Chemical Constitution of Saline Solutions. 299 
the green hydrated nickel bromide; the green dihydrate, and brown hexa-hydrate 
of cobalt iodide. 
The first is a familiar example: it is crimson, and readily changes to purple 
by loss of water on rise of temperature ; the second salt consists of a rich grass- 
ereen ageregation of crystals. When dissolved in as little water as possible a 
similar dark green solution is formed. ‘The latter salt occurs in dusky reddish* 
brown hexagonal prisms, a saturated solution of which at 16° and 20° has a similar 
though deeper colour. Other illustrations of this are afforded by copper and 
nickel compounds. ‘There are, however, a few salts, and these are generally very 
soluble substances, which do undergo sensible alterations in colour, which altera- 
tions have been observed in each case to correspond with that produced by a 
state of partial or complete dehydration. Such salts are the cupric chloride and 
and the hydrated nickel bromide. 
CuCl,2H,OF is a pale blue salt; but its solution is grass-green, similar 
in colour to that of the monohydrated, CuCl,,H,O. When exposed to the action 
of moist air, the blue crystals absorb water, gain weight, and, in doing so, turn 
green, and become moistened with a solution of the salt. A green solution may 
be obtained which will not deposit the salt CuCl,2H,O, unless evaporated to 
such a degree that the whole liquid becomes nearly solid. This salt can scarcely 
be contained in the solution; it must be formed from the liquid as the salt 
solidifies. 
CuBr,‘5H,0 is of a golden green colour ; its solution in water is intensely dark 
brown, of the same colour as a solution of the compound CuBr, when dissolved in 
alcohol or ina minimum of water. ‘The brown solution can be obtained in sucha 
condition that it does not deposit the salt CuBr,-5H,O0, but only the anhydrous 
salt CuBr,. The salt NiBr,-"6H,O undergoes a similar change. 
It may here be remarked that whether the brown solution of cupric bromide 
deposits anhydrous salt or the hydrate CuBr,5H,0, depends upon the tem- 
perature. 
The following experiment shows how the hexahydrated cobalt chloride may 
be partially dehydrated by solution in a solvent other than water :— 
The crystals were dissolved in strong alcohol of 98 per cent., or there- 
abouts, forming a beautiful deep blue solution; on partial evaporation, without 
heat, crystals were deposited, which, on analysis, proved to be the original 
hexahydrate. This is proved by the following analytical numbers:—At a 
temperature of 100°, 2 grs. of the salt lost 0°605 grs. of water, corresponding to 
30°25 per cent. ‘The conversion of the hexahydrate into the dihydrate at 100° 
«A statement in the last edition of Watts’ Dictionary is, in this particular, inaccurate. The salt is 
described as being red. 
+ Jour. Chem. Soe., vol. 13, p. 256, 1875. 
