1819.] extracted from Pyrites at Faklun. 105 



obtaining metallic seleniurets with fixed proportions is doubtless 

 to precipitate metallic solutions with seleniuretted hydrogen gas ; 

 but we may likewise obtain the protoseleniurets by heating the 

 metals with an excess of selenium, and drawing off this excess 

 by distillation. 



1. Seleniuret of Potassium. — Selenium, when heated with 

 potassium, combines with it, and occasions a red heat, which 

 sublimes a small quantity of the compound. Seleniuret of 

 potassium constitutes a metallic button, of the colour of iron, 

 which separates easily from the glass, and which has a crystal- 

 lized and radiated fracture. It dissolves in water without the 

 disengagement of gas. The solution has a deep red colour, 

 similar to that of strong beer. The acids precipitate selenium 

 from it, because the hydroseleniuret of potash formed by the 

 solution has the property of dissolving the excess of selenium 

 present, and of forming with it a seleniuretted hydroseleniuret of 

 potash. 



If we mix selenium with an excess of potassium, the combina- 

 tion takes place with a strong explosion, and the mass is thrown 

 out of the vessel by excess of potassium, which is converted 

 into vapour by the heat. The compound, when thrown into 

 water, is dissolved with the disengagement of hydrogen gas ; 

 but notwithstanding this circumstance, the liquid assumes a red 

 colour. 



2. Seleniuret of Zinc. — It is equally difficult to combine this 

 metal with selenium as it is with sulphur. If we heat together 

 zinc and selenium in vessels in which the air cannot be received, 

 the selenium melts, and spreads itself on the surface of the zinc, 

 which becomes, as it were, amalgamated with it. By increasing 

 the heat, we cause the selenium to volatilize, leaving the zinc 

 covered with a yellows-coloured pellicle. If, on the other hand, 

 we bring zinc heated to redness in contact with the vapour of 

 selenium, the mass takes fire, explodes, and the inner surface of 

 the vessel is covered with a pulverulent substance of a lemon 

 colour, which retains its colour when cold. This powder is 

 seleniuret of zinc, very analogous to sulphuret of zinc, which, 

 when produced in the same way, is a yellowish-grey, non- 

 metallic powder. We easily see that the yellow powder is not 

 an oxide of zinc, as nitric acid dissolves it with the evolution of 

 nitrous gas. In this case, the powder becomes first red by the 

 solution of the zinc, and the separation of the selenium, which 

 afterwards dissolves in the acid. 



3. Seleniuret of Iron. — If we mix iron filings and selenium in 

 powder, and heat the mixture to redness, the iron combines on 

 the surface with selenium, but without any combustion ; but if we 

 put selenium at the bottom of a glass tube, introduce iron filings 

 above it, and then heat strongly, the selenium is volatilized, and 

 its vapours, passing through the hot iron, combine with it, pro- 

 ducing an ignition which continues as long as any selenium is 



2 



