Physics. — "Investigation hy means of X-rays of the cry stal - 

 structure of white anil grey tin. 111. The structure of grey tin" . 

 Communication N°. 2h from the Laboratory of Physios and 

 Physical Chemistry of the Veterinary College at Utrecht, by 

 A. J. Biji, and N. H. Kolkmeuer. (Communicated on behalf 

 of Prof. W. H. Keesom, Directoi- of the Laboratory, by Prof. 

 H. Kamkrlingh Onnks). 



(Communicated in the meeting of September 28, 1918). 



In this communication we shall dednce the crystal-structure of 

 grey tin from the Röntgenogram, taken by us and represented l)y 

 a drawing in Communication N". J (June 1918 p. 408) at the same 

 time as that of white tin. With this aim in the (irst column of 

 table 1 are given the distances of the intersections of the interference- 

 lines with a plane, through the axis of the incident beam ot 

 X-rays and perpendicular to the lengthdirection of the preparation, 

 to the point where this axis, prolonged, would meet the . film, 

 measured on the tilni when developed on a plane and corrected for 

 thickness of preparation (Comp. Comm. N'. %i, p. 496). The inten- 

 sities are denoted by vf \ ery feeble, f feeble, m modei-ate, s strong, 

 and vs very strong. The second column contains the values of 

 sin*\^ deduced therefrom, (radius of camera 27,3 m.m., to be 

 diminished by half the thickness of the film, that is by 0,1 m.m.). 



By multiplying these values by 0,808, the square of the 

 proportion of the wave-lengths oi Cuk^^ and C'^a^, the values which 

 might originate from /^-radiation, can be separated, and so a list can 

 be composed which contains ^f-values exclusively. By using a general 

 method of computation, in which we proceeded from an arbitrary 

 system of axes and on which we shall perhaps publish another paper 

 the gi-ey tin appeared to be regular with great probability. In that 

 case our \alues must fidtill the equation : 



sin^ '^ = .4(7/,,» r /','4 /'/)= ^, (/'.N /',' I /'.'), 

 2 4a 



in which ^ is a constant, h^Ji^, and A, indices of Millkh, A wave- 

 length of the Röntgen-radiation, a edge of elementary cube. 



So we have only to deduce the constant A and from that the 

 number of atoms in the elementary cube a\ A provisional calcu- 



33* 



