136 GENERAL SCIENCE 



with a rubber stopper and invert it on a ring stand (Figure 118) and 

 pour cold water over it. The water in the flask will boil vigor- 

 ously. When the boiling point is reduced as low as possible, remove 

 the stopper and take the temperature. Why do we need to boil 

 the water some time before starting the experiment? Why is it 

 difficult to cook eggs or potatoes by boiling on high mountains ? 



Laws of Ebullition. 



1. Under constant pressure every liquid has a definite 

 boiling point. 



2. While the liquid is boiling the temperature remains 

 constant until all is vaporized. 



3. The boiling point varies with the pressure, the 

 greater the pressure the higher the boiling point and vice 

 versa. 



EXERCISES AND QUESTIONS 



1. Why do telegraph wires sag more in summer than in winter ? 



2. What temperature Fahrenheit is equal to 35 Centigrade? 



3. A rod 40 inches long expands A of an inch when heated 50. 

 How much would it expand if heated 1? 



4. Why are railroad tracks not laid so that the ends meet when 

 laid in winter? 



5. How could you make an air thermometer? 



6. To what temperature must a quart of air at C. be heated 

 to double its volume ? 



7. Why does freezing often burst water pipes? 



8. Will roads dry faster on a still or windy day? 



9. Why does sweet oil evaporate so slowly? 



10. How do salts in solution affect the boiling point of water? 

 Test. 



11. How may we separate alcohol and water? 



