22 



HYDRATES IN AQUEOUS SOLUTION. 



Aluminium and ferric chlorides contain 6 molecules of crystal water, yet 

 they show much greater lowering than the ternary chlorides with 6 mole- 

 cules of water of crystallization. This is to be accounted for by the fact 

 that the chlorides of iron and aluminium are quaternary electrolytes each 

 molecule dissociating into four ions. 



Turning to fig. 15, relations similar to those pointed out above are 

 seen to exist for the bromides. Sodium bromide, unlike sodium chloride, 



I 2 



Concentration 

 FIG. 15. 



crystallizes with 2 molecules of water. It falls considerably above potas- 

 sium bromide, just as we should expect it to do. Lithium bromide, with 

 3 molecules of crystal water, occupies a still higher position in the figure. 

 Passing to the ternary bromides, barium bromide, with 2 molecules of water 

 of crystallization, shows greater lowering than the binary electrolyte, lithium 

 bromide, as we should expect; it also gives considerably smaller lowering 

 of the freezing-point than strontium, calcium, and magnesium bromides, 

 each with 6 molecules of water of crystallization. 



Relations of an exactly similar character are shown by fig. 16, for the 

 iodides. 



