1. E. C. Lathrop, Rice J. Ann. (1952) 13.
2. T. F. Clark, Mod. Plastics 28 (1949) 164.
3. R. V. Williamson, T. F. Clark and T. R. Naffziger, ibid. 23 (1946) 177.
4. Mc. R. Daniel, Rice J. 49 (1946) 14.
5. R. V. Williamson and E. C. Lathrop, Mod. Plastics 28 (1951) 126.