CARBON DIOXIDE IN FERMENTATION 



119 



128. To Prepare Carbon Dioxide. When marble and 

 soda are treated with a dilute acid, carbon dioxide is formed. 

 Since the gas is only slightly soluble, it escapes. It 

 may be collected over water, just as oxygen and hydrogen 

 are (cf. 50 and 103), or, since it is 1J^ times as heavy as 

 air, it may be allowed to pour out of the delivery tube 

 (Fig. 102) into a bottle of air. In a r \ 



short time all the air will be replaced by 

 carbon dioxide. We can prove this by 

 putting a burning match into the bottle ; 

 the match will "go out." 



Carbon dioxide may be poured, like 

 water, from one bottle into another. 



129. Carbon Dioxide in Fermenta- 

 tion. When fruit juices, like apple 

 juice and grape juice, stand exposed to 

 the air, they "work," or ferment. If 



we examine the fermenting juice, we find that it is 

 warmer than the surrounding air, that a gas comes off 

 from it, and that the sweet taste of the juice is changed 

 to the taste of dilute alcohol. The cause of the fermenta- 

 tion is the yeast plant. The spores, that is, seedlike bodies 



(cf. 323), of wild yeast fall into 

 the fruit juice, and sprout, and 

 in their growth change the sugar 

 of the juice into alcohol and 

 carbon dioxide (Fig. 103). 



If we put prepared yeast ("com- 

 pressed" yeast or "dry" yeast) into a 

 dilute solution of molasses, the fer- 



Fia. 102. 



The carbon dioxide falls 

 into the bottom of the 

 bottle, and pushes the 

 air upward. 



FIG. 103. 

 Yeast Cells Budding. 



