51. Q. Why is this called a cross-compound compressor?

[Illustration: Diagram of 8-1/2" Cross Compound Compressor. The

High Pressure Steam (Low Pressure Air) Piston on Its Upward Stroke

Fig. 4.]

A. Because both steam and air are compounded, that is, the steam is used

the second time before it is exhausted to the atmosphere, while the air

is compressed the second time before it is delivered to the main

reservoir.