Index of content:
Volume 11, Issue 2, 01 February 1943
11(1943); http://dx.doi.org/10.1063/1.1723803View Description Hide Description
The most probable distributions of molecular sizes are calculated for certain types of branched‐chain polymers. The results represent an extension of the previous work of Flory, who showed that very large polymeric molecules appear suddenly at a critical extent of reaction, which is predicted to occur very nearly at the experimentally observed gel point. This transition from liquid to gel is shown to be analagous to the condensation of a saturated vapor. It is believed that the size distributions obtained herein will aid in a study of viscosity‐molecular weight relationships in branched‐chain polymers.
11(1943); http://dx.doi.org/10.1063/1.1723804View Description Hide Description
The electron affinity of chlorine has been determined to be 85.84±1.0 kcal./mole by measureing the ratio of ions to electrons leaving a hot tungsten surface in contact with a low pressure of gas containing chlorine atoms. Both Cl2 and SnCl4 were used as carrier gases.
11(1943); http://dx.doi.org/10.1063/1.1723805View Description Hide Description
The usual calculation of the electrical capacity of the double layer from ζ‐potentials is in error because (1) the electrogravitational plane of the outer charge is not at a distance 1/k and (2) the inner charge is not in the ζ‐potential plane. An equation is derived which makes allowance for the distribution of charge on both sides of the ζ‐potential plane. Calculations from ζ‐potentials of glass in dilute aqueous solutions of simple salts give values which increase from about 1μf/cm2 at 10−5 molar to about 25μf/cm2 at high salt concentrations (1 molar). The equations are related qualitatively to electrocapillary phenomena.
11(1943); http://dx.doi.org/10.1063/1.1723806View Description Hide Description
The root mean square lengths of trans‐, cis‐, and random rubber‐like hydrocarbon molecules are calculated. These results are compared with the maximum possible lengths of the trans‐ and cis‐varieties and interpreted from the point of view of recent theories of rubberelasticity. It is found that the cis‐structure should be more elastic than the trans‐structure but the calculated difference is not large. The theory is probably sufficient to account for the properties of polychloroprene as compared to natural rubber, but stearic forces are necessary to explain the lack of elasticity in balata or gutta‐percha.
11(1943); http://dx.doi.org/10.1063/1.1723807View Description Hide Description
Earlier experiments with 15 strong electrolytes have been extended to 38 and there continues to be a striking correspondence between the rate of variation of the partial molal ionic volume with concentration and the rate of variation of water structure as crudely indicated by the x‐ray diffraction pattern. The concentration in mole fraction of the solutions varied from 0.001 to 0.096 having a mean of 0.028. The influences of concentration on adiabatic compressibility and of solubility on the variation of water structure are mentioned. Qualitative explanation of the effect of the ions in solution may be obtained by assuming a direct effect on the breaking of H bonds and the indirect effect of altering the pure temperature expansion of the water.
11(1943); http://dx.doi.org/10.1063/1.1723808View Description Hide Description
It has been shown that the condition of equality of gas and burning velocities, required for stabilization of a flame above a burner, is established near the rim of the orifice or an obstruction within the stream by the effects of friction and inhibition of the explosive reaction. This condition is maintained between two critical gradients of the gas velocity at the solid surface, the lower gradient bordering on the flash‐back and the upper gradient on the blow‐off range. Values of the gradients in the range of laminar flow were determined by hydrodynamic equations from gas flow and tube dimensions; and their independence of tube diameter, except for extreme sizes, has been demonstrated both for upright and inverted flames. In the latter the critical velocity gradient for blow‐off was also found to be independent of the diameter of the centrally mounted wire within a considerable range. The effect of the surrounding atmosphere on the critical blow‐off gradient has been shown. The gas‐flow pattern was studied experimentally by photographing stroboscopically illuminated magnesium oxide dust particles. No appreciable redistribution of velocities over the cross section of the stream was observed below the combustion zone. The burning velocity was found constant over the surface of the inner cone, except at the tip, where it increases to the axial gas velocity, and at the base, where it decreases to zero. The experimental flame cone outline and flow pattern agree with the theoretical within the limitations imposed by simplifying assumptions. The temperature distribution in the flame was determined by the sodium line‐reversal method, only the center of the flame being colored, and observations of the width and emission spectrum of the luminous combustion zone were made. In natural gas‐air flames C–C and C–H bands are observed in the zone, and the temperature rises gradually behind the zone to a maximum that corresponds to the theoretical flame temperature. In natural gas‐oxygen flames no C–C or C–H bands are observed; and the temperature attains a maximum, exceeding the theoretical, immediately behind the combustion zone. Temperature distribution and flow pattern have been correlated. The flow pattern of inverted flames was also studied with particular attention to the region of flame attachment just above the central wire where the formation of an annular vortex is demonstrated. An interpretation of the formation of polyhedral flame cones, described by Smith and Pickering, has been given.