JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS TABLE I. STABILISATION OF FOAM BY NONYL ALCOHOL Volume in c.c. of C9OIt added to 12 c.c. (SDS) C•, 0- 0 0,001 0. 002 0.003 0. 004 0.005 0.006 Laminae stability before breakage 9sec. 9sec. 2min. 8min. 15min. 10min. 8min. Figure 3. Effect of nonyl alcohol on the surface tension of Na dodecyl sulphate (M/300) 124

MOLECULAR INTERACTION IN BULK SOLUTION tained in the presence of nonyl alcohol are indicated in Table 1. The stability of these laminae is of the same order as those measured •from a sodium oleate solution or even greater 4. The analogy of such mixed solu- tions and sodium oleate is also, shown by their similar surface activity. Figure 3 sho,ws that, with increasing amoup*s of nonyl alcohol, the sur- face tension decreases and reaches a minimum value of 27 dynes. This corresponds to a surface pressure of 45 dynes 4 which is equal to the collapse pressure of penetrated monolayers of cetyl alcohol and cetyl sulphate. Furthermore, the mixed solution SDS--C.•OH give laminae of stratified step-like structure, but unfortunately the photograph show- ing this is not suitable for reproduc- tion. This is similar to the structure obtained by Perrin '• and Lawrence' for sodium oleate. In the first case the lamina is formed by a series of bimolecular leaflets of a mixed structure $DS- C9OH, whereas in the latter case the structure is stabilised by the fatty acid map. It appears, therefore, that the molecular association between long chain ionic detergents and polar compounds is responsible for the greater surface activity of sodium oleate and that the alkyl sulphates may be brought to the same level after their association with long chain polar compounds into a mixed structure. (The author's present address -is: The Chemistry Department, Kirtg' s College, London.) ]•EFE RENC E S (1) Schulman & Stenhagen. Proc. Royal Soc. B 1938, 126, 356. (2) Matalon & Schulman. Trans-Farad (Discussion), 1949, No. 6, 29. (3) Matalon, Salton, Cohen. Nature, Vol. 167. Feb. 10th, 1951, p.241. (4) Matalon. "Surface Chemistry" (Butterworths), 1949, p.195. (5) Perrim Kolli Zetsch. 1938, 51 3. (6) Lawrence. "Soap Films" (G. Bell & Sons Ltd.), 1929. Figure 1 (page 123) shows the effec• of heptyl alcohol on the foaming properties of Na dodecyl sulphate in aqueous solution. The volume of alcohol present in 120 cc M/300 (SDS) is indicated in each tube. Figure 2 demon- strates •he effect of long chain alcoh,ols on the foaming properties of Na dodecyl sulphate in aqueous solution, M/300. 125