310 BONES. 



830. In stating that boiled bones form a better 

 manure than raw or unboiled ones, it is of course ev- 

 ident that the operation of boiling cannot in any way- 

 increase the absolute quantity of manure which they 

 can supply, but merely renders them more rapid in 

 their action ; as they become less lasting in their 

 effects, in exact proportion to the rapidity of their 

 action when first used. 



831. As phosphate of lime is insoluble in pure 

 water, and but slightly soluble in water containing 

 carbonic acid, and as the most valuable component 

 of bone is phosphate of lime, we should be led to 

 expect that they would form a lasting manure, pro- 

 ducing a beneficial effect so long as any of the phos- 

 phate of lime remains unabsorbed. As the quantity 

 of this substance which plants are able to obtain from 

 bone in one season is comparatively small, it has been 

 proposed to mix with bones some substance which 

 shall render the phosphate of lime more soluble. 



832. The cheapest and most convenient substance 

 for this purpose is sulphuric acid or oil of vitriol (179, 

 245) ; this forms with bones a compound called " su- 

 perphosphate of lime," one of the most valuable of 

 the artificial manures yet proposed. 



833. Crushed bones, either burnt, or in the raw 

 state (the former, however, being preferable), are 

 mixed in a leaden vessel with sulphuric acid ; after a 

 short time the acid is found to have completely de- 

 composed the bones and reduced them to the state of 

 a moist solid, which, however, may be easily rubbed 



