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SECTION XII. 



He plants evaporate by night bad air, 

 and foul the common air which 

 Jurrounds them; yet this is far 

 over -balanced by their beneficial 

 operation in the day, 



THE bad air which plants yield 

 by night is fo inconfiderable in com- 

 panion of the quantity of dephlo- 

 gifticated air which they yield by 

 the day-time, that it amounts to 

 very little. By a rough calculation 

 I found, that the poifonous air 

 yielded during the whole night by 

 any plant could not amount to one- 

 hundredth part of the dephlogifti- 

 cated air which the fame plant 

 yielded in two hours time in a fair 

 day. But, from my experiments, 



one 



