210 



HYDRATES IN AQUEOUS SOLUTION. 



freezing-point lowcrings of these solutions. With the exception of the 

 second or third member, the numbers in the last column of table 106 become 

 gradually larger as the concentration of the solution increases. 



The electrical conductivities, together with the corresponding concentra- 

 tions of the solutions containing cobalt chloride and aluminium chloride, 

 are given in table 107. The numbers in the second and fourth columns are 

 expressed in reciprocal ohms and reciprocal centimeters. 



TABLE 107. 



The data in the above table are plotted in fig. 74. The abscissa denote 

 concentration, and the ordinates signify conductivity. The mean curve has 

 a decided maximum like the curves for the solutions containing calcium 

 chloride and calcium bromide. There is this difference, however, between 

 the curve of fig. 74 and the other two curves, namely, that whereas the 

 maximum of the curve associated with aluminium chloride corresponds to 

 a concentration of about 1.1, the maxima for the other two dehydrating 

 agents in question occur at the concentrations 2.5 and 2.3. 



When a sufficient quantity of water is added to a solution of cobalt chloride, 

 which had previously been made blue by the admixture of a solution of some 

 one of the three dehydrating agents under investigation, the solution turns 

 back to the characteristic cobalt red. It was thought that by adding water 

 to a chosen solution of the given series, until the color of this solution became 

 practically the same as that of the solution containing a somewhat smaller 

 amount of the dehydrating agent, it might be possible to obtain some facts 

 which would bear a quantitative relation to the hydrates formed in the solu- 

 tions. If it were possible to take infinitesimal steps such data might be 

 obtained. But obviously such a process can not be realized experimentally. 

 In practice either one of two difficulties presents itself: (a) The successive 

 solutions differ so little in concentration that the volume of water which 

 had to be added to the more concentrated solution to bring its color to that 

 of the less concentrated one, is too small to be accurately measured unless 



