136 TRANSMISSIVITY IN PASSIVE IRON WIRES 



namic" rather than a "static" type of equilibrium; and there is seen 

 an interesting analogy to the process by which a protoplasmic 

 structure such as the plasma membrane maintains intact its struc- 

 tural continuity and dependent properties (semipermeability, polariza- 

 biHty, etc.) during Hfe. 



The brief duration of the period of activity in a wire activated in 

 stronger solutions of nitric acid indicates a rapid reformation of the 

 film, implying a correspondingly active local oxidation. The frequent 

 failure of transmission in solutions stronger than 85 per cent (of 1.42 

 HNO3) probably indicates a too intense oxidizing action, which inter- 

 feres with the local reduction on which transmission depends. This 

 view is confirmed by the fact, repeatedly verified throughout the pres- 

 ent investigation, that mechanical activation is more readily induced 

 in weaker than in stronger acid. In general, activation is favored by 

 conditions that promote reduction (like making the metal cathodal) 

 and hindered by conditions of the reverse type. This is illustrated 

 by the following experiment. When two passive iron wires are placed 

 side by side about 2 cm. apart in 60 per cent HNO3 and connected 

 through a key with the poles of a single Edison cell (about 0.9 volt), 

 it is usually found, on closing the circuit, that the current is insufficient 

 to activate the cathodal wire. During the flow of the current, how- 

 ever, this wire is more readily activated by scraping with a glass slide 

 than while the current is not flowing; conversely, the anodal wire, 

 during the flow of the current, is much more resistant to mechanical 

 activation than before. But immediately after breaking the current 

 the anodal wire becomes temporarily more reactive than normally — 

 an effect due probably to its being now the cathode of the reverse 

 or polarization current. Electrical activation is similarly modified by 

 the passage of a constant current between a passive wire and the acid 

 in which it is immersed; for example, while a current from five cells 

 (about 4.5 volts) was passing through a passive wire anode immersed 

 in 70 per cent HNO3, touching with zinc caused a local activation 

 which was conducted for only a few centimeters from the region of 

 contact; after the current was broken the wave was transmitted as 

 usual for the whole length of the wire. All the above effects indicate 

 how closely the behavior of passive wires depends upon the condition 

 of the surface film and upon the rate and character of the chemical 



