of air ftill continued to do fo. Of this one instance occurred in the year 1771, a sprig of mint having grown in a jar of this kind of air, from the 25th of July to the 17th of August following; and another trial I made, with the fame fuccefs, the 7th of July 1772, the plant having grown in it from the 29th of June preceding. In this cafe also I found that the effect was not owing to any virtue in the leaves of mint; for I kept them conftantly changed in a quantity of this kind of air, for a confiderable time, without making any fenfible alteration in it.

These proofs of a partial restoration of air by plants in a state of vegetation, though in a confined and unnatural fituation, cannot but render it highly probable, that the injury which is continually done to the atmosphere by the refpiration of fuch a number of animals, and the putrefaction of fuch maffes of both vegetable and animal matter, is, in part at least, repaired by the vegetable creation. And, notwithstanding the prodigious mass of air that is corrupted daily by the above-mentioned causes; yet, if we confider the immenfe profufion of vegetables upon the face of the earth, growing in places fuited to their nature, and confequently at full liberty to exert all their powers, both inhaling and exhaling, it can hardly be thought, but

that

that it may be a fufficient counterbalance to it, and that the remedy is adequate to the evil.

Dr. Franklin, who, as I have already obferved, faw fome of my plants in a very flourishing state, in highly noxious air, was pleased to exprefs very great fatisfaction with the refult of the experiments. In his anfwer to the letter in which I informed him of it, he says,

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"That the vegetable creation should reftore "the air which is fpoiled by the animal part of "it, looks like a rational system, and feems to "be of a piece with the reft. Thus fire puri"fies water all the world over. It purifies it "by distillation, when it raises it in vapours, "and lets it fall in rain; and farther ftill by fil"tration, when, keeping it fluid, it suffers that "rain to percolate the earth. We knew be"fore that putrid animal fubftances were con"verted into sweet vegetables, when mixed with "the earth, and applied as manure; and now, "it seems, that the fame putrid substances, "mixed with the air, have a fimilar effect. "The strong thriving state of your mint in pu"trid air feems to fhew that the air is mended by taking something from it, and not by adding to it." He adds, "I hope this will

give fome check to the rage of destroying
trees that
that grow near houses, which has

"accompanied our late improvements in gar

dening, from an opinion of their being un"wholesome. I am certain, from long obfervation, that there is nothing unhealthy in the "air of woods; for we Americans have every "where our country habitations in the midit "of woods, and no people on earth enjoy bet"ter health, or are more prolific."

Having rendered inflammable air perfectly innoxious by continued agitation in a trough of water, deprived of its air, I concluded that other kinds of noxious air might be restored by the fame means; and I prefently found that this was the case with putrid air, even of more than a year's standing. I fhall obferve once for all, that this process has never failed to restore any kind of noxious air on which I have tried it, viz. air injured by refpiration or putrefaction, air infected with the fumes of burning charcoal, and of calcined metals, air in which a mixture of iron filings and brimftone, that in which paint made of white lead and oil has stood, or air which has been diminished by a mixture of nitrous air. Of the remarkable effect which this process has on nitrous air itself, an account will be given in its proper place.

If this process be made in water deprived of air, either by the air-pump, by boiling, or by dif tillation,

tillation, or if fresh rain-water be used, the air will always be diminished by the agitation; and this is certainly the faireft method of making the experiment. If the water be fresh pumpwater, there will always be an increase of the air by agitation, the air contained in the water being fet loose, and joining that which is in the jar. In this case, also, the air has never failed to be restored; but then it might be fufpected. that the melioration was produced by the addition of fome more wholesome ingredient. As these agitations were made in jars with wide mouths, and in a trough which had a large furface expofed to the common air, I take it for granted that the noxious effluvia, whatever they be, were first imbibed by the water, and thereby tranfmitted to the common atmosphere. In fome cafes this was fufficiently indicated by the difagreeable fmell which attended the opera

tion.

After I had made thefe experiments, I was informed that an ingenious phyfician and philofopher had kept a fowl alive twenty-four hours, in a quantity of air in which another fowl of the fame fize had not been able to live longer than an hour, by contriving to make the air, which it breathed, pafs through no very large quantity of acidulated water, the furface of which was not expofed to the common air; and that

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even when the water was not acidulated, the fowl lived much longer than it could have done, if the air which it breathed had not been drawn through the water.

As I should not have concluded that this experiment would have fucceeded so well, from any obfervations that I had made upon the fubject, I took a quantity of air in which mice had died, and agitated it very ftrongly, first in about five times its own quantity of distilled water, in the manner in which I had impregnated water with fixed air; but though the operation was continued a long time, it made no fenfible change in the properties of the air. I also repeated the operation with pump-water, but with as little effect. In this cafe, however, though the air was agitated in a phial, which had a narrow neck, the surface of the water in the bafon was confiderably large, and exposed to the common atmosphere, which must have. tended a little to favour the experiment.

In order to judge more precisely of the effect of thefe different methods of agitating air, I transferred the very noxious air, which I had not been able to amend in the leaft degree by the former method, into an open jar, standing in a trough of water; and when I had agitated it till it was diminished about one third, I found