EVIDENCE FOR THE EXISTENCE OP HYDRATES. 25 



nitrate diagram, alone, will show an unmistakable relation between the 

 lowering of the freezing-point and the water of crystallization possessed by 

 the salts in question. 



Relations such as those pointed out above, between different salts of the 

 same acid, are all that could reasonably be expected to exist. Certain 

 relations, however, of interest and importance in this connection are found 

 between the salts of different acids. 



If we compare the results plotted in curves in figs. 14 to 17 for the 

 chlorides, bromides, iodides, and nitrates, we shall find abundant evidence 

 bearing on the relation between freezing-point lowering and water of crys- 

 tallization. Chlorides, bromides, iodides, and nitrates that crystallize with- 

 out water all show a molecular lowering of between 3 and 4, and this 

 increases very slightly, if at all, with the concentration. 



As far as the comparison can be carried, lithium chloride, with 2 molecules 

 of water, gives less lowering than lithium bromide or lithium iodide with 

 3 molecules of water, and just about the same lowering as lithium nitrate 

 with 2 molecules of water of crystallization. 



Lithium bromide, with 3 molecules of water, gives about the same lowering 

 as lithium iodide, which has the same amount of water of crystallization. 



Sodium bromide, with 2 molecules of water, gives very nearly the same 

 lowering as sodium iodide, which has the same number of molecules of water 

 of crystallization. 



Barium chloride has the same number of molecules of water of crystalli- 

 zation as the bromide and iodide. Since barium chloride has only a slight 

 solubility in water, comparison of freezing-point lowerings must be limited 

 to dilute solutions. The freezing-point lowerings of the three salts are just 

 about the same in the dilute solutions, although in the more concentrated 

 solutions the iodide shows greater lowering than the bromide. 



If we compare the chlorides, bromides, and iodides of the alkaline earths, 

 which contain each 6 molecules of water of crystallization, we shall find 

 that the lowerings of the freezing-point produced by them are all of the 

 same order of magnitude. We shall, however, see that the bromides give 

 somewhat greater lowering than the chlorides, and the iodides even greater 

 lowering than the bromides. 



As far as comparisons can be made, it seems that the nitrates produce 

 about the same lowerings as the corresponding chlorides with an equal 

 number of molecules of water of crystallization, and, therefore, somewhat 

 less than the corresponding bromides and iodides. 



The quaternary chlorides of aluminium and iron can not be compared, at 

 present, with respect to their freezing-point lowering, with the correspond- 

 ing bromides and iodides, because the latter have not yet been investigated. 



