Tioo Fluids, and of Tivo Metals not in Contact. 493 



alone, therefore, no measure for the diiference of the electro- 

 motive forces here entering into action, the determination of 

 which, however, is the sole object of the present inquiry. I 

 have therefore, in the following experiments, chiefly directed 

 my attention to the accurate determination of the direction of the 

 current; its relative intensity, being dependent on too many 

 circumstances, is only given approximately : the magnitude of 

 the deflections of the needle were, however, always carefully 

 noted. 



M. Vorsselman de Heer, in his valuable memoir on Electric 

 Telegraphy*, states of this numerator, after having observed 

 that it depends on the nature of the metals, and not on their 

 dimensions ; that its value is not altered when salts, alkalies, or 

 acids, which, like sulphuric acid, or nitric acid, are not electro- 

 lyzable, are added to the water ; but that it undergoes a change 

 when the body which is added is itself an electrolyte, for in- 

 stance hydrochloric acid, in which case the numerator would 

 be smaller. 



According to Faraday, who, however, is not acquainted with 

 Ohm's theor}', this numerator would be greater, the stronger 

 the; affinity of the positive metal, the zinc, is for the oxygen, 

 chlorine, or electro-negative constituent of the fluid in general ; 

 it must, however, be here observed, that we possess at present 

 nothing more than approximate valuations from which we may 

 judge of the energy of a chemical affinity. 



The main result of my experiments has proved in the most 

 positive manner that the value of the numerator in Ohm's for- 

 mula, or the magnitude of the electromotive force in general is 

 altered, sometimes increased, sometimes diminished, by any sub- 

 stance added to the ivater, be it an electrolyte or not, and indeed 

 {which shoiddbe well observed') increased for one metal combina- 

 tion, and diminished, for another, by the same substance, added to 

 the water in the same 'proportion. 



Nor have I been able to find that this force stands in direct 

 ratio to the energy of the affinity between the jwsitive metal and 

 the negative constituent of the fluid. It is weak in cases ivhere 

 this energy must be considered as strong, and on the contrary 

 strong where but a weak affinity can be admitted. Frequently, 

 indeed, a current originates, and at times a powerful one, ivhere, 

 to judge from the affinity, not the slightest action should be ex- 

 pected. 



Sufficient proofs of this will be found in the statements con- 

 tained in the following Tables. 



To render these Tables intelligible, it may be observed that 



* Poggendorifs Jnnale^i, vol. xlvi. p. 516. 



