CONDUCTIVITY OF SODIUM HYDROXIDE IN AQUEOUS SOLUTION. 301 



EXPERIMENTAL RESULTS. 



The general nature of the experimental results may he indicated by giving 

 conductivity-temperature curves for two different concentrations. In Diagram X. 

 are given (1) a curve showing the influence of temperature on the molecular 

 conductivity of a normal (4 -per cent.) solution; this curve shows a well-marked 

 point of inflexion at 48 C.,* and is typical of the curves for moderate dilution. (2) A 

 similar curve for a 40-per cent, solution, which is not inflected between C. and 

 100 C., and may be regarded as typical of the behaviour of concentrated solutions. 

 The data on which these curves are based are shown in Table XIX., p. 305. 



The variation of the temperature of inflexion with the concentration of the solution 

 is shown in Table XV. and Diagram XL, and presents some interesting features. 

 The minimum value for the temperature of inflexion is at 48 C. in a normal solution, 

 but a rapid rise occurs as the concentration is increased, and at 25 per cent. NaOH 

 (8*5 N) the inflexion has risen to 100 C. ; above this concentration the inflexion is no 

 longer observed between C. and 100 C., but the formulae described below indicate 

 that even at the highest concentrations the temperature of inflexion is only a few 

 degrees above 100 C. The most dilute solutions also appear to give curves which are 

 not inflected, but we are unable at present to supply definite data with reference to 

 the variations in the temperature of inflexion at concentrations below normal. 



In explanation of the great variations in the character of the conductivity- 

 temperature curves, it should be recalled that the point of inflexion is in the neigh- 

 bourhood where the increase of conductivity due to increasing fluidity begins to be 

 overbalanced by the diminution of conductivity due to decay of ionisation with rising 

 temperature. Now in the most dilute solutions " ionisation " is nearly complete, and, 

 as the coefficient of ionisation is thus not greatly influenced by temperature, the form 

 of the curve is determined mainly by changes in the viscosity of the solution. So also 

 in the most concentrated solutions the alterations of viscosity are so great that any 

 changes in the coefficient of iouisation are only of secondary importance. It is, there- 

 fore, only at intermediate dilutions that the point of inflexion can be observed at 

 temperatures between C. and 100 C. 



Another way of showing the great difference in the influence of temperature on the 

 conductivity of concentrated and dilute solutions is by calculating the ratios KQ, K w and 

 K 100 of the conductivities at C., 50 C. and 1 00 C. to those at 18 C ; in Table XV 

 the ratio given is that of the molecular conductivities, since a correction has been 

 introduced for the alteration of volume-concentration produced by the contraction or 

 expansion of the solution. The figures given in the table are plotted in Diagram XIV., 

 and indicate very clearly the more important characteristics of the different solutions. 



Having determined the temperature coefficients for a considerable range of dilutions, 



* In the curve showing the influence of temperature on the specific conductivity (compare Table XVII., 

 p. 303) the inflexion is at 44 C. 



