The New York herald. [volume] (New York [N.Y.]) 1840-1920, 1853-08-04

infable process for causing the eectrotyps to
separate from the original plate This in principle wa.
the forces which determine the two plates That sleight
Of the blacksmith. by which he breaks . bar Of
Gne notch in IT, is at I'll the basis Of Z the process
used for preventing the adhesion On experimenting
on,n ON Of S psy
found that 1t too akin to metallic cohesion to
permit hn Aims of those substances between
din ipisbipg the cohesion.
The operation for preventing adhesion now performed
is entirely chemical and consequently far more delicate
than the mechanical opera OF coating plate with
air powders &C. The plate to be elsctrotyped, is
made chemically clean and washed with alcoholic
lutn of iodine and then exposed for hour to
sunlight the solar rays portion Of the iodine to
rise in vspor, forming extremely low atmosphere of
into the electrotyppg connections the newly formed
copper combines ~h the iodine thus both plates
faced With thin film of iodid which admits of the
Least force determining line of cleavage along the
faces.
The chemical action Of the iodine though causing the
plates separate hhe the lamnea Of mica does not
in the least mar the po'iAh Of the faces Although
the face must be admitted to be eorroded. whea
sion % Is trians in neehaoicsi ' view; the the iodine iodine
solution used for preparing the plate Is very weak,
containing only grsu Of the halogsn to grains
(over three pnts) OF slcoho and Mr. Mathot, who has
the laboratory in charge has calculated that the film of
iodid is fer less than the tenhousandth part OF mil
varsby given good results at the Coast Survey os aud
the copying bained by it far perfect than that
obtained by former Methods for in defiance OF the most
dextereus manipulation an excess Of will choke
scme of the finer lines and when air 6m Is used,
bubbles very liable to be retained the catting
The beauty and deicacy Of the views the CHARTS Of
the survey. at the fair show that the copying
feet The chemical process has the advantage als In
point of time the largest plate can be prepared in an
hour while the mechanical methods require several days.
The other improvements introduced by the Coast Sur
vey in the metallic virtues Of the eecr0t0pes and
the time and facility OF conducting the
tions The objections which beset the earlier operations
in electro mealurgy toftness and friaby Ia the
neral with tness and in the deposition.
Specimens of electro copper exhibited fully equal to
the best fire made metal in tenAcy, hardness and elias
ITCHY. The plates cast uniformly eighth
OF an inch in thickr and work well compared
with the originals that the first duplicate of the largest
plate exhibited printed near two thousand copies with
cut showing tigps Of Yet the original, from the
fneness Of the work. estn ated capable Of fur
nishing only eight hundred copies
chief feature in the electro metaurgic operations
OF the coast survey is tho OF hot elecroyes for
the reduction Of "copper" this, while greatly improving
the quality Of the wo has much reduced the time,
that which formerly the work of month now
be done in q few days
1t has been frequently proposed by persons not tho
roughly with this subject to steel pl8
inttead OF copper the s.eel will print greater
Der Of copies But this ia only putting the evil off in
point of time for the steel plate will eventually
But is not only the getting Of many dupli;ate
that eectrotype the preference 1t Is brought
to bear in the production of the engraved plate,
ard greatly reduces the time for getting large
cravings As but artist work at plate at q
time, the time for producing plate must be propor
tonae to its sze To abfidge this time the plate Is
cut in sections and distributed among
many artists When the done the electro
typst pisces them in conjunction and takes entire
cast as though they but 1t can readily be
seen frcm this that there need longer be limit to
the of work theet sni that ma ps Of
cities need longer be pictures of the past but repre-
sentat0ns Of things which are.