420 PROCEEDINGS OP THE AMERICAN ACADEMY. 



conductivity in bromine solutions has appeared. The extraordinarily 

 interesting and puzzling phenomena that he has studied appear to have 

 little in common with those we are about to discuss, notwithstanding the 

 close relationship between bromine and iodine. 



Iodine bears no resemblance to any of the other dissociating solvents, 

 except bromine, which have been studied. One property, however, it 

 possesses in common with them all, the tendency to form complexes.* 

 Thus Walden and Centnerszwer have shown liquid sulphur dioxide to be 

 an excellent dissociating agent, f and have also pointed out the large 

 number of complexes into which this substance enters. J Ammonia, 

 which forms such a bewildering number of complex compounds, has been 

 shown by Franklin and Kraus § to be one of the very best dissociating 

 solvents. The case of water is too familiar to dwell upon. 



The complexes in which iodine occurs have, with the exception of the 

 polyiodides, been little studied, but doubtless a very large number could 

 be isolated. Almost all salts increase the solubility of iodine in water, 

 indicating the formation of complexes. The various solvents too, in 

 which iodine dissolves with a brown color, are known to enter into 

 combination with it. || 



The dielectric constant of iodine has not been determined, as far as we 

 know. 



In undertaking the investigation of iodine solutions we had the option 

 of making a cursory study of a large number of substances or a more 

 thorough study of some one substance. Choosing the latter course we 

 have determined with a fair degree of accuracy the conductivity of solu- 

 tions of potassium iodide in liquid iodine at temperatures from 120 

 degrees to 1G0 degrees, and in concentrations ranging from a few thou- 

 sandths normal up to 10 times normal, — a range in which the specific 

 conductivity increases 10,000 times. 



Experimental Method. 



The conductivity cells were of the form shown in Figure 1 . They 

 were made of two tubes 1^ cm. in diameter and 15 cm. long, joined 

 below by a smaller tube 8 or 10 cm. long and 3 mm. in diameter. The 

 ends of the cell were closed by tight-fitting glass stoppers. The elec- 



* See Abegg, Zeit. elek. Chem., 5, 353 (1899). 



t Zeit. phys. Chem., 39, 513 (1901). 



J Zeit. phys. Chem., 42, 432 (1903). 



§ Amer. Chem. Jour., 23, 277 (1900). 



|| Stromholm, Zeit. phys. Chem., 44, 721 (1903). 



