THE DETERAIINATION UF PiiUSrHURlC OXIDE, 



PARTICULARLY IN FERTILISERS, SOIL 



EXTRACTS, AND THE LIKE. 



By Beknarj) de Cohgny MARCiiAND, B.A.. D.Sc. 



i^Read July lo, 1918.) 



The methods that have from time to time been proposed for 

 the determination of phosphoric oxide are innumerable. We 

 do not propose to enter into a discussion of the merits and 

 demerits of these methods but to draw attention to a simple and 

 rapid method which presents many advantages over some of the 

 processes commonly employed. The method cannot be said to be 

 original, as it is merely a combination of two well-known 

 methods which have been largely employed in fertiliser analysis. 



The method is due to the late H. J. Vipond, Chemist, 

 Department of Agriculture, and is a combination of von Lorenz's 

 method of precipitation for ammonium phosphomolybdate and 

 Pemberton's volumetric method for the dejtermination of the 

 precipitate. 



Von Lorenz's method of precipitation involves a departure 

 from the i:sual methods used for precipitation of the ammonium 

 phosphomolylxlate in that no ammonium nitrate is used, while 

 ammonium sulphate is used instead. The underlying idea of 

 von Lorenz's procedure is the precipitation of a phosphomolyb- 

 date of constant composition which can be converted into a form 

 in which it can easily be weighed, while by the use of compara- 

 tively large volumes of strong acids possible interference of silica 

 and organic compounds is prevented. 



When von Lorenz''' first published his method it attracted 

 very little attention, but Neubauer (in the Meetings of the Ver- 

 band Landwirtschaftlicher Versuchs-Stationen im Deutschen 

 Reiche) took the mauer up and succeeded in getting the method 

 adopted as an official method of the Verband. Neubauerf has 

 also modified the method in two details, which appear to be 

 improvements on the original method. 



We do not propose to describe the original method, or Neu- 

 bauer's modifications, except in so far as it is used in the modi- 

 fication adopted by Vipond. 



Solution of the phosphoric oxide may be made by any of 

 the methods employed generally, e.g., for the determination of 

 the total phosphoric oxide in fertilisers, the substance is boiled 

 with nitric acid, or soil extracts are ignited and ground, as pro- 

 posed by Neubauer. J and generally adopted by agricultural 

 chemists and the phosphoric oxide dissolved by means of dilute 

 sulphuric acid. 



* Landw. Versuchs Stationen (1901), 55, 183. 

 i Zeit. Anal. Chem. (1912), 51, i6r. 

 tl.ainh<.'. I'erss. Stat. (1906), 63, T41. 



