156 REFRIGERATION AND REFRIGERATOR INSULATION ON BOARD SHIP. 
relatively small sizes of machines, the use of this design of machine was prohibi- 
tively expensive. 
In cases where the escape of gases would not be serious and where, on the other 
hand, cost of operation would be an important item, and where large quantities 
of refrigeration were required—especially in cases where a separate engine-room 
could be provided for the machine—the ammonia and carbonic-acid type of machine 
has been the ruling type. In merchant service there are a number of these machines 
placed directly in the main engine-room. It is unnecessary to dwell upon the matter 
of locating the machine in this way to the engineer who has been through the experi- 
ence of an accident or the unexpected escape of gases. For the engineer who has 
not been through an experience of this kind, discussing the subject will not carry 
great weight. Human nature seems very much to prefer the process of locking the 
stable after the horse has been stolen. , 
As has already been indicated, the ammonia or the carbonic-acid type of ma- 
chine is undoubtedly the best type of machine for cases where the capacity required 
is considerable and where a separate engine-room can be provided. In the choice 
of machines for this service there is a selection to be made between the open type 
of machine in which the stuffing box is arranged on the piston rod, and the enclosed 
crank-case type. In larger units the open type of machine is, of course, almost in- 
variably used. In the writer’s judgment this type of machine is distinctly better for 
the small as well as for the larger work. The open-type machine has the advan- 
tage in the matter of taking up wear and constantly and readily keeping the machine 
in its best state of efficiency. It has the further advantage of not wearing nearly as 
rapidly as does the enclosed crank-case design. 
Consider first the matter of the stuffing box. Where this is on the piston rod, 
and especially where the stuffing box is fitted with springs and with an oil lantern 
connecting to the low-pressure side of the machine, it is possible to run with a stuff- 
ing box so loose that the outer gland moves back and forth against the springs 
with each stroke of the piston and yet with no odor of ammonia discernible. The 
wear on the piston rod in this case is relatively small. 
Compare with this the wear on the stuffing box on the shaft of an enclosed crank- 
case machine. The wear on this shaft is concentrated at one particular point. The 
stuffing box is ordinarily not difficult to keep tight or approximately tight, but when 
it comes to replacement the piston rod of the open-type machine is a very much less 
expensive part to replace and one very much more easily replaced than is the crank- 
shaft of the enclosed-type machine. 
The capacity of a refrigerating machine, of course, falls off with increase in the 
clearance in the cylinder. A moment’s consideration will show very clearly the sim- 
plicity of adjusting clearance in the open type of compressor and the very serious 
difficulty in making the corresponding adjustment in the enclosed-type machine. 
Turning now to the Audiffren-Singrun Refrigerating Machine, in this type of 
machine the problem of a stuffing box is met by closing all of the working parts of 
the machine within a hermetically sealed drum. Referring to the sectional view of 
