808 MK. W. R. BOUSFIELD AND DR. T. M. LOWTJY ON THE ELKCTHICAL 



representation of the different types of conductivity-temperature curve, but also 

 because a definite physical meaning can be assigned to each of the coefficients. 

 Moreover, the formula has a special value because it renders it possible more or 

 less accurately to resolve the two opposing influences to which the conductivity- 

 temperature curves owe their peculiar form. Although it is not possible to test, by 

 direct experiment, the accuracy or otherwise of the constants which we have deduced 

 for the temperature variations of the coefficient of ionisation and the ionic mobilities, 

 the constants are of the right order of magnitude for the physical properties which 

 they are intended to represent. 



Thus the constant n, which we may term the index of mobility, varies from 1*5 

 for water to 4'5 for a 50-per cent, solution of sodium hydroxide. Although these 

 values were deduced entirely from electrical measurements, it was expected that they 

 would be comparable with the indices in SLOTTK'S viscosity formula, and the values 

 of n, given in Table XIX., cover almost the whole range of variation of this constant 

 in the viscosity measurements of THORPE and RODGER. A high constant represents 

 a rapid decrease of viscosity, and may usually be attributed to rapid depolymerisation 

 of the liquid. It is noteworthy that values of n, comparable with those given in 

 our table for concentrated solutions of sodium hydroxide, were observed only in the 

 case of the alcohols : ethyl alcohol, n = 4'37 ; isopropyl alcohol, n = 4'9 to 3'4 ; amyl 

 alcohol, n = 4 '3 ; all of which are known to exist largely in the form of complex 

 molecules. 



The constant b is related by the expression b = 1/T to the " conductivity zero " T 

 of the solution (BOUSFIELD and LOWRY, loc. cit., p. 44), and although this zero does 

 not represent an actual physical fact, it gives a valuable mental picture of the way in 

 which the increase of viscosity at low temperatures tends to destroy the conductivity 

 of the solution. The values of T are given in the eighth column of Table XIX., and 

 correspond closely with the conductivity zeros deduced from a simple parabolic 

 formula for the influence of temperature on conductivity. 



The constant a, tabulated in the third column of Table XIX., measures the rate of 

 decay of ionisation with rising temperature, and is greatest in the most concentrated 

 solutions. 



Points of Inflexion. The alx>ve expression for the influence of temperature on 

 conductivity enables us to calculate the positions of both the points of inflexion and 

 the maximum of conductivity of our general curve. The results are given in 

 Table XIX., which shows under l and 0% the temperatures corresponding to the 

 lower and upper points of inflexion in the curve of molecular conductivity, whilst the 

 temperature of maximum conductivity is given by (#i+# 2 ). ^ ne va l ues f ^i> 

 occurring as they do within or close to the experimental range of temperatures, 

 represent actual physical facts, but the values of 2 and ^(Oi+d 2 ) can only be 

 regarded as an approximation to the probable behaviour of the solutions at higher 

 temperatures. 



