318 



LIQUEFACTION. 



496. Laws of Fusion. It has been found by 

 experiment that the following statements are true : 



(1.) Every solid begins to melt at a certain temperature 

 which is invariable for the given substance if the pressure 

 be constant. When cooling, the substance will solidify at 

 the temperature of fusion. 



(2.) The temperature of the solid, or liquid, remains at 

 the melting point from the moment that fusion or solidi- 

 fication begins until it is complete. 



(a.) If a flask containing ice be placed over a fire, it will be found 

 that the hotter the fire the more rapid the liquefaction, but that if 

 the contents of the flask be continually stirred, the thermometer 

 will remain at C. until the last bit of ice is melted ( 478). If 

 sulphur be used instead of icCj the tem- 

 perature will remain at 115C. until the 

 sulphur is all melted. (Fig. 244.) 



497. Reference Table of Melt- 

 ing Points : 



Alcohol, - - - .. Never frozen. 

 Mercury, .... 38.8C. 

 Sulphuric acid, - - 344 



Ice, - 0. 



Sulphur, --- - 115. 



Lead, - - - - 326 



Zinc, .... 425 



Silver (pure), - - 1,000 



Gold (pure), - - 1,250 



Iron (wrought), - - 1,600 

 Mote. The higher temperatures in this 

 244. table are only approximate. Certain 



bodies soften and become plastic before they melt. In this condition 



glass is worked and iroii is welded. 



498. Vaporization. If, after liquefaction, further 

 additions of heat be made, a point will be reached at which 

 the heat will overbalance both the cohesion and the 

 pressure of the atmosphere and the liquid pass into the 

 aeriform condition. This change of form is called vapor- 



