19 
of carbonic acid, corresponding, nearly, with the 
quantity of oxygen gas, which the air, employed in 
the experiment, actually contained. 
225. There is, however, one possible source of 
fallacy in these experiments, which our friend Mr 
Murray, who repeatedly witnessed their progress, 
and has expressed himself fully satisfied of their ap- 
parent accuracy, has since suggested, to which it be- 
comes us to attend. " The plants submitted to ex- 
periment, both in the experiments of Scheele and of 
Mr Ellis, were," he observes, " those the white 
and succulent stems of which are large in proportion 
to their leaves, such, for example, as peas and mus- 
tard. Now, it appears from the experiments of In- 
genhousz and Saussure, that it is only by the green 
parts of plants that carbonic acid is decomposed and 
oxygen evolved ; while from the white and succulent 
parts, it is established by Saussure, that carbonic 
acid is formed by the action of the oxygen of the 
surrounding air upon them *." A similar objection, 
occurred to Dr Henry, who saw the experiments re- 
peated in June 1 807, and satisfied himself of their 
general accuracy in other respects, by obligingly 
taking the trouble to analyse the residual air. 
226. In order to meet this objection, it is neces- 
sary to recur again to experiment, and to employ 
plants of a greater age, or such as have no white 
parts belonging to them. With this view, we pro- 
cured several plants, which grew in small garden 
pots, and placed them to vegetate in given quantities 
* Syst, Cheni. vol. iv. p. 53. 1st edit. 
B 2 
