Heated upon charcoal, metallic arsenic is volatilized before it melts, and incrusts the charcoal in the flame of oxidation as a white deposit of arsenious acid.  This sublimate appears sometimes of a greyish color, and takes place at some distance from the assay.  When heated slightly with the blowpipe flame, this sublimate is instantly driven away, and being heated rapidly in the reduction flame, it disappears with a light blue tinge, while the usual alliaceous or garlic smell may be discerned.

Arsenious acid sublimes in both glass tubes very readily, as a white crystalline sublimate.  These crystals appear to be regular octahedrons when observed under the microscope.  Upon charcoal it instantly volatilizes, and when heated, the characteristic garlic smell may be observed.

Arsenic acid yields, heated strongly in a glass tube closed at one end, oxygen and arsenious acid, the latter of which sublimes in the cool portions of the tube.  Compounds of arsenic produce, in consequence of their volatility, no reactions with fluxes.  Being heated upon charcoal with carbonate of soda, they are reduced to metallic arsenic which may be detected by the alliaceous odor peculiar to all the arsenic compounds when volatilized.

NINTH GROUP.—­COPPER, SILVER, GOLD.

These metals are not volatile, neither are their oxides.  They are reduced to the metallic state, by fusion with carbonate of soda, when they melt to a metallic grain.  The oxides of silver and gold are reduced per se to the metallic state by ignition.  In the reduction of the oxides of this group, no sublimate is visible upon the charcoal.

(a.) Copper (Cu).—­This metal occurs in the metallic state, also as the protoxide, and as oxides combined with acids in different salts (carbonate of copper as malachite, etc.) The sulphide of copper is the principal ore of copper occurring in nature.  In the metallic state, copper is of a red color, has great lustre and tenacity, is ductile and malleable, and crystallizes in octahedrons and cubes.  It melts at a bright red heat, is more difficult than silver to fuse, but fuses more readily than gold.  It absorbs oxygen while melting.  There arises from its surface a fine dust of metallic globules, which are covered with the protoxide.  The surface of the metal is likewise covered with the protoxide.  Copper exposed to moist air tarnishes, and is converted into hydratic carbonate of copper.  When ignited in the open air, it is soon covered with the brownish-red protoxide.

([chi].) Protoxide of Copper (Cu^{2}O).—­This oxide occurs in nature, crystallized in octahedrons of a ruby-red color, of a lamellar structure, and transparent.  Artificially prepared, it forms a powder of the same color.  It is decomposed by dilute acids into salts of peroxide and metal.  It is converted by ignition, with free access of air, into peroxide.