VOLTAIC POTENTIAL DIFFERENCE BETWEEN CONDUCTORS. 



remembering that V^is negative, while V f x is positive, the following data 

 appear: 



The large nucleation obtained here for copper remains unexplained. 

 It was somewhat reduced in other similar experiments, but remained 

 high. Since V'^-}- V x = 1-65, slight differences in contact would produce 

 a serious effect. From these data it follows, finally, that the voltaic 

 contact zinc-copper is 0.367 volt. After cleansing with acids data like 

 Al-Cu = o-58 volt, Al-Zn = o.o6 volt, or Zn-Cu = o-52 volt were obtained, 

 which varied again after other treatment. 



74. Further experiments. Conclusion. In addition to the above 

 experiments, a great variety were made, as, for instance, with weaker 

 radium (single tubelets) in the core of the condenser ; with radium inside 

 and outside of the condenser; with the metal surfaces cleansed with acids, 

 or polished, or aged, etc. A few data may be referred to here. 



The highest nucleation for an aluminum core charged with radium 

 tubelets occurs in case of a copper envelope for the condenser. Some- 

 what smaller values occur for zinc and brass, and the smallest for alumi- 

 num shells. The agreement is usually unsatisfactory. The voltaic con- 

 tacts are such as to place zinc-copper at 0.4 to 0.6 volt. The data for 

 groups of radium tubes are larger than the values computed from indi- 

 vidual tubes, N=\/N 1 2 + N 2 2 + . . . ., probably from the effect of 

 secondary radiation and non-uniform ionization. We may also ascribe 

 the high ionization in a copper shell as compared with a low ionization 

 in an aluminum shell to the same cause. If the radium is placed without 

 the condenser the voltaic contacts do not appreciably differ from the 

 values found when the radium tubelets lie in the core. One may note 

 that even in the aluminum-aluminum condenser the voltaic contact is 

 not zero but about 0.05 volt. In other instances non-commutated electro- 

 motive forces often appear. The contact Al-Zn is peculiarly variable even 

 as to sign. 



As a whole these experiments lead to no general conclusion of relevancy 

 here and they have therefore been withheld from detailed consideration. 



Finally, to detect the source of the electromotive force in the electro- 

 meter, this was replaced by another instrument, No. 2, of the same kind, 



