THE CITRIC SOLUBILITY OF MINERAL 

 PHOSPHATES 



By J. F. TOCHER, D.Sc, F.I.O. 



Consulting Chemist to the HiyhlunA and Agrieidtural Societij oj Scotland; 

 Lecturer on Statistics, Vnirersity of Aberdeen. 



(With 8 Diagrams.) 



I. INTRODUCTORY. 



The Fertilisers and Feedin.ii Stuffs Act 1906, Section 10, defines the 

 expressions "soluble" and "insoluble" to mean that the fertilising con- 

 stituent is soluble or insoluble in water, or, if specified in the invoice, 

 to mean that the fertilising constituent is soluble to the extent guaranteed 

 in a solution of citric acid, or other solvent, of the prescribed strength. 

 In particular the section defines the percentage of soluble phosphate and 

 the percentage of insoluble phosphate to mean respectively the percentage 

 of tribasic phosphate of Ume equivalent which has been, or that which 

 has not been, rendered soluble. "Citric solubihty" under the Act is 

 further and more definitely defined in the FertiHsers and Feeding Stuffs 

 General Regulations 1906 as follows : 



"When, in an invoice relating to hasic slag or basic superfhos-phate, 

 it is specified that a certain percentage of the phosphate contained in 

 the basic slag or superphosphate is soluble in citric acid, this shall be 

 taken to mean that it is capable of being dissolved to the extent of such 

 percentage when 5 grams of the fertiliser and 500 cubic centimetres of 

 water, containing 10 grams of citric acid, are continuously agitated in 

 a flask or bottle of about 1 htre capacity for the period of half an hour 

 at the ordinary temperature." 



It is clear from these regulations that "citric solubihty" refers to 

 ba.sic slags and "basic superphosphates "^ and that the citric solubihties 

 of basic slags and of basic superphosphates have to be determined at 

 "room" temperature by means of a 2 per cent, solution of citric acid, 

 the duration of contact being limited to half an hour in a quantity of 



^ The seller need not, unless he chooses to do so, f^ive any (guarantee of citric .solubility. 



