Description of the Process of Manufacturing Coal Gas, for the Lighting of Streets Houses, and Public Buildings / With Elevations, Sections, and Plans of the Most Improved Sorts of Apparatus Now Employed at the Gas Works in London and the Principal Provincial Towns of Great Britain; Accompanied With Comparative Estimates, Exhibiting the Most Economical Mode of Procuring This Species of Light

where A represents the surface illuminated by one of the lights only; B, the surface illuminated by the other light; C, the perfect shadow from which both lights are excluded. It will easily be understood that the lights about D and E, near the angle F, will fall with equal incidences when the double shadow is made to occupy the middle of the paper; and consequently, if one or both of the lights be removed directly towards or from the paper, as the appearances may require, until the two shadows at E and D have the same intensity, the quantities of light emitted by each, will be as the squares of the distances from the paper.

By experiments of this kind, many useful particulars may be shewn; for, since the cost and duration of candles, and the consumption of coal gas, or oil in lamps, are easily ascertainable, it may be shewn whether more or less light is obtained at the same expense during a given time, by burning a number of small lights, instead of one or more of greater intensities. And thus we may compare the power of different kinds of lamps or candles, with gas lights of different intensities, so as to determine the relative cost of each particular kind of the combustible substance employed for furnishing light. For example; if a candle and a gas burner supplying coal gas, adjusted by a stop-cock, produce the same darkness of shadow, at the same distance from the wall, the strength or intensity of light is the same.

An uniform degree of intensity of the gas light may readily be produced, by opening or shutting the stop-cock, if more or less light be required, and the candle kept carefully snuffed to produce the most regular and greatest quantity of light. The size of the flame, in experiments of this kind, of course becomes unnecessary, and will vary very much with the quality or chemical constitution of the coal gas. The bulk of the gas consumed, and the weight of tallow or oil used by weighing the candle or oil before and after the experiment furnish the data for calculating the relative cost of tallow, or oil and gas, when compared with each other.

The following statement exhibits the quantity of coal gas consumed in a given time, by different kinds of argand lamps. An argand burner which measures in the upper rim half an inch in diameter, between the holes from which the gas issues, when furnished with five apertures ¹⁄₂₅ part of an inch in diameter, consumes two cubic feet of gas in an hour, when the gas flame is one and a half inch high. The illuminating power produced by this burner is equal to three tallow candles eight in the pound.

An argand burner three quarters of an inch in diameter between the holes in the upper rim, and perforated with holes, ¹⁄₃₀ of an inch in diameter, consumes three cubic feet of gas in an hour, when the flame is two and a quarter inches high, and produces a light equal in intensity to four tallow candles, eight in a pound.

An argand burner seven-eighths of an inch in diameter, perforated with eighteen holes ¹⁄₃₂ of an inch in diameter, consumes when the flame of the gas is three inches high, four cubic feet of gas in an hour, and produces a light equal in intensity to six tallow candles, eight in the pound.

When the flame obtained by these kind of burners rises to a greater height, than what has been stated, the combustion of the gas is imperfect, the intensity of the light becomes diminished, and there is a waste of gas. The same holds good with regard to the size of the holes from which the gas issues; if the holes be made larger than ¹⁄₂₅ part of an inch in these kind of burners, the gas is not completely burnt, and its illuminating power decreases.

The height of the glass which surrounds the flame, should never be less than five inches, and the interval for the current of air within and without the flame, ought to bear the usual proportion adopted for the combustion of oil in the common argand lamps of similar diameters.

Ventilation of Apartments lighted by Coal Gas.

Before means had been devised for the effectual purification of coal gas, a disagreeable odour was found to attend its combustion in an impure state, and hence an opinion became prevalent, that the benefit of this new species of illumination must be confined to open places, and that it could not with any regard to pleasure or salubrity, be adapted to private dwellings.

The art of purifying coal gas, has at length however, been carried to such a perfection, that every possibility of a disagreeable odour arising from its combustion has been wholly removed, in all cases where attention is paid to the perfect combustion of the gas, by keeping the flame of the same of a proper magnitude.

And since this improvement, the use of coal gas, as a means of illumination has become as general, and has been found attended with as superior advantages within doors as without, and hence a vast number of dwelling houses are now lighted throughout with gas.

Although there is no occasion therefore, to make provision for ventilating apartments where gas light is employed, on account of any odour which it can produce when honestly used, so that the combustion is perfect, yet on other accounts such means of ventilations are very salutary and necessary.

The flame of coal gas produces a degree of heat,[52] which in some places, such as large public offices, and warehouses of dry goods, is a strong additional recommendation in favour of its use, (page 15,) while in others, on the contrary, such as small rooms numerously frequented, and shops containing commodities requiring to be kept cool, it can only be used beneficially when means are provided for conveying away the heated air.

The best method for this purpose is to make an aperture of about two or three inches in diameter into the chimney near the ceiling, and inserting into it a tube bending upwards into the interior of the chimney. A complete ventilation of the room will thus be established, by producing an extra vent which will be amply sufficient for carrying off the heated air. The aperture can easily be masked with some ornamental open work, corresponding with the style of the room.

If there happens to be no chimney in the apartment, the ventilator may be made in the ceiling, and the tube may be carried between the ceiling and the floor above, into the open air. The mode of ventilation now suggested, has been uniformly found most efficient, and has, under existing circumstances, a decided superiority over another method, which we see in some instances adopted. This method consists in enclosing the gas burner in a bell-shaped glass, from the upper part of which a large copper tube proceeds, and leads out into the open air. It is certain that by this means not only the heated air is carried off, and the possibility of any waste gas escaping into the apartment is also completely prevented. But at the same time, by taking away all occasion for a prudent limitation in the use of the gas, it exposes it to a degree of improvident waste, in the hands of dishonest and careless individuals, which must prove ruinous to the manufacturer. The mode of regulating the light of the flames by means of the governor, of which a description has been given, page 232, indeed provides a check against such waste, and there can be no doubt that in proportion as this instrument gets into general use, the objection on this score must of course fall to the ground; but under any circumstances the inelegance of the contrivance of such an object in a chamber, as the large branching tube, must always induce a preference, for the more simple, and for all necessary purposes, equally efficient method, of the ventilator before described.

PART XV.

Gas from Coal Tar.

Although the tar which forms one of the products obtained from the decomposition of pit coal, in the manufacture of coal gas, has become an article of commerce, being found applicable to most of those purposes to which vegetable tar has hitherto been used, it appears from experiments made on a large scale, that instead of thus disposing of the coal tar, it is more profitable, under certain circumstances, to submit this substance to a destructive distillation, for the purpose of obtaining from it carburetted hydrogen gas, which it is capable of affording, not only in abundance, but of a superior quality.

The chief circumstances which must determine the manufacturer of coal gas in this respect, is the price at which he can sell the coke produced in his establishment. If the price of this article is high, if he finds a ready market for coke, there is every reason to believe, that the manufacturer will find it more to his advantage to dispose of the tar, and to manufacture gas from coal alone, in order to increase his store of coke. But if coke happens to be at a low price, and not disposable with advantage, the manufacturer will do well to make the coal go as far as possible in the production of gas, and under such circumstances he will keep and convert the tar into gas, thus consuming less coal and having less of the burdensome article, coke, to dispose of.

The profit however, to be gained from the sale of coke, must be both certain and considerable, to induce a preference for the former course; because the decomposition of coal tar, besides superseding a proportionate quantity of coal, is attended with several other very tempting advantages.

From experiments lately made in the metropolis on this subject, in which I have been engaged, it appears that in all large gas light establishments, where the quantity of coal tar rapidly accumulates, and must be got rid of, and in all places where the tar cannot be sold for more than four shillings the hundred weight, it will be certainly advantageous to the manufacturer to decompose the tar for the production of carburetted hydrogen gas.

The price of coal cannot effect the operation, because where coal bears a high price, the manufacturer of the tar gas, will diminish the quantity of coal which he would otherwise be called upon to employ for the production of the requisite quantity of gas. And in places where coal is cheap, the decomposition of the tar will be attended with less expence.

The carburetted hydrogen gas produced from coal tar, possesses a greater illuminating power than the gas obtained from coal.[53] It consists chiefly of supercarburetted hydrogen or olifiant gas, and a less quantity of it is of course sufficient.

The gas thus obtained, is purified likewise with far greater facility, taking only one hundred and twentieth part of the quantity of quicklime which is required for the purification of carburetted hydrogen obtained from pit coal. The apparatus for the production of carburetted hydrogen from coal tar, is moreover less bulky, less expensive, and less complicated; and it can be managed by fewer workmen. And as the combined result of these several advantages, it is obvious, that by the substitution of coal tar, the new mode of lighting by gas can be pursued on a smaller scale; which it can never be with any profit, where coal itself is immediately employed for the production of the gas.

The apparatus employed by Mr. Clegg, for the distillation of tar, is extremely simple. It consists of two hollow cast iron cylinders, twelve inches in diameter, and nine feet long, furnished with moveable lids or mouth pieces, and joined together at the extremity opposite to the mouth piece. These cylinders are fixed in a brick furnace, so that each inclines eleven degrees, one above and the other below the horizontal base of the furnace.

When the apparatus has acquired a dull red heat, the coal tar is suffered to flow into the upper cylinder, by small portions at a time.

The tar is contained in a closed vessel, situated at any convenient place above the apparatus. It has a small aperture for the admission of air. But as a sufficient small quantity of viscid tar does not flow freely in a thin stream, a larger portion than is wanted, is made to flow first into a a small box, upon the apex of a pyramid which divides the stream, so that the excess runs off by a waste pipe, whilst a due quantity only is conveyed into the retort where it is decomposed.

This apparatus[54] therefore differs only from the apparatus described in the Journal of Science and the Arts, 1816, No. II., p. 282; that the cylinders may be detached, for cleaning them out more conveniently.

The following statement exhibits the result of a series of experiments, made (1816,) at the Westminster Chartered Gas Light Establishment,[55] for the purpose of ascertaining how far, and under what circumstances the decomposition of coal tar is a measure of economy.

Two tar retorts worked seven hours, produced 3054 cubic feet of gas. The quantity of tar decomposed, amounted to 354 lb. therefore 8 cubic feet of gas, (omitting fractions), were obtained from 1 lb. of tar.

Two tar retorts, worked nine hours, produced 4591 cubic feet of gas. The quantity of tar decomposed, was 525 lb. Hence 1 lb. of tar yielded nearly 8³⁄₄ cubic feet of gas.

Fifteen cwt. 16 lb. of tar, produced 16,112 cubic feet of gas, = 9¹⁄₂ cubic feet of gas, to 1 lb. of tar.

Five cwt. 3 quarters, 22 lb. of tar, produced 6660 cubic feet of gas, = 10 cubic feet of gas to 1 lb. of tar.

Five cwt. 17 lb. of tar, produced 5193 cubic feet of gas, = 9 cubic feet of gas to 1 lb. of tar.

One cwt. 81 lb. of tar, produced 1737 cubic feet of gas, = 9 cubic feet of gas to 1 lb. of tar.

One cwt. 30 lb. of tar, produced 1313¹⁄₂ cubic feet of gas, = 8 cubic feet of gas to 1 lb. of tar.

Five cwt. of tar, produced 5880 cubic feet of gas, = 10¹⁄₂ cubic feet of gas to 1 lb. of tar.

Two cwt. of tar, produced 2072 cubic feet of gas, = 9¹⁄₂ cubic feet of gas to 1 lb. of tar.

Three cwt. 18 lb. of tar, produced 3717 cubic feet of gas, = 10¹⁄₂ cubic feet of gas to 1 lb. of tar.

Two cwt. 6 lb. of tar, produced 2242¹⁄₂ cubic feet of gas, = 9³⁄₄ cubic feet of gas to 1 lb. of tar.

From the preceding operations it becomes obvious, that 9¹⁄₂ cubic feet of gas, were obtained in the large way from 1 lb. of tar. But this proportion appears evidently too small, our own operations assign fifteen cubic feet of gas to one pound of tar. Professor Brande, obtained eighteen cubic feet[56] from the same quantity of tar.

Gas from Oil.

“Messrs. J. and P. Taylor[57] are the first persons who have resorted to oil as a substance from which gas for illumination could be easily and cheaply prepared; and in the construction of a convenient apparatus for the decomposition of this body, they have fully shewn its numerous advantages over coal, while they have afforded the means of producing the most pure and brilliant flame from the inferior and cheap oils, which could not be used in lamps. The apparatus for the purpose is much smaller, much simpler, and yet equally effectual, with the best coal gas apparatus. The retort is a bent cast iron tube, which is heated red by a small convenient furnace, and into which oil is allowed to drop by a very ingenious apparatus; the oil is immediately volatilized, and the vapour in traversing the tube becomes perfectly decomposed. A mixture of inflammable gases, which contains a great proportion of olifiant gas passes off; it is washed by being passed through a vessel of water (which dissolves a little sebacic acid, and which seldom requires changing), and is then conducted into the gasometer.”

“The facility and cleanliness with which gas is prepared from oil in the above manner, may be conceived from the description of the process. A small furnace is lighted, and a sufficient quantity of the commonest oil is put into a small iron vessel, a cock is turned, and the gas after passing through water in the washing vessel, goes into the gasometer. The operation may be stopped by shutting off the oil, or, to a certain extent, hastened by letting it on more freely; the small quantity of charcoal deposited in the retort is drawn out by a small rake, and the water of the washer is very rarely changed.”

“The gas prepared from oil is very superior in quality to that from coal; it cannot possibly contain sulphuretted hydrogen, or any extraneous substance; it gives a much brighter and denser flame; and it is also more effectual, i. e. a lesser quantity will supply the burner with fuel. These peculiarities are occasioned, in the first place, by the absence of sulphur from oil, and then by the gas containing more carbon in solution. As the proportion of light given out by the flame of a gaseous compound of carbon and hydrogen, is in common circumstances in proportion to the quantity of carbon present; it is evident that the gas which contains a greater proportion of olifiant gas, or supercarburetted hydrogen than coal gas, will yield a better and brighter light on combustion.”

“It is necessary, in consequence of the abundance of charcoal in solution, to supply the gas when burning with plenty of atmospheric air, for as there is more combustible matter in a certain volume of it, than in an equal volume of coal gas, it of necessity must have more oxigen for its consumption.[58] The consequence is, that less gas must be burnt in a flame of equal size, which will still possess superior brilliancy; that less is necessary for the same purpose of illumination; and that less heat will be occasioned. From five and a half to six cubical feet of coal gas are required to supply an Argand burner for an hour; two cubical feet to two and a half of that from oil, are abundantly sufficient for the same purpose.”

“One important advantage gained by the circumstance, that so small a quantity of this gas is necessary for burners is, that the gasometer required may be small in proportion. The gasometer is the most bulky part of a gas apparatus, and that least capable of concentration; and where-ever it is placed, it occupies room to the exclusion of every thing else. Some very ingenious attempts have been made to diminish its size and weight, as in the double gasometer,[59] and others, but without remarkable success. Here, however, where the room required to contain the gas is directly diminished, the object is so far obtained; and when that takes place to one half, or even one third, it is of very great importance. It in a great number of cases brings the size of the apparatus within what can be allowed in private houses; and in consequence of the rapidity with which the retort can be worked, the gasometer may again be reduced to a still smaller size.”

“Another advantage gained by the small quantity of gas required for a flame, is the proportionate diminution of heat arising from the lights. The quantities of heat and light produced by the combustion of inflammable gases are by no means in the same constant relation to each other; one frequently increases, whilst the other diminishes; and this is eminently the case when coal gas and oil gas are burned against each other. The quantity of heat liberated is, speaking generally, as the quantity of gas consumed, and this is greatest with the coal gas; but the quantity of light is nearly as the quantity of carbon that is well burnt in the flame, and this is greatest in the oil gas.”

“The very compact state in which the apparatus necessary for the decomposition of oil can be placed, the slight degree of attention required, its certainty of action, its cleanliness, and the numerous applications which it admits of in the use of its furnace for other convenient or economical purposes, render it not only unobjectionable, but useful in manufactories and establishments; and these favourable circumstances are accompanied, not from any inferiority in the flame or increased expense, but by an improved state of the first, and saving in the latter.”

“Messrs. Taylor have shewn great ingenuity in the construction of their whole apparatus, but the washer and gasometer deserve particular notice for their remarkable simplicity also. In the washer, two planes are fixed in a box or cistern, in a direction not quite horizontal, but inclined a little in opposite directions; the planes are traversed nearly across by slips of wood or metal, fixed in an inclined position on the under surface, and which alternately touch one side of the cistern, leaving the other open and free. These planes being immersed in water, the gas is thrown in under the lowest ridge, and by its ascending power is made to traverse backward and forward along the ridges fixed on the planes, until it escapes at the highest part of the uppermost ridge. Thus, with a pressure of five or six inches of water only, it is made to pass through a distance of fourteen or sixteen feet under the surface of the fluid, and becomes well washed.”

“The smaller gasometers are made of thin plate iron, and being placed in a frame of light iron work, look more like ornamental stoves than the bulky appendages to a gas apparatus, which they supply. The larger ones are made very light, and when in pieces very portable, by being constructed of a frame of wood work, in the edges of which are deep narrow grooves; plates of iron fit into these grooves, which being caulked in and painted over, make a light and tight apparatus. These are easily put together in any place, and may therefore be introduced into a small apartment, or other confined space, where a gasometer already made up would not enter.”

For the following additional information on this subject, I am indebted to Messrs. J. and P. Taylor.

“The economy of obtaining gas for the production of light from oil, may be judged of from the following data.”

“One gallon of common whale oil, produces about ninety cubic feet of gas.[60] An argand burner required a cubic foot and a half of gas per hour; and consequently a gallon of oil when converted into gas, will supply the same burner for sixty hours. The expence of the gas at a moderate price of oil, will be, allowing for coals, labour, &c. for producing the gas, three farthings per hour, and such a burner will give a light, equal in intensity, to two argand lamps, or ten mould candles.”

“The expence of an argand oil lamp, is usually admitted to be, about three halfpence per hour. Now supposing ten candles to be burning, four to the pound (two pound and a half,) they will cost 2s. 11d. of which one-tenth part will be consumed in each hour. The cost of the tallow light is then three pence halfpenny per hour.”

“If wax candles be employed, the expence of the light equal to an oil gas burner for one hour, by the same mode of reckoning, allowing the candle to burn ten hours, and taking the price of the wax candles, at 4s. 6d. per pound, will be about 14d.”

“The comparative account will therefore stand thus:

“These calculations on the cost of light from oil gas, are taken at the usual price of good whale oil, but cheaper oils will answer the purpose nearly as well, and as many of these are often to be procured, the whole expence becomes materially reduced by their use.”

PART XVI.

Other products obtainable from Coal, namely:—Coal Tar—Pitch—Coal Oil—Ammoniacal Liquor, and conversion of the latter into Carbonate, and Muriate of Ammonia.

Coal Tar.

The coal tar is so called from its resembling common tar in its appearance, and most of its qualities.

This substance is deposited in the purification of the coal gas, in a separate vessel destined to receive it. See fig. 3, plate I.

In the year 1665, Becher, a German chemist, brought to England his discovery for extracting tar from coal, this distillation he performed in close vessels. It is not mentioned in the records of the time, whether Becher obtained, or rather collected, any other articles than the tar.

Several works have been, at different times, erected both in England and on the continent, to procure from coal a substitute for tar; but they have turned out unprofitable speculations.

In 1781, the Earl of Dundonald invented a mode of distilling coal in the large way, which enabled him not only to form the coke, but, at the same time, to save and collect the tar. Even this process, however, for which a patent was taken out, gained very little ground. Its object was too limited; for though some of the proximate constituent parts of coal were procured, they were obtained at an expence that nearly balanced the profits; and no attention whatever was paid to the coal gas, which constitutes by far the most valuable part obtainable from pit coal.

Coal tar is now used with advantage largely in the Royal Navy, and also for painting and securing wood that is exposed to the action of air. The wood being warmed, the tar is applied cold, and penetrating into the pores, gives the timber an uncommon degree of hardness and durability.

The quantity of tar obtainable from a given quantity of coal, varies according to the manner in which the decomposition of the coal is affected. See page 122.

The tar obtained from Newcastle coal is specifically heavier than that produced from cannel coal; hence it sinks in water, whereas the latter swims on the surface of that fluid.

To render coal tar fit for use, it requires to be evaporated to give it a sufficient consistence. If this process be performed in close vessels, a portion of an essential oil is obtained, which is known by the name of

Coal Oil.

To obtain this oil, a common still is charged with coal tar, and, being properly luted, the fire is kindled and kept up very moderate, for the tar is very apt to boil up in the early part of the process. The first product that distils over is principally a brown ammoniacal fluid, mixed with a good deal of oil. As the process advances, and the heat is increased, the quantity of ammoniacal liquor lessens, and that of oil increases, and towards the end of the distillation the product is chiefly oil.

The oil and ammoniacal water which distil over do not mix, so that they may be easily separated by decantation. The oil is a yellowish inferior kind of naptha, which is very useful in painting ships, and for making common varnishes. It has lately been employed as a substitute for whale oil, to be burnt in out door lamps.

The contrivance by means of which this oil is burnt in lamps[61] consists of a fountain reservoir to supply and preserve a constant level. The burner with its wick is placed in the axis of the lamp, and supplied with the oil from the fountain reservoir, placed on the outside of the lamp. The air is admitted by an aperture at the bottom of the lamp. The current of air in passing through the lamp envelopes the burner and urges the flame, which is extremely bright; but it is essential that the flame should be small. The draught tube proceeding from the centre of the reflector above the flame carries away the smoke.

1430 pounds of coal tar, produce 360 pounds of essential oil. The residue left after the distillation is

Pitch.

If the coal tar is wanted to be converted into pitch, without obtaining the oil which it is capable of furnishing, the evaporation of it may be performed in a common boiler; but as it is extremely liable to boil over, the greatest precaution is necessary in conducting the evaporation. A spout or rim is added to the common boiler into which the tar spreads itself as it rises, and by this means becomes cooled, and the boiling over is checked.

1430 pounds of coal tar produce 9 cwt. of pitch. A subsequent evaporation with a gentle heat, converts the coal pitch into a substance greatly resembling asphaltum.

Manufacture of Carbonate of Ammonia from the Ammoniacal Liquor of Pit Coal.

The ammoniacal liquor obtained in the gas light manufacture, is employed for the production of carbonate of ammonia. The average quantity of this liquor, obtainable from a chaldron, (27 cwt.) of Newcastle, or Sunderland coal, amounts to from 180 to 220 pounds. It is chiefly composed of carbonate and sulphate of ammonia. The quantity of ammonia contained in it, varies considerably. The strongest liquor is obtained from coal that readily cake, (page 45); a gallon (or eight and a half pounds weight) of ammoniacal liquor usually requires for saturation, from fifteen to sixteen ounces of sulphuric acid of a specific gravity 1,84. The weakest ammoniacal liquor is obtained from those species of coal which do not cake, and which by a single combustion are reduced to light ashes. It requires only from eight to ten ounces of sulphuric acid, of the before mentioned specific gravity for its saturation.

The following process is employed in the large way, for obtaining carbonate of ammonia from the ammoniacal liquor. To 108 gallons[62] of the liquor contained in a cask, are added 125 pounds[63] of finely ground sulphate of lime, which has been previously deprived of moisture by heat. The cask is bunged up, and the mixture after being stirred together for a few minutes, is left undisturbed for three or four hours. Sixteen ounces of sulphuric acid are then added, the mixture is again agitated, and is again suffered to stand undisturbed for four or six hours. If the liquor be now examined, it will turn blue litmus paper, red.

In this operation a double decomposition takes place, the sulphate of lime yields part of its sulphuric acid, to the carbonate of ammonia of the liquor, to form sulphate of ammonia, and the carbonic acid of the ammonia, combines with the lime of the sulphate of lime, to form carbonate of lime, which falls to the bottom, the supernatant fluid contains in solution, sulphate of ammonia.

When the liquor has become clear, it is pumped out of the barrel into shallow cast iron boilers, where it is evaporated slowly. During this process, a portion of sulphate of lime is deposited which is removed, and as the liquor becomes more concentrated, part of the sulphate of ammonia begins to crystallize and falls to the bottom. It is shovelled out from time to time into wicker baskets, placed slanting over the rim of the boiler, that the liquor which drains off from the crystals may not be lost, and lastly the whole fluid is evaporated to dryness.

108 gallons of ammoniacal liquor from Newcastle coal, produce upon an average, one and a half cwt. of dry sulphate of ammonia. To decompose it, one cwt. is mixt with one quarter of a cwt. of finely ground chalk, previously deprived of moisture by heat. The mixture is introduced (as expeditiously as possible) into cast iron retorts,[64] heated nearly to a dull redness, and when the lid of the retorts have been rendered air tight, the fire is raised gradually till the retorts are of a strong red heat. The carbonate of ammonia developed from the contents of the retorts, is made to sublime into a leaden barrel-shaped receiver, connected with the retorts, by means of a pipe four inches in diameter, proceeding from the upper extremity of each retort, and opposite to the mouth piece. The leaden receiver is furnished with a leaden cover, fitting into a groove, where it is made air tight by lute. The receiver which is supported upon a stand is provided at its base, with a small pipe, furnished with a stopper. This pipe is left open till the liquid products are got rid of during the sublimatory process. In the centre of the cover, or at any other convenient part of the apparatus, is made a small hole, slightly stopped with a wooden peg, to give vent to the elastic fluid that becomes evolved during the process.

The time requisite for the operation depends on the mode in which the retorts are set, the temperature kept up and other practical circumstances. A charge of 120 pounds of the mixture of sulphate of ammonia and chalk in one retort, is usually decomposed in twenty-four hours. When the operation is at an end, and the receiver having become cold, the cover is taken off, and the sublimed carbonate of ammonia adhering to the sides of the receiver is detached by a chissel and mallet, and after being freed from any casual impurities, is packed up in stone jars for sale.

One cwt. of dry sulphate of ammonia, produces from sixty pounds, to sixty-five pounds, of pure carbonate of ammonia. In some establishments, the carbonate of ammonia is subjected to a second sublimation by means of a gentle heat; but this is quite unnecessary if the process has been conducted carefully.

Manufacture of Muriate of Ammonia from the Ammoniacal Liquor of Coal.

It must be obvious that the ammoniacal liquor may be employed with great advantage for the production of muriate of ammonia. For if the solution of sulphate of ammonia obtained from the ammoniacal liquor by means of sulphate of lime, as before stated, be mixed with common salt, (or any other muriate) another decomposition takes place. The muriatic acid of the common salt, unites to the ammonia of the sulphate of ammonia, and produces muriate of ammonia, and the sulphuric acid of the sulphate of ammonia, combines with the soda of the common salt, and produces sulphate of soda, or glauber salt.

The liquor containing these two salts being evaporated, the glauber salt begins to crystallize, and is removed from time to time. The evaporation is continued till as much as possible of the glauber salt has been separated, and the muriate of ammonia begins to crystallize on the surface of the fluid in the form of a feathered star. The remaining fluid is then run off into coolers, and deposits little else than muriate of ammonia, till it gets below the temperature of 76° Fahr. at which time the crystals are to be removed, lest they should be mixed with glauber’s salt which now begins to be again deposited. After the muriate of ammonia has been suffered to drain in baskets, it is heated in shallow pans to drive off as much water of crystallization as possible. It is then removed whilst still hot, into earthenware jars, glazed within, and fitted with a cover, (having a hole of about half an inch in diameter in its centre,) luted on with clay. The jars are put in a cast iron pot over a strong fire, in a furnace capable of containing from six to eighteen jars, surrounded with sand up to the edge of the pot, and also having about two and a half inches of sand on the cover, confined by an iron ring about three inches deep, and two inches less in diameter than the cover, in order that if the luting should give way in any part, it may be repaired without suffering the covers (which should be kept during the sublimation at about 320° Fahr.) to be cooled by the removal of a large portion of the sand.

These earthen jars may be filled to within two inches of the top, with the dried salt gently pressed in, but not rammed close; and the fire which has been lighted some time before, is now to be raised gradually till the iron pots are of a pretty strong red heat all round, being so placed by mean of flues in the furnace that the upper part may be first heated, the bottom resting on solid brick work.

During the first impression of the heat, a portion of the salt carrying with it a quantity of watery vapour not separated during the drying of the salt, will escape through the hole in the cover, which must be left open till all the aqueous part is exhaled: this is known by bringing a piece of cold smooth iron plate near the hole, in order to condense the sublimate, which becoming more and more dry, at length attaches itself firmly to the plate, in the form of a dry semi-transparent crust.

At this time the hole is to be stopped with lute, more sand is to be put on the cover, and the heat continued till it is judged that nearly the whole of the muriate of ammonia is sublimed. The time requisite for this purpose depends on the construction of the furnace, the size of the pots, the briskness of the fire, and other circumstances only to be learnt by experience.

The process should be stopped before the sublimation has entirely ceased, as the heat in some parts of the jar may be too great when it is nearly empty, and either by volatilizing a part of the salt itself, or elevating a portion of foreign matter from which it can never be kept wholly free, and thus giving the cake a yellow tinge, and a scorched, opake, crackled appearance.

The same defects are likely to happen, when any part of the luting having given way, is obliged to be repaired by wet lute, when the sublimation is pretty far advanced: consequently glass vessels are preferable, except on account of the expence, as they must always be broken to pieces in order to get out the cake: the earthenware jars on the contrary will serve for several sublimations, even the covers, if well glazed, will last two operations. The sublimation being finished and the apparatus having become sufficiently cool, the tops of the jars are to be taken off, and the cakes of sal-ammoniac that are found adhering to them are to be separated, and placed for a day or two in a damp atmosphere, which softens their surface a little, and thus facilitates the removal of any superficial impurities. Lastly, the cakes are packed up in casks for sale.

The excise laws have hitherto operated strongly against the establishment of manufactories of muriate of ammonia in England. Hence an immense quantity of sulphate of ammonia obtained from the gas light ammoniacal liquor, is exported from this country to the continent, solely from the extreme rigour of the excise relating to the use of common salt, and it is only this that has hitherto prevented the establishment of manufactories of sal-ammoniac from the ammoniacal liquor of the gas light process upon a large scale.

Chemical manufactories, of all others, will least bear excise, because many of them are worked according to secret processes, which, if made public, must pass into other countries; and the greatest part of the profit ceases together with the export. The vexatious introduction of excise officers into manufacturing laboratories, it is evident, puts an end to all secrecy of operation. There are several chemical processes which interruption will extremely injure, and others which it totally destroys, and as on the whole they in general are of a nature in which interference of others is most peculiarly vexatious, in all probability, if the excise be extended to manufactures of this nature, it will eventually put a stop to most of them, and greatly injure the revenue by causing thereby to cease the duties which at present arise from the exports and imports to a large amount, now depending on the chemical trade of Great Britain.

We have now gone through all the improvements by which the gas light manufacture has been distinguished during the interval which has elapsed since the publication of our former work[65] on this subject; and perhaps the reader may be inclined to think, from the extraordinary height to which improvement has been carried in this art, that little or nothing more remains to be desired with regard to it. Let it be remembered, however, that the whole art is only in its infancy. There is yet a wide field for improvement in the construction of the apparatus. Ingenious men may speculate from what has been done, to what remains to be effected, which no doubt will lead to objects of the greatest utility, and most extended national importance.