56 GENERAL SCIENCE 



the top, through which the gas of the burning coal can 

 escape. While the coal is burning a large flame of fire 

 can be seen at this opening. After the gas has been 

 driven out of the coal and burned, a large hole is made 

 in the side of the oven and the coke is taken out for 

 shipment. 



40. Preparation of Carbon Dioxide. Carbon dioxide 

 (062) is composed of the two simple elements, carbon and 

 oxygen. One atom of carbon and two of oxygen make 

 the molecule of carbon dioxide. Whenever the oxida- 

 tion of carbon or its compounds occurs, 

 carbon dioxide is formed. It is very difficult 

 to get it in pure form by any oxidizing pro- 

 cess, as other gases are mixed with 

 it. So we shall have to resort to 

 the use of compounds containing 

 carbon and oxygen in the 

 proper combination to be 

 liberated in the form of car- 

 bon dioxide (CO 2 ). 



If baking powder is placed 

 MAKING CARBON DIOXIDE in water or baking soda in 

 By pouring hydrochloric acid on vinegar, carbon dioxide will 



marble chips. . ... . T . . . .. 



be liberated. If marble, lime- 

 stone, or chalk is placed in dilute hydrochloric acid 

 (HC1), carbon dioxide will be evolved. To collect the 

 effervescing gas, place the marble in a large test tube or 

 a bottle, close it with a rubber cork containing a thistle 

 tube and a delivery tube. Have the delivery tube bent 

 and long enough to extend to the bottom of a test tube 

 or bottle as shown in the illustration. Now pour a little 

 hydrochloric acid into the thistle tube, and the carbon 

 dioxide will pass out through the delivery tube into 



