Viscosities of C cesium Salts. 5 



acid exhibited only a slight maximum near its center, which showed 

 that the two liquids possessed about the same small effect, each on the 

 association of the other. On the other hand, the curve for formic acid 

 and water was practically a straight line, indicating that neither solvent 

 altered appreciably the association of the other. 



The reason for the maximum in such viscosity curves and their rela- 

 tion to conductivity having been explained, the effect of certain salts 

 in lowering the viscosity of the solvent remained to be interpreted. 

 Potassium, rubidium, and caesium salts, as has already been stated, 

 were known to lower the viscosity of water. These elements occupy 

 the highest maxima on the atomic volume curve and, as Wagner has 

 shown, they possess negative viscosity coefficients in water which vary 

 directly as their volumes. The explanation offered by Jones and 

 Veazey to account for these facts was that salts of these metals lower 

 the viscosity of the solvent by introducing into it ions which are so 

 large that when mixed with the molecules of the solvent they lower the 

 total frictional surfaces exposed to one another. That certain salts of 

 potassium do not produce this effect is due to the fact that the viscosity 

 of the solution is also a function of the anions as well as of the cations. 

 When the volume of the anion is very small, the negative effect of the 

 cation on the viscosity of the solution is more than overcome, and 

 positive viscosity results. 



Applying this hypothesis of Jones and Veazey to mixed solvents, 

 Jones and his co-workers have been able to explain a number of facts 

 which otherwise appear to be inexplicable. For example, it has been 

 found that rubidium halides and potassium iodide lower the viscosity 

 of binary mixtures of the alcohols and of acetone with water which 

 contain as much as 50 per cent water ; while the corresponding increase 

 in viscosit}' takes place in all mixtures containing the larger percentage 

 of alcohol. The explanation of this fact follows at once from what 

 has been stated above. These salts lower the viscosity of water and 

 increase the viscosity of the other solvents in which they dissolve. On 

 mixing the two, as soon as the association of the alcohol is sufficiently 

 diminished so that the solvent aggregates become smaller than the par- 

 ticles of the dissolved substances, the total frictional surface between 

 the two becomes less and negative viscosity results. 



In glycerol as a solvent, not only were rubidium salts and some 

 potassium salts found to lower the viscosity of the solvent, but also cer- 

 tain of the ammonium salts. So great was the negative viscosity effect 

 produced by concentrated solutions of rubidium salts, that an increase 

 in the conductivity of these solutions over that of the more dilute 

 solutions was noted, although the ionization of the more dilute solu- 

 tions was undoubtedly greater than that of the more concentrated. 

 Ammonium salts were found to be more closely allied to salts of rubi- 

 dium than to those of potassium, in respect to their effect on viscosity. 



