THE PHOSPHORUS GROUP OF FERTILIZERS 33 



phosphorus in fertilizers, but for most arable purposes both 

 will be required. Probably fertilizers containing two ingre- 

 dients are often sources of loss, since one of the ingredients is 

 likely to be in excess. This loss can only be avoided if very 

 careful study is made of the conditions, and the ratio of nitro- 

 gen to phosphorus adjusted to suit the special requirements. 

 Bones. — Bones became very popular as soon as the early 

 ideas of phosphatic manure became at all widespread. The 

 bones of animals invariably contain some grease. The amount 

 of grease varies with the bone, but on the general average a 

 raw bone or rag bone contains about 12 per cent, water, 28 per 

 cent, nitrogenous organic matter, 10 per cent, fat, 44 per cent, 

 tri-calcium phosphate, and 5 per cent, calcium carbonate. 

 There are also traces of magnesia and fluorine. Large bones 

 of such a composition are very slow in decomposing in the 

 soil, and may be regarded as having no practical value. 

 If they are finely ground their value is greatty increased, but 

 the fat content acts as a preservative and diminishes the 

 value. Fortunately, the fat can be made a better use of. 

 Under the best systems the rag bones are extracted with 

 petroleum spirit, and the grease obtained is a valuable 

 product. The extraction of the fat renders the bones 

 porous, easy to grind, and available after application to 

 the soil. The high-class bone meal obtained in this way 

 will often have over 5 per cent, of nitrogen, and about 40 

 per cent, to 45 per cent, of tri-calcium phosphate. In some 

 works, however, the fat is removed b}^ a process of steaming 

 and boiling, which removes a good deal of gelatine as well 

 as fat. The remaining bones from this process are very 

 porous, grind very easily, and are far more readily available 

 to plants. According to the degree of treatment the bones 

 have received, the composition will vary from 3 per cent, 

 nitrogen and 50 per cent, tri-calcium phosphate to i per 

 cent, nitrogen and 60 per cent, tri-calcium phosphate. The 

 term '* bone meal " is commonly understood to mean 

 materials containing 4 or 5 per cent, nitrogen, which have 

 been obtained by some petroleum extraction ; whilst the term 

 " bone flour " is commonly understood to mean the materials 

 D. 3 



