(_c._) _Gold_ (Au).--This metal occurs mostly in the metallic state, but frequently mixed with ores, and with other metals. Gold crystallizes in cubes and octahedrons, is of a beautiful yellow color, great lustre, and is the most malleable and ductile of all the metals. It melts at a higher temperature than copper, gives a green colored light when fused, and contracts greatly when cooling. It does not oxidize at ordinary temperatures, nor when heated much above them. It is soluble in nitro-hydrochloric acid (_aqua regia_). ([chi].) _Protoxide of Gold_ (Au^{2}O).--This oxide is a dark violet colored powder which is converted by a temperature of 540° into metallic gold and oxygen. It is only soluble in aqua regia. Treated with hydrochloric acid, it yields the chloride of gold and the metal. With aqua ammonia, it yields the fulminating gold, which is a blue mass and very explosive. ([chi].) _Peroxide of Gold_ (Au^{2}O^{3}).--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. ([chi].) _Protoxide of Molybdenum_ (MoO).--This oxide is a black powder. ([chi].) _Deutoxide of Molybdenum_ (MoO^{2}).--This oxide is a dark copper-colored crystalline powder. _Reactions before the Blowpipe._--Metallic molybdenum, its protoxide and binoxide, are converted in the oxidation flame into molybdic acid. This acid fuses in the flame of oxidation to a brown liquid, which spreads, volatilizes, and sublimes upon the charcoal as a yellow powder, which appears crystalline in the vicinity of the assay. This sublimate becomes white after cooling. Beyond this sublimate there is visible a thin and not volatile ore of binoxide, after cooling; this is of a dark copper-red color, and presenting a metallic lustre.