t may be seen, then, that
the apparatus will have a considerable useful effect without its being
necessary to waste the electric energy beyond measure.

_Industrial Apparatus._--We have shown how the very concise researches
of Commandant Renard have fixed the best conditions for the
construction of an industrial voltameter. It remains for us to
describe this voltameter itself, and to show the rendering of it.

[Illustration: FIG. 3.--PLANT FOR THE INDUSTRIAL ELECTROLYSIS OF
WATER.]

The industrial voltameter consists of a large iron cylinder. A battery
of such voltameters is shown to the left of Fig. 3, and one of the
apparatus, isolated, is represented in Fig. 4. The interior electrode
is placed in an asbestos cloth bag, which is closed below and tied at
its upper part. It is provided with apertures which permit of the
ascent of the gases in the interior of the cylinder. The apparatus is
hermetically sealed at the top, the two electrodes being naturally
insulated with rubber. Above the level of the liquid the interior
electrode is continuous and forms a channel for the gas. The hydrogen
and oxygen, escaping through the upper orifices, flow to the
compensator. The apparatus is provided with an emptying cock or a cock
for filling with distilled water, coming from a reservoir situated
above the apparatus.

[Illustration: FIG. 4.--DETAILS OF AN INDUSTRIAL VOLTAMETER.]

The constants of the voltameter established by Commandant Renard are
as follows:

Height of external electrode 3.405 m.
" internal " 3.290 "
Diameter of external " 0.300 "
" internal " 0.174 "

The iron plate employed is 2 millimeters in thickness. The electric
resistance is about 0.0075 ohm. The apparatus gives 365 amperes under
2.7 volts, and consequently nearly 1 kilowatt. Its production in
hydrogen is 158 liters per hour.

It is clear that, in an industrial exploitation, a dynamo working
under 3 volts is never employed. In order to properly utilize the
power of the dynamo, several voltameters will be put in series--a
dozen, for example, if the generating machine is in proximity to the
apparatus, or a larger number if the voltameters are actuated by a
dynamo situated at a distance, say in the vicinity of a waterfall.
Fig. 3 will give an idea of a plant for the electrolysis of water.

It remains for us to say a few words as to the net cost of the
hydrogen and