Ammonia from Bones.—The ammoniacal liquor from bones yields, according to Muspratt, from lb. to 14 lb. of ammenic chloride per gallou ; but, as he has pointed out, this quantity is subject to much variation from many causes. Since the amount of ammonia obtained depends upon the nitrogenous substances present, such as gelatine and chondrin, it is evident that the extraction of these matters for the manufacture of glue or size must seriously impair the banes for the produc tion of ammonia. As 100 parts of gelatine yield about 20 parts of ammonia, it is evidently more profitable to convert all the matter removable by boiling into glue than to turn it into ammonia. When gelatine is submitted to dry Astillatiun, it yields carbonate, sulphide, and cyanide of ammonium, amines or ammonia-like substances, pyridane bases, pyrrol, and other compounds.
From whatever source the ammoniacal liquor is obtained, its conversion into liquor ammonia or salts is generally effected by the same processes.
Volcanic the neighbourhood of volcanoes, or coal mines which have been set on fire, ammonia, generally as chloride, is found. The principal source of volcanic ammonia is the crude bemeic nee l from the lagoons of Tuscany. It exists principally in the form of double sulphates, which is set free on the addition of soda-ash in the manufacture of borax. The carbonate of ammonia which escapes is collected in a suitable receiver, and after a second purification takes the form in which it is found in commerce. Messrs. Howard and Sons, Stratford, Essex, manufac ture large quantities of ammoniacal compounds from this source, which are extensively used in pharmacy. The ammonia salts thus obtained are p.rfeetly free from all traces of oily matter and other impurities which accompany its production from gas or bone liquor. Volcanic ammonia is free from pyriol, and the substances met with iu ammonia from gas or bone liquor. The salts obtained from this source, when pure, disappear when heated, without leaving any carbona ceous residue. Pyrrol is detected by the purple colour which it strikes when an excess of nitric or sulphuric acid is poured into a solution of an ammoniacal salt.
Chloride of Ammonium.—For the production of this salt on the commercial scale, several methods are in use for the treatment of the ammoniacal liquor, by substituting sulphuric acid for the hydrochloric acid and sulphates for chlorides ; the same methods are applicable for the manufacture of the sulphate of ammonium.
By the addition of acid to the crude liquor :—The liquor when received at the works is pumped into large tanks, which are capable of holding two or three hundred thousand gallons each ; it is pumped from these tanks into circular vats, or tuns, for working. These vats contain sufficient
space to allow the working up of about 20,000 gallons of crude liquor at one operation.
Hydrochloric acid is then added, and the escaping gases, which are highly disagreeable and dangerous, are conducted to the furnace and burnt. The amount of acid required varies with the strength of the liquor ; to determine the amount, a trial should be first made, and the quantity of acid required to give a distinctly acid reaction should be used. The whole is agitated whilst the acid is being added, and allowed to settle. The acid, combining with the ammonia, sets free a quantity of oily matter, which floats on the surface of the solution of the chloride, and by subsidence the heavier impurities from the tar settle to the bottom.
Means are provided for drawing off the solution at different heights in the vats, so that the disturbance may be as little as possible. It is conveyed by troughs to the evaporators, which are usually square or rectangular, and constructed of cast-iron plates bolted together. They are heated by the waste heat from the furnaces, or if a fire be used, the flues are constructed so as to heat the liquid upon the whole surface of the bottom, as well as the sides. The liquid, when sufficiently concentrated, is transferred to the crystallizing pans or tubs. Care is taken that the liquid during the concentration does not become too acid; this is avoided by the addition of ammonia liquor from time to time.
Large crystals are to be avoided, as they lead to embarrassment in the subsequent steps of the manufacture. As the crystallization proceeds, the crystals which form on the surface are broken up by frequent agitation. A fair crop of crystals being obtained, the mother liquor is drawn off, and conveyed again to the evaporators. The salt thus obtained contaios a large quantity of tarry matter ; a great deal of this can be removed by washing the crystals with a warm concentrated solution of the salt and draining, or by one or more recrystallizations. By cautiously heating the crude salt so that it does not sublime, the water and free acid are removed, and the tarry matter to which it owed its black colour is decomposed; this is more completely effected if the crude salt be somewhat acid. The dry salt, which is now of a dark greyish colour, is ready for the subliming pots.