33 



The elastic properties of platinum change by less than 0.01% per degree centigrade; 

 therefore, the temperature dependence of A -€7-^ has been ignored . Unfortunately, 

 the behavior of Teflon under compression appears to be complex, involving a 2 .3% 

 contraction in volume at 5000 atm at room temperature. (l^* ^^> 1°' ^0) The pro- 

 posed phase diagram for Teflon is shown in Figure 15 . Values of A V/V for Teflon 

 at the appropriate pressures and temperatures were read from a plot of the data 

 of Weir(21) (Figure 16). Over the pressure range of our experiments, changes 

 due to change in the dimensions of platinum parts were relatively small, so when 

 S and r are expressed in cm, equation (9) becomes 



Icp = 2r^ 



1/3 (A V/V) 



1.077. (10) 



As mentioned above, r, was determined from conductivity measurements imme- 

 diately prior to the application of pressure. 



Examination of the results summarized in Tables IX to XI (see Section 

 VI) shows that the variation with pressure of the constant of TJC-1 is quite appreci- 

 able and represents about a 6% decrease at 30, 000 lb/in. 2 „ 



In the case of the glass capillary cell, the pressure dependence of the 

 cell constant takes a very simple form f t^p /ii/i '\U ^ ^^^ ^^ '^o) 



^■' "" -7 

 k = k /(I - 1.08 X 10 P), (11) 



where P is now in lb/in. 2. When P is expressed in bars the constant becomes 

 1 .57 X 10~" . In contrast with the pronounced pressure dependence of the Teflon 

 cell constant, the constants for the glass cells increase only a few tenths of a 

 percent at 20, 000 lb/ in .2 , 



Although the Teflon and glass cells have entirely different pressure 

 dependencies of their cell constants, results obtained with these two types of cells 

 were in surprisingly good agreement (see Figure 22) , 



I. EQUILIBRATION 



In our first experiment the electrical resistance of a 0.010 M KCl solu- 

 tion was measured as the pressure was continuously varied from 15 to 100, 000 

 lb/in. "^ and back to 15 lb/in. 2 „ The pressure was varied rapidly, and the run 

 was completed in about two hours . Serious hysteresis was observed (Figure 17); 

 that is, the curve did not retrace itself as the pressure was decreased. This 

 hysteresis was attributed to failure of the system to thermally equilibrate. This 

 possibility was experimentally checked and confirmed. 



Arthur Sl.littlcJnt. 



S-700 1-0307 



