Contact Potential Phenomena between Metals. 



24? 



shown by curve (b) and Table L, and it remained stationary 

 as long as the brass was charged. 



(o) The brass plate and vessel A were earthed quickly,, 

 and the reading returned again to that representing the 

 contact potential difference, and the figures and curve for 

 this return were found to be the same as those for (b). 



Similar tests were made with different plates and similar 

 results obtained. Each set of three could be repeated as 

 often as desired when the contact potential remained con- 

 stant. In Table I. the results for lead-brass and zinc-brass 

 are given. (In fig 3 the curves for zinc-brass are shown.) 

 The electrometer readings are reduced to volts, and in the 

 case of the lead-brass two series are inserted in order to- 

 demonstrate the accuracy of repetition. 









Table I. 









Lead-brass. 



Z 



nc-brass. 



Time after 



















start,. 



(a). 



(a). 



(*)*• 



(*)*- 



(o). 



(o). 



(a). 



(b)* and (c). 



sec. 



o-ooo 



0-000 



0000 



o-ooo 



o-ooo 



o-ooo 



o-ooo 



o-ooo 



15 „ 



0223 



0-222 



0-284 



0-282 



0-284 



0-282 



0-186 



0215 



30 „ 



0-303 



0-303 



0-313 



0-314 



0313 



0-313 



0-317 



341 



45 „ 



0-339 



0-341 



0343 



0343 



0346 



• . • 



0-402 



0-422 



1 min. sec. 



0-345 



0346 



0-346 



0-346 



0-347 



• •• 



0-454 



0-465 



„ 15 „ 



0-350 



0351 



0-352 



0-350 



0-352 



• • • 



0-485 



0-490 



„ 30 „ 



• • • 



• • • 



0-356 



• • • 



0356 





050J 



0-505 



„ 45 „ 



% •• 



. .. 





• > • 



.. 



• •• 



0-511 



0-513 



2 „ „ 



356 



0-358 



0-356 





0356 





0-518 



0-518 



3 „ „ 



0-360 



0-360 



0-358 



0-360 



0358 



0-360 



0-522 



0-522 



4 „ „ 



0300 



0-361 



0-360 



0-361 



0-359 



0-360 



0523 



0-523 



* The values given in the columns for (b) represent the results obtained by 

 subtracting each of the readings from 0'360 in the case of the lead-brass and 

 from 0*523 in the case of the zinc-brass, in order to express the creep in the 

 same direction, and thus facilitate comparison. 



(The slower initial rate of increase in the case of the zinc-brass readings 

 was due to the use of a lower charging potential for the electrometer.) 



The complete agreement of curves (b) and (c) with each 

 each other and their disagreement with curve (a), considered 

 in conjunction with the results of the insulation tests, cannot 

 be attributed to effects due to electric absorption in the 

 sulphur. These curves can, however, be explained on the 

 ass unption of definite charged layers, and lead to a simple 

 means of tracing electrically the actual formation of the 

 layers. Suppose that the vessel A and both plates are 

 earthed, and that the air is not ionized, then, calling the 

 potential of the brass V 1? and the potential of the plate 

 (J, V 2 , we have on the brass a layer at a potential Y x + a 1? and 



