144 DISCUSSION OF EVIDENCE. 



With salts that crystallize without water there is only a very slight 

 increase in the molecular lowering of the freezing-point with increase 

 in the concentration of the solution. The salts of lithium, which 

 crystallize with the same amounts of water, give approximately the 

 same depressions of the freezing-point. 



If we compare the salts of the alkaline earths that crystallize with 

 6 molecules of water, they produce approximately the same lowerings; 

 the nitrates of iron and aluminium with 8 and 9 molecules of water 

 give greater lowerings than the corresponding halogens with 6. 



In the first case we have kept the acid constant and compared with 

 one another the salts of the different metals with the same acid. In the 

 second case we have kept the metal constant, and compared the salts of 

 a given metal with different acids. In both cases the relation between 

 lowering of the freezing-point of water by the dissolved substance and 

 water of crystallization of the dissolved substance manifests itself. 



These salts that crystallize with the largest amounts of water produce 

 the greatest molecular lowering of the freezing-point of water. The 

 work was done with concentrated solutions, and it has already been 

 pointed out that for such substances the molecular lowering of the 

 freezing-point increases with the concentration of the solution. 



We must now ask what bearing has this relation on the question of 

 hydration or non-hydration in aqueous solution? A moment's thought 

 will show that the bearing is a very direct one. If hydrates exist in 

 aqueous solution, those substances which in such solutions would form 

 the most complex hydrates would be the substances that would crystal- 

 lize from aqueous solutions with the largest amounts of water. This is 

 the same as to say that those substances which, in the presence of a large 

 amount of water, have the greatest power to combine with water, would, 

 other things being equal, be the ones to bring with them, out of aqueous 

 solution, the largest amounts of water as water of crystallization. 



We could not, however, expect one of these phenomena to be strictly 

 a linear function of the other, since there are undoubtedly other factors, 

 such as shape of molecules, angles of crystals, etc., coming into play 

 in determining the exact composition of crystals. 



That a relation such as was pointed out above holds so well and so 

 generally for such a large number of substances is very significant 

 and early led me to believe that the suggestion of hydration in general 

 in aqueous solution contained more truth than I imagined when it 

 was first suggested. 



Having found a relation such as the above, we were led to look about 

 for others that would bear directly or indirectly on the problem in 

 hand. Before taking up these, another feature of the work of Getman 

 must be briefly discussed. 



