TRANSPORTATION OF FISHERY PRODUCTS 313 



cooling mixture used. The cars are fitted with floor racks and permanent side and 

 end- wall flues for air circulation. 



In these cars the circulation of the heat-carrying air is lateral rather than 

 longitudinal. Because of the shorter circulation path and the logical position of 

 the cooling tanks, lower mean and more uniform temperatures than those in 

 the end-bunker car are attainable. Frequency of reicing is less critical and the 

 bunkers need not be kept full as is the case with end-bunker cars. Some economy 

 of ice is possible at the end of trips since coohng is unaffected by the quantity 

 of the coohng mediiim. 



Although the overhead system of cooling is more logical and effective than 

 the end-bunker system, it is not especially favored in the United States, as it is in 

 Canada, mainly because of the alleged increased difiBculty in icing. Many 

 American yards have special icing facilities designed specifically for end-bunker 

 cars. The cost of any changes brought about by a new car design would neces- 

 sarily include the cost of servicing facilities, and some railroad officials hold that 

 the change-over from the end-bunker system to the overhead system is too costly. 



"Dry-Ice" Cars 



A number of systems employing "Dry Ice" as the refrigerant have been explored 

 in railway cars. These vary in principle from blocks of "Dry Ice" placed in over- 

 head tanks, the carbon dioxide gas evolved being permitted to gravitate to the 

 floor through wall flues, to comphcated control mechanisms which automatically 

 maintain a given temperature in the car by regulating the amount of heat to gain 

 access to the "Dry Ice." 



The Broquinda System. The Broquinda system employs "Dry Ice" to cool a 

 secondary hquid which has a low freezing point and a high coefficient of thermal 

 expansion. The essential elements of this system consist of an insulated outer com- 

 partment which is accessible through the roof of the refrigerator car and which 

 contains a metal "Dry-Ice" receptacle surrounded by a jacket which contains the 

 secondary liquid. The jacket, in tiun, is connected top and bottom to a system of 

 finned coils suspended from the ceiling of the car. A regulating valve controlled 

 by a thermostat is connected in the coil circuit. Railway cars are fitted with two 

 such units, one situated at each end of the car, and the coils extend to the center. 



The operation is very simple. "Dry Ice," placed in a special compartment 

 through the roof hatch, cools the liquid in the jacket. This cold, dense hquid 

 passes into the coohng coils through the lower connection and is warmed and 

 expanded by the heat taken up within the car. The warmed, less dense hquid 

 returns to the jacket through the upper connection and is cooled there by carbon 

 dioxide. The rate of circulation of the secondary hquid is regulated by the valve 

 and thermostat, and thus the temperature in the car is controlled. Since it is re- 

 ported that temperatures within the car can be controlled within narrow limits 

 (actual limits not given) and that the system can be used for shipments of fresh 

 and frozen commodities, it could have application in the transportation of fish. Its 

 main limitations at the moment, as far as fish are concerned, are the cost and 

 availability of "Dry Ice." 



Although the Broquinda system can be made efficient with reference to the 

 utilization of "Dry Ice," since even the carbon dioxide gas evolved before it escapes 

 can be brought to absorb heat from the space to be cooled, there are many centers 



