LABORATORY EXERCISES. 



b. When the flame is extinguished cover 

 the bottle with the glass. Cau- 

 tiously smell of it. What is the 

 gas? (Compare with experiments 

 f, B, i, 3.) What are the phys- 

 ical properties of this gas? 



4. Thrust a burning stick into a third bottle 



of oxygen. 



a. What do you observe? 



b. Remove the stick quickly and blow 



out the flame, leaving a glowing 

 end. Again thrust the stick into 

 the jar of oxygen. What is the 

 result ? 



c. Repeat the preceding experiment sev- 



eral times. What do you finally 

 observe? Explain this fact. 



d. Into the bottle put some clear lime- 



water and shake. What is the re- 

 sult and what do you infer ? (Com- 

 pare experiment J, D, 4.) 



5. Heat the end of a picture-wire and dip it 



into sulphur. When the little ball of 

 sulphur is burning well, lower the heated 

 picture-wire into the fourth jar of oxy- 

 gen. Describe the result. Will iron 

 burn in the air? 



6. Did the oxygen burn in any of the preced- 



ing experiments? Does the oxygen of 

 the air ever catch fire? How do you 

 know? What, then, does the oxygen do 

 in each experiment? 



