Polymerization in Cadmium Iodide Solutions. 461 



an excess of Od++ ions resultinsj from the ionization of the 

 associated molecules, and it would also be expected that the 

 difference, if due to this cause, would decrease with increasing 

 dilution, as is in fact the case. It is probable, however, that 

 the actual difference between the degrees of ionization of these 

 two salts is considerably smaller than these results would indi- 

 cate, for the error in determining 7 by the above method may 

 easily be rather large. 



The work of Walton,* whose kinetic method for determin- 

 ing iodine ion concentrations has already been referred to, is of 

 interest here, since his results yield values of (!') which can 

 be compared with those in Table I. Unfortunately, Walton's 

 experiments with cadmium iodide were confined to solutions 

 more dilute than 05 molar. The comparison is shown in 

 Table III, the second horizontal line giving the values of (I^) 

 calculated from Walton's resultsf while the third contains our 

 values for the same quantity. Figures enclosed in parentheses 

 were obtained by graphical interpolation. 



Table III. 



(Cdla) 49 10 19-4 31-8 42-1 



(I') Walton 6-5 (12) 19*3 26*5 81-2 



(T) V. N. & B. 10-5 (14) (20) 



The two sets of results agree in order of magnitude, though 

 Walton's values are higher and increase more rapidly with tlie 

 concentration. Since Walton's method has not yet been very 

 thoroughly studied, particularly as to its sensitiveness toward 

 secondary catalytic influences, the results of the electromotive 

 force measurements deserve the greater weight. 



Freezing Point Measurements. 



Since the purpose of these measurements was to determine 

 the efi:ect of successive additions of iodine upon the freezing 

 point of a given cadmium iodide solution, it was necessary to 

 employ a method of the " undercooling " type, the very con- 

 venient and accurate method of Eoloff,:}: as improved by 

 Richards,§ being excluded by the fact that it would not per- 

 mit the concentration of the cadmium iodide to be kept con- 

 stant. After unsuccessful attempts to obtain suflicient accuracy 

 with the aid of a modified Beckmann apparatus, using a cry- 

 ohydric mixture for the cooling bath, and other special precau- 



*Zeitsclir. phys. Chem., xlvii, 185, 1904. 



f These values were obtained by dividing the observed velocity constants 

 in each case by 1'45, the average value of the ratio, Velocity constant / (I'), as 

 found by Walton's experiments with KI, Nal, and NH4I. 



:j:Zeitschr. phys. Chem., xviii, 572, 1895. 



y Jour. Am. Chem. Soc, xxv, 291, 1903. 



