Bismuth
A somewhat brittle metal, the color of which may be termed yellowish-white. It is a little harder than lead. Bismuth is found natural but impure in different parts of Europe, in the veins or fissures of other rocks; also in combination with sulphur, arsenic, and oxygen. The pure metal is obtained by heating the impure metal, or native bismuth, in inclined cast-iron tubes, where the metal is volatilized and, the vapors condensing, run into receiving-vessels, and finally into moulds, where it solidifies with a crystalline texture.
At a high temperature, bismuth is slightly volatile and oxidizes rapidly. Its fusing-point is 507 deg., but it alloys with other metals to form fusible mixtures, which melt even below 212 deg.
The specific gravity of this metal is 9.8.
The fusibility of other metals is increased by bismuth, and its peculiar property of expanding while cooling makes it highly valuable as an ingredient in type-founders' alloys.
A slight addition of mercury imparts greater fusibility to bismuth alloys. Alloys containing bismuth should always be cooled quickly, to prevent the separation of bismuth.
Gold alloyed with bismuth forms a brassy composition of a brittle nature and the ductility of gold is impaired even by its fumes. It is seldom that bismuth is employed alone in the arts, but it forms an important ingredient in many mixtures for solder, type-metal, fusible alloys, etc.
Bismuth is separated from lead by dissolving the mixed metal in nitric acid; add caustic potash in excess, and the oxides of bismuth and lead will be precipitated, but the lead oxide will be at once redissolved by the alkali. The oxide of bismuth can then be separated by filtration, washed, and ignited. See SOLDERS; TYPE-METAL; FUSIBLE ALLOYS; SEPARATING METALS; EXPANDING ALLOYS.