92 Van Name and Huff- — Estimation of 



The methods of analysis to be described were devel- 

 oped to meet the need for accurate analytical processes 

 for the special purposes of a research upon hypophos- 

 phoric acid, the results of which will be published in 

 subsequent articles. 



I. The Estimation of Phosphorous Acid in the Presence 

 of Hypophosphoric Acid. 



A solution of phosphorous acid, slightly less than tenth 

 normal in reducing power, was prepared by dissolving 

 in water the crystallized acid (furnished by Baker and 

 Adamson). This solution, which contained a little phos- 

 phoric acid as impurity, was standardized by three 

 independent methods as follows : 



(a) As Magnesium Pyrophosphate. — To estimate the 

 phosphoric acid present, measured portions of the solu- 

 tion were treated with magnesium chloride mixture under 

 the conditions recommended by Gooch and Austin. 5 The 

 precipitate was dissolved in a little hydrochloric acid and 

 reprecipitated by ammonia. Rupp and Fink 6 have 

 shown that a double precipitation is necessary to free 

 the precipitated ammonium magnesium phosphate from 

 phosphite.. The precipitates were ignited and weighed 

 as magnesium pyrophosphate. Other measured portions 

 of the original solution were treated with aqua regia and 

 evaporated as far as possible over a water bath, thus 

 oxidizing the phosphorous acid to phosphoric acid, which 

 was then precipitated as above and weighed as magne- 

 sium pyrophosphate. From the difference in the results 

 before and after oxidation the phosphorous acid content 

 of the solution was calculated. Two determinations, 

 using 45 cm 3 portions of the solution gave, respectively, 

 0.2524 — 0.0366 = 0.2188, and 0.2523 — 0.0366 = 0.2187 

 grm. Mg,P 2 7 , equivalent to 0.003583 and 0.003582 grm. 

 H 3 P0 3 per cm 3 . 



(b) As Mercurous Chloride. — Adherence to the direc- 

 tions for this method of estimating phosphorous acid, as 

 given in the standard text-book of Treadwell-Hall 7 led 

 to several failures from incomplete precipitation. Pro- 



5 This Journal, 7, 187, 1899. 



6 Ber. ehem. Ges., 35, 3692, 1902. 



"'Analytical Chemistry", 3rd English ed., pp. 374 and 372. The condi- 

 tions recommended are the same for phosphorous as for hypophosphorous 

 acid. 



