Prof. Graham on Water as a Constituent of Salts, 419 



acid in vacuo, without artificial heat, than by drying it at 212° 

 under the atmospheric pressure, and that the mechanical wa- 

 ter retained by the crystals of this salt may exceed 3 per cent, 

 of their weight. 



Anhy- 

 drous 

 Salt. 



"A 

 "J 



Dried on water-bath at 212°, 

 for three days, or till 

 ceased to lose weight ... 



Dried on nitre-bath at 238°, 1 

 for three days j 



Dried in vacuo over sulphuric" 

 acid for seven days, or till 

 it ceased to lose weight; 

 therm, from 65° to 74^° ..._ 



Crystals pounded, and slightly") 

 dried at 80°, so as not to (^ 

 injure the lustre of an en- f 

 tire crystal J 



Same crystals not deprived") 

 of mechanical water by the ^ 

 above treatment J 



Composition of sulphate of"^ 

 copper and potash with two )> 

 atoms of water (by theory) J 



Composition of do. with six 1 

 atoms of water (by theory) j 



19-6 

 22-06 



22-97 



13-94' 

 23-79 



Water. 



2-21 

 2-37 



1-61 



3-4 

 8-64 



Anhy- 

 drous 

 Salt. 



100 

 100 



100 



100 



100 



100 

 100 



Water. 



11-27 

 10-74 



7-09 



32*25 



36*22 



10-77 

 32-33 



I have confirmed the observation of Berzelius, that a c(m- 

 centrated solution of this salt, when boiled, deposits an inso- 

 luble subsalt, containing sulphate of potash, but which is de- 

 composed by washing, and cannot be had in a proper state 

 for analysis. But the crystals of the double salt are quite so- 

 luble after being heated to 212°, so that they do not undergo 

 the same change as their solution does at that temperature. 



This double salt retains its blue colour after being fused at 

 a red heat and cooled, and does not become white like the 

 sulphate of copper. Indeed it appears, that, to be coloured, 

 the salts of the oxide of copper require the addition of some 

 other constituent, such as saline water, sulphate of potash, or 

 ammonia. Hence, if the absolute sulphate of copper could 

 be obtained in a crystallized state, it would be a colourless 

 salt. 



3H2 



