EVAPORATION 



35 



the spout, and on reaching the cold bottle condenses and 

 drops into the bottle as pure water. The impurities remain 

 behind in the kettle. Water freed from impurities in this way 

 is called distilled water, and the process is called distillation 

 (Fig. 19). By this method, the salt water of the ocean may be 

 separated into pure 

 drinking water and 

 salt, and many of the 

 large ocean liners 

 distill from the briny 

 deep all the drinking 

 water used on their 

 ocean voyages. 



Commercially, distil- 

 lation is a very impor- 

 tant process. Turpen- 

 tine, for example, is 

 made by distilling the 

 sap of pine trees. In- 

 cisions are cut in the 

 bark of the long-leaf pine trees, and these serve as chan- 

 nels for the escape of crude resin. This crude liquid is 

 collected in barrels and taken to a distillery, where it is 

 distilled into turpentine and rosin. The turpentine is the 

 product which passes off as steam, and the rosin is the mass 

 left in the boiler after the distillation of the turpentine. 



26. Evaporation. If a stopper is left off a cologne bottle, 

 the contents of the bottle will slowly evaporate ; if a dish of 

 water is placed out of doors on a hot day, evaporation occurs 

 very rapidly. The liquids which have disappeared from the 

 bottle and the dish have passed into the surrounding air in the 

 form of vapor. In Section 20, we saw that water could not 

 pass into vapor without the addition of heat ; now the heat 



water tanie 



FIG. 19. In order- that the steam which passes 

 through the coiled tube may be quickly cooled and 

 condensed, cold water is made to circulate around 

 the coil. The condensed steam escapes at w. 



