306 Hartipy— The Action of Heat on the Absorption Spectra and 
the same colour. It is impossible to believe that the latter compound is 
not dehydrated when it enters into solution in this case. I have failed to 
obtain any distinct compound of alcohol with cupric chloride; and, even if such 
could be formed, it is very unlikely that the colour of an alcoholate would be that 
of a solution of the anhydrous salt. 
On the Compounds formed in Aqueous Solutions. 
With regard to the exact compositions of the compounds formed when 
aqueous solutions are heated from 20° to 100°, there can be no doubt that 
CuCl,2H,O0, on solution in water at 16° or 20°, if the solution be saturated, 
becomes CuCl,"H,O; and, that by heating to 100°, at least a portion of the 
dissolved salt becomes CuCl,, because the change is similar to that which is seen 
when this compound is dissolved in alcohol. At intermediate temperatures, we 
have mixtures of two or more compounds. Likewise, when a blue solution of 
cupric chloride, which undoubtedly contains CuCl,;2H,O, is heated it becomes 
erass-green, and this change is precisely what we know to take place when the 
compound formed is CuCl,-H,O0. Cupric bromide, CuBr.5H,0, undoubtedly 
forms the monohydrate, CuBr,;H,O when the solution is heated. The effect of 
heating a grass-green or even a blue dilute solution, the former of which certainly 
contains the compound CuBr,"5H.O, is to convert it into a brown liquid, con- 
taining apparently the molecule CuBr,;H,O. Similar remarks are applicable 
to the nickel salts, the colour changes of the solutions being related in the same 
way to the colours of the salts in different states of hydration. ‘These changes of 
colour can be accounted for only by dissociation, molecule by molecule of the 
water, from the molecules of the hydrated salts, or, what is the same thing, by the 
existence of different hydrates of the same salt in the solution at different 
temperatures, or in solutions with varying quantities of water at the same 
temperature. 
When saturated solutions of these salts at 15° and 20° are diluted with water, 
heat is in each case evolved. This has been proved in alarger number of instances 
than those which have been referred to; but the following may be cited :— 
A solution of 20 grs. of the pure crystallized CuCl,2H,O0 were dissolved 
in 20 ers. of water at 16°, with an evolution of heat equivalent to 3°6 units per 
kilo of the salts: this was then diluted with 100 grs. of water with a heat evolu- 
lution of 28°8 units. It is evident that chemical combination had taken place 
between the cupric chloride and water upon its dilution with water. 
Cuprie Bromide, CuBro.—10 grs. of the black anhydrous crystals were drenched 
with 5:3 c.c. of water at a temperature of 19°°2; the temperature rose to 27°:0. 
Of the brown solution so formed, 5:0 ¢.c. at 20°°0 were mixed with 4°2 c.c. of 
water at 20°, and the temperature rose to 24°°5, the liquid becoming green. 
