Using the principles of the law corresponding states, adapted to the quantum theory in previous papers 1), a number of properties of He3 can be predicted as to their order of magnitude, which may be of interest for further attempts to separate He3 from the natural isotopic mixture. The critical temperature and pressure are roughly 3.2 to 3.5°K and 0.9 to 1.2 atm respectively. The density at 0°K is about 65% and the internal energy about 35% of the value of He4. The vapour pressure formula should be 10log Pcm = — 1.12/T + 52log T + 1.01 giving at 0.3°K still a vapour pressure of 10-3 mm Hg. Finally the concentration ratios of a dilute mixture of He3 in He4 of vapour and liquid have been calculated and are compared with the experiments of Fairbank, Lane, Aldrich and Nier 5).