3894 theatre lamps.

At the Brick-lane works, 371 retorts were fixed in 1822, 133 being worked on an average of summer and winter. There were 12 gasometers, charged with an average quantity of gas amounting to 197,214 cubic feet. Of coals, 8060 chaldrons were annually consumed; 96,720,000 cubic feet of gas were generated; for the supply of 1978 public lamps, and 7366 private ones, connected with main pipes 40 miles long.

At the Curtain-road gas establishment, there were 240 retorts; but the greatest number worked in 1821 was only 80, and the lowest 21. The six gasometers had an average contents of 90,467 cubic feet. Of coals, 3336 chaldrons were annually consumed, yielding 40,040,000 cubic feet of gas, that supplied 3860 private lamps, and 629 public ones, by means of mains 25 miles long. The above three stations belonged to the London Gas Light and Coke Company.

The City of London Gas Light Company, Dorset-street, had built up 230 retorts, and 6 gasometers, while two were preparing; having a total capacity of 181,282 cubic feet. Of private lamps 5423 were lighted, and 2413 public ones, from mains extending 50 miles. The quantity of coals carbonized amounted to 8840 chaldrons; producing 106,080,000 cubic feet of gas.

The South London Gas Light and Coke Company had mounted at Bankside 143 retorts, with 3 gasometers; the contents of the whole being 41,110 cubic feet, connected with mains from 30 to 40 miles long. At their other station, in Wellington-street, 3 large gasometers were then erecting, with a capacity of 73,565 cubic feet, which were to be supplied with gas from Bankside, till retorts were mounted for them.

The Imperial Gas Light and Coke Company had at that time 6 gasometers in progress at their Hackney station.

In 1822 there were thus four great companies, having in all 47 gasometers at work, capable of containing 917,940 cubic feet of gas, supplied by 1315 retorts, which generated per annum upwards of 397,000,000 cubic feet of gas, by which 61,203 private lamps, and 7268 public or street lamps, were lighted in the metropolis. Besides these public companies, there were likewise several private ones.

1. Of the generation of illuminating gases.—Pure hydrogen gas burns with too feeble a flame to be employed for illumination. But carburetted hydrogen having the property of precipitating its carbon in the act of burning, its solid particles become incandescent, and diffuse a vivid light. The more carbon it contains, the more brightly does it burn. This gas exists in two distinct states of combination. In the first, two measures of hydrogen gas are combined with one measure of the vapour of carbon, forming together one measure whose specific gravity is of course the sum of the weights of the constituents, or 0·559; atmospherical air being 1·000. This is the gas which is found in mines, and is also evolved in ditches from decomposing vegetable matter. In the second, two measures of hydrogen gas are combined with two of gaseous carbon, forming also one volume or measure whose weight or specific gravity is 0·985. This was at one time called the olefiant gas, because when mixed with chlorine an oily looking compound was produced. It may be called as well oil gas, because it is generated in considerable quantities by the igneous decomposition of oil. Thus the olefiant gas contains in the same volume double the quantity of carbon of common carburetted hydrogen, and it burns with a proportionably brighter flame. The gaseous oxide of carbon, as well as sulphuretted hydrogen gas, burns with a feeble blue light, but the latter produces in combustion sulphurous acid, an offensive and noxious gas.

By dry distillation or carbonization in close vessels, all bodies of vegetable and animal origin disengage carburetted hydrogen gas; even charcoal when placed in ignition in contact with steam, by decomposing the water, produces abundance of carbonic acid, carburetted hydrogen, hydrogen, and carbonic oxide. After separating the carbonic acid with lime water, that mixed gas contains in 100 measures, 20 of carburetted hydrogen; the rest being hydrogen and carbonic oxide, so that the gaseous mixture cannot be used for illumination. The best substances for furnishing a gas rich in luminifereous materials are, pitcoal, especially the cannel coal, resin, oil, fats of all kinds, tar, wax, &c. In some cases the gases evolved during the igneous decomposition of bones and other animal matters for the production of ammonia, may be employed for procuring light, but they are apt to emit a fetid odour.

When coals are heated in a cast-iron retort to ignition, the progress of decomposition is as follows. First, and before the retort becomes red hot, steam issues along with the atmospheric air. When the retort begins to redden, tar distils in considerable quantity with some combustible gas, of which hydrogen mixed with ammoniacal gas forms a part. The evolution of gas increases as the retort becomes hotter, with a continual production of tar and ammoniacal liquor as well as sulphurous acid from the pyrites of the coal, which unites with the ammonia. When the retort has come to a bright cherry red heat, the disengagement of gas is most active. By and bye the gaseous production diminishes, and eventually ceases entirely, although the heat be increased. In the retort a quantity of carbonized coal or coke remains, while tar is found at the bottom of the receiver, covered with the ammoniacal liquor, and combined with carbonic and sulphurous acids, and sulphuretted hydrogen.

If during this distillation, the combustible gas be collected and examined at the several stages of the process, it is found to differ extremely in its luminiferous powers. That which comes off before the retort has acquired its proper temperature, gives a feeble light, and resembles the gas obtained by the ignition of moist charcoal, consisting chiefly of hydrogen. That evolved when the retort has just acquired throughout a vivid red heat, is the best of all, consisting chiefly of bicarburetted hydrogen or olefiant gas. From good coal, it consists, for example in 100 measures, of 13 of olefiant gas, 82·5 of carburetted hydrogen, 3·2 carbonic oxide, 1·3 azote; the mixture having a specific gravity of 0·650. At a later period, as after 5 hours, it contains 7 measures of olefiant gas, 56 of carburetted hydrogen, 11 of carbonic oxide, 21·3 of hydrogen, 4·7 of azote; the specific gravity of the whole being 0·500. Towards the end of the operation, as after 10 hours, it contains twenty measures of carburetted hydrogen, 10 of carbonic oxide, 60 of hydrogen, 10 of azote, with a specific gravity of only 0·345. The hydrogen becomes sulphuretted hydrogen, if there be much pyritous matter in the coal. The larger proportion of the gas is disengaged during the first hour, amounting to about one fifth of the whole; in the three following hours the disengagement is tolerably uniform, constituting in all fifty-four hundredths; in the sixth hour, it is one tenth; in the seventh and eighth hours, sixteen hundredths.

From these observations are derived the rules for the production of a good light gas from coals. They show that the distillation should commence with a retort previously heated to a cherry red, since thereby good gas is immediately produced, and a portion of the tar is also converted into gas, instead of being simply distilled over into the condenser pit; that this heat should be steadily continued during the whole operation, from 5 to 8 hours; that it should not be increased, especially towards the end, for fear of generating carbonic oxide and hydrogen gases, as well as of injuring the retort when the cooling agency of gasefication has become feeble; and that the operation should be stopped some time before gas ceases to come over, lest gases with feeble illuminating power should impoverish the contents of the gasometer. Upon the average, a pound of good coal affords four cubic feet of gas, or a chaldron = 26 cwt. London measure, affords from 12,000 to 15,000 cubic feet, according to the form of the retort, and the manner of firing it.

When oil, fats, rosin, tar, &c. are employed for the production of a light gas, it is not sufficient to introduce these substances into the retorts, and to heat them, as is done with coals. In this case, the greater part of them would distil over in the state of volatile oils, and very little gas be generated, only as much as corresponded to the quantity of fat, &c. in immediate contact with the retort. It becomes therefore necessary to fill the retorts with pieces of brick or coke; and to keep them in ignition, while the oil, &c. is slowly introduced into their interior. The fats instantly assume the vaporous state, and thus coming into contact upon an extensive surface with the ignited bricks, are decomposed into combustible gases. A small portion of carbonaceous matter remains in the retort, while much olefiant gas is formed, possessing a superior illuminating power to common coal gas, and entirely free from sulphureous impregnation. The best oil gas is generated at a dull red, a heat much below what is requisite for the decomposition of coal. A more intense heat would indeed produce a greater volume of gas, but of a poorer quality, because the olefiant gas thereby deposits one half of its carbon, and is converted into common carburetted hydrogen. Oil affords at a lively red heat, gases which contain in 100 measures, 19 of olefiant gas, 32·4 of carburetted hydrogen, 12·2 of carbonic oxide gas, 32·4 of hydrogen, and 4 of azote; the mean specific gravity being only 0·590. At a more moderate temperature it yields 22·5 of the olefiant, 50·3 carburetted hydrogen, 15·5 carbonic oxide, 7·7 hydrogen, and 4 azote, with a specific gravity of 0·758. It contains when generated by dull ignition, as is usual in works on the manufacturing scale, in 100 parts, from 38 to 40 of olefiant gas, and besides the carburetted hydrogen, a few per cents. of carbonic oxide and azote, with a specific gravity of 0·900, and even upwards. One pound of oil or fluid fat affords 15 cubic feet of gas; of tar affords about 12 cubic feet; of rosin or pitch, 10 cubic feet.

When the oil gas is compressed by a force of from 15 to 20 atmospheres, as was the practice of the Portable Gas Company, about one fifth of the volume of the gas becomes liquefied into an oily, very volatile fluid, having the specific gravity 0·821. It is a mixture of three fluids (consisting of carburetted hydrogen), of different degrees of volatility. The most volatile of these boils even under 32° F. Some of the vapour of this gas-oil is mixed with the olefiant gas in the general products of decomposition; in consequence of which they are sometimes richer in carbon than even olefiant gas, and have a higher illuminating power. Oil gas contains about 22 per cent. and coal gas about 3⁄4 per cent. of this oily vapour. In the estimations of the composition of the gases given above, this vapour is included under olefiant gas. This vapour combines readily with sulphuric acid, and is thus precipitated from the gaseous mixture. The amount of olefiant gas is shown, by adding to the gas, contained over water, one half of its volume of chlorine, which, in the course of an hour or two, condenses the olefiant gas into an oily looking liquid (chloride of hydrocarbon.) After the mixture, the gases must be screened from the light, otherwise the common carburetted hydrogen would also combine with the chlorine, while water and carbonic acid would make their appearance.

The oil employed for affording gas is the crudest and cheapest that can be bought; even the blubber and sediment of whale oil are employed with advantage. After all, however, coal is so much cheaper, and the gas produced from it is now so well purified, that oil and rosin are very little used in gas apparatus.

Apparatus for Coal Gas.—Coal gas, as it issues from the retort, cannot be directly employed for illumination; for it contains vapours of tar and coal oil, as also steam impregnated with the carbonate, sulphite, and hydrosulphuret of ammonia. These vapours would readily condense in the pipes through which the gas must be distributed, and would produce obstructions; they must therefore be so far removed by previous cooling, as to be liable to occasion no troublesome condensation at ordinary temperatures. The crude coal gas contains moreover sulphuretted hydrogen, whose combustion for light would exhale an offensive sulphureous odour, that ought to be got rid of as much as possible. Carbonic acid and carbonic oxide gases, generated at first from the decomposition of the steam by the ignited coal, enfeeble the illuminating power of the gas, and should be removed. The disengagement of gas in the retorts is never uniform, but varies with the degree of heat to which they are exposed; for which reason the gas must be received in a gasometer, where it may experience uniform pressure, and be discharged uniformly into the pipes of distribution, in order to ensure a steady discharge of gas, and uniform intensity of light in the burners. A coal gas apparatus ought therefore to be so constructed as not only to generate the gas itself, but to fulfil the above conditions.

In fig. 482., such an apparatus is represented, where the various parts are shown connected with each other, in section.

A is the furnace with its set of cylindrical or elliptical retorts, five in number. From each of these retorts, a tube b proceeds perpendicularly upwards, and then by a curve or saddle-tube, it turns downwards, where it enters a long horizontal cylinder under B, shut at each end with a screw cap, and descends to beneath its middle, so as to dip about an inch into the water contained in it. From one end of this cylinder the tube d passes downwards, to connect itself with a horizontal tube which enters into the tar pit or cistern C, by means of the vertical branch f. This branch reaches to near the bottom of the cylindrical vessel, which sits on the sole of the tar cistern. From the other side of the vertical branch f, the main pipe proceeds to the condenser D, and thence by the pipe l, into the purifier E; from which the gas is immediately transmitted by the pipe p into the gasometer F.

The operation proceeds in the following way:—As soon as gas begins to be disengaged from the ignited retort, tar and ammoniacal liquor are deposited in the cylindrical receiver B, and fill it up till the superfluity runs over by the pipe d, the level being constantly preserved at the line shown in the figure. By the same tarry liquid, the orifices of the several pipes b, issuing from the retorts, are closed; whereby the gas in the pipe d has its communication cut off with the gas in the retorts. Hence if one of the retorts be opened and emptied, it remains shut off from the rest of the apparatus. This insulation of the several retorts is the function of the pipe under B, and therefore the recurved tube b must be dipped as far under the surface of the tarry liquid, as to be in equilibrio with the pressure of the gas upon the water in the purifier. The tube b is closed at top with a screw cap, which can be taken off at pleasure, to permit the interior to be cleansed.

Both by the overflow from the receiver-pipe B, and by subsequent condensation in the tube d, tar and ammoniacal liquor collect progressively in the cistern or pit under C, by which mingled liquids the lower orifice of the vertical tube f is closed, so that the gas cannot escape into the empty space of this cistern. These liquids flow over the edges of the inner vessel when it is full, and may, from time to time, be drawn off by the stopcock at the bottom of the cistern.

Though the gas has, in its progress hitherto, deposited a good deal of its tarry and ammoniacal vapours, yet, in consequence of its high temperature, it still retains a considerable portion of them, which must be immediately abstracted, otherwise the tar would pollute the lime in the vessel E, and interfere with its purification. On this account the gas should, at this period of the process, be cooled as much as possible, in order to condense these vapours, and to favour the action of the lime in the purifier E, upon the sulphuretted hydrogen, which is more energetic the lower the temperature of the gas. The coal gas passes, therefore, from the tube f into the tube h of the condenser D, which is placed in an iron chest g filled with water, and it deposits more tar and ammoniacal liquor in the under part of the cistern at t, t. When these liquids have risen to a certain level, they overflow into the tar-pit, as shown in the figure, to be drawn off by the stopcock as occasion may require.

The refrigerated gas is now conducted into the purifier E, which is filled with milk of lime, made by mixing one part of slaked lime with 25 parts of water. The gas, as it enters by the pipe l, depresses the water in the wide cylinder n, thence passes under the perforated disc in the under part of that cylinder, and rising up through innumerable small holes is distributed throughout the lime liquid in the vessel m. By contact with the lime on this extended surface, the gas is stripped of its sulphuretted hydrogen and carbonic acid, which are condensed into the hydro-sulphuret and carbonate of lime; it now enters the gasometer F in a purified state, through the pipe p t, and occupies the space q. The gasometer, pressing with a small unbalanced force over the counterweight s, expels it through the main u u, in communication with the pipes of distribution through the buildings or streets to be illuminated.

The parts A B C D E and F, of which this apparatus consists, are essential constituents of every good coal-gas work. Their construction rests upon peculiar principles, is susceptible of certain modifications, and therefore deserves to be considered in detail.

The Retorts.—These are generally made of cast iron, though they have occasionally been made of baked clay, like common earthenware retorts. The original form was a cylinder, which was changed to an ellipse, with the long axis in a horizontal direction, then into the shape of the letter D with the straight line undermost, and lastly into a semi-cylinder, with its horizontal diameter 22 inches, and its vertical varying from 9 to 12. The kidney form was at one time preferred, but it has been little used of late.

The form of retort represented in fig. 483. has been found to yield the largest quantity of good gas in the shortest time, and with the least quantity of firing. The length is 7⁄2, and the transverse area, from one foot to a foot and a half square. The arrows show the direction of the flame and draught in this excellent bench of retorts, as mounted by Messrs. Barlow.

The charge of coals is most conveniently introduced in a tray of sheet iron, made somewhat like a grocer’s scoop, adapted to the size of the retort, which is pushed home to its further end, inverted so as to turn out the contents, and then immediately withdrawn.

The duration of the process, or the time of completing a distillation, depends upon the nature of the coal and the form of the retort. With cylindrical retorts it cannot be finished in less than 6 hours, but with elliptical and semi-cylindrical retorts, it may be completed in 4 or 5 hours. If the distillation be continued in the former for 8 hours, and in the latter for 6, gas will continue to be obtained, but during the latter period of the operation, of indifferent quality.

The Receiver.—If the furnace contains only 2 or 3 retorts, a simple cylindrical vessel standing on the ground half filled with water, may serve as a receiver; into which the tube from the retort may be plunged. It should be provided with an overflow pipe for the tar and ammoniacal liquor. For a range of several retorts, a long horizontal cylinder is preferable, like that represented at B in fig. 484. Its diameter is from 10 to 15 inches. This cylinder may be so constructed as to separate the tar from the ammoniacal liquor, by means of a syphon attached to one of its ends.

The Condenser.—The condenser, represented in fig. 482., consists of a square chest, g, made of wrought iron plates open at top, but having its bottom pierced with a row of holes, to receive a series of tubes. To these holes the upright four-inch tubes h h are secured by flanges and screws, and they are connected in pairs at top by the curved or saddle tubes. The said bottom forms the cover of the chest t, t, which is divided by vertical iron partitions, into half as many compartments as there are tubes.

These partition plates are left open at bottom, so as to place the liquids of each compartment in communication. Thereby the gas passes up and down the series of tubes, in proceeding from one compartment to another. The condensed liquids descend into the box t, t, and flow over into the tar cistern, when they rise above the level t, t. The tar may be drawn off from time to time by the stopcock. Through the tube k, cold water flows into the condenser chest, and the warm water passes away by a pipe at its upper edge.

The extent of surface which the gas requires for its refrigeration before it is admitted into the washing-lime apparatus, depends upon the temperature of the milk of lime, and the quantity of gas generated in a certain time.

It may be assumed as a determination sufficiently exact, that 10 square feet of surface of the condenser can cool a cubic foot of gas per minute to the temperature of the cooling water. For example, suppose a furnace or arch with 5 retorts of 150 pounds of coal each, to produce in 5 hours 3000 cubic feet of gas, or 10 cubic feet per minute, there would be required, for the cooling surface of the condenser, 100 square feet = 10 × 10. Suppose 100,000 cubic feet of gas to be produced in 24 hours, for which 8 or 9 such arches must be employed, the condensing surface must contain from 800 to 900 square feet.

The Purifier.—The apparatus represented in the preceding figure is composed of a cylindrical iron vessel, with an air-tight cover screwed upon it, through which the cylinder n is also fixed air-tight. The bottom of this cylinder spreads out like the brim of a hat, forming a horizontal circular partition, which is pierced with holes. Through a stuffing box, in the cover of this interior cylinder, the vertical axis of the agitator passes, which is turned by wheel and pinion work, in order to stir up the lime from the bottom of the water in the purifier. The vessel o serves for introducing fresh milk of lime, as also for letting it off by a stopcock when it has become too foul for further use.

The quantity of lime should be proportioned to the quantity of sulphuretted hydrogen and carbonic acid contained in the gas. Supposing that in good coal gas there is 5 per cent. of these gases, about one pound and a half of lime will be requisite for every hundred cubic feet of coal gas generated, which amounts to nearly one-sixteenth of the weight of coal subjected to decomposition. This quantity of lime mixed with the proper quantity of water will form about a cubic foot of milk of lime. Consequently, the capacity of the purifier, that is, of the interior space filled with liquid, may be taken at four-sevenths of a cubic foot for every hundred cubic feet of gas passing through it in one operation; or for 175 cubic feet of gas, one cubic foot of liquor. After every operation, that is, after every five or six hours, the purifier must be filled afresh. Suppose that in the course of one operation 20,000 cubic feet of gas pass through the machine, this should be able to contain 20,000175 = 114 cubic feet of milk of lime; whence its diameter should be seven feet, and the height of the liquid three feet. If the capacity of the vessel be less, the lime milk must be more frequently changed.

In some of the large gas works of London the purifier has the following construction, whereby an uninterrupted influx and efflux of milk of lime takes place. Three single purifiers are so connected together, that the second vessel stands higher than the first, and the third than the second; so that the discharge tube of the superior vessel, placed somewhat below its cover, enters into the upper part of the next lower vessel; consequently, should the milk of lime in the third and uppermost vessel rise above its ordinary level, it will flow over into the second, and thence in the same way into the first; from which it is let off by the eduction pipe. A tube introduces the gas from the condenser into the first vessel, another tube does the same thing for the second vessel, &c., and the tube of the third vessel conducts the gas into the gasometer. Into the third vessel, milk of lime is constantly made to flow from a cistern upon a higher level. By this arrangement, the gas passing through the several vessels in proportion as it is purified, comes progressively into contact with purer milk of lime, whereby its purification becomes more complete. The agitator c, provided with two stirring paddles, is kept in continual rotation. The pressure which the gas has here to overcome is naturally three times as great as with a single purifier of like depth.

Fig. 485. is a simple form of purifier, which has been found to answer well in practice. Through the cover of the vessel A B, the wide cylinder e d is inserted, having its lower end pierced with numerous holes. Concentric with that cylinder is the narrower one s z, bound above with the flange a b, but open at top and bottom. The under edge g h of this cylinder descends a few inches below the end c d of the outer one. About the middle of the vessel the perforated shelf m n is placed. The shaft of the agitator l, passes through a stuffing box upon the top of the vessel. The gas-pipe g, proceeding from the condenser, enters through the flange a b in the outer cylinder, while the gas-pipe h goes from the cover to the gasometer. A stopcock upon the side, whose orifice of discharge is somewhat higher than the under edge of the outer cylinder, serves to draw off the milk of lime. As the gas enters through the pipe g into the space between the two cylinders, it displaces the liquor till it arrives at the holes in the under edge of the outer cylinder, through which, as well as under the edge, it flows, and then passes up through the apertures of the shelf m n into the milk of lime chamber; the level of which is shown by the dotted line. The stirrer, l, should be turned by wheel work, though it is here shown as put in motion by a winch handle.

In order to judge of the degree of purity of the gas after its transmission through the lime machine, a slender syphon tube provided with a stopcock may have the one end inserted in its cover, and the other dipped into a vessel containing a solution of acetate of lead. Whenever the solution has been rendered turbid by the precipitation of sulphuret of lead, it should be renewed. The saturated and fetid milk of lime is evaporated in oblong cast-iron troughs placed in the ash-pit of the furnaces, and the dried lime is partly employed for luting the apparatus, and partly disposed of for a mortar or manure.

By this purifier, and others of similar construction, the gas in the preceding parts of the apparatus, as in the retorts and the condenser, suffers a pressure equal to a column of water about two feet high; and in the last described purifier even a greater pressure. This pressure is not disadvantageous, but is of use in two respects; 1. it shows by a brisk jet of gas when the apparatus is not air-tight, and it prevents common air from entering into the retorts; 2. this compression of the gas favours the condensation of the tar and ammoniacal liquor. The effect of such a degree of pressure in expanding the metal of the ignited retorts is quite inconsiderable, and may be neglected. Two contrivances have, however, been proposed for taking off this pressure in the purifier.

In fig. 486., m m are two similar vessels of a round or rectangular form, furnished at their upper border with a groove filled with water, into which the under edge of the cover fits, so as to make the vessel air-tight. The cover is suspended by a cord or chain, which goes over a pulley, and may be raised or lowered at pleasure. The vessels themselves have perforated bottoms, r r′, covered with wetted moss or hay sprinkled over with slaked and sifted quicklime. The gas passes through the loosely compacted matter of the first vessel, by entering between its two bottoms, rises into the upper space t, thence it proceeds to the second vessel, and, lastly, through the pipe u into the gasometer. This method, however, requires twice as much lime as the former, without increasing the purity of the gas.

The second method consists in compressing the gas by the action of an Archimedes screw, to such a degree, before it is admitted into the purifier, as that it may overcome the pressure of the column of water in that vessel. Fig. 487. exhibits this apparatus in section. D D is the Archimedes worm, the axis of which revolves at bottom upon the gudgeon e; it possesses a three-fold spiral, and is turned in the opposite direction to that in which it scoops the water. The cistern which contains it has an air-tight cover. The gas to be purified passes through the pipe C into the space D, over the water level d; the upper cells of the worm, scoop in the gas at this point, and carry it downwards, where it enters at g into the cavity E of a second cistern. In order that the gas, after it escapes from the bottom of the worm, may not partially return through g into the cavity D, an annular plate g h is attached to its under edge, so as to turn over it. The compressed gas is conducted from the cavity E through the pipe G into the purifying machine; a is a manometer, to indicate the elastic tension of the gas in D. On the top of the worm a mechanism is fitted for keeping it in constant rotation.

A perfect purification of light-gas from sulphuretted hydrogen, either by milk of lime or a solution of the green sulphate of iron, is attended with some difficulty, when carried so far as to cause no precipitation of sulphuret in acetate of lead, because such a degree of washing is required as is apt to diminish its illuminating power, by abstracting the vapour of the rich oily hydrocarburet which it contains. Moreover, the coal gas obtained towards the end of the distillation contains some sulphuret of carbon, which affords sulphurous acid on being burned, and can be removed by no easy method hitherto known. The lime in the purifier disengages from the carbonate and hydrosulphuret of ammonia carried over with the gas, especially when it has been imperfectly cooled in the condenser, a portion of ammoniacal gas, which, however, is not injurious to its illuminating power. The best agent for purifying gas would be the pyrolignite of lead, were it not rather expensive, because it would save the trouble of stirring, and require a smaller and simpler apparatus.

The Gasometer.—The gasometer serves not merely as a magazine for receiving the gas when it is purified, and keeping it in store for use, but also for communicating to the gas in the act of burning such an uniform pressure as may secure a steady unflickering flame. It consists of two essential parts; 1. of an under cistern, open at top and filled with water; and 2. of the upper floating cylinder or chest, which is a similar cistern inverted, and of somewhat smaller dimensions, called the gas-holder: see F, fig. 482. The best form of this vessel is the round or cylindrical; both because under equal capacity it requires least surface of metal, and it is least liable to be warped by its own weight or accidents. Since a cylindrical body has the greatest capacity with a given surface when its height is equal to its semi-diameter, its dimensions ought to be such that when elevated to the highest point in the water, the height may be equal to the radius of the base. For example, let the capacity of the gas-holder in cubic feet be k, the semi-diameter of its base be x, the height out of the water be h; h is = x = ∛k3·14. This height may be increased by one or two feet, according to its magnitude, to prevent the chance of any gas escaping beneath its under edge, when it is raised to its highest elevation in the water.

The size of the gasometer should be proportional to the quantity of gas to be consumed in a certain time. If 120,000 cubic feet be required, for instance, in 10 hours for street illumination, and if the gas retorts be charged four times in 24 hours, 30,000 cubic feet of gas will be generated in 6 hours. Hence the gasometer should have a capacity of at least 70,000 cubic feet, supposing the remaining 50,000 cubic feet to be produced during the period of consumption. If the gasometer has a smaller capacity, it must be supplied from a greater number of retorts during the lighting period, which is not advantageous, as the first heating of the supernumerary retorts is wasteful of fuel. Some engineers consider that a capacity of 30,000 cubic feet is the largest which can with propriety be given to a gasometer; in which case, they make its diameter 42 feet, and its height 23. When the dimensions are greater, the sheet iron must be thicker and more expensive; and the hollow cylinder must be fortified by strong internal cross braces.

The water cistern is usually constructed in this country with cast-iron plates bolted together, and made tight with rust-cement.

In cases where the weight of water required to fill such a cistern might be inconvenient to sustain, it may be made in the form represented in fig. 488.; which, however, will cost nearly twice as much. Parallel with the side of the cistern, a second cylinder C, of the same shape but somewhat smaller, is fixed in an inverted position to the bottom of the first, so as to leave an annular space B B between them, which is filled with water, and in which the floating gasometer A plays up and down. The water must stand above the cover of the inverted cylinder. a and b are the pipes for leading the gas in and out. Through an opening in the masonry upon which the gasometer apparatus rests, the space C may be entered, in order to make any requisite repairs.

The water cistern may also be sunk in the ground, and the sides made tight with hydraulic mortar, as is shown in fig. 489., and to make it answer with less water, a concentric cylindrical mass of masonry may be built at a distance of 2 or 3 inches within it.

Every large gasometer must be strengthened interiorly with cross iron rods, to stiffen both its top and bottom. The top is supported by rods stretching obliquely down to the sides, and to the under edge an iron ring is attached, consisting of curved cast-iron bars bolted together; with which the oblique rods are connected by perpendicular ones. Other vertical rods stretch directly from the top to the bottom edge. Upon the periphery of the top, at the end of the rods, several rings are made fast, to which the gas-holder is suspended, by means of a common chain which runs over a pulley at the centre. Upon the other end of the chain there is a counterpoise, which takes off the greater part of the weight of the gas-holder, leaving only so much as is requisite for the expulsion of the gas. The inner and outer surfaces of the gas-holder should be a few times rubbed over with hot tar, at a few days’ interval between each application. The pulley must be made fast to a strong frame.

If the water cistern be formed with masonry, the suspension of the gas-holder may be made in the following way. A A, fig. 489., is a hollow cylinder of cast iron, standing up through the middle of the gasometer, and which is provided at either end with another small hollow cylinder G, open at both ends and passing through the top, with its axis placed in the axis of the gas-holder. In the hollow cylinder G, the counterweight moves up and down, with its chain passing over the three pulleys B, B, B, as shown in fig. 489. E F are the gas pipes made fast to a vertical iron rod. Should the gasometer be made to work without a counterweight, as we shall presently see, the central cylinder A A, serves as a vertical guide.

In proportion as the gas-holder sinks in the water of the cistern, it loses so much of its weight, as is equal to the weight of the water displaced by the sides of the sinking vessel; so that the gas-holder when entirely immersed, exercises the least pressure upon the gas, and when entirely out of the water, it exercises the greatest pressure. In order to counteract this inequality of pressure, which would occasion an unequal velocity in the efflux of the gas, and of course an unequal intensity of light in its flame, the weight of the chain upon which the gas-holder hangs is so adjusted as to be equal, throughout the length of its motion, to one half of the weight which the gas-holder loses by immersion. In this case, the weight which it loses by sinking into the water, is replaced by the portion of the chain which passing the pulley, and hanging over, balances so much of the chain upon the side of the counterweight; and the weight which it gains by rising out of the water, is counterpoised by the links of the chain which passing over the pulley, add to the amount of the counterweight. The pressure which the gas-holder exercises upon the gas, or that with which it forces it through the first main pipe, is usually so regulated as to sustain a column of from one to two inches of water; so that the water will stand in the cistern from one to two inches higher within, than without the gas-holder. The following computation will place these particulars in a clear light.

Let the semi-diameter of the gas-holder, equal to the vertical extent of its motion into and out of the water, = x; let the weight of a foot square of the side of the gas-holder, including that of the strengthening bars and ring, which remain plunged under the water, be = p; then

1. the weight of the gas-holder in its highest position = 3 p π x;

2. the weight of the sides of the gas-holder which play in the water = 2 p π x;

3. the cubic contents of the immersed portion of the gas-holder = 2 p π x400;

4. its loss of weight in water = 112400 p π x;

5. the weight of the gas-holder in its lowest position = p π x (3 - 112400) = 2·72 p π x;

6. the weight of n inches, height of water = 5612 n π x;

7. the amount of the counterweight = π x (3 p - 56 n12);

8. the weight of the chain for the length x = 112800 p π x.

If we reduce the weight of the gas-holder in its highest and lowest positions to the height of a stratum of water equal to the surface of its top, this height is that of the column of water which would press the gas within the gasometer, were no counterweight employed; it consists as follows;—

9. for the highest position = 3 p56;

10. for the lowest = 2·72 p50;

For the case, when the height of the gas-holder is different from its semi-diameter, let this height = m x; then the height of the water level is

11. for the highest position = p (1 + 2 m56);

12. for the lowest = p (1 + 1·72 m6);

13. the counterweight = π x (p (1 + 2m) - 56 n12);

14. the weight of the equalizing chain = 112800 p π m x.

For example, let the diameter of the gas-holder be 30 feet, the height 15 (the contents in cubic feet will be 10,597), p = 4 pounds; then the counterweight for a height of an inch and a half of water pressure = 3532 pounds; the weight of the chain for a length of 15 feet = 395 pounds. Were no counterweight employed, so that the gas-holder pressed with its whole weight upon the gas, then the height of the equivalent column of water in its highest position = 2·56 inches; and in its lowest, 2·33. The counterweight may hence be lessened at pleasure, if the height of the pressing water-column n be increased. The weight of the equalising or compensating portion of the chain remains the same. When n = 2 inches, for instance, the counterweight = 1886 pounds.

The velocity with which the gas passes along the mains for supplying the various jets of light, may be further regulated by opening the main-cock or slide-valve in a greater or less degree.

Gasometers whose height is greater than their semi-diameter, are not only more costly in the construction, but require heavier counterweights and equilibration chains.

The above estimate is made on the supposition of the gas in the gas-holder being of the same specific gravity as the atmospherical air, which would be nearly true with regard to oil gas under the ordinary pressure. But coal gas, whose specific gravity may be taken on an average at about 0·5, exercises a buoyancy upon the top of the gas-holder, which of course diminishes its absolute weight. Supposing the cubic foot of gas to be = 0·0364 pounds, the buoyancy will be = 0·0364 π x pounds; a quantity which deserves to be taken into account for large gasometers. Hence,

15. the weight of the gas-holder in its highest position = 3 p π x - 0·1143 x;

16. the counterweight = π x (3 p - 56 n12) - 0·1143 x;

17. The weight of the chain for the length x, = 112800 p π x 0·1143 x2;

18. The height of the water pressure for the highest position, without the counterweight = 3 p π - 0·1143 x56 π;

19. the same for the lowest position = 2·72 p56 in feet.

The preceding values of p and x, are,

(16) = 3147; (17) = 203; (18) = 2·44 inches; (19) = 2·33 inches.

The water columns in the highest and lowest situations of the gas-holder here differ about 0·1 of an inch, and this difference becomes still less when p has a smaller value, for example, 3 pounds, or when the diameter of the gas-holder is still greater.

It would thus appear that for coal-gas gasometers, in which the height of the gas-holder does not exceed its semi-diameter, and especially when it has a considerable size, neither a compensation chain nor a counterweight is necessary. The only thing requisite, is to preserve the vertical motion of the gas-holder by a sufficient number of guide rods or pillars, placed either within the water cistern, or round about it. Should the pressure of the gas in the pipe proceeding from the gasometer, be less than in the gasometer itself, this may be regulated by the main valve, or by water valves of various kinds. Or a small intermediate regulating gasometer may be introduced between the great gas-holder, and the main pipe of distribution. With a diameter of 61 feet in the gas-holder, the pressure in the highest and lowest positions is the same.

The gasometers employed in storing up gas until required for use, occupy, upon the old plan, much space, and are attended with considerable expense in erecting. The water tank, whether sunk in the ground, or raised, must be of equal dimensions with the gasometer, both in breadth and depth. The improved construction which we are about to describe, affords a means of reducing the depth of the tank, dispensing with the bridge of suspension, and of increasing at pleasure the capacity of the gasometer, upon a given base; thus rendering a small apparatus capable, if required, of holding a large quantity of gas, the first cost of which will be considerably less than even a small gasometer constructed upon the ordinary plan.

Mr. Tait, of Mile-End Road, the inventor, has, we believe, been for some years connected with gas establishments, and is therefore fully aware of the practical defects or advantages of the different constructions of gasometers now in use. Fig. 490. is a section of Mr. Tait’s improved contrivance; a a is the tank, occupied with water, b b two iron columns, with pulley-wheels on the top, c c, chains attached to a ring of iron, d d, extending round the gasometer, which chains pass over the pulley-wheels, and are loaded at their extremities, for the purpose of balancing the weight of the materials of which the gasometer is composed.

The gasometer is formed by 2 or 3 cylinders, sliding one within the other, like the tubes of a telescope; e, e, e, is the first or outer cylinder, closed at the top, and having the ring of iron d, passing round it, by which the whole is suspended; f f, is the second cylinder, sliding freely within the first, and there may be a third and fourth within these if necessary.

When there is no gas in the apparatus, all the cylinders are slidden down, and remain one within the other immersed in the tank of water; but when the gas rises through the water pressing against the top of the gasometer, its buoyancy causes the cylinder e to ascend. Round the lower edge of this cylinder a groove is formed by the turning in of the plate of iron, and as it rises, the edge takes hold of the top rim of the cylinder f, which is overlapped for that purpose. The groove at the bottom of the cylinder fills itself with water as it ascends, and by the rim of the second cylinder falling into it, an air-tight hydraulic joint is produced.

Thus, several cylinders may be adapted to act in a small tank of water, by sliding one within the other, with lapped edges forming hydraulic joints, and by supporting the apparatus in the way shown, the centre of gravity will always be below the points of suspension. A gasometer may be made upon this plan of any diameter, as there will be no need of frame work, or a bridge to support it; and the increasing weight of the apparatus, as the cylinders are raised one after the other, may be counterpoised by loading the ends of the chains c c.

The water in the gasometer need not be renewed; but merely so much of it as evaporates or leaks out, is to be replaced. Indeed the surface of the water in the cistern gets covered with a stratum of coal oil, a few inches deep, which prevents its evaporation, and allows the gas to be saturated with this volatile substance, so as to increase its illuminating powers.

The gasometer may be separated from the purifier by an intermediate vessel, such as is represented fig. 491., with which the two gas pipes are connected. A is the cylindrical vessel of cast iron, a, the end of the gas pipe which comes from the purifier, immersed a few inches deep into the liquid with which the vessel is about two-thirds filled; b is the gas-pipe which leads into the gasometer, c is a perpendicular tube, placed over the bottom of the vessel, and reaching to within one-third of the top, through which the liquid is introduced into the vessel, and through which it escapes when it overflows the level d. In this tube the liquid stands towards the inner level higher, in proportion to the pressure of the gas in the gasometer. The fluid which is condensed in the gas pipe, b, and in its prolongation from the gasometer, runs off into the vessel A; and therefore the latter must be laid so low that the said tube may have the requisite declivity. A straight stop-cock may also be attached to the side over the bottom, to draw off any sediment.

II. Application of Light-Gas.

1. Distribution of the pipes.—The pressure by which the motion of the gas is maintained in the pipes, corresponds to a certain height of water in the cistern of the gasometer. From the magnitude of this pressure, and the quantity of gas which in a given time, as an hour, must be transmitted through a certain length of pipes, depends the width or the diameter that they should have, in order that the motion may not be retarded by the friction which the gas, like all other fluids, experiences in tubes, and thereby the gas might be prevented from issuing with the velocity required for the jets of flame. The velocity of the gas in the main pipe increases in the ratio of the square root of the pressing column of water upon the gasometer, and therefore by increasing this pressure, the gas may be forced more rapidly along the remoter and smaller ramifications of the pipes. Thus it happens, however, that the gas will be discharged from the orifices near the gasometer, with superfluous velocity. It is therefore advisable to lay the pipes in such a manner, that in every point of their length, the velocity of discharge may be nearly equal. This may be nearly effected as follows;—

From experiment it appears that the magnitude of the friction, or the resistance which the air suffers in moving along the pipes, under a like primary pressure, that is for equal initial velocity, varies with the square root of the length. The volume of gas discharged from the end of a pipe, is directly proportional to the square of its diameter, and inversely as the square root of its length; or, calling the length L, the diameter D, the cubic feet of gas discharged in an hour k; then k = D√L. Experience likewise shows, that for a pipe 250 feet long, which transmits in an hour 200 cubic feet of gas, one inch is a sufficient diameter.

Consequently, 200 : k ∷ 1144 √250 : D√L; and D = √k √L455,000

From this formula the following table of proportions is calculated.

Number of
cubic feet
per hour. Length of
pipe,
in feet. Diameter,
in inches.

50 100 0 ·40

250 200 1 ·00

500 600 1 ·97

700 1000 2 ·65

1000 1000 3 ·16

1500 1000 3 ·87

2000 1000 4 ·47

2000 2000 5 ·32

2000 4000 6 ·33

2000 6000 7 ·00

6000 1000 7 ·75

6000 2000 9 ·21

8000 1000 8 ·95

8000 2000 16 ·65

These dimensions are applicable to the case where the body of gas is transmitted through pipes without being let off in its way by burners, that is, to the mains which conduct the gas to the places where it is to be used. If the main sends off branches for burners, then for the same length the diameter may be reduced, or for like diameter the length may be greater. For example, if a pipe of 5·32 inches, which transmits 2000 cubic feet through a length of 2000 feet, gives off, in this space, 1000 cubic feet of gas; then the remainder of the pipe, having the same diameter, can continue to transmit the gas through a length of 2450 feet = (450,000k), with undiminished pressure for the purposes of lighting. Inversely, the diameter should be progressively reduced in proportion to the number of jets sent off in the length of the pipe.

Suppose for instance, the gasometer to discharge 2000 cubic feet per hour, and the last point of the jets to be at a distance of 4000 feet. Suppose also that from the gasometer to the first point of lighting, the gas proceeds through 1000 feet of close pipe, the diameter of the pipe will be here 4·47 inches; in the second 1000 feet of length, suppose the pipe to give off, at equal distances, 1000 cubic feet of gas, the diameter in this length (calculated at 1500 cubic feet for 1000 feet long) = 3·87 inches; in the third extent of 1000 feet, 600 cubic feet of gas will be given off, and the diameter (reckoning 700 cubic feet for 1000 feet long) will be 2·65 inches; in the fourth and last space (for 200 cubic feet in 1000 feet long) the pipe has a diameter of only an inch and a half, for which, in practice, a two-inch cast iron pipe is substituted; this being the smallest used in mains, into which branch pipes can be conveniently inserted.

The same relations hold with regard to branch pipes through which the gas is transmitted into buildings and other places to be illuminated. If such pipes make frequent angular turnings, whereby they retard the motion of the gas, they must be a third or a half larger in diameter. The smallest tubes of distribution are never less than one fourth of an inch in the bore.

Where, from one central gas work, a very great quantity of light is required in particular localities, there ought to be placed near these spots gasometers of distribution, which, being filled during the slack hours of the day, are ready to supply the burners at night, without making any considerable demand upon the original main pipe. Suppose the first main be required to supply 8000 cubic feet in the hour, for an illumination of 8 hours, at the distance of 2000 feet, a pipe 10⁄3 inches in diameter would be necessary; but if two or three gasometers of distribution, or station gasometers be had recourse to, into which the gas during the course of 24 hours would flow through the same distance continuously from the central gas works, the quantity required per hour from them would be only one third of 8000, = 2666·6 cubic feet; consequently the diameter for such a pipe is only 6·15 inches.

All the principal as well as branch pipes, whose interior diameter exceeds an inch and a half, are made of cast iron from 6 to 8 feet long, with elbow pipes cast in them where it is necessary. These pipe lengths are shown in fig. 492., having at one end a wide socket a, and at the other a nozzle b, which fits the former. After inserting the one in the other in their proper horizontal position, a coil of hemp soaked with tar is driven home at the junction; then a luting of clay is applied at the mouth, within which a ring of lead is cast into the socket, which is driven tight home with a mallet and blunt chisel.

The pipes should be proved by a force pump before being received into the gas works; two or three lengths of them should be joined before laying them down, and they should be placed at least two feet below the surface, to prevent their being affected by changes of temperature, which would loosen the joints. The tubes for internal distribution, when of small size are made of lead, copper, wrought iron, or tin.

Instead of a stopcock for letting off the gas in regulated quantities from the gasometer, a peculiarly formed water or mercurial valve is usually employed. Fig. 493. shows the mode of construction for a water trap or lute, and is, in fact, merely a gasometer in miniature. C D E F is a square cast iron vessel, in the one side of which a pipe A is placed in communication with the gasometer, and in the other, one with the main B. The movable cover or lid H G I K has a partition, L M, in its middle. If this cover be raised by its counterweight, the gas can pass without impediment from A to B; but if the counterweight be diminished so as to let the partition plate L M sink into the water, the communication of the two pipes is thereby interrupted. In this case the water-level stands in the compartment A so much lower than outside of it, and in the compartment B, as is equivalent to the pressure in the gasometer; therefore the pipes A and B must project thus far above the water. In order to keep the water always at the same height, and to prevent it from flowing into the mouths of these pipes, the rim C D of the outer vessel stands somewhat lower than the orifices A B; and thence the vessel may be kept always full of water.

If a quicksilver valve be preferred, it may be constructed as shown in fig. 494. A B are the terminations of the two gas pipes, which are made fast in the rectangular iron vessel M. E is an iron vessel of the same form, which is filled with quicksilver up to the level a, and which, by means of the screw G, which presses against its bottom, and works in the fixed female screw C C, may be moved up or down, so that the vessel M may be immersed more or less into the quicksilver. The vessel M is furnished with a vertical partition m; the passage of the gas from A to B is therefore obstructed when this partition dips into the quicksilver, and from the gradual depression of the vessel E by its screw, the interval between the quicksilver and the lower edge of the partition, through which the gas must enter, may be enlarged at pleasure, whereby the pressure of the gas in B may be regulated to any degree. The transverse section of that interval is equal to the area of the pipe or rather greater; the breadth of the vessel M from A to B amounts to the double of that space, and its length to the mere diameter of A or B. The greatest height to which the partition m can rise out of the quicksilver, is also equal to the above diameter, and in this case the line a comes to the place of b. The vertical movement of the outer vessel E, is secured by a rectangular rim or hoop which surrounds it, and is made fast to the upper part of the vessel M, within which guide it moves up and down. Instead of the lever D D, an index with a graduated plate may be employed to turn the screw, and to indicate exactly the magnitude in the opening of the valve.

In order to measure the quantity of gas which passes through a pipe for lighting a factory, theatre, &c., the gas-meter is employed, of whose construction a sufficiently precise idea may be formed from the consideration of fig. 495., which shows the instrument in a section perpendicular to its axis.

Within the cylindrical case a, there is a shorter cylinder b b, shut at both ends, and movable round an axis, which is divided into four compartments, that communicate by the opening d, with the interval between this cylinder and the outer case. The mode in which this cylinder turns round its axis is as follows:—The end of the tube c, which is made fast to the side of the case, and by which the gas enters, carries a pivot or gudgeon, upon which the centre of its prop turns; the other end of the axis runs in the cover, which here forms the side of a superior open vessel, in which, upon the same axis, there is a toothed wheel. The vessel is so far filled with water, that the tube c just rises above it, which position is secured by the level of the side vessel. When the gas enters through the tube c, by its pressure upon the partition e, (fig. 495.) it turns the cylinder from right to left upon its axis, till the exterior opening d rises above the water, and the gas expands itself in the exterior space, whence it passes off through a tube at top. At every revolution a certain volume of gas thus goes through the cylinder, proportional to its known capacity. The wheel on the axis works in other toothed wheels, whence, by means of an index upon a graduated disc or dial, placed at top or in front of the gas-meter, the number of cubic feet of gas, which pass through this apparatus in a given time, is registered.

B. Employment of the gas for lighting.—The illuminating power of different gases burned in the same circumstances, is proportional, generally speaking, to their specific gravity, as this is to the quantity of carbon they hold in combination. The following table exhibits the different qualities of gases in respect to illumination.

Density or specific gravity. Proportion of light
afforded by
coal gas to oil gas.

Coal gas. Oil gas.

0 ·659 0 ·818 100 : 140

0 ·578 0 ·910 100 : 225

0 ·605 1 ·110 100 : 250

0 ·407 0 ·940 100 : 354

0 ·429 0 ·965 100 : 356

0 ·508 1 ·175 100 : 310

Mean 0 ·529 0 ·96 100 : 272

In the last three proportions, the coal gas was produced from coals of middle quality; in the first three proportions from coals of good quality; and therefore the middle proportion of 100 to 270 may be taken to represent the fair average upon the great scale. On comparing the gas from bad coals, with good oil gas, the proportion may become 100 to 300. Nay, coal gas of specific gravity 0·4, compared to oil gas of 1·1, gives the proportion of 1 to 4. A mould tallow candle, of 6 in the pound, burning for an hour, is equivalent to half a cubic foot of ordinary coal gas, and to four tenths of a foot of good gas. The flame of the best argand lamp of Carcel, in which a steady supply of oil is maintained by pump-work, consuming 42 grammes = 649 grains English in an hour, and equal in light to 9·38 such candles, is equivalent to 3·75 cubic feet of coal gas per hour. The sinumbra lamp, which consumes 50 grammes = 772 grains English, of oil per hour, and gives the light of 8 of the above candles, is equivalent to the light emitted by 3·2 cubic feet of coal gas burning for an hour. A common argand lamp, equal to 4 candles, which consumes 30 grammes = 463 grains English per hour, is represented by 1·6 cubic feet of gas burning during the same time. A common lamp, with a flat wick and glass chimney, whose light is equal to 1·13 tallow candles, and which consumes 11 grammes = 169·8 grains English per hour, is represented by 0·452 of a cubic foot of gas burning for the same time.

Construction of the Burners.—The mode of burning the gas as it issues from the jets has a great influence upon the quantity and quality of its light. When carburetted hydrogen gas is transmitted through ignited porcelain tubes, it is partially decomposed with a precipitation of some of its carbon, while the resulting gas burns with a feebler flame. Coal gas, when kindled at a small orifice in a tube, undergoes a like decomposition and precipitation. Its hydrogen, with a little of its carbon, burns whenever it comes into contact with the atmospherical air, with a bluish coloured flame; but the carbonaceous part not being so accendible, takes fire only when mixed with more air; therefore at a greater distance from the beak, and with a white light from the vivid ignition of its solid particles. Upon this principle pure hydrogen gas may be made to burn with a white instead of its usual blue flame, by dusting into it particles of lamp black; or by kindling it at the extremity of a tube containing finely pulverized zinc. The metallic particles become ignited, and impart their bright light to the pale blue flame. Even platinum wire and asbestos, when placed in the flame of hydrogen gas, serve to whiten it. Hence it has been concluded, that the intensity of light which a gas is capable of affording is proportional to the quantity of solid particles which it contains, and can precipitate in the act of burning. Carbonic oxide gas burns with the feeblest light next to hydrogen, because it deposits no carbon in the act of burning. Phosphuretted hydrogen gives a brilliant light, because the phosphoric acid, into which its base is converted during the combustion, is a solid substance, capable of being ignited in the flame. Olefiant gas, as also the vapour of hydro-carbon oil, emits a more vivid light than common coal gas; for the first is composed of two measures of hydrogen and two measures of the vapour of carbon condensed into one volume; while the last contains only one measure of the vapour of carbon in the same bulk, and combined with the same proportion of hydrogen. Olefiant gas may therefore be expected to evolve a double quantity of carbon in its flame, which should emit a double light.

The illuminating power of the flame of coal gas is, on the contrary, impaired, when, by admixture with other species of gas which precipitate no carbon, its own ignited particles are diffused over a greater surface. This happens when it is mixed with hydrogen, carbonic oxide, carbonic acid, and nitrogen gases, and the diminution of the light is proportional to the dilution of the coal gas.

In like manner the illuminating power of coal gas is impaired, when it is consumed too rapidly to allow time for the separation and ignition of its carbonaceous matter; it burns, in this case, without decomposition, and with a feeble blue flame. 1. This occurs when the light-gas is previously mixed with atmospherical air, because the combustion is thereby accelerated throughout the interior of the flame, so as to prevent the due separation of carbon. A large admixture of atmospherical air makes the flame entirely blue. 2. When it issues, with considerable velocity, from a minute orifice, whereby the gas, by expansion, gets intimately mixed with a large proportion of atmospherical air. If the jet be vertical, the bottom part of the flame is blue, and the more so the less carbon is contained in the gas. The same thing may be observed in the flame of tallow, wax, or oil lights. The burning wick acts the part of a retort, in decomposing the fatty matter. From the lower part of the wick the gases and vapours of the fat issue with the greatest velocity, and are most freely mixed with the air; while the gases disengaged from the upper part of the wick compose the interior of the flame, and being momentarily protected from the action of the atmosphere, acquire the proper high temperature for the deposition of carbon, which is then diffused on the outer surface in an ignited state, and causes its characteristic white light. Hence with coal gas, the light increases in a certain ratio with the size of the flame as it issues from a larger orifice, because the intermixture of air becomes proportionately less. 3. If by any means too great a draught be given to the flame, its light becomes feebler by the rapidity and completeness with which the gas is burned, as when too tall a chimney is placed over an argand burner, see fig. 496. Fig. 497. c, is a view of the upper plate, upon which the glass chimney b rests. The gas issues through the smaller openings of the inner ring, and forms a hollow cylindrical flame, upon the outside as well as the inside of which the atmospherical air acts. The illuminating power of this flame may be diminished at pleasure, according as more or less air is allowed to enter through the orifices beneath. With a very full draught the light almost vanishes, leaving only a dull blue flame of great heating power, like that of the blowpipe, corresponding to the perfect combustion of the gas without precipitation of its carbon. 4. On the other hand, too small a draught of air is equally prejudicial; not merely because a portion of the carbon thus escapes unconsumed in smoke, but also because the highest illuminating power of the flame is obtained only when the precipitated charcoal is heated to whiteness, a circumstance which requires a considerable draught of air. Hence the flame of dense oil gas, or of oil in a wick, burns with a yellow light without a chimney; but when it is increased in intensity by a chimney draught, it burns with a brilliant white flame.

From the consideration of the preceding facts, it is possible to give to coal gas its highest illuminating power. The burners are either simple beaks perforated with a small round hole, or circles with a series of holes to form an argand flame, as shown in fig. 497, or two holes drilled obliquely, to make the flame cross, like a swallow’s tail, or with a slit constituting the sheet of flame called a bat’s wing, like most of the lamps in the streets of London. These burners are mounted with a stop-cock for regulating the quantity of gas.

The height of the flame, which with like pressure depends upon the size of the orifice, and with like orifice upon the amount of pressure, the latter being modified by the stop-cock, is for simple jets in the open air, as follows:—

Length of the flame 2 3 4 5 6 inches

Intensity of the light 55·6 100 150 197·8 247·4

Volume of gas consumed 60·5 101·4 126·3 143·7 182·2

Light with equal consumption 100 109 131 150 150

When the length exceeds five inches, nothing is gained in respect to light. For oil gas the same statements will serve, only on account of its superior richness in carbon, it does not bear so long a flame without smoke. Thus:—

Length of the flame 1 2 3 4 5 inches

Intensity of the light 22 63·7 96·5 141 178

Gas consumed 33·1 78·5 90 118 153

Light with equal consumption 100 122 159 181 174

The diameter of the orifice for single jets, or for several jets from the same beak, is one twenty-eighth of an inch for coal gas, and one forty-fifth for oil gas.

When several jets issue from the same burner, the light is improved by making all the flames unite into one. In this case the heat becomes greater, for the combined flame presents a smaller surface to be cooled, than the sum of the smaller flames. The advantage gained in this way, may be in the ratio of 3 to 2, or 50 per cent. In an argand burner, the distances of the orifices for coal gas should be from ⁄100 to ⁄100 of an inch, and for oil gas ⁄100. If the argand ring has ten orifices, the diameter of the central opening should be = ⁄10 of an inch; if 25 orifices, it should be one inch for coal gas; but for oil gas with 10 orifices, the central opening should have a diameter of half an inch, and for 20 orifices, one inch. The pin holes should be of equal size, otherwise the larger ones will cause smoke, as in an argand flame with an uneven wick. The glass chimney is not necessary to promote the combustion of an argand coal gas flame, but only to prevent it from flickering with the wind, and therefore it should be made so wide as to exercise little or no influence upon the draught. A narrow chimney is necessary merely to prevent smoke, when a very strong light, with a profusion of gas is desired. Oil gas burned in an argand beak requires a draught chimney, like a common argand lamp, on account of the large quantity of carbon to be consumed. The most suitable mode of regulating the degree of draught can be determined only by experiment, and the best construction hitherto ascertained is that represented in fig. 498. Fig. 499. exhibits the view from above, of the rim or ring c, upon which the chimney b stands, and which surrounds the perforated beak. The ring is made of open fretwork, to permit the free passage of air upwards to strike the outside of the flame. The thin annular disc d, which is laid over its fellow disc c, in the bottom of the chimney-holder, being turned a little one way or other, will allow more or less air to pass through for promoting more or less, the draught or ventilation. The draught in the central tube of the burner may be regulated by the small disc e, whose diameter is somewhat smaller than that of the ring of the burner, and which by turning the milled head f, of the screw, may be adjusted with the greatest nicety, so as to admit a greater or smaller body of air into the centre of the cylindrical flame.

In mounting gas-lights, and in estimating beforehand their illuminating effects, we must keep in mind the optical proposition, that the quantity of light is inversely as the square of the distance from the luminous body, and we must distribute the burners accordingly. When for example a gas-light placed at a distance of ten feet, is required for reading or writing to afford the same light as a candle placed at a distance of two feet; squaring each distance, we have 100 and 4; therefore 1004 = 25, shows us that 25 such lights will be necessary at the distance of 10 feet.

Concerning portable gas-light, with the means of condensing it, and carrying it from the gas works to the places where it is to be consumed, we need say nothing, as by the improvements lately made in the purification and distribution of coal-gas, the former system has been superseded.

It is well known that light gas deteriorates very considerably by keeping, especially when exposed to water over an extensive surface; but even to a certain degree over oil, or in close vessels. An oil-gas which when newly prepared has the specific gravity of 1·054, will give the light of a candle for an hour, by consuming 200 cubic inches; will, after two days, give the same light by consuming 215 cubic inches per hour; and after four days, by consuming 240 cubic inches in the like time. With coal-gas the deterioration appears to be more rapid. When newly prepared, if it affords the light of a candle with a consumption of 400 cubic inches per hour; it will not give the same light after being kept two days, except with a consumption of 430 inches; and after four days, of 460. Oil-gas three weeks old has become so much impaired in quality that 600 inches of it were required per hour to furnish the light of a candle. All light gas should be used therefore as soon as possible after it is properly purified.

Economical considerations.—The cost of gas-light depends upon so many local circumstances, that no estimate of it can be made of general application; only a few leading points may be stated. The coals required for heating the retorts used to constitute one half of the quantity required for charging the retorts themselves. When five retorts are heated by one fire, the expenditure for fuel is only one third of that when each retort has a fire. The coak which remains in the retorts constitutes about 60 per cent. of the weight of the original coal; but the volume is increased by the coaking in the proportion of 100 to 75. When the coak is used for heating the retorts, about one half of the whole is required. If we estimate the coak by its comparative heating power, it represents 65 per cent. of the coals consumed. One hundred pounds of good coal yield in distillation 10 pounds of ammoniacal liquor, from which sulphate or muriate of ammonia may be made, by saturation with sulphuric or muriatic acid, and evaporation. The liquor contains likewise some cyanide of ammonia, which may be converted into prussian blue by the addition of sulphate of iron, after saturation with muriatic acid.

Two hundred pounds of coal afford about 17 pounds of tar. This contains in 100 pounds 26 pounds of coal oil, and 48 pounds of pitch. The tar is sometimes employed as a paint to preserve wood and walls from the influence of moisture, but its disagreeable smell limits its use. The coal oil when rectified by distillation, is extensively employed for dissolving caoutchouc in making the varnish of waterproof cloth, and also for burning in a peculiar kind of lamps under the name of naphtha. Oil of turpentine however is often sold and used for this purpose, by the same name. If the coal oil be mixed with its volume of water, and the mixture be made to boil in a kettle, the mingled vapours when passed through a perforated nozzle may be kindled, and employed as a powerful means of artificial heat. The water is not decomposed, but it serves by its vapour to expand the bulk of the volatile oil, and to make it thereby come into contact with a larger volume of atmospherical air, so as to burn without smoke, under a boiler or any other vessel. The pitch may be decomposed into a light-gas.

The relative cost of light from coal gas and oil gas may be estimated as one to six, at least. Rosin gas is cheaper than oil gas. See Rosin.

I shall conclude this article with a summary of the comparative expense of different modes of illumination, and some statistical tables.

One pound of tallow will last 40 hours in six mould candles burned in succession, and costs 8d.; a gallon of oil, capable of affording the light of 15 candles, for 40 hours costs 5s., being therefore ⁄2 of the price of mould candles, and ⁄15 of the price of dips. The cost of wax is about 3⁄2 times that of tallow; and coal gas, as sold at the rate of 9s. for 1000 cubic feet, will be one sixth the price of mould candles; for 500 cubic inches of coal gas give a light equal to the above candle for an hour; therefore 40 × 500 = 20,000 cubic inches = 11·57 cubic feet, worth 1⁄4d., which multiplied by 6 gives 7⁄2d. the average price of mould candles per pound.

The author of the article Gas-light in the Encyclopædia Britannica, observes, in reference to the economy of this mode of illumination, that while the price of coal, in consequence of the abundant and regular supply of that article, is liable to little fluctuation, the cost of wax, tallow, and oil, on account of the more precarious nature of the sources from which they are obtained, varies exceedingly in different seasons. “Assuming that a pound of tallow candles, which last when burned in succession forty hours, costs nine-pence,” (seven-pence halfpenny is the average price), “that a gallon of oil, yielding the light of 600 candles for an hour, costs two shillings,” (five shillings is the lowest price of a gallon of such oil as a gentleman would choose to burn in his lamp), “that the expense of the light from wax is three times as great as from tallow, and that a thousand cubic feet of coal gas cost nine shillings;” he concludes the relative cost to be for the same quantity of light,—from wax, 100; tallow, 25; oil, 5; and coal-gas, 3. I conceive the estimate given above to be much nearer the truth; when referred to wax called 100, it becomes, for tallow, 28·6; oil, 14·3; coal gas, 4·76.

Gas-lighting has received a marvellous development in London. In the year 1834, the number of gas lamps in this city was 168,000, which consumed daily about 4,200,000 cubic feet of gas. For the purpose of generating this gas, more than 200,000 chaldrons, or 10,800,000 cubic feet of coals were required.

For the following valuable statistical details upon gas-light, my readers are indebted to Joseph Hedley, Esq., engineer, of the Alliance Gas Works, Dublin; a gentleman who to a sound knowledge of chemistry, joins such mechanical talent and indefatigable diligence, as qualify him to conduct with success, any great undertaking committed to his care. He has long endeavoured to induce the directors of the London gas-works to employ a better coal, and generate a more richly carburetted gas, which in much smaller quantity would give as brilliant a light, without heating the apartments unpleasantly, as their highly hydrogenated gas now does. Were his judicious views adopted, coal gas would soon supersede oil, and even wax candles, for illuminating private mansions.

Copy of a paper laid before a Committee of the House of Commons, showing not only the relative values of the Gases produced at the undermentioned places, but showing in like manner the relative economy of Gas as produced at the different places, over candles. By Joseph Hedley, Esq.

Names of the Places
where Experiments
were made. Illuminating
power of a
single Jet of
Gas-flame
four inches
high, taken
by a
comparison
of Shadows. The Jet of
Gas burnt,
four inches
high,
consumed
per hour
and was
equal to the
Candles
in the last
column. Gas required
to be equal
to 100 lbs.
of mould
Candles,
6 to the lb.,
9 inches
long each.
Selling
price
of Gas
per meter
per 1000
cubic feet. Cost of
Gas equal
in illumi-
nating
power to
100 lbs. of
candles. Average
discount
allowed
off the
charge
for Gas. Net cost of
Gas equal
to 100 lbs.
of Candles. Specific
gravity
of the
Gas.

Equal to
Candles. Cubic
Feet. Cubic
Feet. s. d. L. s. d. Per
Cent. L. s. d.

Birmingham; - 2·572 1 ·22 2704 10 0 1 7 0 9 1 4 7 ·541

Birmingham and
Staffordshire;
two Companies

Stockport 3·254 ·85 1489 10 0 0 14 11 12 ⁄2 0 13 0 ·539

Manchester 3·060 ·825 1536 8 0 0 12 3 11 ⁄4 0 10 10 ·534

Liverpool Old
Company 2·369 1 ·1 2646 10 0 1 6 5 6 ⁄4 1 4 9 ·462

Liverpool New
Gas Company 4·408 ·9 1164 10 0 0 11 8 6 ⁄4 0 9 10 ·580

Bradford 2·190 1 ·2 3123 9 0 1 8 1 12 ⁄2 1 4 6 ·420

Leeds 2·970 ·855 1644 8 0 0 13 2 6 ⁄4 0 12 4 ·530

Sheffield 2·434 1 ·04 2440 8 0 0 19 6 6 ⁄4 0 18 3 ·466

Leicester 2·435 1 ·1 2575 7 6 0 19 3 15 0 16 5 ·528

Nottingham 1·645 1 ·3 4200 9 0 1 17 9 15 1 11 3 ·424

Derby 1·937 1 ·2 3521 10 0 1 15 4 15 1 10 0 ·448

Preston 2·136 1 ·15 3069 10 0 1 10 8 15 1 6 2 ·419

London 2·083 1 ·13 3092 10 0 1 10 11 none
allowed. 1 10 11 ·412

100 lbs. of candles are estimated to burn 5700 hours.

The candles cost 3l. 2s. 6d.

The Liverpool Old Company have since resorted to the use of Cannel coal, and consequently very nearly assimilate to the Liverpool New Company in illuminating power.

Names of the Places
where Experiments
were made. Illuminating
power of a
single Jet of
Gas-flame
four inches
high, taken
by a
comparison
of Shadows. The Jet of
Gas burnt,
four inches
high,
consumed
per hour
and was
equal to the
Candles
in the last
column. Gas required
to be equal
to 100 lbs.
of mould
Candles,
6 to the lb.,
9 inches
long each.
Selling
price
of Gas
per meter
per 1000
cubic feet.

Equal to
Candles. Cubic
Feet. Cubic
Feet. s. d.

Birmingham; - 2·572 1 ·22 2704 10 0

Birmingham and
Staffordshire;
two Companies

Stockport 3·254 ·85 1489 10 0

Manchester 3·060 ·825 1536 8 0

Liverpool Old
Company 2·369 1 ·1 2646 10 0

Liverpool New
Gas Company 4·408 ·9 1164 10 0

Bradford 2·190 1 ·2 3123 9 0

Leeds 2·970 ·855 1644 8 0

Sheffield 2·434 1 ·04 2440 8 0

Leicester 2·435 1 ·1 2575 7 6

Nottingham 1·645 1 ·3 4200 9 0

Derby 1·937 1 ·2 3521 10 0

Preston 2·136 1 ·15 3069 10 0

London 2·083 1 ·13 3092 10 0

100 lbs. of candles are estimated to burn 5700 hours.

The Liverpool Old Company have since resorted to the use of Cannel coal, and consequently very nearly assimilate to the Liverpool New Company in illuminating power.

Names of the Places
where Experiments
were made. Cost of
Gas equal
in illumi-
nating
power to
100 lbs. of
candles. Average
discount
allowed
off the
charge
for Gas. Net cost of
Gas equal
to 100 lbs.
of Candles. Specific
gravity
of the
Gas.

L. s. d. Per
Cent. L. s. d.

Birmingham; - 1 7 0 9 1 4 7 ·541

Birmingham and
Staffordshire;
two Companies

Stockport 0 14 11 12 ⁄2 0 13 0 ·539

Manchester 0 12 3 11 ⁄4 0 10 10 ·534

Liverpool Old
Company 1 6 5 6 ⁄4 1 4 9 ·462

Liverpool New
Gas Company 0 11 8 6 ⁄4 0 9 10 ·580

Bradford 1 8 1 12 ⁄2 1 4 6 ·420

Leeds 0 13 2 6 ⁄4 0 12 4 ·530

Sheffield 0 19 6 6 ⁄4 0 18 3 ·466

Leicester 0 19 3 15 0 16 5 ·528

Nottingham 1 17 9 15 1 11 3 ·424

Derby 1 15 4 15 1 10 0 ·448

Preston 1 10 8 15 1 6 2 ·419

London 1 10 11 none
allowed. 1 10 11 ·412

The candles cost 3l. 2s. 6d.

The Liverpool Old Company have since resorted to the use of Cannel coal, and consequently very nearly assimilate to the Liverpool New Company in illuminating power.

Memorandum.—It will not fail to be observed that in deducing the comparative value between candles and gas by these experiments, the single jet (and in every instance, of course, it was the same), has been the medium. This however, though decidedly the most correct way of making the comparative estimate of the illuminating power of the several gases, is highly disadvantageous in the economical comparison, inasmuch as gas burnt in a properly regulated argand burner, with its proper sized glass, air aperture, and sufficient number of holes, gives an advantage in favour of gas consumed in an argand, over a jet burner, of from 30 to 40 per cent. At the same time it must not be overlooked that in many situations where great light is not required, it will be found far more economical to adopt the use of single jets, which by means of swing brackets and light elegant shades, becomes splendid substitutes for candles, in banking establishments, offices, libraries, &c. &c.

Note.—In Glasgow, Edinburgh, Dundee, Perth, and the Scotch towns generally the Parrot or Scotch Cannel coal is used; in illuminating power and specific gravity the gas produced is equal to that from the best description of Cannel coal in England. The price per 1000 cubic feet ranges about 9s., with from 5 to 30 per cent. off for discounts, leaving the net price about 9s. to be equal in the above table to 100 lbs. of candles.

Epitome of Experiments made in Gas produced from different qualities of Coal, and consumed in different kinds of Burners:

Tried at the Sheffield Gas Light Company’s Works, and laid before a Committee of the House of Commons. By Joseph Hedley, Esq.

Date
1835. Description
of Burner. Species of
Coal. Specific
Gravity
of Gas. Distance
of Candle
from
Shadow. Gas
consumed
per Hour. Height
of Gas
Flame. Equal to
Mould Tallow
Candles, 6 to
the pound,
9 inches
long each. Gas equal
to 100 lbs.
of Mould
Candles. Cost of Gas
at 8s. per
1000 cubic feet. Cost of 100
lbs. of Mould
Candles at 7s.
6d. per dozen
lbs.

May. Inches. Cubic
Feet. Inches. Candles. Cubic
Feet. L. s. d. L. s. d.

8 Single Jet Deep Pit ·410 75 1 · 4 2 ·36 2415 0 19 3 ⁄2 - 3 2 6

9 Ditto Mortormley ·450 74 ·95 4 2 ·434 2224 0 17 9 ⁄2

9 Ditto Cannel ·660 61 ⁄4 ·7 4 3 ·54 1127 0 9 0

8 - Argand
14 holes - Deep Pit ·410 34 3 ·3 3 ⁄2 11 ·53 1631 0 13 0 ⁄2

9 Ditto Mortormley ·450 33 3 ·1 3 ⁄2 12 ·24 1443 0 11 6 ⁄2

9 Ditto Cannel ·660 29 2 ·6 3 ⁄3 15 ·85 935 0 7 5 ⁄4

Date
1835. Description
of Burner. Species of
Coal. Specific
Gravity
of Gas. Distance
of Candle
from
Shadow. Gas
consumed
per Hour. Height
of Gas
Flame.

May. Inches. Cubic
Feet. Inches.

8 Single Jet Deep Pit ·410 75 1 · 4

9 Ditto Mortormley ·450 74 ·95 4

9 Ditto Cannel ·660 61 ⁄4 ·7 4

8 - Argand
14 holes - Deep Pit ·410 34 3 ·3 3 ⁄2

9 Ditto Mortormley ·450 33 3 ·1 3 ⁄2

9 Ditto Cannel ·660 29 2 ·6 3 ⁄3

Date
1835. Description
of Burner. Species of
Coal. Equal to
Mould Tallow
Candles, 6 to
the pound,
9 inches
long each. Gas equal
to 100 lbs.
of Mould
Candles. Cost of Gas
at 8s. per
1000 cubic feet. Cost of 100
lbs. of Mould
Candles at 7s.
6d. per dozen
lbs.

May. Candles. Cubic
Feet. L. s. d. L. s. d.

8 Single Jet Deep Pit 2 ·36 2415 0 19 3 ⁄2 - 3 2 6

9 Ditto Mortormley 2 ·434 2224 0 17 9 ⁄2

9 Ditto Cannel 3 ·54 1127 0 9 0

8 - Argand
14 holes - Deep Pit 11 ·53 1631 0 13 0 ⁄2

9 Ditto Mortormley 12 ·24 1443 0 11 6 ⁄2

9 Ditto Cannel 15 ·85 935 0 7 5 ⁄4

Copy of Experiments made at the Alliance Gas Company’s Works in Dublin, during the past year 1837. By Joseph Hedley, Esq.

Results of experiments on the qualities of various coals for the production of gas; its value in illuminating power; produce of coke, and quality; and other particulars important in gas-making:—

1st Experiment, Saturday, May 27th, 1837.—Deane coal, (Cumberland). 2 cwt. of 112 lbs. each (or 224 lbs.) produced 970 cubic feet of gas; 4 bushels of coke of middling quality; specific gravity of the gas, 475. Consumed in a single-jet burner, flame 4 inches high, 1⁄10ths cubic feet per hour; distance from shadow 76 inches or 2·3 mould candles. Average quantity of gas made from the charge (6 hours) 4·33 cubic feet per lb., or 9,700 cubic feet per ton of 20 cwt. Increase of coke over coal in measure, not quite 30 per cent. Loss in weight between coal, coke and breize 56 lbs., converted into gas, tar, ammonia, &c.

2nd Experiment, May 28th.—Carlisle coal, (Blenkinsopp). 224 lbs. produced 1010 cubic feet of gas, 4 bushels of coke of good quality though small; increase of coke over coal in measure not quite 30 per cent. Loss in weight, same as foregoing experiment. Average quantity of gas made from the charge (6 hours) 4·5 cubic feet per lb. or 10,080 per ton.

Illuminating power of the Gas.

Consumed
per hour,
single jet. Distance
from
candle. Equal
to
candles. Specific
gravity.

feet. inches.

At the end of the 1st hour 1 ⁄10 70 2 ·72 ·475

Dittodittowith 20-hole
argand burner - 5 25 21 ·33 ·475

When charge nearly off 1 ⁄10 85 1 ·84 ·442

When charge quite off, with
20-hole argand burner - 9 100 not 1 ·256

3rd Experiment, May 29th.—Carlisle coal (Blenkinsopp). 112 lbs. produced 556 cubic feet of gas. Other products, loss of weight, &c., same proportion as foregoing experiment. Average quantity of gas made from the charge (6 hours) 4·96 cubic feet per lb., or 11,120 per ton.

In this experiment the quantity of gas generated every hour was ascertained; the illuminating power, the specific gravity, and the quantity of gas consumed by the single jet with a flame 4 inches high, was tried at the end of each hour, with the respective gases generated at each hour; and the following is a table of results.

RESULTS.

Hour. Gas
produced. Consumed
per hour
per single jet,
4 inches high. Specific
gravity. Distance
of candle
from
shadow. Illuminating
power
equal to
mould candles.

cubic
feet. cubic
feet. inches.

1st. 150 - 11⁄2-10ths.
or 1·15 - ·534 70 2·72

2nd. 120 11 ·495 75 2·36

3rd. 95 12 ·344 75 2·36

4th. 95 15 ·311 80 2·08

5th. 80 17 ·270 85 1·81

6th. 16 29 ·200 100 not one

Total 556 or 92⁄3 or 2 feet 9 inches.

Average of the above gas, 6-hour charge.

92⁄3 16-10ths. nearly ·359 81 2·03

Average of the above gas at 4-hour charge.

115 12⁄3-10ths. ·421 75 2·36

Production of gas in 6 hours 556 feet, or at the rate of 11,120 cubic feet per ton.
Produc Dittof gas in 4 hours 460 feet, or at the rate of 19,200cubic ditto.

The relative value of these productions of gas is as follows, viz.:

11,120 at 16-10ths per hour nearly, (or 1·5916 accurately) and equal to 203 candles; the 11,120 feet would be equal to and last as long as 1597 candles, or 266⁄6 lbs. of candles.

9200 at 12⁄3-10ths. per hour, (or 1·2375 accurately,) and equal to 236 candles; the 9200 feet would be equal to 1949 candles, or 324⁄6 lbs. candles.

Now 266⁄6 lbs. of mould candles, at 7s. 6d. per dozen lbs. will cost 18l. 6s. 4⁄2d., whilst
Now 324⁄6 lbs. of mdo.d cado.es,at 7s. 6d. perdozedo.bs. wdo.ost 10l. 3s.

Shewing the value of 4-hour charges, over 6-hour charges; and of 9,200 cubic feet over 11,120 cubic feet.

Note.—9500 cubic feet of Wigan cannel coal gas are equal in illuminating power to 859 1-6th lbs. of candles, which at 7s. 6d. per dozen lbs. will cost 25l. 10s. 5⁄2d. It is also found that any burner with superior gas, will consume only about half the quantity it would do with common gas.

4th Experiment, May 30th.—Cannel and Cardiff coal mixed ⁄2 and ⁄2, together 112 lbs., produced 460 feet of gas; 2 bushels of coke of good quality; increase of coke over coal in measure about 30 per cent.; loss in weight, 41 lbs.; coke weighed 71 lbs., no breize. Average quantity of gas made from the charge, (4 hours) 4·1 cubic feet, per lb., or 9·200, per ton.

Illuminating power.—At end of first hour.

Candles. Cubic feet.

Distance of candle from
shadow - 73 or 2·49 - Consumed per hour, single
jet, 4 inches high - 12-10ths

At end of 2nd hour, do. 70 or 2·72 Do.umeddo.er hodo. 11⁄2-10ths

At end of 3d hour. This gas very indifferent.

Average of the three 70 or 2·72 Do.umeddo.er hodo. 11⁄2-10ths

Specific gravity 3·44; 5 feet per hour, with a 20-hole argand burner, equal to 14·66 candles.

5th Experiment, May 31st.—Carlisle coal, 112 lbs. produced 410 feet of gas; other products, same as in former experiments with this coal, but heat very low.

Illuminating power and produce of gas.

410 ft - 1st hour 120 cubic feet - Average of this gas: specific gravity, 540; distance of candle from shadow, 55 inches, or 4·4 candles consumed per single jet, 9-10ths of a cubic foot per hour. 20-hole argand burner, 4 feet per hour, equal to 21·33 candles.

2nd 100

3d 90

4th 100

It is possible, from the superior quality of this gas, that a little of the cannel gas made for a particular purpose, may have have got intermixed with it in the experimental gasholder and apparatus.

A variety of other experiments were tried on different qualities of coal, and mixtures of ditto, too tedious to insert here, though extremely valuable, and all tending to shew the superior value of gas produced at short over long charges; and also showing the importance and value of coal producing gas of the highest illuminating power; among which the cannel coal procured in Lancashire, Yorkshire, and some other counties of England and Wales, and the Parrot or splent coal of Scotland, stand pre-eminent.

Note.—In all the foregoing experiments the same single-jet burner was used; its flame in all instances exactly 4 inches high.

The coal when drawn from the retort was slaked with water, and after allowing some short time for drying, was weighed.

A Table of the number of hours Gas is burnt in each month, quarter and year.

Time of Burning. July. Aug. Sep. Oct. Nov. Dec. Jan. Feb. Mar. Apl. May. June. Mid.
quar. Mic.
quar. Xms.
quar. Lady
day
quar. Totl.
of
Year.

o’clock.

From Dusk: to 6 — — 2 31 62 80 65 33 4 — — — — 2 173 102 277 For
Sun-
days
off,
de-
duct
one
sev-
enth.

— 7 — 14 22 62 92 111 96 61 31 4 — — 4 36 265 188 493

— 8 — 40 52 93 122 142 127 89 62 28 4 — 32 92 357 278 759

— 9 13 71 82 124 152 173 158 117 93 58 29 8 95 166 449 368 1078

— 10 44 102 112 155 182 204 189 145 124 88 60 38 186 258 541 458 1443

— 11 75 133 142 186 212 235 220 173 155 118 91 68 277 350 633 548 1808

— 12 106 164 172 217 242 266 251 201 186 148 122 98 368 442 725 638 2173

All night - 217 307 345 421 473 527 512 411 382 295 242 195 732 869 1421 1305 4327

Morning from 4 — 16 48 80 110 137 137 98 71 28 2 — 30 64 327 306 727

— 5 — — 18 49 80 106 106 70 40 3 — — 3 18 235 216 472

— 6 — — — 18 50 75 75 42 9 — — — — — 143 126 269

— 7 — — — — 20 44 44 14 — — — — — — 64 58 122

Time of Burning. July. Aug. Sep. Oct. Nov. Dec.

o’clock.

From Dusk: to 6 — — 2 31 62 80 For
Sun-
days
off,
de-
duct
one
sev-
enth.

— 7 — 14 22 62 92 111

— 8 — 40 52 93 122 142

— 9 13 71 82 124 152 173

— 10 44 102 112 155 182 204

— 11 75 133 142 186 212 235

— 12 106 164 172 217 242 266

All night - 217 307 345 421 473 527

Morning from 4 — 16 48 80 110 137

— 5 — — 18 49 80 106

— 6 — — — 18 50 75

— 7 — — — — 20 44

Time of Burning. Jan. Feb. Mar. Apl. May. June.

o’clock.

From Dusk: to 6 65 33 4 — — — For
Sun-
days
off,
de-
duct
one
sev-
enth.

— 7 96 61 31 4 — —

— 8 127 89 62 28 4 —

— 9 158 117 93 58 29 8

— 10 189 145 124 88 60 38

— 11 220 173 155 118 91 68

— 12 251 201 186 148 122 98

All night - 512 411 382 295 242 195

Morning from 4 137 98 71 28 2 —

— 5 106 70 40 3 — —

— 6 75 42 9 — — —

— 7 44 14 — — — —

Time of Burning. Mid.
quar. Mic.
quar. Xms.
quar. Lady
day
quar. Totl.
of
Year.

o’clock.

From Dusk: to 6 — 2 173 102 277 For
Sun-
days
off,
de-
duct
one
sev-
enth.

— 7 4 36 265 188 493

— 8 32 92 357 278 759

— 9 95 166 449 368 1078

— 10 186 258 541 458 1443

— 11 277 350 633 548 1808

— 12 368 442 725 638 2173

All night - 732 869 1421 1305 4327

Morning from 4 30 64 327 306 727

— 5 3 18 235 216 472

— 6 — — 143 126 269

— 7 — — 64 58 122

Copy of a Paper submitted to a Committee of the House of Commons in the Session of 1837, being a Synopsis of the proceedings of the undermentioned principal Gas-Light Establishments of England; and procured by actual Survey and Experiments between the Years 1834 and 1837. By Joseph Hedley, Esq.

Name of the Place where Gas Works are situated. Price of Gas per Meter, and Discounts allowed. Price of Coal, and Description; delivered per Ton. Average Quantity of Gas made per Ton of Coals. Coke made from a Ton of Coal. Selling Price of Coke. Material used to heat Retorts. Quantity used per Ton of Coal. No. of Public or Street Lamps supplied. Description.
—
Size or Sort. Price paid per Annum for Ditto. Who lights, cleans, puts out, and repairs. No. of Hours, or Time burnt in the Year. Gas consumed in each Lamp per Hour. Rate per Meter Cubic Feet received for Ditto. Amount deducted for cleaning, lighting, extinguishing, providing Lamp Posts; &c. Per Centage of Loss of Gas made. Greatest Quantity of Gas delivered in One Night. Duration of Charges. Method of Purification. Number of Gas Holders. Specific Gravity of the Gas. Distance of Candle from Shadow. Gas equal to Candles. Gas burnt in a single Jet Four Inches high. Gas consumed per Hour with a Four-Inch Flame. Gas Flame reduced to Candle burnt per Hour. Height of Gas Flame equal to Light from Candle.

Cu. ft. L. s. d. s. d. s. d. Cubic Feet. Inch. Candles Cu. ft. Cu. ft. Inch.

Birmingham Gas Company.

10s. per meter cub. feet.

Discounts

10l. to 30l. per
an. 2 ⁄2 per
cent.

30l. to 50l. 5

50l. to 75l. 7 ⁄2

75l. to 100l. 10

100l. & upwards 15

Lump coal from West Bromwich pits risen much of late. 1837, 11s. 10d. 6,500 32 bushels. 2s. 1d. per quarter delivered, or about 3d. per bushel. Slack. About 5 cwt. of slack, at 6s. per ton, 25 per cent. 490 Batswings, 460 30 1
2 10
0 0
0 Company, and provides posts, services, &c. 226 nights, or 2938 hours, 9 months, omitting 5 nights for moons. 5 feet per hour. 30
40 10
18 18 0 Receives net about 6s. 8d. per meter cubic feet. 48 millions in the year. 6 hours. Dry lime. 4, and 2 in the town, and large new gas station. ·453 72 1,929 1 ·22 ·8 2 ⁄2

Birmingham and Staffordshire. 10s. per meter cub. feet. Discounts as above. From West Bromwich pits, 1837, 9s. 3d. 6,500 24 bush. but larger measure than Birmingham. 2s. 10d. per sack of 8 bushels. Slack and Tar. 5 cwt. of slack, at 4s. 25 per cent. 1,500 Batswings. average Ditto. 234 nights, or 3042 hours. Ditto. 1 3 ⁄2 18 0 Receives net about 5s. 6d. per meter cubic feet. 85 millions in the year. Ditto. Ditto. 6, and 6 in the town 7 miles off. ·455 72 1,929 1 ·22 ·8 2 ⁄2

1 18 0

Macclesfield.

10s. per meter cub. feet.

Discounts

A-
bove 50l. and
not
ex-
ceed-
ing 75l. 5 per
cent.

75l. 100l. 7 ⁄2

100l. 125l. 10

125l. 150l. 12 ⁄2

150l. 175l. 15

175l. 200l. 17 ⁄2

200l. & upwards 20 .

Common, 8s. average 1831 6,720 12 cwt. 10s. per ton. Coke. No account kept. 220 Ditto. 2 10 0 Company. 8 months, omitting 5 nights for moons. 4 feet per hour. 3 0 12 0 Could not say. 80,000. Total for year about 15 millions. 8 hours. Ditto. 3 gas holders. Not taken. 70 204 Not taken. ·8 2 ⁄4

Stockport. 10s. per meter cub. feet. Discounts same as Macclesfield. Macclesfield discounts taken from Stockport card. Coal 10s. 6d. cannel 19s. 6d. about half and half used. Average 15s. 1834. 7,800 7 cwt. 6s. 8d. per ton. Coal, coke, and tar. Ditto. 230 Ditto. 2 10 0 Comrs. provide lamps and posts. Company's service light, repair, clean, and extinguish. 8 months. 4 nights omitted for moons. 237 nights—2800 hours. Ditto. 2 6 12 6 Ditto. 65,000. Total for year about 12 millions. Ditto. Ditto. 4 gas holders. ·539 64 2,441 ·85 ·55 2 ⁄8

1834.

2 0 0

1837.

Manchester.

10s. per m. cub. ft. 1834.

9s. and 8s. cu—ft. 1837.

Discounts

50l. and
un-
der 100l. 2 ⁄2 per
cent.

100l. 150l. 5

150l. 200l. 7 ⁄2

200l. 225l. 10

225l. 250l. 12 ⁄2

250l. 300l. 15

300l. 400l. 17 ⁄2

400l. and upwards 20

15s. 2d. average.

Oldham - cannel.

Watergate

Wigan

Mixed, 1834.

9,500 14 cwt. Ditto. Coke. 4, 2-3ds cwt. 2,375 Single-jets and flat flames, about half and half. 1
2 2
0 0
0 Commissioners of police. 3390 hours. 1 foot, 2 feet, per hour. 6
5 6
6 nothing. About 15 to 17⁄2 per cent. receive about 7s. 4d. per meter cubic feet, public and private. Nearly all by meter. 500,000. Total for year 100 millions. 6 hours. Wet lime. 10 gas holders, and 2 in the town. ·534 66 2,295 ·825 ·475 2 ⁄4

Liverpool Old Company, 1834.

10s. per meter cub. feet.

Discounts

10l. & under 50l. 2 ⁄2 per
ct.

50l. to 100l. 5

100l. to 200l. 7 ⁄2

300l. & upwards 10

7s. 3d. per ton of 112 lbs. per cwt. Ormskirk or Wigan slack. 8,200 11⁄4 cwt. 8s. 4d. per ton of 112 lb. per cwt. Slack 7s. 3d. per ton. 6⁄2 cwt. 1,700
30 Batswings,
1 jet,
2 —
3 —
4 — 4
2
2
2
3 10
5
13
2
13 0
0
0
9
11 Company light, clean, put out, and repair. 3600 hours. 5 feet per hour. 4 4 12 0 Could not learn in the absence of the manager. 360,000. Total for year 72 millions. 8 hours, large, retorts holding 6 cwt. each. Wet and dry lime, principally dry. 8 gas holders in all, 4 in the town, 1000 yards off the works. ·462 75 1,777 1 ·1 ·75 2 ⁄8

Ditto ditto. In 1835 this Company resorted to the use of cannel coal similar to the Liverpool New Gas and Coal Company, producing nearly similar results, which see.

Liverpool New Gas and Coke, 1835. 10s. per meter cub. feet. Discounts same as Liverpool Old Company. 18s. all cannel Wigan. 9,500 13 cwt. 7s. 6d. per ton. Coke and slack. 5⁄2 cwt. Only a few. Argands. 4 0 0 Commissioners. 3000 hours. 3⁄2 feet per hour. 5 6 nothing Nearly all by meter. Not sufficiently long at work. 4 hours. Wet lime. 2 large gas holders. ·580 55 3,306 ·9 ·45 2

Bradford, 1834.

9s. per meter cubic feet to large consumers.

Discounts

20l. to 30l. 5 per
cent.

30l. to 40l. 7 ⁄2

40l. to 60l. 10

60l. to 80l. 12 ⁄2

80l. to 100l. 15

100l. & upwards 20

Small consumers, 10s. per meter cub. feet, and 5 per cent. off from 10l. to 20l.

8s. 6d. per ton. 3 sorts used average. Slack 5s. 6d. Low moor 8s. 10d. Catherine slack 8s. 8,000 13 cwt. 12s. per ton. Coke. 8⁄2 cwt. 220 Batswings. 2 12 6 Company light, repair, &c. 8 months, omitting 7 nights, 2600 hours to 4 o’clock in the morning. 5 feet per hour. 3 1 12 6 Receive 8s. per meter cubic feet, less 5⁄2 per cent. 42,500. Total for year 8,619,000. 8 hours. Dry lime. 4 gas holders. ·420 78 1,643 ·12 ·9 3

Leeds, 1834.

8s. per meter cubic feet.

Discounts

2 ⁄2 - per cent.
on half-
yearly
payments - 15l.

5 30l.

7 ⁄2 50l.

10 100l.

8s. per ton average. 2-3ds common 7s. 1-3d cannel, 10s. 6,500 12 cwt. 7s. 6d. per ton. Ditto. 5⁄4 cwt. 517 Ditto. 2 12 6 Commissioners, except extinguishing, for which Company pay 3s. 10d. per lamp. 2330 hours. 4 feet per hour. 5 2 3 10 Receive for public and private 6s. 8d. per meter cubic feet. Public 5s., private 7s. ; meters used to 5 to 1 for private rental. 176,000. Total for year 31 millions. 6 hours. Ditto. 5 gas holders. ·530 67 2,228 ·855 ·51 2 ⁄4

Sheffield, 1835. 8s. per meter cubic feet. Discounts same as Leeds. 7s. 9d. per ton average. 3 sorts used 1, 2-10ths. cannel, at 16s. 8, 2-10ths. deep pit, 7s. 1-10th silk stone, 10s. 8,000 10 cwt. of saleable coke. 10s. per ton. Ditto. 3⁄2 cwt. 600 Ditto. 2 10 0 Company provide lamps, clean, repair, put out, &c. 2200 hours. Ditto. 3 2 ⁄2 18 0 Receive for public and private lts. 5s. per meter cubic feet. Public 3s. 2⁄2d., private 5s. 9⁄2d. Few meters used. 220,000. Total for year 40 millions. Ditto. Ditto. 4 gas holders, and 2 more erecting. ·466 74 1,826 1 ·04 ·735 2 ⁄4

Leicester, 1837.

7s. 6d. per meter cub. ft.

Discounts on half-yearly rental not
exceeding 10l., 5 per cent.

A-
bove 10l. and
not
ex-
ceed-
ing 20l. 7 ⁄2 per
cent.

20l. 30l. 10

30l. 40l. 12 ⁄2

40l. 50l. 15

50l. 60l. 20

60l. & upwards 25

13s. 6d. average. Derbyshire soft coal. 7,500 4 quarters. 10s. 8d. or 2s. 8d. per qr. Coke, tar, &c. About 1-3d of coke. 414 Ditto. 2 18 6 Company light, put out, and clean. From August 14th to September 1st, omitting 3 nights for moons, 3000 hours. 5 feet per hour. 3 4 ⁄4 7 0 Not sufficiently long, at 7s. 6d. Total for year 18 millions. Ditto. Ditto. 3 gas holders, and 1 erecting. ·528 74 1,826 1 ·1 ·75 2 ⁄4

Derby, 1834. 10s. per meter cub. feet. Same coal used as at Leicester. 7,000 Ditto. Ditto. Coke. Ditto. 219 Ditto. 2 2 0 Commissioners light, put out, &c. 2173 hours, from August to May. Ditto. 4 0 — Lose about 17⁄2 per cent. Ditto. Ditto. Wet lime. 4 gas holders. ·448 83 1,453 1 ·2 ·925 3

Discounts 5 to 35 per cent. 2 7 0 nearly.

Nottingham, 1834. 9s. per meter cubic feet. Discounts as above. Ditto. 7,000 Ditto. Ditto. Ditto. Ditto. 300 Ditto. 3 3 0 Commissioners light, clean, repair, &c. All the year, 4327 hours. Ditto. 3 0 — Could not learn. Ditto. Ditto. Ditto. — ·424 90 1,234 1 ·3 1 ·175 3

nearly.

London, 1834. 10s. per meter cub. feet. No discounts. 17s. average. Newcastle. 8,500 36 bush. 12s. per chaldron. Ditto. 13 bush. 26,280 Ditto. 4 0 0 Company light, clean, put out, but not repair. 4327 hours, all the year. 4 feet per hour. 4 0 12 0 Receive for public and private lights 7s. public, 4s. private, 8s. few meters used. Total for year 1000 millions. Longest night 4,910,000. Ditto. Ditto. 130 gas holders. ·412 80 1,562 1 ·13 ·84 2 ⁄4

Ditto, 1837. Ditto. Ditto. 8,500 Ditto. Ditto. Ditto. Ditto. 30,400 Ditto. 4 0 0 Ditto. Ditto. Ditto. 4 0 12 0 Ditto. Total for year 1460 millions. Longest night 7,120,000. Ditto. Ditto. 176 gas holders. ·412 80 1,562 1 ·13 ·84 2 ⁄4

Name of the Place where Gas Works are situated. Price of Gas per Meter, and Discounts allowed. Price of Coal, and Description; delivered per Ton. Average Quantity of Gas made per Ton of Coals. Coke made from a Ton of Coal.

Cu. ft.

Birmingham Gas Company.

10s. per meter cub. feet.

Discounts

10l. to 30l. per
an. 2 ⁄2 per
cent.

30l. to 50l. 5

50l. to 75l. 7 ⁄2

75l. to 100l. 10

100l. & upwards 15

Lump coal from West Bromwich pits risen much of late. 1837, 11s. 10d. 6,500 32 bushels.

Birmingham and Staffordshire. 10s. per meter cub. feet. Discounts as above. From West Bromwich pits, 1837, 9s. 3d. 6,500 24 bush. but larger measure than Birmingham.

Macclesfield.

10s. per meter cub. feet.

Discounts

A-
bove 50l. and
not
ex-
ceed-
ing 75l. 5 per
cent.

75l. 100l. 7 ⁄2

100l. 125l. 10

125l. 150l. 12 ⁄2

150l. 175l. 15

175l. 200l. 17 ⁄2

200l. & upwards 20 .

Common, 8s. average 1831 6,720 12 cwt.

Stockport. 10s. per meter cub. feet. Discounts same as Macclesfield. Macclesfield discounts taken from Stockport card. Coal 10s. 6d. cannel 19s. 6d. about half and half used. Average 15s. 1834. 7,800 7 cwt.

Manchester.

10s. per m. cub. ft. 1834.

9s. and 8s. cu—ft. 1837.

Discounts

50l. and
un-
der 100l. 2 ⁄2 per
cent.

100l. 150l. 5

150l. 200l. 7 ⁄2

200l. 225l. 10

225l. 250l. 12 ⁄2

250l. 300l. 15

300l. 400l. 17 ⁄2

400l. and upwards 20

15s. 2d. average.

Oldham - cannel.

Watergate

Wigan

Mixed, 1834.

9,500 14 cwt.

Liverpool Old Company, 1834.

10s. per meter cub. feet.

Discounts

10l. & under 50l. 2 ⁄2 per
ct.

50l. to 100l. 5

100l. to 200l. 7 ⁄2

300l. & upwards 10

7s. 3d. per ton of 112 lbs. per cwt. Ormskirk or Wigan slack. 8,200 11⁄4 cwt.

Ditto ditto. In 1835 this Company resorted to the use of cannel coal similar to the Liverpool New Gas and Coal Company, producing nearly similar results, which see.

Liverpool New Gas and Coke, 1835. 10s. per meter cub. feet. Discounts same as Liverpool Old Company. 18s. all cannel Wigan. 9,500 13 cwt.

Bradford, 1834.

9s. per meter cubic feet to large consumers.

Discounts

20l. to 30l. 5 per
cent.

30l. to 40l. 7 ⁄2

40l. to 60l. 10

60l. to 80l. 12 ⁄2

80l. to 100l. 15

100l. & upwards 20

Small consumers, 10s. per meter cub. feet, and 5 per cent. off from 10l. to 20l.

8s. 6d. per ton. 3 sorts used average. Slack 5s. 6d. Low moor 8s. 10d. Catherine slack 8s. 8,000 13 cwt.

Leeds, 1834.

8s. per meter cubic feet.

Discounts

2 ⁄2 - per cent.
on half-
yearly
payments - 15l.

5 30l.

7 ⁄2 50l.

10 100l.

8s. per ton average. 2-3ds common 7s. 1-3d cannel, 10s. 6,500 12 cwt.

Sheffield, 1835. 8s. per meter cubic feet. Discounts same as Leeds. 7s. 9d. per ton average. 3 sorts used 1, 2-10ths. cannel, at 16s. 8, 2-10ths. deep pit, 7s. 1-10th silk stone, 10s. 8,000 10 cwt. of saleable coke.

Leicester, 1837.

7s. 6d. per meter cub. ft.

Discounts on half-yearly rental not
exceeding 10l., 5 per cent.

A-
bove 10l. and
not
ex-
ceed-
ing 20l. 7 ⁄2 per
cent.

20l. 30l. 10

30l. 40l. 12 ⁄2

40l. 50l. 15

50l. 60l. 20

60l. & upwards 25

13s. 6d. average. Derbyshire soft coal. 7,500 4 quarters.

Derby, 1834. 10s. per meter cub. feet. Same coal used as at Leicester. 7,000 Ditto.

Discounts 5 to 35 per cent.

Nottingham, 1834. 9s. per meter cubic feet. Discounts as above. Ditto. 7,000 Ditto.

London, 1834. 10s. per meter cub. feet. No discounts. 17s. average. Newcastle. 8,500 36 bush.

Ditto, 1837. Ditto. Ditto. 8,500 Ditto.

Name of the Place where Gas Works are situated. Selling Price of Coke. Material used to heat Retorts. Quantity used per Ton of Coal. No. of Public or Street Lamps supplied. Description.
—
Size or Sort. Price paid per Annum for Ditto. Who lights, cleans, puts out, and repairs.

L. s. d.

Birmingham Gas Company. 2s. 1d. per quarter delivered, or about 3d. per bushel. Slack. About 5 cwt. of slack, at 6s. per ton, 25 per cent. 490 Batswings, 460 30 1
2 10
0 0
0 Company, and provides posts, services, &c.

Birmingham and Staffordshire. 2s. 10d. per sack of 8 bushels. Slack and Tar. 5 cwt. of slack, at 4s. 25 per cent. 1,500 Batswings. average Ditto.

1 18 0

Macclesfield. 10s. per ton. Coke. No account kept. 220 Ditto. 2 10 0 Company.

Stockport. 6s. 8d. per ton. Coal, coke, and tar. Ditto. 230 Ditto. 2 10 0 Comrs. provide lamps and posts. Company's service light, repair, clean, and extinguish.

1834.

2 0 0

1837.

Manchester. Ditto. Coke. 4, 2-3ds cwt. 2,375 Single-jets and flat flames, about half and half. 1
2 2
0 0
0 Commissioners of police.

Liverpool Old Company, 1834. 8s. 4d. per ton of 112 lb. per cwt. Slack 7s. 3d. per ton. 6⁄2 cwt. 1,700
30 Batswings,
1 jet,
2 —
3 —
4 — 4
2
2
2
3 10
5
13
2
13 0
0
0
9
11 Company light, clean, put out, and repair.

Ditto ditto. In 1835 this Company resorted to the use of cannel coal similar to the Liverpool New Gas and Coal Company, producing nearly similar results, which see.

Liverpool New Gas and Coke, 1835. 7s. 6d. per ton. Coke and slack. 5⁄2 cwt. Only a few. Argands. 4 0 0 Commissioners.

Bradford, 1834. 12s. per ton. Coke. 8⁄2 cwt. 220 Batswings. 2 12 6 Company light, repair, &c.

Leeds, 1834. 7s. 6d. per ton. Ditto. 5⁄4 cwt. 517 Ditto. 2 12 6 Commissioners, except extinguishing, for which Company pay 3s. 10d. per lamp.

Sheffield, 1835. 10s. per ton. Ditto. 3⁄2 cwt. 600 Ditto. 2 10 0 Company provide lamps, clean, repair, put out, &c.

Leicester, 1837. 10s. 8d. or 2s. 8d. per qr. Coke, tar, &c. About 1-3d of coke. 414 Ditto. 2 18 6 Company light, put out, and clean.

Derby, 1834. Ditto. Coke. Ditto. 219 Ditto. 2 2 0 Commissioners light, put out, &c.

2 7 0

Nottingham, 1834. Ditto. Ditto. Ditto. 300 Ditto. 3 3 0 Commissioners light, clean, repair, &c.

London, 1834. 12s. per chaldron. Ditto. 13 bush. 26,280 Ditto. 4 0 0 Company light, clean, put out, but not repair.

Ditto, 1837. Ditto. Ditto. Ditto. 30,400 Ditto. 4 0 0 Ditto.

Name of the Place where Gas Works are situated. No. of Hours, or Time burnt in the Year. Gas consumed in each Lamp per Hour. Rate per Meter Cubic Feet received for Ditto. Amount deducted for cleaning, lighting, extinguishing, providing Lamp Posts; &c. Per Centage of Loss of Gas made. Greatest Quantity of Gas delivered in One Night.

s. d. s. d. Cubic Feet.

Birmingham Gas Company. 226 nights, or 2938 hours, 9 months, omitting 5 nights for moons. 5 feet per hour. 30
40 10
18 18 0 Receives net about 6s. 8d. per meter cubic feet. 48 millions in the year.

Birmingham and Staffordshire. 234 nights, or 3042 hours. Ditto. 1 3 ⁄2 18 0 Receives net about 5s. 6d. per meter cubic feet. 85 millions in the year.

Macclesfield. 8 months, omitting 5 nights for moons. 4 feet per hour. 3 0 12 0 Could not say. 80,000. Total for year about 15 millions.

Stockport. 8 months. 4 nights omitted for moons. 237 nights—2800 hours. Ditto. 2 6 12 6 Ditto. 65,000. Total for year about 12 millions.

Manchester. 3390 hours. 1 foot, 2 feet, per hour. 6
5 6
6 nothing. About 15 to 17⁄2 per cent. receive about 7s. 4d. per meter cubic feet, public and private. Nearly all by meter. 500,000. Total for year 100 millions.

Liverpool Old Company, 1834. 3600 hours. 5 feet per hour. 4 4 12 0 Could not learn in the absence of the manager. 360,000. Total for year 72 millions.

Ditto ditto. In 1835 this Company resorted to the use of cannel coal similar to the Liverpool New Gas and Coal Company, producing nearly similar results, which see.

Liverpool New Gas and Coke, 1835. 3000 hours. 3⁄2 feet per hour. 5 6 nothing Nearly all by meter. Not sufficiently long at work.

Bradford, 1834. 8 months, omitting 7 nights, 2600 hours to 4 o’clock in the morning. 5 feet per hour. 3 1 12 6 Receive 8s. per meter cubic feet, less 5⁄2 per cent. 42,500. Total for year 8,619,000.

Leeds, 1834. 2330 hours. 4 feet per hour. 5 2 3 10 Receive for public and private 6s. 8d. per meter cubic feet. Public 5s., private 7s. ; meters used to 5 to 1 for private rental. 176,000. Total for year 31 millions.

Sheffield, 1835. 2200 hours. Ditto. 3 2 ⁄2 18 0 Receive for public and private lts. 5s. per meter cubic feet. Public 3s. 2⁄2d., private 5s. 9⁄2d. Few meters used. 220,000. Total for year 40 millions.

Leicester, 1837. From August 14th to September 1st, omitting 3 nights for moons, 3000 hours. 5 feet per hour. 3 4 ⁄4 7 0 Not sufficiently long, at 7s. 6d. Total for year 18 millions.

Derby, 1834. 2173 hours, from August to May. Ditto. 4 0 — Lose about 17⁄2 per cent. Ditto.

nearly.

Nottingham, 1834. All the year, 4327 hours. Ditto. 3 0 — Could not learn. Ditto.

nearly.

London, 1834. 4327 hours, all the year. 4 feet per hour. 4 0 12 0 Receive for public and private lights 7s. public, 4s. private, 8s. few meters used. Total for year 1000 millions. Longest night 4,910,000.

Ditto, 1837. Ditto. Ditto. 4 0 12 0 Ditto. Total for year 1460 millions. Longest night 7,120,000.

Name of the Place where Gas Works are situated. Duration of Charges. Method of Purification. Number of Gas Holders. Specific Gravity of the Gas. Distance of Candle from Shadow.

Inch.

Birmingham Gas Company. 6 hours. Dry lime. 4, and 2 in the town, and large new gas station. ·453 72

Birmingham and Staffordshire. Ditto. Ditto. 6, and 6 in the town 7 miles off. ·455 72

Macclesfield. 8 hours. Ditto. 3 gas holders. Not taken. 70

Stockport. Ditto. Ditto. 4 gas holders. ·539 64

Manchester. 6 hours. Wet lime. 10 gas holders, and 2 in the town. ·534 66

Liverpool Old Company, 1834. 8 hours, large, retorts holding 6 cwt. each. Wet and dry lime, principally dry. 8 gas holders in all, 4 in the town, 1000 yards off the works. ·462 75

Ditto ditto. In 1835 this Company resorted to the use of cannel coal similar to the Liverpool New Gas and Coal Company, producing nearly similar results, which see.

Liverpool New Gas and Coke, 1835. 4 hours. Wet lime. 2 large gas holders. ·580 55

Bradford, 1834. 8 hours. Dry lime. 4 gas holders. ·420 78

Leeds, 1834. 6 hours. Ditto. 5 gas holders. ·530 67

Sheffield, 1835. Ditto. Ditto. 4 gas holders, and 2 more erecting. ·466 74

Leicester, 1837. Ditto. Ditto. 3 gas holders, and 1 erecting. ·528 74

Derby, 1834. Ditto. Wet lime. 4 gas holders. ·448 83

Nottingham, 1834. Ditto. Ditto. — ·424 90

London, 1834. Ditto. Ditto. 130 gas holders. ·412 80

Ditto, 1837. Ditto. Ditto. 176 gas holders. ·412 80

Name of the Place where Gas Works are situated. Gas equal to Candles. Gas burnt in a single Jet Four Inches high. Gas consumed per Hour with a Four-Inch Flame. Gas Flame reduced to Candle burnt per Hour. Height of Gas Flame equal to Light from Candle.

Candles Cu. ft. Cu. ft. Inch.

Birmingham Gas Company. 1,929 1 ·22 ·8 2 ⁄2

Birmingham and Staffordshire. 1,929 1 ·22 ·8 2 ⁄2

Macclesfield. 204 Not taken. ·8 2 ⁄4

Stockport. 2,441 ·85 ·55 2 ⁄8

Manchester. 2,295 ·825 ·475 2 ⁄4

Liverpool Old Company, 1834. 1,777 1 ·1 ·75 2 ⁄8

Ditto ditto. In 1835 this Company resorted to the use of cannel coal similar to the Liverpool New Gas and Coal Company, producing nearly similar results, which see.

Liverpool New Gas and Coke, 1835. 3,306 ·9 ·45 2

Bradford, 1834. 1,643 ·12 ·9 3

Leeds, 1834. 2,228 ·855 ·51 2 ⁄4

Sheffield, 1835. 1,826 1 ·04 ·735 2 ⁄4

Leicester, 1837. 1,826 1 ·1 ·75 2 ⁄4

Derby, 1834. 1,453 1 ·2 ·925 3

Nottingham, 1834. 1,234 1 ·3 1 ·175 3

London, 1834. 1,562 1 ·13 ·84 2 ⁄4

Ditto, 1837. 1,562 1 ·13 ·84 2 ⁄4

A Table shewing the Rate per Thousand Cubic feet received for any Burner consuming from ⁄2 a Cubic foot to 10 Cubic feet per hour, at any given price per annum, and to the times below stated. By Joseph Hedley, Esq.

Time of Burning per annum. No.
of
Hours.
Single Jets. 2 Jets. 3 Jets. Small Argand. Large Argand. Fancy and extravagant
Burners.

Cub.
ft.
⁄2 Cub.
ft.
⁄4 Cub.
ft.
1 Cub.
ft.
1⁄4 Cub.
ft.
1⁄2 Cub.
ft.
1⁄4 Cub.
ft.
2 Cub.
ft.
2⁄2 Cub.
ft.
3 Cub.
ft.
3⁄2 Cub.
ft.
4 Cub.
ft.
4⁄2 Cub.
ft.
5 Cub.
ft.
6 Cub.
ft.
7 Cub.
ft.
8 Cub.
ft.
9 Cub.
ft.
10

From Dusk to 8 o’clock 781 2 ·56 1 ·706 1 ·28 1 ·026 ·853 ·731 ·64 ·5132 ·4268 ·3658 ·3201 ·2846 ·2561 ·2134 ·1829 ·16 ·1423 ·128

ditto and Sundays 902 2 ·216 1 ·478 1 ·108 ·887 ·739 ·633 ·554 ·4434 ·3695 ·3168 ·2771 ·2464 ·2217 ·1848 ·1584 ·1383 ·1232 ·1108

ditto and from 6 o’clock mornings 1050 1 ·904 1 ·27 ·952 ·762 ·635 ·544 ·476 ·381 ·3174 ·272 ·2381 ·2116 ·1905 ·1587 ·136 ·119 ·1058 ·0952

ditto and Sundays and from ditto 1172 1 ·706 1 ·138 ·853 ·682 ·569 ·487 ·426 ·3412 ·2844 ·2438 ·2133 ·1896 ·1706 ·1422 ·1219 ·1067 ·0948 ·0853

9 o’clock 1054 1 ·896 1 ·264 ·948 ·759 ·632 ·542 ·474 ·3794 ·3162 ·271 ·2371 ·2108 ·1897 ·1581 ·1355 ·1185 ·1054 ·0948

ditto and Sundays 1221 1 ·638 1 ·092 ·819 ·675 ·546 ·463 ·409 ·3376 ·273 ·234 ·2047 ·182 ·1638 ·1365 ·117 ·1024 ·091 ·0819

ditto and from 6 o’clock mornings 1323 1 ·510 1 ·066 ·755 ·604 ·503 ·431 ·378 ·3022 ·2519 ·2158 ·1889 ·1678 ·1511 ·1259 ·1079 ·0945 ·0839 ·0755

ditto and Sundays and from ditto 1490 1 ·342 ·894 ·671 ·536 ·447 ·383 ·335 ·2684 ·2236 ·1918 ·1675 ·1492 ·1312 ·1118 ·0959 ·0839 ·0746 ·0671

10 o’clock 1367 1 ·462 ·974 ·731 ·585 ·487 ·418 ·366 ·2926 ·2438 ·209 ·1829 ·1626 ·1463 ·1219 ·1045 ·0914 ·0813 ·0731

ditto and Sundays 1586 1 ·26 ·84 ·63 ·504 ·42 ·36 ·315 ·2522 ·2101 ·1802 ·1576 ·14 ·1261 ·1051 ·0901 ·0789 ·07 ·0630

ditto and from 6 o’clock mornings 1636 1 ·222 ·814 ·611 ·489 ·407 ·349 ·305 ·2444 ·2037 ·1746 ·1528 ·1358 ·1222 ·1019 ·0873 ·0764 ·0679 ·0611

ditto and Sundays and from ditto 1855 1 ·078 ·718 ·539 ·431 ·359 ·308 ·269 ·2156 ·1796 ·154 ·1347 ·1198 ·1078 ·0898 ·077 ·0674 ·0599 ·0539

11 o’clock 1680 1 ·19 ·794 ·595 ·476 ·397 ·34 ·297 ·238 ·1984 ·17 ·1488 ·133 ·119 ·0992 ·085 ·0744 ·0665 ·0595

ditto and Sundays 1951 1 ·024 ·682 ·512 ·409 ·341 ·293 ·256 ·2048 ·1707 ·1466 ·1281 ·1138 ·1024 ·0854 ·0733 ·064 ·0569 ·0512

ditto and from 6 o’clock mornings 1949 1 ·026 ·684 ·513 ·41 ·342 ·294 ·256 ·2052 ·171 ·1466 ·1282 ·114 ·1026 ·0855 ·0733 ·0641 ·057 ·0513

ditto and Sundays and from ditto 2220 ·9 ·6 ·45 ·36 ·3 ·257 ·225 ·1802 ·1501 ·1286 ·1126 ·1 ·0981 ·0751 ·0643 ·0563 ·05 ·045

12 o’clock 1993 1 · ·668 ·502 ·4 ·334 ·287 ·251 ·2006 ·1672 ·1434 ·1254 ·1114 ·1003 ·0836 ·0717 ·0627 ·0557 ·0502

ditto and Sundays 2316 ·862 ·574 ·432 ·345 ·287 ·247 ·215 ·1726 ·1439 ·1236 ·1079 ·0958 ·0863 ·0719 ·0618 ·0539 ·0479 ·0432

ditto and from 6 o’clock mornings 2262 ·884 ·59 ·442 ·353 ·295 ·255 ·221 ·1768 ·1476 ·1274 ·1105 ·0982 ·0884 ·0737 ·0637 ·0552 ·0491 ·0442

ditto and Sundays and from ditto 2585 ·772 ·514 ·387 ·309 ·257 ·221 ·193 ·1546 ·1289 ·1104 ·0967 ·0858 ·0773 ·0645 ·0552 ·0483 ·0429 ·0387

1 o’clock 2306 ·866 ·578 ·434 ·347 ·289 ·247 ·217 ·1734 ·1445 ·1238 ·1080 ·0962 ·0867 ·0723 ·0619 ·0542 ·0481 ·0434

ditto and Sundays 2681 ·746 ·498 ·373 ·298 ·249 ·213 ·186 ·1492 ·1243 ·1066 ·0932 ·0828 ·0746 ·0621 ·0533 ·0466 ·0414 ·0373

ditto and from 6 o’clock mornings 2575 ·776 ·518 ·388 ·31 ·259 ·222 ·194 ·1552 ·1294 ·111 ·0971 ·0862 ·0776 ·0647 ·0555 ·0485 ·0431 ·0388

ditto and Sundays and from ditto 2950 ·678 ·452 ·339 ·271 ·226 ·193 ·169 ·1356 ·113 ·0968 ·0847 ·0754 ·0678 ·0565 ·0484 ·0424 ·0377 ·0339

All night 4327 ·462 ·308 ·231 ·185 ·154 ·132 ·115 ·6924 ·077 ·066 ·0578 ·0515 ·0462 ·0385 ·033 ·0289 ·0257 ·0231

To use the Table.—Select the hour to which it is agreed the gas is to burn,—9, 10, 11 o’clock, Sundays, &c., as the case may be, and the description of the burner.—Multiply the decimal number opposite to it by the amount in shillings agreed to be paid per annum, and the product will be the sum received per m. cubic feet for the gas.

Example.—Suppose a small argand which should burn 3⁄2 feet per hour, is agreed for till 9 o’clock at 2l. per annum. Look along the line of 9 o’clock till you arrive at the column of 3⁄2 feet per hour, and you find the number, ·271. Multiply this number by 40s. and the result gives 10s. 10d. per m. cubic feet. But suppose instead of keeping to 9 o’clock the party burns till 1 o’clock, Sundays and mornings, and by enlarging the holes or height of flame consumes 8 cubic feet of gas per hour; then you have the number, ·0424, which multiplied by 40s., still the price paid, gives 1s. 8d. per m. cubic feet only, and so on for any greater or lesser variation of the agreement.

The “number of hours” includes ⁄4 of an hour allowed for shutting shops, and 1 hour’s extra burning on Saturday nights.

Time of Burning per annum. No.
of
Hours.
Single Jets. 2 Jets.

Cub.
ft.
⁄2 Cub.
ft.
⁄4 Cub.
ft.
1 Cub.
ft.
1⁄4 Cub.
ft.
1⁄2 Cub.
ft.
1⁄4

From Dusk to 8 o’clock 781 2 ·56 1 ·706 1 ·28 1 ·026 ·853 ·731

ditto and Sundays 902 2 ·216 1 ·478 1 ·108 ·887 ·739 ·633

ditto and from 6 o’clock mornings 1050 1 ·904 1 ·27 ·952 ·762 ·635 ·544

ditto and Sundays and from ditto 1172 1 ·706 1 ·138 ·853 ·682 ·569 ·487

9 o’clock 1054 1 ·896 1 ·264 ·948 ·759 ·632 ·542

ditto and Sundays 1221 1 ·638 1 ·092 ·819 ·675 ·546 ·463

ditto and from 6 o’clock mornings 1323 1 ·510 1 ·066 ·755 ·604 ·503 ·431

ditto and Sundays and from ditto 1490 1 ·342 ·894 ·671 ·536 ·447 ·383

10 o’clock 1367 1 ·462 ·974 ·731 ·585 ·487 ·418

ditto and Sundays 1586 1 ·26 ·84 ·63 ·504 ·42 ·36

ditto and from 6 o’clock mornings 1636 1 ·222 ·814 ·611 ·489 ·407 ·349

ditto and Sundays and from ditto 1855 1 ·078 ·718 ·539 ·431 ·359 ·308

11 o’clock 1680 1 ·19 ·794 ·595 ·476 ·397 ·34

ditto and Sundays 1951 1 ·024 ·682 ·512 ·409 ·341 ·293

ditto and from 6 o’clock mornings 1949 1 ·026 ·684 ·513 ·41 ·342 ·294

ditto and Sundays and from ditto 2220 ·9 ·6 ·45 ·36 ·3 ·257

12 o’clock 1993 1 · ·668 ·502 ·4 ·334 ·287

ditto and Sundays 2316 ·862 ·574 ·432 ·345 ·287 ·247

ditto and from 6 o’clock mornings 2262 ·884 ·59 ·442 ·353 ·295 ·255

ditto and Sundays and from ditto 2585 ·772 ·514 ·387 ·309 ·257 ·221

1 o’clock 2306 ·866 ·578 ·434 ·347 ·289 ·247

ditto and Sundays 2681 ·746 ·498 ·373 ·298 ·249 ·213

ditto and from 6 o’clock mornings 2575 ·776 ·518 ·388 ·31 ·259 ·222

ditto and Sundays and from ditto 2950 ·678 ·452 ·339 ·271 ·226 ·193

All night 4327 ·462 ·308 ·231 ·185 ·154 ·132

To use the Table.—Select the hour to which it is agreed the gas is to burn,—9, 10, 11 o’clock, Sundays, &c., as the case may be, and the description of the burner.—Multiply the decimal number opposite to it by the amount in shillings agreed to be paid per annum, and the product will be the sum received per m. cubic feet for the gas.

Example.—Suppose a small argand which should burn 3⁄2 feet per hour, is agreed for till 9 o’clock at 2l. per annum. Look along the line of 9 o’clock till you arrive at the column of 3⁄2 feet per hour, and you find the number, ·271. Multiply this number by 40s. and the result gives 10s. 10d. per m. cubic feet. But suppose instead of keeping to 9 o’clock the party burns till 1 o’clock, Sundays and mornings, and by enlarging the holes or height of flame consumes 8 cubic feet of gas per hour; then you have the number, ·0424, which multiplied by 40s., still the price paid, gives 1s. 8d. per m. cubic feet only, and so on for any greater or lesser variation of the agreement.

The “number of hours” includes ⁄4 of an hour allowed for shutting shops, and 1 hour’s extra burning on Saturday nights.

Time of Burning per annum. No.
of
Hours.
3 Jets. Small Argand.

Cub.
ft.
2 Cub.
ft.
2⁄2 Cub.
ft.
3 Cub.
ft.
3⁄2 Cub.
ft.
4 Cub.
ft.
4⁄2

From Dusk to 8 o’clock 781 ·64 ·5132 ·4268 ·3658 ·3201 ·2846

ditto and Sundays 902 ·554 ·4434 ·3695 ·3168 ·2771 ·2464

ditto and from 6 o’clock mornings 1050 ·476 ·381 ·3174 ·272 ·2381 ·2116

ditto and Sundays and from ditto 1172 ·426 ·3412 ·2844 ·2438 ·2133 ·1896

9 o’clock 1054 ·474 ·3794 ·3162 ·271 ·2371 ·2108

ditto and Sundays 1221 ·409 ·3376 ·273 ·234 ·2047 ·182

ditto and from 6 o’clock mornings 1323 ·378 ·3022 ·2519 ·2158 ·1889 ·1678

ditto and Sundays and from ditto 1490 ·335 ·2684 ·2236 ·1918 ·1675 ·1492

10 o’clock 1367 ·366 ·2926 ·2438 ·209 ·1829 ·1626

ditto and Sundays 1586 ·315 ·2522 ·2101 ·1802 ·1576 ·14

ditto and from 6 o’clock mornings 1636 ·305 ·2444 ·2037 ·1746 ·1528 ·1358

ditto and Sundays and from ditto 1855 ·269 ·2156 ·1796 ·154 ·1347 ·1198

11 o’clock 1680 ·297 ·238 ·1984 ·17 ·1488 ·133

ditto and Sundays 1951 ·256 ·2048 ·1707 ·1466 ·1281 ·1138

ditto and from 6 o’clock mornings 1949 ·256 ·2052 ·171 ·1466 ·1282 ·114

ditto and Sundays and from ditto 2220 ·225 ·1802 ·1501 ·1286 ·1126 ·1

12 o’clock 1993 ·251 ·2006 ·1672 ·1434 ·1254 ·1114

ditto and Sundays 2316 ·215 ·1726 ·1439 ·1236 ·1079 ·0958

ditto and from 6 o’clock mornings 2262 ·221 ·1768 ·1476 ·1274 ·1105 ·0982

ditto and Sundays and from ditto 2585 ·193 ·1546 ·1289 ·1104 ·0967 ·0858

1 o’clock 2306 ·217 ·1734 ·1445 ·1238 ·1080 ·0962

ditto and Sundays 2681 ·186 ·1492 ·1243 ·1066 ·0932 ·0828

ditto and from 6 o’clock mornings 2575 ·194 ·1552 ·1294 ·111 ·0971 ·0862

ditto and Sundays and from ditto 2950 ·169 ·1356 ·113 ·0968 ·0847 ·0754

All night 4327 ·115 ·6924 ·077 ·066 ·0578 ·0515

To use the Table.—Select the hour to which it is agreed the gas is to burn,—9, 10, 11 o’clock, Sundays, &c., as the case may be, and the description of the burner.—Multiply the decimal number opposite to it by the amount in shillings agreed to be paid per annum, and the product will be the sum received per m. cubic feet for the gas.

Example.—Suppose a small argand which should burn 3⁄2 feet per hour, is agreed for till 9 o’clock at 2l. per annum. Look along the line of 9 o’clock till you arrive at the column of 3⁄2 feet per hour, and you find the number, ·271. Multiply this number by 40s. and the result gives 10s. 10d. per m. cubic feet. But suppose instead of keeping to 9 o’clock the party burns till 1 o’clock, Sundays and mornings, and by enlarging the holes or height of flame consumes 8 cubic feet of gas per hour; then you have the number, ·0424, which multiplied by 40s., still the price paid, gives 1s. 8d. per m. cubic feet only, and so on for any greater or lesser variation of the agreement.

The “number of hours” includes ⁄4 of an hour allowed for shutting shops, and 1 hour’s extra burning on Saturday nights.

Time of Burning per annum. No.
of
Hours.
Large Argand. Fancy and extravagant
Burners.

Cub.
ft.
5 Cub.
ft.
6 Cub.
ft.
7 Cub.
ft.
8 Cub.
ft.
9 Cub.
ft.
10

From Dusk to 8 o’clock 781 ·2561 ·2134 ·1829 ·16 ·1423 ·128

ditto and Sundays 902 ·2217 ·1848 ·1584 ·1383 ·1232 ·1108

ditto and from 6 o’clock mornings 1050 ·1905 ·1587 ·136 ·119 ·1058 ·0952

ditto and Sundays and from ditto 1172 ·1706 ·1422 ·1219 ·1067 ·0948 ·0853

9 o’clock 1054 ·1897 ·1581 ·1355 ·1185 ·1054 ·0948

ditto and Sundays 1221 ·1638 ·1365 ·117 ·1024 ·091 ·0819

ditto and from 6 o’clock mornings 1323 ·1511 ·1259 ·1079 ·0945 ·0839 ·0755

ditto and Sundays and from ditto 1490 ·1312 ·1118 ·0959 ·0839 ·0746 ·0671

10 o’clock 1367 ·1463 ·1219 ·1045 ·0914 ·0813 ·0731

ditto and Sundays 1586 ·1261 ·1051 ·0901 ·0789 ·07 ·0630

ditto and from 6 o’clock mornings 1636 ·1222 ·1019 ·0873 ·0764 ·0679 ·0611

ditto and Sundays and from ditto 1855 ·1078 ·0898 ·077 ·0674 ·0599 ·0539

11 o’clock 1680 ·119 ·0992 ·085 ·0744 ·0665 ·0595

ditto and Sundays 1951 ·1024 ·0854 ·0733 ·064 ·0569 ·0512

ditto and from 6 o’clock mornings 1949 ·1026 ·0855 ·0733 ·0641 ·057 ·0513

ditto and Sundays and from ditto 2220 ·0981 ·0751 ·0643 ·0563 ·05 ·045

12 o’clock 1993 ·1003 ·0836 ·0717 ·0627 ·0557 ·0502

ditto and Sundays 2316 ·0863 ·0719 ·0618 ·0539 ·0479 ·0432

ditto and from 6 o’clock mornings 2262 ·0884 ·0737 ·0637 ·0552 ·0491 ·0442

ditto and Sundays and from ditto 2585 ·0773 ·0645 ·0552 ·0483 ·0429 ·0387

1 o’clock 2306 ·0867 ·0723 ·0619 ·0542 ·0481 ·0434

ditto and Sundays 2681 ·0746 ·0621 ·0533 ·0466 ·0414 ·0373

ditto and from 6 o’clock mornings 2575 ·0776 ·0647 ·0555 ·0485 ·0431 ·0388

ditto and Sundays and from ditto 2950 ·0678 ·0565 ·0484 ·0424 ·0377 ·0339

All night 4327 ·0462 ·0385 ·033 ·0289 ·0257 ·0231

To use the Table.—Select the hour to which it is agreed the gas is to burn,—9, 10, 11 o’clock, Sundays, &c., as the case may be, and the description of the burner.—Multiply the decimal number opposite to it by the amount in shillings agreed to be paid per annum, and the product will be the sum received per m. cubic feet for the gas.

Example.—Suppose a small argand which should burn 3⁄2 feet per hour, is agreed for till 9 o’clock at 2l. per annum. Look along the line of 9 o’clock till you arrive at the column of 3⁄2 feet per hour, and you find the number, ·271. Multiply this number by 40s. and the result gives 10s. 10d. per m. cubic feet. But suppose instead of keeping to 9 o’clock the party burns till 1 o’clock, Sundays and mornings, and by enlarging the holes or height of flame consumes 8 cubic feet of gas per hour; then you have the number, ·0424, which multiplied by 40s., still the price paid, gives 1s. 8d. per m. cubic feet only, and so on for any greater or lesser variation of the agreement.

The “number of hours” includes ⁄4 of an hour allowed for shutting shops, and 1 hour’s extra burning on Saturday nights.

GENERAL SUMMARY.

For lighting London and its suburbs with gas, there are—

18 public gas works.

12publdo.gascompanies.

2,800,000l. capital employed in works, pipes, tanks, gas-holders, apparatus.

450,000l. yearly revenue derived.

180,000 tons of coals used in the year for making gas.

1,460,000,000 cubic feet of gas made in the year.

134,300 private burners supplied to about 40,000 consumers.

30,400 public or street do. N. B. about 2650 of these are in the city of London.

380 lamplighters employed.

176 gas-holders; several of them double ones, capable of storing 5,500,000 cubic feet.

890 tons of coals used in the retorts on the shortest day, in 24 hours.

7,120,000 cubic feet of gas used in longest night, say 24th December.

About 2500 persons are employed in the metropolis alone, in this branch of manufacture.

Between 1822 and 1827 the quantity nearly doubled itself, and that in 5 years.

Between 1827 and 1837 it doubled itself again.

Mr. Kirkham, engineer, obtained a patent, in June, 1837, for an improved mode of removing the carbonaceous incrustation from the internal surfaces of gas retorts. He employs a jet or jets of heated atmospheric air, or other gases containing oxygen, which he impels with force into the interior of such retorts as have become incrusted in consequence of the decomposition of the coal. The retort is to be kept thoroughly red hot during the application of the proposed jets. An iron pipe, constructed with several flexible joints, leading from a blowing machine, is bent in such a way as to allow its nozzle end to be introduced within the retort, and directed to any point of its surface.

I should suppose that air, even at common temperatures, applied to a retort ignited to the pitch of making gas, would burn away the incrustations; but hot air will, no doubt, be more powerful.

GAS-HOLDER; a vessel for containing and preserving gas, of which various forms are described by chemical writers.

GASOMETER, means properly a measurer of gas, though it is employed often to denote a recipient of gas of any kind. See the article Gas-Light.

GAUZE WIRE CLOTH; is a textile fabric, either plane or tweelled, made of brass, iron, or copper wire, of very various degrees of fineness and openness of texture. Its chief uses are for sieves, and safety lamps.

GAY-LUSSITE, is a white mineral of a vitreous fracture, which crystallizes in oblique rhomboidal prisms; specific gravity from 1·93 to 1·95; scratches gypsum, but is scratched by calcspar; affords water by calcination; it consists of carbonic acid 28·66; soda, 20·44; lime, 17·70; water, 32·20; clay, 1·00. It is in fact, by my analysis, a hydrated soda-carbonate of lime in atomic proportions. This mineral occurs abundantly in insulated crystals, disseminated through the bed of clay which covers the urao, or native sesquicarbonate of soda, at Lagunilla in Colombia.

GELATINE; (Eng. and Fr.; Gallert, Leim, Germ.) is an animal product which is never found in the humours, but it may be obtained by boiling with water the soft and solid parts; as the muscles, the skin, the cartilages, bones, ligaments, tendons, and membranes. Isinglass consists almost entirely of gelatine. This substance is very soluble in boiling water; the solution forms a tremulous mass of jelly when it cools. Cold water has little action upon gelatine. Alcohol and tannin (tannic acid, see Gall-nuts) precipitate gelatine from its solution; the former by abstracting the water, the latter by combining with the substance itself into an insoluble compound; of the nature of leather. No other acid, except the tannic, and no alkali possesses the property of precipitating gelatine. But chlorine and certain salts render its solution more or less turbid; as the nitrate and bi-chloride of mercury, the proto-chloride of tin, and a few others. Sulphuric acid converts a solution of gelatine at a boiling heat into sugar. See Ligneous Fibre. Gelatine consists of carbon, 47·88; hydrogen, 7·91; oxygen, 27·21. See Glue and Isinglass.

GEMS, are precious stones, which, by their colour, limpidity, lustre, brilliant polish, purity, and rarity, are sought after as objects of dress and decoration. They form the principal part of the crown jewels of kings, not only from their beauty, but because they are supposed to comprize the greatest value in the smallest bulk; for a diamond, no larger than a nut or an acorn, may be the representative sign of the territorial value of a whole country, the equivalent in commercial exchange of a hundred fortunes, acquired by severe toils and privations.

Among these beautiful minerals mankind have agreed in forming a select class, to which the title of gems or jewels has been appropriated; while the term precious stone is more particularly given to substances which often occur under a more considerable volume than fine stones ever do.

Diamonds, sapphires, emeralds, rubies, topazes, hyacinths, and chrysoberyls, are reckoned the most valuable gems.

Crystalline quartz, pellucid opalescent or of various hues, amethyst, lapis lazuli, malachite, jasper, agate, &c., are ranked in the much more numerous and inferior class of ornamental stones. These distinctions are not founded upon any strict philosophical principle, but are regulated by a conventional agreement, not very well defined; for it is impossible to subject these creatures of fashion and taste to the rigid subdivisions of science. We have only to consider the value currently attached to them, and take care not to confound two stones of the same colour, but which may be very differently prized by the virtuoso.

Since it usually happens that the true gems are in a cut and polished state, or even set in gold or silver, we are thereby unable to apply to them the criteria of mineralogical and chemical science. The cutting of the stone has removed or masked its crystalline character, and circumstances rarely permit the phenomena of double or single refraction to be observed; while the test by the blowpipe is inadmissible. Hence the only scientific resources that remain are the trial by electricity, which is often inconclusive; the degree of hardness, a criterion requiring great experience in the person who employs it; and, lastly, the proof by specific gravity, unquestionably one of the surest means of distinguishing the really fine gems from ornamental stones of similar colour. This proof can be applied only to a stone that is not set; but the richer gems are usually dismounted, when offered for sale.

This character of specific gravity may be applied by any person of common intelligence, with the aid of a small hydrostatic balance. If, for example, a stone of a fine crimson-red colour, be offered for sale, as an oriental ruby; the purchaser must ascertain if it be not a Siberian tourmaline, or ruby spinel. Supposing its weight in air to be 100 grains, if he finds it reduced to 69 grains, when weighed in water, he concludes that its bulk is equal to that of 31 grains of water, which is its loss of weight. Now, a real sapphire which weighs 100 grains in air, would have weighed 76·6 in water; a spinel ruby of 100 grains would have weighed 72·2 in water, and a Siberian tourmaline of 100 grains would have weighed only 69 grains in water. The quality of the stone in question is, therefore, determined beyond all dispute, and the purchaser may be thus protected from fraud.

The sard of the English jewellers (Sardoine, French) is a stone of the nature of agate, having an orange colour more or less deep, and passing by insensible shades into yellow, reddish, and brown; whence it has been agreed to unite under this denomination all the agates whose colour verges upon brown. It should be remarked, however, that the sard presents, in its interior and in the middle of its ground, concentric zones, or small nebulosities, which are not to be seen in the red cornelian, properly so called. The ancients certainly knew our sard, since they have left us a great many of them engraved, but they seem to have associated under the title sarda both the sardoine of the French, and our cornelians and calcedonies. Pliny says that the sarda came from the neighbourhood of a city of that name in Lydia, and from the environs of Babylon. Among the engraved sards which exist in the collection of antiques in the Bibliothèque Royale of Paris, there is an Apollo remarkable for its fine colour and great size. When the stone forms a part of the agate-onyx, it is called sardonyx. For further details upon Gems, and the art of cutting and engraving them, see Lapidary.

GEOGNOSY, means a knowledge of the structure of the earth; Geology, a description of the same. The discussion of this subject does not come within the province of this Dictionary.

GERMAN SILVER. See the latter end of the article Copper.

GERMINATION; (Eng. and Fr.; Das Keimen, Germ.) is the first sprouting of a seed after it is sown, or when, after steeping, it is spread upon the malt floor. See Beer.

GIG MACHINES, are rotatory drums, mounted with thistles or wire teeth for teazling cloth. See Woollen Manufacture.

GILDING (Dorure, Fr.; Vergoldung, Germ.); is the art of coating surfaces with a thin film of gold. For a full discussion of this subject, see Gold. Mr. Elkington, gilt toy maker, obtained a patent, in June, 1836, for gilding copper, brass, &c., by means of potash or soda combined with carbonic acid, and with a solution of gold. Dissolve, says he, 5 oz. troy of fine gold in 52 oz. avoirdupois of nitro-muriatic acid of the following proportions: viz. 21 oz. of pure nitric acid, of spec. grav. 1·45, 17 oz. of pure muriatic acid, of spec. grav. 1·15; with 14 oz. of distilled water.

The gold being put into the mixture of acids and water, they are to be heated in a glass or other convenient vessel till the gold is dissolved; and it is usual to continue the application of heat after this is effected, until a reddish or yellowish vapour ceases to rise.

The clear liquid is to be carefully poured off from any sediment which generally appears and results from a small portion of silver, which is generally found in alloy with gold. The clear liquid is to be placed in a suitable vessel of stone, pottery ware is preferred. Add to the solution of gold 4 gallons of distilled water, and 20 pounds of bicarbonate of potash of the best quality; let the whole boil moderately for 2 hours, the mixture will then be ready for use.

The articles to be gilded having been first perfectly cleaned from scale or grease, they are to be suspended on wires, conveniently for a workman to dip them in the liquid, which is kept boiling. The time required for gilding any particular article will depend on circumstances, partly on the quantity of gold remaining in the liquid, and partly on the size and weight of the article; but a little practice will readily give sufficient guidance to the workman.

Supposing the articles desired to be gilded be brass or copper buttons, or small articles for gilt toys, or ornaments of dress, such as earrings or bracelets, a considerable number of which may be strung on a hoop, or bended piece of copper or brass wire, and dipped into the vessel containing the boiling liquid above described, and moved therein, the requisite gilding will be generally obtained in from a few seconds to a minute; this is when the liquid is in the condition above described, and depending on the quality of the gilding desired; but if the liquid has been used some time, the quantity of gold will be lessened, which will vary the time of operating to produce a given effect, or the colour required, all which will quickly be observed by the workman; and by noting the appearance of the articles from time to time, he will know when the desired object is obtained, though it is desirable to avoid as much as possible taking the articles out of the liquid.

When the operation is completed, the workman perfectly washes the articles so gilded with clean water; they may then be submitted to the usual process of colouring.

If the articles be cast figures of animals, or otherwise of considerable weight, compared with the articles above mentioned, the time required to perform the process will be greater.

In case it is desired to produce what is called a dead appearance, it may be performed by several processes: the one usually employed is to dead the articles in the process of cleaning, as practised by brass-founders and other trades; it is produced by an acid, prepared for that purpose, sold by the makers under the term “deading aquafortis,” which is well understood.

It may also be produced by a weak solution of nitrate of mercury, applied to the articles previous to the gilding process, as is practised in the process of gilding with mercury, previous to spreading the amalgam, but generally a much weaker solution; or the articles having been gilded may be dipped in a solution of nitrate of mercury, and submitted to heat to expel the same, as is practised in the usual process of gilding.

It is desirable to remark, that much of the beauty of the result depends on the well cleaning of the articles, and it is better to clean them by the ordinary processes, and at once pass them into the liquid to be gilded. See Gold, towards the end.

GIN, or Geneva, from Genievre (juniper), is a kind of ardent spirits manufactured in Holland, and hence called Hollands gin in this country, to distinguish it from British gin. The materials employed in the distilleries of Schiedam, are two parts of unmalted rye from Riga, weighing about 54 lbs. per bushel, and one part of malted bigg, weighing about 37 lbs. per bushel. The mash tun, which serves also as the fermenting tun, has a capacity of nearly 700 gallons, being about five feet in diameter at the mouth, rather narrower at the bottom, and 4⁄2 feet deep; the stirring apparatus is an oblong rectangular iron grid, made fast to the end of a wooden pole. About a barrel, = 36 gallons of water, at a temperature of from 162° to 168° (the former heat being best for the most highly dried rye), are put into the mash tun for every 1⁄2 cwt. of meal, after which the malt is introduced and stirred, and lastly the rye is added. Powerful agitation is given to the magma till it becomes quite uniform; a process which a vigorous workman piques himself upon executing in the course of a few minutes. The mouth of the tun is immediately covered over with canvas, and further secured by a close wooden lid, to confine the heat; it is left in this state for two hours. The contents being then stirred up once more, the transparent spent wash of a preceding mashing is first added, and next as much cold water as will reduce the temperature of the whole to about 85° F. The best Flanders yeast, which had been brought, for the sake of carriage, to a doughy consistence by pressure, is now introduced to the amount of one pound for every 100 gallons of the mashed materials.

The gravity of the fresh wort is usually from 33 to 38 lbs. per Dicas’ hydrometer; and the fermentation is carried on from 48 to 60 hours, at the end of which time the attenuation is from 7 to 4 lbs., that is, the specific gravity of the supernatant wash is from 1·007 to 1·004.

The distillers are induced by the scarcity of beer-barm in Holland, to skim off a quantity of the yeast from the fermenting tuns, and to sell it to the bakers, whereby they obstruct materially the production of spirit, though they probably improve its quality, by preventing its impregnation with yeasty particles; an unpleasant result which seldom fails to take place in the whiskey distilleries of the United Kingdom.

On the third day after the fermenting tun is set, the wash containing the grains is transferred to the still, and converted into low wines. To every 100 gallons of this liquor, two pounds of juniper berries, from 3 to 5 years old, being added along with about one quarter of a pound of salt, the whole are put into the low wine still, and the fine Hollands spirit is drawn off by a gentle and well-regulated heat, till the magma becomes exhausted; the first and the last products being mixed together; whereby a spirit, 2 to 3 per cent. above our hydrometer proof, is obtained, possessing the peculiar fine aroma of gin. The quantity of spirit varies from 18 to 21 gallons per quarter of grain; this large product being partly due to the employment of the spent wash of the preceding fermentation; an addition which contributes at the same time to improve the flavour.

For the above instructive details of the manufacture of genuine Hollands, I am indebted to Robert More, Esq., formerly of Underwood, distiller, who after studying the art at Schiedam, tried to introduce that spirit into general consumption in this country, but found the palates of our gin-drinkers too much corrupted to relish so pure a beverage.

GINNING, is the name of the operation by which the filaments of cotton are separated from the seeds. See Cotton Manufacture.

GLANCE COAL, or anthracite, of which there are two varieties, the slaty and the conchoidal. See Anthracite.

GLASS (Verre, Fr.; Glas, Germ.); is a transparent solid formed by the fusion of siliceous and alkaline matter. It was known to the Phenicians, and constituted for a long time an exclusive manufacture of that people, in consequence of its ingredients, natron, sand, and fuel, abounding upon their coasts. It is probable that the more ancient Egyptians were unacquainted with glass, for we find no mention of it in the writings of Moses. But according to Pliny and Strabo, the glass works of Sidon and Alexandria were famous in their times, and produced beautiful articles; which were cut, engraved, gilt, and stained of the most brilliant colours, in imitation of precious stones. The Romans employed glass for various purposes; and have left specimens in Herculaneum of window-glass, which must have been blown by methods analogous to the modern. The Phenician processes seem to have been learned by the Crusaders, and transferred to Venice in the 13th century, where they were long held secret, and formed a lucrative commercial monopoly. Soon after the middle of the 17th century, Colbert enriched France with the blown mirror glass manufacture.

Chance undoubtedly had a principal share in the invention of this curious fabrication, but there were circumstances in the most ancient arts likely to lead to it; such as the fusing and vitrifying heats required for the formation of pottery, and for the extraction of metals from their ores. Pliny ascribes the origin of glass to the following accident. A merchant-ship laden with natron being driven upon the coast at the mouth of the river Belus, in tempestuous weather, the crew were compelled to cook their victuals ashore, and having placed lumps of the natron upon the sand, as supports to the kettles, found to their surprise masses of transparent stone among the cinders. The sand of this small stream of Galilee, which runs from the foot of Mount Carmel, was in consequence supposed to possess a peculiar virtue for making glass, and continued for ages to be sought after and exported to distant countries for this purpose.

Agricola, the oldest author who has written technically upon glass, describes furnaces and processes closely resembling those employed at the present day. Neri, Kunckel, Henckel, Pott, Achard, and some other chemists, have since then composed treatises upon the subject; but Neri, Bosc, Antic, Loysel, and Allut, in the Encyclopédie Méthodique, are the best of the elder authorities.

The window-glass manufacture was first begun in England in 1557, in Crutched Friars, London; and fine articles of flint-glass were soon afterwards made in the Savoy House, Strand. In 1635 the art received a great improvement from Sir Robert Mansell, by the use of coal fuel instead of wood. The first sheets of blown glass for looking glasses and coach windows were made in 1673 at Lambeth, by Venetian artisans employed under the patronage of the Duke of Buckingham.

The casting of mirror-plates was commenced in France about the year 1688, by Abraham Thevart; an invention which gave rise soon afterwards to the establishment of the celebrated works of St. Gobin, which continued for nearly a century the sole place where this highly prized object of luxury was well made. In excellence and cheapness, the French mirror-plate has been, however, for some time rivalled by the English.

The analysis of modern chemists, which will be detailed in the course of this article, and the light thrown upon the manufacture of glass in general by the accurate means now possessed of purifying its several ingredients, would have brought the art to the highest state of perfection in this country, but for the vexatious interference and obstructions of our excise laws.

The researches of Berzelius having removed all doubts concerning the acid character of silica, the general composition of glass presents now no difficulty of conception. This substance consists of one or more salts; which are silicates with bases of potash, soda, lime, oxide of iron, alumina, or oxide of lead; in any of which compounds we can substitute one of these bases for another, provided that one alkaline base be left. Silica in its turn may be replaced by the boracic acid, without causing the glass to lose its principal characters.

Under the title glass are therefore comprehended various substances fusible at a high temperature, solid at ordinary temperatures, brilliant, generally more or less transparent, and always brittle. The following chemical distribution of glasses has been proposed.

1. Soluble glass; a simple silicate of potash or soda; or of both these alkalis.

2. Bohemian or crown glass; silicate of potash and lime.

3. Common window and mirror glass; silicate of soda and lime; sometimes also of potash.

4. Bottle glass; silicate of soda, lime, alumina and iron.

5. Ordinary crystal glass; silicate of potash and lead.

6. Flint glass; silicate of potash and lead; richer in lead than the preceding.

7. Strass; silicate of potash and lead; still richer in lead.

8. Enamel; silicate and stannate or antimoniate of potash or soda, and lead.

The glasses which contain several bases are liable to suffer different changes when they are melted or cooled slowly. The silica is divided among these bases, forming new compounds in definite proportions, which by crystallizing, separate from each other, so that the general mixture of the ingredients which constituted glass is destroyed. It becomes then very hard, fibrous, opaque, much less fusible, a better conductor of electricity and of heat; forming what Reaumur styled devitrified glass; and what is called after him, Reaumur’s porcelain.

This altered glass can always be produced in a more or less perfect state, by melting the glass and allowing it to cool very slowly; or merely by heating it to the softening pitch, and keeping it at this heat for some time. The process succeeds best with the most complex vitreous compounds, such as bottle glass; next with ordinary window glass; and lastly with glass of potash and lead.

This property ought to be kept constantly in view in manufacturing glass. It shows why in making bottles we should fashion them as quickly as possible with the aid of a mould, and reheat them as seldom as may be absolutely necessary. If it be often heated and cooled, the glass loses its ductility, becomes refractory, and exhibits a multitude of stony granulations throughout its substance. When coarse glass is worked at the enameller’s lamp, it is apt to change its nature in the same way, if the workman be not quick and expert at his business.

From these facts we perceive the importance of making a careful choice of the glass intended to be worked in considerable masses, such as the large object glasses of telescopes; as their annealing requires a very slow process of refrigeration, which is apt to cause devitrified specks and clouds. For such purposes, therefore, no other species of glass is well adapted except that with basis of potash and lead; or that with basis of potash and lime. These two form the best flint glass, and crown glass; and they should be exclusively employed for the construction of the object glasses of achromatic telescopes.

GLASS-MAKING, general principles of. Glass may be defined in technical phraseology, to be a transparent homogeneous compound formed by the fusion of silica with oxides of the alkaline, earthy, or common metals. It is usually colourless, and then resembles rock crystal, but is occasionally stained by accident or design with coloured metallic oxides. At common temperatures it is hard and brittle, in thick pieces; in thin plates or threads, flexible and elastic; sonorous when struck; fracture conchoidal, and of that peculiar lustre called vitreous; at a red heat, becoming soft, ductile and plastic. Besides glass properly so called, other bodies are capable of entering into vitreous fusion, as phosphoric acid, boracic acid, arsenic acid, as also certain metallic oxides, as of lead, and antimony, and several chlorides; some of which are denominated glasses. Impure and opaque vitriform masses are called slags; such are the productions of blast iron furnaces and many metallurgic operations.

Silica, formerly styled the earth of flints, which constitutes the basis of all commercial glass, is infusible by itself in the strongest fire of our furnaces; but its vitreous fusion is easily effected by a competent addition of potash or soda, either alone or mixed with lime or litharge. The silica, which may be regarded as belonging to the class of acids, combines at the heat of fusion with these bases, into saline compounds; and hence glass may be viewed as a silicate of certain oxides, in which the acid and the bases exist in equivalent proportions. Were these proportions, or the quantities of the bases which silica requires for its saturation at the melting point, exactly ascertained, we might readily determine beforehand the best proportions of materials for the glass manufacture. But as this is far from being the case, and as it is, moreover, not improbable that the capacity of saturation of the silica varies with the temperature, and that the properties of glass also vary with the bases, we must, in the present state of our knowledge, regulate the proportions rather by practice than by theory, though the latter may throw an indirect light upon the subject. For example, a good colourless glass has been found by analysis to consist of 72 parts of silica, 13 parts of potash, and 10 parts of lime, in 95 parts. If we reduce these numbers to the equivalent ratios, we shall have the following results; taking the atomic weights as given by Berzelius.

1 atom potash = 590 14·67

1 lime 356 8·84

3 silica 1722 42·79 - 71·49

2 silica 1155 28·70

3823 95·00

This glass would therefore have been probably better compounded with the just atomic proportions, to which it nearly approaches, viz. 71·49 silica, 14·67 potash, and 8·84 lime, instead of those given above as its actual constituents.

The proportions in which silica unites with the alkaline and other oxides are modified by the temperature as above stated; the lower the heat, the less silica will enter into the glass, and the more of the base will in general be required. If a glass which contains an excess of alkali be exposed to a much higher temperature than that of its formation, a portion of the base will be set free to act upon the materials of the earthen pot, or to be dissipated in fumes, until such a silicate remains as to constitute a permanent glass corresponding to that temperature. Hence the same mixture of vitrifiable materials will yield very different results, according to the heats in which it is fused and worked in the glass-house; and therefore the composition should always be referrible to the going of the furnace. When a species of glass which at a high temperature formed a transparent combination with a considerable quantity of lime, is kept for some time in fusion at a lower temperature, a portion of the lime unites with the silica into another combination of a semi-vitreous or even of a stony aspect, so as to spoil the transparency of the glass altogether. There is probably a supersilicate, and a subsilicate formed in such cases; the latter being much the more fusible of the two compounds. The Reaumur’s porcelain produced by exposing bottle glass to a red heat for 24 hours, is an example of this species of vitreous change in which new affinities are exercised at a lower temperature. An excess of silica, caused by the volatilization of alkaline matter with too strong firing, will bring on similar appearances.

The specific gravity of glass varies from 2·3 to 3·6. That of least specific gravity consists of merely silica and potash fused together; that with lime is somewhat denser, and with oxide of lead denser still. Plate glass made from silica, soda, and lime, has a specific gravity which varies from 2·50 to 2·6; crystal or flint glass from 3·0 to 3·6.

The power of glass to resist the action of water, alkalis, acids, air, and light, is in general the greater, the higher the temperature employed in its manufacture, the smaller the proportion of its fluxes, and the more exact the equivalent ratios of its constituents. When glass contains too much alkali, it is partially soluble in water. Most crystal glass is affected by having water boiled in it for a considerable time; but crown glass being poorer in alkali, and containing no lead, resists that action much longer, and is therefore better adapted to chemical operations. The affinity of glass for water, or its hygrometric attraction, is also proportional to the quantity of alkali which it contains. In general also potash glass is more apt to become damp than soda glass, agreeably to the respective hygrometric properties of these two alkalis, and also to the smaller proportion of soda than of potash requisite to form glass.

Air and light operate upon glass probably by their oxidizing property. Bluish or greenish coloured glasses become by exposure colourless, in consequence undoubtedly of the peroxidizement of the iron, to whose protoxide they owe their tint; other glasses become purple red from the peroxidizement of the manganese. The glasses which contain lead, suffer another kind of change in the air, if sulphuretted hydrogen be present; the oxide of lead is converted into a sulphuret, with the effect of rendering the surface of the glass opaque and iridescent. The more lead is in the glass, the quicker does this iridescence supervene. By boiling concentrated sulphuric acid in a glass vessel, or upon glass, we can ascertain its power of resisting ordinary menstrua. Good glass will remain smooth and transparent; bad glass will become rough and dim.

The brittleness of unannealed glass by change of temperature is sometimes very great. I have known a thick vessel to fly by vicissitudes of the atmosphere alone. This defect may be corrected by slowly heating the vessel in salt-water or oil to the highest pitch consistent with the nature of these liquids, and letting it cool very slowly. Within the limits of that range of heat, it will, in consequence of this treatment, bear alternations of temperature without cracking as before.

It has been said that glass made from silica and alkalis alone, will not resist the action of water, but that the addition of a little lime is necessary for this effect. In general 100 parts of quartzose sand require 33 parts of dry carbonate of soda for their vitrification, and 45 parts of dry carbonate of potash. But to make unchangeable alkaline glass, especially with potash, a smaller quantity of this than the above should be used, with a very violent heat. A small proportion of lime increases the density, hardness, and lustre of glass; and it aids in decomposing the alkaline sulphates and muriates always present in the pearl ash of commerce. From 7 to 20 parts of dry slaked lime have been added for 100 of silica, with advantage, it is said, in some German glass manufactories, where the alkaline matter is soda; for potass does not assimilate well with the calcareous earth.

In many glass works on the Continent, sulphate of soda is the form under which alkaline matter is introduced into glass. This salt requires the addition of 8 per cent. of charcoal to decompose and dissipate its acid; a result which takes place at a high heat, without the addition of any lime. 88 pounds of quartz-sand, 44 pounds of dry glauber salt, and 3 pounds of charcoal, properly mixed and fused, afford a limpid, fluent, and workable glass; with the addition of 17 pounds of lime, these materials fuse more readily into a plastic mass. If less carbon be added, the fusion becomes more tedious. The two following formulæ afford good glauber salt glass.

1. 2.

Sand 100 60·3

Calcined sulphate of soda 50 26·8

Lime 20 10·8

Charcoal 2·65 2·1

The first mixture has been proved in the looking-glass manufactory of Neuhaus near Vienna, and the second by the experiments of Kirn. The fusion of the first requires 18, of the second 21 hours. The bluish-green tinge which these otherwise beautiful and brilliant glasses possess, is not removable by the ordinary means, such as manganese or arsenic, which decolour alkaline glass. When the sulphate of soda and charcoal are used in smaller proportions, the glass becomes more colourless. The tinge is no doubt owing to the sulphur combining with the oxide of sodium, in some such way as in the pigment ultramarine.

By a proper addition of galena (the native sulphuret of lead), to glauber salt and quartz sand, without charcoal, it is said a tolerably good crystal glass may be formed. The sulphuric acid of the salt is probably converted by the reaction of the sulphuret of lead into sulphurous acid gas, which is disengaged.

One atom of sulphuret of lead = 1495·67, is requisite to decompose 3 atoms of sulphate of soda = 2676. It is stated, on good authority, that a good colourless glass may be obtained by using glauber salt without charcoal, as by the following formula.

Quartz-sand 100 pounds

Calcined glauber salt 24

Lime 20

Cullet of soda glass 12

The melting heat must be continued for 26⁄2 hours. A small quantity of the sand is reserved to be thrown in towards the conclusion of the process, in order to facilitate the expulsion of air bubbles. The above mixture will bear to be blanched by the addition of manganese and arsenic. The decomposition of the salt is in this case effected by the lime, with which the sulphuric acid first combines, is then converted into sulphurous acid, and dissipated. Glass made in this way was found by analysis to consist of 79 parts of silica, 12 lime, and 9·6 soda, without any trace of gypsum or sulphuric acid.

Glauber salt is partially volatilized by the heat of the furnace, and acts upon the arch of the oven and the tops of the pots. This is best prevented by introducing at first into the pots the whole of the salt mixed with the charcoal, the lime, and one fourth part of the sand; fusing this mixture at a moderate heat, and adding gradually afterwards the remainder of the sand, increasing the temperature at the same time. If we put in the whole ingredients together, as is done with potash glass, the sand and lime soon fall to the bottom, while the salt rises to the surface, and the combination becomes difficult and unequal.

Sulphate of potash acts in the same way as sulphate of soda.

Muriate of soda also, according to Kirn, may be used as a glass flux with advantage. The most suitable proportions are 4 parts of potash, 2 of common salt, and 3 of lime, agreeably to the following compositions:—

1. 2.

Quartz-sand 60·0 75·1

Calcined carbonate of potash 17·8 19·1

Common salt 8·9 9·5

Lime 13·3 14·3

For No. 1., the melting heat must be 10 hours, which turns out a very pure, solid, good glass; for No. 2., 23 hours of the furnace are required. Instead of the potash, glauber salt may be substituted; the proportions being then 19·1 glauber salt, 9·5 muriate of soda, 14·3 lime, 75·1 sand, and 1·3 charcoal.

The oxide of lead is an essential constituent of the denser glasses, and may be regarded as replacing the lime, so as to form with the quartz-sand a silicate of lead. It assimilates best with purified pearl ash, on account of the freedom of this alkali from iron, which is present in most sodas.

Its atomic constitution may be represented as follows:—

Computation. Analysis.

Silicic acid 5 atoms = 2877· 59·19 59·20

Oxide of lead 1 = 1394· 5 28·68 28·20

Potash 1 = 590· 0 12·13 9·00

Oxides of iron and manganese — — 1·40

4861· 5 100·00 100·00

The above analysis by Berthier relates to a specimen of the best English crystal glass, perfectly colourless and free from air-bubbles. This kind of glass may however take several different proportions of potash and silica to the oxide of lead.

The composition of mirror plate, as made on the Continent, is as follows:—

White quartz-sand 300 pounds

Dry carbonate of soda 100

Lime slaked in the air 43

Cullet, or old glass 300

The manganese should not exceed one half per cent. of the weight of the soda.

Optical glass requires to be made with very peculiar care. It is of two different kinds; namely, crown glass and flint glass. The latter contains a considerable proportion of lead, in order to give it an increased dispersive power upon the rays of light, in proportion to its mean refractive power.

Optical crown glass should be perfectly limpid, and have so little colour, that a pretty thick piece of it may give no appreciable tinge to the rays of light. It should be exempt from striæ or veins as well as air-bubbles, and have not the slightest degree of milkiness. It should moreover preserve these qualities when worked in considerable quantities. Potash is preferable to soda for making optical crown glass, because the latter alkali is apt to make a glass which devitrifies and becomes opalescent, by long exposure to heat in the annealing process. A simple potash silicate would be free from this defect, but it would be too attractive of moisture, and apt to decompose eventually by the humidity of the atmosphere. It should therefore contain a small quantity of lime, and as little potash as suffices for making a perfect glass at a pretty high temperature. It is probably owing to the high heats used in the English crown glass works, and the moderate quantity of alkali (soda) which is employed, that our crown glass has been found to answer so well for optical purposes.

Practical details of the Manufacture of Glass.

The Venetians were the first in modern times who attained to any degree of excellence in the art of working glass, but the French became eventually so zealous of rivalling them, particularly in the construction of mirrors, that a decree was issued by the court of France, declaring not only that the manufacture of glass should not derogate from the dignity of a nobleman, but that nobles alone should be masters of glass-works. Within the last 30 or 40 years, Great Britain has made rapid advances in this important art, and at the present day her pre-eminence in every department hardly admits of dispute.

There are five different species of glass, each requiring a peculiar mode of fabrication, and peculiar materials: 1. The coarsest and simplest form of this manufacture is bottle glass. 2. Next to it in cheapness of material maybe ranked broad or spread window glass. An improved article of this kind is now made near Birmingham, under the name of British or German plate. 3. Crown glass comes next, or window glass, formed in large circular plates or discs. This glass is peculiar to Great Britain. 4. Flint glass, crystal glass, or glass of lead. 5. Plate or fine mirror glass.

The materials of every kind of glass are vitrified in pots made of a pure refractory clay; the best kind of which is a species of shale or slate clay dug out of the coal-formation near Stourbridge. It contains hardly any lime or iron, and consists of silica and alumina in nearly equal proportions. The masses are carefully picked, brushed, and ground under edge iron wheels of considerable weight, and sifted through sieves having 20 meshes in the square inch. This powder is moistened with water (best hot), and kneaded by the feet or a loam-mill into an uniform smooth paste. A large body of this dough should be made up at a time, and laid by in a damp cellar to ripen. Previously to working it into shapes, it should be mixed with about a fourth of its weight of cement of old pots, ground to powder. This mixture is sufficiently plastic, and being less contractile by heat, forms more solid and durable vessels. Glass-house pots have the figure of a truncated cone, with the narrow end undermost; those for bottle and window-glass, being open at top, about 30 inches diameter at bottom, 40 inches at the mouth, and 40 inches deep; but the flint-glass pots are covered in at top with a dome-cap, having a mouth at the side, by which the materials are introduced, and the glass is extracted. Bottle and crown-house pots are from 3 to 4 inches thick; those for flint-houses are an inch thinner, and of proportionally smaller capacity.

The well-mixed and kneaded dough is first worked upon a board into a cake for the bottom; over this the sides are raised, by laying on its edges rolls of clay above each other with much manual labour, and careful condensation. The clay is made into lumps, is equalized, and slapped much in the same way as for making Pottery. The pots thus fashioned must be dried very prudently, first in the atmospheric temperature, and finally in a stove floor, which usually borrows its heat directly from the glass-house. Before setting the pots in the furnace, they are annealed during 4 or 5 days, at a red heat in a small reverberatory vault, made on purpose. When completely annealed, they are transferred with the utmost expedition into their seat in the fire, by means of powerful tongs supported on the axle of an iron-wheel carriage frame, and terminating in a long lever for raising them and swinging them round. The pot-setting is a desperate service, and when unskilfully conducted without due mechanical aids, is the forlorn hope of the glass-founder.—Quæque ipse miserrima vidi. The celebrated chemist, Dr. Irvine, caught his last illness by assisting imprudently at this formidable operation. The working breast of the hot furnace must be laid bare so as to open a breach for the extraction of the faulty pot, and the insertion of the fresh one, both in a state of bright incandescence. It is frightful to witness the eyes and fuming visages of the workmen, with the blackening and smoking of their scorched woollen clothes, exposed so long to the direct radiations of the flame. A light mask and sack dress coated with tinfoil, would protect both their faces and persons from any annoyance, at a very cheap rate.

The glass-houses are usually built in the form of a cone, from 60 to 100 feet high, and from 50 to 80 feet in diameter at the base. The furnace is constructed in the centre of the area, above an arched or groined gallery which extends across the whole space, and terminates without the walls, in large folding doors. This cavern must be sufficiently high to allow labourers to wheel out the cinders in their barrows. The middle of the vaulted top is left open in the building, and is covered over with the grate-bars of the furnace.

1. Bottle glass.—The bottle-house and its furnace resemble nearly fig. 505. The furnace is usually an oblong square chamber, built of large fire-bricks, and arched over with fire-stone, a siliceous grit of excellent quality extracted from the coal measures of Newcastle. This furnace stands in the middle of the area; and has its base divided into three compartments. The central space is occupied by the grate-bars; and on either side is the platform or fire-brick siege, (seat,) raised about 12 inches above the level of the ribs upon which the pots rest. Each siege is about 3 feet broad.

In the sides of the furnace, semi-circular holes of about a foot diameter are left opposite to, and a little above the top of, each pot, called working holes, by which the workmen shovel in the materials, and take out the plastic glass. At each angle of the furnace there is likewise a hole of about the same size, which communicates with the calcining furnace of a cylindrical form, dome-shaped at top. The flame that escapes from the founding or pot-furnace is thus economically brought to reverberate on the raw materials of the bottle glass, so as to dissipate their carbonaceous or volatile impurities, and convert them into a frit. A bottle-house has generally eight other furnaces or fire-arches; of which six are used for annealing the bottles after they are blown, and two for annealing the pots, before setting them in the furnace.

The laws of this country till lately prohibited the use for making common bottles of any fine materials. Nothing but the common river sand, and soap-boilers’ waste, was allowed. About 3 parts of waste, consisting of the insoluble residuum of kelp, mixed with lime and a little saline substance, were used for 1 part of sand. This waste was first of all calcined in two of the fire arches or reverberatories reserved for that purpose, called the coarse arches, where it was kept at a red heat, with occasional stirring, from 24 to 30 hours, being the period of a journey or journée, in which the materials could be melted and worked into bottles. The roasted soap-waste was then withdrawn, under the name of ashes, from its arch, coarsely ground, and mixed with its proper proportion of sand. This mixture was now put into the fine arch, and calcined during the working journey, which extended to 10 or 12 hours. Whenever the pots were worked out, that frit was immediately transferred into them in its ignited state, and the founding process proceeded with such despatch that this first charge of materials was completely melted down in 6 hours, so that the pots might admit to be filled up again with the second charge of frit, which was founded in 4 hours more. The heat was briskly continued, and in the course of from 12 to 18 hours, according to the size of the pots, the quality of the fuel, and the draught of the furnace, the vitrification was complete. Before blowing the bottles, however, the glass must be left to settle, and to cool down to the blowing consistency, by shutting the cave doors and feeding holes, so as to exclude the air from the fire-grate and the bottom of the hearth. The glass or metal becomes more dense, and by its subsidence throws up the foreign lighter earthy and saline matters in the form of a scum on the surface, which is removed with skimming irons. The furnace is now charged with coal, to enable it to afford a working heat for 4 or 5 hours, at the end of which time more fuel is cautiously added, to preserve adequate heat for finishing the journey.

It is hardly possible to convey in words alone a correct idea of the manipulations necessary to the formation of a wine bottle; but as the manufacturers make no mystery of this matter, any person may have an opportunity of inspecting the operation. Six people are employed at this task; one, called a gatherer, dips the end of an iron tube, about five feet long, previously made red-hot, into the pot of melted metal, turns the rod round so as to surround it with glass, lifts it out to cool a little, and then dips and turns it round again; and so in succession till a ball is formed on its end sufficient to make the required bottle. He then hands it to the blower, who rolls the plastic lump of glass on a smooth stone or cast-iron plate, till he brings it to the very end of the tube; he next introduces the pear-shaped ball into an open brass or cast-iron mould, shuts this together by pressing a pedal with his foot, and holding his tube vertically, blows through it, so as to expand the cooling glass into the form of the mould. Whenever he takes his foot from the pedal-lever, the mould spontaneously opens out into two halves, and falls asunder by its bottom hinge. He then lifts the bottle up at the end of the rod, and transfers it to the finisher, who, touching the glass-tube at the end of the pipe with a cold iron, cracks off the bottle smoothly at its mouth-ring. The finished bottles are immediately piled up in the hot annealing arch, where they are afterwards allowed to cool slowly for 24 hours at least. See Bottle Mould.

2. Broad or spread window glass.—This kind of glass is called inferior window glass, in this country, because coarse in texture, of a wavy wrinkled surface, and very cheap, but on the Continent spread window glass, being made with more care, is much better than ours, though still far inferior in transparency and polish to crown glass, which has, therefore, nearly superseded its use among us. But Messrs. Chance and Hartley, of West Bromwich near Birmingham, have of late years mounted a spread-glass work, where they make British sheet glass, upon the best principles, and turn out an article quite equal, if not superior to any thing of the kind made either in France or Belgium. Their materials are those used in the crown-glass manufacture. The vitrifying mixture is fritted for 20 or 30 hours in a reverberatory arch, with considerable stirring and puddling with long-handled shovels and rakes; and the frit is then transferred by shovels while red hot, to the melting pots to be founded. When the glass is rightly vitrified, settled, and brought to a working heat, it is lifted out by iron tubes, as will be described under the article Crown Glass, blown into pears, which being elongated into cylinders, are cracked up along one side, parallel to the axis, by touching them with a cold iron dipped in water, and are then opened out into sheets. Glass cylinders are spread in France, and at West Bromwich, on a bed of smooth stone Paris-plaster, or laid on the bottom of a reverberatory arch; the cylinder being placed on its side horizontally, with the cracked line uppermost, gradually opens out, and flattens on the hearth. At one time, thick plates were thus prepared for subsequent polishing into mirrors; but the glass was never of very good quality; and this mode of making mirror-plate has accordingly been generally abandoned.

The spreading furnace or oven is that in which cylinders are expanded into tables or plates. It ought to be maintained at a brisk red heat, to facilitate the softening of the glass. The oven is placed in immediate connection with the annealing arch, so that the tables may be readily and safely transferred from the former to the latter. Sometimes the cylinders are spread in a large muffle furnace, in order to protect them from being tarnished by sulphureous and carbonaceous fumes.

Fig. 500. represents a ground plan of both the spreading and annealing furnace; fig. 501. is an oblong profile in the direction of the dotted line X X, fig. 500.

a is the fire-place; b b the canals or flues through which the flame rises into both furnaces; c the spreading furnace, upon whose sole is the spreading slab. d is the cooling and annealing oven; e e iron bars which extend obliquely across the annealing arch, and serve for resting the glass tables against, during the cooling. f f the channel along which the previously cracked cylinders are slid, so as to be gradually warmed; g the opening in the spreading furnace, for enabling the workmen to regulate the process; h a door in the annealing arch, for introducing the tools requisite for raising up and removing the tables.

In forming glass-plates by the extension of a cylinder into a plane, the workman first blows the lump of glass into the shape of an oblong pear, the length of which must be nearly equal to the length of the intended plate, and its diameter such, that the circumference when developed, will be equal to the breadth of the plate. He now rests the blowing-iron on a stool or iron bar, while an assistant with a pointed iron, pierces a hole into the extreme end of the pear, in the line of the blowing-pipe. This opening is then enlarged, by introducing the blade of a pair of spring-tongs, while the glass is turned round; and by skilful management, the end of the pear is eventually opened out into a cylindrical mouth. The workman next mounts upon a stool, and holds the blowing-iron perpendicularly. The blown cylinder is now cracked off, a punto rod of iron having been previously stuck to its one end, to form a spindle for working the other by. This rod has a flat disc on its end, or three prongs, which being dipped in melted glass, are applied to the mouth of the cylinder. By this as a handle, the glass cone is carried to the fire, and the narrow end being heated, is next opened by spring tongs, and formed into a cylinder of the same size as the other end. The cylinder thus equalized, is next cracked or slit down in its side with a pair of shears, laid on a smooth copper plate, detached from the iron rod, spread out by heat into a plane surface, and finally annealed. This series of transformations, is represented in fig. 502., at A, B, C, D, E, F, G, H.

Fig. 503. and 504. represent a Bohemian furnace in which excellent white window glass is founded. Fig. 503. is a longitudinal section of the glass and annealing furnace. Fig. 504. is the ground plan. a is the ash pit vaulted under the sole of the furnace; the fireplace itself is divided into three compartments; with a middle slab at d, which is hollowed in the centre, for collecting any spilt glass, and two hearth tiles or slabs b b. c c are the draught or air holes; e e are arches upon which the bearing slabs f f partly rest. In the middle between these arches, the flame strikes upwards upon the pots g g, placed as closely together as possible, for economy of room. h is the breast wall of the furnace; i, fig. 504., the opening through which the pots are introduced; it is bricked up as soon as they are set. k k, is the base of the cone or dome of the furnace; l l l, the working orifices, which are made larger or smaller according to the size of the glass articles to be made. m is the flue which leads to the annealing stove n, with an arched door. Exterior to this, there is usually a drying kiln not shown in the figure; and there are adjoining stoves called arches, for drying and annealing the new pots before they are set.

The cooling or annealing arch, or leer, is often built independent of the glass-house furnace, is then heated by a separate fire-place, and constructed like a very long reverberatory furnace. See Copper.

The leer pans or trays of sheet iron, are laid upon its bottom in an oblong series, and hooked to each other.

3. Crown-glass.—The crown-glass house with its furnace is represented in fig. 505., where the blowing operation is shewn on the one side of the figure, and the flashing on the other. The furnace is usually constructed to receive 4 or 6 pots, of such dimensions as to make about a ton of glass each at a time. There are, however, several subsidiary furnaces to a crown-house. 1. A reverberatory furnace or calcar, for calcining or fritting the materials; 2. a blowing furnace, for blowing the pear-shaped balls made at the pot-holes, into large globes; 3. a flashing furnace, and bottoming hole for communicating a softening heat, in expanding the globe into a circular plate; 4. the annealing arch for the finished tables; 5. the reverberatory oven for annealing the pots prior to their being set upon the founding siege.

The materials of crown glass used to be, fine sand, by measure 5 parts, or by weight 10; ground kelp by measure 11 parts, or by weight 16⁄2; but instead of kelp, soda ash is now generally employed. From 6 to 8 cwt. of sand, lime, and soda-ash, mixed together in wooden boxes with a shovel, are thrown on the sole of a large reverberatory, such as is represented in the article Copper. Here the mixture is well worked together, with iron paddles, flat shovels, and rakes with long handles; the area of this furnace being about 6 feet square, and the height 2 feet. The heat soon brings the materials to a pasty consistence, when they must be diligently turned over, to favour the dissipation of the carbon, sulphur, and other volatile matters of the kelp or soda ash, and to incorporate the fixed ingredients uniformly with the sand. Towards the end of 3 hours, the fire is considerably raised, and when the fourth hour has expired, the fritting operation is finished. The mass is now shovelled or raked out into shallow cast-iron square cases, smoothed down, and divided before it hardens by cooling, into square lumps, by cross sections with the spade. These frit-bricks are afterwards piled up in a large apartment for use; and have been supposed to improve with age, by the efflorescence of their saline constituents into carbonate of soda on their surface.

The founding-pots are filled up with these blocks of frit, and the furnace is powerfully urged by opening all the subterranean passages to its grate, and closing all the doors and windows of the glass-house itself. After 8 or 10 hours the vitrification has made such progress, and the blocks first introduced are so far melted down, that another charge of frit can be thrown in, and thus the pot is fed with frit till the proper quantity is used. In about 16 hours the vitrification of the frit has taken place, and a considerable quantity, amounting often to the cwt. of liquid saline matter floats over the glass. This salt is carefully skimmed off into iron pots with long ladles. It is called Sandiver or Glass-gall, and consists usually of muriate of soda, with a little sulphate. The pot is now ready for receiving the topping of cullet, which is broken pieces of window glass, to the amount of 3 or 4 cwt. This is shovelled in at short intervals; and as its pressure forces up the residuary saline matter, this is removed; for were it allowed to remain, the body of the glass would be materially deteriorated.

The heat is still continued for several hours till the glass is perfect, and the extrication of gas called the boil, which accompanies the fusion of crown glass, has nearly terminated, when the fire is abated, by shutting up the lower vault doors and every avenue to the grate, in order that the glass may settle fine. At the end of about 40 hours altogether, the fire being slightly raised by adding some coals, and opening the doors, the glass is carefully skimmed, and the working of the pots commences.

Before describing it, however, we may state that the marginal figure 506. shews the base of the crown-house cone, with the four open pots in two ranges on opposite sides of the furnace, sitting on their raised sieges, at each side of the grate. At one side of the base the door of the vault is shewn, and its course is marked by the dotted lines.

Detailed description of the crown-glass furnace, figs. 507. 508.—It is an oblong square, built in the centre of a brick cone, large enough to contain within it, two or three pots at each side of the grate room, which is either divided as shown in the plan, or runs the whole length of the furnace, as the manufacturer chooses. Fig. 507. is a ground plan, and fig. 508. a front elevation, of a six-pot furnace. 1, 2, 3, fig. 507., are the working holes for the purposes of ventilation, of putting in the materials, and of taking out the metal to be wrought. 4, 5, 6, 7, are pipe holes for warming the pipes before beginning to work with them. 8, 9, 10, are foot holes for mending the pots and sieges. 11 is a bar of iron for binding the furnace, and keeping it from swelling.

The arch is of an elliptic form; though a barrel arch, that is, an arch shaped like the half of a barrel cut longwise through the centre, is sometimes used. But this soon gives way when used in the manufacture of crown glass, although it does very well in the clay-furnace used for bottle houses.

The best stone for building furnaces is fire-stone, from Coxgreen in the neighbourhood of Newcastle. Its quality is a close grit, and it contains a greater quantity of talc than the common fire-stone, which seems to be the chief reason of its resisting the fire better. The great danger in building furnaces is, lest the cement at the top should give way with the excessive heat, and by dropping into the pots, spoil the metal. The top should therefore be built with stones only, as loose as they can hold together after the centres are removed, and without any cement whatever. The stones expand and come quite close together when annealing; an operation which takes from eight to fourteen days at most. There is thus less risk of any thing dropping from the roof of the furnace.

The inside of the square of the furnace is built either of Stourbridge fire-clay annealed, or the Newcastle fire-stone, to the thickness of sixteen inches. The outside is built of common brick about nine inches in thickness.

The furnace is thrown over an ash-pit, or cave as it is called, which admits the atmospheric air, and promotes the combustion of the furnace. This cave is built of stone until it comes beneath the grate room, when it is formed of fire-brick. The abutments are useful for binding and keeping the furnace together, and are built of masonry. The furnaces are stoutly clasped with iron all round, to keep them tight. In four-pot furnaces this is unnecessary, provided there be four good abutments.

Fig. 509. is an elevation of the flashing furnace. The outside is built of common brick, the inside of fire-brick, and the mouth or nose of Stourbridge fire-clay.

Fig. 510. is the annealing kiln. It is built of common brick, except round the grate room, where fire-brick is used.

Few tools are needed for blowing and flashing crown-glass. The requisite ball of plastic glass is gathered, in successive layers as for bottles, on the end of an iron tube, and rolled into a pear-shape, on a cast-iron plate; the workman taking care that the air blown into its cavity is surrounded with an equal body of glass, and if he perceives any side to be thicker than another, he corrects the inequality by rolling it on the sloping iron table called marver, (marbre). He now heats the bulb in the fire, and rolls it so as to form the glass upon the end of the tube, and by a dexterous swing or two he lengthens it, as shewn in I, fig. 511. To extend the neck of that pear, he next rolls it over a smooth iron rod, turned round in a horizontal direction, into the shape K, fig. 511. By further expansion at the blowing-furnace, he now brings it to the shape L, represented in fig. 511.

This spheroid having become cool and somewhat stiff, is next carried to the bottoming hole (like fig. 509.), to be exposed to the action of flame. A slight wall erected before one half of this hole, screens the workman from the heat, but leaves room for the globe to pass between it and the posterior wall. The blowing-pipe is made to rest a little way from the neck of the globe, on a hook fixed in the front wall; and thus may be made easily to revolve on its axis, and by giving centrifugal force to the globe, while the bottom of it, or part opposite to the pipe, is softened by the heat, it soon assumes the form exhibited in M, fig. 511.

In this state the flattened globe is removed from the fire, and its rod being rested on the casher box covered with coal cinders, another workman now applies the end of a solid iron rod tipped with melted glass, called a punto, to the nipple or prominence in the middle; and thus attaches it to the centre of the globe, while the first workman cracks off the globe by touching its tubular neck with an iron chisel dipped in cold water. The workman having thereby taken possession of the globe by its bottom or knobbed pole attached to his punty rod, he now carries it to another circular opening, where he exposes it to the action of moderate flame with regular rotation, and thus slowly heats the thick projecting remains of the former neck, and opens it slightly out, as shewn at N, in fig. 511. He next hands it to the flasher, who resting the iron rod in a hook placed near the side of the orifice A, fig. 509., wheels it rapidly round opposite to a powerful flame, till it assumes first the figure O, and finally that of a flat circular table.

The flasher then walks off with the table, keeping up a slight rotation as he moves along, and when it is sufficiently cool, he turns down his rod into a vertical position, and lays the table flat on a dry block of fire-clay, or bed of sand, when an assistant nips it off from the punto with a pair of long iron shears, or cracks it off with a touch of cold iron. The loose table or plate is lastly lifted up horizontally on a double pronged iron fork, introduced into the annealing arch fig. 510. and raised on edge; an assistant with a long-kneed fork preventing it from falling too rapidly backwards. In this arch a great many tables of glass are piled up in iron frames, and slowly cooled from a heat of about 600° to 100° F., which takes about 24 hours; when they are removed. A circular plate or table of about 5 feet diameter weighs on an average 9 pounds.

4. Flint glass.—This kind of glass is so called because originally made with calcined flints, as the siliceous ingredient. The materials at present employed in this country for the finest flint glass or crystal, are first, Lynn sand, calcined, sifted, and washed; second, an oxide of lead, either red lead or litharge; and third, pearl ash. The pearl ash of commerce must however be purified by digesting it in a very little hot water, which dissolves the carbonate of potash, and leaves the foreign salts, chiefly sulphate of potash, muriate of potash, and muriate of soda. The solution of the carbonate being allowed to cool and become clear in lead pans, is then run off into a shallow iron boiler, and evaporated to dryness. Nitre is generally added as a fourth ingredient of the body of the glass; and it serves to correct any imperfections which might arise from accidental combustible particles, or from the lead being not duly oxidized. The above four substances constitute the main articles; to which we may add arsenic and manganese, introduced in very small quantities, to purify the colour and clear up the transparency of the glass. The black oxide of manganese, when used in such quantity only as to peroxidize the iron of the sand, simply removes the green tinge caused by the iron; but if more manganese be added than accomplishes that purpose, it will give a purple tinge to the glass; and in fact, most manufacturers prefer to have an excess rather than a defect of manganese, since cut glass has its brilliancy increased by a faint lilac hue. The arsenic is supposed to counteract the injury arising from excess of manganese, but is itself very apt on the other hand to communicate some degree of opalescence, or at least, to impair the lustre of the glass. When too much manganese has been added, the purple tinge may indeed be removed by any carbonaceous matter, as by thrusting a wooden rod down into the liquid glass; but this cannot be done with good effect in practice, since the final purple tinge is not decided till the glass is perfectly formed, and then the introduction of charcoal would destroy the uniformity of the whole contents of the pot.

The raw materials of flint glass, are always mixed with about a third or a fourth of their weight of broken crystal of like quality; this mixture is thrown into the pot with a shovel; and more is added whenever the preceding portions by melting subside; the object being to obtain a pot full of glass, to facilitate the skimming off the impurities, and sandiver. The mouth of the pot is now shut, by applying clay-lute round the stopper, with the exception of a small orifice below, for the escape of the liquid saline matter. Flint glass requires about 48 hours for its complete vitrification, though the materials be more fusible than those of crown glass; in consequence of the contents of the pot being partially screened by its cover from the action of the fire, as also from the lower intensity of the heat.

Fig. 512. represents a flint glass house for 6 pots, with the arch or leer on one side for annealing the crystal ware. In fig. 513., the base of the cone is seen, and the glass pots in situ on their platform ranged round the central fire grate. The dotted line denotes the contour of the furnace, fig. 512.

Whenever the glass appears fine, and is freed from its air bubbles, which it usually is in about 36 hours, the heat is suffered to fall a little by closing the bottom valves, &c., that the pot may settle; but prior to working the metal, the heat is somewhat raised again.

It would be useless to describe the manual operations of fashioning the various articles of the flint-glass manufacture, because they are indefinitely varied to suit the conveniences and caprices of human society.

Every different flint-house has a peculiar proportion of glass materials. The following have been offered as good practical mixtures.

1. Fine white sand 300 parts.

Red lead or litharge 200

Refined pearl ashes 80

Nitre 20

Arsenic and manganese, a minute quantity.

In my opinion, the proportion of lead is too great in the above recipe, which is given on the authority of Mr. James Geddes, of Leith. The glass made with it would be probably yellowish, and dull.

2. Fine sand 50·5

Litharge 27·2

Refined pearl ashes (carbonate of potash, with 5 per cent. of water) 17·5

Nitre 4·8

100·0

To these quantities from 30 to 50 parts of broken glass or cullet are added; with about a two-thousandth part of manganese, and a three-thousandth part of arsenic. But manganese varies so extremely in its purity, and contains often so much oxide of iron, that nothing can be predicated as to its quantity previously to trial.

M. Payen, an eminent manufacturing chemist in France, says that the composition of crystal does not deviate much from the following proportions:—

Wood
fire. Coal
fire.

Siliceous sand 3 3

Minium 2 2 ⁄4

Carbonate of potash 1 ⁄2 1 ⁄3

I conceive that this glass contains too much lead and potash. Such a mixture will produce a dull metal, very attractive of moisture: defects to which the French crown-glass also is subject.

The flint-glass leer for annealing glass, is an arched gallery or large flue, about 36 feet long, 3 feet high, 4 wide; having its floor raised above 2 feet above the ground of the glass-house. The hot air and smoke of a fire-place at one end pass along this gallery, and are discharged by a chimney 8 or 10 feet short of the other end. On the floor of the vault, large iron trays are laid and hooked to each other in a series, which are drawn from the fire end towards the other by a chain, wound about a cylinder by a winch-handle projecting through the side. The flint-glass articles are placed in their hot state into the tray next the fire, which is moved onwards to a cooler station whenever it is filled, and an empty tray is set in its place. Thus, in the course of about 20 hours, the glass advances to the cool end thoroughly annealed.

Besides colourless transparent glass, which forms the most important part of this manufacture, various coloured glasses are made to suit the taste of the public. The taste at Paris was lately for opaline crystal; which may be prepared by adding to the above composition (No. 2.) phosphate of lime, or well burnt bone-ash in fine powder, washed, and dried. The article must be as uniform in thickness as possible, and speedily worked into shape, with a moderate heat. Oxide of tin, putty, was formerly used for making opalescent glass, but the lustre of the body was always impaired by its means.

Crystal vessels have been made recently of which the inner surface is colourless, and all the external facets coloured. Such works are easily executed. The end of the blowing-rod must be dipped first in the pot containing colourless glass, to form a bulb of a certain size, which being cooled a little is then dipped for an instant into the pot of coloured glass. The two layers are associated without intermixture; and when the article is finished in its form, it is white within and coloured without. Fluted lines somewhat deeply cut, pass through the coloured coat, and enter the colourless one; so that when they cross, their ends alone are coloured.

For some time past, likewise, various crystal articles have been exhibited in the market with coloured enamel-figures on their surface, or with white incrustations of a silvery lustre in their interior. The former are prepared by placing the enamel object in the brass mould, at the place where it is sought to be attached. The bulb of glass being put into the mould, and blown while very hot, the small plate of enamel gets cemented to the surface. For making the white argentine incrustations, small figures are prepared with an impalpable powder of dry porcelain paste, cemented into a solid by means of a little gypsum plaster. When these pieces are thoroughly dried, they are laid on the glass while it is red hot, and a large patch of very liquid glass is placed above it, so as to encase it and form one body with the whole. In this way the incrustation is completely enclosed; and the polished surface of the crystal which scarcely touches it, gives a brilliant aspect, pleasing to the eye.

An uniform flint-glass, free from striæ, or wreath, is much in demand for the optician. It would appear that such an article was much more commonly made by the English manufacturers many years ago, than at present; and that in improving the brilliancy of crystal-glass they have injured its fitness for constructing optical lenses, which depends not so much on its whiteness and lustre as on the layers of different densities being parallel to each other. The oxide of lead existing in certain parts of a potful of glass in greater proportion than in other parts, increases the density unequally in the same mass, so that the adjoining strata are often very different in this respect. Even a potful of pretty uniform glass, when it stands some time liquid, becomes eventually unequable by the subsidence of the denser portions; so that striæ and gelatinous appearances begin to manifest themselves, and the glass becomes of little value. Glass allowed to cool slowly in mass in the pot is particularly full of wreath; and if quickly refrigerated, that is in two or three hours, it is apt to split into a multitude of minute splinters, of which no use can be made. For optical purposes, the glass must be taken out in its liquid state, being gathered on the end of the iron rod from the central portion of a recently skimmed pot, after the upper layers have been worked off in general articles.

M. Guinand, of Brennets near Geneva, appears to have hit upon processes that furnished almost certainly pieces of flint-glass capable of forming good lenses of remarkable dimensions, even of 11 inches diameter; of adequate density and transparency, and nearly free from striæ. M. Cauchoix, the eminent French optician, says, that out of ten object glasses, 4 inches in diameter, made with M. Guinand’s flint-glass, eight or nine turned out very good, while out of an equal number of object glasses made of the flint-glass of the English and French manufactories, only one, or two at most, were found serviceable. The means by which M. Guinand arrived at these results have not been published. He has lately died, and it is not known whether his son be in possession of his secret.

An achromatic object glass for telescopes and microscopes consists of at least two lenses; the one made with glass of lead, or flint glass, and the other with crown glass; the former possessing a power of dispersing the coloured rays relatively to its mean refractive power, much greater than the latter; upon which principle, the achromatism of the image is produced, by re-uniting the different coloured rays into one focus. Flint glass to be fit for this delicate purpose must be perfectly homogeneous, or of uniform density throughout its substance, and free from wavy veins or wreathes; for every such inequality would occasion a corresponding inequality in the refraction and dispersion of the light; like what is perceived in looking through a thick and thin solution of gum Arabic imperfectly mixed. Three plans have been prescribed for obtaining homogeneous pieces of optical glass: 1. to lift a mass of it in large ladles, and let it cool in them; 2. to pour it out from the pots into moulds; 3. to allow it to cool in the pots, and afterwards to cut it off in horizontal strata. The last method, which is the most plausible, seldom affords pieces of uniform density, unless peculiar precautions have been adopted to settle the flint glass in uniform strata; because its materials are of such unequal density, the oxide of lead having a specific gravity of 8, and silica of 2·7, that they are apt to stand at irregular heights in the pots.

One main cause of these inequalities lies in the construction of the furnace, whereby the bottom of the pot is usually much less heated than the upper part. In a plate glass furnace the temperature of the top of the pot has been found to be 130° Wedgew., while that of the bottom was only 110°, constituting a difference of no less than 2610° F. The necessary consequence is that the denser particles which subside to the bottom, during the fusion of the materials, and after the first extrication of the gases, must remain there, not being duly agitated by the expansive force of caloric, acting from below upwards.

The preparation of the best optical glass is now made a great mystery by one or two proficients. The following suggestions, deduced from a consideration of principles, may probably lead to some improvements, if judiciously applied. The great object is to counteract the tendency of the glass of lead to distribute itself into strata of different densities; which may be effected either by mechanical agitation or by applying the greatest heat to the bottom of the pot. But however homogeneous the glass may be thereby made, its subsequent separation into strata of different densities must be prevented by rapid cooling and solidification. As the deeper the pots, the greater is the chance of unequal specific gravity in their contents, it would be advisable to make them wider and shallower than those in use for making ordinary glass. The intermixture may be effected either by lading the glass out of one pot into another in the furnace, and back again, with copper ladles, or by stirring it up with a rouser, then allowing it to settle for a short time, till it becomes clear and free from air bubbles. The pot may now be removed from the furnace, in order to solidify its contents in their homogeneous state; after which the glass may be broken in pieces, and be perfected by subjecting it to a second fusion; or what is easier and quicker, we may form suitable discs of glass without breaking down the potful, by lifting it out in flat copper ladles with iron shanks, and transferring the lumps after a little while into the annealing leer.

To render a potful of glass homogeneous by agitation, is a more difficult task, as an iron rod would discolour it, and a copper rod would be apt to melt. An iron rod sheathed in laminated platinum would answer well, but for its expense. A stone-ware tube supported within by a rod of iron, might also be employed for the purpose in careful hands; the stirring being repeated several times, till at last the glass is suffered to stiffen a little by decrease of temperature. It must be then allowed to settle and cool, after which the pot, being of small dimensions, may be drawn out of the fire.

2. The second method of producing the desired uniformity of mixture, consists in applying a greater heat to the bottom than to the upper part of the melting pot. Fig. 514. represents in section a furnace contrived to effect this object. It is cylindrical, and of a diameter no greater than to allow the flames to play round the pot, containing from three to four cwts. of vitreous materials. A is the pot, resting upon the arched grid b a, built of fire-bricks, whose apertures are wide enough to let the flames rise freely, and strike the bottom and sides of the vessel. From 1⁄2 to 2 feet under that arch, the fuel grate c d is placed. B C are the two working openings for introducing the materials, and inspecting the progress of the fusion; they must be closed with fire-tiles and luted with fire-clay at the beginning of the process. At the back of the furnace, opposite the mouth of the fire-place, there is a door-way, which is bricked up, except upon occasion of putting in and taking out the pot. The draught is regulated by means of a slide-plate upon the mouth of the ash-pit f. The pot being heated to the proper pitch, some purified pearl ash, mixed with fully twice its weight of colourless quartz sand, is to be thrown into it, and after the complete fusion of this mixture, the remaining part of the sand along with the oxide of lead (fine litharge) is to be strown upon the surface. These siliceous particles in their descent serve to extricate the air from the mass. Whenever the whole is fused, the heat must be strongly urged to ensure a complete uniformity of combination by the internal motions of the particles. As soon as the glass has been found by making test phials to be perfectly fine, the fire must be withdrawn, the two working holes must be opened, as well as the mouths of the fire-place and ash-pit, to admit free ingress to cooling currents of air, so as to congeal the liquid mass as quickly as possible; a condition essential to the uniformity of the glass. It may be worth while to stir it a little with the pottery rod at the commencement of the cooling process. The solidified glass may be afterwards detached by a hammer in conchoidal discs, which after chipping off their edges, are to be placed in proper porcelain or stone-ware dishes, and exposed to a softening heat, in order to give them a lenticular shape. Great care must be taken that the heat thus applied by the muffle furnace be very equable, for otherwise wreathes might be very readily re-produced in the discs. A small oven upon the plan of a baker’s, is best fitted for this purpose, which being heated to dull redness, and then extinguished, is ready to soften and afterwards anneal the conchoidal pieces.

Guinand’s dense optical flint glass, of specific gravity 3·616, consists by analysis, of oxide of lead 43·05; silica 44·3; and potash 11·75; but requires for its formation the following ingredients: 100 pounds of ground quartz; 100 pounds of fine red lead; 35 pounds of purified potash; and from 2 to 4 pounds of saltpetre. As this species of glass is injured by an excess of potash, it should be compounded with rather a defect of it, and melted by a proportionally higher or longer heat. A good optical glass has been made in Germany with 7 parts of pure red lead, 3 parts of finely ground quartz, and 2 parts of calcined borax.

5. Plate glass.

This, like English crown-glass, has a soda flux, whereas flint-glass requires potash, and is never of good quality when made with soda. We shall distribute our account of this manufacture under two heads.

1. The different furnaces and principal machines, without whose knowledge it would be impossible to understand the several processes of a plate-glass factory.

2. The materials which enter into the composition of this kind of glass, and the series of operations which they undergo; devoting our chief attention to the changes and improvements which long experience, enlightened by modern chemistry, has introduced into the great manufactory of Saint-Gobin in France, under the direction of M. Tassaert. It may however be remarked that the English plate-glass manufacture derives peculiar advantages from the excellence of its grinding and polishing machinery.

The clay for making the bricks and pots should be free from lime and iron, and very refractory. It is mixed with the powder of old pots passed through a silk sieve. If the clay be very plastic it will bear its own weight of the powder, but if shorter in quality, it will take only three-fifths. But before mingling it with the cement of old pots, it must be dried, bruised, then picked, ground, and finally elutriated by agitation with water, decantation through a hair sieve, and subsidence. The clay fluid after passing the sieve is called slip (coulis.)

The furnace is built of dry bricks, cemented with slip, and has at each of its four angles a peculiar annealing arch, which communicates with the furnace interiorly, and thence derives sufficient heat to effect in part, if not wholly, the annealing of the pots, which are always deposited there a long time before they are used. Three of these arches exclusively appropriated to this purpose, are called pot-arches. The fourth is called the arch of the materials, because it serves for drying them before they are founded. Each arch has, moreover, a principal opening called the throat, another called bonnard, by the French workmen, through which fire may be kindled in the arch itself, when it was thought to be necessary for the annealing of the pots; a practice now abandoned. The duration of a furnace is commonly a year, or at most 14 months; that of the arches is 30 years or upwards, as they are not exposed to so strong a heat.

In the manufacture of plate-glass two sorts of crucibles are employed, called the pots and the basins, (cuvettes). The first serve for containing the materials to be founded, and for keeping them a long time in the melted state. The cuvettes receive the melted glass after it is refined, and decant it out on the table to be rolled into a plate. Three pots hold liquid glass for six small basins, or for three large ones, the latter being employed for making mirrors of great dimensions, that is, 100 inches long and upwards. Furnaces have been lately constructed with 6 pots, and 12 cuvettes, 8 of which are small, and 4 large; and cuvettes of three sizes are made, called small, middling, and large. The small are perfect cubes, the middling and the large ones are oblong parallelopipeds. Towards the middle of their height, a notch or groove, two or three inches broad, and an inch deep, is left, called the girdle of the cuvette, by which part they are grasped with the tongs, or rather are clamped in the iron frame. This frame goes round the four sides of the small cuvettes, and may be placed indifferently upon all their sides; in the other cuvettes, the girdle extends only over the two large sides, because they cannot be turned up. See m T, fig. 515., p. 590.

The pot is an inverted truncated cone, like a crown glass pot. It is about 30 inches high, and from 30 to 32 inches wide, including its thickness. There is only a few inches of difference between the diameter of the top and that of the bottom. The bottom is 3 inches thick, and the body turns gradually thinner till it is an inch at the mouth of the pot.

The large building or factory, of which the melting furnace occupies the middle space, is called the halle in French. At Ravenhead in Lancashire it is called the foundry, and is of magnificent dimensions, being probably the largest apartment under one roof in Great Britain, since its length is 339 feet, and its breadth 155. The famous halle of St. Gobin is 174 feet by 120. Along the two side walls of the halle, which are solidly constructed of hewn stone, there are openings like those of common ovens. These ovens, destined for the annealing of the newly cast plates, bear the name of carquaises. Their soles are raised two feet and a half above the level of the ground, in order to bring them into the same horizontal plane with the casting tables. Their length, amounting sometimes to 30 feet, and their breadth to 20, are required in order to accommodate 6, 8, or even 10 plates of glass, alongside of each other. The front aperture is called the throat, and the back door the little throat (gueulette). The carquaise is heated by means of a fire-place of a square form called a tisar, which extends along its side.

The founding or melting furnace is a square brick building laid on solid foundations, being from 8 to 10 feet in each of its fronts, and rising inside into a vault or crown about 10 feet high. At each angle of this square, a small oven or arch is constructed, likewise vaulted within, and communicating with the melting furnace by square flues, called lunettes, through which it receives a powerful heat, though much inferior to that round the pots. The arches are so distributed as that two of the exterior sides of the furnace stand wholly free, while the two other sides, on which the arches encroach, offer a free space of only 3 feet. In this interjacent space, two principal openings of the furnace, of equal size in each side, are left in the building. These are called tunnels. They are destined for the introduction of the pots and the fuel.

On looking through the tunnels into the inside of the furnace, we perceive to the right hand and the left, along the two free sides, two low platforms or sieges, at least 30 inches in height and breadth. See figs. 506. 508.

These sieges (seats) being intended to support the pots and the cuvettes filled with heavy materials, are terminated by a slope, which ensures the solidity of the fire-clay mound. The slopes of the two sieges extend towards the middle of the furnace so near as to leave a space of only from 6 to 10 inches between them for the hearth. The end of this is perforated with a hole sufficiently large to give passage to the liquid glass of a broken pot, while the rest is preserved by lading it from the mouth into the adjoining cuvette.

In the two large parallel sides of the furnace, other apertures are left much smaller than the tunnels, which are called ouvreaux (peep holes). The lower ones, or the ouvreaux en bas, called cuvette openings, because being allotted to the admission of these vessels, they are exactly on a level with the surface of the sieges, and with the floor of the halle. Plates of cast iron form the thresholds of these openings, and facilitate the ingress and egress of the cuvettes. The apertures are arched at top, with hewn stone like the tunnels, and are 18 inches wide when the cuvettes are 16 inches broad.

The upper and smaller apertures, or the higher ouvreaux called the lading holes, because they serve for transvasing the liquid glass, are three in number, and are placed 31 or 32 inches above the surface of the sieges. As the pots are only 30 inches high, it becomes easy to work through these openings either in the pots or the cuvettes. The pots stand opposite to the two pillars which separate the openings, so that a space is left between them for one or more cuvettes according to the size of the latter. It is obvious that if the tunnels and ouvreaux were left open, the furnace would not draw or take the requisite founding heat. Hence the openings are shut by means of fire-tiles. These are put in their places, and removed by means of two holes left in them, in correspondence with the two prongs of a large iron fork supported by an axle and two iron wheels, and terminated by two handles which the workmen lay hold of when they wish to move the tile.

The closing of the tunnel is more complex. When it is shut or ready for the firing, the aperture appears built up with bricks and mortar from the top of the arch to the middle of the tunnel. The remainder of the door-way is closed; 1. on the two sides down to the bottom, by a small upright wall, likewise of bricks, and 8 inches broad, called walls of the glaye; 2. by an assemblage of pieces called pieces of the glaye, because the whole of the closure of the tunnel bears the name of glaye. The upper hole, 4 inches square, is called the tisar, through which billets of wood are tossed into the fire. Fuel is also introduced into the posterior openings. The fire is always kept up on the hearth of the tunnel, which is, on this account, 4 inches higher than the furnace-hearth, in order that the glass which may accidentally fall down on it, and which does not flow off by the bottom hole, may not impede the combustion. Should a body of glass, however, at any time obstruct the grate, it must be removed with rakes, by opening the tunnel and dismounting the fire-tile stoppers of the glaye.

Formerly wood fuel alone was employed for heating the melting-furnaces of the mirror-plate manufactory of Saint-Gobin; but within these few years, the Director of the works makes use with nearly equal advantage of pit-coal. In the same establishment, two melting furnaces may be seen, one of which is fixed with wood, and the other with coals, without any difference being perceptible in the quality of the glass furnished by either. It is not true, as has been stated, that the introduction of pit-coal has made it necessary to work with covered pots in order to avoid the discoloration of the materials, or that more alkali was required to compensate for the diminished heat in the covered pots. They are not now covered when pit-coal is used, and the same success is obtained as heretofore by leaving the materials two or three hours longer in the pots and the cuvettes. The construction of the furnaces in which coal is burned, is the same as that with wood, with slight modifications. Instead of the close bottomed hearth of the wood furnace, there is an iron grate in the coal-hearth through which the air enters, and the waste ashes descend.

When billets of wood were used as fuel, they were well dried beforehand, by being placed a few days on a frame work of wood called the wheel, placed two feet above the furnace and its arches, and supported on four pillars at some distance from the angles of the building.

Composition of plate-glass.—This is not made now, as formerly, by random trials. The progress of chemistry, the discovery of a good process for the manufacture of soda from sea salt, which furnishes a pure alkali of uniform power, and the certain methods of ascertaining its purity, have rendered this department of glass-making almost entirely new, in France. At Saint-Gobin no alkali is employed at present except artificial crystals of soda, prepared at the manufactory of Chauny, subsidiary to that establishment. Leaden chambers are also erected there for the production of sulphuric acid from sulphur. The first crop of soda crystals is reserved for the plate-glass manufacture, the other crystals and the mother-water salts are sold to the makers of inferior glass.

At the mirror-plate works of Ravenhead, near St. Helen’s in Lancashire, soda crystals, from the decomposition of the sulphate of soda by chalk and coal, have been also tried, but without equal success as at Saint-Gobin; the failure being unquestionably due to the impurity of the alkali. Hence, in the English establishment the soda is obtained by treating sea-salt with pearl-ash, whence carbonate of soda and muriate of potash result. The latter salt is crystallized out of the mingled solution, by evaporation at a moderate heat, for the carbonate of soda does not readily crystallize till the temperature of the solution fall below 60° Fahr. When the muriate of potash is thus removed, the alkaline carbonate is evaporated to dryness.

Long experience at Saint-Gobin has proved that one part of dry carbonate of soda is adequate to vitrify perfectly three parts of fine siliceous sand, as that of the mound of Aumont near Senlis, of Alum Bay in the Isle of Wight, or of Lynn in Norfolk. It is also known that the degree of heat has a great influence upon the vitrification, and that increase of temperature will compensate for a certain deficiency of alkali; for it is certain that a very strong fire always dissipates a good deal of the soda, and yet the glass is not less beautiful. The most perfect mirror-plate has constantly afforded to M. Vauquelin in analysis, a portion of soda inferior to what had been employed in its formation. Hence, it has become the practice to add for every 100 parts of cullet or broken plate that is mixed with the glass composition, one part of alkali, to make up for the loss that the old glass must have experienced.

To the above mentioned proportions of sand and alkali independently of the cullet which may be used, dry slaked lime carefully sifted is to be added to the amount of one seventh of the sand; or the proportion will be, sand 7 cwt.; quicklime 1 cwt.; dry carbonate of soda 2 cwt. and 37 lbs.; besides cullet. The lime improves the quality of the glass, rendering it less brittle and less liable to change. The preceding quantities of materials suitably blended, have been uniformly found to afford most advantageous results. The practice formerly was to dry that mixture, as soon as it was made, in the arch for the materials, but it has been ascertained that this step may be dispensed with, and the small portion of humidity present is dissipated almost instantly after they are thrown into the furnace. The coat of glaze previously applied to the inside of the pot, prevents the moisture from doing them any harm. For this reason, when the demand for glass at Saint-Gobin is very great, the materials are neither fritted nor even dried, but shovelled directly into the pot; this is called founding raw. Six workmen are employed in shovelling-in the materials either fritted or otherwise, for the sake of expedition, and to prevent the furnace getting cooled. One-third of the mixture is introduced at first; whenever this is melted, the second third is thrown in, and then the last. These three stages are called the first, second, and third fusion or founding.

According to the ancient practice, the founding and refining were both executed in the pots, and it was not till the glass was refined, that it was laded into the cuvettes, where it remained only 3 hours, the time necessary for the disengagement of the air bubbles introduced by the transvasion, and for giving the metal the proper consistence for casting. At present, the period requisite for founding and refining, is equally divided between the pots and the cuvettes. The materials are left 16 hours in the pots, and as many in the cuvettes; so that in 32 hours, the glass is ready to be cast. During the last two or three hours, the fireman or tiseur ceases to add fuel; all the openings are shut, and the glass is allowed to assume the requisite fluidity; an operation called stopping the glass, or performing the ceremony.

The transfer of the glass into the cuvettes, is called lading, (tréjetage). Before this is done, the cuvettes are cleared out, that is, the glass remaining on their bottom, is removed, and the ashes of the firing. They are lifted red hot out of the furnace by the method presently to be described, and placed on an iron plate, near a tub filled with water. The workmen, by means of iron paddles 6 feet long, flattened at one end and hammered to an edge, scoop out the fluid glass expeditiously, and throw it into water; the cuvettes are now returned to the furnace, and a few minutes afterwards the lading begins.

In this operation, ladles of wrought iron are employed, furnished with long handles, which are plunged into the pots through the upper openings or lading holes, and immediately transfer their charge of glass into the buckets. Each workman dips his ladle only three times, and empties its contents into the cuvette. By these three immersions (whence the term tréjeter is derived), the large iron spoon is heated so much that when plunged into a tub full of water, it makes a noise like the roaring of a lion, which may be heard to a very great distance.

The founding, refining, and ceremony, being finished, they next try whether the glass be ready for casting. With this view, the end of a rod is dipped into the bucket, which is called drawing the glass, the portion taken up being allowed to run off, naturally assumes a pear-shape, from the appearance of which, they can judge if the consistence be proper, and if any air bubbles remain. If all be right, the cuvettes are taken out of the furnace, and conveyed to the part of the halle where their contents are to be poured out. This process requires peculiar instruments and manipulations.

Casting.—While the glass is refining, that is, coming to its highest point of perfection, preparation is made for the most important process, the casting of the plate, whose success crowns all the preliminary labours and cares. The oven or carquaise destined to receive and anneal the plate, is now heated by its small fire or tisar, to such a pitch that its sole may have the same temperature as that of the plates, being nearly red-hot at the moment of their being introduced. An unequal degree of heat in the carquaise would cause breakage of the glass. The casting table is then rolled towards the front door or throat, by means of levers, and its surface is brought exactly to the level of the sole of the oven.

The table T, fig. 515., is a mass of bronze, or now preferably cast-iron, about 10 feet long, 5 feet broad, and from 6 to 7 inches thick, supported by a frame of carpentry, which rests on three cast-iron wheels. At the end of the table opposite to that next to the front of the oven, is a very strong frame of timber-work, called the puppet or standard, upon which the bronze roller which spreads the glass is laid, before and after the casting. This is 5 feet long by 1 foot in diameter; it is thick in the metal but hollow in the axis. The same roller can serve only for two plates at one casting, when another is put in its place, and the first is laid aside to cool; for otherwise the hot roller would at a third casting, make the plate expand unequally, and cause it to crack. When the rollers are not in action, they are laid aside in strong wooden trestles, like those employed by sawyers. On the two sides of the table in the line of its length, are two parallel bars of bronze, t, t, destined to support the roller during its passage from end to end; the thickness of these bars determines that of the plate. The table being thus arranged, a crane is had recourse to for lifting the cuvette, and keeping it suspended, till it be emptied upon the table. This raising and suspension are effected by means of an iron gib, furnished with pullies, held horizontally, and which turns with them.

The tongs T, fig. 515., are made of four iron bars, bent into a square frame in their middle, for embracing the bucket. Four chains proceeding from the corners of the frame V, are united at their other ends into a ring which fits into the hook of the crane.

Things being thus arranged, all the workmen of the foundry co-operate in the manipulations of the casting. Two of them fetch, and place quickly in front of one of the lower openings, the small cuvette-carriage, which bears a forked bar of iron, having two prongs corresponding to the two holes left in the fire-tile door. This fork mounted on the axle of two cast-iron wheels, extends at its other end into two branches terminated by handles, by which the workmen move the fork, lift out the tile stopper, and set it down against the outer wall of the furnace.

The instant these men retire, two others push forward into the opening the extremity of the tongs-carriage, so as to seize the bucket by the girdle, or rather to clamp it. At the same time, a third workman is busy with an iron pinch or long chisel, detaching the bucket from its seat, to which it often adheres by some spilt glass; whenever it is free, he withdraws it from the furnace. Two powerful branches of iron united by a bolt, like two scissor blades, which open, come together, and join by a quadrant near the other end, form the tongs-carriage, which is mounted upon two wheels like a truck.

The same description will apply almost wholly to the iron-plate carriage, on which the bucket is laid the moment it is taken out of the furnace; the only difference in its construction is, that on the bent iron bars which form the tail or lower steps of this carriage (in place of the tongs) is permanently fastened an iron plate, on which the bucket is placed and carried for the casting.

Whenever the cuvette is set upon its carriage, it must be rapidly wheeled to its station near the crane. The tongs T above described are now applied to the girdle, and are then hooked upon the crane by the suspension chains. In this position the bucket is skimmed by means of a copper tool called a sabre, because it has nearly the shape of that weapon. Every portion of the matter removed by the sabre is thrown into a copper ladle (poche de gamin), which is emptied from time to time into a cistern of water. After being skimmed, the bucket is lifted up, and brushed very clean on its sides and bottom; then by the double handles of the suspension-tongs it is swung round to the table, where it is seized by the workmen appointed to turn it over; the roller having been previously laid on its ruler-bars, near the end of the table which is in contact with the annealing oven. The cuvette-men begin to pour out towards the right extremity E of the roller, and terminate when it has arrived at the left extremity D. While preparing to do so, and at the instant of casting, two men place within the ruler-bar on each side, that is between the bar and the liquid glass, two iron instruments called hands, m, m, m, m, which prevent the glass from spreading beyond the rulers, whilst another draws along the table the wiping bar c, c, wrapped in linen, to remove dust, or any small objects which may interpose between the table and the liquid glass.

Whenever the melted glass is poured out, two men spread it over the table, guiding the roller slowly and steadily along, beyond the limits of the glass, and then run it smartly into the wooden standard prepared for its reception, in place of the trestles V, V.

The empty bucket, while still red-hot, is hung again upon the crane, set on its plate-iron carriage, freed from its tongs, and replaced in the furnace, to be speedily cleared out anew, and charged with fresh fluid from the pots. If while the roller glides along, the two workmen who stand by with picking tools, perceive tears in the matter in advance of the roller, and can dexterously snatch them out, they are suitably rewarded, according to the spot where the blemish lay, whether in the centre, where it would have proved most detrimental, or near the edge. These tears proceed usually from small portions of semi-vitrified matter which fall from the vault of the furnace, and from their density occupy the bottom of the cuvettes.

While the plate is still red-hot and ductile, about 2 inches of its end opposite to the carquaise door is turned up with a tool; this portion is called the head of the mirror; against the outside of this head, the shovel, in the shape of a rake without teeth, is applied, with which the plate is eventually pushed into the oven, while two other workmen press upon the upper part of the head with a wooden pole, eight feet long, to preserve the plate in its horizontal position, and prevent its being warped. The plate is now left for a few moments near the throat of the carquaise, to give it solidity; after which it is pushed further in by means of a very long iron tool, whose extremity is forked like the letter y, and hence bears that name; and is thereby arranged in the most suitable spot for allowing other plates to be introduced.

However numerous the manipulations executed from the moment of withdrawing the cuvette from the furnace, till the cast-plate is pushed into the annealing oven, I have seen them all performed in less than five minutes; such silence, order, regularity, and despatch prevail in the establishment of Saint-Gobin.

When all the plates of the same casting have been placed in the carquaise, it is sealed up, that is to say, all its orifices are closed with sheets of iron, surrounded and made tight with plastic loam. With this precaution, the cooling goes on slowly and equably in every part, for no cooling current can have access to the interior of the oven.

After they are perfectly cooled, the plates are carefully withdrawn one after another, keeping them all the while in a horizontal position, till they are entirely out of the carquaise. As soon as each plate is taken out, one set of workmen lower quickly and steadily the edge which they hold, while another set raise the opposite edge, till the glass be placed upright on two cushions stuffed with straw, and covered with canvas. In this vertical position they pass through, beneath the lower edge of the plate, three girths or straps each four feet long, thickened with leather in their middle, and ending in wooden handles; so that one embraces the middle of the plate, and the other two, the ends. The workmen, six in number, now seize the handles of the straps, lift up the glass closely to their bodies, and convey it with a regular step to the warehouse. Here the head of the plate is first cut off with a diamond square, and then the whole is attentively examined, in reference to its defects and imperfections, to determine the sections which must be made of it, and the eventual size of the pieces. The pairings and small cuttings detached are set aside, in order to be ground and mixed with the raw materials of another glass-pot.

The apartment in which the roughing-down and smoothing of the plates is performed, is furnished with a considerable number of stone tables, truly hewn and placed apart like billiard tables, in a horizontal position, about 2 feet above the ground. They are rectangular, and of different sizes proportional to the dimensions of the plates, which they ought always to exceed a little. These tables are supported either on stone pillars or wooden frames, and are surrounded with a wooden board whose upper edge stands somewhat below their level, and leaves in the space between it and the stone all round an interval of 3 or 4 inches, of which we shall presently see the use.

A cast plate, unless formed on a table quite new, has always one of its faces, the one next the table, rougher than the other; and with this face the roughing-down begins. With this view, the smoother face is cemented on the stone table with Paris-plaster. But often instead of one plate, several are cemented alongside of each other, those of the same thickness being carefully selected. They then take one or more crude plates of about one-third or one-fourth the surface of the plate fixed to the table, and fix it on them with liquid gypsum to the large base of a quadrangular truncated pyramid of stone; of a weight proportioned to its extent, or about a pound to the square inch. This pyramidal muller, if small sized, bears at each of its angles of the upper face a peg or ball, which the grinders lay hold of in working it; but when of greater dimension, there is adapted to it horizontally a wheel of slight construction, 8 or 10 feet in diameter, whose circumference is made of wood rounded so as to be seized with the hand. The upper plate is now rubbed over the lower ones, with moistened sand applied between.

This operation is however performed by machinery. The under plate being fixed or imbedded in stucco, on a solid table, the upper one likewise imbedded by the same cement in a cast-iron frame, has a motion of circum-rotation given to it closely resembling that communicated by the human hand and arm, moist sand being supplied between them. While an excentric mechanism imparts this double rotatory movement to the upper plate round its own centre, and of that centre round a point in the lower plate, this plate placed on a moveable platform changes its position by a slow horizontal motion, both in the direction of its length and its breadth. By this ingenious contrivance, which pervades the whole of the grinding and polishing machinery, a remarkable regularity of friction and truth of surface is produced. When the plates are sufficiently worked on one face, they are reversed in the frames, and worked together on the other. The Paris plaster is usually coloured red, in order to shew any defects in the glass.

The smoothing of the plates is effected on the same principles by the use of moist emery washed to successive degrees of fineness, for the successive stages of the operation; and the polishing process is performed by rubbers of hat-felt and a thin paste of colcothar and water. The colcothar, called also crocus, is red oxide of iron prepared by the ignition of copperas, with grinding and elutriation of the residuum.

The last part of the polishing process is performed by hand. This is managed by females, who slide one plate over another, while a little moistened putty of tin finely levigated is thrown between.

Large mirror-plates are now the indispensable ornaments of every large and sumptuous apartment; they diffuse lustre and gaiety round them, by reflecting the rays of light in a thousand lines, and by multiplying indefinitely the images of objects placed between opposite parallel planes.

The silvering of plane mirrors consists in applying a layer of tin-foil alloyed with mercury to their posterior surface. The workshop for executing this operation is provided with a great many smooth tables of fine freestone or marble, truly levelled, having round their contour a rising ledge, within which there is a gutter or groove which terminates by a slight slope in a spout at one of the corners. These tables rest upon an axis of wood or iron which runs along the middle of their length; so that they may be inclined easily into an angle with the horizon of 12 or 13 degrees, by means of a hand-screw fixed below. They are also furnished with brushes, with glass rules, with rolls of woollen stuff, several pieces of flannel, and a great many weights of stone or cast-iron.

The glass-tinner, standing towards one angle of his table, sweeps and wipes its surface with the greatest care, along the whole surface to be occupied by the mirror-plate; then taking a sheet of tin-foil adapted to his purpose, he spreads it on the table, and applies it closely with a brush, which removes any folds or wrinkles. The table being horizontal, he pours over the tin a small quantity of quicksilver, and spreads it with a roll of woollen stuff; so that the tin-foil is penetrated and apparently dissolved by the mercury. Placing now two rules, to the right and to the left, on the borders of the sheet, he pours on the middle a quantity of mercury sufficient to form every where a layer about the thickness of a crown piece; then removing with a linen rag the oxide or other impurities, he applies to it the edge of a sheet of paper, and advances it about half an inch. Meanwhile another workman is occupied in drying very nicely the surface of the glass that is to be silvered, and then hands it to the master workman, who, laying it flat, places its anterior edge first on the table, and then on the slip of paper; now pushing the glass forwards, he takes care to slide it along so that neither air nor any coat of oxide on the mercury can remain beneath the plate. When this has reached its position, he fixes it there by a weight applied on its side, and gives the table a gentle slope, to run off all the loose quicksilver by the gutter and spout. At the end of five minutes he covers the mirror with a piece of flannel, and loads it with a great many weights, which are left upon it for 24 hours, under a gradually increased inclination of the table. By this time the plate is ready to be taken off the marble table, and laid on a wooden one sloped like a reading desk, with its under edge resting on the ground, while the upper is raised successively to different elevations by means of a cord passing over a pulley in the ceiling of the room. Thus the mirror has its slope graduated from day to day, till it finally arrives at a vertical position. About a month is required for draining out the superfluous mercury from large mirrors; and from 18 to 20 days from those of moderate size. The sheets of tin-foil being always somewhat larger than the glass-plate, their edges must be pared smooth off, before the plate is lifted off the marble table.

Process for silvering concave mirrors.—Having prepared some very fine Paris plaster by passing it through a silk sieve, and some a little coarser passed through hair-cloth, the first is to be made into a creamy liquor with water, and after smearing the concave surface of the glass with a film of olive oil, the fine plaster is to be poured into it, and spread by turning about, till a layer of plaster be formed about a tenth of an inch thick. The second or coarse plaster, being now made into a thin paste, poured over the first, and moved about, readily incorporates with it, in its imperfectly hardened state. Thus an exact mould is obtained of the concave surface of the glass, which lies about three-quarters of an inch thick upon it, but is not allowed to rise above its outer edge.

The mould being perfectly dried, must be marked with a point of coincidence on the glass, in order to permit of its being exactly replaced in the same position, after it has been lifted out. The mould is now removed, and a round sheet of tin-foil is applied to it, so large that an inch of its edge may project beyond the plaster all round; this border being necessary for fixing the tin to the contour of the mould by pellets of white wax softened a little with some Venice turpentine. Before fixing the tin-foil, however, it must be properly spread over the mould, so as to remove every wrinkle; which the pliancy of the foil easily admits of, by uniform and well-directed pressure with the fingers.

The glass being placed in the hollow bed of a tight sack filled with fine sand, set in a well-jointed box capable of retaining quicksilver, its concave surface must be dusted with sifted wood-ashes, or Spanish white contained in a small cotton bag, and then well wiped with clean linen rags, to free it from all adhering impurity, and particularly the moisture of the breath. The concavity must be now filled with quicksilver to the very lip, and the mould being dipped a little way into it, is withdrawn, and the adhering mercury is spread over the tin with a soft flannel roll, so as to amalgamate and brighten its whole surface, taking every precaution against breathing on it. Whenever this brightening seems complete, the mould is to be immersed, not vertically, but one edge at first, and thus obliquely downwards till the centres coincide; the mercury meanwhile being slowly displaced, and the mark on the mould being brought finally into coincidence with the mark on the glass. The mould is now left to operate by its own weight, in expelling the superfluous mercury, which runs out upon the sand-bag and thence into a groove in the bottom of the box, whence it overflows by a spout into a leather bag of reception. After half an hour’s repose, the whole is cautiously inverted, to drain off the quicksilver more completely. For this purpose, a box like the first is provided with a central support rising an inch above its edges; the upper surface of the support being nearly equal in diameter to that of the mould. Two workmen are required to execute the following operation. Each steadies the mould with the one hand, and raises the box with the other, taking care not to let the mould be deranged, which they rest on the (convex) support of the second box. Before inverting the first apparatus, however, the reception bag must be removed, for fear of spilling its mercury. The redundant quicksilver now drains off; and if the weight of the sand-bag is not thought sufficient, supplementary weights are added at pleasure. The whole is left in this position for two or three days. Before separating the mirror from its mould, the border of tin-foil, fixed to it with wax, must be pared off with a knife. Then the weight and sand-bag being removed, the glass is lifted up with its interior coating of tin-amalgam.

For silvering a convex surface.—A concave plaster mould is made on the convex glass, and their points of coincidence are defined by marks. This mould is to be lined with tin-foil, with the precautions above described; and the tin surface being first brightened with a little mercury, the mould is then filled with the liquid metal. The glass is to be well cleaned, and immersed in the quicksilver bath, which will expel the greater part of the metal. A sand-bag is now to be laid on the glass, and the whole is to be inverted as in the former case on a support; when weights are to be applied to the mould, and the mercury is left to drain off for several days.

If the glass be of large dimensions, 30 or 40 inches, for example, another method is adopted. A circular frame or hollow ring of wood or iron is prepared, of twice the diameter of the mirror, supported on three feet. A circular piece of new linen cloth of close texture is cut out, of equal diameter to the ring, which is hemmed stoutly at the border, and furnished round the edge with a row of small holes, for lacing the cloth to the ring, so as to leave no folds in it, but without bracing it so tightly as to deprive it of the elasticity necessary for making it into a mould. This apparatus being set horizontally, a leaf of tin-foil is spread over it, of sufficient size to cover the surface of the glass; the tin is first brightened with mercury, and then as much of the liquid metal is poured on as a plane mirror requires. The convex glass, well cleaned, is now set down on the cloth, and its own weight, joined to some additional weights, gradually presses down the cloth, and causes it to assume the form of the glass which thus comes into close contact with the tin submersed under the quicksilver. The redundant quicksilver is afterwards drained off by inversion, as in common cases.

The following recipe has been given for silvering the inside of glass globes. Melt in an iron ladle or a crucible, equal parts of tin and lead, adding to the fused alloy one part of bruised bismuth. Stir the mixture well and pour into it as it cools two parts of dry mercury; agitating anew and skimming off the drossy film from the surface of the amalgam. The inside of the glass globe being freed from all adhering dust and humidity, is to be gently heated, while a little of the semi-fluid amalgam is introduced. The liquidity being increased by the slight degree of heat, the metallic coating is applied to all the points of the glass, by turning round the globe in every direction, but so slowly as to favour the adhesion of the alloy. This silvering is not so substantial as that of plane mirrors: but the form of the vessel, whether a globe, an ovoid, or a cylinder, conceals or palliates the defects by counter reflection from the opposite surfaces.

Coloured Glasses and Artificial Gems.—The general vitreous body preferred by Fontanieu in his treatise on this subject, which he calls the Mayence base, is prepared in the following manner. Eight ounces of pure rock-crystal or flint in powder, mixed with 24 ounces of salt of tartar, are baked and left to cool. This is afterwards poured into a basin of hot water, and treated with dilute nitric acid till it ceases to effervesce; when the frit is to be washed till the water comes off tasteless. The frit is now dried and mixed with 12 ounces of fine white lead, and the mixture is to be levigated and elutriated with a little distilled water. An ounce of calcined borax is to be added to about 12 ounces of the preceding mixture in a dry state, the whole rubbed together in a porcelain mortar, then melted in a clean crucible, and poured out into cold water. This vitreous matter must be dried, and melted a second and a third time, always in a new crucible, and after each melting poured into cold water as at first, taking care to separate the lead that may be revived. To the last glass ground to powder, five drachms of nitre are to be added, and the mixture being melted for the last time, a mass of crystal will be found in the crucible with a beautiful lustre. The diamond is well imitated by this Mayence base. Another very fine white crystal may be obtained, according to M. Fontanieu, from eight ounces of white lead, two ounces of powdered borax, half a grain of manganese, and three ounces of rock-crystal treated as above.

The colours of artificial gems are obtained from metallic oxides. The oriental topaz is prepared by adding oxide of antimony to the base; the amethyst from manganese with a little purple precipitate of Cassius; the beryl from antimony and a very little cobalt; yellow artificial diamond and opal, from horn-silver (chloride of silver); blue stone from cobalt. See Pastes and Pigments Vitrifiable.

The following are recipes for making the different kinds of glass.

1. Bottle glass.—11 pounds of dry glauber salts; 12 pounds of soaper salts; a half bushel of waste soap ashes; 56 pounds of sand; 22 pounds of glass skimmings; 1 cwt. of green broken glass; 25 pounds of basalt. This mixture affords a dark green glass.

2. Yellow or white sand 100 parts; kelp 30 to 40; lixiviated wood ashes from 160 to 170 parts; fresh wood ashes 30 to 40 parts; potter’s clay 80 to 100 parts; cullet or broken glass 100. If basalt be used, the proportion of kelp may be diminished.

In two bottle-glass houses in the neighbourhood of Valenciennes, an unknown ingredient, sold by a Belgian, was employed, which he called spar. This was discovered by chemical analysis to be sulphate of baryta. The glass-makers observed that the bottles which contained some of this substance were denser, more homogeneous, more fusible, and worked more kindly, than those formed of the common materials. When one prime equivalent of the silicate of baryta = 123, is mixed with three primes of the silicate of soda = (3 × 77·6) = 232·8, and exposed in a proper furnace, vitrification readily ensues, and the glass may be worked a little under a cherry-red heat, with as much ease as a glass of lead, and has nearly the same lustre. Since the ordinary run of glass-makers are not familiar with atomic proportions, they should have recourse to a scientific chemist, to guide them in using such a proportion of sulphate of baryta as may suit their other vitreous ingredients; for an excess or defect of any of them will injure the quality of the glass.

3. Green window glass, or broad glass.—11 pounds of dry glauber salt; 10 pounds of soaper salts; half a bushel of lixiviated soap waste; 50 pounds of sand; 22 pounds of glass pot skimmings; 1 cwt. of broken green glass.

4. Crown glass.—300 parts of fine sand; 200 of good soda ash; 33 of lime; from 250 to 300 of broken glass; 60 of white sand; 30 of purified potash; 15 of saltpetre (1 of borax), ⁄2 of arsenious acid.

5. Nearly white table glass.—20 pounds of potashes; 11 pounds of dry glauber salts; 16 of soaper salt; 55 of sand; 140 of cullet of the same kind. Another.—100 of sand; 235 of kelp; 60 of wood ashes; 1⁄3 of manganese; 100 of broken glass.

6. White table glass.—40 pounds of potashes; 11 of chalk; 76 of sand; ⁄2 of manganese; 95 of white cullet.

Another.—50 of purified potashes; 100 of sand; 20 of chalk; and 2 of saltpetre.

Bohemian table or plate glass is made with 63 parts of quartz; 26 of purified potashes; 11 of sifted slaked lime, and some cullet.

7. Crystal glass.—60 parts of purified potashes; 120 of sand; 24 of chalk; 2 of saltpetre; 2 of arsenious acid; ⁄16 of manganese.

Another.—70 of purified pearl ashes; 120 of white sand; 10 of saltpetre; ⁄2 of arsenious acid; ⁄3 of manganese.

A third.—67 of sand; 23 of purified pearl ashes; 10 of sifted slaked lime; ⁄4 of manganese; (5 to 8 of red lead).

A fourth.—120 of white sand; 50 of red lead; 40 of purified pearl ash; 20 of saltpetre; ⁄3 of manganese.

A fifth.—120 of white sand; 40 of pearl ash purified; 35 of red lead; 13 of saltpetre; ⁄12 of manganese.

A sixth.—30 of the finest sand; 20 of red lead; 8 of pearl ash purified; 2 of saltpetre; a little arsenious acid and manganese.

A seventh.—100 of sand; 45 of red lead; 35 of purified pearl ashes; ⁄7 of manganese; ⁄3 of arsenious acid.

8. Plate glass.—Very white sand 300 parts; dry purified soda 100 parts; carbonate of lime 43 parts; manganese 1; cullet 300.

Another.—Finest sand 720; purified soda 450; quicklime 80 parts; saltpetre 25 parts; cullet 425.

A little borax has also been prescribed; much of it communicates an exfoliating property to glass.

Tabular view of the composition of several kinds of Glass.

No. 1. No. 2. No. 3. No. 4. No. 5. No. 6. No. 7. No. 8. No. 9.

Silica 71·7 69·2 62·8 69·2 60·4 53·55 59·2 51·93 42·5

Potash 12·7 15·8 22·1 8·0 3·2 5·48 9·0 13·77 11·7

Soda 2·5 3·0 3·0 S. pot.

Lime 10·3 7·6 12·5 13·0 20·7 29·22 0·5

Alumina 0·4 1·2 3·6 10·4 6·01 1·8

Magnesia 2·0 - 2·6 0·6 0·6

Oxide of iron 0·3 0·5 1·6 3·8 5·74 0·4

— manganese 0·2 1·0

— lead 28·2 33·28 43·5

Baryta 0·9

No. 1. No. 2. No. 3. No. 4. No. 5. No. 6. No. 7. No. 8. No. 9.

Silica 71·7 69·2 62·8 69·2 60·4 53·55 59·2 51·93 42·5

Potash 12·7 15·8 22·1 8·0 3·2 5·48 9·0 13·77 11·7

Soda 2·5 3·0 3·0 S. pot.

Lime 10·3 7·6 12·5 13·0 20·7 29·22 0·5

Alumina 0·4 1·2 3·6 10·4 6·01 1·8

Magnesia 2·0 - 2·6 0·6 0·6

Oxide of iron 0·3 0·5 1·6 3·8 5·74 0·4

— manganese 0·2 1·0

— lead 28·2 33·28 43·5

Baryta 0·9

No. 1. is a very beautiful white wine glass of Neuwelt in Bohemia.

No. 2. Glass tubes, much more fusible than common wine glasses.

No. 3. Crown glass of Bohemia.

No. 4. Green glass, for medicinal phials and retorts.

No. 5. Flask glass of St. Etienne, for which some heavy spar is used.

No. 6. Glass of Sèvres.

No. 7. London glass employed for chemical and physical purposes.

No. 8. English flint glass.

No. 9. Guinand’s flint glass.