AR′SENIC

(-se-nĭk). As. Syn. Arsenium ; Arsen′icum , Arse′nium , L.; Arsenik , A.-metall , Ger. Arsenico , Sp., It. The brittle, grey-coloured metal, or metalloid, which forms the base of the white arsenic and orpiment of commerce. Discovered by Geber in the eighth century, but first accurately described by Brandt ( A.D. 1773). The poisonous properties of arsenious acid were not generally known for some centuries after its discovery. As a medicine it was first employed in intermit tents in Hungary. Sources. Arsenic is peculiar to the mineral kingdom. The metallic arsenic of commerce is obtained by roasting arsenical pyrites ( MISPICKEL ), in earthen tubes, or in tubular earthen retorts; the arsenic sublimes, and sulphuret of iron remains behind. On the small scale it is prepared by sublimation from a mixture of arsenious acid and charcoal or black flux. Combined with oxygen it frequently exists in mineral waters; and, in a larger quantity, in certain rivulets and streams. Prep. A mixture of arsenious acid, 1 part; and black flux, 2 or 3 parts; is exposed to a low red heat in a He ian crucible over which is luted a deep empty crucible, or an earthen tube, to receive the metal; the latter being kept as cool as po ible. Charcoal or even oil may be substituted for black flux, and a retort of hard gla may be used, with the same result. Or the following method may be used:—White oxide of arsenic, of commerce, 2 dr.; is placed at the sealed end of a hard German-gla tube ( 1 ⁄ 2 × 18 inches), and covered with about 8 inches of dry and coarsely powdered charcoal; the portion of the tube containing the latter is then raised to a red heat, whilst a few ignited coals are placed beneath the oxide to effect its slow sublimation. The sublimed metal gradually attaches itself to the inside of the tube at its cool extremity. A small charcoal furnace similar to that used for organic analysis should be employed, and the proce conducted under a flue to carry off any fumes that may escape. The open end of the tube should be loosely closed with a cork. Prop. Very brittle, so much so that it may be easily powdered in a mortar; lustre highly metallic; colour steel-grey or bluish-white; texture crystalline; crystals rhombohedrons; sublimes, without fusion, at 356 to 360° Fahr., (and slowly at lower temperatures), in close ve els unaltered, but when exposed to the air with conversion into arsenious acid; at a higher temperature, in open ve els, it burns with a pale-blue flame. Its vapour or fumes have a characteristic alliaceous odour; it is slowly oxidised and di olved by boiling water; but may be preserved unchanged in pure cold water; it rapidly tarnishes in the air, particularly when moist, a black film, consisting of metallic arsenic and arsenious acid forming on its surface; with chlorine, iodine, sulphur, and hydrogen, it unites to form definite compounds. With oxygen it forms acids, but no basic oxide. It combines with the metals in a similar manner to sulphur and phosphorus, the latter of which it resembles in many respects. These compounds are termed AR′SENIDES , formerly Arseniurets . Sp. gr. 5·7 to 5·9; sp. gr. of vapour, 1·0362. Uses, . With copper it forms a white alloy ( PACKFONG ); and it is added to some other alloys to increase their whitene , hardne , and fusibility. In medicine it is only used in combination. In the metallic state it is inert; but, from its great affinity for oxygen, it rapidly becomes oxidised and poisonous; and hence acts as a powerful poison when swallowed, or when rubbed on the skin. Its fumes are also highly poisonous. See Arsenious Acid (and below ).