MECHANICAL REFRIGERATION 169 



must be used quickly, since it will putrefy more rapidly 

 than when fresh. This is partly due to the fact that food 

 just ready to spoil is placed in cold storage to preserve it. 

 Such food will spoil at once when removed from the freez- 

 ing temperature. Possibly, also, the food is slightly changed 

 in its physical nature by the freezing, so that bacteria can 

 more readily act upon it when it is thawed. In many 

 cases, however, especially with fruits, which are not actu- 

 ally frozen, the rapid decay which follows removal from 

 cold storage is due to the large amount of moisture which 

 condenses upon the surface of the cold fruit when it is 

 placed in warm or damp air. Such surface moisture, as 

 we have seen, furnishes the necessary condition for the 

 starting of mold growth. The practical lesson to be learned 

 is that after the material has been removed from the cold 

 storage and warmed up to ordinary room temperatures, it 

 should be consumed as soon as possible, because putrefac- 

 tion and decay are sure to take place speedily. If not used 

 at once, it must be kept in an ice chest. 



Properly controlled, cold-storage plants are of very great 

 value to the public. The objections to them are chiefly 

 two. They enable unscrupulous people to freeze food that 

 is ready to spoil, and therefore not fit for eating, and sub- 

 sequently to put it on the market. They also make it easier 

 to gather great quantities of foods in the hands of a few 

 persons, who, controlling so large a supply, can manipulate 

 prices. Except for these misuses, which can be controlled by 

 law, the cold-storage plant is a great boon to the consumer. 



2. Mechanical Refrigeration in the Home. Of all house- 

 hold devices, the mechanical refrigerator gives the nearest 

 approach to cold-storage conditions. Several t}^es of these 



