[Pg 148]
Example: Required the volume of air in cubic feet under 60.3 pounds gauge pressure per square inch at 115 degrees Fahrenheit.
| P | = | 144 (14.7 + 60.3) | = | 10,800. |
|
| T | = | 115 + 460 | = | 575 degrees. |
|
| Hence v | = | | 53.33 × 575 | | –––––––––––––––––––– | | 10,800 |
| = | 2.84 cubic feet, and |
| Weight per cubic foot | = | | = | | = | 0.352 pounds. |
[Table 27] gives the weights and volumes of air under atmospheric pressure at varying temperatures.
Formula ( [9] ) holds good for other gases with the change in the value of the constant as follows:
| For oxygen 48.24, nitrogen 54.97, hydrogen 765.71. |
The specific heat of air at constant pressure varies with its temperature. A number of determinations of this value have been made and certain of those ordinarily accepted as most authentic are given in [Table 28] .
[TABLE 28]
SPECIFIC HEAT OF AIR
AT CONSTANT PRESSURE AND VARIOUS TEMPERATURES | Temperature Range | Specific Heat | Authority |
|---|
| Degrees Centigrade | Degrees Fahrenheit |
|---|
| -30– 10 | -22– 50 | 0.2377 | Regnault | | 0–100 | 32– 212 | 0.2374 | Regnault | | 0–200 | 32– 392 | 0.2375 | Regnault | | 20–440 | 68– 824 | 0.2366 | Holborn and Curtis | | 20–630 | 68–1166 | 0.2429 | Holborn and Curtis | | 20–800 | 68–1472 | 0.2430 | Holborn and Curtis | | 0–200 | 32– 392 | 0.2389 | Wiedemann | |