Department of Chemical Be sear c7i. 403 



The degree of sensitiveness of the balance therefore in- 

 creased directly as the degree of dilution of the solution. 



A. Curves obtained by Varying the Strength of the 

 Solution at both Metals. 



Nearly all the measurements of electromotive force given in 

 this paper were made with highly pure substances, and in sec- 

 tion "A," with the exception of one instance only (see fig. 8), 

 each curve starts from the potential of unamalgamated zinc 

 and platinum in distilled water at about 16° C. = 1*127 volt. 

 The quantity of distilled water employed as the solvent was 

 in nearly every case 155 grains, and the series of degrees of 

 strength of the solutions of each substance were usually such 

 as could best be worked by the process, i. e. neither too strong 

 nor too weak, and were with different substances either the 

 same or so arranged as to best enable comparisons to be made 

 between the results of the different series of measurements ; 

 they were not always sufficiently strong to fully develop the 

 most characteristic curves. 



For each separate measurement, with the solutions of the 

 halogens and the strong ones of the acids, a fresh portion of 

 the original liquid was taken ; with those of other substances 

 the zinc was so feebly acted upon and the liquid so slightly 

 altered in composition, that this was not found necessary. With 

 solutions of salts, the presence of films of oxide upon the zinc 

 was tested for by replacing the saline liquid by distilled water, 

 and then observing whether the cell was still exactly balanced 

 by a zinc-platinum water one. No trouble was experienced 

 from polarization caused by hydrogen in the platinum plates, 

 nor by atmospheric air dissolved in the water. 



1. Curves of Chlorine, Bromine, and Iodine, 



The range of strength of the. solutions of each substance 

 was from '001 to '01 grain in 155 grains of water. With 

 solutions of these substances the degree of electromotive force 

 increased somewhat with the period of immersion ; this diffi- 

 culty was due to the great chemical energy of the substances, 

 and was overcome by making the fluctuations of the gal- 

 vanometer-needles equal on each side of zero. 



These curves show : — 1st. An increase generally of electro- 

 motive force attending increased strength of solution. 2nd. 

 A much greater increase caused by the first amount of sub- 

 stance added than by the subsequent additions. 3rd. A 

 gradation of degree, both of first increase and of maximum 

 electromotive force in the three curves, varying inversely as 



