THE BEARING OF HYDRATES ON THE TEMPERATURE COEFFICIENTS OF 

 CONDUCTIVITY OF AQUEOUS SOLUTIONS. 



That the electrical conductivity of aqueous solutions of electrolytes, in 

 general, increases greatly with rise in temperature is a well-known fact. 

 This might be due either to an increase in the dissociation of the electro- 

 lyte with rise in temperature, or to an increase in the velocity with which 

 the ions move, or to both. It is not a difficult matter to test the effect 

 of change in temperature on the dissociation of electrolytes. It is only 

 necessary to measure the dissociation directly at different temperatures by 

 the conductivity method. This has been done recently by Jones and West,* 

 for temperatures ranging from zero to thirty-five degrees. The result is, 

 that electrolytes in general are slightly less dissociated at the higher than 

 at the lower temperatures. Noyes and Coolidgef have shown that dissocia- 

 tion decreases rapidly at more elevated temperatures. 



As has been pointed out, this is in accord with the theory of Dutoit and 

 Aston, which makes the dissociating power of a solvent a function of its 

 own association the more associated a solvent the greater its dissociating 

 power. Take a solvent like water; the higher the temperature the less it 

 is associated, and, consequently, the smaller its power to break molecules of 

 electrolytes down into ions. 



Having eliminated the factor of dissociation as increasing the conductivity 

 of electrolytes at the higher temperature, we are forced to conclude that 

 the increase in conductivity with rise in temperature, shown by solutions of 

 electrolytes in general, is due to an increase in the velocities with which the 

 ions move. 



There are a number of factors that determine the velocity with which 

 an ion moves through a solution of an electrolyte. Assuming that the force 

 which drives the ions is constant, the velocity would be conditioned chiefly by 

 the viscosity of the medium through which the ion passed, and the size and 

 mass of the ion ; at the more elevated temperature the force which drives the 

 ion would be greater, and the viscosity of the medium through which the ion 

 moves would be less. Both of these factors would increase the velocity with 

 which the ions move, and, consequently, increase the conductivity as the 

 temperature was raised. 



The object of this section is to call attention to another factor that causes 

 the ions to move faster at the more elevated temperature. The mass of 



*Amer. Chem. Journ., 34, 357 (1905). 

 fZtschr. phys. Chem., 46, 323 (1903). 



153 



