49 
results ; part of the water is decomposed into its consti- 
tuent elements, oxygen and hydrogen ; the oxygen unites 
with the zinc, and the oxide of zinc formed is dissolved 
by the sulphuric acid. A number of atoms of hydrogen, 
equivalent to the oxygen, uniting with the zinc, pass to 
the platina plate, and are then given off in a gaseous form. 
An electric current passes from the zinc through the liquid 
to the platina, and by the metallic circuit or communicating 
wire, from the platina to the zinc ; and if, by means of the 
galvanometer, we examine the quantity and intensity of the 
current passing, we shall find the intensity corresponding 
to four grains supported by the hundred feet coil, and the 
quantity corresponding to the size and distance of the plates, 
and the length of the circuit through which the current has 
to pass ; if we change either of the metallic plates, we shall 
find a difference in the electro-motive force or intensity, 
and a corresponding alteration in the quantity. If we sub- 
stitute for a clean and bright surface of platina, a surface 
of platina, or silver platinised, that is, covered with platina 
in the form of black powder, we shall, without a change of 
intensity, have a considerable change in the quantity of the 
current ; for the hydrogen, which, in the case of smooth 
platina, adhered to the surface, is now given off more freely. 
It therefore appears that the difficulty of getting rid of the 
hydrogen is a resistance to the chemical action, and to the 
current. Again, if we for the plate of platina substitute a 
plate of copper, immersed in a solution of sulphate of cop- 
per, forming Daniel's arrangement, the copper solution 
being prevented from mixing with the dilute sulphuric 
acid in which the zinc is placed, by a diaphragm of porous 
earthenware or other porous material, we shall find that 
hydrogen is not now given off at the copper surface, but 
that the sulphate of copper in the solution is decomposed, 
and metallic copper precipitated on the copper plate. On 
VOL. III. d 
