se 
ROTM en ee 
REFRIGERATION AND REFRIGERATOR INSULATION ON BOARD SHIP. 155 
Comparatively few refrigerator builders have any realization of the vital im- 
portance of having large air passages, or, if the builders of ordinary household re- 
frigerators have this appreciation, they use it to the disadvantage rather than the 
advantage of their design so far as its use to the purchaser is concerned. As already 
pointed out, if the air passages in a refrigerator are choked down, there will be little 
circulation of the air, and the refrigerator will therefore be economical of ice. It will 
be a refrigerator, however, in name only. 
The force that causes the circulation of air in a refrigerator is extremely 
minute, being only the difference of weight between the air in the coil compartment 
and that in the same height of the food storage compartment. If there is a difference 
of even, say, 15 in the temperature between the two compartments the excess weight 
in the one over the other is obviously extremely slight. 
The writer had an opportunity several years ago to make an experiment on re- 
frigerator temperatures that brings out this point very clearly. Plate 77 
shows a section through the refrigerator which was about 8 feet wide and 6 feet 
high. The cooling surface was located in the middle of the refrigerator with a baf- 
fle plate on each side of it, and the passages for the air were identically the same on 
both sides, except that the space leading from the storage compartment to the coil 
surface at the left was 3 inches and that at the right was 4 inches. This difference 
of 1 inch in this one dimension made a difference in the temperatures observed at the 
points marked A and B of one degree, throughout a week test. 
When one considers that the average household refrigerator has air passages 
from 1 to 2 inches (rarely more than this) in depth, and when the average large re- 
frigerator has only 3 or 4 inch passages, in a very great many cases, the desirability 
of further attention to this element in the design of refrigerators is apparent. 
DESCRIPTION OF REFRIGERATING MACHINES. 
The writer will not attempt any elaborate description of the various types of re- 
frigerating machines that are used in marine work. As a matter of fact, practi- 
cally every type of machine that is built has been given more or less trial in this ser- 
vice. He will only attempt to call attention to a few of the considerations that seem 
important in determining the type of machine suitable for any given installation. 
For a number of years the only refrigerating machine that seemed entirely safe 
for use on board ship was the air machine, especially as embodied in the Allen Dense 
Air Machine. The skill required in the operation of these machines and their enor- 
mously high cost of operation was more than counterbalanced by the freedom from 
danger from escaping gases that they gave. There was no need to carry a supply of 
flasks containing gases at high pressure; there was, therefore, freedom from any 
danger to the ship from the presence of these gases, and there was no danger that 
the machine would be shut down from lack of chemicals. There was, of course, 
considerable danger of derangement of the machine in case it was not skillfully 
handled, and, as already suggested, the cost of operation was so high that, except for 
