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XX. On a certain Excretion of Carbonic Acid by Living Plants. By J. Broughton, 
B.Sc., F.C.S., Chemist to the Cinchona Plantations of the Madras Government. 
Communicated by J. D. Hookee, M.B . , F.B.S. 
Received March 31, — Read April 29, 1869. 
While I was engaged in some experimental determinations of the changes that take 
place in the composition of the Cinchona barks after being taken from the tree, a some- 
what singular circumstance was noticed. Some freshly gathered barks being placed in 
a dish over water and covered with a bell-jar, in order to prevent loss of weight by eva- 
poration, it was noticed that after a few hours the level of the water became depressed 
in the jar, and that frequent bubbles of gas escaped through the water. When it is 
remembered that the peculiar tannin of the cinch onse absorbs oxygen from the air, the 
increase in the volume of the air appeared unaccountable. 
A direct experiment was therefore made, in which 5 grms. of the fresh bark of C. offici- 
nalis were placed with 11 ’2 cub. centims. of oxygen over mercury and allowed to remain 
for twelve hours’ darkness, and seven hours’ daylight. At first a considerable absorption 
took place, but soon gas was given off. When the mercury stood at its original level, 
the gas was analyzed. It consisted of 9‘7 cub. centims. of carbonic acid, 1 cub. centim. 
of oxygen, and 0'5 cub. centim. of nitrogen. 
A similar trial was made in which 5 grms. of bark was kept in darkness in 11 '5 cub. 
centims. of oxygen for the same period. The volume of the gas was but 9'6 cub. centims., 
of which 9T cub. centims. was carbonic acid, and 05 cub. centim. was nitrogen. 
These two trials merely showed that the bark, like other vegetable tissues, absorbed 
oxygen and exhaled carbonic acid, and that in the second case the absorption had 
occurred in larger amount than the evolution of carbonic acid. 
As these experiments did not account for the increase in the volume of the gas in my 
first observation, the trial was made of placing, as rapidly as possible, freshly cut strips 
of bark over mercury in a eudiometer. It was soon observed that gas was constantly 
given off from the bark, by the mercury descending in the eudiometer. This gas, on 
being analyzed, was found to be nearly pure carbonic acid. The evolution of gas con- 
tinued for many days. When the bark was removed it was found perfectly fresh and 
healthy, and exhibited none of the reddening which is so characteristic of the Cinchona 
barks after having been exposed to the influence of oxygen ; but as soon as it was 
brought into contact with the air, the greenish tint of the cut surface rapidly became 
brownish-red. The 5 grms. of bark had given off more than double its volume of car- 
bonic acid, under circumstances which entirely precluded the possibility of its being pro- 
duced by the direct oxidation of any constituent of the bark tissues. 
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