EVAPORATION, BOILING TEMPERATURE, ETC. 19 



of water. But 10 centigrade degrees equal 1.8 times 10 Fahrenheit 

 degrees, or 18 Fahrenheit degrees. Therefore, the temperature re- 

 ferred to is 18 Fahrenheit degrees below the melting point of ice. 

 But the melting point of ice is 32 Fahrenheit degrees above the 

 melting point of the mixture of ice and salt, or the zero point on the 

 Fahrenheit scale. Hence the temperature is 32 18 or 14F. 



23. The Boiling Point of Alcohol. 

 Exercise 16. To Determine the Boiling Point of Wood or Grain Alcohol 



Fill a distilling flask half full of alcohol. Put in some glass beads 

 or nails. Insert the stopper and thermometer, adjusting the ther- 

 mometer in height so that the bulb will extend somewhat below the 

 side tube and still be above the base of the neck of the flask. Clamp 

 the flask in the ring stand at the proper height above the alcohol 

 lamp or burner. Set the stand in a 

 metal tray such as a large dripping 

 pan. Place a clean vessel close under 

 the side delivery tube to catch the con- 

 densed vapor as it drips from the tube. 

 Since alcohol is inflammable it should be 

 handled with care. Before lighting the 

 lamp, place a piece of cardboard between 

 the flask and the delivery tube to avoid any 

 possibility of the escaping alcohol vapor 

 being set on flre by the flame (Fig. 12). 



Light the lamp or burner and notice 

 all that takes place as the alcohol is 

 brought slowly to a boil. Record the 

 temperature of the alcohol vapor when 

 the condensed vapor begins to drip 

 from the delivery tube. Should much 

 alcohol vapor escape from the tube 

 before it condenses, moisten a small cloth in cold water and lay 

 it over the delivery tube to keep it cool. Is alcohol vapor visible 

 or invisible? What is the "boiling point" of alcohol? Does it 

 remain constant as the alcohol continues to boil? Does rapid 

 boiling raise the "boiling point?" 



Should the " boiling point" of your sample of alcohol not 

 remain constant but rise with continued boiling your alcohol 

 probably contains water. The simplest test for pure alcohol is 

 the test of the boiling point. Wood alcohol, as pure as can be 

 obtained by distillation, has a constant boiling point of 66C., 



FIG. 12. Distillation of 

 Alcohol. 



