68 CONDUCTIVITY AND VISCOSITY IN MIXED SOLVENTS. 



VISCOSITY AND CONDUCTIVITY. 



The viscosity of a liquid or solution is denned as being the force (in dynes) 

 necessary to move a layer of the liquid or solution one molecule in thickness, 

 and of unit area (1 sq. cm.) over another layer of the liquid, with unit velocity 

 (1 cm. per sec.). The symbol 77 is used for the coefficient of viscosity. The 



fluidity of a liquid is the reciprocal of its viscosity = - 



~n 

 It is plain that the hypothesis of Dutoit and Aston does not go very deeply 



into the phenomena; all that it asserts is that there is a parallelism between 

 the amount of dissociation effected by the solvent and the amount of its own 

 association. The Thomson-Nernst hypothesis, however, offers an explana- 

 tion of more profound significance. 



Dutoit and Friderich l make an attempt to find a connection between con- 

 ductivity, viscosity, and association, and thus take a step in the direction of 

 a more general hypothesis. From a study of the conductivities of solutions 

 of different electrolytes in different solvents they came to the following 

 conclusion : 



The values of M for a given electrolyte dissolved in different solvents are a direct 

 function of the degree of polymerization of the solvents, and an indirect function of 

 the coefficient of viscosity of these solvents. 



The relation was found to hold only in a general way indeed, hardly more 

 than qualitatively. 



When we come to consider the proposed relation, it is difficult to see why 

 it should exist ; it is wholly empirical, and it is not in accord with the hypothe- 

 sis of Dutoit and Aston ; for when complete dissociation is reached the asso- 

 ciation of the solvent is no longer an influencing factor. It is superfluous 

 to discuss the matter further because, as stated, the relation does not hold 

 quantitatively. 



This will suffice to indicate what has thus far been done to show a connec- 

 tion between conductivity and viscosity. The relations hitherto brought 

 to light are qualitative. Of far more importance is the establishment of a 

 quantitative relationship. We shall show that such does exist, and propose 

 the following hypothesis : 



The conductivities of comparable, equivalent solutions of binary electrolytes 

 in certain solvents (methyl and ethyl alcohols, other alcohols of the same series, 

 acetone, etc.} are inversely proportional to the coefficient of viscosity of the solvent 

 in question, and directly proportional to the association factor of the solvent. In 

 case the hypothesis of Dutoit and Aston does not hold for the solvent in 

 question, for " association factor of the solvent" must be substituted " amount 

 of dissociation of the solution." 



1 Bull. Soc. China., [3] 19, 321 (1898). 



