neighborhood of 15,000 amperes. Laboratory voltameters frequently have
a resistance of a hundred ohms; it would require a million in
derivation to produce the same effect. The specific resistance of the
solutions that can be employed in the production of gases by
electrolysis is, in round numbers, twenty thousand times greater than
that of mercury. In order to obtain a resistance of 0.0001 of an ohm,
it is necessary to sensibly satisfy the equation

20,000 l/s = 1/10,000

_l_ expressing the thickness of the voltameter expressed in meters,
and _s_ being the section in square millimeters. For example: For l =
1/10, s = 20,000,000, say 20 square meters. It will be seen from this
example what should be the proportions of apparatus designed for a
production on a large scale.

The new principles that permit of the construction of such voltameters
are as follows: (1) the substitution of an alkaline for the acid
solution, thus affording a possibility of employing iron electrodes;
(2) the introduction of a porous partition between the electrodes, for
the purpose of separating the gases.

_Electrolytic Liquid._--Commandant Renard's experiments were made with
15 per cent, solution of caustic soda and water containing 27 per
cent. of acid. These are the proportions that give the maximum of
conductivity. Experiments made with a voltameter having platinum
electrodes separated by an interval of 3 or 4 centimeters showed that
for a determinate E.M.F. the alkaline solution allows of the passage
of a slighter intenser current than the acidulated water, that is to
say, it is less resistant and more advantageous from the standpoint of