27 



In order to measure Rg directly, the resistance of the cell (TJC-1 

 filled with 0.1 M KCl) in the pressure vessel was measured with an ohmmeter 

 (the bridge could not be balanced) with the grounded lead between the closure 

 and the cell electrode disconnected. The measured resistance was 5000 to 

 5700 ohms, corresponding to a value of C of 280 to 320. This was considered 

 good agreement . 



The variation of C with pressure cannot be measured, but is presum- 

 ably negligible. In the pressure runs, the cell constant at 1 atmosphere is cal- 

 culated directly from R^ and the value of C determined by measurements inside 

 and outside the bath using the appropriate electrolyte (the manner of calculating 

 cell constants is discussed in greater detail below) . The cell constants at given 

 pressures are then calculated on the basis of this cell constant. Thus C becomes 

 absorbed in the cell constant, and the value of the specific conductance becomes 

 very insensitive to the value of C . For example, for 19 .376 o/oochlorinity sea water 

 at 4.82°Ci, with cell GCC-2, the measured value of C is 125, and at a pressure of 

 20, 000 lb/in. 2 the corresponding value of the specific conductance is 0.03811 ohm"l 

 cm" . If the value of C is increased fivefold to 600, the specific conductance be- 

 comes 0.03816 ohm"lcm"l, a change of only 0.13%,; and if C becomes infinite, the 

 specific conductance becomes 0,03817 ohm'-*^ cm"-*^ . 



F. PLUG POSITION AND LIQUID LEVEL EFFECTS 



Although the movable plug of the Teflon Jamieson cell (TJC-1) is located 

 remotely from the electrodes (see Figure 7), there is a detectable influence of 

 plug position on the measured resistance. v-'^^) This effect was measured at 25.2°C 

 and 1 atmosphere, and the following relationship was found to obtain: 



R" = R / (1 + 0.00262 d) (4) 



c c / 



where R" is the resistance of TJC-1 when the lower end of the plug is flush with 

 the lower end of the cell's wall, and d is the displacement (in inches) of the plug. 

 As the pressure is increased, the electrolyte in the cell is compressed and the 

 plug is displaced. Assuming that the variation in cross sectional area of the cell 

 with pressure is negligible, equation (4) can be rewritten in terms of pressure as 



R" = R / (1 - 0.0105 k'P) (5) 



c c / 



where the pressure, P, is in atm and k' is the mean compressibility of the elec- 

 trolyte in atm"-*^. When the electrolyte is water, at 20,000 lb/in. ^ the denomi- 

 nator on the right of equation (5) has the value 0.993 . 



'Axx\m Sl.littlcJnir. 



S- 700 1-0307 



