Salts of Copper, Cobalt, and Nickel, with respect to Atmospheric Moisture. 317 
may be observed to be present simultaneously in the one quantity of salt, two 
solid hydrates and one liquid, the latter being in very small proportion to the 
whole mass. The solid compounds are—first, the dull coal-black dihydrate ; 
secondly, the golden green crystals of the pentahydrate. The liquid hydrate is a 
brown and intensely dark solution. The course of chemical change noticed 
during the absorption of aqueous vapour was a swelling up of the lustrous steel- 
grey mass and its conversion into the porous coal-black dihydrate. There was 
subsequently formed an incrustation of golden green crystals of the pentahydrate, 
which disappeared as the temperature rose, but at points where the salt came 
into contact with the sides of the glass vessel drops of brown liquid were seen. 
These did not dry up or crystallize; neither did they change colour. It was from 
such a solution that only the anhydrous salt could be crystallized, at or about the 
temperature of 60° F.; and it certainly contains either the anhydrous salt or a com- 
pound of no higher degree of hydration than that of the dihydrate. From the 
curve and from the tabular statement it is clear that the most stable condition of 
the salt at ordinary atmospheric temperatures is that of a solution in which the 
total quantity of water is represented by the formula CuBr.3H,0. I have not 
obtained a crystallized solid compound with this composition from such a solution. 
The cupric bromide was never converted quite into the pentahydrate ; and as 
soon as a portion was changed into this compound, it became decomposed by a 
slight rise of temperature. As it is known from previous experiments that the 
pentahydrate liquefies and becomes brown under such conditions, it is only 
reasonable to conclude that the decomposition of the crystals results in the 
formation of the drops of brown liquid. But the peculiar colour and spectrum 
of the solution by which it is distinguished from that of the crystallized solid, 
and also from the fact that attempts to crystallize this solution at a temperature 
of 60°F., or higher than 60° F., have always resulted in the production of the 
anhydrous cupric bromide, I have been led to the conclusion that the penta- 
hydrate is dissociated when simply dissolved in water. At a lower temperature, 
when the solution is not too concentrated, the green pentahydrate may be 
crystallized from the brown solution in magnificently coloured green prisms an 
inch in length, though the colour of the solution does not change, but remains 
brown. 
If the solution be too concentrated, cooling even below 0° does not crystallize it, 
but if it be further concentrated by heat, and cooled, the anhydrous salt crystal- 
lizes out; and also, if the concentrated solution be allowed to remain in an air- 
pump bell-jar over oil of vitriol, the anhydrous salt separates. 
Cobalt Chloride, CoCl,6H,0.—The fluctuations in weight began to be most 
marked when the maximum was 58°5° F., and the minimum 46°:0; also 56°°5 
and 47°°5, respectively. There is a point of stability reached when the mean 
