The Temperature Coefficient of the Photochemical Formation of Hydrogen Chloride.

spacing 23.62; those at 1 and 2, and at 3 and 4 have dyad screw axes parallel to the edge with spacing 6.50. Diphenic Acid.-The analysis of this compound is not complete. The results obtained show that the crystal is orthorhombic with the dimensions a = 14.12, b = 11.90, c = 13.75, and that there are eight molecules in the unit cell. This indicates an arrangement quite different from the other compounds studied as the unit cell is approximately half as long in one dimension and twice as wide in the other two. It is possible that this is caused by the attraction and consequent doubling of COOH groups such as is found in the case of aliphatic compounds. Other compounds now being investigated are: difluoro-diphenic acid, hexachloro-diphenyl, octamethyl diphenyl, diphenyl benzene. Thanks are due Professor Roger Adams for suggesting this research and for providing the necessary materials. 1 J. Am. Chem. Soc., 51, 2796 (1929). 2 Zeit. Krist., 70, 285 (1929). 3 Astbury and Yardley, Phil. Trans. Roy. Soc. London, 224A, 221 (1924). 4Wyckoff, Analytical Expression of the Results of the Theory of Space Group, Carnegie Institute, Washington, p. 51. 6 See papers by Roger Adams and associates on diphenyl derivatives in J. Am. Chem. Soc.