172 Dr. Draper on the Decomposition of Carbonic Acid 



berated ; at first most copiously from the fractured extremity, 

 but as the process of exhaustion goes on it exudes from both 

 faces of the leaf, perhaps by rending open the frail tissue in 

 which it is imprisoned. In leaves that have stomata on one 

 side only, it does not pour forth from those organs in pre- 

 ference to other parts : and from this it may be inferred that 

 it does not normally exist in the intercellular spaces. In a 

 given weight of leaves its amount is very variable, ranging in 

 my experiments from *01 to *02 cubic inch for ten grains of 

 grass leaves. Its constitution as determined by analysis is 

 also variable, but very remarkable ; it contains from 88 to 94 

 per cent, of nitrogen. 



It being therefore understood that in the tissue of the leaf 

 a certain quantity of gas is mechanically included, which gas 

 differs from atmospheric air in the circumstance that it con- 

 tains a larger volume of nitrogen, which may be removed by 

 the air-pump, we are in a condition to understand whether 

 it is this nitrogen which furnishes the supply found in the gas 

 exhaled by leaves. The following experiment proves that it 

 is not. 



I removed by continued boiling and exhaustion all the air 

 dissolved in a solution of bicarbonate of soda. I also removed 

 all the nitrogen from some grass leaves, by placing them in 

 vacuo immersed in water that had been boiled and subse- 

 quently cooled. Then, placing these leaves in the solution of 

 the bicarbonate and in the vessels in which the experiment 

 was finally to be conducted, I kept them in vacuo for an hour. 

 This was done to get rid of that film of atmospheric air which 

 always adheres to the surface of glass vessels, and which might 

 have disturbed the result by furnishing nitrogen. The leaves 

 were now exposed in the saline solution to the beams of the 

 sun, and presently the evolution of gas commenced. When a 

 sufficient quantity was collected, it was found to consist of 88 

 per cent, oxygen and 12 nitrogen. 



Repetitions of this experiment prove that although the ni- 

 trogen mechanically inclosed in the leaf to a certain extent 

 mingles with the oxygen evolved, and indeed it could not be 

 otherwise on account of the diffusion of gases into one an- 

 other, yet the true source is to be sought in some nitrogenized 

 compound present in the leaf, which is undergoing decompo- 

 sition in a regulated way. 



Keeping this fact clearly before us, that the source of the 

 nitrogen found thus in company with the oxygen given off 

 under the influence of light is some nitrogenized body existing 

 in the leaf, the following experiments will show the simple and 

 beautiful law under which this phenomenon is conducted. 



