404 Mr. J. A. Fleming on the new 



lated metal is placed in a liquid capable of acting chemically 

 upon it, a difference of potential is produced between the metal 

 and the liquid, a sudden rise in potential taking place in pass- 

 ing from the metal-surface to the liquid in contact with it, or 

 that the metal becomes negatively and the liquid positively elec- 

 trified, metals differing in the degree of electrification they can 

 produce with any one electrolyte. 



3. But if we ask what are the conditions when two different 

 metals are so immersed, we find the most contradictory state- 

 ments given. Sir W. Thomson expresses his opinion thus in 

 1862 : — " For nearly two years I have felt quite sure that the 

 proper explanation of voltaic action in the common voltaic 

 arrangement is very near Volta's. I now think it quite certain 

 that two metals dipped in one electrolytic liquid will (when po- 

 larization is done away with) reduce two dry pieces of the same 

 metals when connected each to each by metallic arcs to the same 

 potential"*, which seems equivalent to saying that there is no 

 difference of poteutial produced other than that due to dissimilar 

 contact. Thus also Professor Tait : — "By interposing between 

 two metals which have been electrified by contact a compound 

 liquid or electrolyte, these metals are at once reduced to the 

 same potential — a result which could not have been obtained by 

 connecting them by any metallic conductor. By the passage of 

 the electricity a portion of the electrolyte is decomposed, and 

 the potential energy thus developed is equal to that possessed 

 by the electricity while separated in the metals"j\ 



Professor Jenkin advocates essentially the same views : — 

 " When two dissimilar metals are plunged side by side into a 

 liquid such as water or dilute sulphuric acid, they do not exhibit 

 any sign of electrification; the three materials remain at one 

 potential, or nearly so. If while the two dissimilar metals are in 

 the liquid they are joined by metallic contact to terminal pieces 

 of one and the same metal, these terminal pieces will be brought 

 to the same difference of potentials as that which would be pro- 

 duced by direct contact between the dissimilar metals" J. This 

 amounts simply to saying that, as long as no wires are attached 

 to the plates of a single cell, there is no difference of potential ; 

 but that when wires are joined on, the observed difference of 

 potential is due to the contact of the wire with that metal plate 

 to which it is dissimilar. 



Again : — " When a single metal is placed in contact with an 

 electrolyte, a definite difference of potentials is produced between 

 them ; zinc in water becomes negative, copper in water becomes 



* Electrostatics, p. 317, § 400. 

 t Thermodynamics, p. 66, § 116. 

 X Electricity and Magnetism, p. 22. 



