72 



ELEMENTS OF GENERAL SCIENCE 



75. Some further facts about carbon dioxide. Carbon* 



dioxide gas may be made in many ways besides burning. 

 The most convenient, perhaps, is the method of 

 producing it by putting hydrochloric acid on 

 marble (fig. 38). However produced, 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 oxygen, but it- must be remembered 

 that the oxygen atoms are joined to the carbon 

 atoms and therefore 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 

 oxygen to maintain the 

 burning of a flame, and 

 therefore the flame is 

 extinguished. 



Carbon dioxide is 

 about one and one-half 

 times as heavy as air 

 and therefore .can be 

 collected in an open 

 bottle. With care it 



Fit;. 38. A carbon-dioxide generator 



The bottle contains pieces of marble and hy- 

 drochloric acid. The action of the acid on the mav be poured from 

 marble decomposes it, releasing carbon dioxide, O ne bottlp to anntW 

 which escapes through the bent tube. Additional . ail tner ' 

 acid may be added through the funnel It IS familiar to US 



as the gas that bubbles 



our soda water and in other effervescent drinks and 

 as the important substance in chemical fire extinguishers. 

 We make use of it in cooking to raise cake and biscuit 



