188 MANURE. 



out by acid, the animal portion remains, with all the form 

 and bulk of the bone. Bones which are offered in the mar- 

 ket, are quite as rich in the elements above stated, as are 

 unboiled bones. The phosphate of lime is rendered quite 

 soluble by its combination with gelatine and albumen. The 

 class of mixed manures, containing nitrogen, has thus been 

 considered. The principle of their action and the foundation 

 of their value, pointed out. The action of the second class, 

 or that not containing nitrogen, remains to be explained. 



224. All fats and oils exposed to air give off a quantity 

 of carbonic acid, and end by becoming acids. As their ulti- 

 mate elements are the same as those of plants, it may be 

 inferred, that under the influence of growing plants, fats and 

 oils are decomposed and become vegetable food. But there 

 is another action of fats and oils on silicates ; they not only 

 let loose the alkali of silicates by the carbonic acid, which 

 they evolve, but the oils now become acids, immediately 

 combine with this alkali, and imperfect soaps are formed. 

 Soaps are truly chemical salts, and hence we have at once a 

 clew to the action of oil and fat. 



225. Among the most powerful of manures in the class 

 composed of geine and salts, is soot. There is no one sub- 

 stance so rich in both. Its composition allies it to animal 

 solids, and is as follows : 



Geine (ulmin), 30.70 



Nitrogen, 20. 



Salts of lime, mostly chalk, .... 25.31 



Bone-dust, 1.50 



Salts of potash and soda, and ammonia, . . 6.14 



Carbon, 3.85 



Water, 12.50 



100.00 



