152 AMMONIUM, CHLORIDE OF 



When tho liquid sulphate has acquired the density of about 1'IGO, sea-salt should be 

 added, with constant stirring, till tho whole quantity equivalent to tho double decom- 

 position is introduced into tho lead boiler. 



The fluid part must now bo drawn off by a syphon into a somewhat deep reservoir, 

 where the impurities are allowed to subside ; it is then evaporated by boiling till the 

 sulphate of soda falls down in granular crystals, as tho result of the mutual reaction of 

 the sulphate of ammonia and chloride of sodium ; while tho more soluble chloride 

 of ammonium remains in tho liquor. During this precipitation, tho whole must be 

 occasionally agitated with wooden paddles ; the precipitate being in the intervals re- 

 moved to tho cooler portion of tho pan, in order to bo taken out by copper rakes and 

 shovels, and thrown into draining-hoppors, placed near tho edges of tho pan. Tho 

 drained sulphate of soda must bo afterwards washed with cold water, to extract all 

 tho adhering sal-ammoniac. 



Tho liquor thus freed from tho greater part of the sulphate, when sufficiently con- 

 centrated, is to be drawn off by a load syphon into tho crystallisers, where, at tho end 

 of 20 or 30 hours, it affords an abundant crop of crystals of sal-ammoniac. The 

 mother-water may then bo run off, the crystallisors set aslope to drain the salt, and 

 tho salt itself must bo washed, first by a weak solution of sal-ammoniac, and lastly 

 with water. It must bo next desiccated, by tho apparatus fig. 46, into a perfectly 

 dry powder, then put into the subliming stoneware balloons, by means of a funnel, 

 and well rammed down. Tho mouth of tho bottle is to bo closed with a plate or in- 

 verted pot of any kind. Tho fire nrnst be nicely regulated, so as to effect tho subli- 

 mation of the pure salt from the under part of the bottle, with due regularity, into a 

 white cako in the upper part. The neck of the bottle should be cleared from time to 

 time with a long steel skewer, to prevent the risk of choking, and consequent bursting ; 

 but in spite of every precaution, several of tho bottles crack almost in every opera- 

 tion. Ure. 



The pots are of variable dimensions, but those most frequently employed are about 

 18 inches in height in the body, and the cups about 10 or 12 inches, with a breadth 

 of 16 inches at the widest part. 



In Scotland a process somewhat similar is pursued, the salt being sublimed in cast- 

 iron pots lined with fire tiles ; tho condensation being effected in globular heads of 

 green glass, with which each of the iron pots is capped. 



Manufacture of Sal-Armnoniac from Gas-Liquor. By far the largest quantity of the 

 ammoniacal salts now met with in commerce is prepared from ' gas-liquor,' the 

 quantity of which annually produced in tho metropolis alone is quite extraordinary 

 one of tho London gas-works producing in one year 224,800 gallons of gas-liquor, by 

 the distillation of 51,100 tons of coal; and tho total consumption of coal in London 

 for gas-making is estimated at about 840,000 tons. 



The principle of the conversion of the nitrogen of coal into ammonia by destructive 

 distillation, as in the manufacture of coal gas, will be found described in connection 

 with the processes of gas manufacture and the products produced by the destructive 

 distillation of coal. 



In the purification of the coal gas, the bodies soluble in water are all contained in 

 tho ' gas-liquor ' (see COAL GAS), together with a certain quantity of tarry matter. 

 Tho ammonia is chiefly present in the form of carbonate, together with certain 

 quantities of chloride, sulphide, cyanide, and sulphocyanido of ammonium, as well as 

 the salts of the compound ammonias. 



For the purpose of preparing the chloride, if hydrochloric acid be not too costly, 

 the liquor is saturated with hydrochloric acid the solution evaporated to cause the 

 salt to crystallise, and then, finally, the crude sal-ammoniac is purified by sublimation. 



Before treatment with the acid, the liquor is frequently distilled. 



This is generally effected in a wrought-iron boiler, the liquors passing into a modifi- 

 cation of the Coffey's still, by which tho solution of ammonia is obtained freer from 

 tar and more concentrated. 



The Saturation of the Ammoniacal Liquor with the acid is generally effected by 

 allowing tho acid to flow, from a largo leaden vessel in which it is held, into an under- 

 ground tank (Jig. 47) containing tho liquor, which is furnished with an exit tube, 

 passing into a chimney, to carry off the sulphuretted hydrogen and other offensive 

 gases which are disengaged. 



Or, in other works, the gas-liquor is put into largo tuns, and tho acid lifted in gutta- 

 percha carboys by cranes, thrown into tho liquor and stirred with it by means of an 

 agitator ; tho offensive gases being in this case made to traverse tho fire of tho steam- 

 engine. 



Sometimes tho vapours produced in the distillation of the crude gas-liquor are 

 passed in at tho lower extremity of a column filled with coke, down which the acid 

 trickles, 



