MANUFACTURE OF AMMONIA 9 



it may be white, grey, brownish, or yellowish. The grey and 

 brown tints are due to traces of tarry matter, the yellow to a 

 trace of sulphide of arsenic ; this latter only occurs when the 

 sulphuric acid employed has been made from pyrites. Sul- 

 phate of ammonia is generally a nearly pure salt, the London 

 made article contains about 25 per cent of ammonia, while 

 a theoretically pure salt would contain 25f per cent. Country- 

 made sulphate will contain 24-25 per cent of ammonia. 



Sulphocyanate of ammonia is now seldom found in the 

 commercial sulphate. It used to occur when the crude 

 ammoniacal liquor had been directly neutralised by sulphuric 

 acid, or when the ammonia salts collected by purifiers con- 

 sisting of sawdust soaked with sulphuric acid were extracted 

 with water, and the salts obtained by crystallisation. Sulpho- 

 cyanates are easily recognised Sy the blood-red colour which 

 they produce when a drop of a solution of ferric chloride, and 

 a drop of hydrochloric acid, are added to the suspected 

 solution. Sulphocyanate of ammonia contains a much larger 

 percentage of nitrogen than the sulphate, and samples con- 

 taining it are thus apt to appear abnormally good on analysis. 

 Sulphocyanates are very injurious to vegetation, and ought 

 therefore to be carefully excluded from all sulphate of am- 

 monia to be employed as manure. Crude ammonia salts, 

 containing sulphocyanates, can be safely used to some extent 

 in the manufacture of ammoniacal superphosphates, if the 

 ammonia salt is mixed with the ground phosphate before the 

 addition of the sulphuric acid ; under these circumstances the 

 hydrosulphocyanic acid is liberated and volatilised during 

 the heat of the reaction. 



Sulphate of ammonia is not only produced from coal in the 

 manufacture of illuminating gas, it is also now obtained, 

 though to a much less extent, as a product of the manufacture 

 of coke. In the early forms of coke-ovens the coal was 

 allowed to undergo partial combustion in a regulated manner, 

 and the whole of the volatile products was lost. As these 

 volatile products have increased in value the method has been 

 altered, and the coal is now in many cases heated in a closed 

 vessel by the combustion of the gas produced by itself, or 



