1249 



could be observed is that of iroiipyrites and platiumn ; these pheno- 

 mena are most distinct when the place of contact is such as to 

 bring about the strongest unidirectional lesistance. in this case the 

 current must flow from the cryslai to the platinum needle, which 

 in this contact is the weaker current, in contradistinction lo the 

 moljbdenite-contact, a fact which is at once obvious from the perusal 

 of the characteristics of rectitication (cf. below). Here the products 

 of electrolysis consist in a black and a colourless liquid, from the 

 latter of which colourless crystals usually secrete. The phenomena 

 of electrolysis are much weaker than in the molybdeniledeteclor. 

 The applied E. M. F'. may not amount to more than 5 volts because 

 the unidirectional resistance together with the electrolysis will then 

 disappear. This disappearance of the unidirectional resistance has 

 already been found by Flowers for a galenacontact. 



Galena, zincite, copperpyrites, copperglance, bornite and carbo- 

 rundum detectors were also examined. With these contacts no indi- 

 cation of any electrolysis was found. With galena only sometimes 

 a dark spot on the place of contact was visible. Though electrolysis 

 was brought about here by moisture, yet it usually stopped after 

 some moments on account of evaporation of the liquid. However, 

 every time the unidirectional i-esisfance was considerably increased 

 through this operation, and the direction of greatest resistance 

 remained the same as in a fresh contact. 



§ 3. Experiments in vacuo. 



We were not far wrong in supposing that the unidirectional 

 resistance was the consequence of the electrolysis in a damp film 

 in which the originally imperceptible products of electrolysis, if 

 hygroscopic, can extract particles of moisture from the air, so that 

 the electrolytic products become visible. The latter would be the 

 case with ironpyrites and molybdenite. 



A research in vacuo and in hydrogen showed that the unidirectional 

 resistance of the molybdenite detector continued to exist, the electro- 

 lysis, however, not being perceptible now. Nevertheless the uni- 

 directional resistance may in this case still be attributed to an adhering 

 layer, for this layer can only be removed with difïiculty and 

 evidently evacuation is [wholly] insufficient to effect this. 



The unidirectional resistance continued to exist also under a layer 

 of paraffin oil, while it was also impossible here to discover the 

 electrolysis. However, from this experiment the inference should 

 not be drawn that the electrolysis is only a secondary phenomenon 

 not causally connected with the unidirectional resistance. 



