IV.VERY HIGH-PRESSURE COMPRESSORS.
B. High-Duty Apparatus.
2. Hydraulic Piston-Compreseors.-The machines under this
class are but two: one, a very old apparatus, not used at present;
in the second, in which the air is compressed to 25 atmospheres,
the refrigeration is accomplished by injection, and the compression
effected in two unequal cylinders. This machine has not been
subjected to sufficient practical tests to admit any authentic
data being presented.