re usefully described
hereafter (778.).

730. When solutions of caustic potassa or soda, or sulphate of magnesia, or
sulphate of soda, were acted upon by the electric current, just as much
oxygen and hydrogen was evolved from them as from the diluted sulphuric
acid, with which they were compared. When a solution of ammonia, rendered a
better conductor by sulphate of ammonia (554.), or a solution of
subcarbonate of potassa was experimented with, the _hydrogen_ evolved was
in the same quantity as that set free from the diluted sulphuric acid with
which they were compared. Hence _changes in the nature of the solution do
not alter the constancy of electrolytic action upon water_.

731. I have already said, respecting large and small electrodes, that
change of order caused no change in the general effect (715.). The same was
the case with different solutions, or with different intensities; and
however the circumstances of an experiment might be varied, the results
came forth exceedingly consistent, and proved that the electro-chemical
action was still the same.

732. I consider the foregoing investigation as sufficient to prove the very
extraordinary and important principle with respect to WATER, _that when
subjected to the influence of the electric current, a quantity of it is
decomposed exactly proportionate to the quantity of electricity which has
passed_, notwithstanding the thousand variations in the conditions and
circumstances under which it may at the time be placed; and further, that
when the interference of certain secondary effects (742. &c.), together
with the solution or recombination of the gas and the evolution of air, are
guarded against, _the products of the decomposition may be collected with
such accuracy, as to afford a very excellent and valuable measurer of the
electricity concerned in their evolution_.

733. The forms of instrument which I have given, figg. 64, 65, 66. (709.
710. 711.), are probably those which will be found most useful, as they
indicate the quantity of electricity by the largest volume of gases, and
cause the least obstruction to the passage of the current. The fluid which
my present experience leads me to prefer, is a solution of sulphuric acid
of specific gravity about 1.336, or from that to 1.25; but it is very
essential that there should be no organic substance, nor any vegetable
acid, nor other body, which, by being liable to the action of the oxygen or
hydrogen evolved at the