406 PBINCtfLES OF CHEMISTRY 



solution, and afc not too high a (temperature, cuprous oxide is ob- 

 tained. To see this reaction clearly, it is not sufficient to take any 

 cripric salt, because the alkali necessary for the reaction might pre- 

 cipitate cupric oxide it is necessary to add previously some substance 

 which will prevent this precipitation. Among such substances, 

 tartaric acid, C 4 H 6 6 , is one of the best. In the presence of a suffi- 

 cient quantity of tartaric acid, any amount of alkali may be added to a 

 solution of cupric salt without producing a precipitate, because a soluble 

 double salt of cupric oxide and alkali is then formed. If glucose (for 

 instance, honey or molasses) be added to such an alkaline tartariq 

 solution, and the temperature be slightly raised, it" first gives a yellow 

 precipitate (this is cuprous hydroxide, CuHO), and then, on boiling, 

 a red precipitate of (anhydrous) cuprous oxide. If such a mixture 

 be left for a long time at the ordinary temperature, it deposits well- 

 formed crystals of anhydrous cuprous oxide belonging to the regular 

 system. 7 



7 Colourless solutions of cuprous salts may also be obtained by the action of sul- 

 phurous or phosphorous acid and similar lower grades of oxidation on the blue solutions of 

 the cupric salts. This is very clearly and easily effected by means of sodium thio- 

 solphate, N^SgOj, which is oxidised in the process. Cuprous oxide can not only be 

 obtained by the deoxidation of cupric oxide, but also directly from metallic copper itself, 

 because the latter, in oxidising at a red heat in air, first givee cuprous oxide. It is pre- 

 pared in this manner on a large scale by heating sheet copper rolled into spirals in 

 reverberatory furnaces. Care must be taken that the air is not in great excess, and that 

 the coating of red cuprous oxide formed does not begin to pass into the black cupric oxide. 

 If the oxidised spiral sheet is then unbent, the brittle cuprous oxide falls away from 

 the soft metal. The suboxide obtained in this manner fuses, with ease. It is necessary 

 to prevent the access of air during the v fusion, and if the mass contains cupric oxide it 

 must be mixed with charcoal, which reduces the latter. Cuprous chloride, CuCl, corre- 

 sponding with cuprous oxide (as sodium chloride corresponds with sodium oxide), when 

 calcined with sodium carbonate, gives sodium chloride and cuprous oxide, carbonio 

 anhydride being evolved, because it doe's not combine with the cuprous oxide under these 

 conditions. The reaction can b 9 expressed, by the following equation: 2CuCl + Na2CO3 

 = Cu 2 0'+ SNaCl + CO 2 . The cupric oxide itself, when calcined with finely-divided copper 

 this copper powder may be obtained by many methods for instance, by immersing zinc 

 in a solution of a copper salt, or by igniting cupric oxide in hydrogen), give3 the fusible 

 cuprous oxide: Cu + CuO = Cu 3 O. Both the native and artificial cuprous oxide haye-a 

 sp. gr. of 5'6. It is insoluble in water,' and is not acted on by (dry) air. When heated 

 with acids the suboxide forms a solution of a cupric salt and metallic copper for example, 

 Cu 2 + H 2 SO 4 = Cu + CuSO 4 + H 2 O. However, strong hydrochloric acid does not separate 

 metallic copper on dissolving cuprous oxide, which is due to the fact that the cuprous 

 cnloride formed is soluble in strong -hydrochloric acid. Cuprous oxide also, dissolves in, 

 a solution of ammonia, and in the absence of air gives a colourless solution, which turni 

 blue in the air r absorbing oxygen, owing to the conversion of the cuprous oxide into 

 cupric oxide. The blue..solution thus formed may be again reconverted into a colourless 

 cuprous solution by immersing a copper strip in it, because the metallic copper then 

 deoxidises the cupric oxide in the solution into cuprous oxide. Cuprous oxide ,is charac- 

 terised by the fact that it gives red glasses when fused with glass or with salts forming 

 vitreous alloys. Glass tinted with cuprous oxide is used for ornaments. The access of 

 air must be avoided during its preparation, because the colour then becomes green, owing 



