1. J. B. Romero, D. W. Smith, and R. E. Dod, in: Advances in Cryogenic Engineering, Vol. 11, Plenum Press, New York (1966), p. 231.
2. J. B. Romero and D. W. Smith, Personal communication (Sept. 20, 1965).
3. M. Adelberg, in: Applied Cryogenic Engineering, J. Wiley & Sons, New York (1962), Chap. 13.