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I begin to be apprehensive lest, after being considered as a dry experimenter, I should pass, with many of my readers, into the opposite character of a visionary theorist. A good deal of theory has been interspersed in the course of this work, but, not content with this, I am now entering upon a long section, which contains nothing else.
The conjectures that I have ventured to advance in the body of the work will, I hope, be found to be pretty well supported by facts; but the present section will, I acknowledge, contain many random thoughts. I have, however, thrown them together by themselves, that readers of less imagination, and who care not to advance beyond the regions of plain fact, may, if they please, proceed no farther, that their delicacy be not offended.
In extenuation of my offence, let it, however, be considered, that theory and experiment
neT necessarily go hand in hand* every process/be* ing intended to ascertain some particular hypo* the/is, which, in fact, is only a conjecture concerning the circumstances or the cause of some natural operation; consequently that the boldest and most original experimenters are those, who, giving free scope to their imaginations, admit the combination of the most distant ideas; and that though many of these associations of ideas, will be wild and chimerical, yet that others will have the chance of giving rise to the greatest and most capital discoveries; such as very cautious, timid, sober, and slow-thinking people would never have come at.
Sir Isaac Newton himself, notwithstanding the great advantage which he derived from a habit of patient thinking, indulged bold and. eccentric thoughts, of which his Queries at the end of his book of Optics are a sufficient evidence. And a quick conception of distant analogies, which is the great key to unlock the secrets of nature, is by no means incompatible with the spirit of perjeverance, in investigations calculated to ascertain and pursue those analogies.
§ i. Speculations concerning the Constituent Principles of the different kinds of Air, and the Constitution and Origin of the AtmoSphere, dec.
All the kinds of air that appear to me to be essentially distinct from each other are fixed uir, acid and alkaline; for these, and another principle, called phlogiston, which I have not been able to exhibit in the form of air, and which has never 'yet been exhibited by itself in any form, seem to constitute all the kinds of air that I am acquainted with.
Acid air and phlogiston constitute an air which either extinguishes flame, or is itself inflammable, according, probably, to the quantity of phlogiston combined in it, or the mode of combination. When itextinguishes flame, it is probably only so much charged with the phlogistic matter, as to take no more from a burning candle, which must, therefore, necessarily go out in it. When it is inflammable, it is probably ib much charged with phlogiston, that the heat communicated by a burning candle makes it immediately separate itself from the other principle with which it was united, in which separation heat is produced, as in other cases of ignition ; the action and reaction, which necessarily attends the separation of the constituent principles, pies, exciting probahly a vibratory motion in them.
Since inflammable air, by agitation in water, first comes to lose its inflammability, so as to be fit for respiration, and even to admit a candle to burn in it, and then comes to extinguish a candle; it seems probable that water imbibes a great part of this extraordinary charge of phlogiston. And that water can be impregnated with phlogiston, is evident from many of my experiments, especially those in which metals were calcined over it.
Water haying this affinity with phlogiston, it is probable that it always contains a considerable portion of it; which phlogiston having a stronger affinity with the acid air, which is perhaps the basis of common air, may, by long agitation, be communicated to it, so as to leave it over saturated, in consequence of which ic will extinguish a candle,
It is possible, however,, that inflammable air and air which extinguishes a candle may differ from one another in the mode of the combination of these two constituent principles, as well as in the proportional quantity of each; and b.y agitation in water, or long standing, that Qiode of combination may change. This we S 3 know; know to be the case with other substances, a* with milk, from which, by standing only, cream is separated; which, by agitation becomes batter. Also many substances, being at rest, pu-, trefy, and thereby become quite different from what they were before. If this be the case with inflammable air, the water may imbibe either of the constituent parts, whenever any proportion of it is spontaneously separated from the rest; and should this ever be that phlogiston, with which air is but slightly over-charged, as by the burning of a candle, it will be recovered so a state in which a candle may burn in it again.
It will be observed, however, that it was only in one instance that I found that strong inflammable air, in its transition to a state in which it extinguishes a candle, would admit a candle to burn in it, and that was very faintly; that then the air was far from being pure, as appeared by the test of nitrous air; and that it was only from a particular quantity of inflammable air which I got from oak, and which had stood1 a long time in water, that I ever got air which was as pure as common air. Indeed, it is much more easy to account for the passing of inflammable air into a state in which it extinguishes candles, without any intermediate state, in which it will admit a candle to burn in it, than otherwise. This subject requires and deserves farther investigation.