1819.] extracted from Pyrites at Fahlun. 421 



salt by precipitating muriate of barytes with a neutral alkaline 

 seleniate. 



The biseleniate is formed when the carbonate of barytes is 

 dissolved in selenic acid, till all effervescence is at an end. When 

 the solution is evaporated, the biseleniate crystallizes in the form 

 of round grains, which are transparent, and have sometimes a 

 smooth surface. On breaking these grains, we find them com- 

 posed of concentric rays. If the liquid contains no excess of 

 acid but that which is in the biseleniate, and if we allow it to 

 evaporate spontaneously, it deposits a milk-white mass, com- 

 posed of small opaque grains. This mass dissolves slowly in 

 water, and appears at first little soluble ; but when once dissolved, 

 it remains in solution even when a considerable portion of the 

 water is evaporated. A solution of biseleniate mixed with 

 ammonia lets fall the neutral seleniate. 



Two grammes of the neutral seleniate of barytes which had 

 been dried in a red heat, having been dissolved in muriatic acid, 

 left a little selenium, which was made to disappear by the addi- 

 tion of nitric acid. The barytes was then precipitated by means 

 of sulphuric acid. The sulphate of barytes, after being well 

 dried, weighed 1-765 gramme, equivalent to 1-1586 gramme of 

 barytes. Hence 10U parts of selenic acid had been combined 

 with 137-7 parts of barytes, which contain 14-32 of oxygen. 

 This agrees very well with the capacity of saturation of the acid 

 given above. 



1-271 gramme of biseleniate of barytes, deprived of all mois- 

 ture, yielded 0-785 gr. of sulphate of barytes, equivalent to 05153 

 of barytes. Hence 100 parts of selenic acid had been combined 

 with 6 V 8 parts of barytes, or about the half of the base contained 

 in the seleniate. This shows that the same relation exists 

 between these salts as between those which have a base of soda. 



5. Seleniate of Strontian. — The neutral salt is a white insolu- 

 ble powder. The biseleniate may be obtained by dissolving the 

 carbonate of strontian in selenic acid. When the solution is 

 evaporated slowly, the salt is deposited in milk-white crusts, 

 which exhibit no trace of crystallization, and which dissolve 

 again with great difficulty even in boiling water. The dry bise- 

 leniate, when heated, melts at first, and gives out its water, 

 swelling at the same time, and forming a porous mass, from 

 which the heat drives off the excess of acid. The neutral sele- 

 niate which remains does not melt. 



6. Seleniate of Lime.— The neutral salt is but little soluble in 

 water. It precipitates gradually as we dissolve carbonate of 

 lime in selenic acid. When dried, it forms a crystalline powder, 

 soft to the touch, and precisely similar to carbonate of lime. 

 When heated to redness, it liquefies. The melted salt attacks 

 the glass, a kind of effervescence takes place, by which the 

 substance of the glass, and not the melted salt, is filled with 

 small bubbles which dilate, and at last perforate the glass, so 



2 



