370 Wisconsin Academy of Sciences^ Arts^ and Letters. 
In 1882, Miilpert^ made selenic acid by the oxidation of 
seleniuni with ozone. Metzner^ in 1898, showed that the reac¬ 
tion of chlorine on selenious acid is exothermic. The chlorine 
works best with about a ten percent solution of the dioxide. 
When chlorine is in excess the oxidation is complete, but if 
bromine is substituted in the reaction more heat is given off, 
and it requires somewhat of an excess of bromine to complete 
the reaction. The theoretical amount of bromine shows a red 
color in the solution, but all the selenium dioxide is not oxi¬ 
dized. Metzner further proposed a method of oxidation by 
permanganic acid, which he states gives good selenic acid. 
Another method of his depends on the electrolytic decomposi¬ 
tion of copper selenate. 
Other methods that have appeared depend either on the oxi¬ 
dation of selenious acid ® a selenite®, or selenate® by means 
of the electric current, or the oxidation of selenious acid with 
hydrogen peroxide.'^ 
From the foregoing it appears that many methods for the 
preparation of selenic acid have been described; several of 
which seem to be fairly simple. Actually, however, many of 
. ^ 
the essential details are lacking, even though upon them de¬ 
pends the success of the method. 
The method of J. Thomsen will yield excellent selenic acid 
under correct conditions, but it was only through repeated 
failures to obtain a stable preparation of the acid that these 
conditions were recognized and the causes of failure eliminated. 
The main points to be observed are as follows: The prepara¬ 
tion of silver selenite requires pure selenium dioxide. The 
bromine used to convert the silver selenite into selenic acid 
must be free from reducing substances. All dust must be rig¬ 
orously excluded throughout the preparation. 
1C. R. 94, 1186. 
aC. R. 127, 54. 
® Chem Ztg ai, 360. 
* Gazz chim Ital 39, I 50. 
Chem Zentr 1909, I 721. 
®Ber 36, 4262. 
® Jr Am Chem Soc 30, 1374. 
^ Ber 48, 1154. 
