18 
BULLETIN 98, U. S. DEPARTMENT OF AGRICULTURE, 
for, as previously stated, the use of a mixture of salt and ice in a 
refrigerator does not increase the cooling capacity of a given amount 
of ice, but the effect is to cause the ice to melt more rapidly and thus 
absorb heat more quickly. In other words, the melting point of 
ice is lowered when mixed with salt. One pound of ice in melting 
absorbs 144 heat units, either with or without salt. With salt the 
absorption is quickened, hence a lower temperature for a shorter 
time . Therefore there is no gain 
in efficiency by employing a mix- 
ture of salt and ice ; in fact, there 
is a loss in efficiency due to the 
heat of solution. 
Ice bunkers for cooling pur- 
poses, when located over the 
compartment to be cooled, 
should be made in the form of a 
box with one side removed, as 
shown in figure 6, in order to 
assist the air currents. With 
this form of construction the 
air, as it is gradually cooled, 
flows to the left down over the 
ice, while the warm air rises on 
the right to take its place. It 
is obvious that if the bunkers 
should be made in the form of a 
rectangular box the air would 
have a tendency to flow off in all 
directions and give rise to con- 
flicting currents which would re- 
tard the circulation and for the 
same rate of circulation a greater 
difference in temperature between the air in the bunker and that 
in the compartment below would be required. 
Ample spaces for air ducts should be provided between the sides 
of the bunker and the walls of the cold-storage compartment in 
order to permit the air to circulate freely. The cross-sectional area 
of the ducts should be from 10 to 15 per cent of the area of the ceiling. 
The floor of the bunker and the walls of the air ducts should be well 
insulated to prevent the too rapid cooling of the relatively warmer 
ascending air as well as that lying next the floor of the bunker. 
Rapid cooling of the air at these points tends to check the circula- 
tion by reducing the difference in temperature between the warm 
Tr 55 * 
Fig. 6. — Overhead ice bunker. 
