« הקודםהמשך »
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 discovered by the Author ; -- the purification of the atmospherical air by the means of growing plants; and particularly to the remarkable in Auence of the folar light on that process. A continuation is given of the Author's experiments on the green matter. that appears in water exposed to the light ; and which, since his former publication, has been found to be a real vegetable substance; the invisible feeds of which, or at least those parts by which it is propagated, probably float at all times in the atmofphere, and infinuate themfelves into vefsels not perfe&ly closed : for, in water contained in a vessel inverted in quicksilver, this vegetable matter will not be produced.
Any person may soon be satisfied with refpe&t to the vegetable nature of this substance, by placing, as we have done, the glass sliders of a microscope in water exposed to the light; and examining it with a pretty Atrong magnifier, when it first appears : for when it has grown some time, it puts on the appearance only of an unorganised gelatinous mass. One species of it-for there are several, confifts of long and slender filaments, or ra. ther hollow tubes; which frequently, after the Sun has shone some time, present the appearance of strings of beads, in consequence of the numerous bubbles of air contained within their cavities.
The Author appears now to have satisfactorily afcertained the genesis, or real origin, of this pure air ; and to have proved that it is not produced by light, or even by the plants, in consequence of any actual transmutation of one subftance into another, as seems to have been the opinion of Dr. Ingenhousz: but that it is produced, or comes into view, only in consequence of the purification of the impure air, previoufy existing in the water, by the action of the plants upon it; which attract and retain the phlogiston, and then reject or emit the air, now rendered pure by being freed from that principle. But for the particular experimenis from which this conclufion is deduced, the Reader muf consult the work itself.
One of the most curious circumstances relative to the production of depblogisticated air from this water moss, as the Author properly enough calls it, is, that various vegetable and animal substances being put into the water, and which have a tendency to putrify in it, promote nevertheless the production of this pure air, by seeming to furnith a proper pabulum for the water moss, which receives and is nourished by the phlogistic matter contained in these substances; which last, under other circumstances (i.e. if they had been kept in water in the dark,
or been confined by quicksilver) would have become putrid, and have phlogisticated the air, or have furnished inflammable air.
Thus, Tome 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 dephlogisticated air were success fively collected. The cabbage was then soft, but not offensive. The same cabbage being replaced in fresh water, several ounce measures of dephlogisticated air were again produced ; and the cabbage was still soft, and not in the least offensive.
The reason of this, I imagine,' says the Author, ' was, that the phlogiston, which would have constituted the offensive smell of the cabbage (and no putrid vegetable substance is more offensive) was, in this case, imbibed by this water moss, as fast as it was produced by the process of putrefaction; and the vessel being large, there was no superabundant phlogiston to contaminate the air,
On using however a very large proportion of cabbage, and a comparatively small quantity of water, in two vefsels, one of which was set in a dark room, and the other exposed to the fun; 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 strongly inflammable.
The cabbage too was putrid and highly offensive.- Even the water placed in the sun had yielded only an ounce measure and a half of air ; about one-twentieth of which was fixed air, and the rest Nightly inflammable. The cabbage here too was become offensive.
This experiment shews, as the Author observes, that without light, infammable air is produced by the putrefaction of vegetable substances; and it accounts for the production of this kind of air in marshes. The cabbage in the fun also produced in flammable air, though less than that in the dark; because there was too great a quantity of it for the capacity of the vessel, or for the production of pure air. There had also been very little Sunthine; the weather having been rainy or cloudy. .
In another experiment, made with a small quantity of veal; and in which a considerable quantity of dephlogisticated air was produced; though the veal at length lost its coherence, and became putrid ; yet by continuing the process, during which more dephlogisticated' air was produced, the jar was at length found to have nothing offensive in it; the putrid matter having probably been then wholly exhausted, in supplying pabulum to the vegetable matter.
Perhaps the following experiment shews, more satisfactorily than the other, the truth of the hypothesis above suggested; with respect to the agency of putrescent substances in affording a pabulum to
the vegetable matter which emits the dephlogisticated air ; 29. well as in relation to the effect of light, and to the subsequent influence of putrefaction, in destroying the dephlogisticated air already generated.
On the 21st of June, I put a dead mouse into a jar containing 200 ounces of water, inverted in a bason of the same, which I placed in the fun. At the same time, I put another mouse into a jar of the same size, filled with the same water, and placed it in the dark. In this vessel, the water was never discoloured, and very little air was produced; whereas, from the mouse in the sun, there presently issued a quantity of white mucous substance, which foon turned to an intense green, and yielded air most copiously. After some time, the whole jar was full of this thick green matter, and air rose from every part of it; but it was destroyed as soon as it approached the upper part of the jar, where the dead mouse Roated; owing no doubt to the phlogistic matter which issued 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 sun presently yielded permanent air, highly dephlogisticated; whereas that in the dark gave not a fingle bubble : but when I soon afterwards brought it into the sun, it yielded air like the other.
We cannot quit a subject of this general kind, and which requires no profound knowledge in chymistry to be rendered in-, telligible, without transcribing some general reflections of the Author, respecting the wife and provident economy of nature, displayed on lo large a field, and yet on a class of subjects on which her beneficent and extensive operations bad bitherto been carried on in perfect secrecy.
• It is imposible not to observe, from these experiments, the admirable provision there is in nature, to prevent, or lessen, the fatal effects of putrefaction; especially in hot countries, where the rays of the sun are the most direct, and the heat the most intense. For whereas animal and vegetable substances, by simply putrefying, would necessarily taint great masses of air, and render it wholly unfit for respiration, the same substances, putrefying in water, supply a most abundant pabulum for ebis wonderful vegetable substance, the seeds of which appear to be in all places dilpersed invisibly through the atmosphere, and capable, at all icarons of the year, of taking root, and immediately propagating themselves to the greatest extent. By this means, instead of the air being corrupted, a vast addition of the purest, air is continually thrown into it.
. By this means also stagnated waters are rendered much less offensive and unwholesome chan they would otherwise be. That
froth which we also see on the surface of such waters, and which is apt to create disgust, generally consists of the purest dephlo. gisticated air, supplied by aquatic plants which always grow in the greatest abundance, and flourish most in water that abounds with putrid matter. When the sun shines, these plants nay also be seen to emit great quantiries of pure air.
• Even where animal and vegetable substances putrefy in AIR; as they have some moisture in them, various other piants, in the form of mold, &c. find a proper nutriment in them; and by converting a considerable part of the phlogistic effluvium into their own nutriment, arrest it in its progress to corrupt the surrounding atmosphere. So wonderfully is every part of the syrtem of nature formed ; that good never fails to arise out of all the evils to which, in consequence of general laws, most beneficial to the whole, it is neceffarily subject. It is hardly possible for a person of a speculative turn not to perceive, and admire, this most wonderful and excellent provision.'
In the sections immediately following, the Author treats of air produced by substances putrefying in water, and in mercury; and of the inflammable air produced from the paste formed of iron filings and fulphur with water. These observations are followed by others, in which, in opposition to the doctrine of some other philosophers, he snews, that, though the air is phlogisticated by respiration, the perspiration of the body does not injure it. To there succeed some observations and experiments, made with a view to discover the origin of that fixed air which presents itself to observation in respiration and some other phlogiftic processes; and, in particular, to ascertain the quantity of fixed air naturally contained in a given quantity of common air. There are followed by some observations on the respiration of fimes ; and on the production and constitution of dephlogisticated air, particularly on that obtained to commodiously, and in such great plenty, from nitre alone, in an earthen, or rather a coated glass, 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 intense white heat, the Author got no less than 500 ounces of air considerably dephlogisticated, and containing very little fixed air, from two ounces of nitre.-While we are on the sunject of dephlogisticated air, we hall take the opportunity of transcribing an obiervation of the Author's respect ng his opinion that an earth is either the bafis of this and other species of air, or at least exists in a state of folution in them.
• In che rapid production of all kinds of air from earthy mae terials, I have frequently observed that there is a quantity of superfluous white matter deposited in the cold water in which it is received. This earch seems to have been held in solution in the air while it was hot, because it was then quite transparent, and did not become turbid till it was cool; and this is one reason why I think that an earch is the proper basis of all such kinds of air. For if some earth be certainly held in a proper solution, so as to make a constituent part of the air, while hot, as its transparency seems to prove, and it be only deposited 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 should, I should imagine that, as nothing but the acid prins ciple would remain, it would then, like any other acid air, become liable to be immediately absorbed by water.'
The Author's subsequent observations 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 should imagine to be then the same thing, from whatever substance the air had been produced, being then divested of every thing that was peculiar to the substance from which it had been expelled; just as the acid, in the composition of dephlogisticated air, is probably the same thing, whether the air had been produced from materials containing spirit of nitre, or oil of vitriol. If this reasoning be true, we shall be in possession of a method of obtaining a truly primitive earth, or an earthy principle, common to all earths, and all metallic calces whatsoever : since dephlogisticated air may, as I have sufficiently shewn, be produced from them all.'-The Author, however, afterwards relates a few observations which may, perhaps, lead to a contrary conclufion, The matrer certainly deserves a further investigation.
In the 15th section, the Author rectifics a mistake of Dr. Ina 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 sensible advantage, either in point of economy or otherwise, could be derived from the breathing of dephlogisticated air, when resting on lime water. From these experiments of the Author's it appears— that the air confined by Jime water was both diminished and phlogisticated exactly like that which had been confined by common water, by the respiraç tion of [two) mice of cqual size, in the same time. The diminution indeed was, at first, a small matter greater in the air confined by the lime water; because the common water did not imbibe the fixed air so readily: but this made no apparent dif. ference with respect to the mice; and the next day, the two pora
biom them all. may, as I have calces whatlo Principle,
* See M, REVIEW, Vol. lxii. May 1780, p. 3514