ARTIFICIAL REFRIGERATION AND ICE MAKING. LV. 
filling with gas, did not this machine run at a very low speed. 
It may therefore be said that the Auldjo, Antarctic, Frick, and 
Hercules machines perfectly fulfil the first condition. 
2. The piston rod should work gas tight with the minimum of 
friction. The use of oil as a seal to the piston rods of these 
machines has made a seal possible, but with horizontal double 
acting machines like the ‘‘ Linde” this oil has to be pumped by 
special arrangements intoa lantern bush. In all but the Antarctic 
Compound the oil being inside the cylinder is liable to be carried 
into the system, and by coating the interior of the pipe coils affect 
their conducting power. In the Antarctic Compound the rods 
are not ordinary piston rods at all, and the oil is not in the 
cylinder, hence the most perfect seal is obtained without these 
disadvantages, 
3. The whole contents of the cylinder, less the minimum of 
clearance should be discharged at the minimum pressure. In the 
De La Vergne machines the oil ensures the full expulsion of the 
8as, and also in those machines which, like the “Frick,” “Auldjo,” 
and “ Antarctic,” have delivery valves the full area of the cylinder, 
the piston can sweep the full contents out. In certain types of 
machines, which, like the “Hercules,” have two valves on the top 
Cover, their area is limited and the effect cannot be the same. 
While therefore, some machines offer the best facilities for taking 
in the gas, and others have the best arrangements for expelling 
it, the “Antarctic” designs follow the better features of both classes. 
THE DESIGN AND CONSTRUCTION OF THE WHOLE MACHINE. 
The diagram from a steam engine cylinder, as we are all aware, 
is just the reverse of that from a compressor, the maximum pres- 
Sure being exerted upon the piston at the beginning of the stroke 
and reducing rapidly by expansion after the steam is cut off, at 
the time when the resistance of the gas to the compressor piston 
is increasing, 
Some of the illustrations on the walls represent straight line 
compressors, which are double acting with their steam engine 
