32 PLANT PRODUCTS 



Bibliography.) It has the advantage over super-phosphate 

 that it is not acid in character, and, therefore, does not 

 encourage the development of ** Finger and Toe " disease in 

 turnips. Its extreme solubility in very feeble acids makes 

 it practically as available to the plant as super-phosphate. 

 It is also very dry and fine, and easily distributed. A some- 

 what similar material called precipitated bone phosphate 

 is obtained as a by-product of the glue and gelatine manu- 

 facture. (See Bennett.) When bones are treated with cold 

 dilute hydrochloric acid, the framework of the bone is left 

 in gelatine and the calcium phosphate dissolved by the acid. 

 The acid liquids, together with the washings, are then 

 precipitated with just enough lime to recover all the phos- 

 phoric acid, giving a precipitate about half di-calcium 

 phosphate and half tri-calcium phosphate. The two last- 

 named fertilizers are favourites with those who grow turnips 

 on a large scale. 



Bone Black and Bone Ash. — In sugar refineries con- 

 siderable quantities of bone black were used. After a time 

 it is beyond the power of the users to regenerate the bone 

 black for their purpose, and this is then sold as a fertilizer. 

 Bone ash, made either by burning bones or by burning the 

 refuse from the sugar refineries alluded to above, or obtained 

 direct from South America, is used for fertilizing purposes. 

 The difference between used-up bone black and bone ash 

 is, from a fertilizer point of view, of no particular importance, 

 since a few per cents, more or less of carbon will not influence 

 the results. Bone ash is fairly readily available in the soil, 

 and in this respect resembles basic slag. It is, of course, 

 a purely phosphatic manure, and may contain anything 

 up to 85 per cent, of tri-calcium phosphate. It is quite 

 suitable for any of the purposes of precipitated phosphate 

 or basic super-phosphate, but cannot be used as a top 

 dressing like super-phosphate. Bone ash, when finely ground, 

 is almost entirely soluble in weak citric acid. 



Fertilizers containing both Nitrogen and Phosphorus. 

 — ^The different requirements of crops and soils preclude 

 the possibility of any fixed ratio between nitrogen and 



