Chemical Constitution of Saline Solutions. 307 
Cobalt Bromide, CuBr,,6H,O.—10 grs. were drenched with 5 c.c. of water at 15°-0, 
which caused the temperature to fall immediately, and it gradually sank to 8°°5. 
Some of the solid remained undissolved, as was the case with the copper salt. 
Of the solution, 5 ¢.c. were mixed with 5 ¢.c. of water, both liquids being at 16° 
The thermometer rose after the mixing to 16°°5. 
Nickel Bromide, NiBr,6H,0.—10 grs. of the large green crystals were drenched 
with 6 ¢.c. of water at 14°°5. The temperature sank to 11°-0. A saturated solution 
of the salt at 16°°3 was mixed with an equal volume or 5:0 ¢.c. of water at 16°°5, 
when the temperature immediately rose to 18°'1. 
It is evident that in each of these experiments, the cold saturated solution of the 
salt combined with a further quantity of water to form a more complex molecule 
in the solution. The results are even more striking with cobalt iodide. In some 
cases the actual compounds contained in the diluted solutions have been deter- 
mined by the extent to which the freezing point is lowered (Riidorff);* also 
from thermo-chemical measurements (Thomsen),t and from the vapour pressures 
of the solutions (De Coppet).+ 
VI. Conciusion.—Saturated solutions of hygroscopic and deliquescent salts combine 
with water when diluted to constitute molecules of more complex hydrated compounds im 
such solution. 
VIL. 
In reviewing the facts already recorded, we arrive at the following statement 
which may be considered as a law :— 
When a saturated solution of a coloured salt undergoes a great change of colour upon 
dilution, or any remarkable change in its absorption spectrum due to the same cause, 
the dilution is always accompanied by a considerable evolution of heat. 
It is impossible to believe that the rise of temperature, upon dilution, is not 
caused by the formation of a complex hydrated molecule in the solution, because 
the change in colour is precisely that which occurs in the formation of the crystal- 
line hydrates, and is the reverse of that of heat. 
Arguments have been advanced by Ostwald,§ and supported by Ewan,]|| from 
observations on the absorption spectra of very dilute solutions in favour of the 
electrolytic dissociation theory propounded by Arrhenius. ‘‘It is a necessary 
consequence of this theory that] the absorption spectrum of an electrolyte, which 
* Poggendorff’s Annalen, vol. 114, p. 63, 1861, and vol. 145, p. 599, 1872. 
} Thermochemische Untersuchungen, vol. iii., 1883. 
{ Ann. de Chemie et de Phys., vol. xxy., 4th Series, p. 502; also vol. xxvi., p. 98, 1872. 
§ Zeitschr. physik. Chem., vol. 9, p. 579, 1892. || Proc. Roy. Soc., vol. 57, p, 117, 1894. 
4 Nernst’s ‘‘ Theoretical Chemistry.”’ English Edition, pp. 885-837, 1895. 
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