DECOMPOSITION OP CARBONIC ACID, ETC. 93 
acid gas to the sunshine, has completed its function, it has 
appropriated or assimilated all the carbon, and with it a 
certain portion of the oxygen; the residue of the oxygen 
has been evolved, and with it a volume of nitrogen precisely 
equal in amount to the volume of oxygen appropriated by 
the plant. 
This disappearance of oxygen and appearance of nitrogen 
are thus connected with each other: they are equivalent 
phenomena. 
The emission of nitrogen is not a mere accidental result, 
but is profoundly connected with the whole physiological 
phenomena. 
The elementary conditions under which carbonic acid gas 
is decomposed having been thus stated, Prof. D. passed next 
to the description of similar decomposition occurring in the 
case of saline bodies. It has always been a subject of sur- 
prise to chemists, that the powerful affinity by which carbon 
and oxygen are thus held together, should be so easily over- 
come at common temperatures. Even potassium cannot 
decompose carbonic acid in the cold. It might therefore be 
reasonably expected, that the energetic forces which bring 
about this change ought also to effect other remarkable de- 
compositions. In fact the decomposition of carbonic acid is 
only one of a very numerous series. 
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 othe r 
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 
vol. x. — NO. II. 9 
