Electromotive Force to Pressure fyc. Ill 



influence of pressure upon the electric potential of the metal 

 alone and upon that of the liquid alone at each electrode. 



It is probable that an investigation of the effect of pressure 

 upon the electric potential of the metal alone and upon that 

 of the electrolyte alone would yield more uniform results 

 than that of its effect upon the electromotive force of the two 

 substances in mutual contact, because the conditions would then 

 be more simple ; but as the effect upon the potential produced 

 by a single compression would be extremely small, a series of 

 compressions, with the effects of them accumulated by means 

 of an electric condenser as in an influence machine, would be 

 necessary in order to render the effect manifest. Such a 

 research would probably show that pressure increases the 

 positive potential of positive substances and the negative 

 potential of negative ones. As pressure increases electro- 

 motive force it must increase the two kinds of electric potential 

 which constitute that force ; thus in a case where a current 

 occurs with a closed circuit, the two potentials are always pro- 

 duced if the circuit is open. The facts also that the largest 

 currents in the present research usually occurred with the 

 most positive metals and the most negative electrolytes (see 

 exps. 3 and 6), and the smallest frequently, though not in- 

 variably, happened with the most positive electrolytes (see 

 exps. 33, 34, 42, 43, 49, 50), support this hypothesis. Some 

 of the cases in which no appreciable current was produced, 

 or in which reverse ones occurred, might have been due to 

 the pressure increasing the electropositive potential of the 

 liquid as fast as, or faster than, that of the metal. 



Although some effect of the atomic or molecular weights 

 of the substances employed upon the direction or magnitude 

 of the currents must have occurred, none was observed (see 

 Table III.) ; many additional experiments would probably be 

 necessary to properly examine this question. I have not 

 been able to suggest any explanation of the circumstance that 

 diluted acids did not in any case produce a current ; nor have 

 I been able to investigate in what manner the pressure may 

 have affected the direction of motion of the molecules of the 

 combining substances, but possibly some information might 

 be obtained by examining the influence of pressure upon the 

 thermal spectra of the substances and comparing the results 

 with those obtained in this research. As the properties and 

 molecular motions of substances vary with every change of 

 temperature, it is probable that the electromotive force pro- 

 duced by unequal mechanical pressure would vary with the 

 temperature of the metal and electrolyte. 



