Sept., 1936
NOTES
1817
acid at room temperature except at pressures below about 0.2 dyne per cm. The addition of 1.61 g. of nujol to 1 g. of stearic acid in the film forming substances does not seem to increase the area of FROM THE LABORATORIES OF THEROCKEFELLER INSTITUTE the condensed film (Fig. 1, expts. 91 and l l O ) , but FOR MEDICAL RESEARCH RECEIVED JUNE18, 1936 only weakens it at high pressures. NEWYORK,N. Y. The areas given in the figures of this paper represent the area per molecule of the more polar Polymolecular Films constituent (stearic acid, etc.) . BY WILLIAM D. HARKINS AND ROBERT J. MYERS 2. Expanded Films of Oleic Acid.-The Surface films which spread over water are sup- effects are, however, markedly different in cases in posed to be monomolecular. However, Harkins which the acid when alone forms an “expanded” and Morgan‘ were able to produce solid, partly film, as in the case of oleic acid (Fig. 2). Here the
violet before adding the reductant. Otherwise there is no visible change on reducing the dye to the semiquinone state.
28 MIXED FILMS CONTAINING STEARIC ACID
24
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24 28 32 36 40 Area per molecule, sq. A. Fig. 1.-Poly- and mono-molecular films with stearic acid. 20
crystalline films with a mean thickness much greater than this. Thus to a spreading substance whose organic molecules contain a polar group (stearic acid, etc.) they added a thickening or nonpolar substance (phenanthrene). In the present work polymolecular liquid films were produced by thickening the films with a liquid paraffin oil (nujol) of low volatility. ‘1. Condensed Films.-Films of pure stearic acid form condensed films on 0.01 N hydrochloric (1) Harkins and Morgan, R o c . N o t . Asad. Sei.. 11. 681 (1926).
mixed film contains 1.66 parts by weight of the paraffin oil to 1 part of oleic acid. The effect of the paraffin oil is very great, since it raises the surface pressure greatly a t large areas, and decreases it very markedly a t low areas. At 36.4 sq. A. per molecule of oleic acid the pressures are the same for the pure acid and the mixture. 3. Expanded Films of Myristic Acid.-At 22.8’ fJms of pure myristic acid exhibit a kink in the curve at an area of 25.45 sq. A. and a pressure of 17.25 dynts per cm. The addition of 1.67 parts
NOTES
1818
by weight of nujol to 1 part of myristic acid removes the kink and increases the film pressure at any given area. The increase is particularly great at the lower pressures (larger areas). With a greater proportion of nujol (9.08 parts) the phenomenon encountered with oleic acid is found,
Vol. 58
4. Films of Pentadecylic Acid (Fig. 4).-The addition of 1.5 g. of the paraffin oil to 1 g. of pentadecylic acid increases the film pressure very greatly, both above and below the kink in the curve. However, a t about 20 sq. k.per molecule the two sets of curves cross. The curve for experi-
Area per molecule, sq. A. Fig. 2.-Poly- and mono-molecular films with oleic acid.
that is, the paraffin oil increases the pressure at ment 97 indicates that the tetradecane has evaplarge molecular areas and decreases it a t the lower orated. areas. The decrease in surface pressure a t the 5. Surface Potentials of Polymolecular 5 exhibits interesting relations lower areas becomes much more marked as the Films.-Figure amount of paraffin oil is increased (expt. 104, and shows that there is a kink in the potential area curves of both the pure acid and the mixture. Fig. 3).
Fig. 3.-Poly-
and mono-molecular films with myristic acid,
1819
NOTES
Sept., 1936 28 24
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20
Polymolecular films exhibit many interesting relations, and many of these are under investigation in this Laboratory. At constant pressure many polymolecular, as well as monomolecular, films shrink with time. This shrinkage is very marked with pentadecylic acid at areas just below and pressures just above that of the kink in the curve. UNIVERSITY OF CHICAGO CHICAGO, ILLINOIS
RECEIVED JUNE
Micro Determination of Active Hydrogen with Deuterium Oxide BY ROGERJ. WILLIAMS
The usual methods of determining active hydrogen involving the use of a Grignard reagent, cannot be applied to highly water soluble materials which do not dissolve in ethers or other organic 22, 1936 solvents,
