DECOMPOSITION OF CARBONIC ACID. 41 



both the carbonic acid which is in contact with them externally, and 

 that which is dissolved in the water absorbed by their woody tissue. 

 He took two branches of a peach-tree, and introduced them into a 

 couple of bell-glasses filled with water from the same spring.* The 

 lower end of each branch dipped into a flask. One of the flasks 

 was filled with water charged with carbonic acid ; the other con- 

 tained air : the two bell-glasses were exposed to the light. The 

 leaves of the branch whose extremity dipped into the solution of 

 carbonic acid, disengaged 99.4 cubic inches of oxygen gas under 

 the bell which covered it : the leaves of the other branch only pro- 

 duced 52.2 cubic inches in the same time. 



This experiment does not perhaps afford all the sufl^cient evi- 

 dence of the decomposition of gaseous carbonic acid as it occurs in 

 the atmosphere, and mixed with a great mass of air. It appears, 

 however, that the leaves of plants have the power of decomposing 

 the gaseous carbonic acid which is mixed with the air, and that 

 even witb surprising rapidity. 



In the summer of 1840, 1 introduced into a balloon of the capacity 

 of about twelve quarts and a half, and furnished with three tubulures 

 or openings, the branch of a vine in full growth and bearing tw^enty 

 leaves. The woody part of the branch was fixed by means of a collar 

 of caoutchouc to the lower orifice of the balloon ; a fine tube, intend- 

 ed to establish a communication between the interior of the vessel 

 and the outer air, was introduced into the superior tubulure ; the 

 lateral opening communicated by means of a tube with an apparatus 

 which measured with great accuracy the quantity of carbonic acid 

 contained in the atmosphere. 



In this experiment the air, before reaching the apparatus for 

 measuring the carbonic acid, passed through the great balloon con- 

 taining the vine branch. The rate with which the air passed through 

 the apparatus was regulated by the flow of an aspirator, and was at 

 the rate of about twelve quarts per hour. 



The apparatus was exposed to the sun ; the experiment beginning 

 at eleven and finishing at three o'clock. 



If one experiment it was found, all corrections made, that the at- 

 mospheric air, after having passed through the balloon, contained in 

 volume 0.0002 of carbonic acid gas ; the air of the adjoining court 

 contained at the same moment 0.00045 of carbonic acid. 



In another experiment, the air, after having passed over the leaves, 

 contained but 0.0001 of carbonic acid ; the air of the court contsin- 

 ing 0.0004 of the same gas. In traversing the space in which tiie 

 vine branch, exposed to the light of the sun, was included, therefore 

 the air was deprived of three fourths of the whole quantity of car- 

 bonic acid which it contained. 



In operating with the same apparatus during the night, opposite 

 results were obtained ; the air in traversing the balloon generally 

 acquired a quantity of carbonic acid, the double of that which the 

 atmosphere contained at the same moment. 



* This was common water containing carbonic acid 

 4* 



