Reduction to the ideal gaseous state

Reduction to the Ideal Gaseous State.—In order to avoid complications, which, though appearing in the liquid state, are much more important with gases, we must reduce the specific heat of gases, whether measured at constant pressure or at constant volume, to the ideal gaseous state. This can be done by means of the two equations, derived from the Second Law — 

It is most simple to use the excellent equation of state due to Daniel Berthelot. For ideal gases, for which 

We shall not go into details in this connection, and I shall only emphasize that, for exact theoretical investigations, reduction to the ideal gaseous state is always necessary and can, moreover, always be done quite safely. Molecular heats at constant volume and constant pressure may be calculated, by means of Berthelot s equation, for any density which is not too great, from the critical pressure and the critical temperature if there is a reliable measurement available at a particular pressure for the required temperature. 

All subsequent considerations of specific heat in this book concern the values calculated to the state of ideal gas for rarefied gases this recalculation is superfluous. 

In the table on next page are given some results of our measurements of molecular heat at constant volume, using, of course, also the results of the older researches of Regnault, E. Wiedemann, Strecker, Holborn, and Henning, etc. 

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