128 GENERAL SCIENCE 



Temperature, Btu. and Calorie. The word temperature is a 

 word of Greek origin meaning, " to measure heat." It, however, 

 does not mean to measure the amount of heat but the degree of 

 heat. Every one knows that a barrel of water at 60 F. requires 

 more heat to heat it to 80 F. than does a quart of water, from 

 60 F. to 80 F.; in fact, it would require 125 times as much heat 

 to heat the water in the barrel. The degree of heat is measured 

 by the thermometer, and the amount of heat by the B.T.U. (British 

 Thermal Unit). From now on this unit will be written "Btu." 



The amount of heat required to heat 1 pound of water 1 F. 

 is called a Btu. This unit is used in our country and in England. 

 In many of the other countries of the world heat is measured by the 

 calorie, which means the amount of heat required to heat 1 gram 

 cf water 1 C. 



Place a pound of water in a large dish and 1, gram of water in an evap- 

 orating dish. Heat both to boiling point after taking the temperature of 

 the water in both dishes. What thermometers would you use? How many 

 Btu. would be required to heat the pound of water? How many calories 

 to heat the gram of water? How many calories would be required to heat the 

 pound of water to boiling? 



Latent Heat. Ice has a temperature of 32 F., and ice water, 

 also, has the same temperature. Some people might think the ice 

 was colder than the water. If a piece of ice is placed in a dish and 

 allowed to melt, the temperature of the mixture remains about 32 F. 

 or C. until the ice is melted. This shows that a great deal of heat 

 is used to melt the ice without raising the temperature. The heat 

 which is used to melt the ice is called latent heat (hidden heat). 



Ice melting in the refrigerator takes heat from the food and air 

 of the box. This heat is in the water, and is removed from the box 

 as the water runs out. When water freezes, large quantities of heat 

 are given off. For every pound of water which freezes, 143 Btu. 

 are released to the surrounding atmosphere, and the same amount 

 of Btu. is taken from the atmosphere for each pound of ice 

 melted. 



Put a small amount of ice water in an evaporating dish. Heat the water 

 to boiling point, noting the time required. Boil the water until it has all 

 changed to steam, noting the time required. 



