Order of Metals Changed by Dilution 291

order must again be changed (969); nay, more, that with the
same acid, and merely by changing the proportion of dilution,
such alteration of the order must take place (974, 976).

980. Thus it appears, as before remarked (970), that to apply
the theory of contact electromotive force to the facts, that
theory must twist and bend about with every variation of
chemical action; and after all, with every variety of contact,
active and inactive, in no case presents phenomena independent
of the active exertion of chemical force.

981. As the influence of dilution and concentration was so
strong in affecting the relation of different parts of the same
metal to an acid, making one part either positive or negative to
another, I thought it probable that, by mere variation in the
strength of the interposed electrolyte, the order of metals when
in acids or other solutions of uniform strength might be changed.
I therefore proceeded to experiment on that point, by com-
bining together two metals, tin and lead, through the galva-
nometer (903); arranging the electrolytic solution in tube No. i,
strong on one side and weak on the other: immersing the wires
simultaneously, tin into the strong, and lead into the weak
solution, and after observing the effect, re-cleaning the wires,
rearranging the fluid, and reimmersing the wires, the tin into
the weak, and the lead into the strong portion. De la Rive has
already statedl that inversions take place when dilute and
strong sulphuric acid is used; these I could not obtain when
care was taken to avoid the effect of the investing fluid (906):
the general statement is correct, however, when applied to
another acid, and I think the evidence very important to the
consideration of the great question of contact or chemical action.

982. Two metals in strong and weak solution of potash.—Zinc
was positive to tin, cadmium, or lead, whether in the weak or
strong solution. Tin was positive to cadmium, either in weak
or strong alkali. Cadmium was positive to lead both ways, but
most when in the strong alkali. Thus, though there were
differences in degree dependent on the strength of the solution,
there was no inversion of the order of the metals.

983. Two metals in strong and weak sulphuric acid.—Cadmium
was positive to iron and tin both ways: tin was also positive to
iron, copper, and silver; and iron was positive to copper and
silver, whichever side the respective metals were in. Thus none
of the metals tried could be made to pass the others, and so
take a different order from that which they have in acid uniform

1 Annales de Chimie, 1828, xxxvii. p. 240.ith nitric acid and iron or silver