Passage of Electricity through Liquids, 275 



whole of the partial molecules which are in contact with one 

 another, the case may occur, that one of several salts dissolved 

 simultaneously in the same will be decomposed, but the others 

 or the liquid itself will not undergo decomposition. 



The quantity — in the expression 4, § 52, is the same for all 



molecules of the different chemical combinations contained in 

 the column of liquid, but the quantity (Be — BV) is different. 

 Now, if 



(Be-BV)±>R 



(that is, greater than the force which, owing to chemical mole- 

 cular forces, holds the partial molecules together), then a sepa- 

 ration of the partial molecules takes place. If this is not the 

 case, then no decomposition of the corresponding chemical com- 

 bination is perceived. 



This appears to be the reason why, when an electrical current 

 passes through saline solutions, there is usually only a decom- 

 position of the salt and not of the solvent ; for the electrical 

 forces are sufficient to separate the partial molecules of the salt 

 from one another, but not those of the solvent. 



According to expression 4, a decomposition of the water in the 

 same aqueous saline solution must be set up when the section of 

 the liquid is diminished. 



The opinion that in the same aqueous saline solution it is 

 sometimes the water which is decomposed and sometimes not, 

 has been already advanced by Magnus-^, who pointed out the 

 limit of intensity of the current by which the decomposition of 

 a salt or of one constituent of a saline solution occurs (which he 

 terms limit or limiting value f) as independent, first of the mag- 

 nitude of the electrodes, secondly of the tendency to decompo- 

 sition of the different constituents of the electrolytes, and thirdly 

 of the proportion in which these are found in the solution. 



This view of the matter was opposed by Hittorf J, who con- 

 ceived the phenomenon observed by Magnus, that at the cathode, 

 with a current of definite density in a solution of blue vitriol, no 

 hydrogen is liberated, to be a secondary chemical effect, because 

 hydrogen in statu nascente has the property of reducing copper 

 from blue vitriol. 



- Now, in order to decide this question, I have performed the 

 following experiments. A prism-shaped trough, 136-5 millims. 

 long, 25 miUims. broad, and 50 millims. high, made of glass 

 plates fastened together with sealing-wax, was divided into two 



* Pogg. Ann. vol. cii. (1867) p. 33, § 61. 



t Ibid. p. 15, § 31. X Ibid. vol. cvi. (1859) pp. M^-'db^. 



T2 



