OF SALTS IN ETHYL ALCOHOL AND WATER. 89 



DISCUSSION OF THE RESULTS. 

 VISCOSITY AND FLUIDITY. 



Viscosity data have been obtained in the various mixtures of alcohol 

 and water that have been studied, both for the solvents and the N/8 

 solutions of potassium and sodium iodides. The values for the more 

 dilute solutions approach those for the solvents too closely to be accu- 

 rately differentiated from them. The results are given in tabular form, 

 together with a representative table of temperature coefficients for the 

 range of temperature over which the work was carried out, i. e., 15, 

 25, and 35. 



Table 25 gives the values found for potassium iodide, and table 27 

 similar values for sodium iodide. It will be seen that the effect of these 

 salts on the viscosity of alcohol-water mixtures is comparatively small 

 for the N/8 solutions. In no instance does the decrease in fluidity, 

 which corresponds to an increase in viscosity, exceed a few per cent, 

 and in certain of the mixtures containing the smaller percentage of 

 alcohol a marked increase in the fluidity is to be noted. This will be 

 discussed when each salt is taken up separately. 



In all mixtures of alcohol and water from 100 per cent alcohol to that 

 containing 60 per cent alcohol, both potassium and sodium iodides show 

 a marked increase in the viscosity of the solvents at the temperatures 

 studied. Beyond this point the effect on the viscosity is somewhat 

 different for each salt. 



From the 60 per cent solvent down to the per cent, i. e., pure water, 

 potassium iodide lowers the viscosity of the solvent to an appreciable 

 extent at 15. At 25 no negative viscosity effect is to be noted until the 

 30 per cent mixture is reached. At this point a corresponding decrease 

 was also noted at 35. Potassium iodide, therefore, may be said to 

 increase the viscosity of all mixtures of alcohol and water from 100 per 

 cent alcohol to 30 per cent alcohol at 25 and 35, and to decrease the 

 viscosity of all the other mixtures up to and including pure water. 



The shifting of the point at which the fluidity curve for the salt 

 crosses that for the solvent is to be accounted for by the change in 

 association of the solvent with rise in temperature. Since a rise in 

 temperature causes a breaking down of the molecular aggregates of the 

 solvent giving ultimate particles of smaller volumes, it follows that 

 this would tend to shift the transition-point towards one extreme or the 

 other. Since potassium iodide increases the viscosity of mixtures con- 

 taining a high percentage of alcohol, the shifting takes place towards 

 the water end of the curve. 



The points discussed above are shown graphically by figures 35 and 

 36, which represent the curves for solvent and solutions at 15 and 25. 

 Table 26 contains the temperature coefficients of fluidity for the solvent 

 and N/8 potassium iodide, for all percentages of alcohol and water 

 studied. They are seen to decrease in value with rise in temperature 



