Chloral hydrate CCI3CII (OH) 2is peculiar in its molecular structure having two hydroxyl groups attached to a single carbon atom. This substance can easily be obtained as colorless crystals by mixing equivalent amounts of choral and water. From oscillation photographs taken with Cu-Karadiation about each of the crystallographic axes and the absence of the piezoelectricity, the dimensions of the unit cell and the space group were determined as follows: a=11.57±Q.02kX, b=6.04±0.02 kX, c=9.60±0.02 kX, z=4 and C2h1P2/c. Making use of the Patterson and Marker diagrams obtained from the intensity data of about 400 reflections, a set: of atomic parameter values which account satisfactorily for the observed intensities were obtained (See table I and II) . The molecular structure is found to be of thetransform with respect to the H and C1 atoms. The intra- and intermolecular atomic distances are listed in Table III. The observed bond lengths C—O 1.47—1, 48 kX are somewhat greater than the single covalent radii sum 1.42 kX, given by Pauling. From the intermolecular atomic distances, it is suggested that the cohesive force existing between molecules in the [100] direction may be of the van der Waats' type, while the hydrogen bonds may chiefly he responsible for linking molecules within the (100) plane.
