308 Mr. A. Tribe on Electrolysis. [Feb. 17, 



Since bromine and iodine chloride appear to have the same volume in 

 union with ethene that they have when uncombined, it is not unreason- 

 able to suppose that the same may be true of ethene itself, viz. that at 

 its boiling-point it would possess the same volume which it has in the 

 bromide and chloriodide at their respective boiling-points. On this as- 

 sumption the specific gravity of liquid ethene would be — 



Calculated from C 2 H 4 Br 2 0-641 



„ C 2 H 4 IC1 0-624 



III. " Experimental Contributions to the Theory of Electrolysis/' 

 By Alfred Tribe, Lecturer on Chemistry in Dulwich Col- 

 lege. Communicated by J. H. Gladstone, Ph.D., Fullerian 

 Professor of Chemistry in the Royal Institution. Received 

 January 13, 1876. 



In July 1800 Nicholson and Carlisle first effected the decomposition 

 of water by the pile of Volta ; and they were not a little surprised when 

 the constituent gases of the water appeared separately at some con- 

 siderable distance from each other*, but they offered no opinion as to 

 the cause of so singular a phenomenon. A little later Cruickshank also 

 decomposed water by the pile, and, for the first time, many metallic 

 salts f. He also, like Nicholson and Carlisle, was much struck by the 

 appearance of the compounds round poles separated some distance, and 

 attempted to explain the phenomenon by supposing that the principle of 

 galvanism could exist in an oxygenated and deoxygenated condition — 

 that in entering water at the negative end, it combined with oxygen, 

 liberating hydrogen, and that on arriving at the positive end the oxygen 

 either escaped or combined with the wire*. 



This hypothesis, which involves the idea of an imponderable capable 

 of combining with ponderables, underwent various modifications by 

 Eourcroy and Vauquelin and Thenard, and by Dr. Bostock and others. 



But the next step of importance to the theory of electrolysis was the 

 idea of the passage into or through the liquid of one or both constituents 

 of the electrolyte, which was first roughly foreshadowed by an anonymous 

 correspondent of Nicholson's Journal (vol. iv. p. 472), and which was 

 thus more explicitly expressed in 1807 by Sir H. Davy : — " The oxygen 

 of a portion of water is attracted by the positive surface at the same 

 time that the other constituent part, the hydrogen, is repelled by it, and 

 the opposite process takes place at the negative surface ; and in the 



* Nicholson's Journal, Old Series, vol. iv. p. 183. 

 t Ibid. p. 189. 



\ Ibid. New Series, vol, iii. p. 9. 



