648 
1 the distance from the central part of the image on the film to 
the interference fringes, expressed in 0,1 mm. and the estimated 
= é ee 
intensities. In the columns 2 are given the values of 10° sin? — 
calculated from these data. In the ordinary way the numbers, refer- 
ring to B-lines, have been separated. In accordance with the cubic 
erystal-form of both substances it was then found that the values 
of 10°. sin? 9 of the a-lines possess a common factor viz. for the 
chlorate A, — 13,79 and for the bromate A, = 13,16. The columns 
3, 5, 6, and 8 contain derived from these the indices triplets (resp. 
the sums of their squares) of the lines; the columns 4 and 7 the 
values of 10° sin’ > calculated with the mentioned values of A. 
From the obtained values of A, we find, in connexion with the 
molecular weights, the densities (resp. 2,496 and 3,254), the number 
of Avocapro 6,062.107*) and the wave-length of the Cu, -radiation 
ey 
(1,537.10—8 ecm) for the number of molecules per elementary cell 
resp. 3,98 and 3,93. This number is therefore for both 4°). 
This gives for the edge of the elementary-cell 6,55.10-S and 
6,74.10 8 for chlorate and bromate resp. 
Then we investigated which grouping of these 4 Na-, 4 Ct resp. 
Br- and 12 O-particles in the cell fulfils the symmetry demands 
that can be derived from the erystal-forms (viz. three binary axes, 
four polar ternary axes, rotation of the plane of polarisation). The 
model obtained in the following way fulfils these demands (see fig. 1). 
Divide the cell into 8 cubes, draw in four of them that have 
only edges in common a cross-diagonal so that they do not 
intersect. Place on one of the diagonals arbitrarily a sodium- and a 
halogen-particle. The places of the other sodium- and halogen-par- 
ticles are then found directly by means of the ternary axes. 
Place one oxygen-particle arbitrarily, the places of the other ones 
follow then again. 
The described model cannot cover its mirror-image (see fig. 2) 
which is in agreement with the optical activity. 
For the calculation of the places of the atoms we chose as para- 
meters, one of the three equal rectangular coordinates of one of 
the sodium particles a (expressed in the side of the cell as unit), 
one of the three equal coordinates of one of the halogen particles 
1) The essential difference with the model given by BECKENKAMP (l.c. p. 300) 
is that there this number is 10 (or 2 in a cube with an edge of half the value), 
which is in contradiction with our film. 
