The Bloomfield times. [volume] (New Bloomfield, Pa.) 1867-187?, 1871-07-18
SCIENTIFIC READING.
Electrotypes and StereOtypes.

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NNHESE have taken very important
place among the useful arts The
process is very simple for stereotypes,
but for eleotrotypes is rather more COM
plex, though easily understood. a f.
A galvanic current has the property,
under certain conditions, of deeomposing
many chemical compounds If the ends
of the two wires connected with battery
be inserted in vessel, of water, and a
current of sufficient power made to pass
from one to the other through the water,
the latter is decomposed into its elements,
which are the gases hydrogen and oxygen
One gas will rise in bubbles from one
wire end, aud the other from the other.
These wire ends are called electrodes
Many other substances, if dissolved in
water, will decompose much more readily;
as, for example, sulphate of "copper" com
monty known as blue vitriol. This is a
compound of sulphuris acid and copper,
and it takes much less power to separate
the two than to resolve water into its
component parts. AS the current passes
through the solution of blue vitriol the
ulphurie acid appears at one electrode
and the pure copper at the other. The
sulphuric acid thus set free from its pre-
vious combination will at once attack its
electrode, if it be of any metal for which
it has affinity. As the wires are generally
copper, it, of course, produces new blue
vitriol at the expense Of the electrode
which is thus eaten away. Meanwhile
the other electrode is receiving continual
accession of copper which is deposited
upon it. If now there be attached to this
wire cast of any kind, which tits desired
toreproduce in copper, the metal is deposit
ed upon it as long as the galvanic current
is flowing and doing its work A perfect
copy, taking every minutest hair line, is
thus obtained in pure copper and, if the
surface of the cast or mold be properly
protected, the copy may be readily remov-
ed after it is complete. The process
might be continued until the deposit of
copper should become indefinitely thick,
but for economy in expense it is usually
arrested when there is only a very thin
layer, and into this packing of soft metal
is run, in order to give stiffness. By this
simple means any thing may be copied
with absolute accuracy, whether it be o
seal or medal, or an engraved plate, Or q
leaf, or even Photographic negative
the one condition being that the picture
or device depend on an uneyenness Of
surface. Engraved plates, especially
those of the great masters, are very cost.
ly, and yet, after a certain number Of
proofs have ben printed they lose, by
wearing, much Of their delicacy in the
finest lines and touches. The first thou
sand impressions are far more valuable
than any taken subsequently. The diff
Guilty is now obviated by electrotypes, a:
the original plate coming from the hand
of the artist need never be put under the
printing press, to lose its sharpness o.
outline. Copies can be taken indefinite
ly, and the originals of great work pre-
served for all time. So, also, by some
newly discovered device, a printed en-
craving, of which the plate is lost oi
ruined, may be used to reproduce new
plate as perfect as the original z..'r
The difference between electrotypes ant
stereotypes is that for the latter the ,typl
metal is put at once into the mold with
out being faced up with the copper, am
though just as perfect is not as durable