nto a plate, connected at one end to a copper wire.
There is another plate of carbon, not precisely the same as that used for
arc lights or ordinary batteries, but somewhat lighter in texture. This
plate is perforated, and provided with small wooden pegs. The sodium plate
is wrapped in silk paper, and pressed upon the carbon in such a manner
that the wooden pegs penetrate the soft sodium. For greater security the
whole is tied together with a few turns of fine iron wire; care being
taken that the wire does not form an electric contact between the sodium
and the carbon. The element is then complete, the carbon and the small
copper wire being the electrodes. The sodium, on exposure to the air,
becomes oxidized, forming caustic soda, which with the moisture of the air
dissolves, and drains gradually away in the form of a concentrated
solution; thus constantly exposing the fresh surface of the metal, which
renders the reaction continuous. The price of the element is lower than
would be expected at first sight from the employment of so expensive a
metal. The present cost of sodium is 10 frs. per kilogramme; but M.
Jablochkoff thinks that on the large scale the metal might be obtained at
a very low figure. The elements are grouped in sets of ten, hung upon rods
in such a manner that the solution as formed may drain off. Such a battery
continues in action as long as the air contains moisture; the only means
of stopping it is to shut it up in an air-tight case. The electro-motive
force depends on the degree of humidity in the air, and also upon the
temperature.

* * * * *

ANALYSIS OF PERFUMED SCOURING PASTES.--The analysis of No. 1 resulted in
water and traces of myrbane oil, 3.66 per cent.; fatty acid, melting at
104 deg. F., 54.18 per cent.; iron peroxide, 10.11 per cent.; silicic acid,
14.48 per cent.; alumina, 17.31 per cent.; lime and magnesia, traces. The
iron peroxide is partly soluble in hydrochloric acid, the alumina entirely
so as silicate. The scouring paste, therefore, is composed of 54 per cent.
fatty (palm oil) acid, 10 per cent. jeweler's rouge, 32 per cent.
pumice-stone powder.

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SOUND SIGNALS.

In Appleton's "Annual Cyclopaedia" for 1883, Mr. Arnold B. Johnson, Chief
Clerk of the Lighthouse Board, contributes a mass of very interesting
information, under the above title. His descriptions of the most approved
inventions relatin