EVAPORATION, BOILING TEMPERATURE, ETC. 15 



Often both scales are placed upon the same thermometer 

 stem. It is also true that the scale may extend far above the 

 boiling point of water and far below the melting point of the 

 mixture of ice and salt. 



19. Determining the Freezing Point on a Thermometer. 



Exercise 12. Testing a Thermometer for the Freezing Point 



Suspend a funnel in the ring of an iron support. 

 Clamp a thermometer by means of the burette 

 clamp at such a height that the bulb hangs well 

 down in the throat of the funnel. Pack the funnel 

 full of finely broken ice or snow, heaping it well up 

 around the stem of the thermometer. The stem 

 should be surrounded with ice or snow up as nearly 

 as possible to the point marked 0C., or 32F. Keep 

 plenty of ice or snow in the funnel and see that it 

 remains tightly packed around the thermometer 



for some minutes. Does your thermometer record FlG> 9 Freezing 



correctly the freezing point of water? If not, point of water, 

 what is the amount of the error? (Fig. 9.) 



Even very good thermometers are often slightly incorrect. 



BOILING POINT 



20. The Temperature of Boiling Water. 



DEFINITIONS. A liquid is said to EVAPORATE when it changes 

 from the liquid form to the vapor form at the surface only. 



A liquid is said to BOIL when it changes to the vapor form be- 

 neath the surface and the bubbles of vapor rise to and escape from 

 the surface. 



A liquid is said to be VAPORIZED whenever it changes to vapor. 

 A liquid is vaporized when it evaporates or boils. 



Exercise 13. To Determine the Temperature of Boiling Water 



Fill a 4-oz distilling flask half full of water. Slip a chemical 

 thermometer into the hole in a rubber stopper. Push the ther- 

 mometer far enough through the stopper so that the bulb will dip 

 into the water when the stopper is fitted into the mouth of the flask. 

 Before inserting the stopper and thermometer it is well to place a 



