HEAT 133 



volume at zero for each degree Centigrade of rise in tem- 

 perature. This number is called the coefficient of expan- 

 sion of gases. If a gas is cooled from zero, it contracts 

 at the same rate ; however, before it reaches 273 it 

 becomes a liquid and so no longer obeys the law stated 

 above. All gases have been liquefied by low temperature 

 and great pressure. 



Fusion. Changing a body from a solid to a liquid 

 form is called fusion. Other terms which have the same 

 meaning are liquefaction and melting. The reverse 

 process is called freezing or solidification. It is a well- 

 known fact that the melting point of ice and the freezing 

 point of pure water is the same, 32 F. or C. Other 

 substances have different melting points, but in every case 

 the melting point and the solidifying point of a substance 

 is the same. 



Table of Melting Points 



Alcohol - 130.5 Lead 326 



Mercury - 39 Zinc 433 



Ice . . Silver 950 



Lard 33 Copper 1100 



Paraffin 54 Cast iron 1200 



Sulphur 115 Platinum 1775 



Tin . .... . ; . . . 232 Iridium 1950 



Experiment 36. Place some pieces of ice in a beaker and heat 

 slowly over a small flame. Stir the ice and water constantly with 

 a thermometer and note the temperature from time to time. 



Most liquids decrease in volume when they solidify, 

 but the opposite is true of water, liquid iron, and a few 

 other substances in which there is a sudden marked in- 

 crease in volume at the moment of solidification. Water 

 increases about nine per cent on freezing, and the force 

 exerted is great enough to burst the usual containers such 

 as water pipes and pitchers and other household utensils. 



