338 SELENIUM. 



burns with a flame, white at the base, and of a bluish green at 

 the point and edges, but not strongly luminous ; selenious acid 

 at the same time condenses as a white sublimate, iri long quadri- 

 lateral needles. Its vapour has the colour of chlorine. The 

 same acid is the sole product of the action of nitric or nitromu- 

 riatic acid upon selenium, and is obtained on slowly cooling the 

 liquor, in large prismatic crystals, striated lengthwise, which 

 have a considerable resemblance to nitre. These crystals are 

 hydrated selenious acid. This acid is largely soluble, both in 

 water and alcohol. It is decomposed when in solution and sele- 

 nium precipitated by zinc, iron or sulphite of ammonia, with 

 the assistance of a free acid. The selenite of ammonia is also 

 decomposed by heat and leaves selenium. The selenious is a 

 strong acid, displacing nitric and hydrochloric acids from their 

 combinations, but is displaced in its turn by the more fixed acids, 

 sulphuric, boracic, &c. 



Selenic acid, SeO 3 . Selenium is brought to this superior 

 state of oxidation at a high temperature, by fusion with nitre, 

 a process which affords the seleniate of potash. The selenic acid 

 is precipitated from that salt by the nitrate of lead ; and the 

 insoluble seleniate of lead, after being washed, is diffused 

 through water and decomposed by a stream of sulphuretted 

 hydrogen gas, which converts the lead into insoluble sulphuret 

 of lead and liberates selenic acid. A solution of this acid may 

 be concentrated till its boiling point rises to 536, but above 

 that temperature it changes rapidly into selenious acid, with 

 disengagement of oxygen. Its density is then 2.60, and it con- 

 tains little more than a single equivalent of water, and therefore 

 corresponds with the protohydrate of sulphuric acid, or oil of 

 vitriol. Selenic acid has never been obtained in the anhydrous 

 condition. Zinc and iron are dissolved by this acid, with the 

 evolution of hydrogen gas ; and with the aid of heat it dissolves 

 copper and even gold, an operation in which it is partially con- 

 verted into selenious acid. But it does not dissolve platinum. 

 To precipitate its selenium, the acid may be digested with 

 hydrochloric acid, which occasions the formation of selenious 

 acid and the evolution of chlorine, and then sulphurous acid 

 throws down the selenium. The compounds of selenic acid 

 with bases, so much resemble the corresponding sulphates, in 

 their crystalline form, colour and external characters, that they 

 can only be distinguished from them by the property which 



