20 TJJE PLAiNT, 



Oxygen is tlie carrier Avliicli enables it to change its 

 condition. For instance, let us suppose that we 

 liave a certain quantity of charcoal ; this is nearly 

 pure carbon. We ignite it, and it unites with the 

 oxygen of the air, becomes carbonic acid, and floats 

 away into the atmosphere. The wind carries it 

 through a forest, and the leaves of the trees with 

 their millions of mouths drink it in. By the 

 assistance of light it is decomposed, the oxygen is 

 sent off to make more cai'bonic acid, and the carbon 

 is retained to form a pai-t of the tree. So long as 

 that tree exists in the form of wood, the carbon will 

 remain unaltered, but when the wood decays, or is 

 burned, it immediately takes the form of carbonic 

 acid, and mingles with the atmosphere ready to be 

 again taken up by plants, and have its carbon de- 

 posited in the form of vegetable matter. 



The blood of animals contains carbon derived 

 from their food. This unites with the oxygen of the 

 air drawn into the lungs and forms carbonic acid. 

 Without this process, animals could not live. Thus, 

 while by the natural operation of breathing, they 

 make carbonic acid for the uses of the vegetable 

 world, plants, in taking up carbon, throw off oxygen to 

 keep up the life of animals. There is perhaps no way 

 in which we can better illustrate the changes of form 

 in carbon than by describing a simple experiment. 



Take a glass tube filled with oxygen gas, and 

 put in it a lump of charcoal, cork the ends of the 

 tube tightly, and pass through the corks the wires 

 of an electrical battery. ]3y pass'ug a stream vi' 



