416 M. BECQUEREL ON CHEMICAL DECOMPOSITION AND 



soldered or only touch one another at given points. In the first case 

 the current has always the same direction, whether we heat the wire to 

 the right or the left of the points of junction ; in the second it is not 

 so. The only difference arises from there being in the one only simple 

 contact, while in the other there is contact accompanied by a chemical 

 action which determines the formation of an oxide or a sulphuret. 



3. The folloAving experiment shows the influence of chemical action 

 in phaenomena of this kind. If a piece of sulphur be burnt at one of 

 the extremities of a copper wire which forms the circuit of a galvano- 

 meter, and the other end be placed over it at the moment that the com- 

 bustion is in full power, the current of electricity which then takes place 

 is one of the most energetic, and more intense than the one which pro- 

 ceeds from a simple difl'erence of temperature. 



Suppose now a tube curved in the form of a U, containing a solution 

 of nitrate or of sulphate of copper ; plunge into each branch a cop- 

 per wire, communicating with the end of a wire forming the apparatus 

 we have just described ; after one hour's experiment that end which cor- 

 responds to the negative side is covered with copper precipitated in a 

 metallic state, while the other is sensibly oxidized. Two tin wires, pre- 

 pared in the same manner as the copper wires, and plunged into a so- 

 lution of hydro-chlorate of tin, give the same results; that is, that wire 

 which communicates with the negative side will be covered with cry- 

 stals of tin ; wires of zinc, silver and lead, plunged in their respective 

 solutions exhibit the same phsenomena. 



Platina wires are without action in a solution of platina. We here 

 perceive the influence of the chemical action which takes place between 

 the wires and the solutions upon electro-chemical decomposition. 



Platina, gold, and silver wires, plunged in solutions of lead, tin, or cop- 

 per, and prepared as those above, are equally without action on them, 

 although the current has always the same intensity. 



When two silver Mires are plunged into solutions of sulphate or ni- 

 trate of copper, the positive wire is always attacked by the acid, and 

 the precipitate is not sensibly formed on the negative wire. The oxy- 

 gen and the acid appear therefore in this case to be more easily trans- 

 ported to the positive pole than the copper to the negative pole. 



Platina wires produce a precipitate in nitrate of silver as well as silver 

 Avires, with this difference that it is more abundant on those of silver than 

 on those of platina. This difference appears plainly by immersing at 

 the same time a silver wire rolled round a platina wire in a solution. 



Thus, we see that with weak currents of equal intensity, the easily re- 

 ducible metals are disposed to be precipitated more readily from their 

 solutions upon plates of the same than upon plates of any other metal 

 than that which enters into the solution, and which does not of itself pro- 

 duce a precipitate, as iron when plunged into a solution of copper does 



I 



