52 Gooch and Clemons—Determination of 
of standard oxalic acid added to the solution acidified with sul- 
phurie acid, subsequently determining the excess of oxalic acid 
in the warmed solution by addition of more permanganate. 
The difference between the amount of permanganate actually 
used and that required to oxidize the known amount of oxalic 
acid introduced should naturally be the measure of the tellu- 
rous acid acted upon. Brauner found, however, an error in 
the process, by no means inconsiderable, due to the decompo- 
sition of the permanganate outside the main reaction. In a 
subsequent paper from this laboratory* it was shown that if 
the precaution is taken to restrict the amount of sulphuric acid 
present in the solution when the permanganate acts the sec- 
ondary decomposition involving loss of unutilized oxygen is 
kept within narrow bounds. In our work upon the oxidation 
of selenious acid we have followed the suggestions gained in 
the treatment of tellurous acid by Brauner’s method. 
The selenium dioxide which we employed was prepared from 
so-called pure selenium by dissolving the element in strong 
nitric acid, removing the nitric acid by evaporation, treating 
the aqueous solution with barium hydroxide to throw out any 
selenic acid formed in the oxidation, evaporating the solution 
to dryness, and subliming and re-subliming the residue in a 
current of dry air until the product was white. The oxide 
thus prepared was weighed out for individual experiments or 
was dissolved in a standard solution from which definite por- 
tions were drawn for use. 
In the first series of experiments, the results of which are 
recorded in Table I, the selenium dioxide was dissolved in 
100 em* of water, 10 cm® of sulphuric acid of half-strength 
were added, an approximately decinormal standardized solution 
of potassium permanganate was added until the characteristic 
color predominated over that of the brown hydroxide deposited 
during the oxidation, oxalic acid in solution of known strength 
was introduced until the excess of permanganate had been 
destroyed and the insoluble hydroxide dissolved, and, finally, 
after heating the solution to about 80° C., more of the perman- 
ganate was added to the color reaction. The final volume 
varied from 250 em* to 350 cm’, so that the sulphuric acid 
(absolute) present varied from about five per cent at the start 
to from one and a half to two per cent at the end. 
When the permanganate is first introduced into the acidified 
solution the color vanishes, leaving a clear colorless liquid, but 
as more is added the solution becomes yellow and deepens 
gradually in color to a reddish brown, until turbidity due to 
the deposition of a brown hydroxide of manganese ensues, and 
finally the characteristic color of the permanganate is plainly 
* Gooch and Danner, this Journal, xliy, 301. 
