Tri- Bromide Equilibria. 



115 



in the ratio Znlj.KI, the constant K^ calculated from the total 

 iodide concentration, that is, upon the assumption that the 

 power of each iodide to combine with iodine is unaltered by 

 the presence of the other, has the normal value. It is worth 

 noting that this is a case where some slight tendency toward 

 complex salt formation might possibly have been anticipated, 

 but is in no way indicated by the results. 



Cadmium iodide, on the other hand, furnishes an example of 

 abnormal behavior. (See Table YIIl.) This salt gives, as 

 compared with normal cases, a much larger value of K^ which, 

 moreover, increases rapidly with the iodide concentration, but 

 tends at high dilution to approach the normal value. This is 

 evident in the following tabular comparison of the values of 

 K^ for potassium and cadmium. The iodide concentrations 

 are expressed in gram-equivalents per liter. 



Iodide 

 concentrations 



h\ for KI 



K, for Cdl„ 



0-02 



0-25 



0-5 



1-0 



= 0-0014 



0-0014 



0-0013 



0-0013 



= 0-0023 



0-0082 



0-0137 



0-0234 



For constant iodide and varying iodine concentration, however, 

 the constancy of K^ may be fairly good, even in an abnormal 

 case. 



Table IX. 



Cadmium Potassium Iodide. 



CdT2.2KI. 



a - 0-23 molar Cdl2.2KI. 



(21) + (Sis) = 4a = 0-92 molar. 



h 



35-78 



I 



•53 

 •11 

 •16 



•308 

 -839 



226-3 

 103-4 

 46^4 

 34-79 

 13-15 

 5-21 



c 

 590 

 583 



580 

 580 



578 

 578 



0-0096 

 0-0092 

 0^0091 

 0-0090 

 0-0091 

 0-0100 



mean u-00933 



Table X. 

 Mercuric Potassium Iodide. 



Hgl2.2KI. 

 a =0-125 molar Hgl2.2KI. 



(2I) + (2l3)=4a - " 

 h g c 



14-34 45-1 85-7 



5-83 

 3-512 



2-284 



45-1 



25-81 



16-58 



10-05 



6-03 



0*5 molar. 



0-0185 

 0-0178 

 0-0171 

 0^0173 

 0^0160 



85^5 



85 



85 



85 



mean 0^0173^ 



In the case of the double iodides Cdl2.2KI, and Hgl^.SKI 

 (Tables IX and X) abnormality of the same general nature is 

 apparent. Pure mercuric iodide could not be studied by this 

 method on account of its insolubility in water. 



The experiments conducted with bromine in equilibrium 

 with bromides were confined to cases in which abnormal 

 behavior was to be expected from analogy with the correspond- 

 ing iodides. The results are given in Tables XI to XIY. For 

 bromides the normal value of K^ at 25°, as shown by Jakow- 



