16 BULLETIN 17. U. S. DEPARTMENT OF AGRICrLTTBE. 
In order to give credit to those ears in which low temperature? 
prevailed at the bunker. H in formula 2 must be a function of the car 
temperature. The cars were iced 24 hours before loading, and the 
inside car temperature decreases eontmually from the time of icing 
until the door is opened for loading. Therefore 24 of the total 
number of hours are constant. The variable portion then becomes 
H : where 
H = 24-H 1 3) 
EP represents the number of hours between loading and the time at 
which the temperature at the bunker begins to rise. 
The bunker should cool the air from the temperature prevailing 
at the center of the car to that prevailing at the bunker, the temper- 
ature maintained at the center depending on the insulation of the 
car and the circulation of air. The total refrigerating effect might 
be expressed as degree-hours; that is. if the temperature at the 
center is C and that at the bunker is B and this difference in tem- 
perature is maintained for H 1 hours, the refrigerating effect is H 1 
C— B degree-hours. If no salt had been used on the ice the 
bunker air would he 32° F.: but the total refrigerating effect is the 
same whether the ice melts slowly or rapidly, and therefore the 
degree-hours at this temperature are C — 32) H 11 . Hence 
CC-B) EP 
As shown by Table 2. 32 : F. C C.) is too warm for the best 
results in poultry transportation. The temperature should be 
30° F. — 1.1° C.) or lower. In determining the efficiency of the 
car for maintaining a temperature of 30° F... this number should be 
substituted hi the formula, which then becomes 
C-B.IT 
H- = C30 (o) 
FT 1 represents the number of hours after loading at which the 
bunker temperature would have started to rise if the bunker had 
been producing air at 30° F. —1.1° C.)- This reduces all of the car 
temperatures to a comparative basis: the compensating formula 
would then be 
r . 142 1-40.5 X 
S T-/ 24-H - 
and. by substitution, the efficiency formula becomes 
„!_ 142 I -40. 5 y 
,C-B \ (6) 
*-* (^- H1 c^i) 
The efficiency of the car will vary inversely as R 1 , since the greater 
amount of heat transmitted indicates lower efficiency. If E is the 
index of efficiency, then E = ^- 1 
