Salts of Copper, Cobalt, and Nickel, with respect to Atmospheric Moisture. 319 
slightly moist than when quite dry, because it is wetted with the darker solution. 
In the deliquesced hydrates we have mixtures of the monohydrated cupric 
chloride, of a very dark rich green, of the dihydrate pale blue, and of a trihy- 
drate, with a paler blue colour, the colour of the two latter being masked by that 
of the first compound. Similarly, but in a much more marked degree, cupric 
bromide and nickel bromide change colour, the lower hydrates bemg much 
more intensely coloured than those containing more water. Nickel iodide 
behaves also in a similar manner. 
ConcLUSIONS. 
These observations show that the bromides are more deliquescent than 
chlorides, and the iodide than the bromides; also that the most stable liquid 
hydrates are those of nickel iodide, with 23 and 21 molecules of water, while 
next in order are the cobalt bromide and nickel bromide, with 18 molecules ; 
cobalt chloride, with 11 molecules; cupric bromide, with 4 molecules; and cupric 
chloride, with 3 molecules of water. 
This is also the case with cobalt iodide, but no figures are given here because 
the salt is decomposed by light. It is a substance so deliquescent that if a moist 
salt be placed in a bell-jar with oil of vitriol and cobalt iodide standing side by 
side in separate vessels, the cobalt iodide increases in weight more rapidly than 
the sulphuric acid. The cupric brontide was never quite converted into the 
pentahydrate, and as soon as a portion changed into this compound it became 
decomposed by a slight rise of temperature. 
The chemical relationship of the absorbed water to the salt is shown by the 
fact that the three metals do not differ largely in atomic mass, the differences in 
the molecular mass of each of the salts being principally due to the atomic masses 
of the halogen elements, which differ widely. 
It is also evident that it is not any one constituent of the salt, but the salt 
molecule as a whole which combines with the water. For instance :— 
Formule. Molecular Mass. Hydrate formed. 
CuCl. 134°6, CuCl,:3H,0. 
CuBr,. 223°6. CuBr,'4H,0. 
CoCl.. 130:0. CoCl,°11H.0. 
CoBry. 219°0. CoBr,:18H,0. 
NiBr,. 218°7. NiBr.18H,0. 
Nil.. 312°7. Nil,-23H.0. 
Furthermore, that the attraction of the salt for water is independent of the 
molecular mass of the salt. For example, cobalt chloride absorbs more water 
than cupric chloride; also cobalt and nickel bromide than cupric bromide. 
