22] AIR while, in such complaints, the most powerful remedies have been un- able to compensate the want of this necessary article. Air vitiated by the different pro- cesses of respiration, combustion, and putrefaction, or which is suf- fered to stagnate, becomes prejudi- cial to the human frame : hence large cities, public assemblies, hos- pitals, burying-grounds^ &:c. are in- jurious to health, and often produc- tive of coritagidds disorders. Plants and vegetables possess the wpnderful property of restoring the purity of air. This, however, takes place only in the day-time, and when they arc exposed to the. light of the sun : for at night they dis- charge their noxious particles, and corrupt the atmosphere. Never- theless, the disadvantage arising from their impure exhalation dur- ing ihe night, is far exceeded b] benefits produced in the day-time ; as the former does not amount to a hundredth part of the pure vital air, which is generated by the same plant, in the course of two hours of a fine day. It has been asserted, that the purity of air may be also restored by wetting a cloth in w a- ter mixed with quick-lime, hanging it in a room until it become dry, and renewing the operation so long as it appear needful. Air has been most successfully applied to various purposes of do- mestic economy, and in many branches of the useful arts ; such as in the construction of wind-mills, air-guns, stoves, &c. A mode of forwarding the distil- lation of salt water at sea, has been discovered, and consists simply in blowing currents of air through the distilled fluid. The same me- thod has also been successfully cm- AI R ployed to take off the unpleasant taste which is sometimes found in milk. Dr. Reich, of Erlang, describes a particular machine for the pur- pose of extracting air from the in- testines, and thus procuring instant relief in a complaint called tr Tikes, or the dry windy dropsy. A small tube with a cock having a valve on its side, and so constn I as to turn quickly, is airixed to the common clystering machine. Upon each successive introduction, the cock must be turned, in order to admit the air into the tube, and then quickly closed. Air which is rarefied, ascends. This is particularly exemplified in the periodical sea and land b; of hot climates ; where, in conse- quence of the reflection of the sun . the earth's- unequal, surface, the lover land-air become., highly
- d. and lises inio the upper at-
mo! phere, while me sea-air, being cool and deVise, rashes in to supply its place. Upon this principle, M. Van Makum, a Dutch chemist, has discovered a method of purifying assembly-rooms by a tin tube of nine inches diameter, and ten feet lengthy to the lower surface of which lamps are suspended, for the purpose ot rarefying the air, and .it to ascend through the cieling of the room. Dr. Hales has described the J effects produced in French prisons, by long air-trunks fixed through die cielmgs of wards in gaols, to cany oiY the foul vapours which exhale, bom die prisoners : he declares that it has not only pre- served many of their lives, but pre- yented them from communicating infectious distempers to persons as- sembled in the courts of judicature. We
