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there was no difference of fpecific gravity difcernable between the true and factitious Air, neither was there any difference found between their elasticities.
The Air was thus produced by means of fire ; but the pro- duction, fixation, and abforption of Air, may alfo arife from effervefeence and fermentation, by the "mixture of variety of jblids and fluids. And this method of producing, of abforb- ing, and of fixing the elaftic particles of Air, by effervefeence and fermentation, feems to be more according to nature's ufual way of proceeding, than the other by fire. Thus half a cubic inch of oyfter-fhell, and a cubic inch of oil of vi- triol, generated thirty-two cubic inches of Air. But a cubic inch ot lemon juice, and near an equal quantity of fpirit of hartfhorn, per fe, that is, not made with lime, did, in four hours, abforb three or four cubic inches of Air ; and the fol- lowing day, it remitted or generated two cubic inches of Air ; the third day, turning from very warm to cold, it again ab- ibrbed that Air, and continued in an abforbing Hate for a day or two.
It alfo appears, from the fame ingenious author's experiments, that there is great plenty of Air incorporated into the fub- ftance of vegetables, which, by the action of fermentation, is roufed into an elaftic ftate. Thus forty-two cubic inches of ale from the tun, which had been fet to ferment thirty-four hours before, generated, from the 2d of March to the 9th of June, 639 cubic inches of Air, with a very unequal pro- greffion, more or lefs, as the weather was warm, cool, or cold, and fometimes upon a change from warm to cool, it reforbed Air, in all, thirty-two cubic inches. Peafe, wheat, and barley, do alfo, in fermentation, generate great quantities of Air.
That this Air arifing in fuch great quantities, from ferment- ing and diffolving vegetables, is true permanent Air, is certain, by its continuing in the fame expanded elaftic ftate for many weeks and months ; which expanding watery vapours will not do, but foon condenfe when cold. And that this new ge- nerated Air is elaftical, appears not only from its dilating and contracting wirh heat and cold, as common Air does, but alfo by its being compreffible, in proportion to the in- cumbent weight, as Mr. Hales found, by two ingenious ex- periments. See Veget. Stat. chap. 6. exper. 88, 89. If to the Air generated from a veffel of any vegetable liquor, by fermentation, we add the Air that might "afterwards be obtained from it, by heat, or diftillation ; and to that alfo the vaft quantity of Air, which is found to be contained in the tartar which adheres to the fides of the veffel ; it will follow, that Air makes a very confiderable part of the fubftance of vegetables, as well as of animals.
But it is reafonable to think, that moft of thefe aflive par- ticles of the new generated Air were in a fixed ftate in the vegetable fubftance, before they were roufed and put into an aflive repelling ftate, by fermentation and fire. For if they were in an elaftic ftate, in an apple, for inftance, of fixteen fquare inches furface, this fruit generating forty-eight times its bulk of Air, this Air, when compreffed in the apple, muft confequently be forty-eight times, at leaft, more denfe than common Air, and therefore cannot be retained by a force lefs than forty-eight times the weight of our atmofphere ; which, upon a furface of fixteen fquare inches, would amount to 11776 pounds. Now, the expanfive force of the com- preffed Air muft alfo be equal to this, action and reaction being equal. But fo great a force muft tear the apple to pieces. It feems therefore, that moft of thefe particles of Air were in a fixed ftate, ftrongly adhering to, and wrought into the fubftance of the apple ; although, on the other hand, • it be evident, from fome of Mr. Halcs's experiments, that innumerable bubbles of Air inceffantly rife through the fap of vines, and that we may therefore prefume, there is a confiderable quantity of Air in vegetables, upon the wing, and in a very aflive ftate, efpecially in warm weather, which increafes their aaivity. V. Veget. Stat, exper. 34, 38. Air may alfo be produced from mineral fubftances, by the action of fire in diftillation ; and the ingenious author fo often quoted fhews us alfo, by many experiments, that great plenty of Air is generated by fome fermenting mineral mixtures, abforbed by others, and by others alternately generated and abforbed ; and it was remarkable, that the fame mixtures changed from generating to abforbing, and, vice verfci, fome- times with, and fometimes without any fenfible alteration of the temperature of the Air. Hales, Veget. Stat, exper. 90, 91, &c.
Some mixtures have a very Strong abforbing effect. Thus two cubic inches of lime, and an equal quantity of fal armo- niac, abforbed 115 cubic inches of Air- Hales, ib. exper. ico. Filings of iron alio, with fpirit of nitre, either with an equal quantity of water, or without water, abforbed Air, but moft without water; whereas one fourth of a cubic inch of filings ot iron, and a cubic inch of oil of vitriol, with three times its quantity of water, generated 108 cubic inches of Air. Id. exper. 94.
Burning and flaming bodies, as alfo the refpiration of ani- mals, deftroy the elafticity of the Air in part ". Thus burn- ing of nitre, although it produce a large quantity of new Air, yet the elafticity of this Air daily dtcrcafes, in the fame man- SurPL. Vol. I.
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ner as Mr. Haukfbee b obferved the Air of fired gun-powder to do.— [ a Hales, Exper. 102. b Pbyftco-Mcchan Exper. P* B3.J
By the burning of rags dipped in melted brimftone, in a clofe veflel ? one tenth of the whole Air of the vefiel was abforbed. And it was obfervable, that more Air in proportion was ab- forbed in fmall vefTels than in large ones. The like happens by the burning of a candle. And the Air abforbed by burn- ing brimftone, or the flame of a candle, does not recover its elafticity again. Hales, ib. exp. 104.
A grofs Air loaded with vapours, is more apt, In equal times, to lofe its elafticity in greater quantities, than a clear Air, Mr. Hales obferved, as to the burning of candles in clofe vefTels, that where the vefTels are equal, and the fize of the candles unequal, the elafticity of more Air will be de- ftroyed by the large, than by the fmall candle. And where candles are equal, there moft Air,, in proportion to the bulk of the vefTel, will be abforbed in the fmalleft veffel ; though, with equal candles, there is always moft elaftic Air de- ftroyed in the largeft veffel, where the candle burns longeft. The fame author tells us, he was never able to deftroy the whole elafticity of any included bulk of Air, whether com- mon or faclitious. The reafon of which he takes to be, that when any quantity of Air is faturatcd with abforbing vapours to a certain degree, no more elaftic Air is abforbed, not- withftanding that the fame quantity of abforbing fubftances would, in a larger quantity of Air, have abforbed much more, Ib. exper. 106. in fin.
Dr. Mayow found, that a moufe abforbed one fourteenth of the whole Air in a glafs veffel. Mr. Hales tried the experi- ment with a full grown rat. The creature lived about four- teen hours, in which time, the quantity of elaftic Air ab- forbed was above one twenty-feventh of the whole, and nearly the fame with what wasf abforbed by a candle. And in thefe experiments with animals, as alfo in the cafe of burning brim- ftone and candles, more Air was found to be abforbed in large vefTels, than in fmall ones ; and vice verfa, more Air, in proportion to the capacity of the vefTel, was abforbed in fmall than in large vefTels. Ib. exper. 107.
The elafticity of the Air is alfo greatly deftroyed by the ref- piration of human lungs. See Respiration and Lungs. The fudden and fatal cffecT. of noxious vapours has generally been fuppofed to be wholly owing to the lofs and wafte of the •vivifying fpirit of Air. But this effect may not unreafonably be alfo attributed to the lofs of a confiderable part of the Air's elafticity, and the groffnefs and denfity of the vapours, with which the Air is charged ; for mutually attracting particles, when floating in fo thin a medium as Air, will readily coa- lefce into grofler combinations. And this effect, of vapours having not been duly obferved before, it was concluded that they did not affect, the Air's elafticity j and that, confequently, the lungs muft needs be as much dilated in infpiration by this, as by a clear Air. But Mr. Hales found, by an experiment made on himfelf, that the lungs will not rife, and dilate as ufual, when they draw in fuch noxious Air, which decreafes faft in its elafticity. For having made a bladder very fupple by wetting of it, and then cut off fo much of the neck, as would make a hole wide enough for the biggeft end of a large foflet to enter, to which the bladder was bound faft ; and having blown up the bladder, he put the fmall end pf the foflet into his mouth, and, at the fame time, pinched his noftrils clofe, that no Air might pafs that way, fo that he could only breathe to and fro the Air contained in the blad- der, which, with the foflet, contained feventy-four cubic inches. In lefs than half a minute, he found a confiderable difficulty in breathing, and was forced to fetch his breath very faft; and, at the end of the minute, the fuftocating un- eafinefs was fo great, that he was forced to take away the bladder from his mouth. Towards the end of the minute, the bladder was become fo flaccid, that he could not blow it above half full, with the greateft expiration he could make ; and, at the fame time, he could plainly perceive that his lungs were much fallen, in the fame manner as when we breathe out of them all the Air we can at once. Hence it appeared^ that a confiderable quantity of the elafticity of the Air in the bladder and his lungs was deftroyed ; and that when the fuf- focating quality of the Air of the bladder was greateft, it was with much difficulty that he could dilate his lungs a very little.
The ingenious author thinks, from this, and feveral other experiments, that the life of animals is preferved rather by the elaftic force of the Air a£ting on their lungs, than by its vi- vifying fpirit ; and that candles and matches ceafing to burn, foon after they are confined in a fmall quantity of Air y feems not to be owing to their having rendered that Ait effete, by having confumed its vivifying fpirit ; but fhould rather be owing to the great quantity of acid fuliginous vapours, with which that Air is charged, which deftroy a good deal of its elafticity, and very much clog and retard the elaftic motion of the remainder. See Animal Li?e and Fire. It feems evident alfo, from Mr. Halcs's experiments, that the matter often loft in the chemical analyfes of bodies is elaftic Air , a very active principle in fire, but not elemental fire, as Lemery, and other chernifts, fuppofe. See Fire.
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