Next, we may learn what part of the Wood it is that is the _combustible_ matter, for since we shall find that none, or very little of those fluid substances that are driven over into the Receiver are _combustible_, and that most of that which is left behind is so, it follows, that the solid _interstitia_ of the Wood are the _combustible_ matter. Further, the reason why uncharr’d Wood burns with a greater flame then that which is charr’d, is as evident, because those waterish or volatil parts issuing out of the fired Wood, every way, not onely shatter and open the body, the better for the fire to enter, but issuing out in vapours or wind, they become like so many little _æolipiles_, or Bellows, whereby they blow and agitate the fir’d part, and conduce to the more speedy and violent consumption or dissolution of the body.
Thirdly, from the Experiment of charring of Coals (whereby we see that notwithstanding the great heat, and the duration of it, the solid parts of the Wood remain, whilest they are preserv’d from the free access of the air undissipated) we may learn, that which has not, that I know of, been publish’d or hinted, nay, not so much as thought of, by any; and that in short is this.
First, _that the Air_ in which we live, move, and breath, and which encompasses very many, and cherishes most bodies it encompasses, that this Air is the _menstruum_, or universal dissolvent of all _Sulphureous_ bodies.
Secondly, _that this action_ it performs not, till the body be first sufficiently heated, as we find requisite also to the dissolution of many other bodies by several other _menstruums_.
Thirdly, _that this action_ of dissolution, produces or generates a very great heat, and that which we call Fire; and this is common also to many dissolutions of other bodies, made by _menstruums_, of which I could give multitudes of Instances.
Fourthly, _that this action_ is perform’d with so great a violence, and does so minutely act, and rapidly agitate the smallest parts of the _combustible_ matter, that it produces in the _diaphanous medium_ of the Air, the action or pulse of light, which what it is, I have else-where already shewn.
Fifthly, _that the dissolution_ of sulphureous bodies is made by a substance inherent, and mixt with the Air, that is like, if not the very same, with that which is fixt in _Salt-peter_, which by multitudes of Experiments that may be made with _Salt-peter_, will, I think, most evidently be demonstrated.