426 Berzclius on a new Mineral Body, [Dec. 



heated, it gives out in the first place its water of crystallization, 

 and becomes of a liver-brown colour. At a higher temperature, 

 it melts, and becomes black. It then begins to boil, gives out 

 its acid, and leaves at last only solid oxide of copper. 



The subperseleniate of' copper is a pistachio-coloured insoluble 

 powder, obtained by precipitating persulphate of copper by a 

 seleniate of ammonia with excess of base. It is soluble in an 

 excess of ammonia. When heated, it becomes black, and gives 

 out its water ; it then swells up, and loses its acid. 



24. Perseleniate of Tin. — This salt is a white powder insoluble 

 in water, but soluble in concentrated muriatic acid. Water 

 precipitates it from that solution. It is decomposed by heat, 

 giving out first its water, then its acid, and the oxide of tin 

 remains. I have not examined the combination of protoxide of 

 tin with selenic acid. It is probable that it partakes of the 

 properties of the protoseleniates of iron and mercury, and that 

 it reduces a portion of its acid by the influence of a stronger 

 acid, or even by heat, in order to form a higher degree of oxi- 

 dation. 



25. Protoseleniate of Mercury. — Selenic acid precipitates the 

 soluble salts containing protoxide of mercury. The precipitate 

 is a white powder, insoluble even in an excess of acid. When 

 heated, it melts, and forms a mass of a very deep-brown colour. 

 The colour diminishes as the matter cools, and the mass when 

 solid has a lemon-yellow colour. If we raise the temperature a 

 little higher, the salt begins to boil, and distils over in brown 

 drops, which, on cooling, consolidate into an amber-coloured 

 mass, most frequently transparent. Caustic potash decomposes 

 this salt, separates the acid, and leaves the oxide in the state of 

 a black powder. Muriatic acid decomposes it also, even when 

 it has been melted ; it dissolves the oxide of mercury with a 

 little of the selenic acid, and leaves selenium reduced, just as I 

 described the phenomenon when speaking of the seleniuret of 

 mercury. 



26. Perseleniate of Mercury. — The neutral salt obtained by 

 saturating selenic acid with red oxide of mercury, or procured 

 by double decomposition, is a white insoluble powder, or at least 

 very little soluble. 



The biperseleniate is obtained when to selenic acid a sufficient 

 quantity of peroxide of mercury is added to occasion a com- 

 mencement of the formation of neutral seleniate. The liquid is 

 filtered, and then evaporated till it is sufficiently concentrated to 

 yield crystals. It produces very large prismatic crystals, 

 striated longitudinally, which contain a great deal of water of 

 combination. It is very little soluble in alcohol. The alkalies 

 decompose it with difficulty ; even caustic potash does not 

 entirely separate the oxide of mercury. Ammonia and the alka- 

 line carbonates occasion no precipitate in it. The biperseleniate 

 of mercury has exactly the same taste as the corresponding 



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