376 SCIENCE PROGRESS. 



velocity past each other. Consider what will occur if they 

 move with unequal speeds. Suppose that the anions move 

 faster than the kations. In that portion of the solution 

 which surrounds the anode, ions will arrive faster than in 

 the portion surrounding the kathode, while those leaving it 

 leave more slowly. Hence the strength of the solution 

 near the anode will become greater than that of the solu- 

 tion near the kathode. In the case of an electrolytic cell 

 with platinum electrodes, in which the quantity of salt in 

 solution continually diminishes, this implies that more of 

 the salt decomposed will come from the neighbourhood of 

 the kathode than from the neighbourhood of the anode, 

 and that the quantities of salt taken from the solutions near 

 the anode and kathode, respectively, are in the ratio of the 

 velocity of the kation to the velocity of the anion. 



In nearly every case phenomena of this kind are actually 

 found to occur. Thus, if an electrolytic cell, with platinum 

 electrodes, containing a solution of hydrochloric acid, is 

 divided into three portions by partitions of porous earthen- 

 ware, when the current is passed no change occurs in the 

 central division, but the strength of solution in the divisions 

 containing the electrodes becomes less — the anode division 

 losing its contents much faster than the kathode division. 

 From this observation Hittorf concluded by the reasoning 

 given above that the hydrogen travelled faster than the 

 chlorine. He described the phenomenon as the "Migra- 

 tions of the ions ". Let us, for example, take the case of a 

 solution whose strength is one-tenth of a gram-equivalent 

 of hydrochloric acid (3*64 grams) per litre. We should find 

 that when such a solution is electrolysed, out of each gram 

 of HC1 decomposed, "21 gram was taken from the anode 

 solution, and 79 gram from the kathode solution. The 

 ratio of the velocities of the hydrogen and chlorine ions 

 must therefore be as 79 : 21. 



Now the relative velocity of the ions past each other 

 is the sum of the opposite absolute velocities. We have, 

 therefore, only to divide the relative velocity, '00357 centi- 

 metres per second, into two parts, in the ratio 79 : 21, in 

 order to find that in a decinormal solution of hydrochloric 



