(_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. ([beta].) _Oxide of Copper_ (CuO).--This oxide is a dark-brown or black powder. It is dissolved by acids, with a blue or green-colored solution. It is soluble in aqua ammonia, and the solution is of a dark blue color. _Reactions before the Blowpipe._--Oxide of copper exposed upon platinum wire to the inmost flame (the blue flame), communicates to the external flame a green color. Heated upon charcoal in the oxidation flame, it melts to a black ball, soon spreads over the charcoal, and is partially reduced. Exposed to the reduction flame, at a temperature which will not melt copper, it is reduced with a bright metallic lustre, but as soon as the blast ceases, the surface of the metal becomes oxidized, and appears dark brown or black. If the temperature is continued still higher, it melts to a metallic grain. _Borax_ dissolves the oxide of copper in the flame of oxidation to a clear green-colored bead, even if the quantity of oxide be quite small, but by cooling, the bead becomes blue. In the flame of reduction upon platinum wire, the bead soon becomes colorless, but while cooling presents a red color (protoxide of copper). This bead is opaque, but, if too much of the oxide is added, a part of it is reduced to metal, which is visible by breaking the metallic grain. Upon charcoal, the oxide is reduced to the metal, and the bead appears colorless after cooling. With the addition of some tin, the bead becomes brownish-red and opaque after cooling.