120 CARBON AND ITS COMPOUNDS . 



mentation is rapid. In three or four days the liquid can be distilled, 

 and alcohol can be obtained in the first droppings from the condenser. 

 The alcohol comes over before the water does (c/. 83). 



When bread is made, carbon dioxide is produced by the action of 

 yeast upon sugar and flour, and causes the dough to rise. The 

 alcohol vapor also assists; but both alcohol and carbon dioxide are 

 largely expelled in the baking. 



130. Baking Powders. Other sources of carbon 

 dioxide are used to "raise" biscuits and cake; these are 

 called "baking powders." Common baking powder 

 contains baking soda, cream of tartar, and starch. The 

 correct proportion is two parts of cream of tartar to one 

 of baking soda. The soda is the source of the carbon 

 dioxide, just as the marble is when we prepare the gas in 

 the laboratory. The cream of tartar is the acid. The 

 carbon dioxide passes off as it raises the dough, while the 

 other product of the action, sodium potassium tartrate, 

 is left in the baked article. It is important that the 

 solid substances formed by baking powder, which are 

 left in the food, shall not be harmful to the persons eat- 

 ing them. Acid phosphate baking powders contain acid, 

 calcium phosphate instead of cream of tartar. 



131. Carbon Dioxide as a Fire Extinguisher. Since 

 carbon dioxide does not permit burning to continue, it 

 can be used like water to put out fires. There is a great 

 advantage in using it if the fire is small, for the carbon 

 dioxide does not damage the things that do not burn, 

 while water does. It cannot be used for large fires, 

 because it cannot be put into the burning material in 

 large enough amounts. A chemical engine consists of a 

 strong vessel in which carbon dioxide is generated from 



