Irving Langmuir

The Role of Attractive and Repulsive Forces in the Formation of Tactoids, Thixotropic Gels, Protein Crystals and Coacervates

The formation of tactoids from thixotropic sols, of Schiller layers from iron‐oxide sols, the separation of tobacco virus solutions and bentonite sols into two liquid layers and the crystallization of proteins are regarded as examples of unipolar coacervation (micelles having like charges) which must involve attractive forces.Kallmann, Willstatter, Freundlich, De Boer, Hamaker, Houwink and others have assumed that the attraction is due to van der Waals forces. They have also analyzed the stability of colloid systems by diagrams giving the potential energy as a function of the distance between micelles. It is now shown that the Coulomb attraction between the micelles and the oppositely charged ions in the solution gives an excess of attractive force which must be balanced by the dispersive action of thermal agitation and another repulsive force. Thus there is no need to assume long range van der Waals forces. The past use of energy diagrams is criticized because it has ignored the effect of the thermal agi...

Oil Lenses on Water and the Nature of Monomolecular Expanded Films

A higher hydrocarbon, such as tetradecane, on the surface of water forms a circular lens. The condition for the formation of such stable lenses is that the spreading coefficient FS = γ1 — γ2 — γ12 shall be negative. As the volume of the oil lens is increased, the thickness t at the center slowly approaches a limiting value given by t∞2 = —2Fsρ1/gρ2(ρ1 — ρ2). Equations are given by which FS can be accurately determined from measurements of the radii of large lenses of known volume. The magnitude of the linear tension at the lens boundary is also calculated. Experiments with tetradecane on water at 25°C give FS = —6.2 dynes cm—1 and γ = 26.9. When hydrophilic molecules are introduced into the interface between the lens and the water, they give a spreading force F12 which causes a decrease in — FS and in t. When t<0.1 mm gravitational effects are negligible and the lens degenerates into a duplex film. If such a film is confined by a movable barrier (piston), the force per unit length F exerted on the barrier...

THE PRODUCTION OF RAIN BY A CHAIN REACTION IN CUMULUS CLOUDS AT TEMPERATURES ABOVE FREEZING

Abstract The effect of surface tension in causing the evaporation of the smaller droplets in clouds with simultaneous growth of the larger droplets is an important factor determining the early stages of cumulus cloud droplets. The process is too slow to account for the formation of raindrops. If larger droplets are produced near the top of the cloud by the melting of snowflakes (Bergeron-Findeisen) they may grow to raindrop size by accretion due to coalescence with cloud droplets. A quantitative theory is developed for the efficiency of the accretion process considering the trajectories of the small droplets moving near the surface of the larger falling drop. Heavy rain consisting of large drops frequently forms in tropical clouds which lie wholly below the freezing level (‘warm’ clouds). Large summer cumulus clouds with tops above 23,000 ft, reaching above the freezing level (‘cool’ clouds), after seeding with dry ice have given heavy rain of large drops which reach the ground within fifteen to twenty mi...

The mechanism of the surface phenomena of flotation

This paper deals with the theory underlying the flotation process which is important in the separation of ores. Attention is called to a theory of adsorption and surface tension which greatly aids understanding of flotation phenomena, and which therefore should prove useful in the understanding of flotation. The author adopts the view that condensation, crystallization, surface tension, adsorption, etc., are manifestations of forces of the same kind as those involved in the formation of chemical compounds, and explains flotation by reference to these forces. In a second section of the article a series of experiments with oil films on various surfaces is described. A brief section at the ends returns to the theory of flotation, referring to the implications of his theoretical discussion and experimental results to the formation of froth, the oiling of the solid, and the contact angle of solid particles.

The pressure effect and other phenomena in gaseous discharges

Abstract In the positive column of the mercury are the electrons have velocities distributed in accord with Maxwells law, and the directions of motion are distributed nearly at random. The average velocity of the electrons is approximately independent of the arc current but depends on the pressure. The average kinetic energy of the electrons, expressed in terms of the corresponding voltage, is 3.9 volts at 1 bar pressure, 2.9 at 4.4 bars and 1.7 at 33 bars. Isolated electrodes, or glass surfaces, in the uniformly ionized gas of the arc, become charged 5 to 15 volts negatively with respect to the gas. The wall of the tube thus absorbs all positive ions moving towards it, but repels all but a minute fraction of the electrons, so that these act largely as if specularly reflected from the wall without loss of energy or momentum. The impact of the postive ions on the wall causes a heating effect on the wall which ranges from 15 to 50 per cent. of the total energy in the positive column. The momentum delivered to the wall by the ions is the probable cause of the pressure effect observed by Hamburger and Skaupy by which the pressure of the gas near the anode is greater than at the cathode. Equations are derived by which this pressure effect may be calculated. The results are in rough agreement with the meager experimental data available. Two methods are described for measuring the space potential in ionized gases. The first consists in the use of a hot sounding electrode whose potential is adjusted until the electrons emitted by it are just able to escape. The second is based upon a kink observed in a semi-logarithmic plot of the current voltage curve of a cold sounding electrode, which occurs when the electrode reaches the same potential as the surrounding space.

Über elektrische Entladungen in Gasen bei niedrigen Drucken

ZusammenfassungEs wird eine Theorie der Entladung in Gasen bei niedrigen Drucken entwickelt und durch einwandfreie Potentialmessungen geprüft. Es wird weiter die Geschwindigkeitsverteilung der Ladungsträger gemessen und dem Maxwellschen Gesetz entsprechend gefunden. Es ergeben sich daraus Temperaturen bis zu etwa 800000. Dabei zeigt sich, daß sich die Maxwellsche Geschwindigkeitsverteilung in einem Strahl von anfänglich homogener Geschwindigkeit auf einer viel kürzeren Wegstrecke einstellt, als dies auf Grund der gaskinetischen freien Weglängen zu erwarten ist, und es werden verschiedene Möglichkeiten zur Deutung dieses überraschenden Phänomens diskutiert.

The condensation pump: An improved form of high vacuum pump

Abstract Two new types of condensation pump are described, one built wholly of glass and the other wholly of mental. In these pumps a blast of mercury vapor carries the gas into a condenser. This action is similar to that in a steam ejector and in a Gaede diffusion pump. The method by which the gas is brought into the mercury vapor blast in the condensation pump is based on a new principle which is essentially different from that employed in the steam ejector or Gaede diffusion pump. In the new pumps the gas to be exhausted is caught by the blast of vapor and is forced by gas friction to travel along a cooled surface. By maintaining this surface at such a low temperature that the condensed mercury does not re-evaporate at at appreciable rate, it is possible to keep the mercury vapor from escaping into the vessel being exhausted. The action of this pump therefore de- pends primarily upon the fact that all the atoms of mercury strik- ing a mercury-covered surface are condensed (no matter what the temperature), instead of even a fraction of them being reflected from the surface. It is for this reason that the term condensation pump is proposed. The condensation pump is characterized by extreme speed (3000–4000 Cc. per second, or even more, if desired), by sim- plicity and reliability, and by the absence of lower limit (other than zero) to which the pressure may be reduced. By the aid of this pump pressures lower than 10−5 bars have been produced and measured. To obtain the full benefit of the high speed of these pumps, it is necessary to use connecting tubing of very large size. Equa- tions are given by which the effect on the speed of exhaustion produced by tubing of any given dimensions may be calculated.

An Extension of the Phase Rule for Adsorption under Equilibrium and Non‐Equilibrium Conditions

An adsorption field is defined as a homogeneous part of a solid or liquid surface on which adsorption can occur. In presence of adsorbable components each field contains one or more surface phases. Adsorption experiments have demonstrated that in many cases all the intrinsic properties of an isolated surface phase are variables characterized by C+1 degrees of freedom (F) where C is the number of components. If this surface phase postulate (S.P.P.) applies to each surface phase in a system, then, for a system in a state of complete equilibrium, F has the value F0 = C+S —Pv—Ps+2 where S, Pv and Ps are the numbers of fields, volume phases and surface phases, respectively. By considering the possible mechanisms, such as interphase mobility and vapor interchange by which equilibrium may be attained, this phase rule is extended to states of partial equilibrium, for example, cases where the surface phases and the volume phases are at different temperatures. The effects of electric fields are considered. Non‐equi...

Tungsten Lamps of High Efficiency-I

1. The efficiency at which the larger sizes of tungsten lamps may be profitably run, is limited principally by the blackening of the bulb. 2. It has usually been considered that the blackening of ordinary lamps was due very largely, if not entirely, to the presence of residual gases. The evidence which has led to this belief is discussed. 3. The sources of gases within the lamp are studied, and the principal gases are found to be water vapor, carbon dioxide, carbon monoxide, hydrogen, nitrogen, and vapors of hydrocarbons. 4. The specific effects produced by these and other gases are determined. It is found that water vapor, which has long been known to be harmful, is the only one that produces perceptible blackening of the bulbs. 5. The blackening by water vapor is due to a cyclic process in which the water oxidizes the tungsten and is itself reduced to atomic hydrogen. The tungsten oxide volatilizes and deposits on the bulb, where it is reduced by the atomic hydrogen to metallic tungsten and water vapor is again formed. 6. Attempts to materially improve the life of lamps by the more complete removal of water vapor result in failure. It is therefore concluded that, although water vapor is usually the cause of the short life of poorly exhausted lamps, yet it is not the cause of blackening in well exhausted lamps. 7.

Nature of the Cyclol Bond

THE confirmation by X-ray data1,2 of C2, the A 288-residue cage structure proposed for the insulin molecule3, makes it of interest to consider the nature of the cyclol bond, upon the postulation of which this structure and the cyclol theory of protein structure in general4 depend.The making and breaking of a cyclol bond between an NH group of a polypeptide chain and a CO group of the same or of another polypeptide chain, requires only the migration of an H atom thus: