1824.] produced by the Contact of Metals with Liquids, 8fC 43 



same metal, and the liquid with the finger ; thus the electro- 

 motive action arising from the. contact of the metal under exa- 

 mination with the copper was destroyed, and only the electricity 

 which it had acquired by its contact with the solution remained 

 on the upper plate of the condenser. It is sometimes necessary 

 to place a slip of paper between the metal experimented on and 

 the copper, for the apparatus is so sensible, that a very slight 

 difference in the state of their surfaces would modify the electro- 

 motive action. 



Operating in this way, it was found that by contact with an 

 alkaline solution, the metal, whenever its electrical state can be 

 determined, becomes negative ; and positive with an acid ; but 

 with silver, and in many other instances, the electro-motive 

 action is too feeble to be rendered sensible. 



These results confirm and extend the observations formerly 

 made by Sir Humphry Davy on the electrical effects produced 

 by the contact of metals with acids and alkalies, in a perfectly 

 dry and solid state, between which there is consequently no 

 chemical action ; for they prove that similar effects ensue when 

 the latter substances are in solution, and even when in some 

 cases the contact is accompanied by incipient chemical action. 



In order to understand what is the influence of the fluids in- 

 terposed between the plates of the voltaic instrument, and 

 whether it has any other action than that of a mere conductor to 

 transmit the electro-motive action of the metals from one to the 

 other, it is necessary to ascertain what happens when an acid or 

 alkaline solution is placed between two dissimilar metals. For 

 this purpose, the copper capsule, filled with either an acid or 

 alkaline solution, was placed on the upper plate of the conden- 

 ser, as before ; the solution was then touched with a plate of 

 zinc (taking care not to touch the copper with it), and the lower 

 plate of the condenser with the finger, and after a lapse of 

 twenty seconds, the upper plate was removed ; the gold leaf 

 flew to the positive pole ; consequently the copper capsule had 

 become positive. 



The experiment was reversed by using a capsule of zinc filled 

 with either solution ; and the lower plate of the condenser was 

 touched with a plate of zinc to destroy the electro-motive action 

 between the capsule and the plate, and a plate of copper, held 

 between the fingers, was immersed in the solution. On raising 

 the upper condensing plate, the gold leaf flew to the negative 

 pole, and consequently the zinc capsule had become negative. 

 We see from those two experiments, that when zinc and copper 

 are separated by an acid or alkaline solution, the copper 

 becomes positive and the zinc negative ; just the reverse of 

 what takes place between these metals by simple contact. 



" We have also," says M. Bequerel, " examined what takes 

 place on the contact of a metal with a saline solution ; as cop- 



