LEWIS AND WHEELER. — CONDUCTIVITY OF SOLUTIONS. 431 



However, fully as convincing evidence is offered by the fact demon- 

 strated by Arrhenius * that the dissociation of an electrolyte in water is 

 always diminished by the addition of a non-electrolyte (in other words 

 a very poor electrophile) such as sugar or glycerine. 



When now we consider, instead of water, other solvents which are 

 much poorer electrophiles, we should expect results of the same general 

 character, except that the change in dissociating power should be much 

 more pronounced when a strong electrophile is added. So we may ex- 

 plain in these cases deviations from the mass law so great that the degree 

 of dissociation increases with the concentration, as in the case of potassium 

 iodide in iodine. 



The Conductivity of Pure Iodine. 



Does absolutely pure iodine conduct the current ? If so, is this con- 

 ductivity metallic or electrolytic? If the latter, what are the ions? 

 These are not the least interesting questions raised by our work. 



The preparation and study of pure iodine present some difficulties. It 

 seems that iodine acts to some degree upon glass and platinum, and that 

 it therefore absorbs some impurity when it is sublimed and collected upon 

 glass and also when it stands in the cell. For this reason we resublimed 

 some of our best iodine in a simple apparatus made entirely of quartz, 

 and from this transferred it directly to a conductivity cell made of a 

 quartz tube 6-8 mm. in diameter and about 15 cm. long, bent in the 

 form of a U. This was placed in the thermostat, and electrodes of 

 platinum-iridium were introduced just before measuring the conductivity. 



The specific conductivity of the iodine obtained in this way was not 

 less than that of the iodine previously used, in fact never less than 

 3 X 10 -5 . Similar results were obtained with iodine twice sublimed in 

 quartz. 



We do not feel entirely safe, however, in drawing conclusions from 

 these results until we explain a very perplexing decrease in conductivity 

 which was observed when the iodine stood for any length of time in the 

 thermostat. It is hard to account for this unusual behavior. It may 

 be due to some gradual molecular change in the iodine, or to the escape 

 of water or other impurity taken from the air during sublimation, or even 

 to an absorption of impurities while standing, although no case is known 

 where the conductivity of a pure electrolytic conductor is lowered by im- 

 purities. One experiment was made with iodine sublimed in quartz in a 



* Zeit. phys. Chem., 9, 489 (1892). 



