11 



of this constituent. They are valuable as they contain nitrogen and phosphoric 

 acid. Ground raw hones may contain about 3Cr per cent, of organic matter, with 

 perhaps 3 to 4 per cent, of nitrogen and about 20 per cent, of phosphoric acid. 

 Raw bones, however, also contain considerable fat. This ingredient is objection- 

 able since it hinders the decomposition of the organic matter after the bones 

 are applied to the soil, and it also renders it practically impossible to reduce 

 the bones to a finely divided condition before applying. For this reason, and 

 also in order to extract gelatine, they are submitted to the action of steam under 

 pressure and thus robbed of their fat and some of the gelatine and brought into 

 a condition to be easily reduced to a fine state. This steamed hone meal will con- 

 tain 1 or 2 per cent, or under some methods of extraction even more, nitrogen, 

 with from 20 to 25 per cent, of phosphoric acid. The phosphoric acid is chiefly 

 in the form of tri-calcic phosphate, which is insoluble in water; consequently, 

 the finer the bones are ground the more rapidly the material will come into 

 solution in the soil. Bones are particularly valuable for their phosphoric acid, 

 and are usually classed as a phosphatic manure. 



Tankage. 



Tankage is a nitrogenous product and consists chiefly of dried animal Avastes 

 from slaughter houses. It varies somewhat in composition since it includes other- 

 wise unsalable parts of the carcass, as bones, flesh, hair, hoof, horn, etc. The 

 keratine substances do not decompose readily in the soil, consequently, while tankage 

 may be approximately as rich in nitrogen as dried blood and meat meals, it is 

 not so valuable because it does not give as quick returns. It usually contains 

 a varying quantity of phosphoric acid. 



Fish Manuee. 



The bodies of fish are highly nitrogenous and their bones contain large 

 quantities of phosphates. Sometimes the refuse from the fish canneries is incor- 

 porated in these fish manures. In general, the most objectionable feature to them 

 is the oil which they contain, as this hinders the fermentation and decay of the 

 materials by repelling the water. 



Naturally, this manure varies widely in composition. American dried fish 

 refuse is said to contain about 7 per cent, of nitrogen and about the same amount 

 of phosphoric acid. 



Vegetable Eefuse. 



Certain forms of vegetable refuse, as oil cakes, husfe, etc., which are left 

 after the oil is extracted from certain seeds arc sometimes used as a fertilizer. 

 These materials are frequently highly nitrogenous and contain a considerable 

 quantity of phosphates and potash. Some of them decompose slowly in the soil 

 and are not quick acting manures. These materials are usually used as cattle 

 feeds, but in some cases owing to the presence in the seed of poisonous or unpalat- 

 able substances, they are used in the making up of certain forms of fertilizers. 

 They may contain as much as 5 per cent, of nitrogen, 1 to 2 per cent, of potash 

 and 3 to 3 per cent, of phosphoric acid. 



