BONES. 809 



825. The drainage-water of towns, generally con- 

 taining, as it does, urine, refuse from the kitchens, 

 soap, &c., is an excellent manure; the most valuable 

 substances which it contains exist in a state of solu- 

 tion; the mud which falls to the bottom when it is 

 left to stand at rest, is comparatively speaking of 

 little value. 



826. The last animal manure which it is necessary 

 to speak of is bones, though, as their chief value con- 

 sists in the inorganic matters which they contain, 

 they might almost be classed amongst the inorganic 

 manures. 



827. Bones consist of earthy matters together with 

 a quantity of gelatine and fat ; the value of bones 

 as a manure consists in their mechanical effect on the 

 texture of the soil, the earthy substances which they 

 supply (876), the ammonia given out during the decay 

 of the gelatine or glue, and the carbonic acid and 

 hydrogen supplied by the fat (595). 



828. The quantity of putrefiable matter in bones 

 is small in proportion to their whole weight, and its 

 decomposition is retarded by the large quantity of 

 earthy matter they contain ; hence bones form a good 

 and lasting manure. 



829. Boiled bones form a better manure than raw 

 or- green bones, ^fhis appears to be caused by the 

 removal of fat by boiling ; the fat which bone con- 

 tains retards the decomposition of the gelatine, and 

 probably also renders the phosphate of lime less so- 

 luble than it is when the oil is removed. 



