154 



AMMONIUM, CHLORIDE OF 



inconvenient in the subsequent process of sublimation, the liquor is agitated from time 

 to time. The crude mass obtained, which is contaminated with tarry matter, freo 

 acid, and water, is next dried, by gently heating it on a cast-iron plate under a dome. 

 The greyish- white mass remaining is now ready to bo transferred to the sublimers. 



The method of sublimation generally adopted in this country consists in beating 

 down into the metal pots, shown in Jiff. 49, the charge of dry coarsely crystallised sal- 



ammoniac. These pots are heated from below and by flues round the sides. The 

 body of the subliming vessel is of cast-iron, and the lid usually of load, or, less fre- 

 quently, iron. There is a small hole at the top, to permit the escape of steam, 

 sometimes loosely closed by a plug of sal-ammoniac, which is removed from time to 

 time to observe the progress of the sublimation ; great attention is requisite in the 

 management of the heat, for if it be applied too rapidly a large quantity of sal-am- 

 moniac is carried off with the steam, or even the whole apparatus may be blown up ; 

 whilst, if the temperature bo too low, the cake of sal-ammoniac is apt to be soft and 

 yellow. 



The sublimation is never continued until the whole of the salt has been volatilised, 

 since the heat required would decompose the carbonaceous impurities, and they, emit- 

 ting volatile oily hydrocarbons, diminish the purity of the product. In consequence 

 of this incomplete sublimation, a conical mass (shown in the fig. 49) is left behind, 

 called the ' yolk.' After cooling, the dome of the pot is taken off and the attached 

 cake carefully removed. This cake, which is from 3 to 6 inches thick, is nearly pure, 

 only requiring a little scraping, where it was in contact with the dome, to fit it for 

 the market. 



Modifications of the Process. If, as is often the case, sulphuric acid is cheaper or 

 more accessible than hydrochloric, the gas liquor is neutralised with sulphuric acid, 

 and then the sulphate of ammonia thus obtained is sublimed with common salt 

 (chloride of sodium), and thus converted into sal-ammoniac. 



NH'O. SO 8 + NaCl , = NH 4 Cl + NaO. SO 3 . 



Wad 



2MTH'C1 + Na-SO 1 . 



(NH'jZSO 1 + 



Mr. Croll has taken out a patent for converting crude ammonia into the chloride, 

 by passing tho vapours evolved in the first distillation through the crude chloride of 

 manganese, obtained, as a by-product in tho preparation of chlorine, for the manu- 

 facture of chloride of lime : crude chloride of iron may be used in the same way. 



Mr. Laming patented in July, 1843, the substitution of a solution of chloride of 

 calcium for treating the crude gas-liquor, instead of the mineral acids. Mr. Hills, 

 August, 1846, proposed chloride of magnesium for use in the same way; and several 

 other patents have been taken out by both thoso gentlomon, for the use of various 

 salts in this way. 



Manufacture of Sal-Ammoniac from Guano. Mr. Young took out a patent, Novem- 

 ber llth, 1841, in which ho describes his method of obtaining ammonia and its salts 

 from guano. He fills a retort, placed vertically, with a mixture of two parts by weight 

 of guano, and one part by weight of hydrate of lime. Thoso substances are thoroughly 

 mixed by giving a reciprocating motion to the agitator placed in the retort; a moderate 

 degree of heat is then applied, which is gradually increased until tho bottom of tho 

 retort becomes red-hot. The ammoniacal gas thus given off is absorbed by water in 

 a condenser, whilst other gases, which are given off at tho same time, being insoluble 

 in water, pass off. Solutions of carbonate, bicarbonate, or sesquicarbonato of ammonia 

 are produced, by filling tho condenser with a solution of ammonia, and passing car- 



