C J 97 ] 
but not exceedingly well, thefe eleven days; on which 
account, I had deferred making the trial fo long. 
This reftored air was affedied by a mixture of ni- 
trous air, almoft as much as common air. 
As this putrid air was thus eafily reftored to a 
conftderable degree of fitnefs for refpiration, by 
plants growing in it, I was in hopes that by the 
lame means it might in time be fo much more 
perfectly reftored, that a candle would burn in 
it; and for this purpofe I kept plants growing 
in the jars which contained this air till the 
middle of Auguft following, but did not take fuffi- 
cient care to pull out all the old and rotten leaves. 
The plants, however, had grown, and looked fo 
well upon the whole, that I had no doubt but that 
the air muft coiiftantly have been in a mending 
ftate ; when I was exceedingly furprized to find, 
on the 24th of that month, that though the air in; 
one of the jars had not grown worfe, it was no 
better, and that the air in the other jar was lo much 
worfe than it had been, that a moufe would have 
died in it in a few feconds. It alfo made no effer- 
vefcence with nitrous air, as it had done before. 
Sufpedting that the fame plant might be capable 
of reftoring putrid air to a certain degree only,, 
or that plants might have a contrary tendency in, 
fome ftages of their growth, I withdrew the old 
plant, and put a frefh one in its place ; and found 
that, after feven days, the air was reftored to its 
former wholefome ftate. This fa£t I conlider as a 
very remarkable one, and well deferving of a far- 
ther invefrigation, as it may throw more light upon 
the principles of vegetation. It is not, however, 
7 a fingie - 
