Some Physical Properties of Compressed Gases, III. Hydrogen

The compressibility data on hydrogen taken at the Reichsanstalt, the Leiden, and the Fixed Nitrogen Research Laboratories have been smoothed, averaged, and extra-polated to cover the range -215°C to 500°C and to 1200 atm. A sensitive graphical scheme for getting derivatives makes possible the calculation of some physical properties of gases; those on nitrogen and carbon monoxide have been published. The properties so calculated are specific volume, density, temperature and pressure expansion coefficients, fugacity, $C_p$, $C_p-C_v$, $C_v$, and $\mu$. These are exhibited in graphs and a table that cover the temperature and pressure ranges mentioned above, except that it was not possible to calculate heat capacities and Joule-Thomson coefficient below -75°C. The expansion coefficients $\left(\frac{T}{v}\right){\left(\frac{\mathrm{dv}}{\mathrm{dT}}\right)}_p$ and $-\left(\frac{p}{v}\right)\left(\frac{\mathrm{dv}}{\mathrm{dp}}\right)$ decrease monatonically from unity as the pressure increases from 0 to 1200 atm., along all isotherms within the range studied. This is in contrast with the behavior of nitrogen and carbon monoxide; with these gases the expansion coefficients along isotherms at low and ordinary temperatures at first increase with pressure, then drop back to unity and after that decrease as the pressure is increased. Fugacity is tabulated at integral temperatures and pressures throughout the entire range. The $C_p-C_v$ vs. $p$ isotherms all show a maximum at about 500 atm. At -75°C, $C_p$ increases 0.95 cal./mole deg. as the pressure changes from 0 to 1200 atm. The increase $\Delta C_p$ with pressure becomes less as the temperature is raised. At 500°C it amounts to only 0.08 cal./mole deg. in 1200 atm. $\Delta C_p$ is several times smaller for hydrogen than for nitrogen or carbon monoxide. The $C_v$ vs. $t$ isobars from 0 to 600 atm. form a family of almost parallel curves. At higher pressures a distinct maximum appears at about 50°C. The Joule-Thomson coefficient is +0.21 deg./atm. at -75° and zero pressure; it is 0 at -75° and 25 atm., and becomes negative at higher pressures. It is 0 at -62° and zero pressure. At higher temperature it is negative at zero pressure and decreases still further with increase in pressure. $\mu$ vs. $t$ isobars and $p$ vs. $t$ $\mu =\mathrm{constant}$ curves exhibit the calculated values of the Joule-Thomson coefficient. The compressibility data from which these calculations are made are probably for a 1:3 para ortho mixture, though there may be some question about this, particularly at extremely low temperatures. Values for the second virial coefficient are given. They follow the equation $B=17.42+314.7\mathrm{} T^{-1\mathrm{}} -2111\mathrm{}\times {10}^2{T}^{-2\mathrm{}}$ cc/mole from -75° to 500°C within 0.05 cc/mole.