﻿REFRIGERATION OF DBBSSED POULTBY. IX TRANSIT. 19 



proof under the continual stress and strain to which refrigerator 

 cars are subjected. Cracks in the boards and punctures in the 

 paper lining soon appear and, with the resulting air circulation, heat 

 is directly transferred from the outside to the inside. A heat insu- 

 lator is a nonconductor of heat. Heat is a form of energy trans- 

 ferred in waves of extremely small length from one molecule to 

 another. Since the molecules in solid bodies are closer together than 

 those of gases, the solids are the better heat conductors. The more 

 numerous the air spaces in a solid body the more efficient it will be 

 as an insulator. 



Cork, the best known insulator, contains innumerable air spaces, 

 and its texture renders it almost impervious to water. It contains 

 but small amounts of gums and resins and practically no nitrogenous 

 material which might serve as a medium for bacterial growth and 

 thus produce decay. Cork, however, has not been used to any 

 extent in car construction, perhaps on account of its expense and 

 the difficulty of its application. 



Wool and hair felt are good insulators as long as they are kept dry, 

 but their high percentage of nitrogenous material makes them good 

 bacterial media when moist. Organic oils and acids also aid in their 

 decomposition. These materials, when once moist, seldom dry out, 

 and the result is putrefaction, giving rise to offensive odors, which 

 contaminate the goods in the car. This decomposition not only 

 destroys the insulator itself but rots the board lining with which it 

 comes in contact. Some of the vegetable or cellulose fiber insulators 

 are perhaps slightly more resistant to moisture and bacterial action, 

 but in time they also become moist and their chemical decomposition 

 is hastened by the alkalies present in such material. Of the insu- 

 lators mentioned, mineral wool is the least subject to decay, but, 

 on the other hand, its physical nonadhesive properties hinder the 

 manufacture of strong material, and its insulating qualities are not 

 as good as those of some of the other nonconductors, although it has 

 the advantage of being fireproof. 



Careful consideration of insulation is therefore one of the prime 

 factors in car construction. The material must be of such a nature 

 that it will remain in position, not settling down and leaving hollow 

 spaces in the upper portion of the side walls. It should be impervious 

 to moisture, or be securely protected by moisture-proof material, and 

 as free as possible from decomposable organic matter. The neces- 

 sary thickness of the insulation depends on the nature of the goods 

 to be transported. Investigations in fruit transportation have shown 

 that temperatures as low as 40° F. are very satisfactory for citrus 

 fruits, but the results with poultry indicate that lower temperatures 

 are essential for a maximum preservation of this class of goods. 

 Aside from the nature of the lading, the question of insulation is one 



