The Artist's Assistant, In the Study and Practice of Mechanical Sciences: Calculated for the Improvement of Genius. Illustrated with Copper-Plates — Birmingham, [ca. 1785]

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THE ARTIST'S ASSISTANT. 285

Permutation of lead into filver :—Take fine lead,
Calcine it with common fait, or elfe with that fort of
fait which is extracted from the dregs, fxces, or ca-r
put mortuum of faltpetre and vitriol calcinated both
together ; foak the whole warmly with oil of vitriol
till you make it come into an uncluous pafte ; this
you will put into a pot or crucible, well luted, and
placed in a pan full of fand, with which you will
cover it over intirely. Make under this a digefting
fire ; that is to fay, fuch a fire as is neceffary to
warm the fand ; keep it fo for ten days, then take
off" your matter and teft it. Out of one hundred
and five pounds of lead, vou will draw five marcs,
or two pounds and a half weight, of filver capable
to ftand the teft.

Tranfmutation of iron into copper: —Iron is eafily
changed into copper by means of the vitriol; to
do this you put your iron ftratum fuper flratum in a
defcenforium, and fet it over a ftrong blaft fire,
pufhed by bellows, till the iron melts and flows into
copper ; you muft not forget, when you have made
your beds of vitriol, to water them a little over
with vinegar faturated of faltpetre, alkaline, and
tartar falts and verdigrife.

Spots very effetluaily taken out of filk, linen, or
woollen :—Spirits of turpentine twelve drops, and
the fame quantity of fpirits of wine ; grind thofe
with an ounce of pipe-maker's clay, and rub the
fpots therewith; you are to wet the compofition
when you do either filk, linen, or woollen with it ;
jet it remain till dry, then rub it off, and the fpot
or fpots will difappear. The ingenious Dr. Godfrey
fays, that true fpirits of falts. is the only thing to

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