Volume 15, Issue 8, 01 August 1947
Index of content:
15(1947); http://dx.doi.org/10.1063/1.1746588View Description Hide Description
Gelatino‐silver halide photographic films increase in electrical conductivity on exposure to light at intensities corresponding to exposures within the normal photographic range, and above. The spectral distribution of this change in conductivity in films containing, respectively, photographic sensitizing dyes, and no dye, is found to be parallel with the spectral distribution of photographic sensitivity— the wave‐lengths of maximum and minimum sensitivity in the two effects are identical and coincide with absorption maxima and minima, and there is a general parallelism in the efficiency of a dye in sensitizing the two effects to light not absorbed by the silver halide. The conclusion is drawn that the observed changes in conductivity represent a photo‐conductivity originating in the photo‐liberation of electrons within the silver halide, the primary act of the photographic process.
The photo‐currents are proportional to the applied field up to strengths of at least 140 volts per millimeter, and at intensities of illumination within the normal photographic range and somewhat above, are proportional to the intensity. At still higher light intensities, the photo‐currents verge towards a dependence on the square root of the intensity. The change in the intensity relation is interpreted as representing the passage from a situation, at low intensities, in which most of the electrons are captured by foreign traps to that, at high intensities, in which recombination with bromine atoms predominates.
It is shown that a sensitizing dye acts by causing the liberation of an electron within the conduction band of the silver halide under the stimulus of light absorbed by the dye but whether the process involves direct electron‐transfer or energy‐transfer is left open.
Determination of the Ranges of the Fission Fragments Emitting Delayed Neutrons. Chemical Identification of the 4.51‐Sec. Delayed Neutron Activity15(1947); http://dx.doi.org/10.1063/1.1746590View Description Hide Description
The ranges of the fission fragments leading to delayed neutron emission have been determined by absorbing the fragments in Al and counting the penetrating activity. The delayed neutron activities and their corresponding ranges in Al corrected for source thickness are: 4.51 sec., 4.05±0.03 mg Al/cm2; 55.6 sec., 3.98±0.06 mg Al/cm2; 1.52 sec., 3.63±0.12 mg Al/cm2; 22.0 sec., 3.21±0.04 mg Al/cm2. Comparing the range of the 4.51‐sec. activity with that of the 55.6‐sec. Br, one finds that mass assignments possible for the 4.51‐sec. activity are 86 to 90. Similarly, the range of the 1.52‐sec. activity is compared to that of the 22.0‐sec. I, and the possible mass assignments found are 129 to 135.
Chemical separation of Br from irradiated uranyl nitrate resulted in the identification of the 4.51‐sec. activity as an isotope of Br.
15(1947); http://dx.doi.org/10.1063/1.1746591View Description Hide Description
The infra‐red spectrum of gaseous ketene has been studied from 2.5μ to 25μ with a spectrometer using LiF, NaCl, and KBr prisms. A perpendicular band at 3162 cm−1 with components relatively free of perturbations has been resolved, and the intensity alternation associated with the twofold axis observed. All fundamental vibrational frequencies have been assigned. A normal coordinate treatment of the general H 2 XYZ molecule has been made and reasonable force constants for ketene calculated.
15(1947); http://dx.doi.org/10.1063/1.1746593View Description Hide Description
Thermal Properties of Cyclopentane and Its Use as a Standard Substance in Low Temperature Thermal Measurements15(1947); http://dx.doi.org/10.1063/1.1746595View Description Hide Description
The thermal properties of cyclopentane were redetermined in the Penn State isothermal calorimeter and adiabatic calorimeterB′ and the results compared with other investigations. It is concluded that the heat capacity results of Penn State adiabatic calorimeterB′, those of the National Bureau of Standards, and those of the Bureau of Mines Laboratory at Bartlesville, Oklahoma, are in satisfactory agreement, under normal operating conditions, above 30°K.
15(1947); http://dx.doi.org/10.1063/1.1746597View Description Hide Description
The heat capacity of benzene vapor was measured at two or more pressures at each of five temperatures in the range 68° to 198°C; and values of Cp o, the heat capacity in the ideal gas state, were obtained. By assuming a moderate degree of anharmonicity of the vibrations, it was possible to obtain excellent agreement between values of Cp o calculated statistically from spectroscopic data, and the observed values. An empirical equation for the second virial coefficient of benzene vapor was obtained from the observed values of (∂Cp /∂P) T , and heat of vaporization and vapor pressure data.
15(1947); http://dx.doi.org/10.1063/1.1746599View Description Hide Description
The differential equations are solved for the time‐dependent flow of heat through a composite cylinder. The composite cylinder is assumed to be thermally insulated at the outer boundary and to consist of a cylindrical core, initially at the uniform temperature U 0, surrounded by a cylindrical shell, initially at temperature zero. Included in this paper are corresponding treatments for composite slabs of finite and infinite widths.
15(1947); http://dx.doi.org/10.1063/1.1746601View Description Hide Description
The distribution of frequencies of normal modes of vibration of a monatomic square lattice is obtained as a function of the force constants of the lattice. Since the forces between pairs of atoms in the lattice are short ranged, interactions between all atoms, other than nearest and next nearest neighbors, are neglected.
Two constants, α and γ, are used to describe the lattice. α is a force constant derived from the interaction of nearest neighbors, and γ is that derived from the interaction of next nearest neighbors.
According to the Debye continuum theory the frequency spectrum, or density of normal modes, should be a linear function of the frequency. In the Born‐Karman atomic model used in the present paper it is shown that this is only the case at very low frequencies and that there actually exist two sharp infinities in the frequency spectrum.
We define g(ν) so that g(ν)dν is the number of normal modes of vibration with frequencies between ν and ν+dν. A closed expression involving complete elliptic integrals is obtained for g(ν) when τ=[1+(α/2γ)]−1=⅓. For general values of τ<½, g(ν) is shown to have the following properties:
(a) The largest frequency, ν L , occurs atwhere M=mass of each atom.
(b) There is an infinity in g(ν) at ν=ν L τ½.
(c) The second infinity is at , and .
(d) As ν/ν L →0, g(ν) is linear in ν.
The Application of Ultrasonic Waves to the Study of Electrolytic Solutions I. A Modification of Debye's Equation for the Determination of the Masses of Electrolytic Ions by means of Ultrasonic Waves15(1947); http://dx.doi.org/10.1063/1.1746602View Description Hide Description
Debye's equation for the alternating potential which should accompany the passage of ultrasonicwaves through an electrolytic solution is modified and extended by the addition of terms representing corrections for relaxation forces, electrophoreticeffects,thermal diffusion, and the pressure gradient associated with the material wave.
15(1947); http://dx.doi.org/10.1063/1.1746604View Description Hide Description
The absorption spectra of triborine‐triamine or borazole, B3N3H6, has been studied with a fluorite vacuum spectrograph in the region 2250–1700A in n‐heptane solution. The compound was prepared by the reaction between diborane and ammonia.
Four diffuse bands are found, starting at 1995A, with spacing about 900 cm−1. These seem analogous to the 2000A bands of benzene, but the intensity is about 10 times smaller. A strong continuum, like the 1800A benzene peak, has its maximum at 1720A or below. No bands like the benzene 2600A group were found, though they would have been seen if their intensities had been only 1/20th that of the latter.
The spectrum of a boron hydride, B5H9, has also been obtained but shows only a featureless continuum in this wave‐length region.
15(1947); http://dx.doi.org/10.1063/1.1746606View Description Hide Description
Commitments regarding additional research on the properties of water in the region below 200°C made on the occasion of the Third International Conference on Steam Tables in 1934 have been largely completed. Correlation of all new data using James A. Beattie's determinations of the relation of the International temperature scale of 1927 to the thermodynamic scale discloses a high degree of thermodynamic consistency from 0° to 150°C between thermal data, vapor pressures, and equation of state information. The proposed vapor pressures over the temperature range are probably accurate to ±0.002°C. New measurements of vapor pressure over the range are, however, desirable but the ultimate in refinements of temperature control and pressure accuracy should be sought if the indicated discrepancies are to be resolved. Tables of vapor pressure, pressure‐temperature derivatives, essential temperature‐scale magnitudes, enthalpies, and entropies are given. An equation of state for steam is reported from 0° to 460°C, valid for low pressures and based on the ensemble of volume data and enthalpypressure coefficients available.
- LETTERS TO THE EDITOR
15(1947); http://dx.doi.org/10.1063/1.1746608View Description Hide Description
15(1947); http://dx.doi.org/10.1063/1.1746610View Description Hide Description
15(1947); http://dx.doi.org/10.1063/1.1746613View Description Hide Description
15(1947); http://dx.doi.org/10.1063/1.1746615View Description Hide Description