A New Method of Measuring the Variation of the Specific Heats (cp) of Gases with Pressure

A method is described whereby the ratio of c_p at a high pressure to c_p for the same gas at a pressure of one atmosphere taken as a standard is determined. The continuous flow principle is used in such a way that the necessity for measuring gas flow and heat input is avoided. A stream of gas at high pressure is brought to a temperature t₁ and passed through a heat interchanger acquiring there a temperature t₂ after which it is throttled to atmospheric pressure, brought to a temperature t₃ and returned to the heat interchanger, where its temperature again becomes t₂. The ratio of c_p at a high pressure to that at atmospheric pressure is equal then to (t₃-t₂)(t₂-t₁) plus certain small corrections. Measurements on commerical oxygen taken at a mean temperature of 26° C and pressures ranging from 15 to 100 atmospheres indicate a pressure coefficient of this ratio of 0.00165+/-0.00005 per atmosphere.