Per-seleniate of mercury is a white insoluble powder.
The bi-fierseleniate is lormed by dissolving peroxide of mercury in selenic acid, and evaporating till crystals are formed. When a solution of this salt is mixed with sulphurous acid, proto-seleniate of mercury and selenium are precipitated.
Seleniate of manganese is a white powder, which, when exposed to the air, attracts oxygen, and the acid is disengaged. This salt possesses the property of de stroying glass.
Seleniate of silver is white. It is soluble in boiling nitric acid, and when water is added to the solution, it is deposited in acicular crystals. It is composed of 100 acid, 205.75 base.
Seleniate of cobalt is a rose-coloured insoluble powder. Seleniate of nickel, when dry, is pale green. Proto-seleniate of cerium is a white powder, soluble in selenic acid, forming bi-seleniate.
Per•seleniate of uranium is a yellowish powder, which is decomposed by heat. It is soluble in selenie acid, and forms bi-ficrseleniate.
Seleniuretted hydrogen and bases. The hyd•o-seleniu vets of the fixed alkalies are easiest formed by passing a current of the gas through a solution of these bodies. When scleniuretted hydrogen and ammonia in the state of gas are brought into contact, they combine and form a powder of a pale red colour.
The hydro-seleniurets of lime, baryta, strontia, and magnesia, are, soluble. The hydro-seleniurets of the other earths are insoluble.
Berzelius has not examined particularly the proper ties of the hydro-seleniurets. When seleniuretted hy drogen was passed through lime water, a reddish pow der was precipitated. The clear liquor kept in a phial, not well stopped, became red on the surface, which gra dually descended, till the whole acquired the same co lour. A reddish substance was then deposited, and the fluid became colourless. According to Berzelius, the coloured solution contained seleniuretted hydro-seleniu ret of lime. The hydro-seleniurets of the alkalies are likewise decomposed when kept in contact with air, and selenium is separated, forming a pellicle on the surface of the fluid. If the separation of the metal occur slowly, and if the vessel be not agitated, the selenium is depo sited in the dendritic form.
All the metallic solutions are precipitated by the al kaline hydro-seleniurets. The precipitates from the salts of zinc, manganese, cerium, and probably also uranium, are hydro-seleniurets. Those from the other metallic salts are selenimets.
From the properties of selenium we may consider it as more nearly allied to sulphur than to any other sub stance ; at the same time its high metallic lustre and specific gravity would induce us to class it among the metals. Berzelius thinks that it belongs to the division of these bodies, called electronegative, or those which, by their combination, generate acids ; among these are arsenic and tellurium, to which also it seems nearly allied.
It may be considered as another substance added to that class of bodies which generate acids by their union both with oxygen and hydrogen.
Berzelius has found selenium in two other minerals, the one of these is a seleniuret of copper, mixed with carbonate of lime, the other, which was obtained from a copper mine of Skrickerum, he found contained Professor Stromeyer, when examining a compound of zinc, prepared at the chemical laboratory of Salsgitter, which was supposed to contain iron, from its acquiring a yellow colour when heated, discovered that this property was owing to the presence of a peculiar metal not pre viously known, to which he has given the name of cad mium. He has since found this substance in tutia, and in several of the other co:npounds of zinc. It exists also, according to him, in metallic zinc, though in very small quantity.
Previous to the experiments of Stromeyer, a prepa ration of zinc from Silesia was thrown aside by the apothecaries for containing arsenic, because, when dis solved in acid, it was found by Roloff to give a yellow precipitate on the addition of sulphuretted hydrogen, which was considered by him to be orpiment. Roloff, however, in repeating his experiments, ascertained that this precipitate was not occasioned by arsenic, but by another metal, not then known.