1.25 | 18.37 | 3.67 | 0.8536 | 94.8 | 34.8 1.50 | 22.05 | 7.35 | 0.7501 | 124.9 | 64.9 1.75 | 25.81 | 11.11 | 0.6724 | 151.6 | 91.6 2.00 | 29.40 | 14.70 | 0.6117 | 175.8 | 115.8 2.50 | 36.70 | 22.00 | 0.5221 | 218.3 | 158.3 3.00 | 44.10 | 29.40 | 0.4588 | 255.1 | 195.1 3.50 | 51.40 | 36.70 | 0.4113 | 287.8 | 227.8 4.00 | 58.80 | 44.10 | 0.3741 | 317.4 | 257.4 5.00 | 73.50 | 58.80 | 0.3194 | 369.4 | 309.4 6.00 | 88.20 | 73.50 | 0.2806 | 414.5 | 354.5 7.00 | 102.90 | 88.20 | 0.2516 | 454.5 | 394.5 8.00 | 117.60 | 102.90 | 0.2288 | 490.6 | 430.6 9.00 | 132.30 | 117.60 | 0.2105 | 523.7 | 463.4 10.00 | 147.00 | 132.30 | 0.1953 | 554.0 | 494.0 15.00 | 220.50 | 205.80 | 0.1465 | 681.0 | 621.0 20.00 | 294.00 | 279.30 | 0.1195 | 781.0 | 721.0 25.00 | 367.50 | 352.80 | 0.1020 | 864.0 | 804.0 --------+-----------+-----------+----------+------------+---
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A cubic foot of free air at a pressure of one atmosphere (equal to 14.7 pounds above a vacuum) at a temperature of 60 degrees, when compressed to twenty-five atmospheres, will register 367.5 pounds above a vacuum (352.8 pounds gauge pressure), will occupy a volume of 0.1020 cubic foot, will have a temperature of 864 degrees, and the total increase of temperature is 804 degrees.

The thermal results of air compression and expansion are shown by the accompanying diagram.

The horizontal and vertical lines are the measures of volumes, pressures and temperatures.  The figures at the top indicate pressures in atmospheres above a vacuum, the corresponding figures at the bottom denote pressures by the gauge.  At the right are volumes from one to one-tenth.  At the left are degrees of temperatures from zero to 1,000 Fahrenheit.  The two curves which begin at the upper left hand corner and extend to the lower right are the lines of compression or expansion.

The upper one being the Adiabatic curve, or that which represents the pressure at any point on the stroke with the heat developed by compression remaining in the air; the lower is the Isothermal, or the pressure curve uninfluenced by heat.  The three curves which begin at the lower left hand corner and rise to the right are heat curves and represent the increase of temperature corresponding with different pressures and volumes, assuming in one case that the temperature of the air before admission to the compressor is zero, in another sixty degrees, and in another one hundred degrees.