128 CONDUCTIVITY AND VISCOSITY IN MIXED SOLVENTS. 



SOLUTIONS. 



In making up mixtures of solvents, x c. c. of an alcohol or of acetone 

 were diluted to 100 c. c. Such a solution was designated as a mixture of 

 11 x per cent alcohol" or "z per cent acetone." Since acetone has a large 

 coefficient of expansion, it was necessary to make up the mixtures at the same 

 temperature (18). The alcohol or acetone was always brought to this 

 temperature before making up the mixture. 



In making up the mother-solution the exact amount of the salt was weighed 

 into a measuring-flask and, after addition of a portion of the solvent, the sub- 

 stance was dissolved and the flask filled to the mark. Since heat was gen- 

 erated and there was a rise in temperature, the solution was brought to the 

 designated temperature before diluting to the mark. The various concen- 

 trations were obtained by successive dilution, the mother-solutions being the 

 starting-point. Where the quantity to be used was too small to be measured 

 with accuracy, one of the intermediate solutions was taken as a starting- 

 point for further dilution. 



CONDUCTIVITY MEASUREMENTS. 



In all determinations of conductivity from 3 to 5 different resistances were 

 used. The values for the molecular conductivity (//,), given in the tables, 

 are, therefore, the mean of several determinations. The determination of 

 the cell constants was carried out by the method employed by Jones and 

 West. 1 Cells calibrated in this manner gave very accurate results. The 

 constants were checked at frequent intervals. After being used the cells 

 were not allowed to remain in contact with the solution, since small quantities 

 of salt are absorbed by the electrodes. They were allowed to remain empty 

 after being dried out with alcohol and ether, since acetic acid is formed by 

 the action of the platinum on the alcohol and ether in the presence of air, 

 but they were always filled with pure distilled water when not in use for any 

 appreciable time. 



Solutions of potassium chloride, N/50 and N/500, were used in deter- 

 mining the cell constants. The conductivity of the former was taken as 

 129.7 at 25; 136.5 at 25 being taken as the value of p, for the N/500 solu- 

 tion of potassium chloride. 



In the following tables v= number of liters of solution containing a gram- 

 molecular weight of the salt; /^0 = molecular conductivity at 0; ^25 = 

 molecular conductivity at 25. The temperature coefficients are obtained by 

 dividing the increase in the conductivity per degree by the conductivity at 

 the lower temperature. The expression that was applied is 



25 



'Amer. Chem. Journ., 34, 357 (1905). 



