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

by Friedrich Christian Accum

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.