ATMOSlniERIC AIR AS THE I^OOIl OF PLANTS. ,39 



binned or decays in contact with the air. It is like oxy- 

 gen, colorless, but it has a peculiar pungent odor and 

 pleasant acid taste. 



The composition of carbonic acid is evident from what 

 has been said as to its production from carbon and oxygen. 

 It consists of two atoms, or 3:2 parts by weight, of oxygen, 

 united to one atom, or 12 parts, of carbon. Its symbol is 

 COjj. In the subjoined scheme are given its symbolic, 

 atomic, and percentage composition. 



At. wt. Per cent. 



C = 13 27.27 



Oo = 32 73.73 



CO2 = 44 100.00 



In a state of combination carbonic acid exists in nature 

 in. immense quantities. Limestone, marble, and chalk, 

 contain, when pure, 44 per cent of this acid united to lime. 

 These minerals are in chemical language carbonate of lime. 

 Common salteratus is a carbonate of potash, and soda- 

 salasratus is a carbonate of soda. 



From either of these carbonates it is easy to separate 

 this gas by tiie addition of another and stronger acid. 



For this purpose we may employ the Rochelle or Seidlitz powders so 

 commonly used in medicine. If we mingle together in the dry state the 

 contents of a blue paper, which contains carbonate of soda, with those of 

 a white paper, which consist of tartaric acid, nothing is observed. If, 

 however, the mixture be placed at the bottom of a tall bottle, and a little 

 water be poured upon it, at once a vigorous bubbling sets in, which is 

 caused by the liberated carbonic acid.* 



Some important properties of the gas thus set free may be raadily 

 made manifest by the following experiments. 



a. If a burning taper or match be immersed in the gas, the flame is 

 immediately extinguished. This happens because of the absence of free 

 oxygen. 



6. If the mouth of the bottle from which carbonic acid is escaping be 

 held to that of another bottle, the gas can be poured into the second ves- 

 sel, ou account of its density being one-half greater than that of the air. 

 Proof that the invisible gas has thus been transferred is had by placing 



* Chalk, marble, or salaeratus, and chlorhydric (muriatic) acid, or strong vine- 

 gar (acetic acid) can be equally well employed. 



