Department of Chemical Research.. 421 



The two curves are very different. The greatest variation 

 of electromotive force was at the zinc, and was = *103 volt, 

 whilst that at the surface of the platinum was only = *04 volt. 



The results show that the change of electromotive force 

 which occurred on gradually heating an electrolyte and the 

 two metals in it is a concrete effect of two influences, one of 

 which is situated at the surface of the positive metal and the 

 other at that of the negative one. Each of these two in- 

 fluences itself would also probably be a compound effect of 

 the separate actions of heat upon the metal and upon the 

 liquid. 



These general effects of variation of temperature described 

 in sections " C " and " D " are very similar to those of change 

 of strength of liquid given in sections " A" and " B." 



E. General and Theoretical Considerations. 



The evidence obtained by this research shows : — 1st. That 

 every different electrolytic substance when in aqueous solution 

 gives, by varying the degree of strength of its solution (or by 

 varying its temperature), a different curve of electromotive 

 force. 2nd. That this curve is characteristic of the substance. 

 3rd. That under these conditions, substances which constitute 

 a recognized chemical group yield a series of curves which 

 usually exhibit a gradation of likeness of form. 4th. That 

 the degrees of electromotive force of such a group usually 

 vary in magnitude inversely as the amounts of the atomic 

 and molecular weights of the substances. 5th. That a much 

 greater increase of electromotive force is usually caused by 

 the first amount of substance added to the water than by the 

 subsequent amounts. 6th. That the chemical union of two 

 substances to form a soluble salt is attended by a definite 

 decrease of electromotive force and a definite change of form 

 of curve. 7th. That the substitution of one halogen, acid, or 

 metallic base for another in the composition of a soluble 

 electrolytic salt, is accompanied by a definite amount of change 

 of that force and of the form of its curve ; and it will be 

 possible to trace, by means of these changes, the presence of 

 each halogen, acid, and metal in the various solutions of its. 

 salts. 8th,. That isomeric, solutions, of electrolytic substances 

 give different curves under the same conditions, and may thus 

 be distinguished from each other. 9th. That molecular and 

 chemical changes and their rates, in electrolytes, may be 

 examined and measured by this method. And 10th. That if 

 the solutions of the substances are too weak, the characteristic 

 forms and differences of the curves are not fully developed, 



