HYDROGEN AND SELENIUM. 405 



and no persulphuret of hydrogen is formed. The oily fluid pro- 

 duced by the first mode of mixing has considerable analogy in 

 its properties to the peroxide of hydrogen, and appears, like 

 that compound, to have a certain degree of stability imparted 

 to it by contact with acids, while the presence of alkaline bodies 

 on the contrary, give its elements a tendency to separate. 



Thenard has observed other points of analogy between these 

 compounds. Like peroxide of hydrogen, the persulphuret pro- 

 duces a white spot upon the skin. The latter compound is also 

 resolved into sulphuretted hydrogen and sulphur by all the 

 bodies which effect the transformation of the former into water 

 and oxygen, such as charcoal powder, platinum, iridium, gold, 

 peroxide of manganese, and the oxides of gold and silver, which 

 when the persulphuret is dropt upon them, are decomposed in 

 an instant, and even with ignition. The persulphuret of hydro- 

 gen undergoes spontaneously the same decomposition, even in 

 well closed bottles, w r hich are apt, on that account, to be broken. 

 It is soluble in ether, but the solution soon deposits crystals of 

 sulphur. Thenard finds this body not to be uniform in its 

 composition, the proportion of sulphur often exceeding consi- 

 derably 2 proportions to 1 of hydrogen. The oily fluid may, 

 therefore, be sometimes one and sometimes another compound 

 of sulphur and hydrogen.* 



SECTION II. 

 HYDROGEN AND SELENIUM. 



Seleniuretted hydrogen, H Se. One compound of these ele- 

 ments is known, which is obtained by processes similar to those 

 already described, and possesses considerable analogy to sul- 

 phuretted hydrogen. It is a colourless gas, soluble in water, 

 and readily decomposed by the conjoint action of water and air, 

 with precipitation of selenium. All metallic solutions, even 

 those of zinc and iron, when neutral, are precipitated by solution 

 of seleniuretted hydrogen, and the metallic seleniurets are gene- 

 rally black or dark brown, with the exception of those of zinc, 

 manganese and cerium, which have a flesh colour. The odour 

 of this gas is exactly similar to that of sulphuretted hydrogen, 

 but it was found, by Berzelius, to exercise so violent an action 



* An. de Ch. etdc Ph. t. -18, p. 79. 



