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Page 6
Its electromotive force is very nearly one volt. Its internal
resistance is very low. We may estimate it at 1/3 or 1/4 of an ohm for
polar surfaces one decimeter square, separated by a distance of five
centimeters.
The rendering of these couples is considerable; the small cells shown
in Figs. 1 and 2 give about two amperes in short circuit; the large
one gives 16 to 20 amperes. Two of these elements can replace a large
Bunsen cell. They are remarkably constant. We may say that with a
depolarizing surface double that of the zinc the battery will work
without notable polarization, and almost until completely exhausted,
even under the most unfavorable conditions. The transformation of the
products, the change of the alkali into an alkaline salt of zinc, does
not perceptibly vary the internal resistance. This great constancy is
chiefly due to the progressive reduction of the depolarizing electrode
to the state of very conductive metal, which augments its conductivity
and its depolarizing power.
The peroxide of manganese, which forms the base of an excellent
battery for giving a small rendering, possesses at first better
conductivity than oxide of copper, but this property is lost by
reduction and transformation into lower oxides. It follows that the
copper battery will give a very large quantity of electricity working
through low resistances, while under these conditions manganese
batteries are rapidly polarized.
The energy contained in an oxide of copper and potash battery is very
great, and far superior to that stored by an accumulator of the same
weight, but the rendering is much less rapid. Potash may be employed
in concentrated solution at 30, 40, 60 per cent.; solid potash can
dissolve the oxide of zinc furnished by a weight of zinc more than
one-third of its own weight. The quantity of oxide of copper to be
employed exceeds by nearly one-quarter the weight of zinc which enters
into action. These data allow of the reduction of the necessary
substances to a very small relative weight.
The oxide of copper batteries have given interesting results in their
application to telephones. For theatrical purposes the same battery
may be employed during the whole performance, instead of four or five
batteries. Their durability is considerable; three elements will work
continuously, night and day, Edison's carbon microphones for more than
four months without sensible loss of power.
Our elements will work for a hundred hours through low resistances,
and can be worked at any moment, after several months, for example. It
is only necessary to protect them by a cover from the action of the
carbonic acid of the atmosphere.
We prefer potash to soda for ordinary batteries, notwithstanding its
price and its higher equivalent, because it does not produce, like
soda, creeping salts. Various modes of regeneration render this
battery very economical. The deposited copper absorbs oxygen pretty
readily by simple exposure to damp air, and can be used again. An
oxidizing flame produces the same result very rapidly.
Lastly, by treating the exhausted battery as an accumulator, that is
to say, by passing a current through it in the opposite direction, we
restore the various products to their original condition; the copper
absorbs oxygen, and the alkali is restored, while the zinc is
deposited; but the spongy state of the deposited zinc necessitates its
being submitted to a process, or to its being received upon a mercury
support. Again, the oxide of copper which we employ, being a waste
product of brazing and plate works, unless it be reduced, loses
nothing of its value by its reduction in the battery; the
depolarization may therefore be considered as costing scarcely
anything. The oxide of copper battery is a durable and valuable
battery, which by its special properties seems likely to replace
advantageously in a great number of applications the batteries at
present in use.
* * * * *
FARCOT'S SIX HORSE POWER STEAM ENGINE.
This horizontal steam engine, recently constructed by Mr. E.D. Farcot
for actuating a Cance dynamo-electric machine, consists of a cast iron
bed frame, A, upon which are mounted all the parts. The two jacketed,
cylinders, B and C, of different diameters, each contains a
simple-acting piston. The two pistons are connected by one rod in
common, which is fixed at its extremity to a cross-head, D, running in
slides, E and F, and is connected with the connecting rod, G. The head
of the latter is provided with a bearing of large diameter which
embraces the journal of the driving shaft, H.
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