BONES AND SULPHURIC ACID. 311 



to powder, and used in any way as manure, either 

 alone, or mixed with dry soil. 



834. The effect thus produced by the sulphuric 

 acid is very simple ; burnt bones consist of phosphate 

 and carbonate of lime, the latter in a far smaller pro- 

 portion than the former ; when sulphuric acid is pour- 

 ed over burnt bones the carbonate of lime is wholly 

 decomposed, being converted into gypsum or sulphate 

 of lime (245) ; the phosphate of lime is partly de- 

 composed, the sulphuric acid takes from it the great- 

 er part of the lime forming gypsum, whilst the rest 

 of the lime being still combined with the phosphoric 

 acid, constitutes a very sour and easily soluble salt, 

 a biphosphate or superphosphate of lime. 



835. As the most valuable part of this manure is 

 soluble in water, it may easily be used as a liquid, 

 being dissolved in water. Whether used dry or in 

 solution, it is most advantageous to use with it some 

 manure containing ammonia, such as yard dung, 

 guano, or any of the strong animal manures. 



836. It is frequently the custom to mix a consi- 

 derable quantity of earth or soil with putrefying 

 animal manure. This to some extent is a good prac- 

 tice; the earth added prevents too rapid putrefaction, 

 and retains some of the products of decomposition; 

 a considerable quantity of ammonia, which would 

 otherwise be lost, is absorbed by the soil (162). The 

 addition of burnt clay or charcoal is useful for a 

 similar reason. 



837. The use of lime, on the other hand, is de- 



