ELECTRICAL CONDUCTIVITIES, ETC. 



The cells were generally covered with a little platinum black, to increase the 

 sharpness of the minimum in the reading on the bridge. The cylindrical type of 

 cell, however, was never blackened. 



The platinum plates used as electrodes were cut from sheet platinum about 1 mm. 

 thick. The relatively thick plates were much less liable to bend and change the 

 constant after it was once determined. 



CELL CONSTANTS. 



The cell constants were determined with standard solutions of potassium chloride 

 whose molecular conductivity at 25 was determined with a high degree of accuracy. 

 The cells to be used with the more concentrated solutions, and whose plates were 

 therefore most widely apart, were all standardized with a n/50 solution of potassium 



m 



Fig. 1. 



Fig. 2. 



chloride. The cells to be used with the more dilute solutions were all standardized 

 with a n/500 solution of the same salt, while the cylindrical cells were standardized 

 with a w/2000 solution of potassium chloride. The solutions of potassium chloride 

 of different concentrations were used for the different cells, in order that the resist- 

 ance to be thrown into the rheostat would be of the order of magnitude to give a 

 sharp reading on the bridge. 



The cell constants in every set of cells used in this work were redetermined once or 

 twice a month during the entire time that this series of investigations was in 

 progress. With reasonably careful handling the constant of any cell underwent 

 very small change during an entire year's work. 



When the cells were used over the temperature range 35 to 65, certain precau- 

 tions were necessary in connection with the constants. It was found that at these 



