46 
ed, that, in certain circumstances, growing vegeta- 
bles purify the air, yet such concession would not 
destroy the fact, that, in other circumstances, they 
cause its deterioration ; and the imperfections, and 
contrarieties, which have been demonstrated in the ex- 
periments themselves, altogether annihilate their au- 
thority in establishing the general conclusion, which 
he has sought to deduce from them. 
264. But in the experiments, which we before 
published (32. 3. 4.), we endeavoured to shew, from 
a careful observation and analysis of the air before 
and after the experiment, not only that a substitution 
of carbonic acid for oxygen gas took place in vege- 
tation, but that the bulk of acid produced correspond- 
ed nearly, if not exactly, to that of oxygen gas 
which disappeared. In the experiments, also, which 
have now been related (236.), where the air was ex- 
amined before the oxygen gas was entirely consumed, 
the bulk of acid abstracted by lime water, and the 
bulk of oxygen gas removed by phosphorus, com- 
posed together almost exactly the absolute quantity 
of oxygen which the atmosphere originally contain- 
ed ; which coincidence appears to us decisive, not only 
of the conversion of the oxygen gas into carbonic acid, 
but proves, farther, that none of this gas is retained 
by the living plant. We may add, that the results 
obtained by Hales, by Scheele, by Ingenhousz, and 
by Senebier, concur, more or less completely, to es- 
tablish the same position, which is still farther forti- 
fied by the analogy derived from the case of seeds 
(208.), and by the inconsistency of supposing, with- 
out any better evidence than conjecture* that, while 
