503 



latioii pointed to about eight atoms per cube, wliicli suggests the 

 structure of diamond. So we tried to get agreement of our interference- 

 lines with the stiucture of diamond. 



Using the atomic-weight (119,0) and ihe specitic weigiit of grey 

 till at 18° C. (5,751j, Avogadko's number (6,06.10") and the wave- 

 length of the /v-series of copper-radialion (r; 1,541.10 ^, ,-? 1,385. JO ~'^) 

 Jj,^ 0,0141 and .4,3 = 0,0114 are found. Nearlj' in agreement with 

 this we tind as a mean from the observed lines ^j: = 0,01422 

 and .4^ = 0,01149. The third column gives the values of sm*^//J, 

 computed with the last-mentioned values of Ay, so far as I hey give 

 occasion to interference-lines. 



From Drbue's structure-factor it can be deduced namely, that 

 for the structure of diamond interference-lines can only be got, 

 when /<,, A, and A, are all even or all odd, and when in case they 

 are even, their sum can be divided by 4. The expression Aj' -f- /<,' -|- //«* 

 then becomes 3, 8, 11 and so on, see the sixth column; in the tifth 

 column the corresponding values of h^, h, and Ii^ are given. 



The intensity, given in the fourth column is found by dividing 

 64 (A/ -|- Aj^ -|- /<3*) in the product of the number of planes and 

 the square of the absolute value of the structure-factor. To this 

 intensity only so much value must be attached that only the inten- 

 sities of three successive lines must be compared. 



The seventh, eighth, and ninth columns relate to ^i-lines. 



On comparing the observed and computed values of si?i* ^/,0 a 

 satisfactory agreement appears to exist, also in coimection with the 

 intensity. 



The two smallest squares of sines are not satisfactory ^). About this 

 Comm. N°. 2a p. 498 gives information. 



When it is examined whether all lines, nhich must be expected 

 on the ground of the structure mentioned, are present, it appears, 

 that of the expected «-lines not a single is lacking; some of the 

 jMines however appearingly have too small an intensity, and so are not 

 observed on the Röntgenogram. 



From the values of A^ and A^, deduced from the observations, 

 we found for a, the edge of the elementary cube 6,46. 10"*^ cm. 

 at 18° C. For the distance of two nearest atoms 2,80.10"^ cm. is 

 thus deduced. 



In the grey tin with its diamond-structure, which silicium pos- 

 sesses too, the tetravalency clearly makes its appearance, whilst in 

 the tetragonal modification, in which each atom is surrounded by 



1) Comp. P. Debije, Physik. ZS. 18 (1917), p. 488. Note. 



