152 Intelligence and Miscellaneous Articles. 



soluble hydrates, an alkaline reaction is observed above the bound- 

 ary in the dilute solution, even with no great difference of con- 

 centration when dimethyl-orange is present, but not with less 

 sensitive reagents. Ghnelin* found in the electrolysis of Na 2 S0 4 

 in water, and of CaN 2 6 in water, in the presence of tincture of 

 mallow, that the formation of acid or of alkali started from the 

 electrode, and proceeded slowly towards the boundary. Davy 

 observed this also with K 2 S0 4 in water and solution of litmus. 



Observations made using the far more sensitive dimethyl-orange 

 as reagent do not confirm this. A rapid alkalinity is observed 

 about a millimetre above the boundary, and with great differences 

 of concentration the reaction takes place as rapidly above the 

 boundary as at the electrode. 



As regards the cause of this deposition at the boundary, which 

 was first observed by Faraday in the case of magnesium sulphate, 

 Gr. "Wiedemann t ascribes it to the different degrees of migration 

 in the solutions. KohlrauschJ has objected to this, that a 

 difference-rate of migration of the two solutions can only affect 

 the change of concentration at the boundary, but cannot produce 

 any excess of one ion. 



From Hittorf s numbers for the rate of migration, the following 

 conclusions may be formed : — 



The influence of dilution on the rate of migration is seen to 

 differ with the nature of the electrolyte. In most cases the migra- 

 tion of the anion decreases with increasing dilution, that of the 

 kation increases in the same degree. With chloride of potassium 

 the rates of migration are independent of the concentration ; with 

 the nitrates of silver, potassium, and sodium, the migration of the 

 anion increases with dilution, that of the kation decreases. 



If now the processes above the boundary had their origin in the 

 difference of the values for the migration a formation of hydrate 

 might take place in most cases, potassium chloride could show no 

 change above the boundary independent of differences of concen- 

 tration, or at any rate very small ones, while with nitrates of 

 silver, potassium, and sodium a formation of acid is to be expected. 

 But the experiments, using dimethyl-orange as a reagent, are in 

 disagreement with this ; for with the same direction of current 

 chloride of potassium as well as the last-mentioned salts show the 

 same behaviour above the boundary as the other solutions. 



Hence there remains so far only Kohlrausch's explanation, which 

 sees in the action of water in electrolysis the cause of the processes 

 at the boundary, and according to which these phenomena must 

 necessarily follow. It would be desirable that the experiments 

 should be made on a sufficiently large scale to examine the products 

 qualitatively and quantitatively. — "Wiedemann's Annalen, No. 4, 

 1893. 



* Wiedernaim's Electricitat, vol. ii. pp. 599 & 614. 



f EUctr. vol. ii. p. 607. 



\ Wied. Ann. vol. xxvi. p. 210, 1885. 



