22 
BULLETIN 17. r. S. DEPARTMENT OF AGRICULTURE. 
layer of C and D. the difference in side-wall insulation does not seem 
sufficient to account for the difference in efficiency. The striking 
difference in the four types of cars is in the roof insulation. Types 
A and B. with the low efficiency, have but 1 inch of insulation, and 
that is divided into two layers with interrening air space. Type 
C has 1J inches of solid insulation, and D has two layers, each 
1 inch thick. There are undoubtedly several factors which govern 
the efficiency of a car. but it is worthy of note that the indices of 
efficient- v of Table 5 seem to vary in about the same way as the 
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7: - 7. — ?: c; ; - . :;3ns showing floor insulation of different types of refrigerator cars: a, i yj - A 7 
:. type C; d, type D: e, floor insulation separated into three layers:/, 1-inch layer of hair felt with two 
uninsulated subfloors. 
roof insulation. The floor insulations of the four types are about 
the same and are verv similar in thickness to the walls. 
ICE BUNKERS. 
Each of the types A. B. C. and D is equipped with a characteristic 
ice bunker. Type A uses the siphon bunker shown in figure S, 
Type B has the galvanized-iron box shown in figure 9. the box being 
perforated to allow the air to come in contact with the ice. Type 
C has two large, reenforced wire baskets (fig. 10), which permit free 
contact with the air. In front of the basket ice holder there is an 
insulated wall, with an open space at the top of the car for the admis- 
sion of warm air and a similar space at the bottom for the escape of 
the cold air. Type D uses the iron tanks shown in figure 11. With 
such tanks the ice can be crashed very fine, permitting a imiform 
