Selenium

SELENIUM, Selenum (from the Greek selene - moon), a solid metalloid with the chemical symbol Se; atomic weight 79.2; in the periodic system it occupies the 34th place, 4th in group VI. It is found in nature often in small quantities and almost always accompanies sulfur, sulfur compounds (pyrites), etc. Selenium belongs to the sulfur group and is similar to it in its chemical properties. Selenium is obtained from chamber lead sludge during the production of sulfuric acid, from residues (anode sludges) during the electrolysis of copper, etc. Selenium is allotropic and is obtained in several modifications - from a red amorphous to a black crystalline mass. Melting point 217°. In industry, selenium is used in glass manufacturing for decolorization and in photoelectric cells. Selenium compounds are poisonous; hydrogen selenide, H₂Se, acts very strongly on the eyes and respiratory tract. Salts of selenic acid, H₂SeO₄, are many times less poisonous than selenite salts. Selenium is used for the treatment of skin diseases (prurigo, eczema), and for the treatment of malignant tumors (cancer). In the latter case, selenium was used in the form of colloidal selenium, selenium salts, and most often in the form of the compound eosin-selenium. Some authors noted the softening of tumors, a decrease in secretions, and an improvement in ulcerative processes, but favorable clinical results could not be obtained. Selenium (Na₂SeO₃ and CaSeO₃) is used most often intravenously, then intramuscularly; subcutaneous use is painful. Usual doses contain 0.0005-0.005 g of metallic selenium. Ointments for skin diseases contain red selenium precipitate (2 : 30). Among the side effects upon intravenous administration, transient phenomena such as chills, collapse, cyanosis, and numbness of the extremities are noted. Detection in forensic cases. After the destruction of parts of the viscera with hydrochloric acid and potassium chlorate (see Poisons, isolation) and after the removal of chlorine, the liquid is saturated with hydrogen sulfide (see Poisons, isolation). The precipitate is treated with ammonium carbonate (to separate arsenic sulfide), then in a porcelain dish while heating on a water bath with concentrated nitric acid and evaporated to dryness. The residue is dissolved in concentrated sulfuric acid, freed from the residue of nitric acid by heating, and reactions for selenic acid are performed with the solution: 1) when mixing the sulfuric acid solution with ground codeine, an emerald-green coloration appears, passing into blue-green, blue, and finally, upon standing for a long time, into olive; 2) the sulfuric acid solution is diluted with an equal volume of water and 1 cm³ of the mixture is poured into 3 cm³ of Bettendorff's reagent (a solution of stannous chloride in concentrated hydrochloric acid): a red precipitate of metallic selenium forms; with small quantities, a brown coloration gradually appears; 3) hydrogen selenide, obtained by the action of forensically pure zinc on the sulfuric acid solution, gives the Gutzeit test (see Arsenic, methods of detecting arsenic) with silver nitrate, similar to arsine, but is completely retained by lead acetate, similar to hydrogen sulfide.