MEASURING OF HEAT 



131 



Specific Heat. Not all substances require the same number of 

 Btu. to heat 1 pound of the substance 1 F. or 1 gram of it 1 C. 

 The amount of heat required to heat 1 gram of any substance 1 C. 

 is called the specific heat of that substance. It takes less heat to 

 heat 1 pound of tin 10 than it does to heat 1 pound of water. 



It requires very little heat to heat mercury, which makes it a 

 valuable substance for thermometers. 



TABLE OF SPECIFIC HEAT 



Water 1.00 



Copper 091 



Alcohol 62 



Iron 113 



Soapstone .21 



Glass 198 



Aluminum. 214 



Tin 055 



Limestone 217- 



Mercury 033 



Sand 19 



Olive oil 31 



Wood 65 



Lead 031 



Glycerin 55 



Marble 21 



Salt 17 



Brick .2 



Marble 215 



Air.. .238 



From the table it will be seen why soapstone discs are used in 

 fireless cookers in place of iron discs. 



Experiment to Show Specific Heat. Heat in boiling water several pieces 

 of different metals of the same weight. Take several cans of the same size and 

 material and containing each the same amount of water at a uniform tempera- 

 ture. Into each can drop a piece of metal, and see which heats the water the 

 most. That metal has evidently the highest specific heat of the metals used. 



Melting and Solidifying. Different substances melt at differ- 

 ent temperatures. The melting point is called the fusion point. 

 The reverse of this process is called freezing or solidifying. Nearly 

 all substances remain at the temperature of the melting point until 

 completely changed into a liquid. A few substances, such as 

 sealing wax and butter, continue to become warmer as they melt. 



Impurities affect the melting point. Salt is often used to melt 

 ice, as the presence of salt causes the ice to melt at a lower tempera- 

 ture. The use of salt in the ice cream freezer is readily understood, 

 since the temperature of the melting solution is about 32 F. below 

 freezing point. 



Impurities in water, such as salt, produce a low freezing point. 



