Conductivities and Viscosities in Formamid and in Mixed Solvents. 75 



bell-jar was closed with a rubber stopper carrying the thermometer and 

 pump connection. At about 90 mm. of mercury water boils at 49.6. 

 The heater maintained a temperature of 65, the suction pump a 

 vacuum of 70 to 80 mm., so that with the rapid circulation of the warm 

 residual air over the material and the drying agent all traces of moisture 

 could be removed from a sample with much greater ease than in an 

 ordinary vacuum desiccator. 



PROCEDURE. 



Each "set" (i. e., M/2, M/4, M/10, M/50, etc.) of solutions in pure 

 formamid were made up the day before the conductivity measurements 

 were taken, since experiments showed that measuring the solutions 

 on the same day they were prepared did not increase the accuracy of 

 the work. In the case of mixed solvents, however, it was necessary 

 to make up the solutions and measure them the same day. 



Cells were read consecutively in the 15, 25, and 35 baths. This 

 order was always followed. The bridge readings, however, could be 

 duplicated for the more concentrated solutions when allowed to come 

 to temperature again in the 15 or 25 baths. 



The molecular conductivity values were repeated for a number of 

 salts, representing each series measured, to within 0.5 mm. reading 

 on the bridge for all more concentrated solutions. Therefore, consider- 

 ing the errors in making up "check" solutions, the values below should 

 be approximately correct. 



In the tables all conductivity values are expressed in reciprocal ohms 

 and are the molecular conductivities of gram-molecular weights of the 

 various salts. These molecular conductivities (ju v ) were calculated 



from the formula // = K-T, where K represents the cell constant, v the 



volume of concentration, R the resistance in ohms as measured by the 

 rheostat, (a) and (6) the readings on the two sides of the bridge. The 



percentage dissociation, a, was calculated from the equation a = - X 100, 



/A 00 



where ju > is the highest value of // obtained. 



The temperature coefficients in conductivity units (T) were derived 



by means of the formula - " ._./ = T, in which pjt represents the 



molecular conductivity at the higher temperature t, and /*' at the 

 lower temperature t'. The coefficients expressed as percentages were 



T 

 calculated from the formula A = -' 



The values representing the molecular conductivity in these tables 

 are mean of three bridge-readings involving different values for R. The 



