84 



CHEMISTRY. 



102. Carbonic Anhydride. Having given you an account 

 of the element carbon, we will now notice a gas formed by 

 the union of this element with oxygen, viz., carbonic anhy- 

 dride.* This is formed whenever carbon is burned in oxy- 

 gen, as in the experiment in 57. So, also, when a diamond 

 is burned in oxygen, this, being pure carbon, unites with the 

 oxygen to form carbonic anhydride. This gas is one of the 

 products of all ordinary combustion, the result of the union 

 which takes place between the oxygen of the air and the 

 carbon in the combustible substance. Thus the carbon 

 of wood, oil, tallow, illuminating gas, etc., unites, in the 

 act of burning, with the oxygen of the air, and forms this 

 gas. 



103. Common Mode of Obtaining Carbonic Anhydride. 

 Put into a flask, Fig. 21, some small bits of chalk or marble, 



Fig. 21. 



and pour upon them some hydrochloric acid. The gas will 

 bubble up, and, forcing out the air before it, will pass through 



* This gas used to be called carbonic acid, but chemists have decided 

 that it is not a true acid because it contains no hydrogen, hence it is now 

 known as carbonic anhydride. 



