645 
roomtemperature cubic tetartohedral forms. Both of the chlorate and 
of the bromate two enantiomorphous forms occur. In connexion 
with this phenomenon the crystals themselves show rotation of the 
plane of polarisation for every direction of the rays, while the 
solutions are non-active. The polar ternary axes are electric axes. 
With regard to these properties we thought it desirable to determine 
the structure of these crystals. 
BECKENKAMP *) investigated already this structure theoretically ; his 
conclusions were however not confirmed by our investigations. 
W. H. and W. L. Brace’) simply mention, that in the crystals 
of sodium-chlorate the places of the sodium- and Cl-atoms differ 
very little from those in sodium-chloride. From the following it will 
be evident that on the whole we agree with this opinion. 
JararrR and Haca ®) took Lauxz-photograms of NaClO,; they did not 
derive details on the structure from them. 
§ 3. The apparatus used. This was equal to that, described 
in a preceding communication *). This time the finely powdered 
substance was divided as equally as possible by means of a little 
collodion on a glass rod (diameter + 0,1 mm.) in a layer less than 
0,5 mm. The rod was fixed to the lid of the camera; by means 
of this lid it could be turned about its length axis during the expo- 
sure in order to avoid the seratches on the interference fringes 
caused by greater crystal-particles, which hinders the determination 
of the intensities °). Because of the small depth of the layer the 
correction for the thickness of the rod, given in Communication 
N°. 2°), was now much smaller than it was then. The glass core 
of the rod gave no difficulties. 
§ 4. Calculation of the crystal-structure. In the tables I and II 
are to be found for the chlorate resp. the bromate in the columns 
1) Comp. J. BECKENKAMP, Z. f. anorg. u. allg. Chemie, 110, (1920) p. 290. 
*) W. H. and W. L. Brace, X-Rays and Crystal-Structure, London 1918. p. 178. 
5) F. M. JazGer. These Proceedings Vol. 17 (1915) p 1204. 
4) A. J. Bij and N. H. KorkMeijer, These Proceedings 21 (1918) p. 408. 
Communication NO, 1. 
5) That these scratches touch the interference fringes has been explained l.c. 
p. 407. This time some films taken without turning of the rod showed also inter- 
secting scratches; this intersecting can be explained in the indicated way when 
the height of the exposed part of the substance is taken into consideration. By 
decrease of this height the intersections vanished. 
6) A. J. Bir and N. H. Korkuemwer, These Proceedings, 21 (1918) p. 496, 
Comm. NO. 1. 
