182 . DECOMPOSITION OF SALINE BODIES. 



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 continued 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. 



804. 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 solu- 

 tion 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 becomes half full. On de- 

 tonation with hydrogen this gas proves to be rich in oxygen. 



805. 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 decom- 

 posed. From this it would seem that carbonate of soda itself should be decomposed, 

 and experiment verifies the conclusion ; for, on using that salt instead of the bicarbo- 

 nate, the evolution of oxygen goes on precisely in the same way. 



806. As in these experiments solid salt dissolved in water is decomposed, it is obvious 

 that the function by which the leaves accomplish this is very different from that of res- 

 piration. It is not respiration, but a true digestion. 



807. LIEBIG has shown that ammonia exists in the ascending sap. It is probable, 

 therefore, that it does not undergo final change before reaching the upper face (sky- 

 face) of the leaf. There, if it be in the form of a carbonate, it unquestionably is con- 

 cerned in decomposition. With the natural experiment before us, we might expect 

 that the carbonate of ammonia used in place of the soda salts of the last experiment 

 would yield like them. Accordingly, it will be found, by using the officinal sesqui- 

 carbonate of ammonia, that leaves effect its decomposition. In numerous experiments 

 it has yielded me gas frequently containing more than 90 per cent, of oxygen. 



808. In every instance which I have examined, the gas evolved from leaves is not 

 pure oxygen, but, as has been said, a variable mixture of oxygen and nitrogen. This 

 result is of uniform occurrence ; I have observed it in low latitudes, where the sun is 

 extremely brilliant, in the case of different plants ; and on referring to Dr. DAUBENY'S 

 paper ,it will appear that he has uniformly recognised the same result in England. 

 The very remarkable qualities which certain nitrogenized substances are known to 

 exhibit, acting as ferments as they are undergoing decay, might lead to the suspicion 

 that the decomposition of carbonic acid by leaves is due to the action of some nitro- 

 genized body, the eremacausis of which is promoted by the rays of the sun. 



