78 PRESERVATION OF FOOD BY REFRIGERATION ; 
screen, both sides of which, or 1,368 sup. feet, would be 
available both for radiation and also for contact of cold air. 
As the area of the walls, floor, and ceiling is 1,278 sup. 
feet, by giving an additional 1,368 feet we double the area 
available for radiation. On the plan of fig. 6, the area of 
surface available for contact of cold air is that of the walls, 
floor, and ceiling=1,278 feet, together with the surfaces of 
the 60 quarters, making 1,278+780=2,058 sup. feet. By 
the addition of the screens a total of 2,058+1,368=3,426 
sup. feet, becomes available as against 2,058 without the 
screens, and when it is remembered that it is by con- 
tact of cold air only that the heat is removed (radiation 
acting as an intermediate factor in the case), it is evident 
that we shall have increased our power very largely. 
The heated air should be removed from the room in the 
usual manner, that is, from the top, and, contrary to the plan 
generally adopted in the refrigerating rooms as at present 
constructed, the cold air should be admitted at the bottom. 
There are several good reasons why this should be done, 
which it is well to enumerate. First is the fact illustrated 
in fig. 3, plate II., where it is shown that the loss by con- 
tact of cold air depends upon the circulation of the cold 
air upwards, and that if the current is intercepted or 
stopped the air is not able to get away with the heat. 
2nd. Warm air being less dense than cold air, its natural 
place is above, and anything retarding its rise interferes 
with the natural and complete circulation. 3rd. That air 
containing moisture is lighter than dry air at the same 
temperature, and as it is very important to remove the 
moisture from the surface of the meat, especially at the 
commencement of the operation, it is most desirable to 
have, on this account, a distinct upward circulation. 
The only reason given for admitting the cold air at the 
top is that the temperature is rendered thereby alike at the 
top and bottom of the room. It cannot increase the cir- 
culation, as it is impossible to get the warm air out of the 
room quicker than the cold air is put in. Why it should be 
thought advisable to have an equal temperature above and 
below is not apparent. The object we have in view is the 
removal of the heat, and not to keep the temperature of 
the room even, and this will be best accomplished by pro- 
