1 70 Mr. J. Brown on Dropping-Mercury Electrodes. 



cell thus arranged was charged as before, and after stopping 

 the charging current observations were taken of the E.M.F. 



From this Table it appears that the rate of fall is very much 

 slower than before. This is especially marked in Exp. III., 

 where the strength of the acid in the jar is nearer the possible 

 maximum producible in the interstices of the spongy materials. 



It may be worth notice, that the value of the E.M.F. to 

 which the cells finally rise in Exps. I., II., and III. of the 

 first series is very nearly the same as that to which they fall 

 in the first two experiments of the second series. If the rise 

 is due, as we think, to the diffusion inwards of the stronger 

 acid, some such agreement might be expected. 



We therefore regard the abnormal E.M.F. as due to the 

 inequality of acid strength, and its gradual disappearance as 

 due to equalization of strength produced by diffusion. 



XIX. On Dropping-Mercury Electrodes. By J. Brown*. 



IN Prof. Ostwald's Reply f he is scarcely correct in descri- 

 bing my paper % as a " supposed disproof of v. Helmholtz's 

 theory." It was perhaps unnecessary to disprove what had 

 not been proved. V. Helmholtz put forward an explanation 

 based on several unproved hypotheses. I offered what ap- 

 peared to me a simpler and more probable theory. Prof. 

 Ostwald, however, goes further ; and there arises the question 

 whether many of the supporters of v. Helmholtz's theory 

 would accept Prof. Ostwald's exposition of it, or the predic- 

 tions which he founds so easily upon it. He is, however, so 

 sure of his ground as to go the length of prophesying in his 

 fourth paragraph (p. 480) what will happen if I try a certain 

 experiment. Well, that experiment I had of course already 

 repeatedly tried before I made any assertion as to the result ; 

 and now, to make sure, I have repeatedly tried it again, and 

 so far from the current being " much weaker " than in the 

 previous case, as Prof. Ostwald implies that it obviously must 

 be, I am unable to detect a mean difference of one half per 

 cent, between them. Any subsequent decrease of the current 

 by polarization of the resting mercury is explained equally by 

 either his hypothesis or that which 1 advocate, as is also the 

 current referred to in the last paragraph of his reply. 



It is after all possible that the initial equality of these cur- 

 rents (however this may affect Prof. Ostwald's view) might, 

 by the adoption of some further not impossible hypotheses, be 

 made to agree provisionally with the view of v. Helmholtz, 



* Communicated by the Author. 



t Phil. Mag. June 1890. \ Ibid. May 1889. 



