406 



and succeeded in determining the strnctnre of these modifications 

 of carbon. 



In connection witli tlie investigations, wliicli have alreadj- been 

 made of silicium, lead, and the modifications of carbon, we have 

 iti this investigation set ourselves the task, to determine the structure 

 of still another element of this group of the periodical system, the 

 tin namely in two of its modifications, the grey and the white ones. 



The X-rays were for the greater part of our photos fnrnished by 

 a Röntgen-tube, constucted after a drawing, which Prof. Dkbuk and 

 Dr. ScHERRER kindly procured us, and which must be considered 

 as a modification of the tube, constructed by Rausch von Traubenberg ^). 

 The aniicathode was a copper one, the |)arallel-spark-length (point- 

 disc) measuied 6 cm. The X-rays left the lid)e by an aluminium 

 window of 0,02 mm. thickness, afterwards passed a lead .screen, 

 thickness 34 mm. with an opening of 2 mm. diameter and entered 

 then a cylindrical camera of 27,3 mm. radius. In the axis of the 

 camera the material, to be investigated, was placed in the form of 

 a bar of 2 mm. diameter. The white tin bar was filed from a 

 thicker bar, which for the diminution of the crystals and in order to 

 obtain irregulai- orientation of these, was beaten for some time 

 with the hamniei'. The grey tin was pressed into a small bar. 

 We obtained this material through the kindness of Prof. Cohen, 

 to whom we therefore render our thatdcs- A photographical film 

 (thickness 0,2 mm.) was stretched along the wall of the camera 

 and pressed against it by springs. The exposition-time was 4 hours. 



During the preparative experiments we observed that in excess 

 of the interference-lines of the tin, still others were obtained, of two 

 different kinds. The first resembled hyperbolas, the centre of 

 which was in the point, where the beam of characteristic rays, 

 after having passed the investigated preparation on both sides, fell 

 on the film. They must be ascribed to the interference of rays, 

 which are diffracted by the silver-bromide of the film. The second 

 kind had the same direction of curvature as the lines, which originated 

 from the prepaiation in the axis of the camera, they intersected 

 these lastmentioned however at some points, which indicated, that 

 here too the origin was not to be sought for in the preparation. 

 We got the evidence, that the origin of them was to be found in 

 the back-opening of the lead screen, which opening was in the wall 

 of the camera. We got rid of the first kind of undesired lines by 

 making a circular hole in the film, at the place, where the beam 



1) H. Rausch von Teaubenberg, Physik. ZS. 18 (1917), p. 241. 



