1819.] extracted from Pyrites at Fahlun. 427 



muriate. It is fusible in its water of crystallization, which eva- 

 porates by little and little. The anhydrous salt is not fusible, 

 and sublimes without alteration when heated. A solution ot 

 biperseleniate of mercury, mixed with sulphurous acid, gives 

 immediately a white or greyish precipitate of protoselemate of 

 mercury ; but some moments after, this precipitate assumes a 

 fine cinnabar colour, owing to a portion of reduced selenium, 

 which is deposited so uniformly on the seleniate that we might 

 say that it is combined with it. 



The red oxide of mercury digested with selemc acid till the 

 neutral perseleniate has begun to form, is always intimately 

 mixed with this perseleniate, which renders its colour more pale. 

 This oxide produces, at first view, the singular phenomenon of 

 evolvincr at once oxygen gas and a sublimate of protoselemate ot 

 mercury. The reason is, that the uncombined oxide is decom- 

 posed by the heat, and the reduced mercury enters into combi- 

 nation with the perseleniate, and converts it into protoselemate, 

 which, at that temperature, is volatile, and sublimes. ; 



97 Seleniate of Silver.— Selenic acid precipitates a solution 

 of nitrate of silver. The white precipitate is a neutral seleniate. 

 It dissolves in small quantity in boiling water. Boiling nitric 

 acid dissolves it entirely, but it precipitates again when cold 

 water is added to the solution. If we mix a boiling-hot nitric 

 solution of this salt with boiling water, and allow the mixture to 

 cool slowly, the seleniate of silver forms small acicular crystals. 

 Lio-ht does not blacken it. The seleniate melts almost at the 

 same temperature as the muriate of silver, and becomes transpa- 

 rent like it. When cooled, it forms a white, opaque, triable 

 mass having a crystalline texture. In a red heat, exposed to a 

 current of air, it allows oxygen gas and selenic acid to escape, 

 while it becomes covered with a pellicle of metallic silver. 



0-687 o-rammes of seleniate of silver, which had been strongly 

 heated, but not melted, were dissolved in boiling nitric acid, 

 and the solution was poured in a solution of common salt, the 

 resulting muriate of silver weighed 2-235 grammes, equivalent to 

 1-8082 gramme of oxide of silver. Therefore 100 parts of 

 .elcnic acid had been combined with 205-75 parts of oxide ot 

 .silver, the oxygen of which is 14-2. This agrees very well with 

 the experiment described above. 



(To be continued.) 



