52 



Conductivity of Aqueous Solutions. Part II. 



18. CHANGE OF THE EQUIVALENT CONDUCTANCE WITH THE 



TEMPERATURE. 



We shall in this section confine our considerations almost wholly to 

 the effect of temperature on the conductance (A ) extrapolated for zero 

 concentration ; for at higher concentrations the equivalent conductance 

 of the salt is the product of two factors the degree of ionization of the 

 salt and the equivalent conductance of its ions ; and the first of these 

 factors is best discussed separately, as will be done in section 19. 



Attention may first be called to the fact that the limiting conductances 

 of the two salts approach equality as the temperature increases ; thus the 

 ratio of A 0( N a ci) to A 0( kcd has the following values at the various temper- 

 atures : 



The percentage difference in the migration-velocities of the potassium 

 ion and sodium ion, therefore, becomes less, the higher the temperature. 



In order to show more clearly the character of the relation between 

 migration-velocity and temperature we have calculated the mean temper- 

 ature-coefficients (AA /A) for the successive temperature-intervals, and 

 these were found to be as follows : 



It will be seen that up to about 156 the temperature-coefficient of the 

 conductance values extrapolated for zero concentration increases steadily, 

 and then, between 156 and 281, decreases markedly in the case of potas- 

 sium chloride and remains nearly constant in the case of sodium chloride, 

 while above 281 a pronounced increase again takes place with both salts. 



It is also of interest to compare the fractional change in equivalent 

 conductance with that in the viscosity of the water ; for the former is doubt- 

 less more closely related to the latter than to any other simple physical 

 property. The viscosity (77) of water has been measured by several 

 experimenters at temperatures below 100 and by de Haas at 124, 142, 

 and 153.* In the table on the next page are given in the same columns the 

 ratio (A ) t2 : (A ) tl for potassium chloride and */ tl : rj t2 for water for a 

 number of consecutive pairs of temperature. The values of the viscosity rj 



*See Landolt-Bornstein-Meyerhoffer, Physigalisch-chemische Tabellen, p. 76. de 

 Haas' values are 0.00223 at 124, 0.00193 at 142, and 0.00181 at 153. 



