Index of content:
Volume 18, Issue 4, 01 April 1950
18(1950); http://dx.doi.org/10.1063/1.1747650View Description Hide Description
To the definition of the state of ``liquid with thermally fixed structure'' is added that of ``liquid with chemically fixed structure.'' Polystyrene is combined with increasing proportions of divinylbenzene. The resulting space network is represented analytically by means of the definition of a mesh width. The second‐order transition temperatures of these copolymers are determined from V—T curves. They obey a function where the constant 586[Me·T] characterizes the stiffening of the polystyrene by the addition of divinylbenzene. These polystyrene space networks are capable of being thermally activated up to a critical mesh width of 4 C atoms. The mesh widths are of varying sizes, the distribution is called the ``polydictiality.'' The mesh distribution function can be obtained from the V—T curves. The capacity of the space network to be thermally activated ceases fairly suddenly. This can be understood from a function of the capacity to be activated. The experimentally determined mesh distribution functions are expressed by means of a Gauss error curve. The width of this curve, about 1.7, is in surprising agreement for all copolymers. This means that approximately 50 percent of all meshes lie around the average mesh width with a variation of ±2 meshes. The method can be applied to all cross‐linked high polymers.
18(1950); http://dx.doi.org/10.1063/1.1747651View Description Hide Description
The moments of inertia of some typical molecules with one internal rotational degree of freedom are obtained for all possible configurations; also the directions of the axes of least and greatest inertia. The dependence on the values of the structural parameters is discussed and illustrated.
18(1950); http://dx.doi.org/10.1063/1.1747652View Description Hide Description
Pleochroism in O–H···O–H bands and > CH2 bands of polyvinyl alcohol is studied in the 0.6–3.7μ‐region, using a quartz recording spectrograph in the 0.6–2.7μ‐region and a high dispersiongrating instrument with a selenium polarizer in the 2.5–3.7μ‐region. Weak pleochroism in the fundamental ν(O–H) bands suggests that either some of the conclusions drawn from x‐ray determinations may be in error or that there may be appreciable departure of the positions of the H atoms from the O–O lines. Dichroic bands caused by bound water are also found in this region, complicating interpretation and perhaps explaining discrepancies between this work and that of Elliott, Ambrose, and Temple. Evidence is presented for the presence of ``free'' carbinol O–H units in the crystalline regions of well‐dried specimens. Pleochroic bands at 2941 cm−1 and 2906 cm−1 are tentatively assigned to > CH2 ν a and ν s fundamentals, respectively.
18(1950); http://dx.doi.org/10.1063/1.1747653View Description Hide Description
A number of organic compounds have been studied for a comparison of photovoltaic behavior and fluorescent properties. No definite correlation could be found between visual fluorescence and the photovoltaic response. The photopotentials were measured by using a platinum point as the irradiatedelectrode connected to a vacuum tubeelectrometer. The irradiatedelectrode is assumed to act as a collector in the ``space charge'' of the photoactive molecules. Both positive and negative photopotentials were obtained. Compounds possessing a carbonyl group adjacent to an aromatic nucleus invariably produced a positive photopotential.
18(1950); http://dx.doi.org/10.1063/1.1747654View Description Hide Description
The effects of pressure, temperature, and exciting intensity on the lifetime of fluorescence of acetone and biacetyl vapor have been investigated. The pressure dependence of the lifetime in acetone was interpreted in terms of the formation of double molecules, and part of the temperature dependence was interpreted in terms of the formation of double molecules. The lifetime in biacetyl was found to be independent of pressure at a constant temperature, but dependent on temperature. The effect of oxygen on the lifetime in biacetyl was explained by assuming a simple Stern‐Volmer mechanism for quenching. The lifetimes of fluorescence in both acetone and biacetyl were found to be dependent on the incident intensity. This effect was explained by assuming that the fluorescing molecules of both compounds were quenched by the products of photochemical decomposition.
18(1950); http://dx.doi.org/10.1063/1.1747655View Description Hide Description
The lifetime of fluorescence of solid acetone was found to be a function of temperature, and of an unknown parameter which was interpreted as the state of aggregation of the sample. Both of these effects were interpreted in terms of the exciton theory, in which a quantum of electronic excitation energy is capable of wandering through the crystal before it is emitted as light.
18(1950); http://dx.doi.org/10.1063/1.1747656View Description Hide Description
An absorption band of low intensity has been found in the 2800 to 3400A region for solutions of melamine, trimethylol melamine, trimethyl ether of trimethylol melamine, hexamethylol melamine, and cyanuric chloride. The band has also been observed in gaseous melamine at elevated temperatures. The band is believed to be due to a singlet‐triplet transition, rather than analogous to the 2600A absorption system of benzene.
18(1950); http://dx.doi.org/10.1063/1.1747657View Description Hide Description
A single exposure photographic method for the measurement of depolarization factors in Raman spectroscopy is described. The accuracy of the results was tested by measurements with carbon tetrachloride and chloroform. The depolarization factors found for highly polarized lines were in good agreement with those given by the photoelectric method rather than with those of other photographic investigations.
18(1950); http://dx.doi.org/10.1063/1.1747658View Description Hide Description
The limitation placed upon the stroboscopically illuminated particle method of measuring the normal burning velocity by the heat capacity of the particles is discussed. A supplementary method of measuring the normal burning velocity using a modified Gouy procedure is presented. The line between the dark and light spaces on shadow photographs, taken at different distances from the flame to the film, is used in this method to define the flame area. This area is then extrapolated to the diametral plane of the flame. This procedure gives results that are consistent with the particle method of determining the normal burning velocity and its use is justified empirically. Burning velocities of propane‐air flames are given.
18(1950); http://dx.doi.org/10.1063/1.1747659View Description Hide Description
To facilitate the calculation of the thermodynamic properties of internal rotators lying outside the limits of available tabulations, methods of determining the energy levels are studied for the purpose of finding the most expeditious route to accurate results. It proves to be unnecessary in any case to calculate many levels from the wave mechanics. A partition function is set up in terms of the correct ground state and a series of approximate levels derived from the old quantum theory, and this is corrected to constancy by the successive substitution of correct levels, starting with the first excited state. A set of levels obtained in this way which gives the correct partition function always leads to correct values of all the thermodynamic properties.
To obtain accurate energy levels, the continued fractions of Koehler and Dennison are recommended as most convenient.
18(1950); http://dx.doi.org/10.1063/1.1747660View Description Hide Description
From the Gibbs theory of surface tension general equations are deduced for the change of surface tension with curvature in the system having an arbitrary number of components but no insoluble surface film. For the special case that the surface layer is spherical, the equations are shown to be reducible, by an appropriate choice of auxiliary Gibbs surfaces, to a simple form identical with that recently found by Tolman for the system of one component. Some of the consequences of physical interest following from the equation for the spherical surface layer are pointed out.
18(1950); http://dx.doi.org/10.1063/1.1747661View Description Hide Description
The appearance potentials of some metastable transition peaks in normal butane, isobutane, the butenes, and 1,3‐butadiene have been studied along with the parent ions in each metastable transition. A comparison shows that in most cases studied, an additional energy of about 2 ev is required for the formation of the metastable state. However, in the case of normal butane, two transitions were studied in which no additional energy was required within an experimental error of 0.3 ev. Evidence is presented which indicates that in some cases the appearance potentials of ions in hydrocarbon spectra are affected by these metastable ion contributions. This effect may account for some of the unexplained discrepancies found in published data on hydrocarbon gases. Check values of some ions in methane, ethane, and propane were taken to determine the performance of the instrument. A comparison of these results is made with previously published data.
18(1950); http://dx.doi.org/10.1063/1.1747662View Description Hide Description
The ratio cp/cv at room temperature has been determined for He, A, H2, N2, O2, CO2, N2O, SO2, CH4, and C2H4 by a method of self‐sustained oscillations. The results are reproducible to within 0.1 percent and agree with the best values reported by other observers to within 0.1 percent. The method requires the measurement of a temperature, a pressure and a period of oscillation. The theory of the self‐sustained oscillations has been developed to include the effects of the mass of the oscillating gas, damping, heat conduction, and the departure of the behavior of actual gases from the ideal gas law.
18(1950); http://dx.doi.org/10.1063/1.1747663View Description Hide Description
The low velocityscattering of H+, H2 +, and H3 + in both normal and isobutane has been measured at ion velocities of less than 150 volts. Ion neutralization was detected and measured for all three ions in both hydrocarbons. The potential functions between the ion and molecule as evaluated from the elasticscattering have been obtained for all three ions in both hydrocarbons. For H+ these functions in both hydrocarbons have the same form with the same values of the exponent over the same range of distance. The force constant, however, is considerably greater for the branch chain compound. For certain ranges of distances the potential functions of the three different ions in both of the hydrocarbons show values of the exponent less than 4. For substances possessing no permanent dipole similar results have previously been obtained only in those cases where there is a potentiality of chemical combination.
18(1950); http://dx.doi.org/10.1063/1.1747664View Description Hide Description
The infra‐red spectrum of C2Cl4 through long paths has been obtained in the region 2.5–25μ. As many combination tones as possible were observed. An assignment of the fundamentals has been made which interprets satisfactorily 16 lines in the Raman spectrum and 24 bands in the infra‐red spectrum.
18(1950); http://dx.doi.org/10.1063/1.1747665View Description Hide Description
The ratios of the partition functions of the tritium halides to their respective protium halides have been calculated. These are combined with one another to give the exchange equilibria between the six pairs of tritium and protium halides. The exchange equilibria with water are calculated. From the exchange equilibria between the tritium halides and protium and the free energy of dissociation of the protium halides, the dissociation equilibria of the tritium halides have been calculated.
The experimental data on the dissociation of HI are reviewed and it is shown that the data of Taylor and Crist on DI and HI are self‐consistent as well as in good agreement with theory. The heat of formation of HI at absolute zero, ΔH 0 0, is found to be − 1007±10 calories per mole.
18(1950); http://dx.doi.org/10.1063/1.1747666View Description Hide Description
The infra‐red absorptionspectrum of gaseous 1,1‐difluoro−2,2‐dichloroethylene between 2 and 22.6μ has been investigated with a prism spectrometer of high resolution. The Raman spectrum of CF2:CCl2 in the liquid state has been photographed with a three‐prism glass spectrograph of linear dispersion 15A/mm at 4358A. Quantitative polarization measurements have been made. The 12 fundamental vibration frequencies have been assigned, and the observed vibration spectra have been interpreted in detail.
18(1950); http://dx.doi.org/10.1063/1.1747667View Description Hide Description
The kinetics of the migration of sodium ions through crystalline quartz plates has been studied. This migration, which was induced by an electric field, is assumed to take place through tunnels inherent in the crystal structure and parallel to the principal axis of the quartz. It was shown that the only important mechanism of current flow is the migration of sodium ions through the quartz plate. The activation energy is from 22 to 25 kcal. and depends upon the potential gradient. The rate of migration of the sodium ions is essentially independent of the concentration of the sodium ions.
18(1950); http://dx.doi.org/10.1063/1.1747668View Description Hide Description
The mercury photosensitized reactions of methyl alcohol have been investigated at pressures of 30 and 100 mm Hg and over a temperature range from 25° to 500°C. Below 400°C the products are almost entirely hydrogen and ethylene glycol and small amounts of carbon monoxide, formaldehyde and methane. It has been established that the primary step in the reaction mechanism is . There is considerable supporting evidence that the alternative split into H+CH3O does not occur.
Above 400°C the rates of production of CH2O and CO become significant and increase with rising temperature which has been explained by the fact that the decomposition of the CH2OH radical is taking place. An activation energy of 29 kcal. has been obtained for this decomposition reaction.
On the Photographic Reciprocity Law Failure and Related Effects. II. The Low Intensity Sequence Effect18(1950); http://dx.doi.org/10.1063/1.1747669View Description Hide Description
A quantitative theory of all details of the low intensity sequence effect is given on the basis of the following assumptions. A monatomic Ag speck is unstable against thermal agitation, a diatomic speck is stable, but for development a speck of more than two atoms is required. The theory is based on that for low intensity failure as developed in paper I.