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 hydi-ation 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 CuBr2''3H20. I have not 

 obtained a crystallized solid compound with this composition from such a solution. 



The cupric bromide was never converted quite into the pentah3'drate ; 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 jjeculiar colour and spectrum 

 of the solution by which it is distinguished from that of tlie 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, CoCl3"6H20. — 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 



