3 io HERMANN VON HELMHOLTZ 



move with the positive electricity kations, and those charged 

 with the negative electricity anions ; the kation therefore travels 

 to the electrode to which the positive electricity of the fluid is 

 directed, to the kathode, and the anion to the anode, whence the 

 same electricity streams into the fluid. Faraday discovered the 

 law that governs the whole of modern electro-chemistry, viz. 

 that there is always equivalence of electrical and chemical 

 motion in each section of an electrolytic conductor, so that 

 precisely the same quantity of positive or negative electricity 

 moves along with each monovalent ion, or each valency of a 

 multivalent ion, and accompanies it inseparably in all the 

 motions which it makes through the fluid. Helmholtz called 

 this quantity the electrical charge of the ion. Assuming that 

 electricity also is divided into certain elementary quantities, or 

 atoms of electricity, he concludes that each ion, so long as it 

 moves through the fluid, must be united with one electrical 

 equivalent for each of its valencies. Separation can only occur 

 at the surfaces of the electrodes, so that if these exert sufficient 

 electromotive force, the ions will give up their previous charges 

 of electricity, and become electrically neutral. Maintaining 

 the law of the conservation of energy, as well as the strict 

 validity of Faraday's law of electrolysis, as fundamental principles, 

 he finds that if the hydrogen and oxygen of the water could be 

 dissociated without losing their electrical charges, they would 

 exert a reciprocal attraction equal to the gravitation of masses 

 which exceeded them 400,000 billion times in weight. In the 

 further investigation of the mode in which the motions of the 

 ponderable molecules are affected by these forces, Clausius had 

 shown that the electrical forces tend to maintain an even 

 distribution of the antagonistic ions throughout the fluid, so 

 that all parts of it are neutralized both electrically and chemically ; 

 but that the least external electromotive force suffices to disturb 

 the uniformity of this distribution. But when an ion parts with 

 its charge of electricity, the electrical forces of the battery 

 encounter a resistance which entails a very considerable 

 expenditure of work before it can be overcome. This happens 

 if the ions, as they lose 'their electrical charges, are simul- 

 taneously separated from the fluid as gases, or in the form of 

 solid metallic layers. The chemical association of two elementary 

 substances of great affinity produces quantities of heat which 



