inquiry, which was received by the Royal Society on Nov. 30, 1833,
though not so important as those which precede and follow it,
illustrates throughout his strength as an experimenter. The power
of spongy platinum to cause the combination of oxygen and hydrogen
had been discovered by Dobereiner in 1823, and had been applied by
him in the construction of his well-known philosophic lamp. It was
shown subsequently by Dulong and Thenard that even a platinum wire,
when perfectly cleansed, may be raised to incandescence by its
action on a jet of cold hydrogen.

In his experiments on the decomposition of water, Faraday found that
the positive platinum plate of the decomposing cell possessed in an
extraordinary degree the power of causing oxygen and hydrogen to
combine. He traced the cause of this to the perfect cleanness of
the positive plate. Against it was liberated oxygen, which, with the
powerful affinity of the 'nascent state,' swept away all impurity
from the surface against which it was liberated. The bubbles of gas
liberated on one of the platinum plates or wires of a decomposing
cell are always much smaller, and they rise in much more rapid
succession than those from the other. Knowing that oxygen is
sixteen times heavier than hydrogen, I have more than once concluded,
and, I fear, led others into the error of concluding, that the smaller
and more quickly rising bubbles must belong to the lighter gas.
The thing appeared so obvious that I did not give myself the trouble
of looking at the battery, which would at once have told me the nature
of the gas. But Faraday would never have been satisfied with a
deduction if he could have reduced it to a fact. And he has taught
me that the fact here is the direct reverse of what I supposed it to
be. The small bubbles are oxygen, and their smallness is due to the
perfect cleanness of the surface on which they are liberated.