d of
its mephitic part; then light the tinder, and introduce it quickly with
the wire upon which it is fixed, into the bottle which you stop up with
the cork A, as is shown in the figure (17 Plate IV.) The instant the
tinder comes into contact with the vital air it begins to burn with
great intensity; and, communicating the inflammation to the iron-wire,
it too takes fire, and burns rapidly, throwing out brilliant sparks,
which fall to the bottom of the vessel in rounded globules, which become
black in cooling, but retain a degree of metallic splendour. The iron
thus burnt is more brittle even than glass, and is easily reduced into
powder, and is still attractable by the magnet, though not so powerfully
as it was before combustion. As Mr Ingenhouz has neither examined the
change produced on iron, nor upon the air by this operation, I have
repeated the experiment under different circumstances, in an apparatus
adapted to answer my particular views, as follows.

Having filled a bell-glass (A, Plate IV. Fig. 3.) of about six pints
measure, with pure air, or the highly respirable part of air, I
transported this jar by means of a very flat vessel, into a quicksilver
bath in the bason BC, and I took care to render the surface of the
mercury perfectly dry both within and without the jar with blotting
paper. I then provided a small capsule of china-ware D, very flat and
open, in which I placed some small pieces of iron, turned spirally, and
arranged in such a way as seemed most favourable for the combustion
being communicated to every part. To the end of one of these pieces of
iron was fixed a small morsel of tinder, to which was added about the
sixteenth part of a grain of phosphorus, and, by raising the bell-glass
a little, the china capsule, with its contents, were introduced into the
pure air. I know that, by this means, some common air must mix with the
pure air in the glass; but this, when it is done dexterously, is so very
trifling, as not to injure the success of the experiment. This being
done, a part of the air is sucked out from the bell-glass, by means of a
syphon GHI, so as to raise the mercury within the glass to EF; and, to
prevent the mercury from getting into the syphon, a small piece of paper
is twisted round its extremity. In sucking out the air, if the motion of
the lungs only be used, we cannot make the mercury rise above an inch or
an inch and a half; but, by properly using the muscles of the mouth, we
can,