M. Mitsclierlich 07i a new Acid of Selenium. S97 



The composition of selenic acid was ascertained by means 

 of the seleniate of soda. The fused salt was boiled so long 

 with muriatic acid, that on adding muriate of baryta no 

 cloudiness ensued,, a circumstance which proved both the ab- 

 sence of sulphuric acid, and the decomposition of all the sele- 

 nic acid. After separating the baryta by sulphuric acid, the 

 selenious acid was decomposed by means of the sulphite of soda; 

 and 4.880 of the seleniate of soda thus yielded 2.020 of pure se- 

 lenium. But since, according to the foregoing analysis, 100 

 parts of selenic acid, saturate 72.89 of potash, or 48.30 of so- 

 da, it follows that 4.880 of seleniate of soda must contain 3.29 

 of selenic acid. This acid must therefore be composed of 

 61.40 parts of selenium, and 38.60 of oxygen. 



According to Berzelius, selenious acid is formed of 100 

 parts of selenium, and 40.33 of oxygen. Consequently, if 

 the oxygen in selenic and selenious acids is in the ratio of 3 to 

 2, the former should be composed of 100 parts of selenium, 

 and 60.495 of oxygen, or should contain 37.68 per cent, of 

 oxygen. It appears from the numbers procured by this cal- 

 culation, that the quantity of selenium, as obtained by ana- 

 lysis, is somewhat too small. This is owing to the loss of a simi- 

 lar quantity of that principle. To eifect the entire decomposition 

 of the seleniate of soda, it is necessary to boil it several times 

 with muriatic acid, and during this operation a little sele- 

 nious acid is volatilized. The precise composition of the se- 

 lenic acid is best ascertained by the analysis of the seleniates, 

 in which case the quantity of oxygen in the acid is inferred 

 from that of the base. 



According to the analysis of the seleniate of potash, the se- 

 leniates are so constituted that 100 parts of the acid saturate 

 a quantity of base which contains 12.56 of oxygen. i 



Properties of the Selenic Acid.- — This acid is a colourless 

 liquid, which may be heated to 280° C. without appreciable 

 decomposition ; but above that point the decomposition com- 

 mences, and it becomes rapid at 290° C. giving rise to oxygen 

 and selenious acid. Heated to 165° C. its density is 2.524 ; 

 at 267^^ it is 2.60, and at 285° it is 2.625, but a little selenious 

 acid is then present. Obtained by the process above-mention- 

 ed, selenic acid always contains water, but it is very difficult 



