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dical view of the principal articles which are treated of in this volume.

The first five sections of this work contain several interesting obfervations and experiments, relative to that great process of nature difcovered by the Author;-the purification of the atmospherical air by the means of growing plants; and particularly to the remarkable influence of the folar light on that process. A continuation is given of the Author's experiments on the green matter that appears in water expofed to the light; and which, fince his former publication, has been found to be a real vegetable subftance; the invifible feeds of which, or at leaft thofe parts by which it is propagated, probably float at all times in the atmofphere, and infinuate themfelves into veffels not perfectly closed: for, in water contained in a veffel inverted in quickfilver, this vegetable matter will not be produced.

Any perfon may foon be fatisfied with refpect to the vegetable nature of this fubftance, by placing, as we have done, the glass fliders of a microscope in water expofed to the light; and examining it with a pretty ftrong magnifier, when it firft appears : for when it has grown fome time, it puts on the appearance only of an unorganifed gelatinous mafs. One fpecies of it-for there are several, confifts of long and flender filaments, or rather hollow tubes; which frequently, after the Sun has fhone fome time, prefent the appearance of ftrings of beads, in confequence of the numerous bubbles of air contained within their cavities.

The Author appears now to have fatisfactorily afcertained the genefis, or real origin, of this pure air; and to have proved that it is not produced by light, or even by the plants, in confequence of any actual tranfmutation of one fubftance into another, as feems to have been the opinion of Dr. Ingenhoufz: but that it is produced, or comes into view, only in confequence of the purification of the impure air, previously exifting in the water, by the action of the plants upon it; which attract and retain the phlogifton, and then reject or emit the air, now rendered pure by being freed from that principle. But for the particular experiments from which this conclufion is deduced, the Reader muft confult the work itself.

One of the most curious circumftances relative to the production of dephlogifticated air from this water mofs, as the Author properly enough calls it, is, that various vegetable and animal fubftances being put into the water, and which have a tendency to putrify in it, promote nevertheless the production of this pure air, by feeming to furnish a proper pabulum for the water mofs, which receives and is nourished by the phlogistic matter contained in thefe fubftances; which laft, under other circumftances (i. e. if they had been kept in water in the dark,

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or been confined by quickfilver) would have become putrid, and have phlogisticated the air, or have furnished inflammable air.

Thus, fome fresh cabbage having been put into a large jar, filled with rain water, and inverted in a bason of the fame; in about a month, two portions of dephlogifticated air were fucceffively collected. The cabbage was then foft, but not offenfive. The fame cabbage being replaced in fresh water, feveral ounce measures of dephlogifticated air were again produced; and the cabbage was ftill foft, and not in the leaft offenfive.

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The reafon of this, I imagine,' fays the Author, was, that the phlogiston, which would have conftituted the offenfive fmell of the cabbage (and no putrid vegetable fubftance is more offenfive) was, in this cafe, imbibed by this water mofs, as fast as it was produced by the procefs of putrefaction; and the veffel being large, there was no fuperabundant phlogifton to contaminate the air.'

On ufing however a very large proportion of cabbage, and a comparatively small quantity of water, in two veffels, one of which was fet in a dark room, and the other expofed to the fun s the results were remarkably different. In less than a week, fixteen ounce measures of air had been produced in the vessel placed in the dark; no part of which was dephlogisticated: one third part being fixed air, and the remainder ftrongly inflammable. The cabbage too was putrid and highly offenfive.-Even the water placed in the fun had yielded only an ounce measure and a half of air; about one-twentieth of which was fixed air, and the reft flightly inflammable. The cabbage here too was become offenfive.

This experiment fhews, as the Author obferves, that without light, inflammable air is produced by the putrefaction of vegetable fubftances; and it accounts for the production of this kind of air in marfhes. The cabbage in the fun alfo produced inflammable air, though less than that in the dark; because there was too great a quantity of it for the capacity of the veffel, or for the production of pure air. There had also been very little funshine; the weather having been rainy or cloudy.

In another experiment, made with a fmall quantity of veal; and in which a confiderable quantity of dephlogisticated air was produced; though the veal at length loft its coherence, and became putrid; yet by continuing the procefs, during which more" dephlogisticated air was produced, the jar was at length found to have nothing offenfive in it; the putrid matter having probably been then wholly exhaufted, in fupplying pabulum to the vege

table matter.

Perhaps the following experiment fhews, more fatisfactorily than the other, the truth of the hypothefis above fuggefted; with respect to the agency of putrefcent fubftances in affording a pabulum to

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the vegetable matter which emits the dephlogisticated air; as well as in relation to the effect of light, and to the fubfequent influence of putrefaction, in destroying the dephlogisticated air already generated.

On the zift of June, I put a dead mouse into a jar containing 200 ounces of water, inverted in a bason of the fame, which I placed in the fun. At the fame time, I put another mouse into a jar of the fame fize, filled with the fame water, and placed it in the dark. In this veffel, the water was never difcoloured, and very little air was produced; whereas, from the mouse in the fun, there prefently iffued a quantity of white mucous fubftance, which foon turned to an intense green, and yielded air moft copioufly. After fome time, the whole jar was full of this thick green matter, and air rofe from every part of it; but it was deftroyed as foon as it approached the upper part of the jar, where the dead mouse floated; owing no doubt to the phlogistic matter which iffued from it.

In order to verify this, I threw out the mouse, and dividing the turbid green water into two parts, I put one half into a retort exposed to the fun, and the other into an equal retort which I placed in the dark. The water in the fun presently yielded permanent air, highly dephlogifticated; whereas that in the dark gave not a fingle bubble: but when I foon afterwards brought it into the fun, it yielded air like the other.'

We cannot quit a fubject of this general kind, and which requires no profound knowledge in chymiftry to be rendered intelligible, without tranfcribing fome general reflections of the Author, refpecting the wife and provident ceconomy of nature, displayed on fo large a field, and yet on a class of fubjects on which her beneficent and extenfive operations had hitherto been carried on in perfect fecrecy.

It is impoffible not to obferve, from thefe experiments, the admirable provifion there is in nature, to prevent, or leffen, the fatal effects of putrefaction; especially in hot countries, where the rays of the fun are the most direct, and the heat the most intense. For whereas animal and vegetable fubftances, by fimply putrefying, would neceffarily taint great maffes of air, and render it wholly unfit for refpiration; the fame fubftances, putrefying in water, supply a most abundant pabulum for this wonderful vegetable fubftance, the feeds of which appear to be in all places difperfed invifibly through the atmosphere, and capable,, at all icafons of the year, of taking root, and immediately propagating themfelves to the greatest extent. By this means, inftead of the air being corrupted, a vaft addition of the pureft, air is continually thrown into it.

By this means alfo ftagnated waters are rendered much less offenfive and unwholefome than they would otherwife be. That

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froth which we alfo fee on the furface of fuch waters, and which is apt to create difguft, generally confifts of the pureft dephlogifticated air, fupplied by aquatic plants which always grow in the greatest abundance, and flourish most in water that abounds with putrid matter. When the fun fhines, thefe plants may also be seen to emit great quantities of pure air.

Even where animal and vegetable fubftances putrefy in AIR; as they have fome moisture in them, various other plants, in the form of mold, &c. find a proper nutriment in them; and by converting a confiderable part of the phlogiftic effluvium into their own nutriment, arreft it in its progrefs to corrupt the furrounding atmosphere. So wonderfully is every part of the fyftem of nature formed; that good never fails to arife out of all the evils to which, in confequence of general laws, most beneficial to the whole, it is neceffarily fubject. It is hardly poffible for a perfon of a fpeculative turn not to perceive, and admire, this most wonderful and excellent provifion.'

In the fections immediately following, the Author treats of air produced by fubftances putrefying in water, and in mercury; and of the inflammable air produced from the paste formed of iron filings and fulphur with water. Thefe obfervations are followed by others, in which, in oppofition to the doctrine of fome other philofophers, he fnews, that, though the air is phlogifticated by refpiration, the perfpiration of the body does not injure it. To thefe fucceed fome obfervations and experiments, made with a view to discover the origin of that fixed air which presents itself to obfervation in refpiration and fome other phlogiftic proceffes; and, in particular, to afcertain the quantity of fixed air naturally contained in a given quantity of common air. Thefe are followed by fome obfervations on the refpiration of fishes; and on the production and conftitution of dephlogifticated air, particularly on that obtained fo commodiously, and in fuch great plenty, from nitre alone, in an earthen, or rather a coated glafs, retort.-Towards the end of the volume it appears that in a retort of a peculiarly refractory earth, made for the Author by Mr. Wedgwood, and in an intenfe white heat, the Author got no lefs than 500 ounces of air confiderably dephlogifticated, and containing very little fixed air, from two ounces of nitre. While we are on the funject of dephlogisticated air, we fhall take the opportunity of tranfcribing an oblervation of the Author's refpecting his opinion that an earth is either the bafis of this and other fpecies of air, or at least exifts in a state of folution in them.

In the rapid production of all kinds of air from earthy materials, I have frequently obferved that there is a quantity of fuperfluous white matter depofited in the cold water in which it is received. This earth seems to have been held in folution in the

air while it was hot, because it was then quite tranfparent, and did not become turbid till it was cool; and this is one reason why I think that an earth is the proper bafis of all fuch kinds of air. For if fome earth be certainly held in a proper folution, fo as to make a conftituent part of the air, while hot, as its transparency feems to prove, and it be only depofited by cold; Some of the earth must be retained by it, in every degree of heat, and therefore in the temperature of the atmosphere. And perhaps no degree of cold can deprive it of all the earth that it contains. If it fhould, I fhould imagine that, as nothing but the acid principle would remain, it would then, like any other acid air, become liable to be immediately abforbed by water.'

The Author's fubfequent obfervations on this head merit the attention of those who cultivate the higher chemistry, and who wish to inquire into the nature of the chemical elements, as they are called, of earth and air.

This earthy matter, when incorporated in the air, I fhould imagine to be then the fame thing, from whatever fubftance the air had been produced, being then divefted of every thing that was peculiar to the fubftance from which it had been expelled; juft as the acid, in the compofition of dephlogisticated air, is probably the fame thing, whether the air had been produced from materials containing fpirit of nitre, or oil of vitriol. If this reafoning be true, we fhall be in poffeffion of a method of obtaining a truly primitive earth, or an earthy principle, common to all earths, and all metallic calces whatfoever: fince dephlogifticated air may, as I have fufficiently fhewn, be produced from them all.'-The Author, however, afterwards relates a few obfervations which may, perhaps, lead to a contrary conclufion. The matter certainly deferves a further investigation.

In the 15th fection, the Author rectifies a mistake of Dr. Ing genhoufz-(for a mistake it undoubtedly is, and we accordingly noticed it formerly in our account of his work *) by direct experiments. From these it is rendered evident, as we inferred a priori, that no fenfible advantage, either in point of œconomy or otherwife, could be derived from the breathing of dephlogifticated air, when refting on lime water. From these experiments of the Author's it appears that the air confined by lime water was both diminished and phlogisticated exactly like that which had been confined by common water, by the refpira tion of [two] mice of equal fize, in the fame time, The dimi nution indeed was, at firft, a fmall matter greater in the air confined by the lime water; because the common water did not imbibe the fixed air fo readily: but this made no apparent difference with respect to the mice; and the next day, the two por

*See M, REVIEW, vol. lxii. May 1780, p. 351.

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