﻿REFRIGERATION OP DRESSED POULTRY IN TRANSIT. 15 



R = B. t. u. of heat transmitted through 1 square foot in one day, 

 for each degree difference in temperature; or the amount of re- 

 frigeration which must be supplied for each square foot of car 

 surface in a day, for each degree difference in temperature between 

 the atmosphere and the inside. 



With thermograph records of the temperature at both bunker and 

 center of car, a fairly accurate average inside temperature may be 

 obtained. The daily maps of the Weather Bureau afford excellent 

 atmospheric data, and with accurate re-icing records the formula 

 gives a very serviceable working comparison of refrigerator cars. 

 The commercial re-icing records are not sufficiently exact for mathe- 

 matical calculations of efficiency. It is also very difficult to determine 

 from commercial records the weight of the ice which remained in the 

 car bunkers at the end of the haul, and it is consequently impossible to 

 calculate the amount of ice melted. But as it was extremely desirable 

 to make some kind of a comparison of cars which might serve as a 

 working basis or beginning for future experiments, it became neces- 

 sary to devise a formula which would make R a function of the initial 

 icing, which in these experimental shipments is of acceptable accuracy. 



Other factors being constant, a comparative efficiency of cars could 

 be calculated by noting the length of time between the initial icing 

 and the hour at which the temperature on the inside of the car begins 

 to rise; this hour indicates that the ice has spent its maximum 

 strength. No ice is put into the car during this interval. The 

 formula then becomes 



142 1 + 40.5 N m 



^ " S(T-<)H H 



H = the number of hours between icing and the moment at which 

 the temperature in the car begins to rise. R 1 , no longer properly 

 designated as B. t. u. because the car still contains unmelted ice, 

 becomes an arbitrary number, but still remains a comparative index 

 of efficiency. 



One other correction must be introduced. If the salt, on account 

 of physical conditions in the ice bunker, melts very rapidly and 

 dissolves in the smallest possible amount of water or melted ice, it 

 will lower the temperature of the resulting solution very much more 

 than when it dissolves more slowly and in a larger quantity of water. 

 One per cent of salt with snow or crushed ice lowers the temperature 

 of the mixture on an average of about 1.1° F. between 0° concentration 

 and the point of saturation. If sufficient salt is added to completely 

 saturate the resulting'solution, it is possible to reduce the temperature 

 to about —6° F. ( — 21.1°C). It is evident that if very low tempera- 

 tures are produced, the ice will begin to lose its force sooner than if 

 higher temperatures had prevailed, because the total amount of 

 refrigeration available is the same in each case. 



