plants, he examined the air of the first glass, and 
found it to be considerably vitiated, and to contain 
a little carbonic acid, which he ascribed to the noc- 
turnal effect of vegetation ; while the air, in the two 
other glasses, contained one-fifth of acid, and was 
greatly more vitiated. Similar experiments were 
made on three different portions of common air 3 
and with nearly the same results *. In the shade, 
he adds, plants deteriorate the air as much as in per- 
fect darkness, although the colour, which they as- 
sume in darkness, differs much from that which 
they acquire in the shade ; for, in the latter, they re- 
tain their verdure, while, in the former, they become 
white or yellow f. 
292. Besides these experiments on the power pos- 
sessed by plants of purifying the air vitiated by the 
several processes of respiration, vegetation, and com- 
bustion, Dr Ingenhousz made various others with 
the leaves of plants immersed in water, and exposed 
to the light of the sun. From these experiments, he 
was led to conclude, that plants not only correct im- 
pure air in the space of six days or more, as Priest- 
ley's experiments seemed to indicate, but that they 
perform this important office in a very few hours ; 
that this operation is not owing to vegetation, but to 
the influence of the solar light on plants ; that plants 
possess the power of giving out, in a pure state, the 
air which they contain and have derived from the 
atmosphere ; that this operation commences some 
* Exper. t. ii. p. 45. 46. 
t Ibid. p. 47- 
