32 Profe8»or A. Orum Brown [Jan. 31, 



Society. The purpose of these investigations was attained, and it 

 was completely proved that in reference to their behaviour as electro- 

 lytes there was no difference between say potassium chloride and 

 potassium nitrate, except that in the latter some ammonia was formed 

 at the cathode by the reducing action of the nascent hydrogen, and it 

 was clearly shown that from au electrolytic point of view all the 

 oxygen acids and their salts fell into line with hydrochloric acid and 

 the chlorides, and that NH4 was electrolytically perfectly analogous 

 to K. There is, however, an interest in these papers beyond this 

 important result. In the earlier part of the work the authors mea- 

 sured the amount of electrolysis not only by " the amount of ions 

 disengaged at either or both electrodes by the primary action of the 

 current or the secondary action of the elements," but also tried to 

 obtain a check to this way of measuring, by using a diaphragm in 

 the electrolytic cell, and analysing the contents of the two parts of 

 the cell, the one on the anode side and other on the cathode side of 

 the diaphragm. This check was " founded on the hypothesis that 

 the voltaic decomposition of an electrolyte is not only effected by the 

 disengagement of its anion and cation at their respective electrodes, 

 but by the equivalent transfer of each to the electrodes, so that the 

 measure of the quantity of matter translated to either side of the 

 diaphragm might be taken as the measure of the electrolysis." They 

 soon found that this hypothesis was unfit to give any such measure- 

 ment, and in the paper of 1844 state that their results show that the 

 hypothesis of equivalent transfer of the ions, "although generally 

 received, is itself destitute of foundation." 



The non-equivalent transfer of the ions, incidentally observed by 

 Daniell and Miller, and imperfectly measured by them in a few 

 cases, was made the subject of a long and elaborate series of experi- 

 ments by Hittorf. The work extended over six years from 18o3 to 

 1859 * and is a monument of patient labour and of happy adaptation 

 of means to a clearly perceived end. The importance of the work 

 was not at first recognised by either physicists or chemists, indeed 

 its meaning was scarcely understood. I shall try to put before you 

 as shortly as I can an outline of the ideas involved in the work, and 

 of the most important conclusions arrived at by Hittorf. As the 

 anions and the cations are separated at their respective electrodes in 

 equivalent quantity, that is, in the case where the valency of anion 

 and cation is the same, in equal numbers, it never occurred to any 

 one to doubt that they travelled towards the electrodes at the same 

 rate, until Daniell and Miller showed that this hypothesis is errone- 

 ous. To follow their reasoning and that of Hittorf we may take an 

 imaginary case, and suppose an electrolyte MX with its cation M 

 and its anion X of such character that these ions when separated at 

 the electrodes can be removed from the solution completely and at 



* Hittorf, Pogg. Ixxxix. p. 177 (1853) ; xcviii. p. 1 (1856) ; ciii. p. 1 (1858) ; 

 cvi. pp. 337 and 513 (1850). Arch. Neerland. (II.) vi. p. 671 (1901). 



