1819.] extracted from Pyrites at Fahlun. 99 



I think I have ascertained that it is capable of combining with 

 three times as much selenium as it contains at first. I weighed 

 a portion of the saturated compound, and then decomposed it by 

 water. I washed and dried the selenium separated by this 

 liquid, and its weight exceeded a little three times that of the 

 selenium in the portion dissolved by the water; but it was 

 obvious that the whole of the muriatic acid had not been 

 removed, as the filter was corroded by it during the drying. If 

 this compound be a muriate of the oxide of selenium and not a 

 solution of selenium in a muriate, the oxide of selenium which i'c 

 contains should be a compound of two atoms of radical and one 

 of oxygen. This is the case likewise with the oxide of sulphur 

 supposed to exist in the muriate of the oxide of sulphur (the 

 protochloride of sulphur of the new hypothesis respecting the 

 nature of muriatic acid). 



Reduction of Selenium to the State of a Combustible. — Selenic 

 acid is easily reduced both by the moist and the dry way. A 

 solution of selenic acid mixed with muriatic acid produces no 

 trace of chlorine, even when heated. If into this solution we 

 introduce a piece of zinc or of polished iron, the metal imme- 

 diately assumes the colour of copper, and the selenium is gra- 

 dually precipitated in the form of red, or brown, or blackish 

 flocks, according as the temperature is more or less elevated. If 

 we mix selenic acid with sulphuric acid, the selenium precipi- 

 tates more slowly, and contains sulphur. If the selenic acid 

 contains arsenic acid, or seleniate of mercury, the selenium is 

 still more difficult to be precipitated by zinc or iron. 



The most convenient mode of separating selenium from a solu- 

 tion is to render the liquid slightly acid, and then to pour into it 

 sulphite of ammonia. The uncombined acid disengages the 

 sulphurous acid, by the action of which the selenic acid is, 

 gradually decomposed. The liquid, at first limpid, assumes a 

 yellow colour, becomes muddy, acquires a fine red colour, and 

 after an interval of some hours deposits red flocks in abundance, 

 The selenium is not completely precipitated cold, the liquid must 

 be boiled for half an hour, during which fresh sulphite of 

 ammonia must be occasionally added. The precipitate formed 

 by boiling is dark grey, or almost black. If the liquid contain 

 nitric acid, the selenium is not completely precipitated till after 

 the whole nitric acid is decomposed by the sulphurous acid. In 

 such a case, it is better to add muriatic acid to the liquid, and to 

 evaporate till the nitric acid be decomposed, to redissolve in 

 water, and then and sulphite of ammonia. 



I have already mentioned that when seleniate of potash is 

 heated with muriate of ammonia, selenium is obtained by the 

 deoxidizing property of the ammonia ; but in this case we 

 always lose a small quantity of selenium which conies over with 

 the water in the form of an acid ; and if the heat be not conti- 

 nued long enough, the upper layer in the retort may contain 



c 2 



