1256 



boniite detector bas sucli a strong unidirectional resistance. For, 

 curve G may be legarded as a superposition of curves CI and B\, 

 the latter first being turned 180°. 



ZiDcite-molybdenite. in order to test this statement, the crj'stals 

 zincite and molybdenite, each of which in combination with platinum 

 exhibits such different charactei-istics, can be brought in contact 

 with each other. That this contact has a very pronounced unidirect- 

 ional resistance, appeais from the following characteristic. 



From zincite to molybdenite 



1 2 3 4 5 6 7 8 9 10 11 12 Volt. 



1 2 4 6 7 9 12 14 18 29 49 79X0,0001 Ampere. 



From molybdenite to zincite 

 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 Volt. 

 1 5.5 15 26 39 51 64 75 86 98 110 123x0.0001 Amp. 



Moreover it follows that the unidirectional resistance of the zincite- 

 platinnm contact must be attributed to the same cause as that of 

 the molybdenite contact, e.g. to electrolytic polarisation. 



Galena-platinuin. A gelena detector usually yielded a charact- 

 eristic agreeing with curve B\. Occasionally the characteristic agreed 

 more with curve CI, the resistance being now greatest in the 

 opposite direction. Both curves soon altered with time. Curve K\ 

 was obtained after a current of 0,005 Amp. had first passed during 

 15 minutes through the contact from the galena to the platinum, 

 the contact |)res8ure being very slight. It was not possible to extend 

 the curve into the first qiuidrant because with too high a voltage the 

 curve would again pass into curve III. If a cuirent of 0.01 Amp. 

 was now sent from platinum to galena during 15 minutes, the 

 characteristic K\\ was obtained. Curves I and II clearly show that 

 the real resistance of the contact is represented by curve III and 

 is the same in all three cases. Curve I points to an E. M. F. of 

 polarisation with a maximum of 0,25 Volt, whereas the maximum 

 in the other direction could not be measured. Curve II points to 

 two maxima; 1,4 Volt and 0,1 Volt. The existence of these two 

 characteristics can hardly be attributed to anything else than to 

 changes caused by the passage of the current through the contact 

 which can only be of an electrolytic nature. 



Ironpyrites-platiDum. The characteristic H of an ironpyrites- 

 platinum contact does not show anything new after the preceding. 

 Electrolysis was only observed in this crystal under the microscope 

 after we were satisfied, on the authority of the above considerations, 

 that the uiiidiiectional resistance is due to electrolytic polarisation. 



