COPPER, ,SILVER, AND GOLD 413 



water of crystallisation, which it only parts with entirely at a high 

 temperature (220) and then gives a white powder of the anhydrous 

 sulphate ; and the latter, on further calcination, loses the elements of 

 sulphuric anhydride, leaving cupric oxide, like all the cupric salts. The 

 anhydrous (colourless) cupric sulphate is sometimes used for absorbing 

 water ; it turns blue in the process. It offers the advantage that it 

 retains both hydrochloric acid and water, but not carbonic anhydride. 11 

 Cupric sulphate is used for steeping seed corn ; this is said to prevent 

 the growth of certain parasites on the plants. In the arts a consider- 

 able quantity of cupric sulphate is also used in the preparation of other 

 copper salts for instance, of certain pigments u bis and a particularly 



very small change in this angle; (6) that the other angles and the ratio of the 

 axes of. the crystals exhibit a similar variation ; and (7) that thus the variation of the 

 form is chiefly determined by the atomic weight of the alkaline metal. As an example 

 we cite the magnitude of the inclination of the axes of R 2 M(SO4) 2 ,6H 2 O. 



R= K Rb Cs 



M = Mg 75 d 12' 74 1' 4 72 54' 



Zn 75 12' 74 7' 72 59' 



Cd 74 7' 72 49' 



Mn 78 8' 72 53' 



Fe 75 28' 74 16' 78 8' 



Co 75 5' 73 59' 72 52' 



Ni 75 0' . 73 57' 72 58' 



Cu 75 32' 74 42' 73 50' 



This shows clearly (within the limits of possible error, which may be as much as 

 W) the almost perfect identity of the independent crystalline forms notwithstanding the 

 difference of the atomic weights of the diatomic elements, M = Mg : . . Cu. 



" In addition to what has been said (Chapter I., Note 65, and Chapter XXII., 

 Note 85) respecting the combination of CuSO4 with water and ammonia, wo may add 

 that Lachinoff (1893) showed that CuSO 4 ,5H 2 O loses 4|H 2 O at 180, that CuSO 4 ,5NH 5 

 also loses 4|NH 3 at 320, and that only H 2 O and iNH 3 remain in combination with 

 the CuSO 4 . The last $H 2 O can only be driven off by heating to 200, and the last 

 |NH 5 by heating to 860 Ammonia displaces water from CuSO 4 ,5H 2 O, but water 

 cannot displace the ammonia from CuSO^SNfi^. If hydrochloric, acid gas "be passed 

 over CuSO 4 ,5H 2 O at the ordinary temperature, it first forms CuSQ 4 ,5H 2 O r 8&Cl, and 

 then CuSO 4 ,2H 2 0,2HCl. When air is passed over the latter compound it passes into 

 CuSO 4 H 2 O with a small amount of HC1 (about HC1). At 100. Cu.SO 4 ,5H 2 O in a 

 stream of hydrochloric acid gas gives CuSO 4 4H 2 O,2HCl, and then CuSO^ILjOHCl, 

 whilst after prolonged heating- CuS0 4 remains, which rapidly passes into CuS0 4 ,5H 2 

 when placed under a bell jar over water. Over sulphuric acid, however, CuSO 4 ,5H 2 O 

 only parts with 8H 2 O, and if CuSO 4 ,2H 2 O be placed over water it again forma 

 CuS0 4 ,5H 2 O, and so on. 



11 bis Commercial blue vitriol generally contains ferrous sulphate. The salt is purified 

 by converting the ferrous salt into a ferric salt by heating the solution with chlorine or 

 nitric acid. The solution is then evaporated to dryness, and the unchanged cupric sul- 

 phate extracted from the residue, which will 'con tain the larger portion of the ferric 

 oxide. The remainder will be separated if cupric hydroxide is added to the solution andi 

 boiled ; the cupric. oxide, CuO, then precipitates the ferric oxide, Fe 2 O 3 , just as it is itself 

 precipitated by silver oxide. But the solution will contain a small proportion 1 of a basic 

 salt of copper, and therefore sulphuric acid must be added to the filtered solution, and the 

 salt allowed to crystallise. Acid salts are not formed, and cupric sulphate itself has an 

 acid reaction on litmus paper. 



