A I R 



A I R 



of nitre, 01' aqu;;foitis, readily evaporates by the fire : 

 yet if there be any putrefied urine near the place, the vo- 

 latile fpirit will be fixed, and full down in form of Ai^uA 



SKCUNDA. 



4. Air brings many quiefcent bodies into aftion ; /'. e. 

 excites their latent powers. Thus, if an acid vapour be 

 diffufed through the air, all the bodies of which that is 

 the proper mcnllruum, being diffolved by it, are brought 

 into a Rate proper for action. 



In the various operations of chemiftry, air is a very nc- 

 ceffary and important agent, the refult of particular pro- 

 celfcs depending on its prefence or abfence, on its being 

 open or enclofcd. Thus the parts of animals and ve- 

 getables can only be calcined in open air ; in clofe vcfTels 

 they never become any other than black coals. And thefe 

 operations are effefted by the changes to which the air 

 is liable. Many inllances might be alledged to this pur- 

 pofe. Let it fufficc to obferve, that it is very difficult 

 to procure oil of fulphur, per campanam, in a clear dry 

 atmofphere ; but in thick moill air it may be obtained 

 with greater eafe, and in larger quantities. So pure well- 

 fermented wme, if it be canied to a place where the air 

 is replenilhed with the fumes of new wine, then fermenting, 

 will begin to ferment afrefli. 



The changes in the air arife from various caufes, and 

 are obfervable not only in its mechanical properties, fuch 

 as gravity, deniity, &c. but in the ingredients that com- 

 pofe it. Thus, at Fafhlun, in Sweden, noted for copper- 

 mines, the mineral exhalations affeft the air in fuch a man- 

 ner, as to difcolour the fdver coin in purfes ; and the fame 

 effluvia change the colour of brafs. In Carniola, Cam- 

 pania, &c. where are mines of fulphur, the air fometimes 

 becomes very unwholefome, which occafions frequent epi- 

 demic difeafes, &c. 



The effluvia of animals alfo h.ave their effeft in varying 

 the air, as is evident in contagious difeafes, plagues, murrains, 

 and other mortalities, which are fpread by an infefted ai'"- 



The fudden and fatal effeft of noxious vapours has gene- 

 rally been fuppofed to be principally, if not wholly, owing 

 to the lofs and wafte of the vivifymg fpirit of air. But Dr. 

 Hales attributes this efFeft to the lofs of a confidcrable part 

 of the air's elajlicity, and to the grolTnefs and denfity of the 

 vapours with which the air is charged. He found, by an 

 experiment made on himfelf, that the lungs will not rife and 

 dilate as ufual, when they draw in fuch noxious air, the 

 elallicity of which lias been eonfiderably diminllhed. For 

 having made a bladder veiy fupple by wetting it, and then 

 cutting off fo much of the neck as would make a hole wide 

 enough to admit the biggcft end of a large foffet, to which 

 the bladder was bound ; and then having blown the bladder, 

 he put the fmall end of the foffet into his mouth, and, at 

 the fame time, pinched his noflrils fo clofe, that no air might 

 pafs that way, and he could only breathe to and fro the air 

 contained in the bladder, which, \\'\\\\ the foffet, contained 

 feventy-four cubic inches. In lefs than half a minute, he 

 found a confidcrable difficulty in breathing ; and at the end 

 of a minute, the bladder was become fo flaccid, that he 

 could not blow it above half full, with the greateft expira- 

 tion which he could make ; and at the fame time, he coidd 

 plai;ily 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 he concluded, that a confiderable quantity 

 of the elallicity of the air was deflroyed ; and that when the 

 fuffocating quality of the air was the greateil, it was with 

 mucfi difficulty that he could dilate his lungs in a very fmall 

 degree. From this, and feveral other experiments, lie in- 

 ferred, that the life of animals is prefcrved rather by the 



Vol.. I. 



elaflic force of tlic air acting on their lungs than by its vivi- 

 f) ing fpirit ; and that candles and matenes ccafe to burn, 

 after having been confined in a fmall quantity of air, not 

 bccaufe they have rendered the air effete by confuming its 

 vivifying fpirit, but becaufe they have difchargcd a great 

 quantity of acid fuliginous vapours, which partly defhoyits 

 elallicity, and retard the elaflic motion of the remainder. 

 He likewife found, that air, which paffed through cloths 

 dipped in vinegar, could be breathed to and fro as long 

 again as the like quantity of air, which was not thus pu- 

 rified ; fo that fprinkling the decks of fliips with vinegar 

 may refrefli the air ; and this is confinned by experience. 

 But where the corruption of the air is much greater, a? in 

 clofe prifons, &c. nothing can be an adequate and effeftua! 

 remedy but a ventilator. He obferved, likewife, that air 

 is not difqualified for refpiration merely by the additional 

 moiflure which it receives, but by fome bad quality in that 

 moiflure. See his Statical EfTays, vol. i. p. 250. vol. ii. p. 

 320, &c. 



Dr. Pricflley obferves, that, when animals die upon be- 

 ing put into air, in which other animals have died, after 

 breathing in it as long as they could, it is plain that the 

 caufe of their death is not the want of any pabulum i<it,r, 

 which has been fuppofed to be contained in the air ; but 

 becaufe the air is impregnated with fomething flimulating 

 to their lungs; for they almofl always die in convulfions, and 

 are fometimes affefted fo fuddenly, that they are irrecover- 

 able after a fingle infpiration. And he has found the fame 

 effcft from many other kinds of noxious air. He concludes, 

 from fubfequent experiments, that the air becomes phlogi- 

 flicated in its paffage through the lungs, by means of the 

 blood. Experiments and Obfei"vations on Air, vol. i. p. 71. 

 vol. ii. p. 31. vol. iii. p. 55. See AzoT, Blood, and 

 Respiratiox. 



Vegetables likewife produce a change in the flate of the 

 air. Thus when a great part of the clove trees, which 

 grow fo plentifully in the ifland of Temate, was felled at 

 the folicitation of the Dutch, in order to heighten the value 

 of that fruit, fuch a change enfued in the air, as fliewcd 

 the fiuutary effefts of the effluvia, or rather of the vegetation 

 of the clove-trees, and their bloffoms ; the whole ifland footi 

 after they werecut down, being exceeding fickly. SeeAzor. 



The air is alfo liable to alterations from the feafon of the 

 year. Thus few fubterraneous effluvia are emitted in the 

 winter, becaufe the pores are locked up by the froft, or 

 covered by fnow ; the fubterraneous heat being at work, 

 and preparing a heat to be diieharged in the enfuing fpring. 

 Again, from the winter foliliee to the fummcr folflice, the 

 fun's rays become more and more perpendicular, and confe- 

 quently their impulfe on the earth's furface more powerful ; 

 fo that the glebe, or foil, is more and more relaxed, foftcned, 

 and putrefied, till he amves at the tropic ; where, with the 

 force of a chemical agent, he refolves the fuperiicial parts 

 of the earth into their conflituent principles, water, oil, 

 fait, &c, which are all fwcpt away into the atmofphere. 



The height and depth of the air prodiice a farther altera- 

 tion ; the exhalations not rifing high enough in any great 

 quantity, to afcend above the tops of high mountains. 



From fome experiments with air-balloons, it has been 

 proved, that the air of the higher regions is more impure 

 than that at the furface of the earth ; which is reafonably 

 aferibcd to the oxygen fupplied by vegetation to the lower 

 and contiguous flratum of air. 



Nor mufl drought and moillure be denied their fliare, in 



varying the flate of the atmofphere ; in Guinea, the heat, 



with the moillure, conduces fo much to puticfaclion-, tliat 



the purtll white fugars are often full of maggots ; a<id their 



3 N drug* 



