It is found, using Bridgman's data for H2O, N2, and Ar, that theVhyphen;Tisobars, though curved at medium pressures, become good straight lines at the same higher pressures for which the isothermal relationp= CeB/Vbegins to hold (above 1000 kg/cm2for gases, and above 4000 for liquids). Aside from the surprising linear variation ofVwithTunder these extreme conditions, the most remarkable feature of theVhyphen;Tplots is the apparent convergence of all the isobars (for a given gas) to a common intercept on theVcoordinate (at 0deg;K). The isobars for gases therefore can be represented by the equation,V=V0+apT,whereV0is the incompressible molar volume of the substance at 0deg;K. Eliminatingapfor two different temperatures at constant pressure gives an exactVhyphen;Trelation for high pressures comparable to Charles' law,V2equals;V1lpar;T2sol;T1rpar;plus;V0lpar;1minus;T2sol;T1rpar;.The slopeapof the isobars decreases with increasing pressure, and it is found thatapsime;Rprime;/p,whereRprime; is a new gas constant for high pressures, which at first increases somewhat with pressure, and reaches the samelimitingvalue of32Rat 6000 atm for both N2and Ar.
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