no PHOSPHATIC MANURES [chap. 



dissolved bones by being mixed with enough sulphuric 

 acid (see p. 124) to convert about half the phosphates into 

 a soluble condition ; steamed bone meal is also often 

 treated with acid, but the product is not regarded by the 

 trade as dissolved bones, but should be called soluble 

 bone compound or some other name not implying that 

 it has been made from unchanged bones and acid only. 



There are thus four classes of bone fertilisers — (i) 

 the bone itself deprived of fat and crushed into the 

 state of -l-inch or ^-inch bones or bone meal ; (2) 

 steamed bone flour, from which most of the nitrogenous 

 material has been removed ; (3) dissolved bone con- 

 sisting of No. I treated with acid ; (4) bone compound, 

 generally consisting of No. 2 treated with acid and 

 perhaps fortified with nitrogen from some extraneous 

 source. Table XXXII. shows a number of typical 

 analyses of these substances. 



Bone meal, by far the most abundant of these 

 products, is a somewhat gritty powder with a strong 

 and distinctive smell, which should not contain less 

 than 45 per cent of calcium phosphate. The per- 

 centage of nitrogen is more variable : good fresh 

 English samples sometimes show 5, but 4 per cent, 

 is good, and Indian samples which have been much 

 weathered and are a little decayed fall to 3 or even 

 lower; this nitrogen is not present in a very active 

 form, the cartilage being slow to decompose in the 

 soil. Of the phosphates in bones about one-half can 

 be dissolved on shaking up i gramme of the bone meal 

 with I litre of i per cent, citric acid solution, which 

 would show that the phosphoric acid is easily available. 

 However, there is plenty of experimental evidence that 

 bone meal is rather slow acting as a source of phosphoric 

 acid, probably because of its comparative coarseness 

 and the consequent small surface of the manure 



