400 Gooch and Hvans—Reduction of Selenic 
Art. XLUI.— The Reduction of Selenic Acid by Hydrochloric 
Acid; by F. A. GoocH and P. S. Evans, JR. 
[Contributions from the Kent Chemical Laboratory of Yale College—XLV.] 
It has long been known that selenic acid is reducible by 
hydrochlorie acid with evolution of chlorine, but the reaction 
was regarded as more or less uncertain until Petterson showed* 
that conditions of action may be secured under which the 
reduction proceeds so regularly that the chlorine evolved may 
be estimated iodometrically and taken as the measure of the 
selenic acid originally present, or of the selenious acid pro- 
duced. According to this method of determination, it is only 
necessary to boil a solution of selenic acid in hydrochloric acid 
of moderate concentration, and if the solution is not too dilute 
the reduction is obtained in a few moments. Petterson did 
not, however, fix with exactness the limits of dilution within 
which a successful determination of the selenic acid may be 
expected. The object of this paper is to record the results 
which we have obtained in studying more closely the condi- 
tions necessary to an accurate and rapid reduction. We have 
used in our experiments solutions of selenic acid prepared by 
oxidizing pure, white, resublimed selenium dioxide according 
to the method laid down in a previous paper from this labora- 
toryt for the quantitative determination of that substance. A 
portion of the crystalline oxide, approximately two grams, was 
carefully weighed, dissolved in 120 cm* of water containing 
one-twelfth of its volume of sulphuric acid, and treated with a 
strong solution of potassium permanganate until the color 
characteristic of a distinct excess of that reagent prevailed dis- 
tinctly over that of the brown oxide of manganese thrown 
down in the oxidation. The liquid was warmed to about 50° C., 
bleached by oxalic acid, and the excess of this reagent was 
destroyed by more permanganate. On account of the tend- 
ency of manganous salts, when present in considerable amount 
in warm solutions containing but little free acid, to react upon 
any considerable excess of permanganate with the deposition 
of higher oxides of manganese, it is generally necessary to 
repeat the bleaching and oxidizing process two or three times 
before the final color of a slight excess of the permanganate 
remains in clear solution and indicates the completion of the 
oxidation of the selenium. Finally, the liquid was filtered, 
diluted carefully to the volume of one liter, and used as a stan- 
dard solution. 
* Zeitschr. Anal. Chem., xii, 287. 
+ Gooch and Clemons: this Journal, 1, 51. 
