Department of Chemical Research. 409 



5. Curves o/HCl, HBr, and HI. 

 b. Strong Solutions. 



These solutions were one hundred times stronger than the 

 previous ones in order to fit them for comparison with those 

 of the corresponding salts ; they contained from '10 to 1*0 

 grain of substance in 155 grains of water. The degrees of 

 electromotive force of the solution of hydrochloric acid were 

 variable, and those of the other two acids less so. 



These curves are drawn upon a scale 2*92 times as large 

 vertically as those of the previous ones, in order to fit them 

 for comparison with those of the corresponding salts. They 

 show : — 1st. A general increase of electromotive force attend- 

 ing gradually increased strength of liquid. 2nd. A much 

 larger increase produced by the first amount of substance 

 added than by the succeeding ones. 3rd. A gradation of 

 degree of general increase of such force varying inversely as 

 the magnitudes of the molecular weights of the substances. 

 And 4th. A great dissimilarity of form characteristic of each 

 individual substance. 



By comparison with the curves yielded by the weak solu- 

 tions of the three acids, those of the strong ones show : — 1st. 

 A much greater increase of electromotive force, both on the 

 addition of the first amount of the substance and by the subse- 

 quent additions. 2nd. A more distinct relation of those 

 increases to the magnitudes of the molecular weights of the 

 substances. 3rd. Much more characteristic curves. And 4th. 

 A much greater degree of irregularity of form of curve ; this 

 greater irregularity of form was a genuine effect, and was not 

 due to temporary fluctuations of the current. 



6. Curves of HC1 with Cadmium as Positive Metal. 



The range of degrees of strength of the solutions in this 

 case was the same as that of the " strong " solution of the 

 same acid in the immediately previous group of acids, and the 

 scale of magnitude upon which the curve is drawn is the 

 same. The electromotive force was variable, owing to the 

 strength of the solutions, and of course started from a lower 

 point than when zinc was used as the positive metal. 



On comparing the curve with the one yielded by zinc in the 

 same degrees of strength of solution of the same acid, we 

 find : — 1st. Quite a different form of curve. 2nd. A smaller 

 increase of electromotive force on adding the first portion of 

 acid. 3rd. A general decrease of that force by the further 

 additions. And 4th. A curve characteristic of the substance. 



Phil. Mag. S. 5. Vol. 29. No. 180. May 1890. 2 I 



