Morris—The Preparation of Selenic Acid 
371 
Selenium dioxide of excellent quality is prepared in the fol¬ 
lowing manner: Selenium is dissolved in nitric acid^ specific 
gravity I .25 and the solution ■ evaporated to dryness. The im¬ 
pure dioxide resulting is heated to a temperature just below 
that at which it will sublime in order to remove the excess of 
nitric acid. After the dioxide is dissolved in water^ barium 
hydroxide is added until no further precipitate of barium sulf¬ 
ate forms. This is filtered off, and the solution again evapor¬ 
ated to dryness. 
Selenium dioxide does not melt under atmospheric pressure, 
but may be sublimed as pure white needle shaped crystals, 
which are commonly several inches long. 
During the sublimation very small amounts of impurities 
such as dust from the air, or lint from the towels used in clean¬ 
ing the apparatus will reduce the selenium to its red form, 
thus contaminating the sublimate. Frequently the crystals 
are half red and half white so that a separation is impossible. 
In case the quantity of impurities is such that a white sub¬ 
limate can not be obtained easily, the selenium should be fur¬ 
ther purified in the following manner. The solution of the 
dioxide in water is acidified with hydrochloric ucid, wmrmed, 
and treated with sulphur dioxide. The precipitated selenium 
is filtered on an asbestos felt, washed with water, dissolved in 
nitric acid, and treated as previously described. When free 
from reducing materials the selenium dioxide sublimes white. 
A convenient apparatus for sublimation consists of an evap¬ 
orating dish in which are placed three funnels fitting one in¬ 
side the other. Slow sublimation is most efficient. Sublima¬ 
tion in a current of oxygen has been recommended, but this 
is not necessary. 
The bromine on the American market was found to contain 
impurities of a reducing character which make it absolutely 
unfit for use in the preparation of selenic acid without care¬ 
ful purification. Bromine is such an unusual source of re¬ 
ducing materials that its quality may easily escape question. 
The stability of the selenic acid, however, is largely dependent 
on the purity of the bromine. 
The interfering substances are removed from the bromine 
by treatment with a mixture of chromic and sulfuric acids and 
by subsequent distillation. The bromine, after standing with 
the acids for several days or until the evolution of carbon di- 
