Licence: Public Domain Mark
Credit: Qualitative chemical analysis / by C. Remigius Fresenius. Source: Wellcome Collection.
Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.
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![[§ 120. contact witli water and air, it becomes covered with a green crust of basic carbonate of oxide of copper; and when ignited in the air it be- comes coated over with suboxide and oxide. In hydrochloric acid and dilute sulphuric acid, it is insoluble or nearly so, even on boiling. Nitric acid dissolves the metal readily. Concentrated sulphuric acid converts it into sulphate of oxide of copper, with evolution of sulphurous acid. 2. Cuprous oxide or suboxide of copper, Cu^O [Ou^O], is red, its hydrate is yellow; both change to oxide when ignited in the air. On treating the suboxide with dilute sulphuric acid, metallic copper separates, whilst sulphate of oxide of copper dissolves; on treating suboxide of copper with hydrochloric acid, white cuprous chloride is formed, which dissolves in an excess of the acid, but is reprecipitated on adding water. 3. Oxide of copper is a black powder, which is not decomposed at a red heat; at a very high temperature, however, it loses oxygen and is converted into suboxide; its hydrate, CuO,HO [CuH^O^],is light blue. Both oxide of copper and its hydrate dissolve readily in hydrochloric, sulphuric, and nitric acids. 4. Most of the neutral salts of oxide of copper are soluble in water; the soluble salts redden litmus, and those containing volatile- acids suffer decomposition when heated to low redness, with the excep- tion of the sulphate, which can bear a somewhat higher temperature.. They are usually white in the anhydrous state ; but the hydrated salts, are generally blue or green, and their solutions exhibit the same colour, even when considerably diluted. 5. Siilphuretted. hydrogen and sxilphide of ammonium pro- duce in alkaline, neutral, and acid solutions brownish-black precipitates of sulphide of copper, CuS [CuS].* This sulphide is insoluble in dilute acids and in caustic alkalies. Hot solutions of sulphide of potas- sium and sulphide of sodium remove sulphur but do not dissolve it, or only to a very trifling extent; it is a little more soluble in sulphide of ammonium, however, especially when yellow and hot, so that this re- agent is not well adapted to effect the perfect separation of sulphide: of copper from other metallic sulphides. Sulphide of copper is readily decomposed and dissolved by boiling nitric acid, but it remains alto- gether unaffected by boiling dilute sulphuric acid. It dissolves com- pletely in solution of cyanide of potassium, if freshly precipitated. If the solutions of salts of copper contain a very large excess of a con- centrated mineral acid, sulphuretted hydrogen produces a precipitate only after the addition of water. 6. Potassa or soda produces a light-blue bulky precipitate of hydrate of oxide of copper, CuO,HO [CuH^OJ. If the solution is highly concentrated, and the precipitant is added in excess, the precipitate turns brownish-black after the lapse of some time, and loses its bulkiness, even in the cold ; but the change takes place immediately if the precipitate is boiled with the liquid in which it is suspended, and which must, if necessary, be diluted for the purpose. This change is brought about by the conversion of the blue hydrate of oxide of copper, into another hydrate containing less water. The light-blue hydi-ate dis- solves in a large excess of very concentrated potassa or soda, forming a blue solution. * According to J. Thomsen this precipitate is Cu^Sj + S [Cu^Sj + S].](https://iiif.wellcomecollection.org/image/b21966953_0170.jp2/full/800%2C/0/default.jpg)
