MARKET PREPARATION, TRANSPORTATION, STORAGE 269 



383. The refrigerator-car consists of an insulated com- 

 partment at the ends of which ice is stored. In cooler 

 weather, when ice is not being used, ventilators at the ends 

 of the car are left open. In refrigeration, the cooling of 

 the fruit is accomplished by the circulation of air. The 

 cold air about the ice in the bunkers, being heavier than the 

 warmer air in the body of the car, sinks down and flows out- 

 ward along the floor, displacing the warmer air, which rises 

 and gradually moves along the ceiling to the ice bunkers 

 where it is cooled and passes downward. Thus there is a 

 continuous air circulation downward through the ice bunkers 

 and upward among the tiers of fruit packages. The cooling 

 capacity of the air is greatest at the bottom of the car, and 

 diminishes as the air passes upward. As the air circulation 

 is due solely to the difference in density or weight of the cold 

 air columns within the ice bunkers and the warmer air in the 

 body of the car, the movements of the air currents are sluggish 

 and, therefore, do not cool the fruit quickly, especially if 

 there is any considerable heat leakage into the car. The 

 amount of heat leakage is determined primarily by the 

 efficiency of the insulation but this is not of the highest type, 

 owing to limitations of cost and weight in car construction. 

 The leakage is naturally greatest when the difference in tem- 

 perature within and without the car is at a maximum. It is 

 impossible to prevent this leakage entirely even with the 

 best insulation and car construction now in use. 



384. Limitations. The refrigerator-car is not to be con- 

 sidered in the same class with the cold storage warehouse 

 plant. The insulation is not as efficient and the methods of 

 stacking and piling the fruit are such that there is serious 

 interference with the circulation of the air within the car. 

 Moreover, the refrigerating medium (usually ice alone) is not 

 as efficient as the material used in mechanically cooled ware- 

 house plants. For these reasons, the temperature within the 

 refrigerator-car is not as uniform as is necessary for the safe 



