136 



GENERAL SCIENCE 



so as to allow the shelf inside to be about half as high as the sides of the cake 

 tin. Drill a hole through the center of the shelf and two small holes on each 



side of the center hole. Fit a one- 

 hole rubber stopper through the hole. 

 Extend a glass or metal funnel 

 through the stopper so that the bowl 

 of the funnel is toward the bottom 

 of the dish. The stem of the funnel 

 must be short enough to be covered 

 with water/ All bottles inverted on 

 this shelf must have the neck of the 

 bottle extending under water about 

 | inch. 



Fill two bottles with water. Cover 

 FIG. 104. each with a piece of glass and invert 



on the shelf of the cake tin, which 



we now call a pneumatic trough. Remove the glass covers, and be sure the 

 bottles are full of water, and all air bubbles removed. Place under the 

 funnel (called a bell) a small piece of fused sodium peroxide. The gas which 

 rises to replace the water is oxygen. 



The two holes will allow the water to escape quickly from the inverted bottles as the oxygen 

 enters. 



Light a soft wood splinter. After it has burned a moment, 

 blow it out. A small spark will glow on the end of the splinter. 

 Insert the splinter in the bottle of oxygen while the spark is still 

 glowing. What happens will show something about the power 

 of oxygen to make things burn. The oxygen itself does not 

 burn, as the splinter may be removed, blown out, and rein- 

 serted several times, taking fire each time without setting the gas 

 (oxygen) on fire. 



So active is this gas that iron wire may be made to burn in 

 it. Insert into the bottle of oxygen a piece of picture wire on 

 which there is a little burning sulphur. The wire should burn 

 brilliantly. 



Amount of Oxygen in the Air. It was seen from the experiment 

 with the candle under the bottle tha.t air is not made up entirely 

 of oxygen. There was much air in the bottle after the candle went 

 out. About one-fifth of the air is oxygen. The remaining part of the 

 air is chiefly nitrogen, water and dust. A small amount of a gas 

 known as Argon is also present. Nitrogen is a gas which will not 



