Some Physical Properties of Compressed Gases. II, Carbon Monoxide

The writers have adjusted and extrapolated the compressibility data obtained by Bartlett and his collaborators on carbon monoxide, so that accurate $p-v-T$ relations from -70° to 400° and up to 1200 atm. are available. The relatively low pressure isotherms of Scott at 25° and of Goig-Botella at 0°, 12.44°, and 20.22° are included. Derivatives are obtained by the graphical scheme used for similar calculations on nitrogen. The specific volume, density, expansion coefficients — $\left(\frac{p}{v}\right){\left(\frac{\mathrm{dv}}{\mathrm{dp}}\right)}_T$ and $\left(\frac{T}{v}\right){\left(\frac{\mathrm{dv}}{\mathrm{dT}}\right)}_p$ fugacity, $C_p$, $C_p-C_v$, $C_v$, Joule-Thomson coefficient $\mu$ are calculated and shown in curves and a table for 14 pressures and 11 temperatures in the range -70° to 400° and 25 to 1200 atm. In particular, $C_p$ vs. $p$ isotherms, $C_v$ vs. $t$ isobars, $t$ vs. $p\mu =\mathrm{const}$. graphs are shown; among the last, the $\mu =0\mathrm{}$ curve is the inversion curve. There are no direct experimental data for comparison. On account of similarity in the molecular structure and the spectra of the molecules CO and ${\mathrm{N}}_2$, one might look for some correspondence in the physical properties of the two gases. In general, the trends of the two are qualitatively similar. The $C_p-C_v$ vs. $p$ isotherms all show a maximum. This maximum is very flat at the highest temperatures and comes at about 700 atm. As the temperature decreases, the maximum becomes pronounced and moves to lower pressures; it comes at about 200 atm. along the -50° and -70° curves. Along the -70° isotherm a second maximum appears at about 550 atm., but it is not evident at higher temperatures. ${\mathrm{C}}_p-C_v$ approaches $R$, of course, along all isotherms as the pressure is decreased to zero. $C_p$ is obtained by adding $\Delta C_p$ to ${C_p}^{*}.{C_p}^{*}$ denotes the heat capacity for a given temperature at zero pressure; $\Delta C_p$ is the change in $C_p$ with pressure along a given isotherm. It is evaluated thru $\int 0^{p}T{\left(\frac{d^{2}v}{d{T}^2}\right)}_p\mathrm{dp}$. The derivative occurring under the integral sign is obtained by the authors' graphical scheme at a sufficient number of points for mechanical integration under the isotherm. Along isotherms at 50° and lower, $C_p$ increases rapidly with pressure and reaches a maximum at about 300 atm. Changes in pressure above 500 atm. cause only relatively small changes in $C_p$ at any temperature. Above 200 atm. and below 0°, $C_p$ increases rapidly as the temperature is lowered. The $C_v$ vs. $t$ isobars show that from 300 to 1200 atm. $C_v$ has a minimum at about 100°. On the low temperature side of this minimum the curves are very steep; along the 1200 atm. isobar $C_v$ drops from 4.4 $R$ at -70° to 2.57 $R$ at 100°. Above 100°, $C_v$ is only a few hundredths cal./mole deg. higher than ${C_v}^{*}$ for pressures up to 400 atm; further increase in pressure to 1200 atm. raises $C_v$ only a few tenths. Below 25°, $C_v$ for $p=25\mathrm{}$ is slightly less than ${C_v}^{*}$. Below 0°, $C_v$ at 100, 150, and 200 atm. drops far below ${C_v}^{*}$ as the temperature is lowered. A graph showing $\Delta \equiv v\left(\frac{\mathrm{pv}}{RT-1\mathrm{}}\right)$ vs. $\rho$ isotherms and isobars is shown, the data for which are listed in the table. This graph is very convenient for interpolating $p-v-T$ data. Having given two of the three $p-v-T$ coordinates, the third is quickly estimated from the graph, or is readily computed more exactly by reading the ordinate $\Delta$ and solving $\Delta =v\left(\frac{\mathrm{pv}}{RT-1\mathrm{}}\right)$ for the unknown desired. Values for the second virial coefficient are found. They are expressible by $B=58.03-19.84\mathrm{} T^{-1\mathrm{}}$ cc/mole between -70° and 400°.