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 accompaniéd by a chemical 
action which determines the formation of an oxide or a sulphuret. 
3. The following experiment shows the influence of chemical action 
in phenomena of this kind. Ifa 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 difference 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 ery- 
stals of tin; wires of zine, silver and lead, plunged in their respective 
solutions exhibit the same phenomena. 
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 wires 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 
wires, 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. 
