64 MOLECULAR WEIGHT AND POLYMERISM 



already mentioned is adopted whether based on the law 

 of absorption, on the freezing point, or on direct measure- 

 ment of osmotic pressure; and the confirmation that 

 Arrhenius' conception has received lies in the agreement 

 between the value of i so obtained and that independently 

 reached on the basis of that conception. 



In the first place then we must consider the relation 

 between i and the conductivity. 



Electrolytes have, it is known, a conductivity which, 

 referred always to the same say normal concentration, 

 increases with increasing dilution. Calling this the mole- 

 cular conductivity ^ the conductivity of mercury at o 

 being taken as unity, and the number multiplied by io 7 

 for convenience we have for KNO 3 at 1 8, according to 

 Kohlrausch : 



i.e. a number which increases asymptotically as the dilution 

 becomes greater. The explanation of this fact on Arrhenius' 

 theory is that with the dilution comes an increasing ionic 

 decomposition according to the equation 



KN0 3 = (K) + (N0 3 ), 



+ 



where (K) and (N0 3 ) represent the positively and negatively 

 charged ions respectively. This decomposition is practically 

 complete for the limiting value 



Theoretically it would only be reached on infinite dilution, 

 and is therefore represented by /z^. 



If the conductivity depends, as we have assumed, only on 

 the ions present, the quotient 



