influence or indifference of
extensive variations in the size of the electrodes, for which purpose
instruments like those last described (709. 710. 711.) were used. One of
these had plates 0.7 of an inch wide, and nearly four inches long; another
had plates only 0.5 of an inch wide, and 0.8 of an inch long; a third had
wires 0.02 of an inch in diameter, and three inches long; and a fourth,
similar wires only half an inch in length. Yet when these were filled with
dilute sulphuric acid, and, being placed in succession, had one common
current of electricity passed through them, very nearly the same quantity
of gas was evolved in all. The difference was sometimes in favour of one
and sometimes on the side of another; but the general result was that the
largest quantity of gases was evolved at the smallest electrodes, namely,
those consisting merely of platina wires.

715. Experiments of a similar kind were made with the single-plate,
straight tubes (707.), and also with the curved tubes (708.), with similar
consequences; and when these, with the former tubes, were arranged together
in various ways, the result, as to the equality of action of large and
small metallic surfaces when delivering and receiving the same current of
electricity, was constantly the same. As an illustration, the following
numbers are given. An instrument with two wires evolved 74.3 volumes of
mixed gases; another with plates 73.25 volumes; whilst the sum of the
oxygen and hydrogen in two separate tubes amounted to 73.65 volumes. In
another experiment the volumes were 55.3, 55.3, and 54.4.

716. But it was observed in these experiments, that in single-plate tubes
(707.) more hydrogen was evolved at the negative electrode than was
proportionate to the oxygen at the positive electrode; and generally, also,
more than was proportionate to the oxygen and hydrogen in a double-plate
tube. Upon more minutely examining these effects, I was led to refer them,
and also the differences between wires and plates (714.), to the solubility
of the gases evolved, especially at the positive electrode.

717. When the positive and negative electrodes are equal in surface, the
bubbles which rise from them in dilute sulphuric acid are always different
in character. Those from the positive plate are exceedingly small, and
separate instantly from every part of the surface of the metal, in
consequence of its perfect cleanliness (633.); whilst in the liquid they
give it a hazy