56 MANUFACTURE OF FERTILIZING MATERIALS 



previously fermented in heaps, the nitrogenous 

 matter becomes more readily assimilable. 



Bones are also more available as manure when 

 they have been steamed for the removal of fat. 

 Boiled bones which have been passed through the 

 glue-maker's hands contain a smaller proportion of 

 nitrogen than do raw bones. The boiled bones 

 can be more finely ground and divided than is 

 represented by the condition of bone meal; the 

 fine product is known as bone flour. Dissolved 

 bones is the product of the treatment of bones with 

 commercial sulphuric acid. 



Ammonium Sulphate. This is produced as a 

 by-product in the destructive distillation of coal. 

 The working up of gas liquor for ammonium 

 sulphate is carried out in the following manner: 

 The liquor is heated to drive off the free ammonia 

 and the vapor is absorbed in sulphuric acid, form- 

 ing ammonium sulphate, which crystallizes and is 

 periodically fished out. It is the common practice 

 in some countries to use only that part of the am- 

 monia which is liberated on distilling the gas liquor 

 a" one, but sometimes the fixed ammonia is liber- 

 ated by the addition of lime. Pure ammonium 

 sulphate contains 21 per cent of nitrogen, corre- 

 sponding to 25.75 per cent ammonia, and is a col- 

 orless salt. The commercial product varies in 

 color from gray to brown, owing to the presence of 

 tarry matter, and is sometimes yellowish from the 

 presence of arsenic; this body is formed by the 

 action of the hydrogen sulphide from the gas liquor 



