348 REPORT— 1887. 



of propyle is only a very bad conductor ; therefore the current does not pass in a 

 sensible way, and we cannot observe the decomposition. In this respect we may 

 refer to the researches of Mr. Bleekrode, in Holland, and Mr. Bartoli, in Italy. 



But, on the other side, we find well-known electrolytes exchanging their ions 

 with elements of other compounds which, without any doubt, are not their ions. 

 So, for instance, chlor-acetic acid (CHjClOOOH), or the ethylic ether of this acid,- 

 and iodide of potassium exchange between each other the chlorine and iodine, 

 though assurediv the ions of chlor-acetic acid are not CI and CH„COOH, but 

 CH^CICOO andH. 



Another difficulty is offered by the alloys. A former observation of Mr. 

 G6rardin that amalgams of sodium grow brittle on one or the other electrode was 

 refuted in my laboratory about eleven years ago by Dr. Obach.' His researches 

 were made with the greatest care, and extended over different alloys, even those 

 which contained definite equivalents of their elements, and which from their other 

 properties seemed to be definite chemical compounds. But no decomposition was 

 observed. Somewhat later Mr. Haga, in Holland, made analogous experiments 

 with the same result. It would give me great satisfaction if Pi-ofessor Austen 

 should confirm these observations. 



After these experiences we must confess that as yet we do not know the general 

 definition of an electrolyte and of its ions. 



II. There is another open question, whether water takes part in the electro- 

 lysis of a dissolved electrolyte. You have heard from Dr. Lodge that the answer 

 to this question is generally negative. On the other hand, Professor F. Kohl- 

 rausch,- in his very remarkable paper on the conduction of some electrolytes in 

 very diluted solutions, came to the opinion that in these solutions water is also 

 decomposed. It would be very desirable that further researches should be made 

 on this subject. 



III. Let us neglect the surely very insignificant decomposition of water, and 

 assume that it plays only a secondaiy part in the electrolysis of solutions. Then 

 we may enter upon the consideration of their electrical resistance. 



It is now generaUy admitted, as I detailed so long ago as the year 1858,^ that 

 the electrical resistance of a solution is determined by the mechanical resistance 

 (friction) the bodies set free by the current encounter in the liquid, by which means 

 the lost motion is transformed into a quantity of heat proportionate to the elec- 

 trical resistance. In the same year I compared this friction with the viscosity of 

 the liquid. I believe this has been often misunderstood, for I find it stated in some 

 memoirs that I should have said the viscosity of a liquid represents directly its 

 resistance. On the contrary, and specially in a paper of the year 1856, I have 

 shown that the friction corresponding to viscosity is different from the friction in 

 the electrolysis of solutions. 



In the year 1870, in the second edition of my 'Treatise on Galvanism,' vol. i. 

 p. 432, 1 have further detailed the three points separately to be considered in this 

 electrolysis, viz., 1st, the friction of the ions in the liquid ; 2nd, the friction of the 

 dissolved electrolyte in the liquid ; Srd, the friction of the whole solution in the 

 vessel, the electrical endosmose. I am happy to state that on these points I agree 

 with my excellent friend, Professor Quinclse, who independently and nearly con- 

 temporaneously evolved the same ideas. 



We will omit the electrical endosmose, which can be eliminated, and deal only 

 with the first two points. 



The friction of the ions alone has been further treated by Professor F. Kohl- 

 rausch, and with the help of the admirable experiments of Professor Hittorf on the 

 migration of ions, and his own most elaborate researches on conductivity, he has 

 shown that, independently of the compound decomposed, each ion has its own 

 constant velocity in the same solvent. The discrepancies which were observed 

 in stronger solutions disappear, as Professor F. Kohlrausch has stated, in most 



' Obach, Pogg. Ann. Ergdnzungslani, vii. 1876, p. 280. 

 - F. Kohlrausch, Wied. Ann. xxvi. 1885, p. 211. 

 » G. W. Pogg. Ann. civ. 1858, p. 169. 



