388 ELEMENTARY LESSONS ON [CHAP. XL 



each H atom uniting with the Cl atom belonging to the 

 neighbouring molecule, a + half molecule of hydrogen 

 being liberated at the kathode, and a half molecule 

 of chlorine at the anode. This action would leave the 

 molecules as in 3, 3, and would, when repeated, result 

 in a double migration of hydrogen atoms in one direc- 

 tion and of chlorine atoms in the other, the free atoms 

 appearing only at the electrodes, and every atom so 

 liberated discharging a certain definite minute charge of 

 electricity upon the electrode where it was liberated. 1 



Clausius has sought to bring the ideas of Grotthuss 

 into conformity with the modern kinetic hypothesis of 

 the constitution of liquids. Accordingly, we are to 

 suppose that in the usual state of a liquid the molecules 

 are always in movement, gliding about amongst one 

 another, and their constituent atoms are also in move- 

 ment, and are continually separating and recombining 

 into similar groups, their movements taking place in all 

 possible directions throughout the liquid. But under 

 the influence of an electromotive-force these actions are 

 controlled in direction, so that when, in the course of the 

 usual movements, an atom separates from a group it 

 tends to move either toward the anode or kathode ; 

 and if the electromotive force in question be powerful 

 enough to prevent recombination, these atoms will be 

 permanently separated, and will accumulate around the 

 electrodes. This theory has the advantage of account- 

 ing for a fact easily observed, that an electromotive force 

 less than the minimum which is needed to effect com- 

 plete electrolysis may send a feeble current through an 



1 Mr. G. J. Stoney has lately reckoned, from considerations founded on 

 the size of atoms (as calculated by Loschmidt and Sir W. Thomson), that 

 for every chemical bond ruptured, a charge of io~ 20 of a weber is trans- 

 ferred. This quantity would appear therefore to be the natural atomic 

 charge or unit. To tear one atom of hydrogen from a hydrogen compound 

 this amount of electricity must be sent through it. To liberate an atom of 

 zinc, or any other di-valent metal from its compound, implies the transfer 

 of twice this amount of electricity. 



