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In previous communications (Rideal et al . 1933, 1935) from this laboratory it has been shown that the course of chemical reactions proceeding in monomolecular films or monolayers at air liquid interfaces, can be followed by means of observation of the changes in phase boundary potential and surface pressure or tension. It seemed possible that a further advance in the elucidation of the complex mechanism of lytic, sensitizing, agglutinating and immunity reactions might be made by a closer study of the behaviour and interaction of a number of biologically active substances in the form of monolayers, especially as it appears that several of these biological processes take place under conditions similar to those existing in the films. It is found that if an extremely dilute solution of a suitable molecular species be injected under a monolayer of another, under the correct inter­acting conditions, a phenomenon which we may term film penetration is observed. The chief characteristics of film penetration are an immediate large rise in surface pressure of the film, a decrease or increase of the surface potential, according to the magnitude of the dipole moments of the pene­trating polar group, compared to that of the film-forming molecule, and the strong stability of the resultant new film. It appears that the process of penetration is completed when a mixed film, consisting of equimolecular proportions of the original film material and the penetrating substance, is formed. The final value of the phase boundary potential is found to correspond exactly with that shown by the equimolecular mixed film spread on the surface and compressed to maximum pressures.

In previous papers of this series (1) it was shown that the method of surface potentials could be developed to give quantitative measurements of the physico-chemical properties of unimolecular films at an air liquid interface. Several problems of fundamental importance arise when a closer investigation is made of the true meaning of the phrase “surface potential of a unimolecular film.”

Molecular orientation in a film formed at an air liquid interface was ascribed by Hardy to an inwardly directive attractive force along the normal to the surface, the condition of minimum potential involving two terms, one relating to the variation in density, the other to the orientation of the field with the "polar" groups, which are accordingly attracted inwards towards the bulk phase. That "polar" groups do in fact posses large fields is confirmed from an examination of the electric moments of compounds containing these groups. In previous communications it was shown that the characteristics and phase of films could be affected not only by alterations in the variables of temperature and two dimensional pressure as shown experimentally by Langmuir and by Adam, but also by altering the extent of the adhesion of the asymmetrically situated polar group to the substrate. Alterations in the extent of this adhesion will naturally affect the field and it is the object of this communication to attempt an examination of the behaviour of films from this point of view. The modification of an interfacial potential difference produced by the presence of a unimolecular film was shown by Helmholtz to be given by the expression 4 πn μ = ∆V where the change in potential ∆V is caused by n molecules per square centimetre of the film forming substance, each molecule possessing an average electric moment of effective vertical component μ.

It was shown in Parts I and II that the vertical component of the mean molecular electric moment, μ¯, calculated with the aid of the Helmholtz equation 4 πn μ¯ = ∆V was dependent on the state of the film. Th experiments of Lyons and Rideal ( loc. cit. ) indicated that the state of a film could be altered not only by means of the usual variables, the two dimensional pressure F, and the temperature T, but also by the extent of the adhesion of the polar group to the substrate, conveniently altered in the case of acids by a change in the p H of the solution. That the change in this adhesion could not be attributed to the ionisation of the acid alone was shown by the fact that great changes in the stability of the film could be made over ranges of p H well outside the range of dissociation; further for identical hydrogen ion activities the effects of different anions possessing various capillary activities were widely diverse, e. g., the surface film on a citrate buffer behaves as if it were relatively more acid, and that on a borate buffer as if it were relatively more alkaline than the bulk phase.

The concept of the orientated monolayer as constituting the state of matter, in what was termed by the late Sir William Hardy the boundary state, is such an important one in the interpretation of the phenomena involving both equilibria and kinetics at interfaces that it is necessary to examine with some care the premises on which it rests. From the evidence accumulated with the aid of the Langmuir trough we can infer that a film of a long chain fatty acid floating on a water surface consists of a monomolecular array or monolayer of molecules with their hydrophilic groups immersed in the water and the hydrophilic chain extended above the surface. The method, however, provides no information on film uniformity, and it seemed desirable to check this assumption by direct methods. Two direct methods are available: an optical and an electrical. By determining both the relative phase retardation and the ratio of the relexion coefficients, which a beam of polarized light suffers on reflexion from a clean water surface and from one covered with a monolayer, and with the aid of Strachan's development of the Drude equations it is possible to determine the scattering indices of the film material in the planes both parallel and perpendicular to the surface. The following figures give the values obtained for a myristic acid film:— Acid in bulk .... 3·5 10 -22 cc -1 In plane of film ... 2·8 10 -22 cc -1 Normal to film .... 4·1 10 -24 cc -1 It is important to note that in the plane of the film the material possesses optical properties similar to those obtained in the bulk phase, but reveals a much smaller scattering component in the direction perpendicular to the surface. These measurements provide an optical confirmation of the Hardy Langmuir principle of molecular orientation and, further, the method permits us to examine the film for uniformity.

X -ray and microscopic examinations of multilayers of certain long-chain esters deposited on transparent bases have been made. An X -ray photograph of a stationary multilayer of ethyl stearate is apparently identical with that obtained by rotating a single crystal of β -ethyl stearate about the long axis of the cell. The spots previously observed on oscillation photographs of multilayers of ethyl stearate are in reality parts of circles, successive arcs of which appear on increasing the angle of incidence of the X -rays on the multilayer. These facts reveal that the multilayer consists of microcrystals all oriented with one axis in common, this axis being the normal to the surface of the multilayer. The single crystals appear to have grown without interruption throughout the entire thickness of the multilayer, which in these investigations was about 1000 mol. thick.

When a dispersion of rubber (4 per cent) in benzene is treated with sulfur monochloride (1 per cent) at room temperature, the solution becomes opaque and gelation occurs in a few minutes. With a more dilute dispersion of rubber (1 per cent), Meyer and Mark obtained a weak gel, which could be broken up by stirring to give, after one hour, a pale yellow precipitate, corresponding to the formula C10H16SCl2. By analogy with the reaction of ethylene and sulfur monochloride, these workers proposed the following reaction process: (see PDF for diagram) The so-called cold-vulcanization process, which is essentially the above reaction, thus appears to correspond to the cross-linking of adjacent isoprene units by means of thioether-bond formation. This result contrasts with the hot sulfur vulcanization process, where the reaction does not involve the sulfurization of any appreciable number of olefinic groups. The mechanism of the cold vulcanization process is unknown. However, it is known that certain comme...

When a dispersion of rubber (4 per cent) in benzene is treated with sulfur monochloride (1 per cent) at room temperature, the solution becomes opaque and gelation occurs in a few minutes. With a more dilute dispersion of rubber (1 per cent), Meyer and Mark obtained a weak gel, which could be broken up by stirring to give, after one hour, a pale yellow precipitate, corresponding to the formula C10H16SCl2. By analogy with the reaction of ethylene and sulfur monochloride, these workers proposed the following reaction process: (see PDF for diagram) The so-called cold-vulcanization process, which is essentially the above reaction, thus appears to correspond to the cross-linking of adjacent isoprene units by means of thioether-bond formation. This result contrasts with the hot sulfur vulcanization process, where the reaction does not involve the sulfurization of any appreciable number of olefinic groups. The mechanism of the cold vulcanization process is unknown. However, it is known that certain commercial sulfur vulcanization accelerators speed up the above gelation process to a remarkable extent. The present work describes an attempt to investigate the kinetics of the reaction between rubber and sulfur monochloride, with the eventual view of establishing the mechanism of the process. In general, two main methods have been developed for assessing reaction velocities. They are the dilatometric method and a more arbitrary time-of-gelation method. While the former method is of importance in studying the more detailed quantitative features of the reaction, the latter method is of help as a powerful auxiliary. Although it is not yet possible to propose a clear-cut mechanism for the vulcanization process, certain kinetic features have been established, and indications of the most fruitful lines of attack are presented.

A new electrolytic selenium photo‐cell is described and its characteristics given as a function of operating voltage, temperature, external resistance, and time. Data are included indicative of its response to unmodulated, modulated, and monochromatic light; comparison is made with cells of similar type or possessing similar characteristics; and a method of compensating for the dark current of photo‐cells is shown.An electronic circuit is also described which can greatly improve the voltage output of the photo‐element. It is generally applicable to photo‐conductive and photo‐voltaic cells.

The experiments carried out with a variety of pure surface active agents, employed in flotation of ores as either collectors or frothers, show that (a) long chain homologues of alcohols and alkyl sulphates react strongly with xanthates at the air/liquid interface (Langmuir-trough experiments), (b) the molecular interactions between frothers and collectors occur at the solid/liquid interface — if the solid is suitably coated by collector molecules (frother adsorption tests), (c) the effects of molecular associations collector-frother are evident in frothing and flotation results. The measurements of air/water/solid and oil/water/solid contact angles (carried out under variable conditions as regards concentration of the surface active agents, pH, time of conditioning and presence of complexing agents in the oil phase) reveal the importance of the density of collector-coverage. The results have been applied to the stability and to the inversion of phase-continuity of oil/water emulsions stabilized by solid powders. A mechanism for attachment of suitably collectorcoated particles to an air bubble is postulated.

The emission, excitation, and absorption spectra of silver‐activated alkali halides have been investigated. Three absorption bands due to ionic silver have been observed in NaCl, NaBr, KCl, and KBr, and the growth of these bands with silver concentration has been studied. In each of these crystals the two shorter‐wavelength bands are ascribed to isolated silver ions, while the band of longest wavelength is ascribed to pairs of silver ions.Upon x‐ray irradiation as many as five new absorption bands arise in certain alkali halides in addition to the F band. Excitation into three of these bands (designated as the B, C, and D bands) produces luminescence, the emission spectrum being different for each band. The B band is attributed to a center consisting of an electron trapped at a silver ion adjacent to a halogen‐ion vacancy; the C band to an electron trapped at a complex of two silver ions adjacent to a halogen‐ion vacancy; and the D band to a hole trapped at an alkali‐ion vacancy adjacent to a silver ion.

In Part I a method was described for the determination of the change in interphase potential at an air liquid interface caused by the presence of a unimolecular film of myristic acid and the values for this change (∆V) were plotted as a function of the molecular area. On application of the Helmholtz equation ∆V = 4 πn μ we obtain a mean value for the vertical component of the molecular electric moment of a molecule of myristic acid when present in a film in the expanded state of μ = 2.29. 10 -19 e. s. u.

Important information concerning the nature of the luminescent centre may be derived from comparatively simple physical measurements. Comparison of the temperature dependences of luminescence efficiency and decay rate gives information about the location of dissipative transitions and permits the calculation of activation energies and frequency factors for these transitions in certain cases. Information concerning the interaction of activators with their environment, as in sensitized luminescence and concentration quenching, is also derivable from these measurements. From additional measurements of the low temperature absorption and emission-band peaks and widths and the band-width variation with temperature, the configuration co-ordinate curve of a centre can be derived experimentally. Information concerning energy transfer in non-photoconducting sensitized phosphors may be obtained from measurements of absorption (reflexion) spectra or of quantum efficiency as a function of composition. Similar measurements can demonstrate the formation of pairs or higher aggregates of activators and lead to a determination of oscillator strength.

The gelation of aluminium soaps in hydrocarbon has been studied by investigating: (1) the degree of association of aluminium alkoxides, (2) the effect of moisture on the viscosity of benzene solutions of aluminium soaps prepared in situ by the reaction of fatty acids with aluminium alkoxides, (3) the properties of monolayers of aluminium soaps spread on water. Results indicate that the product of reaction between an aluminium alkoxide and a fatty acid is a di-soap and that gelation only takes place when the third valency of the aluminium atom is occupied by a hydroxyl group.

The surface activity of systems in a metastable or supersaturated state can be of importance in biological processes and the phenomenon of adhesion since the free energy of nucleation is utilizable for transport of material into interfaces. Crystalline aescin, a saponin, ground down to small particle sizes is used as an example. Thermodynamic data confirm the applicability of theKelvin equation. The micelle forming capacity of the molecule tends to stabilize the supersaturated state. Combination of theories of nucleation with those of micelle formation indicates such a buffering effects.

Oil/water contact angles, coefficient of friction and electron diffraction have been used to study the adsorption of three long chain surface-active substances (a fatty acid, a sulphate and a substituted amine, from aqueous solution on to electropolished copper, aluminium and iron. According to the pH of the solution, the adsorption occurs by one of the following processes (a) physical adsorption, (b) chemisorption, (c) adherence of a precipitate, (d) sensitised adsorption to form a mixed film. Certain applications e.g. lubrication and the prevention of fretting corrosion, are discussed in relation to the structure and rate of adsorption of the four types of film. The first requirement for an efficient lubricant film is the chemisorption of the long chain compound as a basic metal soap. The film is considerably strengthened by subsequent adsorption of a less polar compound, such as cholesterol, by process (d). A suitable vehicle for the two compounds is an oil/water emulsion.

In Parts I and II (Schulman and Rideal 1937) it was shown that on injection into the substrate beneath a uniform coherent monolayer of substances in minute quantities, one of two distinct types of interaction could be observed. In one case the injected molecules penetrated the surface film to form a mixed equimolecular monolayer, in the other the injected molecules were adsorbed on to the film to form a double layer, in some cases very rigid or tanned skins being formed by cross-linking. It appeared that in the former case equimolecular complexes were formed between the associating molecules, the term “complex” being used to designate a combination of measurable stability in stoichiometric ratio between the two reactants

Preliminary observation is made of the absorption spectra of four alkali halides (LiF, NaCl, KCl, and KBr) at various intervals after bombardment, at room temperature, with a 2 microsecond pulse of 2 MeV electrons. The absorption is measured spectrographically using an underwater uranium spark light source which can be triggered either “simultanously” with the electron beam or after a predetermined delay of a few microseconds or longer. In addition to the expected intense and persistent F-bands, transient absorption bands in the ultraviolet are observed in all cases, some with lifetimes of the order of a few tens of microseconds at room temperature, and others which persist along with the F-band. These transient bands appear to be due to trapped-hole centres such as the VK-, H-, or V1-centres, which previously have been observed only at low temperatures. Es wurden Absorptionsspektren von LiF-, NaCl-, KCl- und KBr-Kristallen zu verschiedenen Zeiten nach dem Beschus mit einem Elektronenimpuls untersucht. Die Impulsbreite betrug 2 μ, die Elektronenenergie 2 MeV. Die Absorption wurde spektrographisch mit Hilfe einer Unterwasser-Uran-Funkenquelle gemessen. Die Lichtquelle konnte entweder simultan mit dem Elektronenstrahl oder nach einer vorausberechneten Verzogerungszeit von ≧ 10−6 s ausgelost werden. Zusatzlich zu den erwarteten intensiven und stationaren F-Banden wurden in allen Fallen zeitlich veranderliche Banden im UV beobachtet. Einige dieser Banden hatten eine Lebensdauer der Grosenordnung 10−5 s bei Raumtemperatur, wahrend andere Banden ebenso wie die F-Bande zeitlich unveranderlich waren. Die zeitabhangigen Banden scheinen durch Zentren mit angehafteten Lochern, wie z. B. VK-, H-oder V1-Zentren bedingt zu sein, die fur gewohnlich nur bei tiefen Temperaturen beobachtet werden.

THE film technique permits us not only to examine the progress of chemical and enzyme reactions in monolayers but also to investigate mixed films, for example, lipo proteins, and the effects of injecting various reactants beneath monolayers. It has been found1 that the reactions of monolayers of lipoids such as cholesterol with substances injected into the substrate are dependent both on the nature of the polar group and on that of the hydrocarbon ‘tail’ of the injected reactant. Similar conclusions can be drawn as to the extent of reaction with monolayers of proteins. The possibilities in this case are somewhat more complex, for the protein monolayer must be regarded as a triplex system, the extended polypeptide chains separating an upper hydrophobic layer from a lower hydrophilic one, the latter containing the polar groups of the side chains of the protein.

It is shown that multiple readings of thermoluminescent dosimeters can be made by using the ``steady‐state'' phosphorescence brightness at a temperature well below the glow peak temperature. Following such readings the devices can be read in the normal way, with appropriate calibration factors to correct for the partial exhaustion of the phosphor by the phosphorescence readings. The behavior of dosimeters in the phosphorescence method of reading appears to be more dependent on constructional details than in the normal thermoluminescent method.

Since 1967, work has been underway at The Johns Hopkins University, Applied Physics Laboratory and School of Medicine, and also at Pacesetter Systems, Inc., Sylmar, California (since 1969) on a rechargeable cardiac pacemaker that should not have to be replaced during the patient’s lifetime. The most important element of this pacemaker is the rechargeable, space-type, hermetically sealed, nickel-cadmium cell. The concept of using a rechargeable cell for an implantable cardiac pacemaker is not new. Commercial quality, nickel-cadmium cells have been tried unsuccessfully in implantable pacers on several occasions (1,2,3,4). These cells have typically failed in six months or less because they lose their voltage due to a decrease in energy storage capacity when operated at body temperature. However, since the mid-1950’s, the United States space effort alone has provided between 20 and 25 million dollars in research and development funds (not including funds expended for cell production) to perfect the hermetically sealed, nickel-cadmium cell (5). This intensive support has resulted in a cell with vastly improved capability (e.g., low self-discharge) and reliability.

A one-stage technique for creating complete heart block and implanting a permanent cardiac pacemaker in the dog is described. The animal test model has been used in the development of a rechargeable pacemaker system over a five-year period. In vivo testing led to the identification and solution of several problems in the laboratory prior to clinical use of the system.

Surface pressures and potentials of mixed monolayers of dicetyl phosphate-cholesterol, dipalmitoyl lecithin-cholesterol, egg lecithin-cholesterol, and phosphatidic acid-cholesterol were measured. The surface potential is shown to be a more reliable parameter for the study of interactions in monolayers than the surface pressure. Monolayers of dicetyl phosphate-cholesterol follow the additivity rule for area/molecule whereas lecithin-cholesterol monolayers deviate from it. The reverse is true for the additivity rule with regard to surface potential/molecule. Thus, the surface potential indicates that there is no interaction (or complex formation) between lecithin and cholesterol, but that there is ion-dipole interaction between dicetyl phosphate and cholesterol, as well as between phosphatidic acid and cholesterol. The apparent condensation of mixed monolayers of lecithin when cholesterol is added is explained by a consideration of molecular cavities or vacancies caused by thermal motion of the fatty acyl chains, the size of these cavities being influenced by the length and degree of saturation (especially the proportion of monounsaturation) of the fatty acyl chains and the extent of compression of the monolayer. The cholesterol molecules occupy these cavities and therefore cause no proportional increase in area/molecule in the mixed monolayers. Monolayers are liquefied by the presence of cholesterol as well as of unsaturated fatty acyl chains; in contrast, Ca(++)tends to solidify lecithin monolayers. The available evidence suggests that cholesterol can both impart fluidity to the monolayer and occupy the molecular cavities caused by the fatty acyl chains.

SUMMARY: Isotherms of the absorption of polymyxin E by Bacillus subtilis, Pseudomonas denitrificans and Streptococcus faecalis after 20 min. contact with the antibiotic were determined. Tested on seven different bacteria, the maximum amounts of polymyxin E absorbed showed that the polymyxin-sensitive bacteria were capable of absorbing much greater quantities of the antibiotic than resistant organisms. When the bacteria were suspended in buffer solutions, the ultraviolet spectra of their supernatant fluids showeda maximum absorption at 260 mp.; purines and pyrimidines contribute to this maximum. Addition of polymyxin E to suspensions of sensitive bacteria caused an immediate increase in the height of this maximum. Similar treatment of resistant organisms caused very little immediate increase in the amount of 260mp. absorbing material released. On prolonged incubation of untreated and polymyxin E treated cells there was a steady increase in the amount of 260mμ. absorbing cell solutes released into the suspension media. Within the pH range 4.4-7.6 no optimum pH value was found for the polymyxin E absorption process or for the cellular release mechanism. The absorption isotherms of polymyxin E obtained with cell-wall preparations derived from sensitive and resistant bacteria showed that cell walk derived from sensitive organisms bound more polymyxin E than cell-wall preparations from resistant organisms. On treatment of sensitive bacteria with concentrations of polymyxin E less than those required for 99 yo killing in 20 min. at 25O°, there was a linear relationship between the amounts of 260 mp. absorbing material released and the percentage of cells killed. Complete saturation of sensitive organisms with the antibiotic was not necessary to kill the cells. The amounts of polymyxh E. required for 99.5 % killing corresponded closely to those suflicient for the formation of a closely packed monolayer within the bacterial cell wall. It is suggested that, i t these bactericidal concentrations, polymyxin E combines with and thereby disorganizes the structures responsible for the maintenance of osmotic equilibrium within the cell wall.

Surface potentials of mixed monolayers of dicetyl phosphate and eicosanyl trimethylammonium bromide (1:1) were the same on subsolutions of 0.02 M NaCl or 0.01 M CaCl(2), which indicated that ionic phosphate does not interact with Ca(++) in the presence of a neighboring trimethylammonium group. Surface potential-pH plots of dicetyl phosphate, and of dipalmitoyl, egg, and dioleoyl lecithins showed that as the pH of the subsolution is decreased the phosphate groups in the monolayer are neutralized in the order: dicetyl phosphatedipalmitoyl lecithinegg lecithindioleoyl lecithin. The binding of cations (Na(+), Ca(++)) to the phosphate group of lecithin also showed the same order. The binding of Ca(++)) to egg phosphatidic acid monolayers, as measured by the increase in surface potential, is considerably greater than that to egg lecithin. These results suggest that there is an internal salt linkage between the phosphate and trimethylammonium groups on the same lecithin molecule. An increase in unsaturation of fatty acyl chains increases the intermolecular spacing, which reduces the ionic repulsion between polar groups, and hence strengthens the internal salt linkage. The results support the concept of a vertical rather than coplanar orientation of the phosphoryl choline group with respect to the interface. A position has been proposed for Ca(++) in the dipole lattice of lecithin from a consideration of the surface potential measurements.

IT is generally accepted that sodium taurocholate is a good lytic agent for erythrocytes, and a great number of reports on haemolysis by this substance have been published1. Abnormal sigmoid timedilution curves are sometimes reported for taurocholate lysis, and frequent reference is made to the instability of the taurocholate solutions used by these authors. One report2 states qualitatively that a synthetic specimen of taurocholate was “moderately lytic”, whereas a specimen prepared from natural sources was “strongly lytic”. Two other reports3 also give a much lower haemolytic activity for taurocholate than that generally accepted.