Refrigeration 149 



Heat of fusion. The heat taken up by the ice merely 

 liquefies it and is equal to the amount of heat given up by the 

 water in changing into ice, after it reaches the freezing tempera- 

 ture. The amount of heat required to melt or fuse ice is called 

 the hidden or latent heat of melting or fusion. 



Assume that ice with a temperature of 32 F., or C., is 

 put into a refrigerator. An amount of heat which will raise 

 the temperature of an equal weight of water from the freezing 

 point to approximately 150 F., must be absorbed by the ice 

 in melting. This amount of heat is taken from the air and the 

 food in the refrigerator. The waste water of melting ice is 

 often about 32 F. If made to circulate over the inner surfaces 

 of the compartments, it will absorb more heat and drain off 

 with a temperature as high as 38 F. This of course means 

 economy in ice. 



Exercise. The latent heat of melting is 142 B. T. U. per pound 

 (for the meaning of B. T.U., page 142). Suppose a refrigerator with 

 a capacity for 50 pounds of ice melts 20 pounds a day. The quan- 

 tity of heat required is 



20 X 142 = 2840 B. T. U. 



Assume also that the waste water has a temperature of 38 F. 

 This has taken from the air and contents of the refrigerator an amount 

 of heat equivalent to 



20 (38-32) or 20 X 6 = 120 B.T.U. 



That is, the total quantity of heat which the ice in melting and the 

 water in warming to 38 F. have taken up is 2840 + 120 or 2960 

 B. T. U. 



The heat of fusion applied generally. All liquids may be 

 converted into solids, just as all gases may be changed into 

 liquids, by lowering their temperature below a certain point. 

 Changing any solid into a liquid involves latent heat. Mer- 

 cury, for instance, solidifies at about 39 C. or F. It be- 

 comes liquid by absorbing exactly as much heat as it gives up 

 in becoming solid. Now the point at which mercury or any 



