Cuprous Oxide

Cuprous Oxide (red oxide, sub-oxide), $\backslash text\{Cu\}\_2\backslash text\{O\}$. This is obtained by heating to redness the black oxide with nearly its own weight of finely divided copper in a well-covered crucible, to protect the mixture from the oxidising action of the air. It is got as a hydroxide by adding grape-sugar to a solution of sulphate of copper, and then caustic soda, till a blue precipitate, which is first formed, is redissolved. The solution, on being gently warmed, deposits the hydroxide as a rich orange-yellow powder. On continuing the heating till the liquid has reached the boiling-point, and maintaining the ebullition for some time, the powder changes into the red anhydrous oxide. This oxide is used in colouring glass a fine ruby tint. It is not acted on by air or moisture, and for this reason is produced on copper surfaces as a bronze to keep the metal itself from becoming stained. The salts of this oxide are generally colourless, but they are liable to absorb oxygen and pass into the blue-coloured cupric salts. Cuprous chloride is the most important salt, being used for absorbing carbonic oxide in gas analysis.