4 o 



COMMON PHENOMENA DUE TO HEAT 



will gradually become warmer. A red-hot iron placed on a 

 stand gradually cools, but warms the stand. A hot body 

 loses heat as long as a cooler body is near it; the cold object 

 is heated at the expense of the warmer object, and one loses 

 heat and the other gains heat until the temperature of both is 

 the same. Now the hot water in the tub gradually loses heat 

 and the cold air of the room gradually gains heat by convec- 

 tion, but the amount given the room by convection is small 

 compared with the large amount set free by the condensing 

 steam. 



Distillation. When impure, muddy water is boiled, drops 

 of water collect on a cold plate held in the path of the steam, 

 but the drops are clear and pure. When impure water is 



boiled, the steam from it 

 does not contain any of 

 the impurities because 

 these are left behind in 

 the vessel. If all the 

 water is allowed to boil 

 away, a layer of mud or 

 of other impurities will be 

 found at the bottom of the 

 vessel. Because of this 

 fact, it is possible to 

 purify water in a very 

 FlG ^ 23 ' 7 l n r ^ tha u the st u am ^f pas f e ^ S simple way. Place over 



through the coiled tube may be quickly cooled r 



and condensed, cold water is made to circulate a fire a large kettle closed 

 around the coil. The condensed steam es- ^ for & t which 



capes at w. 



is long enough to reach 



across the stove and dip into a bottle. As the liquid boils, 

 steam escapes through the spout, and on reaching the cold bottle 

 condenses and drops into the bottle as pure water. The im- 

 purities remain behind in the kettle. Water freed from im- 



