Nichols and Franklin — Electromotive Force. 297 



a two-fluid battery, the iron submerged in weak sulphuric acid, 

 the platinum in the above solution, the E. M. F. became l - 39 

 volts. When the iron in the last case was submerged in dilute 

 hydrochloric acid the result was nearly the same, the E. M. F. 

 being 1'41 volts. In sulphuric acid containing potassium per- 

 manganate the same metals gave 1*44 volts, which rose to 1'60 

 volts when the platinum and solution were placed in a porous 

 cup and the iron was dipped in sulphuric acid containing no 

 oxidizing agent. Iron and platinum in ferrous chloride showed 

 only "74 volts, but a two-fluid battery with iron — dilute hydro- 

 chloric acid — ferrous chloride — platinum gave l - 07. 



In all these cells the electro-motive force obtained by the 

 solution of iron with ferric reaction was smaller than when a 

 ferrous reaction occurred. The application of this fact in the 

 explanation of the electro-motive force of magnetization is very 

 manifest. When the poles of an electrode within the magnetic 

 field are exposed to action, the gathering of the salts of iron 

 around the exposed surface tends to bring about a change from 

 ferric to ferrous reaction and to increase the electro-motive 

 force. A corresponding decrease follows when a neutral sur- 

 face is exposed within the field. The extent to which the 

 electro-motive force of a cell in which a ferric reaction is tak- 

 ing place may be reduced by briskly stirring the solution and 

 exposing the surface of the iron to the fresh acid, thus doing 

 mechanically what is done magnetically when the reaction 

 occurs, at a neutral surface, within the field, was shown by 

 the following experiment. A one-fluid cell, consisting of iron 

 and platinum in nitric acid diluted with four parts of water, 

 had an electro-motive force of 1"07 volts. Stirring reduced it 

 to '95 volts. When left undisturbed it immediately regained 

 its former intensity. 



The electro-motive force developed between the poles of one 

 iron electrode placed within the magnetic field and the neutral 

 parts of a similar electrode in the same cell, will also exist be- 

 tween the poles and intermediate portions of a single piece of 

 iron. Consequently there will always be local action between 

 different portions of the surface of iron exposed to chemical 

 action within the field, the currents passing through the liquid 

 from the regions nearest the induced poles. 



It is doubtless to this local voltaic action, which has its 

 source in the electro-motive force of magnetization, that the 

 various phenomena, described in our papers on the chemical 

 "behavior of iron in the magnetic field ',* and on the destruction 

 of the passivity of iron by magnetization,^ are to be ascribed. 



*This Journal, vol. xxxi, p. 272. f Ibid., vol. xxxiv, p. 419, Dec, 1887. 



Am. Jour. Sol— Third Series, Vol. XXXV, No. 208.— April, 1888. 

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