136 



SULPHATE OF AMMONIA 



pelled as ammonia, which is carried away in the vapours and gases 

 simultaneously produced. The most important operation of this kind 

 is the distillation of coal, and it is mainly from this source that the 

 supplies of ammonium compounds are obtained. Ordinary coal con- 

 tains a little over 1 per cent of nitrogen, and when burnt in the usual 

 way, this nitrogen escapes into the air, mainly in the free state. When 

 coal is distilled, however, a portion of the nitrogen is liberated as am- 

 monia and is found in the so-called "ammoniacal liquor" which 

 results from the cooling of the vapours evolved during the distillation. 

 Coal is distilled for the production of coal-gas for illuminating purposes 

 and also, in a somewhat different manner, for the manufacture of the 

 special coke used in iron smelting. Gas works and coke ovens thus 

 provide a large share of the " ammoniacal liquor " which forms the 

 raw material for the manufacture of ammonium salts. A similar 

 operation is the distillation of the bituminous shales used in the 

 Scotch paraffin industry, while the production of pig iron is sometimes 

 effected by the use of coal instead of coke, and, in this case, arrange- 

 ments are sometimes made by which the ammonia and tarry products 

 which are evolved during the first stages of the heating of the coal, 

 may be collected. Another source of ammonia is the liquid condensed 

 from the " producer gas " and " water gas," formed when a current of 

 air or steam is forced over red-hot coal. 



The product obtained in any of these processes is a complex mix- 

 ture consisting of an aqueous solution of ammonium sulphide, car- 

 bonate, thiosulphate, thiocyanate and chloride. 



The composition of gas liquor may be gathered from the following 

 analyses of products obtained from the Leeds gasworks, I in 1883 l 

 and II in January, 1901 2 : 



1 S. Dyson, Jour. Soc. Chem. Ind., 1883, 229; Jour. Chem. Soc., 1884, Ab- 

 stracts, 928. 



2 A. W. Cooke, Jour. Soc. Chem. Ind., 1901. This sample represented the 

 yield of three works, a total of about 6000 tons of liquor. For an account of the 

 composition of gas liquor obtained at various stages of the distillation, etc., vide 

 L. T. Wright, Journal of Gas Lighting, 48, 280 ; or abstract in Jour. Soc. Chem. 

 Ind., 1886, 655. 



