104 Berzelius on a new Mineral Body, [Aug, 



of the phosphorus decomposes the water, which becomes impreg- 

 nated with seleniuretted hydrogen gas, acquires a hepatic odour, 

 becomes muddy, and deposits selenium when left in contact 

 with the air. If we boil the phosphorus in a caustic potash ley, 

 it dissolves, and the liquid contains phosphate with hydrosele- 

 niuret of potash, and when left exposed to the air lets fall sele- 

 nium, just as if it were a pure hydroseleniuret of potash. 



Seleniuret of Carbon. — I have not examined whether selenium 

 and carbon are capable of combining ; but some phenomena 

 which take place when the alkaline seleniates are decomposed by 

 charcoal at a high temperature lead me to suspect that such a 

 combination may exist. We may presume likewise that it ought 

 to be analogous to the sulphuret of carbon, and that, like that 

 substance, it is capable of combining with the saline bases. 



7. Metallic Seleniurets. 



Selenium combines with the metals, and on that occasion 

 performs the part of an electronegative substance. With the 

 greater number of them, it produces the phenomena of fire, as 

 sulphur does, but with less intensity. 



The reason why it does not produce fire with all of them is 

 the same as for sulphur ; namely, that several of the metals which 

 ought theoretically to produce the phenomena of fire with the 

 greatest intensity require a much higher temperature to produce 

 the combination than the boiling point of selenium. The conse- 

 quence is, that the selenium evaporates before the mixture 

 acquires a sufficient degree of heat to produce the combination 

 with rapidity. This is the case with iron and zinc. 



The seleniurets have mostly the same external characters as 

 the corresponding sulphurets. They have in general a metallic 

 aspect ; they are, with a few exceptions, more fusible than the 

 metals which they contain ; and when they are heated to redness 

 in the air, the selenium burns slowly with a blue flame, giving 

 out the odour of horseradish. It is much more difficult to sepa- 

 rate the selenium by roasting than the sulphur, because selenium 

 has a weaker affinity for oxygen. The metallic seleniurets are 

 soluble in nitric acid, though less easily than the same metals 

 without selenium. Some, however, as seleniuret of mercury, 

 are scarcely attacked by nitric acid. 



Selenium evidently combines with the metals in definite pro- 

 portions. In this respect, selenium corresponds with sulphur. 

 Thus copper is capable of uniting with two proportions of sele- 

 nium, one of which is obtained, when a salt containing peroxide 

 of copper is precipitated by seleniuretted hydrogen gas. On 

 distilling this precipitate, one half of the selenium is volatilized, 

 and there remains in the retort a protoseleniuret of copper. This 

 compound occurs in nature as a mineral, as I shall have occasion 

 to show hereafter. It is well known that this is exactly the case 

 with the compounds of sulphur and copper. The best way of 





