VAPORIZA TION. 



323 



duction of the tension lessens the work necessary to boiling. There 

 being enough heat in the water to do this lessened amount of work, 

 the water again boils and increases the pressure until the boiling 

 point is raised above the present temperature of the water. The 

 flask may be drenched and the water made to boil a dozen times in 

 succession with a single heating. The experiment may be made 

 more striking by plunging the whole flask under cool water. 



5O5. The Culinary Paradox. The same prin- 

 ciple may be illustrated by the apparatus represented in 

 Fig. 248. The re- 

 ceiver R, having 

 been exhausted with 

 an air - pump, is 

 closed by the stop- 

 cock s. The flask F 

 is half full of water 

 and heated by a 

 lamp placed be- 

 neath. As the water 

 boils, the steam es- 

 capes through the 

 open stop-cocks a 

 and c. When the steam has expelled the air from F, 

 close a and c, removing the lamp at the same time. 

 The water gradually cools and ceases to boil. Water may 

 be dashed over F and the water made to boil as in the last 

 experiment. When this has been done a few times, the 

 water may he allowed to come to rest. It will be several 

 degrees below the boiling point. Opening a and s, the 

 vapor of F escapes into R and the water begins to boil 

 vigorously. By keeping R cool, the water in F may be 

 made to boil for a considerable time. 



5O6. Papin's Digester. At high elevations water boils at 

 a temperature too low for culinary purposes. Persons living there 



FIG. 248. 



