THE STRUCTURE OF MOLECULES. 471 
ment of positive and negative ions, there being no grouping of the atoms into 
molecules. ‘The valency of the K atom cannot be represented by a single bond, 
but must be uniformly distributed around the atom among six neighbouring 
chlorine atoms. In many compounds a complex group of atoms forms the 
negative ion instead of a single atom. When electronegative ions are in com- 
bination there is evidence of a definite linking into molecules or atomic groups, 
of which CO, in calcite is an example. 
The distances between atoms in the crystal structure are explicable in terms 
of Langmuir’s conception, the electrons being arranged on a series of spherical 
shells whose diameters increase in arithmetical progression. ‘lhe evidence given 
by the diffraction of X-rays is not in agreement with such a supposition. Some 
idea of the distribution of electrons about the nucleus may be got from measure- 
ment of the intensity of reflection of X-rays by a crystal. ‘This intensity 
depends on the amount of X-rays scattered by a single atom, and that in its 
turn on the number and arrangement of electrons in the atoms. Recent measure- 
ments of the amplitude of waves diffracted by sodium and chlorine (Bragg, 
James and Bosanquet, Phil. Mag., March and July, 1921) show that the distri- 
bution of electrons in those atoms is very different from that pictured. ‘here is 
a far greater density of electrons near the centre of the atom than in the outer 
region. ‘This is inconsistent with the Langmuir arrangement of stationary 
electrons on spherical shells. The success of Langmuir’s model in explaining 
complex compounds does not depend on any assumption as to the exact structure 
of the atom, but on the fundamental conceptions of combination through 
electrostatic attraction and by electron sharing. 
Prof. J. R. Partincron.—l. Translational and rotational energies are 
approximately represented by the theory of equipartition; any excess of C, 
above 6 is approximately parallel with the activities in non-polar gases. 
2. Translational energy on the basis of the quantum theory with the collision 
frequency yv, is 2°98 for all gases, but the By values are of the same order as 
the observed values of C,. ‘he rotational frequencies may be whole multiples 
of the translational. 
3. The value of » in 7 = 1, ( L me where 7 = viscosity, T = temperature, is 
273 
related to the critical pressure : n = 0:642 + 0-00116 p, + 0:0000399 p,?. 
4. The molecular heat of hydrogen is not satisfactorily represented by Einstein’s 
formula with By = const. (Eucken), or Byoc VT (Nernst). It is represented by 
Debye’s formula with By = 65// T. 
5. The model of the nitrogen molecule on Bohr’s theory has the correct energy if 
three coplanar rings of 8, 4 and 2 electrons, between the two nuclei, are assumed, 
and vy = Aw/B cos ¢, as in Kriiger’s theory. 
Prof. A. O. Ranxine.—It is possible in several cases to obtain support from 
the kinetic theory of gases for the views propounded to-day by Dr. Langmuir. 
The dimensions of the molecule Cl,, for example, as estimated from the 
viscosity, are found to be very nearly those which we should expect if the 
molecule is like two argon atoms with their outer electron shells contiguous, 
as electron sharing would involve. Similar relations exist between bromine 
and krypton, and between iodine and xenon. In the same way it may be 
shown that the molecules CO, and N,O, to the nearly identical physical 
properties of which Dr. Langmuir has called attention, are each of them 
kinetically equivalent to three neon atoms in a straight line with contiguous 
outer electron shells. 
Further confirmation comes from the consideration of the two gases krypton 
and methane, in relation to rubidium and ammonium, according to the theory 
under discussion. If we could shear from an atom of Rb its single outer electron, 
and also rob its nucleus of one positive charge, the remainder would be an atom 
of Kr. The same process applied to the group NH, would convert the nitrogen 
atom into carbon, and leave us with the molecule CH,. ‘hus methane bears 
to ammonium precisely the same relation as krypton bears to rubidium. Now, 
it is well known that the same salts of Rb and NH, are not only completely 
isomorphous, but are of nearly equal molecular volume. Or the domains occupied 
by Rb and NH, in crystals are almost identical. We should anticipate, there- 
fore, that an atom of krypton and a molecule of methane would have the same 
