ARTIFICIAL REFRIGERATION AND ICE MAKING. pak 
1. There are no piston rods proper as the cylinders are open 
mouthed and face one another. 
2. The two pistons are so connected that a passage through the 
centre of thém permits the flow of gas directly from the low to 
the high pressure cylinder, without going outside and through 
connecting pipes. 
3. The two cylinders are enclosed in a casing, so that any 
possible leakage past the piston is intercepted and again drawn 
in at the suction valye, and they are made simple castings without | 
belts or passages to affect the homogeneous character of the metal. 
4. The enclosing casing can be filled up with several inches of 
oil in the bottom without any being put in the cylinders proper, 
and the seal thus made renders leakage of gas through the 
Stuffing boxes impossible. 
5. The valves can be made as large as desired for the area 
required, and can be all inspected and taken out by opening only 
two doors. 
6. Owing to the work being divided between the up and down 
strokes, and the proportion of the pistons being as 3 : 1, the 
effective pressure reached in the first stage or down stroke is only . 
about one-half of the ultimate pressure, and as the pressure on one- 
third of the area of the large piston is neutralised by the pressure 
on the small piston during the down stroke, the eftective stress or 
load is only about one-third of what it would be in an shoal 
Single acting compressor, During the up stroke it is manifest 
that with only one-third the area, a given ultimate —, of 
gas can offer only one-third the resistance which an Oey 
compressor piston would exert on the working parts of the machine. 
7. The resistance at any time to the pistons of a given sized 
Compressor under this system are from one-third to two-fifths of 
that exerted in an ordinary compressor, but the work is cintetonted 
practically throughout the whole of the two strokes, instead of 
being confined to the latter portion of one stroke only. 
