charged ions are being formed. It would suggest that RuO and Ru02 are mobile surface species that can nucleate into the growing oxide. Ru03+ and Ru04+ already have substantial partial pressures and are chemically less likely to form oxide. The presence of Ru2032+ and possibly Ru203+ would imply that RuO and Ru02 are reaction partners contributing to the oxide. However, a more detailed study is needed to confirm the existence of the singly charge species. Should the high mass peak be the dimer (Ru02)2+, it would confirm the presence of diffusing and reacting Ru02 molecules analogous to the W03 species on oxidizing tungsten. The point will be scrutinized in future studies with a higher resolution instrument. From the above information, the following mechanism is suggested:

In part 1 the experimental data on the surface tensions of sodium dodecyl sulphate (S.D.S.) solutions in a number of different sodium chloride concentrations at 20", 40" and 60°C are presented. The effect of salt on the force-area curves of S.D.S. is compared with that predicted from recent theories.

SUMMARYI. The force-area characteristics of monolayers of saturated and unsaturated phospholipids have been studied.2. Interaction in phospholipid monolayers depends on the nature of the fatty acid constituents of the phospholipid, and on the temperature.3. The mean area per molecule in mixed films of cholesterol with (I,2-distearoyl)-3-lecithin and (I,2-didecanoyl)-3-1ecithin at 22 ° practically followed the simple additivity rule.4-A condensing effect of cholesterol was evident with films of (I-stearoyl-2-lauroyl)-3-1ecithin; (I,2-ditetradecanoyl)-3-1ecithin, (I-stearoyl-2-oleoyl)-3-1ecithin and the corresponding ethanolamine analogue, as well as with (I,2-dioleoyl)-3-1ecithin at 22 °. At 5 ° the condensation effect with (I,2-ditetradecanoyl)-3-1ecithin was much reduced.5. The very expanded films of synthetic lecithins and phosphatidyl ethanolamines containing linoleic and linolenic acid showed no appreciable condensation effects with cholesterol.6. The behaviour of the mixed cholesterol-phospholipid films is governed by a number of factors, including Van der Waals' interactions, configurational entropy effects and alterations in the structure of water adjacent to the monolayers. These factors depend on chain length and degree of unsaturation.

Differential scanning calorimetry was applied to investigate the formation of tetrahydrofuran (THF) and cyclopentane (CP) clathrate hydrates. An emulsion technique was developed to determine the hydration number and the enthalpy of CP hydrate dissociation to liquid water and liquid cyclopentane, which were found to be 16.8 ( 0.7 and 82.3 kJ/mol CP, respectively. The hydration number corresponds to the theoretical number of 17 if all of the large cavities in the structure II hydrate are occupied. Experiments with water-in-CP emulsions did not identify homogeneous nucleation for the hydrate since ice and hydrate always formed together on supercooling. With water-in-heptane emulsions, for which no hydrate forms, the homogeneous ice supercooling limit was -37.8 °C. With the CP emulsion, ice and hydrate formed close to this temperature. For bulk THF/ H 2 O solutions, even at the hydrate stoichiometric molar ratio of 1:17, ice and hydrate were found to form in the same crystallization event upon cooling, which impeded the identification of the homogeneous nucleation temperature of the hydrate. To overcome this, a method based on emulsification of stoichiometric THF/water solutions in an immiscible fluorocarbon fluid enabled determination of the homogeneous nucleation of THF hydrate without the formation of ice. The homogeneous THF hydrate nucleation temperature was -32 °C. We believe this is the first measurement of homogeneous nucleation of a clathrate hydrate. Our experimental results suggest that ice is a good nucleating agent for heterogeneous formation of clathrate hydrates, whereas the hydrates are not efficient nucleators for ice.

We report rheological, microscopic, and calorimetric studies of the crystallization of long chain n-paraffins and their mixtures from model waxy oils and the effect of microcrystalline poly(ethylene-butene) (PEB) random copolymers. Optical micrographs and differential scanning calorimetry (DSC) reveal that the crystals formed from decane solutions of binary mixtures of C36 + C32 and of C32 + C28 are of mixed composition, whereas solutions of C28 + C24, C36 + C28, C32 + C24, and C36 + C24 form separate crystal phases. There is no miscibility when the difference in carbon number between two long chain n-paraffins ∆n c > 4. These findings agree with Kravchenko's prediction for crystallization of molten binary n-alkane mixtures. However, the crystallization of long chain n-paraffins from decane solution gives a stable crystal structure directly, while from the melt it tends to pass through a metastable rotator phase. Since PEB can either self-assemble into a needlelike structure or cocrystallize with long chain n-paraffins to form small thin sheets in decane, mixtures of wax and PEB formed quite complex shapes such as rodlike or shuttle-like structures, particularly for the longer paraffin chains. These structures reduce the yield stress of the cold model waxy oil as compared with the platelike crystals formed in the absence of PEB. PEB10, which has an average of 10 ethyl side groups per 100 carbon atoms in the polymer backbone, is more effective in reducing the yield stress than PEB7.5 except for the mixture C36 + C28. All the other mixtures of paraffins with PEBs show intermediate rheological properties between those of the single paraffin components.

The variation with pH of the surface potentials of spread monolayers of weak acids or bases may be used to calculate the intrinsic ionization constants of the film-forming molecules. The method is valid for condensed monolayers at the air/water interface for regions of a low degree of ionization only. The intrinsic constants for stearic acid and nonadecylamine monolayers are similar to the ionization constants for short-chain fatty acids and amines in aqueous solution. The relations between this and other methods of treating the ionization of a weak acid or base in a surface are discussed.

Using compression techniques, surface pressure (II) against area ( A ) isotherms are measured as a function of temperature for insoluble monolayers of 1,2-distearoyl-sn-glycero-3-phosphorylcholine spread at the n-heptane/aqueous sodium chloride interface. Problems of spreading are resolved and accurate results at moderate and high IT are presented. The results show an almost first order phase change which is very temperature sensitive. Various forms of the Clapeyron analysis are applied to the data to calculate the heats of the phase change and to assess variations arising from the choice of a close-packed area. These heats vary with temperature but not with salt concentration or pH over the range studied. Results on 1,2-dioleoyl-sn-glycero-3-phosphorylcholine show no such phase changes.

The Gibbs adsorption isotherm is applied to the penetration of long-chain ionic molecules into an insoluble monolayer held at constant area at the air/water interface. Uncertainties arise in the calculation of the surface densities of the penetrating molecules. These uncertainties are due iirstly to the possibility of ion exchange (surface hydrolysis), and secondly to the perturbation of the insoluble component and the introduction of assumptions as to the chemical potential of the insoluble component of the mixed film. These uncertainties are largely avoided with a condensed insoluble film spread on a solution containing excess neutral electrolyte. The theory is applied to the interaction of cholesterol monolayers with sodium dodecyl sulphate in solution.Schulman and Rideall and Schulman and Stenhagen 2 used the term " monolayer penetration " to describe the interaction of an insoluble monolayer spread at a phase boundary with a soluble surfaceactive species in one phase. The molecules of the soluble compound enter the surface and interact with the insoluble component both at the head groups and hydrocarbon chains. The effects of varying chain length and head group have been studied in some detail.l.2 The interaction can be measured in two ways. Firstly, the film pressure can be kept constant and the reaction followed by observing the increase in area of the f i l m . This approach has been examined recently by Goddard and Schulman.3 The second method is to maintain the film at constant area and to measure the surface pressure changes on adding the penetrating substance to the sub-solution. This method has not been studied in detail hitherto and is considered here. The present results are principally for the interaction of cholesterol and a series of dodecyl detergents. The maximum pressures obtained on penetration did not exceed the collapse pressure of cholesterol by more than 2 dynelcm in any experiment.