1 70 Dr. Draper on the Decomposition of Carbonic Acid 



In fact, as I shall now proceed to show, the decomposition of 

 carbonic acid is only one of a very numerous series. 



The alkaline bicarbonates, as is well known, undergo de- 

 composition by a slight elevation of temperature. When boiled 

 with water they gradually give off their second atom of acid, 

 and slowly pass into the condition of neutral carbonate. This 

 easy decomposibility led me to inquire whether green leaves, 

 under the action of the sunlight, would effect the liberation 

 and subsequent reduction of the acid. In the following ex- 

 periments it is to be observed, that the boiling is not con- 

 tinued long enough to affect to any extent the constitution of 

 the salt, and in each case any portion of free carbonic acid 

 extricated during the cooling of the liquid was removed by the 

 action of the air-pump. The solution when finally used 

 contained no gaseous matter, but only the salt dissolved in 

 water. 



Having boiled some distilled water to expel all gaseous 

 matter, dissolve in it a small quantity of bicarbonate of soda. 

 Introduce into a test tube some leaves of grass, fill the tube 

 with the saline solution which has been once more boiled to 

 expel any air it may have obtained from the dissolving salt, 

 and invert the tube in some of the solution in a wine glass, 

 after having carefully removed all adhering bubbles of air 

 from the leaves by a piece of wire, or in any other convenient 

 manner. This arrangement kept in the dark undergoes no 

 change ; but, if brought into the sunshine, bubbles of gas are 

 rapidly evolved, and in the course of a few hours the tube be- 

 comes half-full. On detonation with hydrogen this gas proves 

 to be rich in oxygen. 



I made some attempts to discover how much oxygen could 

 in this way be evolved from known quantities of bicarbonate 

 of soda, supposing it probable that the second atom of carbonic 

 acid being removed and decomposed, the process would cease. 

 I need not detail the result of those trials; they indicated that 

 the supposition I had formed was not correct. The process is 

 not limited to the removal and decomposition of the second 

 atom, but goes forward, the first atom itself being in like 

 manner decomposed. From this it would seem that car- 

 bonate of soda itself should be decomposed, and experiment 

 verifies the conclusion ; for on using that salt instead of the 

 bicarbonate, the evolution of oxygen goes on precisely in the 

 same way. 



As in these experiments solid salt dissolved in water is de- 

 composed, it is obvious that the function by which the leaves 

 accomplish this is very different from that of respiration. It 

 is not respiration, but a true digestion. 



