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XXVI. The Crystalline Structure of Antimony. By P. W. 

 James, M. A., B.Sc, and Norman Tunstall, B.Sc, Lec- 

 turers in Physics in the University of Manchester*. 



ANTIMONY crystallises in the dihexagonal-alternating 

 class of the hexagonal system. As in the case of 

 calcite, the crystalline symmetry is that of a rhombohedron, 

 the three edges of the rhombohedron which meet in the 

 trigonal axis being taken as the axes of the crystal. The 

 angle between any two of these edges is 86° 58', and the 

 angle between the rhombohedral faces 100 : 010 is 92° 53', 

 so that the antimony rhomb is a slightly distorted cube. 

 The crystals have a very perfect cleavage at right angles to 

 the trigonal axis and parallel to the (111) planes, and a 

 somewhat less perfect one parallel to {110}. 



From some observations made in 1914, Sir W. H. Bragg 

 and Prof. W. L. Braggf concluded that the arrangement of 

 the atoms in Antimony was similar to that in diamond, except 

 that the whole structure was distorted along the trigonal 

 axis. As the observations on which this conclusion was based 

 were incomplete, it was suggested by Prof. W. L. Bragg 

 that it would be worth while to repeat them more carefully. 

 This has now been done, and it has been found that a struc- 

 ture similar to that of diamond will not explain the spectra 

 observed from the various faces. 



The observations were made with the X-ray spectrometer, 

 a bulb with a palladium anticathode being used, and five 

 faces in all were examined. The (111) and (110) faces 

 were obtained by cleavage from a large mass of crystals, and 

 surfaces parallel to the (100), (110), and (111) planes were 

 ground on slices of the crystal, the angles which they made 

 with the cleavage planes having been calculated. Antimony 

 is very brittle, and no distorted surface layer appears to be 

 formed by grinding, for the ground faces were found to 

 reflect X-rays nearly as well as the natural ones. 



The positions and relative intensities of the spectra 

 observed from the various faces are shown diagrammatically 

 in fig. 1. The glancing angles for the first-order spectra 

 were as follows : — 



(100) (110) (110) (111) (111) 

 5° 27' 7° 24' 7° 50' 4° 26' 19° 14'. 



The sines of these angles are in the ratio 



1 : P36: 1-44: 0-815: 1-760. 



* Communicated by Prof. W. L. Bragg. 

 f 'X-rays and Crystal Structure/ p. 227. 

 Phil. Mag. S. 6. Vol. 40. No. 236. Aug. 1920. R 



