Irreciprocal Conduction. 129 



(b) On Sulphuric Acid and Caustic Potash. 



Ohm* employed a galvanometer in studying the unipolar 

 conductivity of these liquids. The instrument was placed in 

 series with 1-6 single fluid zinc-copper cells, and a voltameter 

 containing strong sulphuric acid. Employing electrodes of 

 platinum, gold, silver, copper, iron, lead, and tin, he found that 

 the deflection obtained on first making the circuit speedily 

 sank to a very small amount. He showed that the cause dimi- 

 nishing the current was between the anode and the acid; for 

 on bridging across the anode and the liquid by some moist 

 threads the deflection was immediately increased to the ori- 

 ginal amount. Also, in the case of the oxidizable metals, by 

 diluting the liquid in the neighbourhood of the anode the 

 current was greatly increased, whilst a dilution of the liquid 

 near the kathode produced no effect. Further, replacement 

 of the anode by a clean electrode produced the original de- 

 flection for a time, whilst changing the kathode made no 

 difference. He finally concludes that the fall of the current 

 is due to the development of a force at the anode. This con- 

 clusion he verified by the use of an electroscope. Thus 

 strong sulphuric acid is classed amongst the negative unipolar 

 conductors f. 



Ohm also experimented with various electrodes in strong 

 potash solution, which led him to regard the latter as a 

 positive unipolar conductor. 



3. Experiments and Theory of Christiani. 

 The only modern contribution of importance to the subject 

 of irreciprocal conduction is the pamphlet J produced by the 

 late Prof. Christiani, whilst working in the laboratory of Du 

 Bois Raymond. He investigated generally the case of elec- 

 trolysis with unequal-sized electrodes, and comes to the con- 

 clusion that, as a rule, with low E.M.FVs the current is able to 



* Schweigger's Journal, lx. (1830) p. 32. 



t It seems probable that what Ohm observed was a decrease of cur- 

 rent due — (1) in the case of the oxidizable electrodes to a transition re- 

 sistance caused by the formation of a badly conducting salt-layer on the 

 anode in strong sulphuric acid ; (2) in the case of platinum and gold in 

 sulphuric acid and potash solution to polarization, this polarization being 

 of a unipolar nature, that is to say it was much greater at one electrode 

 than at the other. We do not believe that Ohm ever observed the phe- 

 nomenon of unipolarity in strong sulphuric acid with electrodes of plati- 

 num or gold due to a transition resistance. This conclusion is supported 

 by comparing Wiedemann, Elcctricitat , Band ii. pp. 629, 657. 



X Ueher irreciproke Leituny elect rischer Stroma. Berlin : Friedlander 

 und Sohn (1876). Contains 174 pages and 15 plates. 



Phil. Mag. S. 5. Vol. 26. No. 159. Aug. 1888. K 



