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THE FARMERS HANDBOOK. 



manure. It is more particularly adapted to light soils, and is sometimes 

 disappointing on heavy elays, the probable reason for which is that in stiff 

 clay soils it is more or less protected from putrefaction (which we have seen 

 is the cause of its efficacy) by the absence of air and moisture. 



Boiled or steamed bones or bone-meal. — When bones or bone-meal are 

 boiled, and more effectually when they are subjected to steam, the ossein of 

 the bone is gelatinised, and more or less removed, whilst the fat is also 

 removed, the resulting compound being, therefore, poorer in nitrogen, but 

 richer in phosphoric acid. The treatment renders them more friable, and 

 they are easily reduced to fine powder. The removal of the fatty matter 

 also renders them more easily decomposed in the soil, as fresh bones are more 

 or Jess protected from external action by the presence of the fat. Not 

 only is the proportion of phosphoric acid increased, but the rapidity of 

 action of the product, and its consequent effectiveness as a manure, is 

 increased, at the expense, of course, of the nitiogen, which may be reduced 

 1 or 2 per cent., as is shown in the table below. 



Bone-ash. — The residue left after the calcination of bones consists, as we 

 have seen, mainly of phosphate of lime, and contains no nitrogen. It is not 

 largely used as a manure. It is dissolved in the soil by carbonic acid, and 

 conveyed thus directly to the plant. 



Bone-black is the product of charring bones. The broken bones are sub- 

 jected to strong heat in closed iron cylinders, whereby they are converted 

 into bone-charcoal, on exactly the same principle that wood is converted 

 into wood-charcoal. The volatile matter of the bones is driven off in the 

 form of gas, water, oil, and tar, and the carbon present is for the most part 

 left mixed as charcoal with the mineral matter of the bones. This product 

 is largely used by sugar-refiners for removing the colouring matter from raw 

 syrups. After it has been used for this purpose a certain number of times 

 it becomes unserviceable, and can be obtained at a cheap rate for manurial 

 purposes. It may be applied directly to the soil as a phosphatic manure or 

 better converted into superphosphates by treatment with acid. 



The following table shows the alteration in composition which bones 

 undergo when subjected to the above methods of treatment. The analyses 

 are not analyses of the same sample but represent fairly the average com- 

 position of the several products. The analyses of bone-black were kindly 

 supplied by the Colonial Sugar Company, and represent their " char " before 

 and after it had been used for the purpose of refining : — 



