Note 11 — Chapter XXIV · COPPER, SILVER, AND GOLD

In addition to what has been said (Chapter I., Note 65, and Chapter XXII., Note 35) respecting the combination of CuSO4 with water and ammonia, we may add that Lachinoff (1893) showed that CuSO4,5H2O loses 4¾H2O at 180°, that CuSO4,5NH3 also loses 4¾NH3 at 320°, and that only ¼2O and ¼NH3 remain in combination with the CuSO4. The last ¼H2O can only be driven off by heating to 200°, and the last ¼NH3 by heating to 360°. Ammonia displaces water from CuSO4,5H2O, but water cannot displace the ammonia from CuSO4,5NH3. If hydrochloric acid gas be passed over CuSO4,5H2O at the ordinary temperature, it first forms CuSO4,5H2O,3HCl, and then CuSO4,2H2O,2HCl. When air is passed over the latter compound it passes into CuSO4H2O with a small amount of HCl (about ⅛HCl). At 100° CuSO4,5H2O in a stream of hydrochloric acid gas gives CuSO4,¼H2O,2HCl, and then CuSO4,¼H2O,HCl, whilst after prolonged heating CuSO4 remains, which rapidly passes into CuSO4,5H2O when placed under a bell jar over water. Over sulphuric acid, however, CuSO4,5H2O only parts with 3H2O, and if CuSO4,2H2O be placed over water it again forms CuSO4,5H2O, and so on.