A I R 



^rugJ foon lore tlieir virliie ; and many of ihem grow vcr- 

 mi'io'js : it is nAded, that in the inaiid of St. J^.g") tliey are 

 obliged to expofi^thcir fwect-meats daily to the iuii, in or- 

 il^r to txJiale the moiilure contradtd in the night, which 

 would othcrvvife occafion them to putrefy. 



On this piinciple depend the Ihudturc and ufe of the 



BYGROMETIR. 



For the reirafting power of air; fee Rekraction. 



After all, fonie of our more eurious and penetrating 

 natunilifts have obferved certain efTeiSts of iiir, which do not 

 r.ppear to fi'llow fioin any of tlie properties, or materials 

 above recited. In this view, Mr. Boyle has conipofed a 

 ircatife of fufpieions about fome unknown properties ot the 

 air. The planomena of lire and flame in viiiuo feem, ac- 

 cording to him, to argue fonie unknown vital fublhmce 

 diffnfed through the air, on account of which that (Und be- 

 comes fo neceliaiy to the fubfillence of flame. BnfFon fup- 

 pofes that air is ncceffary to the fubfillence of fire, be- 

 caiife it is moft adapted to acquire that expanfive motion, 

 which is the principal property of fire. On this account 

 fire combines with air; in preference to any other fubllance, 

 and in a more inlinrate manner, as being of a nature moll 

 nearly approaching to its own ; and therefore air is the 

 proper aliment and moll powerful affillant of fire. Hilt. 



Nat. Supp. vol. i. . . n r 



According to Dr. Prleftley, the air is a menllrunm for 

 the phlogilton emitted by burning bodies ; which mull ceafe 

 to burn when that mcnllruum is laturated with it. And lie 

 accounts in the fame manner for the fuffocation of animais 

 in a confined fpace. Wh-.n the phlogifton, emitted by 

 burnino- bodies and breathing animals, can no longer be ab- 

 forbed by the ambient air, both Ufe and flame are extinguifli- 

 ed. Exp. and Obf. &c. vol. i. 



For the modern hypothefis, with regard to this fubjeft, 

 fee Combustion- and Phlogiston. 



Thus we find, that many caufes combine to produce very 

 confiderable alterations in the (late of the air, whereby it 

 becomes lefs fit for refpiration, and other purpofes of na- 

 ture ; and if there were no provifion for relloring its falu- 

 brity, it mi-.ft, in time, become univerfally injurious and 

 fatrd. Dr. Prieftley, in the eourfe of his inquiries on. this 

 fnbjcifl, has difcovcred the great rellorativcs, which are pro- 

 vided for this pui-pofe. One of thefe is vegetation. In 

 order to afcertain this faft, he put a fprig of mint, in a 

 vigorous ftate, under a glafs jar, inverted in water ; and he 

 found, contrary to his expeftation, that this plant not only 

 «:ontiniied to \\\'e, though in a languifliing way, for two 

 months ; but that the confined air was fo little corrupted by 

 the effluvia of the mint, that it would neither cxtinguifh a 

 candle, nor kill a fmall animal, which he conveyed into it. 

 He found, likewife, that air, vitiated by a candle left in it 

 till it was burnt out, was perfeilly reliored to its quality 

 of fupporting flame, after another fprig of mint had vege- 

 tated in it for fome time. And, in order to fliew that the 

 aromatic flavour of the plant had no fliare in producing this 

 effeft, he obferved, in a variety of other experiments, that 

 vco-etablcsof an offenfive fmell, and even fuch as had fcarce 

 any fmtll at all, but were of a quick growth, proved the 

 bell for this purpofe. Nay, more, the virtue of growing 

 vegetables was found to be an antidote to the baneful qua- 

 lity of air, conuptcd by animal refpiration and putrefac- 

 tion ; and he infers from a number of fimilar fails, that the 

 injury, which is continually done to the atmofphere, by the 

 refpiration of fo many animals, and the putrefaftion of fuch 

 irAiTes of both vegetable and animal matter, is, in part at 

 lealt, repaired by the vegetable creation ; and notwithftand- 

 •iag the prodigious mafs of air that is corrupted daily by the 



AIR. 



above mentioned caufes ; yet, if we confider the immenfe 

 profufion of vegetables upon the face of the earth, growing 

 in places fuited to their nature, and confcquently at full 

 liberty to exert all their powers, both inhaling and exhaling, 

 it can hardly be thought, that the remedy is not adequate 

 ■ to tiie evil. Dr. Franklin, in a rcfleiSion on this difeovcry, 

 exprelles his hope, that it will give fome cheek to the rage 

 of dellroying trees that grow near houfes, which has ac- 

 companied our late improvements in gardening, from an 

 opinion of their being unt^'holclcme ; adding, from long 

 obfervation, that there is nothing unhealthy in the air of 

 woods, " fir.ce the Americans have their country liabita- 

 tions in the midll of woods, and no pe<iple on earth enjoy 

 better health, or are more prolific." Dr. Prieilley has 

 fince difcovered that light is necefiary to enable plants to 

 purify air : hoivever, pure air is not produced by light or 

 plants, but only by the purification of the impure air to 

 which the plants have aecei'u. Obf. and Exp. on Air, vol. >. 

 p. r8, 24, &c. 



The fea, and other large bodies of water, are the fecond 

 refouree, which nature has provided for reftoring the falu- 

 brity of corrupted air. Dr. Prieilley found, tl'.at all kinds 

 of noxious air were reliored by continued agitation in a 

 trough of water ; the noxious effluvia being firil imbibed by 

 the water, and thereby tranfmitted to the common atmof- 

 phere. And he hence concludes, that the agitation of the 

 fea, and of large lakes and rivers, muil be highly ufeful for 

 the purification of the atmofphere ; the putrid matter being 

 ablorbed by the water, and imbibed by marine, and other 

 aqiuitie plants, or apphed to purpofes yet unknown. Exp. 

 and Obf. vol. i. fe£l. 2. and /j.. 



This ingenious philofopher apprehends, that the agita- 

 tion of water, and the vegetation of plants, purify noxious 

 air, by abforbing part of the phlogifton with which it is 

 loaded ; and that this phlogiilic matter is the moft elTential 

 p:irt of the food and fupport of both vegetable and animal 

 bodies. lb. vol. i. p. 158, 139. 



Dr. Prieftley, improving upon the experiments and in- 

 veftigations of Boyle, Hales, Brownrigg, Black, Macbride, 

 C;'.vendi'h, and others, has dlfcovered many fpecies of air, 

 extracted by various proceifes from different kinds of fuh- 

 ftances ; of which a fummar)- account will be given in the 

 eourfe of this work. See alfo his curious and valuable Ex- 

 periments and Obfervations on different Kinds of Air, in 

 five volumes. And for a compendium of the hiilory of dif- 

 coveries on this fubjedl, Lavoilicr's Effays Phyfical and Che- 

 mical, vol. i. 



For the refinance of the air, fee Resistance. 



Air, unjulation ci. See Sound and Undulation. 



Air, in Chai'i^iy, See Gas. 



Air, yf/m'/fjp/.iericf common air, Gas atmofphenq:!e,_ Fr, 

 Atmofpheric air does not appear to have been the fubjedl of 

 chemical inveftigation before the time of Boyle ; for though 

 Ariftotle, Pliny, and Paracelfus, have written largely con- 

 cerning this fluid, they have confined themftlves to the imper- 

 feft examination uf fome of its phyfical properties, to the men- 

 tion of a few obvious fafts, and to the invention of hypo- 

 thefes, which, as they do not profefs to be founded on ex- 

 periment, may, in the prefent Hate of knowledge, be fafely 

 neglefted. 



it was, indeed, natural, that the great improver of Otto 

 Guericke's original air-pump, fond as he was of chemical 

 purfults, Ihould exercife his talents. in refearches on the pro- 

 perties of the atmofphere, more efpecially as, from the 

 number of fubftanccs continually affuraing the form of va- 

 pour, it was not Improbable that common air fliould prove 

 a vcrj- heterogeneous aisd eafilj' decompofable mixture. The 



' difficulty, 



