CONDUCTIVITY OF SODIUM HYDROXIDE IN AQUEOUS SOLUTION. 255 



combination with the solvent is an essential part of the process of ionisation, and are 

 of opinion that in the case of dilute aqueous solutions ionisation is simply a final stage 

 in the process of hydrate formation, whereby the hydrated molecule is resolved into 

 two or more hydrated ions. As evidence in support of this view is to be found not 

 only in the observations now recorded, but also in a wide range of current literature, 

 we have reserved the fuller discussion of this theory for a separate communication. 

 The chief features of the paper may be described under four headings : 

 (1.) Tlie Influence of Temperature on Conductivity. In our former paper (' Roy. 

 Soc. Proc./ 1902, vol. 71, pp. 42-54) we were able to give a general curve expressing 

 the relation tetween conductivity and temperature over the whole range of tempera- 

 ture within which electrolysis is possible. This general curve was arrived at from a 

 consideration of the experimental data with reference to composite electrolytes of all 

 classes, ranging from glass to solutions in liquid ammonia and sulphur dioxide. These 

 scattered olwervations we were enabled to piece together by a theoretical considera- 

 tion of the influences which determine the change of conductivity with temperature. 

 In the present paper we have been able to give quantitative expression to these 

 different factors, and have obtained results which afford a complete confirmation of 

 our earlier conclusions. 



In the formula = ^10~ <rf (l+fcO'', which we have used to represent the relation 



*o Po 

 between specific conductivity and temperature, allowance lias been made for each of 



the three factors which influence the conductivity. Changes of concentration are 

 allowed for by introducing as a factor the ratio pi/p , which expresses the change of 

 density between and t. Changes of ionic mobility have been allowed for by 

 introducing a factor (l-\-bt)" similar to that used by SLOTTE to represent the 

 variations of fluidity with temperature. Changes in the coefficient of ionisation 

 have been allowed for by introducing a factor 10~"' similar to that used by ABEGO to 

 express the decay of specific inducthv capacity as the temperature risea 



Although these factors may not represent perfectly the variations of ionic mobility 

 and of ionisation with temperature, the formula has been found to give a satisfactory 

 representation of the experimental facts over a wide range of temperature. It 

 accurately expresses the varied types of conductivity-temperature curves recorded in 

 the present paper, and indicates not only the point of inflexion which is observed in 

 moderately dilute solutions of sodium hydroxide between 50 C. and 100 C., but also 

 the maximum conductivity and the second point of inflexion shown in our general 

 conductivity-temperature curve. 



Even more important is the fact that by means of this formula it is possible, for 

 the first time as we believe, to analyse the conductivity-temperature curves for 

 concentrated as well as for dilute solutions, and to estimate separately the effects 

 produced by the increase of mobility and by the decay of ionisation which accompany 

 a rise of temperature. 



