SALTS OF COPPER. 583 



the other soluble salts of copper, the sulphate has an acid reac- 

 tion ; it is used as an escharotic. The water in this salt may 

 be reduced to 1 eq. at 212 ; above 400 it is anhydrous and 

 white. Although pure sulphate of copper does not crystallize 

 with 7 HO, yet, when mixed with sulphates of magnesia, zinc, 

 nickel, and iron, it crystallizes along with these isomorphous 

 salts in the form of sulphate of iron. At a strong red heat, it 

 fuses and loses acid. The anhydrous sulphate absorbs 2| eq. of 

 ammonia, and forms a light powder of a deep blue colour. 

 When ammonia is added to a solution of sulphate of copper, 

 an insoluble subsulphate is first thrown down, which is redis- 

 solved as the addition of ammonia is continued, and the usual 

 deep azure blue ammoniacal solution formed. The ammoniacal 

 sulphate may be obtained in beautiful indigo-blue crystals, by 

 conducting a stream of ammoniacal gas into a saturated hot 

 solution of the sulphate : it is CuO, SO 3 HO + 2NH 3 (Berzelius.) 

 These crystals lose 1 eq. ammonia and 1 eq. water at 390 (Kane), 

 and are converted into a green powder, CuO, SO 3 + NH 3 , or 

 (NH 3 CuO)SO 3 (page 415); by the cautious application of a 

 heat not exceeding 500, the whole ammonia may be got rid of, 

 and sulphate of copper quite pure remains behind. Sulphate 

 of copper forms the usual double salts with sulphate of potash 

 and with sulphate of ammonia. A saturated hot solution of 

 the double sulphate of copper and potash allows a remarkable 

 double subsalt to precipitate in crystalline grains, KO, SO 3 + 

 3(CuO, SO 3 )+CuO, HO + 3HO. A corresponding seleniate 

 falls, under the boiling point, and always in crystals. The 

 ammoniacal and double salts of sulphate of copper may be 

 represented thus : 



Sulphate of copper (blue vitriol) . . . CuO, SO 3 , HO + 4HO 

 Sulphate of copper and potash . . . CuO, SO 3 , (KO, SO 3 ) + 6HO 

 Hydrated ammoniacal sulphate of copper CuO, SO 3 , HO + 2NH 3 

 Preceding salt dried at 300 .... (NH 3 CuO), SO a 

 Rose's ammoniacal sulphate . . . . CuO,SO s + (NH 3 CuO)SO 3 + 4NH 3 

 Do. heated to 350 CuO, SO 3 + (NH 3 CuO) SO 3 . 



Several subsulphates of copper have been formed. A green 

 powder is obtained by digesting hydrated oxide of copper in a 

 solution of sulphate of copper, of which the constituents are, 

 according to Berzelius, SO 3 , 3CuO and 3HO. The bluish green 

 precipitate which falls when ammonia is added to sulphate of 



