Constitution of the Subsalts of Copper. 501 



green tint lost 2* grs., and 36*1 3 lost 2*2 grs. of water, equiva- 

 lent to 2 equivalents of water from 294, the equivalent num- 

 ber of the pentasulphate of copper, SO s 5CuO, 6HO, thus 

 altering its constitution to the formula SO a SCuO, 4 HO. 

 Besides the subsulphates of copper already described, two 

 others are stated to exist, a disulphate and an octosulphate of 

 copper. Dr. Thomson describes the first, the disulphate, as 

 produced " when crystals of the blue sulphate are dissolved 

 in water and the solution boiled for a long time with a quan- 

 tity of black oxide of copper, equal to that contained in the 

 salt," and states it to consist of SO a 2CuO, but gives no 

 water as a constituent of it. L. Gmelin, on Thomson's au- 

 thority, directs that equal equivalents of the sulphate and 

 oxide of this metal be digested together for some months to 

 obtain the green disulphate. I tried both these plans ; by boil- 

 ing, at various intervals during ten weeks, equivalents of sul- 

 phate and oxide, I obtained the trisulphate of copper, SO a 

 3CuO, 2HO, a green-coloured powder; by digesting an equi- 

 valent of each for thirteen weeks the tetrasulphate, SO a 4CuO, 

 4HO, was produced; even when excess of sulphate of copper 

 was boiled with the precipitated and washed oxide still the 

 subsulphate, SO a 3CuO, 2HO, was formed ; and when in ad- 

 dition to these unsuccessful attempts to obtain it, the modes 

 described being so distinct and easy of execution, we take into 

 consideration that water is not mentioned as a constituent of 

 this disulphate, which is also described as a green-coloured 

 powder, — and no salt of copper whatever is known that pos- 

 sesses a green or a blue colour unless water be present — I 

 am compelled to deny the existence of Thomson's disulphate. 

 Of the non-existence of the octosulphate of Dr. Kane I am 

 not prepared to speak so decidedly ; the evidence of the exist- 

 ence of such a salt is so complete and circumstantial, that on 

 a prima facie view of the description and analysis of this salt 

 in the paper " On the Compounds of Ammonia," it almost 

 compels belief. The production of this very singular salt is 

 dependent, according to Dr. Kane's description, upon " the 

 quantity of alkali employed in the precipitation ; where potash 

 had been used, there were two distinct precipitates produced, 

 the one the bluish-green generally described, the other ' the 

 octosulphate' of a clear grass-green, resembling that of hy- 

 drated oxide of nickel. When ammonia was employed the 

 former alone was produced, and the formation of the latter was 

 found to occur where the whole of the copper had been thrown 



down, but the liquor had not yet begun to react alkaline 



It was found in the first instance accidentally, but I have since 

 seldom failed in preparing it completely pure." The process 



