OCTOBEE 9, 1896.] 



SCIENCE. 



509 



stance decomposed is called electrolyte. 

 The battery terminals, or source of current, 

 connected by the electrolyte, are called 

 Electrodes — the one bringing the current to 

 the electrolyte the Anode, the one carrying- 

 it away the Kathode. As a result of the 

 difference of potential of the electrodes, the 

 materially different constituent parts of the 

 electrolyte are impelled to move towards 

 the electrodes; these wandering particles 

 are called ions ; those gathering about or 

 moving towards the anode, anions; those 

 about the kathode, kathions. The chemi- 

 cal changes are observable only at the elec- 

 trodes. Taking as a simple case, ordinary 

 hydrochloric acid — a compound of hydro- 

 gen and chlorine dissolved in water — the 

 passage of the current causes chlorine to 

 appear at the anode and hydrogen at the 

 kathode. The hydrogen and chlorine, while 

 in the solution finding their way to the 

 electrodes, are ions; the chlorine-anion, the 

 hydrogen-kathion. In many cases the ac- 

 tion is not so simple. The electrolytic de- 

 composition may be accompanied by chemi- 

 cal action occurring subsequent to or simul- 

 taneously with the appearance of the ions at 

 the electrodes; the substance formed differ- 

 ing from the ions actually carried to the elec- 

 trode. Changes of this character considera- 

 bly complicate the problem and make the 

 correct interpretation of observed phenom- 

 enadif&cult. This general law may, however, 

 be enunciated: An electrolyte under action 

 Of the current is split into two and only two 

 parts, atoms or groups of atoms, no matter 

 how complex its structure may be. These 

 atoms or atomic groups thus separated , are 

 similar to the ones which exchange places 

 in the ordinary chemical reactions. This 

 early observed law led to the theory advo- 

 cated by Berzelius, that all salts consisted of 

 two atomic groups, one acid the other 

 basic — erroneous, in that the chemical 

 changes subsequent to the electrolytic ac- 

 tion were not properly understood. 



The wondering attention of early inves- 

 tigators had been directed to the curious 

 phenomenon that the substances resulting 

 from electrolysis appeared only at the elec- 

 trodes and were not recognizable in the so- 

 lution between the electrodes. The various 

 theories propounded to explain this vied 

 with one another in improbability. The 

 difficulty of explaining this behavior satis- 

 factorily seems to have led to the abandon- 

 ment of the problem until, in 1805, Chas. 

 J. D. Freiherr Von Grothuss propounded a 

 theory which gave a sufficiently reasonable 

 explanation to be adhered to for fifty years, 

 even quoted to-day in many text-books. 

 Grothuss conceived that each molecule of a 

 chemical compound acted like a conductor 

 consisting of two parts capable of being 

 separated ; these molecules acted upon in- 

 ductively by the charged electrodes, one 

 group would become positively charged, 

 the other negatively, the nature of the 

 charge being determined by the character 

 of the group, being acted upon by attrac- 

 tions and repulsions, varying inversely as 

 the square of the distance from the elec- 

 trodes, the electrified end particles would 

 be attracted to the electrodes ; the remain- 

 ing groups by separation and recombination 

 would at once form a new series of mole- 

 cules as before the action, ready for a repe- 

 tition of the process; no fi:'eely charged 

 groups thus remaining in the mass of the 

 solution between the electrodes. This the- 

 ory demands that the electrical forces be- 

 tween the plates vary inversely as the 

 square of the distance; that, when the 

 force reaches a certain definite magnitude 

 the groups will be separated ; a further 

 consequence is that when this critical force 

 is attained all or a very great number of 

 groups will be separated, instantly, for if 

 this attraction be equal to the force holding 

 the groups together, the whole mass will be 

 in unstable equilibrium, and any increase 

 will cause complete separation of all groups. 



