ON THE HALOGEN HYDRIDES AS CONDUCTING SOLVENTS. 151 



The consideration of these abnormalities has led KAHLENBERG to conclude that the 

 theory of ionic dissociation is not applicable to the majority of conducting solutions. 



It is our object to show that the abnormal behaviour of solutions in the solvents 

 examined by us can be simply and consistently explained in terms of the theory of 

 ARRHENIUS, if the assumption is made that the original dissolved substance, being 

 itself incapable of undergoing ionic dissociation, either polymerises or combines with 

 the solvent to form a compound containing more than one molecule of the solute, and 

 that the polymer, or compound, as the case may be, then acts as the electrolyte. 



Those non-saline organic substances which are able to conduct the current when 

 dissolved in certain solvents are considered by WALDEN (' Zeit. Phys. Chem.,' 1903, 

 43, p. 385) to be abnormal, in view of their usually well-known constitutions and their 

 behaviour in aqueous solutions, but if the foregoing assumption of the formation of 

 compounds be made, these substances are not more abnormal electrolytes than 

 ammonia, which with water forms the compound ammonium hydroxide. 



It has been suggested that the existence of compounds of the solute with the 

 solvent is proved by the abnormal variation of the molecular conductivity, to which 

 reference has been made ; but the following considerations will show that an increase 

 of fi with dilution furnishes no evidence for or against the occurrence of such 

 compounds. 



Let us suppose that a reaction between the solute, AB, and the solvent, CD, takes 

 place according to the equation 



AB + CD^AB, CD, 

 and let 



a b c 



be the active masses of the three substances. 



Now, provided that moderate dilutions are used, we are justified in regarding b as 



constant, when from the law of mass action - = constant. 



a 



Now if conduction is due to the dissociation of the compound ABCD, the number 

 of dissociated molecules is given by etc, where a is the degree of ionic dissociation ; 

 but c = Ka ; therefore the concentration of the ions is equal to poiKa if p is the 

 number of ions formed from one molecule of solute. 



But the specific conductivity K of the solution is proportional to the ionic 



concentration, and therefore 



K = paJcKa = a.K'a (l), 



and since the molecular conductivity 



K 



= - = aK', 

 a 



it must vary with a, that is to say, it must increase with dilution even when a 

 compound of the solute with the solvent is formed. 



