126 



BLOOD BONES 



case the residue can easily be ground to powder. Sometimes the clot 

 only of blood is employed, the clot being produced either by simple 

 separation by a filter or settling, or by the addition of acid or iron salts 

 to the blood. 



The following table will show the fertilising value of various com- 

 mercial forms : 



Blood easily decomposes in the soil, and its nitrogen and phosphoric 

 acid soon become available to the plant. It gives excellent results 

 with wheat. 



Bones are an important manure and are used in many forms. They 

 form the hard framework of the body of an animal and are largely 

 composed of mineral matter mainly phosphate of lime. In addition 

 there are, in fresh or "green" bones, about 30 per cent of organic 

 matter, containing, perhaps, 3 to 4 per cent nitrogen, and a certain 

 amount of fat. This last ingredient is objectionable, since it hinders the 

 decomposition of the organic matter after the bones are applied to the 

 soil, partly mechanically and partly, perhaps, by forming a lime soap 

 which gives an impervious crust to each fragment. Moreover, it renders 

 the grinding or disintegration of the material more difficult. For this 

 reason, and also in order to extract gelatine from the bones, they are 

 often submitted to the action of steam under pressure ; they are thus 

 robbed of a large portion of their fat and some of their nitrogenous 

 matter, and are rendered much more friable and more susceptible to 

 processes of putrefaction and decay. 



Bones, when applied to the soil in large fragments, only slowly be- 

 come assimilable, remaining almost unchanged in some cases, especially 

 on clay soils, for years. They are therefore always now reduced to 

 small fragments before being applied, being graded according to their 

 degrees of fineness, as "half-inch bones," "crushed bones," "bone 

 dust," " bone meal," and "bone flour". Sometimes bones are treated 

 with acid, when the calcium phosphate dissolves, and the organic 

 matter, from which glue is made, is left behind. From the acid solu- 

 tion, by the action of lime, the calcium phosphate can be precipitated 

 and the dried product is sometimes sold as "precipitated bone flour ". 



Large quantities of bones are obtained from towns and they are 

 now imported from America and Africa. They are slow in action and 

 their effect upon a soil often extends over several years. In order to 

 render their action more rapid they are often converted into super- 

 phosphate or " dissolved bones," which will be described hereafter. 



