OTHER CONSTITUENTS OF THE ATMOSPHERE 125 



d. 1707 : 192-194. Preparation and Properties of Carbon 



Dioxide. 



e. 1709 : 244-246. Preparation and Properties of Carbon 



Dioxide. 



Experiment 49. Preparation of Carbon Dioxide the 

 Chemical Engine. 



Apparatus : Bottle 250 c.c., wide mouth, rubber stopper to 

 fit, with two holes, thistle tube with stopcock, right-angle tube, 

 one leg long enough to reach the bottom of the bottle and the 

 other leg drawn out to form a small nozzle. 



Materials : Sodium bicarbonate, hydrochloric acid of full 

 strength, marble. 



a. Fill the bottle nearly full of cold water, and add about 

 two teaspoonfuls of sodium bicarbonate. Insert thistle tube 

 and the right-angle tube in the two holes of the stopper, and 

 push them in so that they both reach nearly to the bottom of 

 the bottle. Shake the bottle gently until the sodium bicar- 

 bonate is dissolved. Then add hydrochloric acid, by means 

 of the thistle tube, allowing only a little to pass at a time. 

 Tip the bottle so that the liquid passes into the sink, for if 

 the liquid touches skin or clothes, they will be burnt by some 

 of the uncombined acid. 



6. Put a few drops of half-strength hydrochloric acid upon 

 marble. The bubbles are carbon dioxide. If hydrochloric 

 acid is placed upon any rock, and bubbles are formed, they 

 indicate that the rock is a carbonate. 



91. OTHER CONSTITUENTS OF THE ATMOSPHERE 



Besides these three principal ingredients, oxygen, nitrogen, 

 and carbon dioxide, there are several others, of which dust and 

 bacteria are the most important. 



