282 M. De la Rive's Researches 



tricities, applies also to the production of electric currents in a 

 pair. In very lively chemical actions the larger proportion of 

 the two electricities developed often undergoes this recompo- 

 sition ; a small part only runs through the whole circuit, espe- 

 cially if it be not a very good conductor ; which is the reason 

 that the strongest currents are not always those produced by 

 the most lively chemical actions, and that in a pair the metal 

 the most attacked is not always the positive one, that is, the one 

 whence the current commences. However, the latter case oc- 

 curs only when each of the two metals of the pair are immersed 

 in different liquids; a single example shall be given. A plate 

 of zinc is placed in concentrated sulphuric acid, and a plate of 

 copper is immersed in nitric acid ; the two acids are imme- 

 diately in contact, and the two metallic plates communicate 

 by means of the wire of a galvanometer. In this pair the 

 zinc is positive though it be much less attacked than the cop* 

 per; because the two electricities developed by the action of 

 the sulphuric acid upon the zinc can be more easily reunited 

 by making the tour of the circuit, than by passing from the 

 sulphuric acid to the zinc, and reciprocally ; while, on the 

 contrary, the two electricities developed by the action of the 

 nitric acid upon the copper reunite immediately with the 

 greatest facility, in consequence of the conductibility of the 

 nitric acid, and the ready passage of the electric current from 

 that acid to the copper ; while to make the circuit they would 

 be obliged to traverse the concentrated sulphuric acid, 

 which is a very imperfect conductor, and pass from the 

 zinc to the acid, — a very difficult passage. Two circumstances 

 prove the exactitude of this explanation : 1. The same result 

 is obtained in the preceding experiment by substituting a plate 

 of zinc, similar to that which is immersed in the sulphuric acid, 

 for the plate of copper immersed in the nitric acid. 2. If a 

 capsule of platina be put upon the plate of the condenser, and 

 filled in succession with nitric acid, and concentrated sul- 

 phuric acid, and a plate of copper or of zinc, held between 

 the fingers, be immersed in the first-mentioned liquid, and a 

 plate of zinc in the second, a much stronger positive electri- 

 city is obtained in the second case than in the first. 



The foreign substances which are often mixed with metals 

 greatly facilitate this immediate recomposition, by giving rise 

 to local actions. Thus, as I have already shown,* the lively 

 action of diluted sulphuric acid upon common zinc is due 

 to a small proportion of iron contained in the zinc, and to the 

 electrical currents which, taking place upon its surface, pass 



• Bibl. Univer., April 1830. [See also Phil. Mag. and Annals, N. S. 

 vol. viii, p. 298. Edit.] 



