Zishment, Netherlund). The lattice thermal expansion perpendicular and parallel to the basal planes of different pyrocarbon structures formed in a ff uidized bed has been measured by X-ray diffraction over the temperature range ZOO-1200ยฐC. The results are correlated to the structuraf parameters characterizing the deposits. 148. Specific heat of soft carbons at low temperatures (0.5*-4~2ยฐK) Part I P. Delhaes* and Y. Hishiyamat (Carbon Research Laboratory, State University of New York at Buffalo, Bu$alo, New York). The specific heat of a soft carbon heat treated in the range 1600"-3100ยฐC was measured using an apparatus built into an He, cryostat. It is found that both the part Iinear with temperature as well as the square and cubic parts increase about in the same proportion with increasing disorder of the lattice. Exact extrapolation to T 9 0 is made difficult by presence of a strong peak at 0.6"K of unknown origin. *State of New York Postdoctoral Fellow. Now back at University of Bordeaux. tCabot Postdoctoral Fellow. *Research sponsored by U.S. Atomic Energy Commission under contract with the Union Carbide Corporation. 153. X-ray measurements of thermal motion in highly oriented pyrolytic graphite J. C. Sparks, Jr. and J. E. Epperson (Metak; and Ceramics Division, ORNL, Oak Ridge, Tennessee). X-ray