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A single-crystal neutron diffraction refinement of the structure of L-asparagine monohydrate, NH2CO(CH2)CHNH2COOH.H20 [space group P2t212t, Z=4, a=5.593(5), b=9.827(10), c= 11.808 (11) A,] has been carried out. Neutron intensities of 890 reflexions (749 non-zero) were measured at a wavelength of 1.041 A, up to sin 0/2= 0.65 A-1. The ten hydrogen atoms in the asymmetric unit were located from a neutron scattering density Fourier map, computed with observed Fo'S as amplitudes and phases derived from the known X-ray positions of the non-hydrogen atoms. The structural parameters were refined by the full-matrix anisotropic least-squares method. Extinction corrections to the observed data were applied by a method due to Zachariasen (Acta Cryst. (1967). 23, 558). The final R value is 0.096. The hydrogen bonding scheme and the conformation of the molecule are discussed.

Berman density balance, using bromoform, as 4.60 + 0.01 g.cm -3. With the above values of axial lengths and the angle fl (V=1871 A3), the molecular weight (M= 648 for Fe7Ss) and the observeddensity, the number of formula units per unit cell is calculated to be 8 (Z = 7.998), and the calculated density is 4.602 g.cm-L The rotation and Weissenberg photographs and the 15 ° oscillation photographs about [010] and [001] of a crystal fragment, detached from hexagonal platelets (off an ore sample from level-16), showed superstructure characteristics having a hexagonal supercell a=6.88, c=22.90__+0.02 A; the high angle reflexions did not show any separation characteristic of the monoclinic system. The conditions limiting possible reflexions are: hh2hl only with l = 2n; hhOl only with l = 2n; and hkil with no conditions except l=2n; indicating the space group as one of P6/mcc (1)~6n), P6cc (C~v). The presence of a number of weak reflexions in the patterns could be explained as being due to the monoclinic phase (see above) which was a minor intergrowth with the hexagonal phase in the crystal fragment. The density for the same crystals was determined as 4.58 + 0.01 g.cm -3 and the number of formula units per unit cell was calculated to be 4 (Z=3.998) from the above values of axial lengths (V= 939 A3), the observed density and the molecular weight [M= 648 for Fe7S8 although the composition might have a slight excess of iron (Desborough & Carpenter, 1965)]; the calculated density is 4.582 g.cm -3.The monoclinic and hexagonal pyrrhotites (superstructure types)were found to be associated mainly with chalcopyrite and pyrite in the ores of different levels (Mukherjee, 1968); the monoclinic phase was predominant in the pyrrhotite-rich ores containing pyrite as a minor constituent, and the hexagonal phase was predominant in the pyrrhotite-poor ores containing chalcopyrite and pyrite as major constituents.The author sincerely thanks Mr G.C. Chaterji, Director General of the Geological Survey of India for his keen interest in the work, and Professor B.S.Basak of the Presidency College, Calcutta, for valuable discussions. The structure parameters of the Tutton salt Cu0NIH4)2(SO4)2.6H20 have been refined by the method of least squares from three-dimensional neutron-diffraction data. The e.s.d.'s of the atomic coordinates are from 0.0010 to 0-0023 ./k for the N, S, O atoms and 0.0025 to 0.0053 A for the H atoms. The value derived for fs, the coherent scattering amplitude of sulfur, is 0.283(4), significantly different from the value 0"31 in Bacon's table; values derived for fo and f~ are also slightly different from the tabulated values. Although the heavy-atom coordinates differ significantly in a purely statistical sense from those of the three-dimensional X-ray analysis of Montgomery & Lingafelter, the two descriptions of the heavy-atom structure agree quite well from the point of view of molecular geometry. The hydrogenbonding pattern from the X-ray study is confirmed. References BERTAUT, E. F. (1953