In general, we use the charcoal support where we wish to reduce
metallic oxides, to prevent oxidation, or to test the fusibility of a
substance. There is another point to which we would direct the
student. Those metals which are volatile in the reduction flame,
appear as oxides in the oxidation flame. These oxides make sublimates
upon the charcoal close in the vicinity of the substance, or where it
rested, and by their peculiar color indicate pretty correctly the
species of minerals experimented upon.

(_b._) _Platinum Supports._--The metal platinum is infusible in the
blowpipe flame, and is such a poor conductor of heat that a strip of
it may be held close to that portion of it which is red hot without
the least inconvenience to the fingers. It is necessary that the
student should be cognizant of those substances which would not be
appropriate to experiment upon if placed on platinum. Metals should
not be treated upon platinum apparatus, nor should the easily
reducible oxides, sulphides, nor chlorides, as these substances will
combine with the platinum, and thus render it unfit for further use in
analysis.

(_c._) _Platinum Wire._--As the color of the flame cannot be well
discerned when the substance is supported upon charcoal, in
consequence of the latter furnishing false colors, by its own
reflection, to the substances under examination, we use platinum wire
for that purpose, when we wish to examine those substances which give
indications by the peculiar color which they impart to fluxes. The
wire should be about as thick as No. 16 or 18 wire, or about 0.4
millimetre, and cut into pieces about from two and a half to three
inches in length. The end of each piece is crooked. In order that
these pieces should remain clear of dirt, and ready for use, they