Exposed to the blowpipe flame, it is instantly volatilized. This is also the case with it when combined with other metals. The oxides of mercury are, in the oxidation and reduction flames, instantly reduced and volatilized. They do not produce any alteration with fluxes, as they are volatilized before the bead melts. Heated with carbonate of soda in a glass tube closed at one end, they are reduced to metallic mercury, which is volatilized, and condenses upon a cool portion of the tube as a grey powder. By cautious knocking against the tube, or by rubbing with a glass rod, this sublimate can be brought together into one globule of metallic mercury. Compounds of mercury can be most completely reduced by a mixture of neutral oxalate of potassa and cyanide of potassium. If the substance under examination contains such a small quantity of mercury that it cannot be distinguished by volatilization, a strip of gold leaf may be attached to an iron wire, and introduced during the experiment in the glass tube. The smallest trace of mercury will whiten the gold leaf in spots. (_b._) _Arsenic_ (As).--This metal occurs in considerable quantity in nature, chiefly combined with sulphur or metals. Arsenic, in the metallic state, is of a whitish-grey color, high lustre, and is crystalline, of a foliated structure, and is so brittle that it can be pulverized. It does not melt, but is volatilized at 356°. Its vapor has a strong alliaceous odor. Arsenic sublimes in irregular crystals. By exposure to the air it soon tarnishes, and is coated black. Being mixed with nitrate of potassa and inflamed, it detonates with vehemence. Mixed with carbonate of potassa, it is inflamed by a stroke of the hammer, and detonates violently. Heated in oxygen gas, it is inflamed, and burns with a pale blue flame to arsenious acid. ([beta].) _Arsenious Acid_ (AsO^{3}).--This acid crystallizes in octahedrons, or, when fused, forms a colorless glass, which finally becomes opaque and enamel-like, or forms a white powder. It sublimes without change or decomposition. When heated for a longer while below the temperature of sublimation, it melts into a transparent, colorless, tough glass. The opaque acid is sparingly soluble in cold water, and still more soluble in hot water. It is converted, by continued boiling, into the transparent acid, which is much more soluble in water. Arsenious acid is easily dissolved by caustic potassa. It is also soluble in hydrochloric acid. This acid occurs associated with antimonious acid, protoxide of tin, protoxide of lead, and oxide of copper. It occurs likewise in very small quantity in ferruginous mineral springs. ([gamma].)_Arsenic Acid_ (AsO^{5}) is a white mass, which readily absorbs moisture and dissolves. It will not volatilize at a low red heat, nor will it decompose. Exposed to a strong heat, it is decomposed, yielding oxygen, and passing into arsenious acid. _Reactions before the Blowpipe._