Intelligence and Miscellaneous Articles. 461 



a column of mercury a metre in length and a millimetre square in 

 section). Taking the same unit as a basis, the electromotive force 

 of a Bunsen's element is equal to 21, and of a DanielPs equal to 12. 

 Hence the electromotive force of a Leclanche's element is only 0*896 

 that of a Daniell's, while from Leclanche's determinations* it is said 

 to be 1*38 as great as that of a Daniell's. 



This difference (1 *38 against 0*896) maybe easily explained. With- 

 out galvanic polarization the electromotive force of such an element 

 should be equal to that of a Bunsen's cell (compare my Lehrbuch der 

 Physik, 7th edit. vol. ii. p. 263). But the degree of polarization de- 

 pends on the strength of the current which the cell furnishes, and 

 therefore on the magnitude of the resistance which is interposed in 

 the circuit. In my experiments the resistance was very small, and 

 hence there was a powerful polarization ; while in Leclanche's ex- 

 periments the current was not so powerful, and the electromotive 

 force was therefore not so greatly weakened as in my experiments. 



Leclanche found the mean resistance of a manganese-cell of mean 

 size (porous cell 15 centims. in height and 6 centims. in diameter) 

 to be equal to 550, taking as unit of resistance an iron wire 4 millims, 

 in diameter and a metre in length. Referred to Siemens's unit, this 

 resistance is 



I 1 A 



r—n — 2 =1-4, 



where n is the resistance of iron as compared with mercury (that is, 

 0*12), and /=550, r-4; while I found r=l'89. The cells with 

 which Leclanche experimented were doubtless somewhat larger than 

 mine. 



I was concerned to ascertain, if possible, the part which the man- 

 ganese plays in this. Leclanche's statements on this point are inade- 

 quate ; for he says (Dingler's Journal) that the manganese rapidly and 

 uniformly absorbs the hydrogen. If by this it is meant that the hy- 

 drogen liberated at the negative pole is immediately oxidized, the state- 

 ment is manifestly incorrect; for then the galvanic polarization would 

 not exist, and the electromotive force would be 21 (that is, equal to 

 that of a Bunsen's cell). But whether the manganese does generally 

 exert an influence on the electromotive force can only be decided 

 by investigating a cell which has just the same structure as a Le- 

 clanche's, but with the difference that the mixture of manganese and 

 carbon is replaced by pieces of carbon (without manganese). For 

 such a cell I found the electromotive force 



e' = 6'16, 

 considerably less, therefore, than the electromotive force of a manga- 

 nese-cell. Hence the voltaic polarization is not entirely removed by 

 the carbon being partly surrounded by manganese, although it is 

 materially lessened. The manganese manifestly gives up some 

 oxygen, although it is not sufficient to oxidize all the liberated hy- 

 drogen. With this agrees the experience, that in Leclanche's cells 

 which had been for some time in use the manganese had lost its 

 activity. — Poggendorff 's Annalen, June 1870. 



* Dingler's Polytechn. Journal, vol. clxxxviii. p. 9/. 



