WORK OF E. G. MAHIN. 



129 



The conductivity of cadmium iodide in water has been studied by Lenz, 1 Grotrian, 2 

 Wershoven, 3 Zelinski and Krapiwin, 4 Fox, 5 and Jones and Lindsay. 6 Hittorf 7 

 determined the apparent transport numbers of the anion in solutions of different con- 

 centrations, and concluded that in the more concentrated solutions double mole- 



++ 

 cules exist, which dissociate to Cd and Cdl 4 . Lenz also believed that the more 



concentrated solutions contain complex anions. McBain, 8 on the other hand, 



followed a different line of argument and decided that double molecules exist, but 



++ 

 that they dissociate to form the ions Cd and 2CdI 3 . The conclusion was reached 



++ 

 that at greater dilutions these ions are also broken down into the simpler ions Cd 



and 31, resulting in a large increase in the molecular conductivity. 



Bein 9 also studied the transport numbers of the anion of cadmium iodide at 

 different temperatures, and showed that there is no perceptible change between 

 20 and 75. 



From the work of Kiimmel 10 it is evident that the apparent transport numbers of 



the halogens reach their minimum values in solutions of the cadmium halides which 



vary in concentration from 0.01 normal to 0.002 norma!. Since the abnormally large 



apparent transport number for the halogen is supposed to be due to the fact that 



cadmium migrates towards both electrodes, this accords with the idea held by 



Hittorf, Lenz, and McBain, that the complex anions break down with increasing 



dilution. 



Table 99. Ionization Constant for Cadmium Iodide in Water. 



Herz and Lewy 11 carried out partition experiments with cadmium iodide in water 

 and amyl alcohol, from the results of which they were led to conclude that complex 

 ions are present in the aqueous solution. 



It is not believed that the highest values for molecular conductivity which have 

 been obtained in the present work are, in any of the solutions except those in water, 

 the ones corresponding to complete dissociation. McBain attributed to Zelinskyand 

 Krapiwin the most accurate work on the conductivity of aqueous solutions of cad- 

 mium iodide, and he regarded 278, a value calculated from their results obtained at 

 18, as the correct value for the maximum molecular conductivity at 25. This 

 corresponds with the results of our measurements, which gave 279 at 25. It is' 

 evident, from an inspection of the values of K calculated from Ostwald's dilution 

 law, that this is very close to the maximum molecular conductivity. The regular 

 decrease in the value of K until the dilution reaches about 0.001 normal may be 



'Mem. de St. Petersb. [7] 30, 64 (1882). 

 2 Wied. Ann.. 18, 190 (1883). 

 sZeit. phvs. Chem.. 5, 481 (1S90). 

 'Ibid, 21/35 (1896). 



Hbid, 41, 458 (1902). 

 "Amer. Chem. Journ.,28, 329 (1902). 

 'Pogg. Ann., 106, 513 (1859). 

 8 Zeit. Elektrochem., 11, 215 (1905). 



"Wiod. Ann., 46, 29 (1892). 

 Ibid., 64, 655 (1898). 

 ''Jahrescher. Schles. Ges. f. vaterland. 

 Kuiter, 1600, Naturw. Sekt., 1-9. 



