31 



Due to limitations of time, we were unable to perform a complete 

 check on the work of Thomas, Thompson, and Utterback, although there ap- 

 pears to exist enough question concerning their work to warrant its repetition 

 with carefully designed conductivity cells . 



H . PRESSURE DEPENDENCE OF CELL CONSTANTS 



The geometrical dimensions of the conductivity cells and hence their 

 cell constants will vary as the hydrostatic pressure exerted on the cells is var- 

 ied, due to the compressibility of the materials of which the cells are constructed. 



The electrodes in the Jamieson cell are remote from the ends of the 

 cylindrical cell, and, as a consequence (except for the effect of the position of 

 the movable plug, discussed above), will have a negligible influence upon the 

 value of the cell constant. Figure 14 represents a cross section of this cell in 

 the region of the electrodes . The inside radius of the cell is r, the distance 

 between the parallel plate electrodes is d, the surface area of the electrodes is 

 A (A = S^, where S is the length of the edge of the square electrode surfaces), 

 and e is the length of the leads from the electrodes to the cell walls „ Now 



d = 2r - 2e (6) 



The linear compressibility, Al/-l^, of platinum at 30° C given by the International 

 Critical Tables(17) is 



M/l = 0.124xl0"^P - 0.63 x lO'^^^P^, (7) 



where P is the pressure in atmospheres . The linear compressibility of Teflon 

 may be approximated by 1/3 of the volume compressibility, (A V/V). Thus (6) 

 becomes 



dp = 2r^(l - 1/3 (AV/V) - 2e^(l - 0.124 x 10"^P + 0.63x lO'-^^P^) 



and the cell constant becomes 



d 2r [l - 1/3(AV/V)] - 2e (1 - 0.124x 10"^P + 0.63x lO'-^^P^) 

 J, - _£^ - -*■ *- J t__ 



^ ^P [Sp(l - 0.124 X 10'^P + 0.63 X lO'-^^P^)] ^ 



(9) 



m>ni>i<M|liHHKa 



Arthur KlLitt\i.3nt. 



S-700 1-0307 



