14 
BULLETIN 17, U. S. DEPAKTMENT OF AGKICULTUKE. 
Table 4. — Comparison of thermograph records of atmospheric temperature and the figures 
obtained by averaging the United States Weather Bureau reports of the maximum and 
minimum daily records for the region through which the cars were passing. 
Experiment 5005. 
Experiment 5006. 
Experiment 5007. 
Date. 
Place. 
ft 
H 
O 
B 
03 
& 
1 
m 
Date. 
Place. 
CUD 
o 
a 
Eh 
s 
03 
U 
cq 
® "K 
go 
$ s 
Date. 
Place. 
ft 
a 
to 
o 
s 
Eh 
3 
c3 
03 
pq 
03 -»J 
c3 ft 
03 03 
1912. 
Mar. 20 
Nashville. . 
Louisville . 
Cincinnati. 
Pittsburgh 
Harris- 
burg 
New York. 
°F. 
70 
48 
30 
35 
35 
34 
42 
°F. 
69 
47 
33 
37 
35 
33 
1912. 
Mar. 29.. 
30.. 
31.. 
Apr. 1... 
2... 
Nashville. . 
Louisville . 
Cincinnati. 
Pittsburgh 
Phila- 
delphia . 
°F. 
57 
54 
55 
56 
60 
56 
54 
50 
58 
54 
56 
1912. 
June 1. . . 
2... 
3... 
4... 
5. .. 
Lexington. 
Cincinnati. 
Marion, 
Ohio. 
Syracuse.. 
New York. 
72 
67 
71 
69 
67 
69 
°.F. 
73 
31 
22 
23 
66 
24 
68 
25 
Average . . 
42 
54 
69 
CALCULATION OF THE INDEX OF EFFICIENCY. 
To compare trie efficiency of the various cars, constructed on widely 
divergent lines, it becomes necessary to reduce the variable functions, 
or influencing factors, to a resultant coefficient. Since the purpose 
of a refrigerator car is to maintain a fixed temperature on the inside, 
regardless of external temperatures, the ultimate question is one of 
heat transmission, or the power of all the contributing factors to over- 
come the heat transmitted from the outside to the inside. Insulation 
efficiency is usually expressed as the number of B. t. u. 1 transmitted 
through 1 square foot of the material in a day, for each degree difference 
in temperature on the colder and warmer sides. Therefore, knowing 
the amount of ice and salt used, the duration of the haul, and the 
average temperatures on the inside and outside, the simplest formula 
for car efficiency would be 
p _ 142 1 + 40.5 N m 
K ~ S (T-0D W 
I = pounds of ice used. 
142 =B. t. u. required to melt 1 pound of ice. s 
N = pounds of salt used. 
40.5 = the endothermic heat of solution of 1 pound of salt in a 10 
per cent solution at 32° F. 
S = the surface exposure of the car. 
T =the average atmospheric temperature. 
t = the average temperature inside of car. 
D = the number of days in the test. 
1 A British thermal unit (B. t. u.) is the quantity of heat required to raise the temperature of a pound 
of pure water 1 degree Fahrenheit. 
