320 



VAPORIZATION. 



oury it displaces. Introducing the same quantity of 

 alcohol into C 3 and of ether into D, they are instantly 

 vaporized, but the mercury will be depressed more by the 

 alcohol than by the water, and more by the ether than by 

 the alcohol. 



(a.) At the beginning of the experiment, the four mercury 

 columns indicated the atmospheric pressure; at the end of the 

 experiment, the column in A indicated the full pressure of the 

 atmosphere ; the columns in B, C and D indicate that pressure 

 minus the tension of their respective vapors. This experiment 

 also shows that, at the same temperature, tlw vapors of different 

 liquids have different tensions, 



501. Ebullition. Ebullition, or boiling, signi- 

 fies the rapid formation of vapor bubbles in the 



mass of a liquid. 

 When a flask con- 

 taining water is 

 placed over the flame 

 of a lamp, the ab- 

 sorbed air that is 

 generally to be found 

 in water is driven off 

 in minute bubbles 

 that rise and escape 

 without noise. As 

 the temperature of 

 the water is raised, 

 the liquid molecules 

 in contact with the 

 bottom of the flask 



become so hot that 

 FIG. 246. . 



the heat is able to 



overcome the cohesion between the molecules, the pressure 



