The preceding experiments on the calcination of metals fuggefted to me a method of explaining the cause of the mischief which is known to arife from fresh paint, made with white-lead (which I fuppofe is an imperfect calx of lead) and oil,

To verify my hypothefis, I first put a small pot full of this kind of paint, and afterwards (which answered much better, by expofing a greater furface of the paint) I daubed feveral pieces of paper with it, and put them under a receiver, and obferved, that in about twentyfour hours, the air was diminished between one fifth and one fourth, for I did not measure it very exactly. This air alfo was, as I expected to find, in the highest degree noxious; it did not effervefce with nitrous air, it was no farther diminished by a mixture of iron filings and brimftone, and was made wholesome by agitation in water deprived of all air.

I think it appears pretty evident, from the preceding experiments on the calcination of metals that air is, fome way or other, diminished in confequence of being highly charged with phlogiston; and that agitation in water reftores it, by imbibing a great part of the phlogistic

matter.

That

That water has a confiderable affinity with phlogifton, is evident from the strong impregnation which it receives from it. May not plants alfo restore air diminished by putrefaction by absorbing part of the phlogifton with which it is loaded? The greater part of a dry plant, as well as of a dry animal substance, consists of inflammable air, or fomething that is capable of being converted into inflammable air; and it feems to be as probable that this phlogistic matter may have been imbibed by the roots and leaves of plants, and afterwards incorporated into their fubftance, as that it is altogether produced by the power of vegetation. May not this phlogistic matter be even the most effential part of the food and fupport of both vegetable and animal bodies?

In the experiments with metals, the diminution of air feems to be the confequence of nothing but a faturation with phlogifston; and in all the other cafes of the diminution of air, I do not fee but that it may be effected by the fame means. When a vegetable or animal fubstance is diffolved by putrefaction, the escape of the phlogistic matter (which, together with all its other constituent parts, is then let loose from it) may be the circumstance that produces the diminution of the air in which it putrefies. It is highly improbable that what remains after an

animal body has been thoroughly diffolved by putrefaction, fhould yield fo great a quantity of inflammable air, as the dried animal fubftance would have done. Of this I have not made an actual trial, though I have often thought of doing it, and still intend to do it; but I think there can be no doubt of the refult,

Again, iron, by its fermentation with brim, ftone and water, is evidently reduced to a calx, fo that phlogiston must have escaped from it. Phlogiston alfo muft evidently be fet loose by the ignition of charcoal, and is not improbably the matter which flies off from paint, composed of white-lead and oil. Laftly, fince spirit of nitre is known to have a very remarkable affinity with phlogiston, it is far from being improbable that nitrous air may also produce the fame effect by the fame means.

To this hypothefis it may be objected, that, if diminished air be air faturated with phlogifton, it ought to be inflammable. But this by no means follows; fince its inflammability may depend upon fome particular mode of combination, or degree of affinity, with which we are not acquainted. Befides, inflammable air seems to confist of fome other principle, or to have fome other conftituent part, besides phlo

gifton and common air, as is probable from that remarkable depofit, which, as I have observed, is made by inflammable air, both from iron and zinc.

It is not improbable, however, but that à greater degree of heat may inflame that air which extinguishes a common candle, if it could be conveniently applied. Air that is inflammable, I obferve, extinguishes red-hot wood; and indeed inflammable fubftances can only be those which, in a certain degree of heat, have a lefs affinity with the phlogiston they contain, than the air, or fome other contiguous fubftance, has with it; fo that the phlogifton only quits one fubftance, with which it was before combined, and enters another, with which it may be combined in a very different manner. This fubftance, however, whether it be air or any thing else, being now fully faturated with phlogiston, and not being able to take any more, in the fame circumftances, muft neceffarily extinguifh fire, and put a stop to the ignition of all other bodies, that is, to the farther escape of phlogiston from them.

That plants restore noxious air, by imbibing the phlogiston with which it is loaded, is very agreeable to the conjectures of Dr. Franklin,

made

a

made many years ago, and expreffed in the following extract from the laft edition of his Letters, p. 346.

"I have been inclined to think that the fluid "fire, as well as the fluid air, is attracted by

plants in their growth, and becomes con"folidated with the other materials of which "they are formed, and makes a great part of "their fubftance: that, when they come to "be digested, and to suffer in the vessels a "kind of fermentation, part of the fire, as "well as part of the air, recovers its fluid "active state again, and diffuses itself in the body, digefting and feparating it; that the "fire fo reproduced, by digeftion and fepara

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tion, continually leaving the body, its place "is fupplied by fresh quantities, arifing from "the continual feparation; that whatever

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quickens the motion of the fluids in an "animal, quickens the feparation, and re-pro"duces more of the fire, as exercise; that all "the fire emitted by wood, and other com

buftibles, when burning, exifted in them before in a folid ftate, being only discovered "when feparating; that fome foffils, as fulphur, fea-coal, &c. contain a great deal of "folid fire; and that, in fhort, what escapes "and is diffipated in the burning of bodies, "befides water and earth, is generally the