The Composition and Use of Fertilizers. 231 



compounds of commerce are supplied for fertilizers. The ma- 

 terials which furnish the greatest proportion of phosphoric 

 acid used in making- fertilizers are the following: Bones, bone-ash, 

 bone-black, bone-meal, fish, phosphatic guano, rock-phosphate, 

 superphosphates, Thomas slag, vegetable matter, etc. 



Bones. — Bones consist of two quite different kinds of mate- 

 rial, in addition to water. The hard portion consists mostly of 

 phosphate of lime, and constitutes from one-half to three-fifths 

 of the weight of the bone. The remaining portion consists 

 largely of a soft, flesh-like substance called ossein, or, more com- 

 monly, gelatin, together with more or less fat. It, is distributed 

 throughout the entire mass of bone and is rich in nitrogen. When 

 bones are burned, the nitrogenous matter is driven off and only 

 the mineral portion or phosphate of lime remains. The amount 

 of nitrogen and phosphate of lime in bones varies with the kind 

 of bone and also with the maimer in which it is treated. Bones 

 of different kinds of animals vary in composition and also dif- 

 ferent bones in the same animal. Age affects composition. The 

 bones of young animals usually contain more nitrogen and less 

 phosphate of lime, the reverse being true of older animals. As 

 bones come into market for nse as fertilisers, their variation of 

 composition is due more to the manner in which they are treated 

 than to differences of composition originally existing in the bones. 

 We find in the market the following forms of bone as the com- 

 mon ones : Raw bone, bone-meal, steamed bone, and bone tankage. 



Raw Bone. — By raw bone is understood bones that have been 

 ground in their natural state without previous treatment, sneh 

 as steaming, boiling, etc. Raw bone contains the fat naturally 

 present in bones and this is objectionable, because it makes grind- 

 ing more difficult and delays the decomposition of the bone in 

 the soil, while fat itself has no value as plant food. Good raw 

 bone should contain 4 to 5 per cent, of nitrogen and 20 to 25 

 per cent, of phosphoric acid, equivalent to 45 to 55 per cent, 

 of phosphate of lime. 



Bone-Mcal goes under various names, such as ground bone, 

 bone-flour, bone-dust, fine bone, etc. These terms are supposed 

 to refer to fineness of division rather than to composition. They 

 are more commonly used of steamed than of raw bone-meal. The 

 fineness of the bone affects its value; the finer the meal, the more 

 readily available is it as plant food. On account of the increased 

 demand for bones for various purposes, and on account of their 

 increasing value, there is considerable tendency to adulterate bone- 



