DOI Page / Citation link:
https://doi.org/10.11588/diglit.19571#0163
THE ARTIST'S ASSISTANT. Mg
the putty into a crucible with fome tallow or other
greafe ;. and give it the heat of fufion, or what is
fufficient to melt it ; fupplying the greafs in frefh
quantities as it burns away, till the calcined tin ap-
pears to have regained its metallic ftate. Suffer then
the remainder of the greafe to burn away, and the
chalk or earth, if any were mixed with it, will be
found fwimming on the furface of the metal ; to
which however the afhes of the greafe mufi be fup-
pofed to have added fome little quantity. There is,
neverthelefs, another body, with which the putty or
calx of tin may be adulterated, that will not difco-
ver itfelf by this method of reduction of the tin.
It is white lead, which, in this manner of treatment,
would run into fufion, and mix with the tin : and
could therefore not be diilinguifhed from it. But it
may be eafily rendered perceptible by another man-
ner of proceeding; which is, to take the puttyfuf-
pecled to be adulterated with it, and having put it
into a crucible, without any admixture, and invert-
ed another crucible over it, as a cover, to give it a
moderate heat, carefully avoiding that the fmoke or
coal of the fire may have any accefs to it to change
its colour. If there be any white lead mixed with
the putty, it will fnew itfelf, when removed from
the fire, and become cold in a yellow or brown co-
lour. If no fuch colour fupervene, but the putty
appear equally white as before it was heated, a con-
clunon may be fafely made, that it was not adulte-
rated by white lead; or that, if fophifticated at all,
it muft be by fome white earth, which may be made
perceptible by the reduction of tin in the manner
before mentioned,
Ultramarine
the putty into a crucible with fome tallow or other
greafe ;. and give it the heat of fufion, or what is
fufficient to melt it ; fupplying the greafs in frefh
quantities as it burns away, till the calcined tin ap-
pears to have regained its metallic ftate. Suffer then
the remainder of the greafe to burn away, and the
chalk or earth, if any were mixed with it, will be
found fwimming on the furface of the metal ; to
which however the afhes of the greafe mufi be fup-
pofed to have added fome little quantity. There is,
neverthelefs, another body, with which the putty or
calx of tin may be adulterated, that will not difco-
ver itfelf by this method of reduction of the tin.
It is white lead, which, in this manner of treatment,
would run into fufion, and mix with the tin : and
could therefore not be diilinguifhed from it. But it
may be eafily rendered perceptible by another man-
ner of proceeding; which is, to take the puttyfuf-
pecled to be adulterated with it, and having put it
into a crucible, without any admixture, and invert-
ed another crucible over it, as a cover, to give it a
moderate heat, carefully avoiding that the fmoke or
coal of the fire may have any accefs to it to change
its colour. If there be any white lead mixed with
the putty, it will fnew itfelf, when removed from
the fire, and become cold in a yellow or brown co-
lour. If no fuch colour fupervene, but the putty
appear equally white as before it was heated, a con-
clunon may be fafely made, that it was not adulte-
rated by white lead; or that, if fophifticated at all,
it muft be by fome white earth, which may be made
perceptible by the reduction of tin in the manner
before mentioned,
Ultramarine