138 Loss of Phosphor ic Add 



nitric acid ; the solution after being diluted to 200 c.c. was found to 

 contain only 0-0983 grm. of P2O5 in the 200 c.c, that is 42-5 % of the 

 weight of the phosphoric acid originally taken. 



The following experiment showed that the loss did not occur when 

 the fusion with ammonium fluoride was omitted. 0-500 grm. of the 

 same material was ignited twice with sulphuric acid and the residue 

 dissolved in dilute nitric acid; the solution after dilution was found 

 to contain 0-201 grm. P2O5 ; that is 99-0 % of the weight of phosphoric 

 acid originally taken. 



Experiments with Apatite. 



0-500 grm. of the apatite was dissolved in dilute nitric acid and the 

 solution made up to 200 c.c. ; the total P2O5 in 200 c.c. was found to 

 be 0-2062 grm. 



When 0-500 grm. of the same sample was fused with 4 grms. of 

 ammonium fluoride and treated as in the case of the calcium phosphate, 

 the 200 c.c. of solution finally obtained contained only 0-0928 grm. PgOg 

 or 45-0 % of the quantity originally taken. 



Summary. 



1. When salts or minerals containing phosphoric acid are ignited 

 with ammonium fluoride as in the ordinary process of analysis of 

 sihcates, considerable loss of the phosphoric acid may occur. It is 

 probable that the phosphorus is volatilised in the form of a phosphorus 

 fluoride. 



2. The loss is least in the case of salts containing an alkali metal. 

 It is less in the case of disodium hydrogen phosphate than in that of 

 potassium dihydrogen phosphate, and is greatest in the case of phosphates 

 of the alkali earth metals, such as calcium phosphate or apatite. 



{Received May ISth, 1916.) 



