36 Conductivities and Viscosities in Pure and in Mixed Solvents. 



Complete dissociation of potassium iodide in formamid is found 

 in the N/200 solution, while in water it is not reached till the N/2048 

 solution. Therefore, in both respects formamid falls in line with the 

 Thomson-Nernst theory. This relation is confirmed by every salt 

 studied in this investigation for which data for comparison are available. 

 The rubidium salts show the stronger dissociating power of formamid 

 much more than some others that were investigated. 



The hypothesis of Dutoit and Aston 1 states that the greater the asso- 

 ciation factor of the solvent the greater its dissociating powers. Table 

 7 shows the relation of formamid to other pure solvents in regard to 

 association factors. The correction and comparisons made above, 

 with reference to the Thomson-Nernst theory, are equally applicable 

 in connection with the Dutoit and Aston theory. 



Jones and Mahin showed that complete dissociation of lithium 

 nitrate in acetone is not reached even when V is 100,000. The signifi- 

 cance of these figures is apparent, if one has in mind the association 

 factors and dielectric constants of formamid, ethyl alcohol, and acetone, 

 given in table 7. 



Jones and Veazey's 2 explanation of the decrease in viscosity produced 

 to the greatest extent by caesium and rubidium salts, and in a less 

 degree by potassium, ammonium, and other salts, all having very large 

 molecular and atomic volumes, has been of special interest in this 

 investigation. They base their hypothesis on the theory of Thorpe 

 and Rodger, that viscosity is due to the friction between the surfaces of 

 the molecules. If the particles of the solute are larger than those of the 

 solvent, the frictional surfaces and, consequently, the viscosity will be 

 decreased. If the added particles are smaller than those of the solvent, 

 the viscosity will be increased by the addition of the solute. The vis- 

 cosity of all the concentrated solutions of salts having very large 

 atomic or molecular volumes, has been found to be less than the solvent 

 in the case of all pure solvents, except acetone, which have previously 

 been studied. The viscosity of formamid has, on the contrary, been 

 increased by every salt used. The complex formamid molecules 

 HCONH2, and its very large association factor (6.18) show that its 

 actual molecule is larger than that of any other pure solvent used in these 

 investigations, and the increase in viscosity by the salts named above 

 confirms this conclusion. The following comparison strikingly illus- 

 trates this relation. A N/2 solution of rubidium iodide in glycerol 

 decreases the viscosity of the solvent 13 per cent, while a N/2 solution of 

 the same salt in formamid increases the viscosity of the solvent 12 

 per cent. This relation will be referred to again in discussing the 

 results of the work with caesium nitrate and chloride. 



K^ompt. Rend., 125, 240 (1897). 



2 Amer. Chem. Journ., 37, 405 (1907); Carnegie Inst. Wash. Pub. No. 80 (1907). 



