108 ELEMENTARY AGRICULTURAL CHEMISTRY 



constituent of the soil, and Is therefore very liable to be lost 

 in the drainage. Hence it should never be applied in heavy 

 dressings, nor much before the crop is sufficiently grown to be 

 able to absorb it. 



It has recently been proposed to manufacture nitrates for 

 agricultural purposes by passing strong electric discharges 

 through air. By this means oxides of nitrogen are produced 

 by the union of nitrogen and oxygen, and if an alkali — e.ff.j 

 soda — be present nitrite and nitrate of the alkali are formed. 

 Where large natural sources of power {e.g.^ Niagara) are 

 available for producing electricity this process might be 

 profitable.* 



Ammonium Sulphate. — This substance is made from the 

 " ammoniacal liquor " of gasworks, coke ovens, or blast-furnaces. 

 When coal, which contains about 1*3 per cent, of nitrogen, is 

 distilled the nitrogen is partly evolved as ammonia, NH3, which 

 dissolves in the water condensed from the steam formed at 

 the same time. The " gas liquor " so obtained contains many 

 compounds of ammonia, the chief being carbonate, chloride, 

 sulphide, and thiosulphate. The total ammonia in the " gas 

 liquor" amounts usually to about 2 per cent. In order to 

 obtain sulphate of ammonia, the " gas liquor " is distilled 

 with lime, and the ammonia gas evolved is led into sulphuric 



acid; 



H3SO, + 2NH3 = (NH,)2S0,. 



The liquid is boiled down, and sulphate of ammonia crystallises 

 out. Important impurities sometimes found in commercial 

 ammonium sulphate are ammonium sulphocyanide, NH^CNS, 

 and arsenious sulphide, AS3S3. The former is derived from the 

 " gas liquor,," the latter from the sulphuric acid, which some- 

 times contains arsenious oxide, AS2O3. Both these substances 

 are plant poisons. 



Ammonium sulphate crystallises in anhydrous crystals, which 



 Kecentlj at Notodden (Norway) by using lime as the alkali, a 

 basic nitrate of lime, capable of successfully competing as a nitrogenous 

 manure with nitrate of soda, has been produced on a large scale. 



