Salts of Cop2-)er, Cobalt, and Nickel, tvith 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 being 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 raj)idly than 

 the sulphuric acid. The cupric bromide was never quite converted into the 

 pentahydrate, and as soon as a jDortion 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: — 



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. 



