CONVECTION 



101 



inside, where the wind cannot disturb the air which is held among 

 the hairs, than if the fur is on the outside. 



Why Water Carries Heat. Water at about 40 F. weighs 

 about 62 1 pounds per cubic foot or 436,961 grains per cubic foot. 

 If the water is heated to boiling, a cubic foot will weigh 418,320 grains, 

 or 18,641 grains less. That is, water weighs, on the average, about 

 108 grains less per cubic foot for every degree Fahrenheit it is heated. 



This is due to the fact that 1728 cu. in. (one cubic foot) of water 

 when heated from 40 F. to 212 F. increases in volume until there 

 are about 77 more cubic inches of water (about 1805 cu. in.). The 

 weight of the cubic foot of hot water is equal to the weight of about 

 1651 cu. in. of the cold water which have expanded to 1728 cu. in. 



WOO GRAINS 

 AT 



<t3606 GRAINS 

 BOILING 



FIG. 79. Why will water as it 

 rise to the top of the vessel? 

 will the water at the top sink? 



heats 

 Why 



FIG. 80. 



The heated -water will be lighter than the cold water; hence, it will 

 rise to the top of a kettle, while the cold water, being heavier, will 

 sink. Naturally, the heat will be carried by the lighter water to the 

 upper part of the vessel. We have already defined this method of 

 carrying heat as convection. 



Experiment to Show how the Water Gets Hot in a Kitchen 

 Boiler. Construct apparatus as shown in the diagram, Fig. 80. Fill 



