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proper fiiliiecta, which are fufceptible of fuch difpofition ; 

 wliicli fluids, from tlie fmoothncfs, round'.icfs, and flippKri- 

 ncl's of their parts, are not. 



liiit Sir llaac Newton (Optics, p. 371.) expliiins the 

 matter olherwii'e ; fuch a texture, he thinks, by no means 

 liifficicnt to account for that vallpowirof elallicity oblVrved 

 in air, which incapable of diffulhujitlelf into above amiUion 

 of tnnes more fpace than it before pofTcffcd. — But, as all 

 bodiei are ihcvvn to liave an attractive and repelling power ; 

 a id as both tlicfe are ftronger in bodies, the denfer, more 

 compad, and Iblid they arc ; hence it follows, that when by 

 )ieal, or any other powerful agent, the attractive force n 

 furmounted, and the particles of the body leparated fo far 

 »s to be out of tlie fphere of attraclion ; the repelling power 

 which then commences makes them recede from each other 

 with a (Irong force proportionable to that with which they 

 before cohered ; and thus tiiey become permanent air. And 

 he has proved, that particles, endeavouring to recede from 

 each other with forces reciprocally proportional to the dif- 

 tance between their centres, will compole an elallic fluid, 

 whofe denfity (hall be proportional to its comprcliion. 

 Hence, fays the fame author, it is, tliat as the particles of 

 permanent air are groflcr, and rife from dcnfer bodies, than 

 thole of tranfient air, or vapour, true air is more ponderous 

 than vapour ; and a moid atmofphere is lighter than a dry 

 one. 



The elaftic power of the air above illullrated and evinced, 

 is the fecond great fource of the eifeCls of this important 

 ■ fluid. By this property, it infinuntes itfelf into the pores 

 of bodies, and by ponclfuig this prodigious facultv of ex- 

 p;inding, which is to cailly excited, it mull neceflarily put 

 the particles of bodies into which it infinuates itfelf into 

 perpetual ofcillations. Indeed, the degree of heat, and the 

 air's gravity and denfity, and confcqueiitly its elali;icity and 

 expaniion, never remaining the fame for the leail fpace of 

 time, there niufl be an inccflant vibration, or dilatation and 

 contraction of all bodies. 



We oblen'e this reciprocation in feveral inftances, parti- 

 cularly in plants, the traches, or air-veffels of whicli per- 

 form the office of lungs ; for the .contained air alternately 

 expanding and contracting, as the heat incrcafes or is dimi- 

 nilhed, by turns comprelfes the veffels, and cafes them again : 

 and tlius promotes a circulation of their juices. See AiR- 



Hence, we find, that no vegetation nor gennination will 

 proceed ;/i ^v/^•«o. Indeed beans Iiave been obferied to sjrow 

 a little tumid therein ; and this has ltd fome to attribute 

 t!iat to vegetation, which was really owing to no other caufe 

 than the dilatation of the air within them. 



The air is very inllrumental in the produdion and growth 

 of vegetables, not only by invigorating their feveral juices, 

 while in an elailic active rtate, but alfo by greatlv contri- 

 buting in a fixed Hate to the union and firm connection of 

 their feveral conllituent parts, and by fupplying them with 

 that food or pahilnm, which contributes to their growth. 



From the fame caufe it is, that the air contained in bub- 

 bles of ice, by its continual adion, burfts the ice ; and thus 

 aifo, as well as by the expanfion of freezing fluids, glafTes 

 and other veflels frequently crack, when their contained 

 liquors are frozen. Thus alfo, entire columns of marble 

 fometimes cleave in the winter time, from fome little bubble 

 of included air's acquiring an increafed eiailicity : and to 

 this it is owing, that few Hones will bear to be heated by 

 the fire without cracking by the expanfive force of the air 

 confined within their pores. From the fame principle arife 

 pulrefriclion -^nd fermentation ; neither of which will proceed, 

 even in the beft difpofed fubjeds, in vacuo. 



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Since we find fuch great quantities of elaftic air, gene- 

 rated in the folution of animal and vegetable fubllances, a 

 good deal mud conllantly arife from the diifolution of thefe 

 elements in the llomach and bowels, which is much pro- 

 moted by it : and refpiration, a!;d even animal life, depend 

 ill a great mcafure upon the air. 



In reality-, all natural corruption and alteration feem fo 

 depend on air ; and met jls, particularly gold, only feem to 

 be durable and incoiTUptible, in virtue of their not being 

 pervious to air. 



Air, e/feCls of the d'ljfsrent in^red'unts of. Air not only 

 ads by its common properties of gravity and elaiiicity, but 

 there are numerous otlier effeds, anfing from the peculiar 

 ingredients of which it conllits. 



"Thus, I. It not only dilfolvcs and attenuates bodies by 

 its preffure and attrition, but as a chaot containing all kinds 

 of menilrua, and confequcntly poflefiing powers for diflblving 

 all bodies. It is known that iron and copper readily 

 diifolve, and become ruily in air, unlefs well defended with 

 oil. Boerhaave afFures us, that he has feen pillars of iron fo 

 reduced by air, that they migiit be crumbled to duft between 

 the fingers ; and as for copper, it is converted by the air 

 into a fubllance much hke the verdigrife produced by 

 vinegar. 



Mr. Boyle relates, that in the fouthern Englith colonies 

 the great guns mil fo faft, that after lying in the air for a 

 few years, large cakes of crocus mortis may be feparated from 

 them. Acoflia adds, that in Peru the air diflolves lead, and 

 conliderably increafes its weight. Yet gold is generally ef- 

 teemed indiflbluble by air ; being never found to contrad 

 mil, though expofed to it ever fo long. In the laboratories 

 of chemiiis, however, where aqua regia is prepared, the 

 air becoming impregnated with an unuiual quantity of this 

 mcnilruum, gold contrads a mil like other bodies. 



J'tones alfo undergo the changes mcident to metals. — 

 Thus, Purbeck Hone, of which Sahfbui-y cathedral con- 

 fifts, is obfci-ved gradually to become fofter, and to 

 moulder awav in the air; and Mr. Boyle gives the fame 

 account of Blackington ftone. He adds, that air may 

 have a confiderable operation on vitriol, even when a 

 ftrong fire could ait no further upon it. And he has 

 found, that the fumes of a corrofive hquor work more 

 fuddenly and manifeflly on a certain metal, when fuftained 

 in the air, than the menllruum itfelf did, which emitted 

 fumes on thofe parts of the metal which it covered ; 

 referring to the effedls of the effluvia of vinegar on 



COPPER. 



The diffolnng power of air is increafed by heat, and bv 

 other caufes. It combines with water ; and, by accefs of 

 cold, depofits part of the matter which was kept diflblved 

 in it, by a greater degree of heat. Hence the water, by 

 being depofited and condenfed upon any cold body, fuch 

 as gliifs, &c. in windows, forms fogs, and becomes ^^fible. 

 Air, hkewife, has been fuppofcd, by means of its diffolving 

 power, to accelerate evaporation and distillation. 

 2. Air volatilizes fixed bodies. Tims, fea-falt, being firll 

 calcined, then fiifed by tb.e fire, and when fufed, expofed 

 to the air to hquify ; when liquified fet to dry, and then 

 fufed again, repeating the operation, will, by degrees, 

 be almoit wholly evaporated ; nothing but a little earth 

 remaining. Helmont mentions it as an arcanum in che- 

 miftry, to render fixed fait of tartar volatile ; but this is 

 eafily effedied by air alone : for, if fome of this fait be 

 expofed to the air, in a place replete with acid vapours, 

 the fait draws the acid to itfelf, and when fatiu-ated with 

 it, is volatile, 



3. Air alfo fixes volatile bodies. Thus, though fpint 

 I of 



