Properties of Steam and Ammonia

Abstract

THESE tables are a great improvement on previous American work in the matter of thermodynamic method and consistency, but the expressions employed for calculating the tables are too complicated to be of practical use for other purposes, though comparing favourably with many empirical formulæ. The author assumes a characteristic equation of the type, V − b = RT/p− (i Σ 3ap½ m/Tⁿ, and deduces consistent expressions for the total heat and the entropy, according to Callendar's method, by the aid of a formula for the specific heat at zero pressure. He objects to Callendar's equation on the ground that it makes the isothermals straight lines on the pv, p diagram, which is well known to be a good approximation at moderate pressures over the experimental range from o° to 200° C., but begins to fail at higher pressures. Linde introduced the factor (i + ap) in the last term to give the desired curvature to the isothermals at high pressures. His equation has been widely adopted in America, but is most unsatisfactory, because it would make steam become a “pluperfect” gas (pv increasing with p at constant t) at a temperature of 400° C., a few degrees above the critical point, which is impossible. The form assumed by Prof. Goodenough escapes this objection, and gives “reasonably good agreement” with throttling experiments, but appears to lead to excessive curvature of the isothermals at low pressures, where they should be very nearly straight, and also gives deficient curvature at high pressures near the critical point, besides making no allowance for the well-known fact that the curvature must change sign at a temperature not far above the critical.

Properties of Steam and Ammonia.

By Prof. G. A. Goodenough. Pp. vii + 108. (New York: J. Wiley and Sons, Inc.; London: Chapman and Hall, Ltd., 1915.) Price 5s. 6d. net.