138 HYDRATES IN AQUEOUS SOLUTION. 



The results are given in tables 38 to 41. The freezing-point lowerings are 

 plotted in figs. 3, 14, 15, 16, and 19, the conductivities in figs. 7 and 22, the 

 refractivities in fig. 23, and the hydrates in figs. 47 and 53. 



The same remarks that were made in connection with the salts of calcium 

 hold almost exactly in the case of the strontium salts. 



The salts of barium differ from the salts of calcium and strontium, in that 

 they crystallize with a smaller number of molecules of water of crystalli- 

 zation. They give a smaller lowering of the freezing-point of water (see 

 tables 42 to 44), as is seen from the curves, figs. 14, 15, and 16. 



The salts of magnesium have been studied pretty thoroughly, and gave 

 very satisfactory results. These results are given in tables 45 to 48. The 

 freezing-point lowerings are plotted in figs. 14, 15, and 24, the conductivities 

 in fig. 25, and the hydrates in figs. 46 and 48. 



The halides of magnesium and the nitrate crystallize, each with six mole- 

 cules of water, and all have large hydrating powers. The complexity of 

 the hydrates increases, with a fair degree of regularity, from the most con- 

 centrated to the most dilute solution. The hydrating power of all of these 

 salts is of the same order of magnitude^ as would be expected, since they 

 have the same power to hold water when out of solution as water of crystal- 

 lization. This is seen especially in the more concentrated solutions, where 

 the experimental errors are relatively small. 



Magnesium sulphate, like all the other sulphates studied, gives abnormal 

 results. It appears to form no hydrates in aqueous solution, notwithstand- 

 ing the fact that it crystallizes with seven molecules of water of crystallization. 

 It is almost certain that this substance has considerable hydrating power, 

 but this is masked in our results by the large amount of polymerization which 

 the sulphates undergo. 



The hydrating power of only one salt of zinc was worked out. The halogen 

 compounds of zinc were too unstable in the presence of water to enable us 

 to work satisfactorily with them. The chloride of zinc showed freezing- 

 point lowerings that were in keeping with its water of crystallization. The 

 nitrate has the hydrating power that would be expected from its water of 

 crystallization. The same remarks can be made in reference to the sulphate 

 of zinc, that have been made in connection with the other sulphates studied. 



The salts of cadmium present a number of features of special interest. 

 In the first place the halogen salts of cadmium either crystallize with a small 

 amount of water, like the chloride, or with none at all, like the bromide and 

 iodide. We should, therefore, expect that these substances would give com- 

 paratively small lowering of the freezing-point of water, and show little or 

 no hydrating power when in aqueous solution. The results given in tables 

 52 to 54 confirm these expectations. The freezing-point lowerings are plotted 



