D. TALMUD and S. BRESLER, Surface Phenomena, L.—M., GTTI, 1934, p. 131, 3000 copies, price 2 rubles.

The monograph under review is an exposition of the work of the Laboratory of Surface Phenomena of the LIKhF, devoted almost exclusively to the study of the surface layers of pure liquids and solutions. A characteristic feature of the monograph is the abundance and originality of the ideas and conceptions it contains concerning the nature of the phenomena studied and the structure of the surface layer, although some of the theories developed by the authors appear not to be proved on the basis of the experimental material presented.

In the first part of the monograph evidence is given for the “quasi-crystalline” structure of the surface layer of pure liquids. However, the formation described by the authors, from molten paraffin at a temperature 2–3° above its melting point, of films covered with a hard crust \(10^{-6}\) cm thick can quite well be explained—as the authors themselves indicate—by the fact that the thinnest “true” crystals formed on the surface of the molten paraffin have a melting temperature somewhat above the normal one, as Garner and Randall** observed for fatty acids. In this case one cannot speak of a quasi-crystalline structure of the surface layer of the liquid, since we are dealing with a two-phase system. The X-ray diagrams of Trillat, to which the authors further refer, testify to the quasi-crystallinity of the surface layer in a very limited number of liquids and to its absence in others. Finally, the electronograms taken by the authors themselves from the surface layer of a liquid do not yet permit definitive conclusions to be drawn; in particular, the fact that the surface layer of liquid mercury gives electronograms corresponding sometimes to a crystalline and sometimes to an amorphous structure points to the possibility of the formation of an oxide film on the mercury surface in these experiments.

** Garner and Randall, Journ. Chem. Soc. 125, 369, 1924.

On the other hand, the following fact argues against the view of the crystallinity of the surface layer of liquids: the “surface heat capacity” (the derivative of heat capacity with respect to surface) of a whole series of liquids—precisely those whose surface tension varies linearly with temperature—is, as Eötvös showed, zero. Meanwhile such a crystalline surface layer ought to have a smaller heat capacity than an equal-by-volume layer inside the liquid. Further, it is not clear why pure liquids do not exhibit surface strength, despite the presence on them of a crystalline “crust.”

In the chapter devoted to the mechanical strength of adsorption layers on the surface of liquids, a very unexpected fact is reported—the existence of such strength in films of the oleic-acid type and in adsorption layers of water-soluble substances, i.e., in cases for which until now this effect had not been detected. At the same time, it turns out that unsaturated adsorption layers possess maximum strength; the authors explain this by the displacement of oriented molecules, occurring with particular intensity in the region preceding saturation. Some perplexity is caused here, however, by the following facts: films, for example, of palmitic acid already have great strength at a surface concentration of \(2 \times 10^{-10}\ \mathrm{mol/cm^2}\), which corresponds to \(80\ \text{\AA}^2\) per molecule. At such a concentration, as electrometric measurements show, separate islands of palmitic acid float on the surface of water, and it is difficult to understand how such a surface possesses greater strength than a continuous film. Further, the maximum strength of oleic-acid films proves to be considerably greater than the strength of a saturated palmitic-acid film. Yet, according to Mukin and Rideal,* about \(10\ \mathrm{dyn/cm}\) is required to rupture the latter. It is quite inexplicable why the numerous investigators who worked with oleic-acid films did not notice such considerable strength in them.

Speaking of solvation of the molecules of the adsorption layer, the authors dwell on the fact that phenol and aniline, dissolved in water, mutually increase one another’s adsorption at the surface and explain this phenomenon by the linkage of phenol molecules with aniline molecules, due to the opposite direction of their dipole moments in the adsorption layer. Meanwhile, as electrometric measurements show,*** the dipole moments of aniline and phenol molecules adsorbed on the surface of aqueous solutions have the same direction.

Very interesting are the measurements of the “surface viscosity” of monomolecular films by means of “flat capillaries,” leading to the result that maximum viscosity is possessed by the optically dense films—unsaturated ones—as well as the elegant method for investigating “two-dimensional reactions” with the aid of the Langmuir balance.

The stability of foam, in the authors’ opinion, is due to the presence of solidified adsorption layers and to the greater or lesser rate of flow of liquid in the flat layer formed by these layers in the capillary.

However, for example, for cetyl alcohol the maximum strength of the adsorption layer is reached at a concentration of \(3\text{–}10^{-10}\ \mathrm{mol/cm^2}\), whereas the stability of the corresponding elementary foam is equal to zero up to \(6 \cdot 10^{-10}\ \mathrm{mol/cm^2}\). Also unclear is the form of the stability curves, which at a certain concentration give a jump from zero to a maximum value. It seems to us that here one should not entirely neglect Gibbs’s views**** on the stability of films, rela-

* Harkins, Journ. Chem. Physics. 1, 852, 1933.
** Mouquin and Rideal, Proc. Roy. Soc. 114 A, 690, 1927.
*** Frumkin, Z. Physikal. Ch. 123, 361, 1926.
**** Gibbs, Coll. Works, vol. I, p. 300.

...which connected the latter with the elastic capillary properties of adsorption layers.*

The authors’ investigations in the field of linear wetting and linear adsorption are of great interest, i.e., phenomena occurring at the boundary of separation of three phases—investigations that lay the foundation for a new direction in capillary physics.

At the end of the monograph the authors set forth works that have direct technical application. By microflotation the authors mean a method for removing capillary-active impurities from solutions (for example, sugar juices) by means of foam. Let us note that this method had already been described earlier by Perrin* (the removal of fatty acids from soap solutions).

The authors develop a number of original ideas when speaking of ordinary flotation; such are the considerations on the strength of films covered with a continuous layer of solid particles, forming, as it were, an arch, and on the significance of the velocity of sliding of particles along the foam films. In assigning a dominant role in the flotation process to the strength of films and to the velocity of sliding of particles, the authors, in our opinion, somewhat underestimate the importance of the wettability of particles and of its alteration under the action of capillary-active substances, as studied by P. Rehbinder.

N. Fuchs

* J. Perrin, Ann. de Physique X, 183, 1918.