Measurements on the velocity of sound as a function of pressure in oxygen gas at liquid oxygen temperatures. Calculation of the second virial coefficient and the specific heats

In continuation of previous investigations made by one of us together with Prof. Keesom on the velocity of sound in gases at low temperatures we have studied oxygen gas at liquid oxygen temperatures by using ultrasonics. The apparatus used is described. We determined the velocity of sound as a function of pressure at seven temperatures obtained with liquid oxygen. The velocity of sound as a function of pressure can be represented by means of a formula of the following form: W=W(1+sp) Where W₀ = ( c _p/c _v) _{p = 0} ( RT/M), ( c _p/c _v) _{p = 0} being the ratio of the specific heats for an ideal gas; R the gas constant, T the absolute temperature, and M the molecular mass. Further s=S/RT,with S2=B+T/λ {dB}/{dT}+{T}/{2λ(λ+1)}{dB}/{dT} in which B represents the second virial coefficient, λ = c _v/R . From these measurements we established a formula for B as a function of T and which is valid between 200°K. and 75°K. We computed also c _p/c _v, c _v and c _p as a function of pressure at five temperatures within the liquid oxygen temperature region.