•182 Mr. R. Sabine on Electricity disengaged 



mercury surface is greatly dependent upon its state of oxida- 

 tion, that the expansion or contraction of sncli a surface is 

 always attended with a corresponding alteration of its electro- 

 positiveness, and, finally, that the motions of mercury elec- 

 trodes, under water or acidulated water, are due principally to 

 the reduction of superficial suboxide. 



The following more systematic series of experiments was 

 undertaken to ascertain the correctness of these conclusions. 



I. Electricity disengaged between Mercury Surfaces. 



In a paper contributed in 1871 to the Royal Society*, " On 

 the Polarization of Metallic Surfaces in Aqueous Solutions," 

 Mr. C. F. Varley made known some experiments by which he 

 had succeeded in producing electric currents between two 

 masses of mercury, the relative exposed surfaces of which, 

 under dilute sulphuric acid, were varied by alternately rising 

 and falling in two funnel-shaped vessels, the mercury surfaces 

 having been previously polarized with hydrogen by connexion 

 with the zinc pole of a battery. Mr. Varley, however, did 

 not observe any current with unhydrogenized mercury when 

 it was pure. In my experiments on the production of currents 

 by mercury surfaces I have carefully avoided any hydrogeni- 

 zing taking place, and have confined my attention to currents 

 set up by the altered electropositive condition through oxida- 

 tion by the atmosphere alone, or by simple contact with the 

 liquid in which the mercury was immersed. 



An insulating trough about 20 Fig- 1. 



x 15 centims., and 7 centims. deep, 

 was constructed with a division in 

 the middle reaching to within a 

 short distance of the bottom, and 

 which divided it into two compart- 

 ments (fig. 1).,. Distilled mercury 

 was carefully poured into two dishes, A and B, one in each com- 

 partment, to the same level, whilst distilled water to the level c 

 covered both the surfaces. Platinum conducting-wires (a 

 and b) inserted through glass tubes enabled the two masses of 

 mercury to be connected with a measuring-instrument. The 

 trough was allowed to rest quietly for a time, until the tem- 

 perature was settled ; then one of the surfaces (A or B) was 

 scraped. Two pieces of glass were taken, one in each hand, 

 and placed upon the middle part of one of the mercury sur- 

 faces, thus \/. They were then quickly separated so as to 

 cause a fresh mercury surface to be exposed ; and at the same 

 instant the release of a discharge-key, in connexion with an 

 * Phil. Trans, vol. clxi. (1871), p. 129. 



