64 



ELEMENTS OF GENERAL SCIENCE 



substance. We shall therefore take the word of the chemist, 

 that this substance which is produced by the burning candle is 

 a compound of carbon and oxygen, and that it is 

 formed by the union of the oxygen of the air and 

 the white-hot carbon particles which we know to 

 be in the flame. 



Chemists also tell us that the proper formula 

 by which to represent a molecule of this gas is 

 CO 2 , and that its name is carbon dioxide. What 

 does this formula mean ? 



65. Some further facts about carbon dioxide. The 

 gas, carbon dioxide, may be made in many ways 



besides by burning. Most 

 convenient, perhaps, is 

 the method of producing 

 it by putting hydro- 

 chloric acid on marble 

 (fig. 36). However pro- 

 duced, it is always the 

 same. If we collect it in 

 a bottle, it is found that 

 the gas is perfectly clear 

 and colorless. It will 

 not burn, but instead it 

 extinguishes fire. It may 

 seem strange that things 

 will not burn in carbon 

 dioxide when the gas is 

 composed partly of oxy- 

 gen, but it must be 

 remembered that the 

 oxygen atoms are joined 

 to the carbon atoms, and therefore they are not free to unite 

 with something else. Since the oxygen atoms will not leave 

 the carbon atoms of the carbon dioxide, there is no free 



FIG. 36. A carbon-dioxide generator 



The bottle contains pieces of marble and hy- 

 drochloric acid. The action of the acid on the 

 marble decomposes it, releasing carbon dioxide, 

 which escapes through the bent tube. Additional 

 acid may be added through the funnel 



