vegetable creation; and that, notwithstanding the prodigious quantity of this fluid that is thus daily contaminated, yet, if we confider the immenfe profufion of vegetables that cover the face of the earth, it can hardly be doubted that they are qualified to counteract and correct this corruption; and that, in fine, the remedy may be thought to be nearly adequate to the evil. He fuppofes likewife that the restoration of the air, thus vitiated, is effected by plants imbibing the phlogifiic matter, with which it is overloaded by the caufes abovementioned.

This falutary effect appears evidently to be the result, not of mere vegetable matter, or of the principles of which it confifts, confidered in a chemical view; but of the vital economy or agency of the plant, confidered as an organised body, or of the powers which it poffeffes in confequence of its being in a ftate of growth, or life. For vitiated air was in no respect meliorated, though the Author frequently, and for a long time, introduced to it a great number of the fresh leaves of mint. On the contrary, a frefn cabbage leaf produced an oppofite effect. On being put into a jar, containing common air, for the fpace of one night only, it fo affected it that a candle would not burn in it the next morning; though it had not acquired any fmell of putrefaction. That the reftoration of the infected air did not depend on the aromatic effluvia of the mint, which was the plant ufually employed by the Author in his experiments, was evident; as it was rendered equally falubrious by introducing groundfel, and ftill more readily by inclosing fpinach, a vegetable of quick growth; by which a jar of burned air was perfectly restored in four days, and another in two.

fin

Paffing over with reluctance the many other curious facts and ingenious reflections contained in thefe two fections, as well as in the third and fifth, where the Author treats of Inflammable Air, and of air rendered noxious, or diminifhed, by means of a pafte made of brimftone, iron filings, and water, ftanding in it; we are induced to dwell more particularly on the fubject of the fixth fection, in which the Author treats of a very gular elaftic fluid, to which, on account of its properties, and the fubftance by means of which it is procured, he has given the name of Nitrous Air. An experiment related by Dr. Hales * gave the Author the first hint of this fubject, which has proved fo fruitful in his hands, and ftill promifes abundant matter for future investigation.

This peculiar fpecies of air is readily procured from iron, copper, brafs, tin, filver, quickfilver, bismuth, and nickel, on adding to them the nitrous acid only; and from gold and the regulus of antimony, by the combination of the fame acid with.

See Statical Effays, vol. I. page 224, and vol. II. page 283.

fea

1

fea falt, or aqua regia. It is procurable likewife from a mixture of the nitrous acid with inflammable fpirits, in the procefs for making nitrous æther without diftillation; and poffibly from moft fubftances containing phlogifton, on which the nitrous acid acts fo as to produce heat and effervefcence.

One of the most confpicuous properties of this kind of air is, that though it is perfectly tranfparent and colourlefs, yet, on being added to common air, the mixture becomes opaque, of a turbid red or deep orange colour; and a confiderable diminution of the bulk of the united fluids is produced, attended with effervescence and heat. If one measure of nitrous air be put to two measures of common air, in the space of a few minutes (by which time the effervefcence will be over, and the mixture will have recovered its tranfparency) there will want about oneninth of the original two measures of common air;-and ‹ in a day or two, there will remain only one fifth lefs than the original quantity of common air.'

I hardly know any experiment,' fays the Author, that is more adapted to amaze and furprize than this is, which exhibits a quantity of air, which, as it were, devours a quantity of another kind of air half as large as itfelf, and yet is fo far from gaining any addition to its bulk, that it is confiderably diminifhed by it. If, after this full faturation of common air with nitrous air, more nitrous air be put to it, it makes an addition equal to its own bulk, without producing the least rednefs, or any other visible effect.'

The effervefcence and diminution thus produced is attended with this remarkable and convenient circumftance, of which the Author foon availed himself, that it is peculiar to the admixture of nitrous air with common air, or with air in fome degree fit for refpiration. For no effervefcence or diminution attends the mixture of nitrous with fixed, or inflammable, or any other air unfit for refpiration. Happily too, the quantity of the diminution, on the admixture of nitrous with atmospherical air, appears to be very nearly, if not exactly, in proportion to the purity or falubrity, of the latter. This difcovery was highly agreeable to the Author, as he was hereby furnished with a teft of the purity of air, much more accurate, and which he could certainly employ with much more fatisfaction, than his former method of trying the falubrity or noxious qualities of different airs, on mice or other innocent animals. And as the degree of diminution proceeds from o, (in the cafe of the admixture of nitrous with thoroughly noxious air) to more than one-third of the whole of any given quantity of air (in the cafe where the atmospherical air is perfectly pure) the Author became thus poffeffed of a prodigioufly large fcale; by which he could diftinguish very minute differences, in the goodness of air, and mea

fure

fure those differences, or the respective degrees of purity, as indicated by the quantity of the diminution, with great exactness. To give an inftance of the accuracy, or fenfibility, of this teft:-the Author observes that, if he did not deceive himself, be has by its means perceived a real difference between the air without doors, and that of his ftudy after a few perfons had been with him in it. And further, a vial of air having been fent him from the neighbourhood of York, it appeared not to be fo good as the air near Leeds; that is, the diminution, on the addition of an equal quantity of nitrous air, was not fo great in the former cafe as in the latter. He even thinks it poffible, by means of this teft, to diftinguifh fome of the different winds, or the quality of the air in different feafons of the year.

As the nature of our work will not permit us to enter into the more complicated experiments relating to nitrous air, we fhall confine ourselves to an enquiry into the chemical nature, or compofition, of this fingular fluid, as collected from this fection, and from the obfervations contained in the second part of this work, where the Author refumes the confideration of this fubject, and recites the many additional discoveries relating to it, made by him fince the publication of the first part.

Nitrous air on being agitated with water, after the same manner in which the Author had formerly impregnated water with fixed air, appeared to him to communicate a very acid tafte to the water; and thence he was led to fufpect that the nitrous acid was contained in it. It appears, however, from a letter of Mr. Bewly's, a correfpondent of the Author, printed in an Appendix to this work, that by agitating water with nitrous air alone, the latter will not be decompounded, or communicate to the water any fenfibly acid impregnation; but that the prefence of common air is abfolutely neceffary to produce these effects: and he accounts for the deception which may naturally be occafioned, on the tafting of the water after fuch agitation, by attributing it to the admixture or commenftruation of the common with the nitrous air, in the neck of the vial, and at the very inftant of applying the latter to the mouth. The juftice of the Author's fufpicion, that the nitrous acid is contained in water impregnated with nitrous air, is confirmed by the fame correfpondent; who obferves that nitrous air, thus decompounded by atmospherical air, and afterwards neutralifed by the addition of a fixed vegetable alcali, furnished him with real cryftals of nitre.

In the profecution of his numerous and curious experiments on this fubject, related in the fecond part of this work, the Author difcovered that nitrous air was decompounded, or re

folved

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folved into its content principles, by an admixture of common air, which lets loose the acid contained in it, and separates it from the phlogiflon, which he supposes to be its other conflituent principle. At the fame time, the phlogifton, entering into and combining itself with the common air, produces a diminution of it, in the fame manner as that principle was found to do, in a variety of other proceffes. There is reafon however to fufpect that the greatest part of the very confiderable diminution, obfervable on the mixture of nitrous with common air, proceeds from the great change produced in the nitrous vapour; which from a ftate of confiderable expanfion, in the form of an elastic fluid, is thus reduced into its fmalleft poffible dimenfions, and condenfed into the fize of a small drop or two of nitrous acid.

The union of the nitrous acid with the phlogifton, or other principle with which it is combined in nitrous air, is indeed fo ftrict, or their affinity to each other is fo ftrong, that this acid, as we have found, will not leave the phlogiston, although a fixed alcali, or even a cauftic calcareous earth, diffolved in water, be prefented to and agitated with it, unless common air be admitted. The nitrous acid, contained in nitrous air, will, for inftance, pafs through a folution of falt of tartar, or through lime water, and will bear being long agitated with thefe fluids, without being neutralifed, or fentibly condenfed. But on inverting the vial, and fuffering common air to enter through the liquor, it immediately and vifibly diffolves the union between the acid and the other principle; and leaves the former at liberty to combine itfelf with the alcali, or cauftic earth of the lime, to a neutral salt

It appears however, from fome of the Author's experiments, that nitrous air alone is capable of being abforbed by, or diffolved in water, by long agitation. In fome of these cafes we should apprehend either that it is decompounded by the air which, as M. de Luc has lately fhewn, is obftinately retained by all water; or probably that water is capable of receiving a fmall portion of it in an undecompounded ftate; in the fame manner as vitriolic ether, which is ufually confidered as infoluble in water, may be totally diffolved in it by adding fresh parcels of that fluid to it.

Out of the many experiments relating to this fluid we shall felect one, which prefents a very amufing phenomenon, that first cafually occurred to the Author, and for fome time exercifed his fagacity; not only in endeavouring to account for the cause of it, but likewife in difcovering the effential circumftances on enable him which the appearance depended, fo as to be enabled to repeat the experiment at his picafure. He at length fucceeded in both

thefe

thefe particulars, and thereby procured a more intimate knowledge of the conftituence of nitrous air than he had been able to acquire before.

On mixing nitrous with common air in an inverted jar placed in a trough of water, when the diminution of the air was nearly completed the jar began to be filled with the most beautiful white fumes, refembling the falling of a very fine fnow. On endeavouring however to repeat the experiment, he was frequently unfuccessful, and fuftained the mortification of baulking the expectations of his friends, to whom he meant to exhibit it. After many trials and reflections on the fubject, he at length discovered the effential circumftances on which the appearance depended; and particularly that it was produced by the volatile aleali emitted from the water, which was in a flight degree putrid. The experiment made in the following manner exhibits this curious appearance to the best advantage.

The fmalleft drop of any volatile alcaline liquor, fuch as fpirit of hartfhorn, or fal ammoniac, or a fmall piece of the folid volatile falt, is put into a tall glass jar containing common air, the mouth of which is stopped with a cork. This jar is intro duced within a larger jar inverted, and containing nitrous air. The moment the cork is removed, by means of a particular contrivance for that purpose, the white clouds abovementioned begin to be formed at the mouth of the jar, and presently defcend to the bottom, fo as to fill the whole, were it ever fo large, as with fine fnow.'-Or a piece of volatile falt, inclofed in a bit of gauze, muflin, or a small net of wire, is fufpended in a jar of common air. Soon after the admiffion of a quantity of nitrous air to it, and when the redness produced by the mixture begins to go off, the white cloud, like fnow, begins to defcend from the falt, as if a white powder was fhaken out of the bag that contains it; and this appearance will last about five minutes.

This white powder, and the white clouds attending this mixture, are nothing more, as the Author jully concludes, than a nitrous fal ammoniac, extemporaneously formed; in consequence of the decompofition of the nitrous air effected by the common air, which receives the phlogifton of the former, and at the. fame time lets loofe its acid, which is now at liberty to unite with the fumes of the volatile alcali, and produce the neutral or ammoniacal falt under the form of a white cloud, or of a powder refembling fnow.

In the feventh and eighth fections, the Author investigates the nature and caufe of the injury done to the air by the fumes of burning charcoal; and of the fimilarly and equally noxious impregnation which it receives from the calcination of metals. In REV. Aug. 1774.

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