CARBON DIOXIDE AND FERMENTATION 41 



EXERCISE 40 

 CARBON DIOXIDE AND FERMENTATION 



Apparatus and Materials. Bottle with glass-plate cover, drinking 

 glass, fruit jar, marble, dilute hydrochloric acid, candle, splinter, lime- 

 water, baking soda, washing soda, sour milk, vinegar, cream of tartar, 

 baking powder, limestone, shells, old mortar, molasses or brown sugar, 

 yeast. 



a. Carbon Dioxide from Carbonates. In a bottle like that 

 of Fig. 18, Exercise 36, put some marble and dilute hydrochloric 

 acid. What happens? Put a burning splinter into the bottle; 

 does it continue to burn? Does the gas burn? 



Put a very short candle into the bottom of a bottle or drink- 

 ing glass, light it, and pour upon it the gas formed from the 

 marble and acid (see Exercise 15). Do not pour out any of the 

 liquid. What is the effect of the gas upon the burning candle? 



6. Treat half a teaspoonful of baking soda with some sour 

 milk, and prove that carbon dioxide is formed. Try washing 

 soda and vinegar. 



c. In a water glass or beaker mix about % of a teaspoonful 

 of baking soda with twice its volume of cream of tartar, and 

 then add water to the mixture. Prove that carbon dioxide is 

 formed. In the same way treat a teaspoonful of baking powder 

 with water, and find what gas is given off. 



d. Treat small lumps of limestone with dilute hydrochloric 

 acid, and prove that carbon dioxide is formed. Do the same 

 with some broken oyster, clam, or snail shells. Try some old 

 mortar in the same way; what gas is given off, and what is the 

 residue that does not dissolve? 



e. Fermentation. In a bottle or fruit jar put 50 cu. cm. of 

 warm (not hot) water and 10 cu. cm. of molasses or brown 

 sugar. Add about 1 cu. cm. of yeast, cover the bottle loosely, 

 and set it where it will remain warm. Watch the contents of 



