Measurements of the osmotic pressure in liquid mixtures of He-3 and He-4 near the lambda line and tricritical point

Values of the concentration susceptibility near the lambda line and tricritical point in liquid mixtures of He-3 and He-4 were calculated from measurements of osmotic pressure differences. Measurements were made by inducing a small He-3 mole fraction difference between two chambers separated by a pressure transducer, and measuring the resulting osmotic pressure difference as a function of temperature. Osmotic equilibrium was established through a Vycor glass superleak, which for He mole fraction x 0.55 functions not only in the super-fluid phase but in portions of the normal fluid region of the phase diagram as well. Measurements were made at four He mole fractions, x = 0.59, x = 0.64, x = 0.68, and x = 0.70.