368 G. Th. Fechner's Justification of the 



that the different electromotive action of the various fluids 

 upon the metals should call forth of itself an apparent reversion 

 of the polarity, since in the latter experiment the fluid, disre- 

 garding the degree of concentration, remains the same. Ac- 

 cording to the chemical view all these cases are easily ex- 

 plained by the general rule, that that metal which is most 

 strongly acted upon by the fluid, is always the positive one 

 (De la Rive in h\s, RechercheSi p. 7.)« 



To this objection I believe I have paid sufficient attention 

 in a detailed memoir respecting the reversions of polarity of 

 the circuit*, and with which undoubtedly De la Rive cannot 

 be acquainted. I have shown that when copper in a solu- 

 tion of sulphuret of potassium is positive with respect to 

 iron, this is caused by a change (perceptible even to the eye) 

 of its surface, which takes place immediately on immersion in 

 a concentrated, gradually on immersion in a diluted solution 

 of sulphuret of potassium, whence therefore in a diluted so- 

 lution the normal divergence also first takes place, and then 

 gradually passes over into the opposed. Besides, the copper, 

 changed in the solution of sulphuret of potassium, is even 

 positive towards iron in other fluids. I have further proved 

 that even in other concentrated fluids and with other metals, 

 in which an electromotive state opposed to the general one 

 may be observed, in general there exists a certain degree of 

 dilution of the fluid, below which the metals indicate at the 

 beginning the normal state, which then gradually passes over 

 into the opposite (if the solution be not too dilute), which also 

 argues a change gradually produced in the surfacesof the metals, 

 although it cannot in every case be demonstrated in a direct 

 manner. 1 have also shown by other different experiments that 

 in these cases the change of the fluid has no influence on the 

 effects. If, moreover, the positive metal happens to be the one 

 which is also alwiiys acted upon most strongly, then this coinci- 

 dence of the two circumstances would in no degree determine 

 which of the two was to be considered as the cause of the other ; 

 as, however, the cases given in my memoir did not include 

 those specifically related by De la Rive of the reverse action of 

 tin and copper in ammonia and of lead and copper in concen- 

 trated nitric acid, I have lately convinced myself that in fact, 

 if we unite tin and copper in officinal liquor ammonice, lead and 

 copper in concentrated nitric acid, even when these liquids are 

 not diluted, the divergence in the beginning indicates the 

 normal positive condition respectively of the tin and the lead, 

 which however after a short time (accordingly as the change 



* Schweigger's Journal, vol. liii. p. 61 — 129, or Biot's Lchrbuch (Precis) 

 vol. iii. p. 93. 



