SELENIUM

(Yunanca köken — orijinale bakınız.) A substance discovered in 1818 by Berzelius. In its general chemical habitudes it bears a resemblance to sulphur. It has hitherto been obtained in very small quantity, and generally occurs in some of the varieties of iron pyrites. It is a brittle, opaque substance, tastele , and inodorous, having something of the appearance of lead, but of a deep red colour when reduced to powder. Its specific gravity is about 4-3. At 212° it becoms soft and tenacious and at 220° is perfectly liquid; at 650° it boils and sublimes. It is insoluble in water, and unaltered by air; and when heated by the blowpipe, so as to become oxidized, it exhales a strong odour of horse-radish. Its equivalent is about 40. It forms an oxide and two acids; the sclenious acid being a compound of1 equivalent of selenium and 2 of oxygen, and the selenic acid of 1 and 3. It also combines with hydrogen, forming the hydro selenic acid, a gaseous compound of 40 selenium + 1 hydrogen. Its odour at first resembles sulphuretted hydrogen, but it afterwards powerfully irritates the nose, excites catarrhal symptoms, and destroys the sense of smell. Dr. Prout has suggested the po ibility of the evolution of this compound by volcanoes, and its diffu sion through the atmosphere as productive of certain forms of the epidemic disorder called influenza. [s. 1122]