436 
direction of the side of the cube is at most 0,4 times the radius of 
the molecule. 
From J. D. van per Waats Sr.’s new considerations published in 
this number of the Proceedings, follows quite in accordance with : 
our calculations that the distance between the molecules of a liquid 
as ether will be smaller at O° than 0,4 of the radius of the 
molecule. 
It follows, therefore, from this that in a liquid phase there exists 
only a small difference between the distance of the centres of gravity 
of the molecule and the diameter of the molecule. 
If we now consider that as a rule the solid phase possesses a 
greater density than the liquid phase, it follows immediately from 
the above calculation that the said difference will be still somewhat 
smaller for the solid phase. 
Accordingly the distance between the molecules in the solid phase 
is small. 
An important conclusion may be drawn from. this for the solid 
substance, which runs: the distance between the atoms which belong 
to different molecules, will depart very little from the distance between 
the atoms in the same molecule, which engenders the possibility that 
these small differences do not find expression in the Röntgenogram. 
The objections advanced here can be entirely obviated by assuming 
that there exist molecules also in the solid phase, and that the distance 
between the atoms in the molecule is of the same value as the 
distance between the atoms of different molecules. 
Considered in this light there is no reason to be astonished that 
the Röntgenogram does not teach us anything about the existence 
of molecules in the solid phase. 
Still it is possible that on refinement of the method of research 
or on enlargement of the Röntgen image the spots betray a composite 
character, and in this case the difference between chemical and 
physical binding might still find expression. Besides the size of the 
spots is often not negiglible with respect to the distances between 
the spots, so that variations are certainly possible in the distances. 
4. It is clear that when special forces make their appearance, 
always between one Na and one Cl atom the symmetry of the 
common salt crystal can change. Now as Brace himself observed *), 
the model NaCl given by him is not in harmony with the sym- 
metry. It does not seem improbable to us that the occurrence of the 
special chemical bindings is just in connection with this lower sym- 
I Proc. Roy. Soc. A 89, 468 (1913); Zeitschr. f. anorg. Chem. 90, 216, 1914. 
