372 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



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the discharge, which is superposed over the first portion, takes place 

 more slowly and is therefore difficult to measure by ballistic methods. 



When alternating currents came into common use, they were imme- 

 diately applied in the study of polarization, and the great majority of 

 the measurements which have been made in late years on aluminium 

 anodes have been made by alternating current methods. We have 

 thought it best to return to the older and more difficult method of the 

 ballistic galvanometer, for previous investigations have shown that the 

 film changes very rapidly in properties from the time a current begins 

 to pass through it, and that every change in the electrical condition of 

 the circuit is accompanied by a time change in the film itself. Alter- 

 nating current measurements cannot give the details of this change, but 

 only an integrated result. 



V. Experimental Results. 



In beginning these measurements we had clearly in mind the diffi- 

 culties mentioned by Streintz (71). The total discharge from an elec- 

 t trolytic cell having an aluminium 



anode extends over a considerable 

 time, and it would seem, therefore, 

 at first sight, that a ballistic method 

 would be poorly adapted to the study 

 of it. It was found, however, by 

 using several ballistic galvanometers 

 of different period, that the error due 

 to the slow residual charge could be 

 neglected ; by using plates of consid- 

 erable surface and low resistance 

 ballistic galvanometers of rather long 

 period, it was practically eliminated. 

 Anodes were formed either from 

 a storage battery or from a dynamo 

 current, and after formation they 

 were charged from a storage battery 

 of small cells capable of giving over 

 500 volts. The time measurements 

 were made by the apparatus shown 

 in Figure 1. This is merely a simple 

 machine which allows a heavy weight 

 to fall, contacts being made and 

 broken by the weight as it passes. 

 The switches to be opened or closed 



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Figure 1. 



Apparatus for charging and dis- 

 charging condensers. 



