78 



METALS. 



Mttal;. 



The ll-seleniatc is obtained by disolving the seleniate 

 ' in the acid, or by adding the salt of iron to a solution 

 of an alkaline bi-seleniate. 



Per-selcniale of iron is procured by double decompo- 

 sition. It is of a yellow colour, and yields its acid by 

 the application of heat. 



J'roto-.rcleninle of copper is obtained by dissolving the 

 protoxide of the metal in selenic acid. It is of a white 

 colour. 



The per-seleniate may be formed by mixing sulphate 

 of copper and bi-seleniate of ammonia. It is insoluble, 

 and affords its acid by heat. 



Seleniate of lead is formed by mixing muriate of lead 

 n-ith seleniate of ammonia in excess. It melts on the 

 application of caloric, and at a white heat it is decom- 

 posed, and sub-seleniate is left in the vessel. 



Seleniate of zinc is insoluble ; the bi-sclenialc is so- 

 luble ; the former, when exposed to heat, generates 

 the snb-seleniale. 



Per-selcniate of tin, is a white powder, insoluble in 

 water, but soluble in muriatic acid. It yields its acid 

 by heat. 



Proto-scleniale of mercury. Selenic acid, when added 

 to a salt of mercury, containing protoxide, throws down 

 a white precipitate. This salt is decomposed by po- 

 tassa, the alkali uniting with the acid. Muriatic acid 

 combines with the oxide and a little of the acid, and 

 leaves selenium reduced. 



Per-seleniate of mercury is a white insoluble powder. 

 The bi-perselcnialc is formed 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-seleniale. 



Per-seleniate of uranium is a yellowish powder, which 

 is decomposed by heat. It is soluble in selenic acid, 

 and forms bi-persekniale. 



Seleniuretled hydrogen and bases. The hydro-seleniu- 

 rets of the fixed alkalies are easiest formed by passing 

 a current of the gas through a solution of these bodies. 

 When seleniuretted 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 sileniuretted 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 

 gradually descended, till the whole acquired the same 

 colour. A reddish substance was then deposited, and 

 the fluid became colourless. According to Berzelius, 

 the coloured solution contained seleniuretted hydro-se- 

 leniuret 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 se- 

 lenium is deposited 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 seleniurets. 



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 divi- 

 sion of these bodies, called electro-negative, 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 mine- 

 rals, the one of these is a seleniuret of copper, mixed 

 with carbonate of lime, the other, which was obtained 

 from a Coppermine of Skrickerum, he found contained 



Silver 38.93 



Copper ..... 23.05 

 Selenium .... 2fi.OO 

 Foreign earthy matter 8.90 

 Loss 3.12 



MeUls. 



100.00 



Cadmium, 



Professor Stromeyer, when examining a compound Cadmium. 

 of zinc, prepared at the chemical laboratory of Sals- 

 gitter, 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 previously known, to which he h;is given 

 the name of cadmium. He has since found this sub- 

 stance in tutia, and in several of the other compounds 

 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. 



Specimens of the Silesian oxide of zinc, and of the 

 precipitate, were afterwards sent to Stromeyer, who 

 ascertained that the phenomena presented by this par- 

 ticular oxide, were owing to the presence of the peculiar 

 metal which he had discovered in the compound of 

 zinc prepared at Salsgitter, and to which he had given 

 the name of cadmium. 



Cadmium is procured by dissolving the substance* 

 containing it in sulphuric acid, and passing a stream 

 of sulphuretted hydrogen through the solution. The 

 precipitate formed, after being well washed, must 

 be dissolved in muriatic acid, and the excess of acid 

 driven off by heat. What remains is dissolved in 

 water, and carbonate of ammonia is added in excess, 



