PHOSPHORUS FERTILIZERS 157 



Littoral. It is said to be a very satisfactory fertilizer, but 

 there is no real evidence to show that it possesses any supe- 

 riority to other phosphates. It can easily be understood that, 

 if the material is applied to land that is lacking in lime, it 

 may have proved superior to superphosphate, or, that where 

 sodium and magnesium are lacking, its advantage may be 

 due to the presence of some of the sodium or magnesium 

 compounds. Until the matter has been more fully dealt 

 with, the production of this article must be looked upon as 

 an enterprise of doubtful value, since the original ground 

 natural phosphates, without any treatment at all, are quite 

 capable of producing satisfactory results on soils very deficient 

 in phosphates. Other similar attempts have been made to 

 calcine rock phosphates, with the idea that they would then 

 form some special new compounds, supposed to be repre- 

 sented by the formula Ca 4 P 2 O 9 . Little experimental 

 evidence is available to suggest that the treatment has ren- 

 dered the material of much greater value than before. A 

 rock phosphate containing large proportions of calcium 

 carbonate might be economically improved by calcining, 

 if only for the reason that the loss of moisture and carbonic 

 acid would save freightage charges. Calcining also mechani- 

 cally disintegrates the mineral, especially when much carbon 

 dioxide is given off in the process. 



Precipitated Bone Phosphate. For the manufacture 

 of certain classes of glue and gelatine, bones are treated with 

 hydrochloric acid. It is preferable that the bones should 

 first of all be extracted with benzine, to obtain them free 

 from fat, as described on p. 73, otherwise the acid acts 

 somewhat slowly. By acting upon extracted bones with 

 hydrochloric acid, the whole of the phosphoric acid contained 

 can be dissolved, leaving the gelatinous substance behind. 

 The equation representing this change is : Ca 3 P 2 O 8 + 4HC1 

 = CaH 4 P 2 Og + 2CaCl 2 . As the mono-calcium phosphate 

 is not perfectly stable in presence of water a slight 

 excess of hydrochloric acid must be used. In the actual 

 course of manufacture, the bones are placed in a wooden 

 vat fitted with a mechanical agitator ; where the bones are 



