

THE 



SOUTH AFRICAN JOURNAL 

 OF SCIENCE, 



CO:\irRISING TPIE REPORT OF THE 



South African Association for the 

 Advancement of Science. 



(1920. BULAWAYO.) 

 VOL. XVll. JULY, 1921. NOS. 3 and 4. 



(3N THE TULFMETEIC DETERMINATION OF 

 PHOSPIIOEIC OXIDE. 



By B. DE C. M Alien AXD, B.A., D.Sf-., 



Chemical Lahoiato) ij, Union Depf. of Agriculture, Pretoria. 



Read Jul)! 15, 1920. 



In a previous communication* a process for tlie deter- 

 mination of phosphoric oxide \yas described ^vhich is chiimed 

 to be as accurate as other methods in common use, and in 

 which the manipuhition is simple and rapid. It was shown 

 that Avhen ammonium phospho-molybdate precipitated by the 

 Lorenz sulphate-molybdate methodf was dissolved in excess 

 of sodium hydroxide, and the excess of alkali determined 

 by titration with acid, the molecular ratio of sodium 

 hydroxide to phosjihoric oxide Avas 50 to 1. The present 

 paper deals with the composition of the ammonium phospho- 

 molybdate precipitate, and with some experiments on the 

 ap})iicability of the method. 



Composition of tiik Precipitate. 



According to von Lorenz, the percentage of pliosphoric 

 oxide in his " Ammonium phosphonnolybdat in seiner 

 molybdanreichsten form " is 3'295. This result was obtained 

 by starting with known quantities of phosphoric oxide and 



* S.A. Journ. of Science, xv, 5, 357 (1918-19). 

 t Landw. Versuchs Stationen, Iv, 183 (1901). 



