A YEAE IN SCIENCE 41 



the flask while it is cooling. When it feels cool, re- 

 move the cotton, insert the thermometer into the liquid, 

 and note the temperature. Shake the liquid until it 

 begins to crystallize. As it does so, carefully observe 

 the changes in temperature. Explain these results. 

 What effect does a body of water which is freezing 

 have upon the temperature of the surrounding 

 atmosphere ? Why ? 



Exercise 18. Change from a Liquid to a Gas. 

 Object: To determine the^heat necessary to convert 

 1 c.c. of water into steam or water vapor. 



Apparatus 



Flask Wire gauze 



Thermometer Bunsen burner 



Asbestos cover for flask Ring stand 



Flame protector Graduate, 100 c.c. 



Directions: Set up apparatus as in Exercise 14. 

 Obtain the heat of the flame as in that exercise. Con- 

 tinue to heat the water, noting the exact instant when 

 it begins to boil. Allow it to boil for ten minutes. 

 Turn off the gas and set the water aside to cool. After 

 cooling, measure the water remaining in the flask. 



Tabulate data as follows : 



1. Amount of water at beginning. 



2. Amount of water at end. 



3. Loss in water (calculated). 



4. Calories given off by flame per minute (calcu- 

 lated). 



5. Length of time water boiled. 



