L02 Van Name <t»<l Huff— A <■/'</* in Mixture. 



and subsequent evaporation was then repeated, after 

 which the residue was taken up with water, transferred 

 to a glass-stoppered flask, and the iodometric analysis 

 carried out as already described. 



If phosphorous acid is present at the outset, the iodo- 

 metric analysis must be carried out upon separate por- 

 tions of the solution before and after hydrolyzing with 

 hypophosphoric acid, and the amount of the latter cal- 

 culated from the difference. This presents no difficulty, 

 and appears to be the most satisfactory method available 

 for the estimation of hypophosphoric acid in the presence 

 of phosphorous and phosphoric acids. 21 



III. Complete Analysis of a Mixture of the Three Acids. 



Three portions of the solution are measured out. In 

 the first the phosphorous acid is determined as described 

 in section I. In the second the hypophosphoric acid is 

 hydrolyzed according to section II and the phosphorous 

 acid then estimated as before, the gain as compared with 

 the first portion giving the content of hypophosphoric 

 acid. In the third portion the reducing acids are com- 

 pletely oxidized by treatment with hot aqua regia and 

 evaporation nearly to dryness, and the total phosphoric 

 acid then estimated by any one of the standard methods. 

 The phosphoric acid originally present is calculated by 

 difference. 



Summary. 



1. An iodometric method for the estimation of phos- 

 phorous acid is described, which is applicable in the 

 presence of hypophosphoric and phosphoric acids. 



2. Hypophosphoric acid can be estimated by first 

 hydrolyzing completely and then following the method 

 just mentioned. 



3. A mixture of phosphorous, hypophosphoric, and 

 phosphoric acids can be completely analyzed by the above 

 processes, combined with the determination (after oxidiz- 

 ing the reducing acids) of the total phosphoric acid. 



4. Incidentally, another volumetric process for the 

 estimation of phosphorous acid is described. This pro- 

 cess, which is a more rapid modification of Kuhling's 

 method, is applicable in the presence of phosphoric but 

 not of hypophosphoric acid. 



21 For criticisms of the method proposed by Eosenheim and Pinsker, Zs. 

 anorg. Chem., 64, 333 ff., see the following article. 



