240 HYDRATES IN AQUEOUS SOLUTION. 



In conclusion, it is appropriate to call attention to certain facts that were 

 brought out by the present investigation, and which have no direct bearing 

 on the theory of hydrates. 



Tables 101 and 103 for the freezing-point lowerings of cobalt chloride, 

 together with either calcium chloride or calcium bromide, show that these 

 solutions change with time. The nature of the change is such as to increase 

 the molecular lowering of the freezing-point; in other words, the solutions 

 undergo hydrolysis. 



Table 108 shows that the volume of water necessary to change a color 

 of the series in question approximately to that of the next more dilute solu- 

 tion of the set decreases as the concentration of the first solution increases. 

 The solutions contain cobalt chloride and aluminium chloride. 



The reason for the decrease just noted is as follows: When the solutions 

 arc very concentrated they contain a relatively small amount of water and, 

 therefore, it requires the addition of only a very small amount of water to 

 change the color of the solution to that of the next lower member of the series. 

 When, on the other hand, the solution contains a larger amount of water to 

 begin with, it takes a greater amount of water than formerly to bring about 

 a definite color change. In other words, the question is one that concerns 

 the ratio of the amount of water added to the quantity already present, and 

 it does not relate primarily to the absolute volume of water concerned. A 

 careful study of the five curves for electrical conductivity shows that the 

 viscosity is chiefly responsible for the decrease in conductivity with increase 

 in concentration of the dehydrating agent, after a maximum of a curve has 

 been reached. Stated in a slightly different way, the decrease in the velocity 

 of the ions is so much greater than the simultaneous increase in the number 

 of ions that the conductivity decreases with increase in concentration. The 

 fact that the maxima of the curves for the solutions that contained the same 

 dehydrating agent occur at approximately the same concentration of this 

 agent, quite independently of the nature of the colored salt in the solution, 

 is due to the relatively small number of ions of the colored salt as compared 

 with the number of ions of the dehydrating agent. Moreover, as would be 

 expected, the greater the viscosity of the dehydrating agent the lower the 

 concentration corresponding to the maximum of the curve. Compare in this 

 connection the calcium chloride solutions with those of aluminium chloride. 



