1. P. L. Barrick, D. H. Weitzel and T. W. Connolly, Proceedings of the 1954 Cryogenic Engineering Conference, p. 210, Boulder, Colorado, September 1954.
2. D. H. Weitzel and L. E. White, Rev. Sci. Instr., 26, 290 (1955).
3. D. H. Weitzel and O. E. Park, Rev. Sci. Instr. 27, 57 (1956).
4. V. J. Johnson, Proceedings of the 1956 Cryogenic Engineering Conference, p. 19, Boulder, Colorado, September 1956.
5. H. B. Weiser, Colloid Chemistry, John Wiley and Sons, Inc., New York (1949).