RECENT PROGRESS IN PHYSICS. 385 



the solution was deprived of copper ; one equivalent of sulphuric acid 

 had passed into the other cell, but the quantity of copper contained 

 in it remained unchanged ; no cop})er, therefore^ had been transferred 

 from the positive to the negative cell. 



Sulphate of zinc acted in the same manner. 



But these results are not to be attributed to the influence of the dia- 

 phragm. When a long syphon tube reversed was filled with a solu- 

 tion of sulphate of copper and at the ends tv/o strips of the same metal 

 were immersed as electrodes, the color of the fluid became lighter at 

 the negative and darker at the j^ositive pole. 



'' By this it appears demonstrated," says Daniell, " that the metals, 

 which are cajmble of decomposing water at ordinary temperatures, or 

 whose oxides are largely soluble in water, are susceptible of transfer- 

 ence in the Voltaic circuit from the zincode (positive) to the planti- 

 node (negative pole,) while those which are not marked by this strong 

 affinity for oxygen remain stationar}^" 



On impartially considering the circumstance that some bases, by the 

 electrolysis of the solutions of their salts, do not pass to the negative 

 pole, the idea occurs that, in this case, the salt is not directly electro- 

 lized, and does not conduct the current, but that its decomposition is 

 only a secondary phenomenon. When metallic copper is precipitated 

 fiom a solution of sulpliate of copper at the negative pole, while no 

 copper is coming from, but one equivalent of sulphuric acid is passing 

 to the positive pole, it can scarcely be otherwise explained than by 

 supposing that SO4H is directly electrolized ; H goes to the negative 

 pole and reduces one equivalent of copper there, SO^ to the positive and 

 evolves one equivalent 0, leaving one equivalent SO3 behind. This, it 

 is true, is not in agreement with Daniell's views as explained in § 171, 

 which, however, apply to all those cases where the bases of the de- 

 composed salt also suffers a transfer, as, for instance, in the electrolysis 

 of KO -\- SO3. 



§177. Becquerel's researches on the laws of electro-chemical decomposi- 

 tion. — The younger Becquerel has also instituted interesting researches 

 on the laws of electrolysis, (An7i. de Chim. et de Phys. Ser. Ill, T. XI, 

 pp. 162 and 257 ; an abstract in Pogg. Ann. LXV, 401.) Faraday 

 had stated, as a principle, that of the different combinations which 

 may take place between two elements only those are decomposed by 

 the current which consist of an equal numlier of equivalents of either. 



Matteucci had already demonstrated the probability that this prin- 

 ciple was not generally applicable, (Bibl. Univers. Ser. nouv., T. XXI, 

 p. 153,) and J3ecquerel has by numerous experiments removed all 

 remaining doubts upon the subject. 



Becquerel first examined several chlorides of metals in the state of 

 fusion as well as in saturated aqueous solutions. In using the fused 

 chlorides the accuracy of the result was disturbed by the circumstance 

 that the chlorine evolved at the positive pole, becoming diffused 

 through the fluid, in part re-dissolved the metal precipitated at the 

 negative pole, tliereby making the quantity obtained always too small. 

 For this reason Becquerel mostly employed the metallic chlorides 

 dissolved in suitable fluids, after having satisfied himself that as much 

 metal is precipitated from the solutions as from the fused chlorides, 

 25 



