CONVECTION 



107 



FIG. 85. Why is the milk 

 on the top shelf? Why 

 will not the milk keep as 

 well on top of the ice? 



Refrigerators. There are two usual types of refrigerators 

 top icing refrigerators and side icing refrigerators. They work 

 on the same principle. The air next to the ice becomes cool, and 

 sinks through the bottom openings of the ice chamber into the main 

 part of the refrigerator, while the warmer air from the upper part of 

 the refrigerator enters the top of the ice 

 chamber and is cooled. There is a continuous 

 circulation of air past the ice and through the 

 food chambers. This circulation is important 

 because it distributes the cooled air to all 

 parts of the refrigerator, and also because on 

 passing the ice, the air loses some of the 

 moisture and the odors which it has taken 

 up from the food, especially that which is 

 not yet cold. Therefore, anything which 

 retards this circulation or stops up the 

 openings of the ice chamber should be 

 avoided. 



The lowest temperature inside a refriger- 

 ator ranges from 44 F. to 57 F., and the highest from 64 F. to 

 72 F. This difference in temperature causes the circulation of the 

 air in the refrigerator. By referring to the diagram it will be seen 

 that the air around the ice weighs more than the air above the ice. 



It has been found that milk kept at 60 F. will develop in one day 

 fifteen times as many bacteria as milk kept at 50 F. The same 

 thing is true of many other foods. It is important, therefore, 

 to find the coldest place in a refrigerator and use this place for foods, 

 such as milk and meats, which need to be kept as cool as possible 

 to prevent spoiling. The coldest place would naturally be directly 

 under the ice. 



Slow melting of the ice does not necessarily indicate a good 

 refrigerator. Unless the ice melts it can absorb no heat, and is 

 therefore of no use in a refrigerator. Protecting the ice in a refriger- 

 ator by covering it up is a good way to save ice, but a poor way to 

 save food. The only proper way to use less ice is by using a refrig- 

 erator with better insulated walls, and by opening the doors as sel- 

 dom and for as short intervals as possible. 



