One of the most remarkable evidences in favour of the Lewis-Langmuir theory of molecular constitution is the close degree of equality between nearly all of the physical constants of the two compounds, carbon dioxide and nitrous oxide. This identity is attributed by Langmuir to the arrangement of external electrons being the same for the molecules of the two gases in question. It is the purpose of the present communication to show that an appeal to the kinetic theory of gases, in conjunction with what is now known from W. L Bragg’s work regarding the dimensions of atoms, produces substantial additional evidence in support of the Lewis-Langmuir views. In particular, it will be shown that the molecules of CO
2
and N
2
O behave not merely as though they had the same size and shape, but as if each of them had an external electron arrangement practically the same as that of
three neon atoms in line and contiguous.
2. This arrangement is precisely that which Langmuir suggests and is represented in fig. 1. A single neon atom is pictured as having eight outer electrons, presumably at the corners of a cube. Other atoms, although deficient in outer electrons, can, by forming molecules in which electrons are shared, attain a stable but multiple neon arrangement. Thus, if fig. 1 be taken to represent the molecule N
2
O, it can be readily seen that the necessary conditions are fulfilled. The total deficiency of outer electrons is 8 (3 for each N atom and 2 for the O atom), and there are thus 24—8 = 16 only available. These serve exactly to complete the arrangement shown, which is like three neon atoms with two faces shared. On the other hand, if the molecule is CO
2
, the electron deficiency is again 8 (2 for each 0 atom and 4 for the C atom), and the same arrangement therefore serves. There is no need, for our present purpose, to distinguish which cube represents any particular atom. The distribution of electrons is, according to Langmuir, externally equivalent to three neon atoms joined together, and is the same for both CO
2
and N
2
O.
The thermal conductivities of carbon monoxide and nitrous oxide