SOME PROBLEMS OF ATMOSPHERIC CHEMISTRY 
tional to the product of the two values of the dipole 
moment. The effect of two dipoles upon each other is 
one of attraction, repulsion, or relative cancellation, 
depending on their mutual positions. It could be as- 
sumed that in gases with freely rotating molecules 
(thermal motion) these forces mutually cancel in the 
mean. Actually, however, according to Wolf [60], the 
rotation is not uniform when dipoles move past each 
other, since the positions of attraction (smaller poten- 
tial energy) are preferred to those of repulsion. In 
addition the dipole movements are probably somewhat 
affected by the electrostatic field, simce by means of 
X-ray techniques Német [40] found a relatively large 
effect of the electrostatic field on the structure of ice. 
The behavior of azeotropic mixtures is further evi- 
dence for the approximate correctness of these con- 
cepts. For example, if HCl of any concentration is 
allowed to evaporate at normal pressure, an equilibrium 
at a concentration of approximately 20 per cent acid is 
reached in which the ratio of acid molecules to water 
molecules is 1g, that is, the same ratio as for an hy- 
drochloriec acid hydrate which has been arranged by 
dipole forces. In effect, therefore, all the molecules 
that were not retained by a small excess of attractive 
forces are vaporized. For the condensation of water 
molecules on HCl it is significant that the recombina- 
tion at normal pressure takes place in the same molecu- 
lar ratio 1g, regardless of whether a concentrated or a 
dilute acid is subjected to distillation. According to our 
present knowledge, this constancy of molecular ratios 
can be explained only by short-range forces pre-ori- 
enting the dipoles prior to condensation. 
Computations from the relatively small Cl- values in 
dew and hoarfrost at the North Sea by Kohler [31], and 
in Ober Schreiberhau by the author, showed that the 
hydrochloric acid nuclei—which were still assumed by 
Kohler to be NaCl nuclei—could have originated from 
a few molecules of HCl with eight times as many 
molecules of water. 
Induction Forces. Vhese forces, which are of electro- 
static nature, originate when one pole induces a dipole 
moment in a neighboring pole; this dipole moment 
points in the direction of the inducing pole so that an 
attraction results between the inducing and induced 
molecules. The attraction is proportional to the product 
of the exciting pole moment (either a permanent dipole 
or an ionized gas molecule) and the induced dipole 
moment. This type of attraction, however, is far less 
significant than the dipole forces of permanent dipoles. 
These induction forces are probably important in con- 
densation on walls by inducing a mirror dipole and are 
important for a similar reason in the case of condensa- 
tion on solid suspended particles. However, for meteoro- 
logical phenomena this is not too important, smce many 
types of solid particles require a higher water-vapor 
saturation to produce condensation than is customarily 
encountered in the atmosphere. Other particles, such 
as ash dust with its hydrophilic compounds, for ex- 
ample, K.CO; or freshly powdered quartz crystals, 
which are characterized by a highly active surface, 
possess readily inducible dipoles. 
1133 
Dispersion Forces. These forces, which are of elec- 
tromagnetic plus electrostatic nature, are based on the 
fact that alternating electric fields are produced as a 
result of the motion of electrons in an excited state. 
Under the influence of these fields, dipole moments, 
whose interaction produces a net attraction, are in- 
duced in each of two or more mutually approaching 
molecules. Their effect is far greater than that of induc- 
tion forces. The dispersion forces are not a function of 
temperature; they are effective for relatively large mole- 
cules, at rather high temperatures, and also for non- 
polar molecules. Their lifetime is extremely short. How- 
ever, with adequate stimulus (ultraviolet radiation), 
the same atoms and molecules can be continuously 
re-excited. 
Importance of the Order of Hydration for the Mode 
of Charging Nuclei. The electrical double-layer, a con- 
sequence of the hydration order, was recognized clearly 
for the first time during the observation of the chemical 
separation in the spray of salt sols already mentioned 
[18]. A description of a separation experiment of this 
type follows. 
The mother liquor used for the atomization in this 
experiment contained Mg, Cl, and K in the following 
proportions: Mg/Cl = 1/440; Mg/K = 1/4. The pH 
value was 7.6. Fine droplets (of the magnitude of con- 
densation nuclei) were produced by a jet of compressed 
air; at various distances from the nozzle they had the 
mean values given in Table IV. 
Tasie [VY. AmrRosoL CHARACTERISTICS IN A 
Spray EXPERIMENT 
Distance of droplets from 
NLOZZLEM CI) Paneer Sao see 0.30 1.50 3.00 
CU Migig Eon tact ie ce nae 83 30 37 
15 Ie oraet eins Mee alert epee oan corre 6.9 6.3 6.3 
Concentration* 
IAG SANE he Cathar BERT Secs Dae 9 2.72 2.72 
I Le oReetis Ca cicteet mis iniee tects 48 40 32 
EG. ALT Shes Rete Reeser nee ite. 25 15 10 
* In per cent of concentration in mother liquor. 
At 1.50 m from the nozzle, after 45 min of atomiza- 
tion, 15 per cent of the total chlorine dissolved in the 
droplets was still present in the form of condensation 
nuclei, and 85 per cent in the gaseous phase, probably 
predominantly as ClO2, Cl, and HCI. 
The results show a strong escape of the Cl, (produced 
autocatalytically), as well as a separation of the Cl, 
component which has remained dissolved from the 
nonvolatile alkalis, and a lower pH value (more acidic) 
in the far-drifting, atomized component. This is possible 
only if there is an excess of cations in the interior of the 
coarse drops and an excess of Cl anions in the outermost 
molecular layer. In the atomization process, portions 
of this layer are removed as most finely divided, far- 
drifting water droplets, while the coarser drops contain- 
ing the bulk of the mass fall to the ground near the 
nozzle. Such an arrangement of the chemical substan- 
ces in the solution can be explained only by hydration, 
according to Born [3]. That is, neutral water molecules 
are attracted by the chemical ions; moreover, this 
