Van Name and Huff — Phosphorous, etc., Acids in "Mixture. 91 



Akt. VII. — The Estimation of Phosphorous, Hypophos- 

 phofic and Phosphoric Acids in Mixture; by R. Gr. 

 Van Name and Wilbert J. Huff. 



(Contributions from the Kent Chemical Laboratory of Yale Univ. — ecxcvii.) 



Since lrypophosphoric acid solutions undergo a gradual 

 hydrolytic decomposition with the formation of phos- 

 phorous and phosphoric acids, the possession of a depend- 

 able method for the quantitative analysis of the resulting 

 mixture is of fundamental importance for any extended 

 study of the properties of lrypophosphoric acid. The 

 standard methods for determining phosphorous acid, as 

 ordinarily carried out, would be inapplicable in the pres- 

 ence of lrypophosphoric acid, while both the iodometric 

 method proposed by Rupp and Fink 1 and the essentially 

 equivalent method of Rosenheim and Pinsker, 2 which the 

 last named authors claim to be accurate in the presence 

 of hypophosphoric acid, are unfortunately unsound. In 

 both the phosphorous acid is oxidized by an excess of 

 iodine in the presence of potassium bicarbonate, and the 

 iodine remaining is titrated with thio sulphate in the 

 bicarbonate solution. Since, however, it has been con- 

 clusively proved that the estimation of iodine by thiosul- 

 phate in the presence of an alkali bicarbonate gives 

 wholly inaccurate results, 3 it is evident that these 

 methods are of little value. 



In connection with a study of the reducing proper- 

 ties of hypophosphorous and phosphorous acid, Sie- 

 verts 4 estimated phosphorous acid by a modification 

 of the method of Rupp and Fink, in which the excess of 

 iodine was determined by arsenic in the bicarbonate solu- 

 tion, thus avoiding the objection above mentioned. This 

 method, though not used or recommended by Sieverts 

 for such a purpose, would in fact be applicable in the 

 presence of hypophosphoric acid, but, as will be shown 

 later, there is an inherent source of error in the method 

 which limits its accuracy. In anything but a very 

 thorough search of the literature this method might 

 easily be overlooked, since the description of it is merely 

 incidental, in an article upon a wholly different subject. 



1 Ber. chem. Ges., 35, 3691, 1902. 



2 Zs. anorg. Chem., 64, 327, 1909, also Pinsker, Dissertation, Berlin, 1909. 

 3 Topf, Zs. anal. Chem., 26, 183-188, 1887; Euff and Jeroeh, Ber. chem. 



Ges., 38, 409, 1905; Ashley, this Journal, 19, 237, 1905. 

 1 Zs. anorg. Chem., 64, 29, 1909. 



