[a9 q 
SECTION XI. 
The plants evaporate by night bad airs. 
and foul the common air which 
furvounds them; yet this. is far 
aver-balanced by their beneficial 
operation in the day. 
‘THE bad air which plants yield 
by night is fo inconfiderable in com- 
parifon 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, 
S865: one — 
ee 
Ree 
“ : 
