hragm: one
side should be filled with a very dilute solution of sulphuric acid,
and the other with either a solution of ferroprussiate of potash, or
muriate of soda, saturated with chloride of silver. The copper plate,
varnished on one side, is united, by means of a copper wire, with a
plate of zinc. The zinc plate being immersed in the acid, and the
copper in the salt, a weak electric current is generated, which
precipitates the silver in a very uniform manner over the entire
surface.

Another Method.--A piece of brass or of polished copper, brass is
preferred, is perfectly planished and its surface made perfectly clean.
A solution of nitrate of silver, so weak that the silver is
precipitated slowly, and a brownish color, on the brass, is laid
uniformly over it, "at least three times," with a camel's hair pencil.
After each application of the nitrate, the plate should be rubbed
gently in one direction, with moistened bitartrate of potassa, applied
with buff. This coat of silver receives a fine polish from peroxide of
iron and buff. Proofs are said to have been taken on it, comparable
with those obtained on French plates.

M. SOLIEL'S PROCESS FOR DETERMINING THE TIME OF EXPOSURE IN THE CAMERA.

M. Soliel has proposed the use of the chloride of silver to determine
the time required to produce a good impression on the iodated plate in
the camera. His method is to fix at the bottom of a tube, blackened
within, a piece of card, on which chloride of silver, mixed with gum or
dextrine, is spread. The tube thus disposed is turned from the side of
the object of which we wish to take the image, and the time that the
chloride of silver takes to become of a greyish slate color will be the
time required for the light of the camera to produce a good effect on
the iodated silver.

INSTANTANEOUS PROCESS FOR PROCURING DAGUERREOTYPES.

The following method of producing Daguerreotypes has by some been named
as above. Most experienced operators have been long acquainted with
the effect of the vapor of ammonia upon the chemically coated plate. I
will here insert Mr. W. H. Hewett's plan of proceeding. This
gentleman, in referring to it (published in 1845), says:

"This improvement consists in using the vapor of ammonia, as an object
to accelerate the action of light upon the plate. The effect is
produced upon a simple iodized plate, but still more upon a plate
prepared in the ordinary way, with both iodine and bromine.