224 CONDUCTIVITY AND VISCOSITY IN MIXED SOLVENTS. 



different mixtures of the solvents are the prime factor in conditioning the 

 maximum in the conductivity curve. 



Some interesting results were obtained in this investigation bearing on the 

 temperature coefficients of conductivity. 



Jones l has recently pointed out the bearing of hydrates on the temperature 

 coefficients of conductivity. Jones and West showed that with rise in temper- 

 ature there is a decrease in the dissociation, and that increase in conductivity 

 with rise in temperature was due primarily to an increase in the velocities 

 with which the ions move. As the temperature is raised the hydrates in 

 combination with the ion become simpler and simpler, and, therefore, the 

 effective mass of the ion decreases with rise in temperature. The ion being 

 smaller and the solvent less viscous, it will move faster the higher the tempera- 

 ture. 



Jones has also pointed out in terms of his hydrate theory that the greater 

 the dilution the greater should be the temperature coefficient of conductivity. 

 The more dilute the solution, the more complex the hydrate; the more complex 

 the hydrate in combination with any given ion, the greater the change in the 

 complexity of the hydrate with rise in temperature. The temperature 

 coefficient of conductivity should, therefore, be greater in the more dilute 

 solution, and such is the fact. The work of McMaster showed that the tem- 

 perature coefficients of conductivity and of fluidity for lithium bromide are 

 of the same order of magnitude, the temperature coefficients for this substance 

 in the mixed solvents all being positive. 



In certain of the mixtures of acetone with the alcohols, cobalt chloride 

 showed negative temperature coefficients of conductivity. This was true in the 

 75 per cent mixture of acetone with methyl alcohol, and also in the 50 per 

 cent and 75 per cent mixtures of acetone with ethyl alcohol. Negative tem- 

 perature coefficients had previously been found in a few cases at low tem- 

 peratures, but in this work negative temperature coefficients were found at 

 ordinary temperatures. 



What is the meaning of negative temperature coefficients of conductivity ? 

 With rise in temperature the solvent becomes less viscous, and this would 

 increase the velocity of the ions. With rise in temperature, however, the 

 association of the solvent becomes less and, consequently, its dissociating 

 power is diminished ; which means that there would be a smaller number of 

 ions present the higher the temperature. These two influences act counter to 

 one another the former increasing the conductivity and the latter diminish- 

 ing it. 



When we have negative temperature coefficients of conductivity, it means 

 that the latter influence more than overcomes the former the decrease in 

 the number of the ions with rise in temperature more than counterbalancing 



1 Carnegie Institution of Washington, Publication No. 60. 



