128 The Citric Soliihilifi/ of Mineral PJwsphates 



The results of this table show that when mineral phosphate is as 

 finely ground as basic slag a fair amount of phosphate is rendered " citric 

 soluble"' by the official method but the "citric solubility" of mineral 

 phosphates appears generally to be much less than the citric solubility 

 of slags, when this test is apphed. 



irr. TITK SCHK^rK of KXrKRTMKXTAI. WORK. 



The citric solubility uf mineral phosjihates was accordingly studied 

 at "room" temperature over a period of 30 minutes agitation: 



(1) In varying dilution, the quantities of acid and mineral phosphate 

 being constant. 



(2) In varying concentrations of acid, the volume of fluid and the 

 weight of mineral phosphate being constant. 



(3) With varying amounts of the phosphatic fertihser, the volume 

 of the fluid and the concentration of acid being both constant. 



In order to compare the citric .solubility of mineral phosphates under 

 the above conditions, with the citric solubiUty of a pure phosphatic 

 compound, a fourth series of experiments was conducted, namely, 



(4) the solubihty of dicalcium phosphate in dilute hydrochloric acid. 

 It is evident that whatever be the value of determining the j)ro- 



portion of citric soluble phosphate in a phosphatic fertiliser, it is neces- 

 sary, for comparative purposes, if other conditions are similar, that the 

 test should be applied in the same way and with the same proportions of 

 citric acid or of other acid and of fertiliser as prescribed officially, for 

 basic slags and basic superphosphates. 



Other conditions are, of course, open to study. For example we could 

 have two of the above factors varying differently with a series of constant 

 values for the third factor. The citric solubility of tricalcium phosphate 

 and other pure phosphatic compounds could be studied and the results 

 compared with the results from the above four series. The writer has 

 not been able to carry out these latter experiments. He therefore sub- 

 mits the results of experimental work under the above four heads'. 



' The writer has to acknowledge his indebtedness to Mi .lnhn I']. Ritchie, M.A., B.Sc., 

 A. I.e., who has performed the necessary analytical determinations in the exi)eriments 

 on mineral phosphates, and has also given valuable assistance in preparing the memoir. 

 He has also to thank Mr W. T. H. Williamson, B.Sc., A.I.C., for the determinations in 

 the case of dicalcium phosphate. 



