64 



LABOKATORY MANUAL 



two tubes ? This may be accurately obtained by taking 

 the readings on the burettes. When the tube contain- 

 ing the most gas is three-fourths full, disconnect the 

 current. Remove the entire apparatus into a trough 

 of water, so that the open ends of the 

 arms are submerged. Then remove each 

 burette separately, the one of less 

 volume first. Cover the mouth of the 

 burette with the finger and invert. 

 Remove the finger and quickly insert 

 a lighted splinter into this gas. What 

 happens? What is this gas? 



Remove the other burette in the same 

 manner as the first. Hold the mouth 

 downward and insert a lighted splinter. 

 What happens? What is this gas? 

 (See Exercise 32.) 



Of what elements is water composed ? 

 What proportion by volume? 



Exercise 38. Composition of Air. 

 Object: To determine the composi- 

 tion of air. 



Fig. 22. 



Pneumatic trough 

 Belljar 



Evaporating dish 

 Phosphorus 

 Lime water 



Apparatus 



Beaker 

 Glass plate 

 Pine splinter 

 Test tube 

 Iron filings 



Directions: A. Fill the beaker with lime water and 



