164 CONDUCTIVITY AND VISCOSITY IN MIXED SOLVENTS. 



pure acetone, or the 75 per cent mixtures of acetone with the alcohols. It is 

 nearly reached only with the pure alcohols. Thus we could not have com- 

 plete dissociation in these mixtures. The conductivity maximum should 

 also manifest itself in the case of cobalt chloride in mixtures of acetone with 

 methyl alcohol, but this is contrary to what we have observed. We there- 

 fore accept the view, held tentatively by Jones and Bingham, that the max- 

 imum in conductivity is due primarily to a change in the dimensions of the 

 ionic spheres. 



Attention should be called to the fact that cobalt chloride, in mixtures of 

 acetone with water, shows a tendency towards a maximum in conductivity in 

 the 75 per cent mixture, notwithstanding the great decrease in fluidity. 



Thus we see that the tendency towards a maximum in conductivity, in 

 mixtures of acetone with other solvents, is very marked. 



Let us now sum up the cases where maxima in conductivity have been 

 obtained in the acetone mixtures. Jones and Bingham obtained the maxi- 

 mum with lithium nitrate and calcium nitrate in mixtures of acetone with 

 methyl or ethyl alcohols. Under similar conditions, we have obtained the 

 maximum in the case of lithium bromide in these mixtures. Cobalt chloride 

 gave the maximum only in a mixture of acetone with ethyl alcohol. 



Jones and Bingham showed that lithium nitrate and calcium nitrate, in 

 mixtures of acetone with water, show a tendency towards a maximum. 

 We have observed the same fact with cobalt chloride in a mixture of acetone 

 with water. 



TEMPERATURE COEFFICIENTS. 



That conductivity is affected by temperature was observed as early as 1844 

 by Ohm. 1 In 1875 it was established by Kohlrausch 3 that the conductivity 

 of aqueous solutions of electrolytes, in general, increases with the temperature, 

 and that, for ordinary temperatures, this relation may be represented by the 

 equation, 



where A represents the molecular conductivity, t the temperature in question, 

 and a is a constant. 



Arrhenius, 3 in 1889, showed, from theoretical considerations, that the 

 relation between conductivity and temperature is not a linear one. He 

 established the fact that conductivity at first increases with rise in tem- 

 perature, reaches a maximum value, and then decreases. He verified this 

 for solutions of hypophosphorous acid and phosphoric acid, the former 

 having a maximum conductivity at about 55 and the latter at 75. 



l Pogg. Ann., 63, 403 (1844). Ztschr. phys. Chem., 4, 96 (1889). 



2 Ibid., 164, 224 (1875). 



