Phofphatic Materials used for Agricultural Purposes. 11 



As both chalk-coprolites and Suffolk-coprolites contain much 

 fluoride of calcium, by determining the amount of phosphates 

 in the usual way by precipitation, fluoride of calcium is thrown 

 down with the precipitate, in consequence of which the amount 

 of phosphate of lime (bone-earth) is stated three to four per cent, 

 higher than it is in reality. The true amount can only be 

 correctly estimated by determining the percentage of phosphoric 

 acid which they contain, and calculating from this acid the 

 amount of bone-earth. In order to ascertain the true proportion 

 of bone-earth in coprolites, and at the same time the exact 

 quantity of other constituents which take up the sulphuric acid 

 with which coprolite powder is mixed in the manufacture of 

 superphosphate, I have made several detailed analyses of average 

 samples of Cambridgeshire coprolites, and obtained the following 

 results : 



Detailed Composition of Average Samples of Cambridgeshire 



No.l. 



Moisture and organic matter .. .. 4-63 



Lime 43-21 



Magnesia 1*12 



Oxide of iron 



Alumina 



* Phosphoric acid 



fCarbonic acid 



Sulphuric acid 



Chloride of sodium 



Potash 



Soda 



Insoluble siliceous matter 



Fluorine and loss 



* Equal to tribasic phosphate of lime \ 

 (bone -earth) / 



t Equal to carbonate of lime 

 Amount of phosphates, determined) 

 in the usual way by precipitation! 



100-00 



54-89 

 15-13 



It will be seen that in the second sample the amount of phos- 

 phates obtained by precipitation is, in round numbers, four per 

 cent, higher, and in the third sample two per cent, higher, than 

 that resulting from the more accurate method of determining the 

 percentage of phosphoric acid, and calculating from it the 

 amount of bone-earth. 



Powerful machinery is required for reducing coprolites to a 

 fine powder. Coarse coprolite powder is not easily acted upon 

 by acid, and has little or no effect upon vegetation. It is there- 

 fore advisable to reduce coprolites to a minute state of sub- 

 division, and to digest them afterwards with a quantity of acid 

 sufficient to saturate all the carbonate of lime and other con- 



