472 Miscellaneous Intelligence, 



muriate of baryta, which would then separate sulphuric acid if 

 present ; the clear solution is to be saturated with carbonate of soda, 

 evaporated to dryness, and the mixture of selenite and nitrate of 

 soda obtained, fuzed in a porcelain crucible over a spirit-lamp. 

 Then proceed by crystallization as before, and a pure S'cleniate of 

 soda will be produced. 



To separate the seleatc acTd,* the solution is to be decomposed by 

 nitrate of lead ; the seleniate of lead is as insoluble as the sulphate, 

 and being: well washed, is to be decomposed by a current of sul- 

 phuretted hydrogen, which has no action on the selenic acid ; the 

 solution being filtered, is to be boiled, and is then diluted selenic 

 acid. Its purity, as respects fixed bodies, is ascertained by its 

 entire volatility ; if sulphuric acid be present, it may be ascer- 

 tained by boiling" a portion with muriatic acid, which produces 

 selenious acid, and then testing by muriate of baryta, a precipitate 

 indicates sulphuric acid. 



From the isomorphism of selenic acid and its salts with sulphu- 

 ric acid and its salts, M. Mitscherlich concluded, that the oxygen in 

 the acid should be to that in selenious acid as 3 to 2 ; and to that in 

 bases when it forms salt, as 3 to 1. These views were confirmed by 

 experiments. From the decomposition of seleniate of potash by 

 muriate of baryta, it appeared that the seleniate was composed of 



Potash 42. 16 ... . oxygen 7.15 



Selenic acid . . 57.84 21.79 



100.00 



The composition of the acid was determined by boiling a cer- 

 tain weight of the seleniate of soda with muriatic acid in excess, 

 and decomposing the selenious acid formed by sulphite of soda ; 

 4.S8 of the salt gave 2.02 of selenium, from which, and the above 

 result, it would appear that the acid is formed of 



Selenium 61.4 



Oxygen 38.6 



100.0 



According to Berzelius, selenious acid consists of 100 selenium, 

 and 40.33 oxygen; and supposing this contains two-thirds the 

 oxygen in selenic acid, the latter should consist of 62.32 and 

 37 . 68. From the analysis above given of the seleniate of potash, 

 it is evident that 100 of selenic acid saturates a quantity of base 

 containing 12.56 of oxygen, which would agree with the latter 

 estimate of selenic acid. 



Selenic acid is a colourless liquid, which may be heated to 536"^, 

 without sensible decomposition ; above that it changes, and is 

 rapidly resolved into oxygen and selenious acid at 554°. Heated to 

 329°, its specific gravity is 2.524 ; at 512°.6 it is 2.6 ; at 509° it is 

 2.625 ; but by that time selenious acid has been formed in it. A 

 portion of concentrated acid, from which the selenious acid had 



