Blumenthal — Preparation of Selenic Acid. 93 



Art. XI. — The Preparation of Selenic Acid and Sodium 

 Selenate for Use as Reagents in the Determination of 

 Bromine in Haloid Salts ; by Philip Lee Blumenthal. 



[Contributions from the Kent Chemical Laboratory of Yale Univ. — ccxxxix] 



Selenic acid and sodium selenate have been proposed in a 

 previous paper from this laboratory* as reagents for the quali- 

 tative elimination of bromine, in determinable form, from 

 haloid salts. These reagents when made by ordinary methodsf 

 may contain contaminating material likely to be objectionable. 

 The following methods have therefore been devised for the 

 preparation of these reagents in such condition that any foreign 

 material remaining in them shall not interfere with the success 

 of the analytical process. 



Selenic Acid. 



The method proposed for the preparation of selenic acid 

 depends upon the action of nitric acid and potassium bromate 

 upon selenious acid, the bromic acid formed reacting with the 

 selenious acid according to the following equation : 



3H 2 Se0 3 + HBr0 3 = 3H 2 Se0 4 + HBr. 



Further action of the bromic acid breaks up the hydrobromic 

 acid, according to the equation 



HBr0 3 + 5HBr = 3Br 8 + 3H 2 0. 



Upon evaporating the solution to low volume, a second libera- 

 tion of bromine accompanied by nitrogen oxides takes place, 

 apparently according to a reaction like the following: 



2HBrO, + 2HN0 3 = 2H 2 ° + Br 2 + 2N ° 2 - 



The free bromine and the nitrogen oxides are, of course, easily 

 volatilized. The preparation of selenic acid based upon these 

 reactions was put to the test as follows : 



Preliminary Test. — Selenious acid was prepared by dissolv- 

 ing elementary selenium in nitric acid and evaporating the 

 solution to dryness. The crude selenious acid so obtained 

 was sublimed from manganese dioxide according to the 

 method used by Norton,;}; and the thin needle-like crystals 

 were bottled as rapidly as possible. A solution convenient for 

 use was made by dissolving 2 grm. of the purified selenium 

 dioxide in 200 cmb of water and a portion of 20 ctn3 , containing 

 0*1 grm. of the dioxide, was used for each test. To each 

 portion, contained in an Erlenmeyer flask, were added 10 cm3 

 of 1*1 nitric acid and a little potassium bromate, and this 

 solution was evaporated to a low volume. When barium 



* Gooch and Blumenthal, xxxv, 54. 



f Gmelin-Krant, Handbook, Anorg. Chem., i, 769, 1907. 



\ This Journal (4), vii, 290. 



