74 HEAT 



Thermometers measure differences of expansion between mercury 

 and glass. 



The "freezing point" of a thermometer is the temperature of 

 melting ice. The " boiling point " mark is the temperature of steam 

 given off by water that is boiling under standard pressure. 

 . = (Cent.X 9 A)+32. 

 = 5 /9(Fahr.-32). 



Degree of heat is temperature. It depends upon the rapidity of 

 molecular motion. 



Quantity of heat in a body depends upon the temperature and the 

 mass; also upon heat capacity (cf. 73). 



The calorie is the unit of heat quantity. 



Heat is distributed by conduction (or contact), by radiation, and bj 

 convection. 



Convection currents are set up in liquids or gases if they are heated 

 from the bottom or cooled from the top. 



The three physical forms of matter are solids, liquids, and gases. 

 They depend on the cohesion and the energy of the molecules. 



Heat of melting, or of fusion, is the number of calories of heat 

 needed to melt 1 g. of a solid. 



Heat of freezing is the number of calories given off in the freezing 

 of 1 g. of a liquid. It is equal to the heat of melting. 



Water expands when it freezes; most liquids contract. 



Heat taken up in the change of liquid to vapor is given off in the 

 condensation of the vapor. 



Compression of a gas liberates heat. Expanding gases take up 

 heat; that is, become cold. 



Kindling temperature is the temperature at which a substance 

 begins to burn. 



A calorimeter is an apparatus in which the heat given off in burn- 

 ing, or in some other change, can be given to some water, and so 

 measured. 



The human body is a complex engine. It uses the changes in its 

 cells and in food to produce heat and the ability to do work. 



Evaporation of perspiration keeps the body's temperature constant. 



Wool makes the best clothing for those exposed to extremes of 

 temperature. 



