58 CONDUCTIVITY AND VISCOSITY IN MIXED SOLVENTS. 



value of the constant as 23.6 and the comparable volume for the mixture as 



48. from the relation - = 23.6 we can find x. We have = 23.6, whence 



x x 



a; = 3.96. 



A mixture of methyl alcohol and water, containing 50 per cent methyl 

 alcohol by volume, has very approximately the composition corresponding 

 to the hydrate CH 3 OH . 3 H 2 O. The existence of alcoholic hydrates has been 

 made probable on other grounds. 



It is possible that such hydrates, in virtue of their complexity, have high dis- 

 sociating power. The greater dissociation found in the 50 per cent mixture may 

 be due to this hydrate, in which four simple molecules combine to form a complex 

 molecule. 



CAUSE OF THE MINIMUM. 



The first observers of the conductivity minimum, Zelinsky and Krapiwin, 

 offered no satisfactory explanation of it. They suggested that it might be 

 connected with the formation of hydrates of methyl alcohol. Further than 

 this they did not go. Jones and Lindsay would explain the existence of the 

 minimum as due to the effect of one associated solvent on the association of 

 another associated solvent (see p. 41). 



The explanation offered by Jones and Lindsay was later strengthened by 

 an investigation by Jones and Murray. They showed, from a study of the 

 freezing-points of solutions of acetic and formic acids, and water acetic 

 acid in formic acid, formic acid in acetic acid, acetic acid in water, etc. 

 that the association of one solvent is apparently diminished by the presence 

 of another associated solvent. 



According to the explanation offered by Jones and Lindsay, the chief cause 

 producing the minimum is a diminution of the dissociation of the dissolved 

 substance, due to a diminution of the association of the solvents, and, conse- 

 quently, a decrease in conductivity. We have shown that, in the 50 per cent 

 mixture of methyl alcohol and water, the dissociation, instead of being di- 

 minished by the presence of the alcohol (or by bringing together water and 

 the alcohol), is actually increased. This fact alone makes it evident that the 

 explanation offered by Jones and Lindsay does not account wholly for the 

 phenomenon. 



Two factors determine conductivity amount of dissociation and ionic 

 mobility. Decrease in one or both of these produces decrease in conductivity. 

 It has been shown that the decrease in conductivity in question can not be 

 due alone to decrease in dissociation. The inevitable conclusion is, then, that 

 it is due to a decrease in ionic mobility. 



A complete explanation of the minimum in conductivity will have to ac- 

 count for the following facts : 



(1) The effect itself. 



