Crystalline Structure of Antimony. 239 



the corresponding calculated intensities are 



8 = 135° 116 : 100: 76 : : 27 



8 = 140° 79 :100 : 56 : 1'3 : 26 



8 = 145° ■ 54:100:42:4-2:24. 



The most likely value of 8 is now 143°, but the general 

 " fit " is not so good. Making this large alteration in the 

 assumed normal intensity series only makes 3° difference in 

 the probable value of 8. But it is practically certain that 

 the true normal intensity series is much more nearly the 

 first series than the second, and we can take as the probable 

 value of 8 



8 = 140° ±2° 



which gives a range of only 0*062 A, within which the Anti- 

 mony atoms of the second lattice may be displaced along the 

 diagonals of the first lattice. 



Distances betioeen the Atoms. 



Any particular atom lies in one of the (111) planes, and is 

 equidistant from three atoms in each of the (111) planes on 

 either side of it. The three atoms in one plane are, however, 

 nearer the given atom than those in the other plane. The 

 distance between the centres of two atoms, such as A and B 

 in fig. 2, in the close pair of planes, which is the closest 

 distance of approach of two o antimony atoms, is 2*87 A with a 

 probable error of +001 A., assuming the limits of error 

 for 8 staled above; and this can, perhaps, be considered as 

 the " atomic diameter" of antimony. For the wider pairs of 

 planes the closest distance of approach of two atomic centres, 

 such as B and E, is 3*37 A. 



The planes thus occur in pairs in which the atoms 

 approach one another closely, the pairs being separated by 

 a wider spacing. It should be noted that the very good 

 cleavage of antimony is parallel to these pairs of planes. 



In conclusion, we wish to express our thanks to Prof. C. A 

 Edwards, of Manchester University, who kindly supplied us 

 with some excellent specimens of crystalline antimony, and 

 to Prof. W. L. Bragg, who suggested the work, and to 

 whom we are indebted for much helpful advice during its 

 progress. 



