160 REFRIGERATION AND ITS USES 



a portion of the moisture will be condensed upon this object, 

 forming dew. This is exactly what takes place when a pitcher 

 or glass of cold water stands for a few minutes on a warm 

 summer day. The pitcher or glass becomes covered with dew. 

 Often dew stands in drops on a pitcher or glass containing ice 

 water. 



187. Why the Air within the Refrigerator is Dry. In 

 many portions of the United States the air on a summer day 

 frequently reaches a temperature of 90F., while at the same 

 time the relative humidity is often as high as 80 or 85 per 

 cent. We see, by reference to Table VII, Art. 185, or to the 

 curve (Fig. 121, B), that this means that the air contains 12 

 or 12.5 grains of moisture per cu. ft. At the same time, 

 the air within the refrigerator is still more nearly saturated. 

 But, since the temperature of that air is not higher than 

 50 or 55F., the largest amount of moisture it can possibly 

 contain is only about 4 or 4.5 grains per cu. ft,, or about one- 

 third of that contained by the air outside. Again, as the air 

 circulates through the ice compartment, much of it actually 

 comes directly in contact with the ice. This must mean 

 that the air for the moment is cooled nearly to 32F., the 

 temperature of the ice. All of the moisture in this air in 

 excess of about 2 or 2.5 grains per cu. ft., therefore, is de- 

 posited in the form of dew upon the ice. Show this to be 

 true by reference to the curve (Fig. 121, C). It is, therefore, 

 evident that the air, as it flows from the ice compartment 

 into the food compartment, does not contain more than 

 about one-fifth, or at most one-fourth, as much moisture as 

 the air in the room. The air, then, as it flows from the ice 

 compartment into the food compartment, is cold and contains 

 but little moisture, notwithstanding the fact that it is saturated. 



188. Effect of the Dry Air within the Refrigerator upon 

 Foods. When this stream of cold, dry air leaves the ice 

 compartment and enters the food compartment, it takes up 

 heat from all the contents of the food compartment. As 

 this air rises in temperature, its capacity for holding moisture 



