([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.

Microcosmic Salt dissolves oxide of copper in the flame of oxidation to a green bead, not so intensely colored as the borax bead.  In the reduction flame the bead, if pretty well saturated, becomes dark-green while hot, and brownish-red when cool, opaque and enamel-like.  If the oxide is so little that no reaction is visible, by the addition of some tin, the bead appears colorless while hot, and dark brownish-red and opaque when cold.

Carbonate of Soda dissolves oxide of copper in the oxidation flame upon platinum wire, to a clear, green bead, which loses its color when cooling, and becomes opaque.

Upon charcoal, it is reduced to the metal, the soda is absorbed by the charcoal, and the metallic particles melt with sufficient heat to a grain.

(b.) Silver (Ag).—­This metal occurs in nature in the metallic state, and in combination with other metals, particularly with lead.  It also occurs as the sulphide in several mines.  It crystallizes in cubes and octahedrons; is of a pure white color, great lustre, is very malleable and ductile, and is softer than copper, but harder than gold.  It is not oxidizable, neither at common temperatures nor at those which are considerably higher.  It is soluble in dilute nitric acid, and in boiling concentrated sulphuric acid.

([chi].) Protoxide of Silver (Ag^{2}O).—­It is a black powder.  It is converted by acids and ammonia into oxide and metal.