Chap. 8.] Means of purifying Air. 409 



what with the prefent evafion of that act, the depofit- 

 ing in vaults, and the frequent breaking up of the 

 ground, and removing putrid bodies, the cafe is not 

 much better ; and indeed much might yet be done to 

 render the air of London more falubrious than it is. 



I have taken no notice of the accounts which fome 

 ingenious men have afforded us of the falubrity of the 

 air in different places, convinced that we are not as 

 yet pofleffed of a complete teft of the falubrity of air; 

 and till this can be procured our only guide muft be 

 experience. 



By agitating putrid and inflammable air in diftilled 

 water, or water from which the air has been expelled 

 by boiling, a considerable diminution will take place, 

 fometimes above a third of the bulk, and the air will 

 be conficlerably purified. Thus the agitation of the 

 fea, and of large lakes, has probably the happieft effect 

 in purifying the atmofphere. 



.Dr. Hales found that air might be breathed much 

 longer, when in the act of refpiration it was made to 

 pafs through feveral folds of cloth dipped in vinegar, 

 a folution of fea fait, or oil of tartar, than when no 

 fuch contrivance was ufed * j the reafon of which is 

 briefly, that thefe fubftances abforb the fixable air which 

 comes from the lungs. 



Putrid air was alfo reftored by a mixture of car- 

 bonic acid air. The experiment was, however, in 

 fome rrieafure rendered doubtful by the air having been 

 palled through a veflel of water in order to its admix- 

 ture. If, however, the fact is well founded; lime kilns 

 in the vicinity of populous cities may poflibly not be 

 fo unwholefome as is generally imagined, as in thole 

 places the putrid air and vapours abound more than 

 jhe carbonic acid. 



Kale's Eff. p. 266, 



The 



