DEOXIDATION OF CARE-ANHYDRIDE. 63 



carbonic anhydride we lately produced in this large gas-bottle 

 by the direct combination of charcoal and oxygen : 



Chalk Chlorhydric Chlor-calcium Water Carb-anhyd. 



CaO.CO, + zHCl = CaCl, + H a O + C0 3 



In the arrangement on the table before you, we are producing 

 a current of carbonic anhydride in a similar manner, by acting 

 upon chalk or, rather, marble, with dilute hydrochloric acid. 

 The gas evolved in the Woulfe's bottle is transmitted over pumice 

 and oil of vitriol to render it dry, and then conveyed to the 

 bottom of an ordinary Florence flask, into which I have dropped 

 a piece of clean metallic sodium. We now apply a large blow- 

 pipe flame to the bottom of the flask so as to heat the contained 

 sodium. There is a little practical difficulty in starting the reac- 

 tion, and perhaps the experiment may not succeed at the first 

 trial, but it is sure to succeed sooner or later. The action is now 

 beginning, and you observe the piece of sodium glowing in the 

 flask. The glowing is soon succeeded by a brilliant combustion, 

 attended by the formation of copious white fumes. The sodium 

 has effected a decomposition of some of the carbonic anhydride, 

 united with its oxygen to form soda, and liberated its carbon in 

 the form of a black mass, which remains, as you see, at the 

 bottom of the flask. 



(66.) The piece of charcoal in this flask then has been ex- 

 tracted from carbonic anhydride, which is itself producible, as I 

 have shown you, by the direct combustion of charcoal in air or 

 oxygen. So that when we act upon oxide of hydrogen with 

 sodium, we separate the oxygen and obtain the hydrogen ; and 

 when we act upon oxide of carbon with sodium we separate the 

 oxygen and obtain the carbon. Now the living plant effects a 

 similar decomposition of these two compounds, but in a gradual 

 manner, which we shall hereafter endeavour to imitate. The 

 plant absorbs oxide of hydrogen or water, and oxide of carbon or 

 carbonic anhydride ; deoxidises both compounds to a more or less 

 complete extent ; evolves the separated oxygen into the atmo- 

 sphere ; and retains the united carbon and hydrogen, with or 



