20 THE PRODUCTION AND USE OF LIGHT 



or 150^F. Ordinary grain alcohol has a constant boiling 

 point of 78C., or 172%F. These are the boiling points at 

 the sea level. In our school rooms these temperatures will be 

 slightly lower. Then, too, our thermometers may not be 

 exactly correct. But in any case the boiling point of pure 

 alcohol will not change with continued boiling. All pure 

 substances in the liquid state have certain constant boiling 

 points. Some are much higher than that of water, for ex- 

 ample, the boiling point of mercury is 357C.; some are much 

 lower, as oxygen, 182C., or hydrogen, 252C. 



DISTILLATION 



24. Boiling Point of a Mixture of Alcohol and Water. If 



pure wood alcohol boils at 66C. and continues to boil at that 

 temperature till all of the alcohol has been turned into vapor 

 the question arises : What would take place if we had a mixture 

 of alcohol and water? With our distilling flask, thermometer, 

 and lamp or burner we can soon answer the question. 



Exercise 16. Distillation of Alcohol 



Fill the distilling flask about one-fourth full of alcohol and add an 

 equal amount of water. Place some beads or small nails in the flask, 

 insert the stopper and thermometer, and place the cardboard be- 

 tween the flask and the side tube. Light the lamp or burner and 

 notice carefully the temperature at which boiling first takes place, i.e., 

 when the first drops of liquid fall from the side tube. Catch this 

 liquid in a beaker or small bottle. Watch the temperature care- 

 fully as the boiling continues. As soon as a little liquid has been 

 caught as it drips from the side tube, perhaps a teaspoonful, remove 

 the vessel and set another in its place. Probably some vapor will be 

 escaping from the side tube. Light this vapor to see if it burns. 

 Continue to watch the temperature at which the liquid in the flask 

 boils. Does the temperature finally reach that of boiling water? 

 How do you account for this fact? About what portion of the entire 

 quantity of liquid has boiled over when the temperature reaches this 

 point? Try to light the vapor now coming over. How do you ex- 

 plain the fact that this vapor will not burn? Remove the lamp. 

 Ihe portion of liquid which DISTILLED over and condensed is called 



DISTILLATE. 



