dry and warm.

The greater number of operators, with whose practice I am familiar,
use, for polishing plates, prepared tripoli, imported from France, or
Browne's rotten-stone. The former of these articles is very
objectionable, inasmuch as there is no positive certainty of being
enabled to procure or make the article of uniform grit--the nature of
the substance rendering, it impossible to reduce it to varying degrees
of evenness, by the well known process of washing, for that purpose,
and the burning of rotten-stone changes its chemical nature somewhat,
at the same time rendering, this invaluable article harsh and gritty.
And especially, no reliance can be placed upon burned rotten stone if
purchased from those who do not give very great attention and care to
its preparation; and the same remarks apply to rouge.

The best article for polishing Daguerreotype plates is rotten-stone,
such as can be procured in any town, prepared after the following
manner: Procure, say half a dozen wide-mouthed bottles, of suitable
dimensions, numbering each from one to six. Put into No. 1 about half
a pound of rotten-stone, and nearly fill the bottle with water. Then,
with a proper stick or spatule, mix well the rotten-stone and water;
after which, let No. 1 rest for, say one minute, then carefully pour
off into bottle No. 2 (or, what would be better, draw off by a syphon)
as much of the floating particles of rotten-stone as is suspended in
the water. Again fill bottle No. 1 with water, agitate it as before,
and decant it to bottle No. 2, care being taken to draw off only the
suspended particles of rotten-stone.

When a sufficient quantity of washings from bottle No. 1 is collected
into bottle No. 2, a similar process must be gone through, as above
stated, for No. 1; the difference being in the care required, and in
the time allowed between the stirring or mixing the rotten-stone and
water. The floating particles of rotten-stone, after four minutes'
subsiding, will be found fine enough for the finest Daguerreotype
polishing required.

A quantity of such washings may be collected in a large bottle, and
allowed to stand a few hours, when all the rotten-stone will have
settled. The water may be poured off and the rotten-stone put into an
evaporating dish, and while being dried, must be constantly stirred to
obtain an impalpable powder.

Further washings may in like manner be resorted to for finer qualities
of rotten-stone. In my