217 



diameter is three centimeters. The top of the cell is drawn to a capillary 

 after the electrodes and cadlmiiun sulphate crj'stals are placed inside. The 

 cell is then immersed in kerosene inside the piezometer. A special cap 

 was made for the piezometer. This cap has two insulated connections 

 leading through it so that the cell can be connected to a potentiometer. 

 The piezometer is connected to the pump with a copper tube of small in- 

 side diameter. The potentiometer (Fig. Ill), is so arranged that the cell 

 can be compared with a standard Weston cell and also so that the differ- 

 ence between the cell under pressure and a second cell can be measured. 

 This second cell is immersed in a quantity of kerosene and placed as close 

 as possible to the piezometer. In this way any fluctuations due to change 

 of room temperature will be avoided. 

 The results are given in Table I. 



TABLE I. 



The results are also shown in a curve (Fig. IV). The average value 



de -f 



of -;— is 6.47 X 10 '' volts per kilogram per square centimeter, 

 dp 



In the previous work a cell was made of heavy glass tubing and sub- 

 jected to pressure up to 75 atmospheres, at which pressure the cell burst. 



The result for this method was 6.02x10""^ volts per atmosphere. 



The result for the piezometer method obtained at that time was 7.6x10"^ 

 volts per atmosphere. Cohen arid Swinge have found the value 6.28x10"^ 

 volts per atmosphere for a pressure up to 750 atmospheres. The E. M. F. 



