M, Mitscherlich on a New Acid of Selenium, 295 



being heated with muriatic acid, the solution yielded a preci- 

 pitate of selenium with sulphurous acid, and likewise retained 

 its transparency when mixed with a salt of baryta. From 

 these characters it results, that the crystals were a compound 

 of potash and a new acid of selenium, isomorphous with sul- 

 phuric acid. As the new acid contains more oxygen than that 

 discovered by Berzelius, it must be called selenic acid, while 

 to the latter the term selenious acid is appropriate. 



Preparation of the new Acid. — This acid is easily formed 

 by fusing the nitrate of potash or soda with selenium, seleni- 

 ous acid, a metallic seleniuret, or a selenite. The seleniuret of 

 lead, as the most common ore of selenium, is preferred ; bjut 

 it is very difficult to obtain pure selenic acid by means of this 

 mineral, because it is generally associated with metallic sulphu- 

 rets. The ore is first treated with muriatic acid to remove the 

 carbonates ; and the residue, which is about a third of the 

 mass, is mixed with its own weight of the nitrate of soda, and 

 thrown by successive portions into a red-hot crucible. The 

 lead is thus oxidized, and the selenium converted into selenic 

 acid, which unites with the soda. The fused mass is then 

 treated with boiling water, which dissolves only the seleniate 

 of soda, and the nitrate and nitrite of soda ; while the insolu- 

 ble matter, when well washed, is quite free from selenium. 

 The solution is quickly made to boil. During the ebullition, 

 anhydrous seleniate of soda is deposited, while, as the liquid 

 cools, nitrate of soda crystallizes. On renewing the boiling and 

 subsequent cooling, fresh portions of the seleniate and nitrate 

 of soda are procured ; and these successive operations are re- 

 peated until the seleniate of soda is entirely separated. This 

 process is founded on the fact, that the seleniate of soda, like 

 the sulphate of that base, is more soluble in water of about 

 91° Fahr. than at higher or lower temperatures. The nitrite 

 of soda, formed during the fusion, is converted into the nitrate 

 by means of nitric acid. > 



The seleniate of soda thus procured always contains a lit- 

 tle sulphuric acid, derived from the metallic sulphurets of the 

 ore ; and it is not possible to separate this acid by crystalliza- 

 tion. All the attempts to separate it by means of baryta 

 were likewise fruitless ; and the only method of effecting this 

 object is by reducing the selenic acid into selenium. This 



