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.
SPECIFIC HEAT OF AIR AT CONSTANT PRESSURE AND VARIOUS TEMPERATURES ______________________________________________________________ | | | | | Temperature Range | | | |_________________________|_______________|____________________| | | | | | | Degrees | Degrees | Specific Heat | Authority | | Centigrade | 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 | |____________|____________|_______________|____________________|
This value is of particular importance in waste heat work and it is regrettable that there is such a variation in the different experiments. Mallard and Le Chatelier determined values considerably higher than any given in Table 28. All things considered in view of the discrepancy of the values given, there appears to be as much ground for the use of a constant value for the specific heat of air at any temperature as for a variable value. Where this value is used throughout this book, it has been taken as 0.24.
Air may carry a considerable quantity of water vapor, which is frequently 3 per cent of the total weight. This fact is of importance in problems relating to heating drying and the compressing of air. Table 29 gives the amount of vapor required to saturate air at different temperatures, its weight, expansive force, etc., and contains sufficient information for solving practically all problems of this sort that may arise.
WEIGHTS OF AIR, VAPOR OF WATER, AND SATURATED MIXTURES OF AIR AND VAPOR AT DIFFERENT TEMPERATURES, UNDER THE ORDINARY ATMOSPHERIC PRESSURE OF 29.921 INCHES OF MERCURY