Department of Chemical Research,. 425 



dissipated by conduction or otherwise, they continue in- 

 cessantly in movement until some cause arises to prevent 

 them," and associating it with Newton's third law of motion, 

 viz., that "the actions of bodies upon one another are 

 always equal and in opposite directions," we are driven to the 

 inference that what we term " chemical affinity," or the 

 immediate active cause of chemical union, is latent or potential 

 molecular motion and the mutual impact and momentum of 

 the molecules of the uniting substances. When two dissolved 

 substances are brought by admixture of their solutions into 

 mutual contact, a portion of the molecular motion of the one 

 substance is neutralized by an equal amount of opposite 

 motion of the other, and the two portions are converte 1 into 

 free heat, electric current, or other form of energy, and the 

 molecules thus brought into nearer proximity retain their 

 new positions and distances : this agrees with the usual evolu- 

 tion of heat, loss of voltaic energy, depression of electromotive 

 force, and frequent increase of density, w T hich occur during 

 chemical union. According to this view, every dissolved 

 chemical compound is an instance of balanced molecular 

 motion, and it is the neutralized portions of motion which 

 escape as heat and electric current. How far there is any 

 originality in these ideas I leave to other persons to decide. 



Many of the facts evolved by the several researches I have 

 referred to point towards the conclusion that measurements 

 of volta-electromotive force and voltaic energy are essentially 

 measurements of " chemical affinity " between the dissolved 

 substance and the positive metal. An analogous idea has 

 already been suggested by other investigators. E. F. Her- 

 roun, adopting a view of Helmholtz's, has inferred that " the 

 electromotive force of a voltaic cell is a measure of the actual 

 transformation of free energy," and concluded that it " fur- 

 nishes a more accurate measurement of the free energy, and 

 therefore of true chemical affinity, than data derived from 

 calorimetric observations " (Phil. Mag. 1888, xxvii. pp. 230, 

 233). The amounts of voltaic energy lost by two substances 

 during their act of chemical union clearly indicate to a large 

 extent the quantities of opposite molecular motion neutralized 

 by their union. For instance, a much larger amount of such 

 motion is neutralized by the union of sodium with chlorine to 

 form sodic chloride than by that of hydrogen with chlorine to 

 form hydrochloric acid ; and no doubt, by investigating the 

 losses of electromotive force and voltaic energy attending the 

 chemical union of substances in aqueous solution, we may 

 learn a very great deal respecting the quantitative relations 

 of " chemical affinity " between metals and electrolytes; bur 



Phil. Mag. 8. 5. Vol. 20. No. 180. May 18H0. 2 K 



