372 Wisconsin Academy of Sciences, Arts, and Letters. 
oxide has ceased, is separated from the green residue that 
forms, and is distilled with fresh portions of the chromic and 
sulfuric acids. Only small amounts of the acids should be 
present during the distillation, as large quantities cause dan¬ 
gerous bumping. The still must be so arranged that no ma¬ 
terial but glass comes in contact with the bromine. Only the 
middle portion of the distillate is collected for use, and must 
be free from chromium and sulfuric acid. The presence may 
be detected by dissolving a few cubic centimeters of the bro¬ 
mine in dilute ammonia, boiling to precipitate any chromium 
present in the reduced condition, which would appear as hyd¬ 
rated chromic oxide, making acid with acetic acid, and adding 
barium chloride to show the presence of sulfuric acid or chrom¬ 
ium as chromate. 
Having obtained pure selenium dioxide and pure bromine, 
the next step is the formation of silver selenite. All glass com¬ 
ing in contact with the preparation is cleaned with a mixture 
of chromic and sulfuric acids, and the water used is distilled 
Prom potassium permanganate and sodium hydroxide. 
A ten percent aqueous solution of the dioxide is treated with 
a slight excess of silver nitrate solution. Silver selenite pre¬ 
cipitates as a white crystalline salt. This is washed by decan¬ 
tation until it is absolutely free from silver nitrate and nitric 
acid. If nitric acid is allowed to remain in the silver selenite, 
it decomposes the hydrogen sulfide used later thus contamin¬ 
ating the selenic acid. 
The silver selenite is suspended in water, and bromine added 
in small portions with vigorous shaking after each addition, 
until the red color of the solution indicates that an excess of 
bromine has been added. The solution is then placed on a 
steam bath for at least twelve hours to complete the oxidation 
and coagulate the precipitate. During all these operations 
care must be taken to exclude dust. The silver bromide is filt¬ 
ered off on well cleaned glass wool. 
The filtrate is concentrated by distilling off the bromine and 
water under reduced pressure. The distillation apparatus is 
so arranged that no corks, or rubber stoppers, come in contact 
with the acid. A Jena glass retort, sealed to a water jacketed 
condenser which in turn is connected to a suction flask and 
pump, serves the purpose very well. A few glass beads 
placed in the retort prevent bumping. 
