306 Hartley — 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 

 CuCl2'2H20, on solution in water at 16° or 20°, if the solution be saturated, 

 becomes CuCL*H20; 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 CuCl2"2H20, is heated it becomes 

 grass-green, and this change is precisely what we know to take place when the 

 compound formed is CuCL'HoO. Cupric bromide, CuBro'oHaO, undoubtedly 

 forms the monohydrate, CuBr2"H20 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 CuBr2'5H20, is to convert it into a brown liquid, con- 

 taining apparently the molecule CuBro'HoO. Similar remarks are applicable 

 to the nickel salts, the colour changes of the solutions being related in the same 

 way to the colours of tlie 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, b}' 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 a larger 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 CuCl2'2H20 were dissolved 

 in 20 grs. 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. 



Cupric 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.c. at 20°"0 were mixed with 4'2 c.c. of 

 water at 20°, and the temperatm-e rose to 24°-5, the liquid becoming green. 



