NATUEE-STUDY LESSONS. 175 



(t) Do you see the vapor at the mouth of the 



tubing ? 

 (j) Do you see it in the test-tube ? 

 (^) How far is the point where you first see it 



from the end of the tube? 

 14. (a) What must be above the water in the test-tube 



and issuing from the end of the tubing ? 

 (3) What is the nature of its temperature ? 

 (c) How does it compare in temperature with the 



vapor rising from a wet roof, or from an 



exposed saucer containing water? 



This invisible, highly-heated vapor is called steam, and this violent pro- 

 cess by which the steam is produced is called boiling. 



LI-CONDENSATION. 



1. (a) Hold a slate close to the mouth of a tube while 



the water which it contains is boiling. 

 (J?) What do you observe on the slate ? 

 (c) Where does it come from ? 



2. Compare the temperature of the slate with that of 

 the steam. 



3. How is the temperature of the vapor affected by 

 contact with the slate ? 



4. What change was effected in the steam by its con- 

 tact with the slate ? 



5. Compare the temperature of the steam issuing from 

 the tube with that of the air of the room. 



6. What effect upon the temperature of the vapor has 

 its contact with the air ? 



7. What was the visible effect of this lowering of the 

 temperature of the vapor? 



