318 HartLey— On the Conditions of Kquilibrium of Deliquescent and Hygroscopic 
temperature is about 57°'75, even when the pressure of aqueous vapour is 0:3, or 
0-4 inches of mercury. 
This represents altogether 12H,O, or the increase over the initial weight of 
the salt is 380°4 per cent., which represents absorbed water. The salt is wholly 
liquid. Before this, however, there is a wavering between eight and nine mole- 
cules of water. 
Cobalt Bromide, CoBr,;6H,0.—The fluctuations occur with a maximum of 61° 
and a minimum of 47°, or a mean of 54°, but the difference amounts to + 0°3 on 
the total weight of 159-4 grs. Thus, for instance, with a tension of aqueous 
vapour of 0-425, a maximum of 63°, and a minimum of 60°, equal to a mean 
temperature of 61°5, we obtain a total weight of 159-98 grs., or very nearly 
60 per cent. over the initial weight of the salt. In these circumstances the salt is 
wholly liquid. 
Nickel Bromide, NiBr..6H,0.—With a maximum temperature of 56°:5, and a 
minimum of 41°-3, equivalent to a mean of 45°, slight variations in weight occur 
very similar to those observed in the case of cobalt bromide, but the excess over 
the initial weight of the salt is 56-02 per cent. on a total of 156-02 grs. This 
salt 1s wholly liquid. 
Nickel Iodide, Nil. 7H,0.*—This salt increased in weight more rapidly than 
any of the others, more especially at first, and showed no fluctuation until it 
became converted into a salt with 23 molecules of water. 
THe Apsorprion or Lieut By Souurions oF Hatorp Saurs or Copprr, NICKEL, 
AND CoBALt. 
The more nearly the copper and nickel salts approach in composition the 
anhydrous state, it is observed that the ereater is the absorption of light by the 
molecules. The effect of diluting the concentrated green solution ef cupric 
chloride produces a blue colour, resembling that of the crystallized hydrate, 
CuCl,2H.O0; and of the brown solution of the cupric bromide, a green and after- 
wards a blue solution, much less absorbent for the rays of white light than the 
original solution. ‘The colour of the dehquescent concentrated solution of cupric 
chloride is, however, still grass-green, and that of the deliquesced cupric bromide 
is brown. These facts, at first sight, appear to be out of harmony with the 
degree of hydration of the salts as determined by the weight of water absorbed 
in the foregoing record of experiments, but the conditions existing in the 
solutions must be taken into account along with the intensity of colour of 
the different compounds. The solution of CuCl,2H,O in a minimum of water 
is much darker than the solid salt, as also is the solid salt darker when very 
* For this formula, see Sci. Trans. Roy. Dub. Soc., vol. vii., ser. 1., 1900, p. 265. 
