1819.] extracted from Pyrites at Fahlun. 425 



a white insoluble powder, which, when dried, assumes a pale- 

 apple-green colour. The biseleniate is soluble, and gives a green 

 mass resembling gum. 



21. Seleniate of' Lead. — Selenic acid precipitates the oxide of 

 lead both from the muriate and the nitrate. The precipitate 

 formed in the latter salt contains always nitric acid. We obtain 

 pure seleniate of lead by mixing muriate of lead with an excess 

 of seleniate of ammonia. A heavy white powder is formed, 

 which speedily falls to the bottom, and is not redissolved by au 

 excess of acid. The seleniate of lead melts like the muriate ; 

 but it seems to require rather a higher temperature. The melted 

 mass is transparent and yellowish ; on cooling, it recovers its 

 whiteness, loses its transparency, and exhibits a crystallized 

 fracture. In a reddish-white heat, the seleniate of lead begins 

 to boil, and selenic acid sublimes. After some time the ebulli- 

 tion stops, and a melted subselemate of lead remains, which, on 

 cooling, is semitransparent and friable. Its fracture exhibits a 

 very crystalline texture. Seleniate of lead still moist, though 

 repeatedly digested in caustic ammonia, does not part with any 

 acid, nor can it be converted in that way into subseleniate. 



It is difficult to decompose seleniate of lead entirely by sul- 

 phuric acid. It is necessary that the acid be concentrated, and 

 boiling. One hundred parts of seleniate of lead yielded 90*63- 

 parts of sulphate of lead, equivalent to 6o'*67 parts of protoxide 

 of lead ; so that 100 parts of selenic acid combine with 200 parts 

 of protoxide of lead, the oxygen of which is 14*342. This agrees 

 with the results given above. 



Two grammes of nitrate of lead dried to a fine powder, dis- 

 solved in water, and the solution then poured into an excess of 

 seleniate of ammonia produced 2*01 grammes of seleniate of lead, 

 dried in a temperature above 212°. Sulphuric acid being added 

 to the liquid from which the seleniate had been precipitated 

 separated 0*0075 gramme of sulphate of lead. This experiment 

 gives likewise 200 of oxide of lead for 100 of acid. We see 

 likewise that seleniate of lead is not absolutely insoluble in 

 water. 



22. Protosefeniate of Copper. — We obtain this salt in the form 

 of an insoluble white powder, when protohydrate of copper is 

 digested in selenic acid. 



23. Perselemate of Copper. — When we mix a hot solution of 

 Sulphate of copper with a solution of biseleniate of ammonia, a 

 vt llowish precipitate fails ha very bulky flocks. This precipitate 

 rapidly diminishes in volume, and in a few moments is converted 

 into a mass of small silky crystals, of a very brilliant greenish- 

 blue colour. These crystals arc a neutral seleniate. The change 

 of the Hocks into crystals seems to be merely a change of aggre- 



ion occasioned by heat. The same thing takes place, but. 

 more slowly, if we mix the ingredients cold. Perselenierte ef 

 copper is neither soluble in water nor in selenic acid. When 



