PIERCE AND EVANS. 



CAPACITY OF CARBORUNDUM. 



807 



excess of these coefficients with B positive over the corresponding 

 values of A positive, or whether on the other hand it is necessary to 

 assume different capacities in the two opposite directions, we have 

 computed approximate values of the integrals in the denominators of 

 equations (17) and (19). These computations were made by omitting 



TABLE III. 



second-order effects and assuming that the electromotive force on 



t t 



charge is -Vi = ^(1 — e *^), and on discharge V2 — Ee ^^. With these 



values of the e. m. f, as functions of t/RC and with the steady 



current-voltage curves of Figures 3 and 4, t/^ and 1/2 were plotted as 



functions of t/EC and integrated by measuring areas, with the result, 



which is only an approximation, that on charge ^ 



C 



". = ^(1-^), 



(22) 



^ An independent investigation of the problem imposing the condition that 



the leak resistance obey Ohm's law (i. e. is independent of voltage) leads also 



exactly to equation (16) for charge and to equation (18) for discharge, with, 



C f 27?\ 

 however, C\ = C'2 = -, 5^ = C f 1 J , approximately. 



(' - f )' 



