Bone Manures 



volatile products, including among others, ammonia 

 is given off into condensers. What is left of the bones 

 is converted into a black spongy charcoal, which 

 makes an excellent decolorant for coloured organic 

 matter. It was used before sulphuric anhydride 

 [SO2] was introduced in the decolouring of syrups, 

 in the manufacture of sugar, etc. For this purpose 

 it was finely ground. When the charcoal had 

 absorbed all that it could retain of the coloured 

 organic matter of the juice, it was calcined afresh, 

 and was used again and again till it lost its 

 sponginess, when it was called " spent charcoal " 

 and was turned to agricultural purposes. 



There are two kinds of charcoal. 



ist. That of sugar manufacturers, which is 

 the most plentiful. It makes a more or less coarse 

 powder, containing about 70 per cent, tricalcic 

 phosphate, 10 to 20 per cent, carbonate of lime, 

 and practically no nitrogen. This is used to greatest 

 advantage on acid lands, where it gives good results. 

 It is often adulterated with earth, ashes, and some- 

 times even by the addition of the burnt residue 

 of distillation, in which case it contains cyanures 

 harmful to vegetation. 



2nd. That of refineries, which, in a dry state, 

 forms a fine powder. This charcoal holds a 

 variable amount of tricalcic phosphate, generally 

 between 50 and 70 per cent. It also contains 

 I to 3 per cent, nitrogen. It is very easily 

 adulterated, since its texture easily hides foreign 

 matters, such as black peat, earth, wood -charcoal, 

 charcoal dust, etc. 



These two animal charcoals are often used 



57 



