Index of content:
Volume 19, Issue 5, 01 May 1951
19(1951); http://dx.doi.org/10.1063/1.1748284View Description Hide Description
1. The existing theories for non‐isothermal processes are discussed. They can be divided into two kinds, depending upon whether or not they take the flow of heat into account. None are able to predict experimental results.
2. A new hypothesis, ``the principle of thermal interaction'' is introduced by employing Onsager's principle of reciprocity and is expressed in terms of Br⊘nsted's energetics.
It states that there is an interaction between the flow of heat and the transport phenomena in a non‐isothermal process in such a way that the loss of work (loss of potential energy) for the transport of entropy bound to chemical substance can be compensated partly or completely by the transport of free entropy contained in the flow of heat in the opposite direction. The result is that any particle will tend to move against the temperature gradient.
3. The new principle is applied to thermocells with a solid electrolyte, and the results predicted are shown to be in agreement with experimental data.
4. The Knudsen equation, applicable to a thermal transpiration cell, is derived without employing the kinetic theory of gases.
19(1951); http://dx.doi.org/10.1063/1.1748285View Description Hide Description
Calculations are made on the binding energy of H3 using the several methods of calculation based on molecular orbitals. The results are compared to the valence bond‐plus‐ionic‐terms treatment of Hirschfelder et al., which employs the most general linear combination of products of atomic orbitals. The antisymmetrized molecular orbital treatment with configuration interaction is only slightly inferior to this treatment, while the other molecular orbital calculations are considerably inferior. These conclusions probably apply to calculations on more complex molecules.
19(1951); http://dx.doi.org/10.1063/1.1748286View Description Hide Description
An examination is made of the allowed sets of four sp 3‐hybrid orbitals satisfying the symmetry requirements of the point groups C 2v and C 3v , the object of the analysis being to aid in the formalization of the study of deviations from the ideal tetrahedral valence angle, found in systems of symmetry lower than Td. Tables of allowed interorbital angles are given.
19(1951); http://dx.doi.org/10.1063/1.1748287View Description Hide Description
The infrared absorptionspectrum of gaseous SF6 has been investigated from 2 to 25μ with prismspectrometers of high resolution. The frequencies of the infrared active fundamentals found by earlier workers have been confirmed with the exception of one, formerly found at 965 cm−1, which is shown to be at 940 cm−1. However, the remainder of the spectrum differs considerably from previous work. With the aid of the Raman data, the observed spectrum has been interpreted in detail.
19(1951); http://dx.doi.org/10.1063/1.1748288View Description Hide Description
A method is described for the calculation of the dependence of the diffusion coefficient on the concentration of diffusing material from data obtained by studying the rates of sorption of vapors by films. The principle of the method is to approximate the actual concentration dependence by a step function. For such a function the differential equations involved can be solved analytically, and the heights of the individual steps can be computed; the step function is then smoothed out by an averaging process. The method has been tried out for the sorption of isobutane by polyisobutylene at 35°C and found to be quite satisfactory.
19(1951); http://dx.doi.org/10.1063/1.1748289View Description Hide Description
A new theory of turbulent burning velocity has been developed. Comparison of the predictions of the theory with turbulent burning‐velocity measurements has led to recognition that the turbulentflame itself generates additional turbulence. A theory has been formulated to explain the production of turbulence by the turbulentflame, which permits calculation of the intensity of flame generated turbulence. A comparison of calculated maximum turbulence intensity values with the turbulence intensities that correspond to the measuredturbulent burning‐velocity data supports this theory.
19(1951); http://dx.doi.org/10.1063/1.1748290View Description Hide Description
This paper describes a new type of experimental method for accurately measuringdiffusion coefficients in gaseous systems.
The change of composition in the diffusion cell is followed by measuring the change in refractive index with an interferometer. Results obtained using this method compare favorably with some values reported in the earlier literature. In addition, values are reported for new systems not studied previously. A comparison is made between measured values and those calculated from viscosity data.
19(1951); http://dx.doi.org/10.1063/1.1748291View Description Hide Description
Three nine‐bond arrangements which are not forbidden in spd hybridization are described. Of these, the tripyramidal arrangement is discussed in detail since it seems most favorable stericly. In this arrangement there are two types of orbitals, six trigonal prism orbitals and three equatorial orbitals. When the average orbital strength is greatest, it equals 2.983. Some light is thrown on the following structures: TaF7 −2, OsF8, and conjectural OsF9 −.
19(1951); http://dx.doi.org/10.1063/1.1748292View Description Hide Description
Solutions of the Fermi‐Thomas‐Dirac equation are given for 24 different elements. Both neutral atom and positive ion solutions are given. These results were obtained by evaluating the series expansion for the FTD function at small distances from the origin and by numerical integration of the differential equation at larger distances. The numerical solutions were done on the ENIAC.
19(1951); http://dx.doi.org/10.1063/1.1748293View Description Hide Description
19(1951); http://dx.doi.org/10.1063/1.1748295View Description Hide Description
The theory of the concentration dependence of the viscosities of solutions is developed for the dumbbell, rigid rod, and flexible chain macromolecules. Both the intramolecular hydrodynamicinteractions between the monomer units of the same molecule and the intermolecular interactions between monomer units of different molecules are considered. The methods of Riseman and Kirkwood are applied throughout. The numerical result of the calculation for the dumbbell shaped molecule is compared with that obtained by Simha.
19(1951); http://dx.doi.org/10.1063/1.1748296View Description Hide Description
The molecular weight and size of polyacrylic acid in solution have been determined by measurement of light scattering. Use was made of Debye's 90° light scattering method employing two different wavelengths of light.
When the reciprocal specific scattering is plotted against concentration for homopolar polymers, a straight line is obtained which is readily extrapolated to zero concentration. Polyelectrolytes, however, are capable of ionizing in aqueous solution, thus becoming electrically charged by amounts depending upon the concentration. The electrostatic repulsion of the charges very probably affects the molecular size and gives rise to peculiar light scattering curves. By utilizing buffer solutions as solvents, the molecular size is held constant and the difficulties involved in the interpretation of scattering data are largely resolved.
The weight‐average molecular weight of a certain sample of polyacrylic acid at pH values of 1.2, 3, 4, and 5 was found to be 206,000±10 percent. Molecular weight values at a particular pH using a specific buffer were reproducible to about ±3 percent. The remainder of the error was attributed to association of buffer ions with the charged polymer. The size of the particles in solution was found to be less than 550A in the low pH regions, with a definite tendency to increase at higher pH values. The slope of the straight line obtained when the reciprocal specific scattering was plotted against concentration was shown to be dependent upon pH. This dependence of slope may be related to particle size and shape.
In a non‐ionizing solvent such as ethanol, the polymer exhibits scattering behavior typical of non‐ionized polymers. The molecular weight of polyacrylic acid under these conditions was found to be 206,000, in agreement with values obtained in buffer solvents.
19(1951); http://dx.doi.org/10.1063/1.1748297View Description Hide Description
From the observed angular dissymmetry of the light scattered by polymer solutions it has been possible to draw conclusions on the average size of the polymercoil. In general, the actual coil diameter found in this way is much larger than that calculated from a model with free rotation. (For polystyrene in benzene the factor is about 3.5.) This increase in size can satisfactorily be attributed to hindering of rotation around the chemical bonds. In order to obtain information about structural details of this hindered rotation, however, the size determination will have to be combined with evidence derived from other sources than light scattering. As such, the dipole moment, as derived from measurements of the dielectric constant of polymer solutions, obviously is a good choice. If a number of units are connected to each other in a chain, the contribution of the whole chain may be larger or smaller than would be the case if the units were free, depending on whether positions of parallelism or antiparallelism of the elementary electric moments are preponderant, taking the average over all the possible forms the coiling molecule can assume. A theory of this effect has been worked out, and experiments have been carried out. One of the examples is polyparachlorostyrene, for which the average contribution to the polarization of one chain element is substantially smaller in the polymer than that of the corresponding monomer.
19(1951); http://dx.doi.org/10.1063/1.1748298View Description Hide Description
Infrared spectra of thin non‐scattering films of NH3 and ND3 were obtained at −190°C. All four fundamentals of both compounds were observed with no evidence of inversion doubling of ν2. The crystal spectrum of NH3 suggests a frequency near 3450 cm−1 for ν3 in the gas. The spectra are in agreement with a molecular crystal having the reported x‐ray symmetry T 4. Two of the five torsional lattice vibrations were probably observed directly and one more strongly indicated in combination bands. A fourth lattice frequency of 53 cm−1 also occurs in combination bands. Since the coupling between the various internal vibrations and between the lattice and internal vibrations proved to be small, the potential function of the crystal was assumed to be separable into an internal and a lattice problem. A normal coordinate treatment of the internal vibrations fits all frequencies to better than one percent.
19(1951); http://dx.doi.org/10.1063/1.1748299View Description Hide Description
The rate of exchange of water between the hydrated forms of Al+++, Cr+++, Fe+++, Ga+++, and Th+4 and the solvent water has been measured in solutions of varying acidity. With the exception of chromic ion, and of ferric ion at low acidity, the exchange is complete in ca 3 min at 25°. For chromic ion, the half‐time for exchange is independent of acidity over a wide range and is ca 40 hr at 1 M salt concentration. The coordination number of chromic ion for water over the entire acidity range is 6.0. The initial hold‐back of oxygen by ferric ion at low acid is slight and is attributed to the presence of polynuclear hydrolyzed species. For all the cations, the distribution of oxygen isotopes in the final solution is noticeably different from random, the cations showing a greater affinity for H2O18 over H2O16.
The rates of exchange are correlated with the electronic structure, which influences the energy required to form the transition state.
19(1951); http://dx.doi.org/10.1063/1.1748300View Description Hide Description
The macroscopic space charge and potential distributions were determined in a uniform column of 0.0024 N KCl solution during electrolysis by the methods used by Reed and Schriever. The platinumelectrodes were 8×8 cm in area and spaced 40 cm apart; their constant potential difference was 8000 mv.
For the first time, all four space‐charge regions were observed in one column of solution directly experimentally. The maximum negative space charge in the cathode region, 45×10−5 statcoulomb/cm3 at x=0.6 cm, and the maximum positive space charge in the anode region, 40×10−5 statcoulomb/cm3 at x=37.7 cm, both fell within the range of such space charges observed by Reed and Schriever.
The potential gradient between x=10 cm and x=35 cm had the constant value of 13.75 mv/mm. Thus, Ohm's law was obeyed in this region. The mean gradient in the first mm next to the cathode was 1130 mv/mm; that in the last mm next to the anode was 1200 mv/mm. The total fall of potential in these two one‐mm layers was thus 29.1 percent of the total fall of potential between the electrodes. For Zn(C2H3O2)2 and CuSO4 the falls in these two layers were respectively only 1 and 1.06 percent of the total; the greatest value observed by Reed and Schriever was 22.5 percent of the total for NiSO4.
It is pointed out that the shapes of the potential distribution curves cannot be explained by phenomena which occur only at, and very near, the electrodes.
19(1951); http://dx.doi.org/10.1063/1.1748301View Description Hide Description
The photolysis of methylamine has been investigated with the purpose of determining the effect of temperature. To minimize the interference due to polymeric liquid formation, the reaction was studied from −15° to 30°C. The energy of activation of amine disappearance was found to be 6 kcal, a minimum value, but which is probably caused by the effect of temperature on the light absorption. The possibility of ethylene diamine as an intermediate undergoing further decomposition or a polymerization‐condensation reaction evolving ammonia is considered. The rates of hydrogen and ammonia production show previously postulated mechanisms to be untenable.
19(1951); http://dx.doi.org/10.1063/1.1748302View Description Hide Description
The polarization of fluorescent radiation of single crystal of anthracene has been measured and this measurement has been utilized to determine the nature and orientation of oscillators. From this measurement it has been found that the oscillators are linear oscillators and their direction is independent of the direction of the electric vector of the incident light vibration. They make an angle of 33° with the b axis of the crystal.
19(1951); http://dx.doi.org/10.1063/1.1748303View Description Hide Description
Recent experiments have indicated that the quasi‐equilibrium Volmer theory of self‐nucleation fails in some cases to predict when the condensation of water vapor or the components of air will occur in the very rapid vapor expansions in a supersonic wind tunnel. By the obtaining of an approximate solution to the non‐steady Becker‐Döring equation for the self‐nucleation of a super‐saturated vapor, an attempt has been made to determine whether the time lag associated with the approach to the steady state rate of formation of condensation nuclei could account for the discrepancies between theory and experiment. A similar calculation, where the work required to form embryos of the condensing phase was neglected, has been carried out by Kantrowitz. In the present paper the work term has been taken into account to a first approximation. Also considered is the time lag arising from the heating of the nuclei due to bombardment by molecules of the condensing phase as well as the time lag resulting from an accommodation coefficient for the liquid nuclei different from unity.
Calculations of the self‐nucleation of water vapor in air and nitrogen in air have been carried out. From the results it appears that the build‐up time is not appreciably lengthened by inclusion of the work term to a first approximation. The results also indicate that, unless the accommodation coefficient should have a value much lower than what appears to be reasonable from meager experimental evidence, the time lag alone could not account for the existing discrepancies between theory and experiment.
19(1951); http://dx.doi.org/10.1063/1.1748304View Description Hide Description
Under certain conditions, interaction between positively charged metal ions in an alloy may be considered to be of minor importance as compared to interaction between conduction electrons and metal ions. Then it follows that the activity of a solute metal 2 dissolved in metal 1 will be increased by a third component if metals 2 and 3 change the valence electron/atom ratio in the same direction. Conversely, the activity of a solute metal 2 will be decreased by a third component if metals 2 and 3 change the valence electron/atom ratio in opposite directions. Reference is made to the change in the solubility of hydrogen in copper by zinc,tin,aluminum,platinum, and nickel as alloying elements, to the change in the vapor pressure of zinc dissolved in copper by aluminum and nickel, and to the change in the activity of alkali metals dissolved in mercury by thallium.
In addition, an equation is derived with the aid of which one may calculate the change in the activity of metal 2 dissolved in metal 1 due to the addition of a solute metal 3 if the changes in the activity coefficients with composition for the binary systems 1–2 and 1–3 are known and interaction between positively charged metal ions can be disregarded. This relation has been confirmed for the systems Hg–Li–Tl, Hg–Na–Tl, Hg–K–Tl, and Hg–Na–K.