ng the mercury is ascertained. Into the top are nicely
fitted two or three iron frames, with shoulders, for the plate to rest
in, suitable for the different sizes of plates. The bath is heated by
means of a spirit lamp placed under it. From two to four ounces of
highly purified mercury are put into the bath at a time.

IV. PLATE BLOCKS AND VICES.--There are several kinds of this article in
use; I shall describe the two best only.

[Illustration: Fig. 10 (hipho_10.gif)]

Fig. 10 gives an idea of the improvement on the English hand block.
The top a is perfectly flat and smooth--a little smaller than the
plate, so as to permit the latter to project a very little all
around--having at opposite angles c c two clasps, one fixed the other
moveable, but capable of being fastened by the thumb screw d, so as to
secure the plate tightly upon the block. This block turns upon a
swivle, b, which is attached to the table by the screw c, This block is
only used for holding the plate while undergoing the first operation in
cleaning.

[Illustration: Fig. 11 (hipho_11.gif)]

Fig. 11, shows the form of Lewis' newly patented plate vice, which for
durability, simplicity and utility is preferable to all others. It
consists of a simple platform and arm of cast iron, the former, a,
having a groove, d, in the centre for fixing the different sizes of
plate beds, e--and the latter supporting the leaves, e f. On this vice
which is secured to a table, or bench, the plate receives its finishing
polish with rouge, or prepared lampblack. Mr. Lewis gives the
following directions for its use. "As the cam wears tighten it with
the adjusting screw (g) so as to allow the lever (f) to fall back into
a horizontal position; the plate being in its place at the time. Oil
the wearing parts occasionally."

Some Daguerreotypists, however, use a foot lathe with buff wheels of
various forms; but this vice is sufficient for all ordinary purposes.

[Illustration: Fig. 12 (hipho_12.gif)]

[Illustration: Fig. 13 (hipho_13.gif)]

V. COATING BOXES.--The usual form for iodine and bromine boxes is see,
at figs. 14 and 15. They are far superior to those in use with the
English operators. Each consists of a wooden box (a,) having firmly
embeded within it a stout glass jar (c), the edges of which are ground.
Over this is placed the sliding cover b, double the length of the box,
one half occupied by a piece of ground glass (e), tightly pressed upon
the glas