The osmotic pressure of 3He-4He mixtures was measured along the phase separation curve at temperatures up to 500 mK by balancing it with the fountain pressure of pure 4He. The usefullness of the secondary osmotic pressure thermometer was reinvestigated.
van de Klundert, L. J. M., Bos, M. R. E., van der Meij, J. A. M., & Steffens, H. A. (1977). The osmotic pressure of 3He-4He mixtures along the phase separation curve. Physics letters A, 62(7), 487-489. https://doi.org/10.1016/0375-9601(77)90076-7