318 THE SO-CALLED SECONDARY ELECTROMOTIVE 



must come into operation with but slight disturbance, and the 

 ' turning-point ' must nearly coincide with the electrode itself. It 

 is thus that wires with thin fluid envelopes give + extrapolar 

 intrapolar after-currents. 



It might thus be predicted that if the thickness of the fluid 

 envelope could be increased by successive steps, then, with a ' two- 

 sided ' polarisable combination, a ' turning-point ' would be found 

 in the extrapolar region, which would rapidly move to a greater 

 distance from the electrode in proportion as the envelope increased 

 in size. This prediction is fufilled by the results of the above- 

 mentioned experiments with the mercury trough. 



Considering the unavoidable conflict in all cases of ' two-sided ' 

 polarisation between the idio- and bi-polar currents, it is not sur- 

 prising that after-currents are found directed both ways, although 

 it may be difficult to explain the phenomena with exactitude. An 

 extrapolar after-current, first + and then , such as occurs with 

 currents of medium strength at the anode of a platinum zinc 

 sulphate schema, would thus mean that in the first moment after 

 the polarising-current was broken the idiopolar current had the 

 mastery, but that in a short time it gave way before the bipolar 

 current; whilst with stronger currents only the latter can be 

 observed 1 . With certain exceptions the decrease in the extrapolar 

 tensions obviously offers a ground for this expression of the state 

 of affairs ; but its actual truth might be shown by special experi- 

 ments, for which however there is no urgent present necessity, 

 since, as we have seen, this special condition does not occur in the 

 case of nerve and muscle. The fact that the biphasic extrapolar 

 after-current of the platinum zinc sulphate schema is more easily 

 produced on the side of the anode than on that of the kathode is 

 possibly connected with the covering of the wire on the kathodal 

 side by a badly-conducting gaseous layer. In favour of this view 

 is the fact mentioned previously that with a platinum in sulphuric 

 acid schema, in which there is development of gas at both poles, 

 the phenomenon appears but seldom and then only in a very rudi- 

 mentary manner. 



Here, then, I conclude the investigation of the polarisation 

 after-currents of the schema. To give a complete theoretical re- 

 presentation of the tension and current distribution would be im- 



1 This may be expressed also as a moving of the 'turning-point' further out. 

 The connection of this phenomenon with one long observed by me in such schemata 

 will be brought forward in another treatise, 



