CONDUCTIVITY OF SODIUM HYDROXIDE IN AQUEOUS SOLUTION. 291 



accurate, it follows that the true value of a for a given concentration and temperature 

 is not a = A/A., as is usually assumed, hut 



A 



*- 



~ 



___ 



A. tt-f-v 

 That is to say, we must correct A for the change of mohility in order to arrive at the 



true value of a. The theoretical corrective factor for A is - " , and we propose to 



t*+v 



call the product of A by this corrective factor the " intrinsic conductivity." It is 

 the value of A reduced to the conditions of mobility which obtain at infinite dilution. 

 For practical purposes, and as a first approximation, we assume that 



tt+t>, _ fluidity at infinite dilution 

 t*+v fluidity at given concentration 



Hence, taking the fluidity of the solvent (water) as unity and measuring the actual 

 ttuidity.y, at the given concentration in these units we have 



u+v / 



Denoting the intrinsic conductivity by I, we have, therefore, I = A//*, I = A., and 

 hence a = I/I.. Whilst A// does not represent the intrinsic conductivity as defined 

 above with complete accuracy, it enables us to make a convenient practical approxi- 

 mation to the true value of a, which is much nearer than the current approximation 

 = A/A. 



The whole correction for changes of mobility is not large except in solutions of 

 considerable concentration, so that any error in the correction applied will produce a 

 much smaller error proportionately in the values deduced for the intrinsic conductivity 

 and for the coefficient of ionisation. We believe, therefore, that by using the ratio 

 a = I/la. = A/A, . l/f, in place of the ratio a = A/A, it will be possible to extend 

 the method of determining a from conductivity measurements to solutions of 

 considerably greater concentration than those for which the validity of the equation 

 a = A/A x can be recognised ; and even in concentrated solutions the intrinsic 

 conductivity deduced from the formula I = A/f will enable a closer approximation 

 to be made to the actual amount of iouisation than has been possible when this could 

 only be deduced from the molecular conductivity of the solution. 



Hitherto the majority of the conductivity measurements that have been made have 

 been concerned with dilute solutions, in which the correction for viscosity is relatively 

 small, but there is little doubt that when the necessary data of conductivity and 

 viscosity are available for concentrated solutions, the study of the intrinsic conductivity 

 of these solutions will lead to results at least as important as those derived from the 

 study of dilute solutions. Unfortunately, the measurements that have been made of 

 the viscosity of aqueous solutions, like those of the conductivity, have in almost every 



2 P 2 



