(χ.) Peroxide of Gold (Au2O3).—This oxide is an olive-green or dark brown powder, containing variable quantities of water. Decomposed at 530°, it yields metallic gold and oxygen.
Reactions before the Blowpipe.—Oxides of gold are reduced, in both the oxidation and reduction flames, to the metal, which fuses to grains.
Borax does not dissolve it, but it is reduced to the metallic state in this flux in either flame. The reduced metal fuses upon charcoal to a grain.
Microcosmic Salt presents the same reactions as borax.
When fused with soda, upon charcoal, the soda is absorbed, and the gold remains as a metallic grain.
TENTH GROUP.—MOLYBDENUM, OSMIUM.
These metals are not volatile, and are infusible before the blowpipe; but some of their oxides are volatile, and can be reduced to an infusible metallic powder.
(a.) Molybdenum (Mo) occurs in the metallic state; also combined with sulphur, or as molybdic acid combined with lead. It is a white, brittle metal, and is unaltered by exposure to the air. When heated until it begins to glow, it is converted into a brown oxide. Heated at a continued dull red heat, it turns blue. At a higher temperature, it is oxidized to molybdic acid, when it glimmers and smokes, and is converted into crystallized molybdic acid upon the surface.
(χ.) Protoxide of Molybdenum (MoO).—This oxide is a black powder.