TA SECTIONAL ADDRESSES, 
2.7x10-° grin. per sq. cm. Hence the number of molecules per 
sq. em. of interface 
aa 
93 
and the surface area per molecule=58 x 10-1* sq. cm. JLangmuir’s 
calculation from Worley’s measurements of the surface tensions of 
aqueous solutions of aniline gives at the air-water surface the value 
34 x 10-** sq. em. for the area per molecule of aniline. We may con- 
clude, therefore, that Lewis’ measurements in this case point to the 
building up of a primary unimolecular layer, unaccompanied by any 
further concentration or ‘condensation’ of molecules or colloidal 
micelles. 
The relation between surface adsorption and fall of interfacial tension 
at a mercury-water interface was further investigated by W. A. Patrick, 
who concluded that, although there was a correspondence between the 
two phenomena, the surface adsorption could not be calculated from 
the simplified Gibbs equation. If we were to accept this conclusion 
as correct, we might find an explanation either in the suggestion made 
above, or in the possible invalidity of conclusions drawn from the use 
of the simplified Gibbs equation ; either because the simplifications intro- 
duced are not justified, or because the existence of electrical or other 
factors requires an extension or elaboration of the original equation. 
This matter has been discussed by Lewis, by A. W. Porter, and by 
various investigators of electro-capillary phenomena. 
From very accurate measurements of the interfacial tensions of the 
aqueous solution-mercury interface, W. D. Harkins has calculated (by 
means of the simple Gibbs equation) that when the interface ‘is satu- 
rated as regards butyric. acid molecules coming from the aqueous 
solution, the surface area per molecule is 36X10-** sq. cm. 
Here, again, we see that a calculation by means of the Gibbs equa- 
tion seems to point to the formation of a primary unimolecular layer. 
Experiments similar to those of Lewis have been very recently made by 
EK. L. Griffin, who has measured directly the adsorption of soaps from 
aqueous solutions at a mineral oil-water interface. The results obtained 
are as follows :— 
m10 KG 06% 10° =O 17 410. 
Average Surface per Molecule 
Substance adsorbed 
Sodium Oleate - . . - 48X10~ sq. em. 
Potassium Stearate ; : LOOT R11 ae, Cha 
Potassium Palmitate  . ; - 30X10-% sq. em. 
These figures are very interesting, for they would appear to indicate 
the formation of unimolecular surface layers. 1t may be mentioned 
here that T. R. Briggs has investigated the adsorption of sodium: oleate 
at a benzene-water interface, and finds that the amount of soap adsorbed 
at the interface increases rapidly at first with small increases in the 
concentration of the solution, and then remains very nearly constant 
while the concentration of the solution undergoes great increase. This 
is just-what one would expect from the building up of a saturated 
surface or surface layer (whether unimolecular or otherwise). 
