FERTILIZERS AND MANURES. 77 



more difficult, and retards the decomposition of the bones 

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

 When bones are steamed the fat is removed, and the bone 

 is more readily ground. Moreover, the chemical nature 

 of the nitrogen compounds appears to be changed in such 

 a manner that the meal undergoes decomposition in the 

 soil more rapidly than in the case of raw bone. The 

 presence of easily decaying nitrogen compounds in bone 

 hastens, in the process of decomposition, to dissolve more 

 or less of the insoluble phosphate. Bone-meal should 

 contain from three to five per cent, of nitrogen and from 

 twenty to twenty-five per cent, of phosphoric acid; about 

 one-third or one-fourth of the latter appears to be in 

 readily available condition. Raw bone-meal generally 

 contains somewhat more nitrogen (one to two per cent.), 

 and rather less phosphoric acid than steamed bone-meal. 



"The fineness of the meal affects its value; the finer 

 the meal the more readily available it is for plant food. 

 On account of the increased demand for bone for various 

 purposes, and on account of their increasing value, there 

 is considerable tendency to adulterate bone-meal with such 

 substances as lime, gypsum, coal-ashes, ground oyster- 

 shells, ground rock phosphate, etc. 



"Phosphatic Guanos, ok Rock Guanos. — Guanos 

 generally consist chiefly of the dung of sea-fowls, though 

 the term is applied to other animal products. They are 

 generally found in beds resembling earthy deposits. The 

 guanos which are called phosphates contain little or no 

 nitrogen. Their phosphoric acid is generally in the form 

 of insoluble phosphate of lime, iron and alumina. These 

 guanos come mainly from certain islands in the Pacific 

 Ocean, and from Caribbean Sea and West India Islands. 

 The amount of phosphoric acid in different guanos is very 

 variable, ranging from below fifteen to over thirty per 

 cent. 



