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.

Heated in a glass tube, closed at one end, it melts to a brown mass, vaporizes and sublimates to a white powder upon a cool portion of the tube.  Immediately above the assay, yellow crystals are visible; these crystals are colorless after cooling, and the fused mass becomes light yellow-colored and crystalline.

Upon platinum foil, in the flame of oxidation, it melts and vaporizes, and becomes light yellow and crystalline after cooling.  In the reduction flame it becomes blue, and brown-colored if the heat is increased.

Upon charcoal, in the reduction flame, it is absorbed by the charcoal; and, with an increase of the temperature, it is reduced to the metal, which remains as a grey powder after washing off the particles of charcoal.

Borax dissolves it, in the oxidation flame, upon platinum wire easily, and in great quantity, to a clear yellow, which becomes colorless while cooling.  By the addition of more of the molybdenic acid the bead is dark yellow, or red while hot, and opalescent when cold.  In the reduction flame, the color of the bead is changed to brown and transparent.  By the addition of more of the acid, it becomes opaque.

Microcosmic Salt dissolves it in the oxidation flame, upon platinum wire, to a clear, yellowish-green bead, which becomes colorless after cooling.  In the reduction flame the bead is very dark and opaque, but becomes of a bright green after cooling.  This is the case likewise upon charcoal.