SELENIOUS ACID. 337 



lions of its discoverer. It has also been found in the Lipari 

 islands in combination with sulphur, and can sometimes be 

 detected in the sulphuric acid, both of Germany and England. 

 It is separated from its combinations with sulphur and metals 

 by a very complicated process, for which I must refer to the 

 works of Berzelius.* 



Properties of selenium. This element is allied to sulphur, 

 and like that body, exhibits considerable variety in its physical 

 characters. When it cools after being distilled, its surface 

 reflects light like a mirror, has a deep reddish brown colour, 

 with a metallic lustre resembling that of polished blood-stone. 

 Its density is between 4.3 and 4.32. When cooled slowly after 

 fusion, its surface is rough, of a leaden grey colour, its fracture 

 fine-grained, and the mass resembles exactly a fragment of 

 cobalt. But as selenium does not' conduct electricity, and its 

 metallic characters are not constant, it is better classed with the 

 non-metallic bodies. Its powder is of a deep red colour. By 

 heat it is softened, becoming semifluid at 212, and fusing com- 

 pletely a few degrees higher. It remains a long time soft on 

 cooling, and may then be drawn out like sealing wax into thin 

 and very flexible threads, which are grey and exhibit a metallic 

 lustre by reflected light, but are transparent and of a ruby red 

 colour by transmitted light. It boils about 650% and gives a 

 vapour of a yellow colour, less intense than that of sulphur, 

 but more so than that of chlorine. The density of this vapour 

 has not been ascertained. 



Selenium combines in three proportions with oxygen, form- 

 ing selenic acid^ which corresponds with sulphuric acid, sele- 

 nious acid corresponding with sulphurous acid, and a protoxide, 

 to which there is no oxide of sulphur analogous. 



Oxide of selenium, SeO. This is a colourless gas, sparingly 

 soluble in water, formed when selenium is heated in air without 

 burning freely. It has a powerful odour, suggesting that of 

 decaying horse-radish, by means of which the smallest trace of 

 selenium may be detected in minerals, when heated before the 

 blow-pipe, this gas being then formed. 



Selenious acid, SeO 2 . Selenium] strongly heated in a glass 

 bulb, with a current of oxygen passing over it, takes fire and 



* Annals of Philosophy, vol. 13, p. 401 ; or An. de Ch. et de Ph. t. 9, p. 160 ; 

 also Berrelius's Trait, t. 1, p. 334, Brussells edition, 1838. 



Z 



