100 Berzelius on a new Mineral Body, [Aug. 



selenium not reduced, which will be obtained by heating the 

 solution of the residual salts in a retort with sulphurous acid. 

 During this reduction, I have always conceived that a selenu- 

 retted gas was formed which was decomposed by the action of 

 the atmospherical air in the receiver, while very thin metallic 

 pellicles were deposited on the surface of the distilled water and 

 on the glass. It appeared to be seleniuretted hydrogen. The 

 quantity of it was inconsiderable. If the seleniate of potash 

 contain arsenic, the reduced selenium likewise contains arsenic ; 

 and, during, the reduction, a gas is disengaged, which smells 

 strongly of garlic. 



5. Seleniuretted Hydrogen Gas. 



If we melt together selenium and potassium, and add water to 

 the fused mass, it dissolves in the liquid without the disengage- 

 ment of any elastic substance. The solution has a deep ale 

 colour, and contains hydroseleniuret of potash. If we add 

 muriatic acid to it, a great proportion of the selenium precipi- 

 tates, and the liquid acquires the smell of sulphuretted hydrogen 

 gas, without any effervescence taking place, unless the solution 

 be very concentrated. 



If we pour diluted muriatic acid on the seleniuret of potash in 

 a small retort, it swells up, becomes red, and a gas is disengaged 

 with effervescence. This gas is seleniuretted hydrogen. If we 

 pass this gas into water deprived of its air by boiling, it is com- 

 pletely dissolved by that liquid. The water acquires no colour; 

 but after some minutes, it becomes slightly opalescent, and 

 deposits a little selenium. This phenomenon is to be ascribed to 

 a residue of atmospheric air. This solution has an hepatic taste, 

 reddens litmus paper, and stains the skin of a brown colour, 

 which water is not capable of removing. In the air, this solu- 

 tion becomes red at the surface, deposits selenium, and is 

 gradually completely decomposed. Nitric acid added in smalL 

 quantity does not decompose the gas, and I have found that 

 after 12 hours, the water still retained the property of precipitat- 

 ing the metallic salts. 'Seleniuretted hydrogen gas makes its 

 escape from water with greater difficulty than sulphuretted 

 hydrogen. This is the reason why water impregnated with it 

 has but a weak smell even when it contains half its volume of the 

 gas. I have not determined the solubility of this gas in water ; 

 but it appears much more soluble than sulphuretted hydrogen 



s as - 



Water impregnated with this gas precipitates all the metallic 

 solutions, even those of iron and zinc when they are neutral. 

 The precipitates are in general black or brown, and assume the 

 metallic lustre when rubbed with a polished hematite. The 

 precipitates of zinc, manganese, and cerium, however, constitute 

 an exception. They have a flesh colour. The brown and black 

 precipitates are metalLc seleniurets ; but the red precipitates, at 



