8 MANUFACTURE OF AMMONIA 



of nitrogen should yield 149 Ibs. of sulphate of ammonia if the 

 whole of the nitrogen were recovered in this form ; in fact, 

 however, a production of 20 or 22 Ibs. is considered to be a 

 fair yield. More than one-half of the nitrogen of the coal 

 remains in the coke ; much appears as nitrogen gas ; a little 

 appears as cyanogen ; some as organic coal-tar compounds ; 

 and only one-fifth, or less, is recovered as ammonia. By 

 mixing a little lime with the coal, or by passing steam through 

 the retorts, a considerably larger amount of ammonia may be 

 obtained ; but such methods cannot be employed when illumi- 

 nating gas is desired, as they deteriorate the illuminating 

 quality of the gas. 



When, however, gas is produced simply for heating pur- 

 poses, it is possible, by burning the coal in a current of steam 

 at as low a temperature as possible, to obtain one-half of the 

 nitrogen as ammonia ; the product of sulphate of ammonia 

 then amounts to about 70 Ibs. per ton of coal. By using gas 

 as fuel in the place of coal, large additional quantities of sul- 

 phate of ammonia might be obtained. 



The ammonia is separated from coal gas partly in the 

 mixed tarry and aqueous products condensed from the gas 

 by cooling, and partly by passing the gas over wet surfaces in 

 the scrubbers. The aqueous liquor, separated from the tarry 

 matter, forms the crude ammoniacal liquor of the gas works. 

 The ammonia in this liquor is present principally as carbonate 

 and sulphide, and to a much smaller extent as thiosulphate, 

 sulphocyanate and chloride. The two first-named compounds 

 are volatile, and are separated by passing a jet of steam 

 through the liquid ; the ammonia of the fixed salts is after- 

 wards volatilised by adding lime to the residual liquid. The 

 carbonate, sulphide, and free ammonia thus volatilised are 

 carried through vessels containing sulphuric acid, sulphate of 

 ammonia is thus produced, while the mixed gases containing 

 much sulphuretted hydrogen are conducted to a furnace to be 

 purified by combustion. The sulphate of ammonia liquors 

 are concentrated in leaden pans, and the sulphate obtained by 

 crystallisation. 



The sulphate of ammonia of commerce varies in colour ; 



