small part where the Flint and Steel first touch: For the Bodies being each
of them so very hard, the puls cannot be far communicated, that is, the
parts of each can yield but very little, and therefore the violence of the
concussion will be _exerted_ on that piece of Steel which is cut off by the
Flint. Thirdly, that the filings or small parts of Steel are very apt, as
it were, to take fire, and are presently red hot, that is, there seems to
be a very _combustible sulphureous_ Body in Iron or Steel, which the Air
very readily preys upon, as soon as the body is a little violently heated.

And this is obvious in the filings of Steel or Iron cast through the flame
of a Candle; for even by that sudden _transitus_ of the small chips of
Iron, they are heat red hot, and that _combustible sulphureous_ Body is
presently prey'd upon and devoured by the _aereal_ incompassing
_Menstruum_, whose office in this Particular I have shewn in the
Explication of Charcole.

And in prosecution of this Experiment, having taken the filings of Iron and
Steel, and with the point of a Knife cast them through the flame of a
Candle, I observed where some conspicuous shining Particles fell, and
looking on them with my _Microscope_, I found them to be nothing else but
such round Globules, as I formerly found the Sparks struck from the Steel
by a stroke to be, only a little bigger; and shaking together all the
filings that had fallen upon the sheet of Paper underneath and observing
them with the _Microscope_, I found a great number of small Globules, such
as the former, though there were also many of the parts that had remained
untoucht and rough filings or chips of Iron. So that, it seems, Iron does
contain a very _combustible sulphureous_ Body, which is, in all likelihood,
one of the causes of this _Phænomenon_, and which may be perhaps very much
concerned in the business of its hardening and tempering: of which somewhat
it said in the Description of _Muscovy-glass_.