The New Student's Reference Work/Compressed Air

Compressed Air. The first scientific knowledge of the power of air was gained in the sixteenth century by Galileo. Air under pressure increases in density and heat, and exerts an increased power in every direction. Hence compressed air is applied in locomotives; and its power is employed in many machine-plants, such as those of mines and water-works. An air-compressor or air-pump is a cylinder fitted with a piston and rod, and with valves at which the free air may enter and with others at which the compressed air may be applied, together with the needful connections of this apparatus with the driving power. In most compressed air "plants," the pressure which is employed is about 80 pounds to the square inch. Air may be liquified at a temperature of 312° below zero. This temperature may be got under a pressure of 1,200 pounds or upwards to the square inch; but the process is thus far not profitable from a commercial standpoint, although there are several ways in which liquid air may be applied.