Journal of Research of the National Bureau of Standards. Section A, Physics and Chemistry最新文献

Experimental measurements of the enhancement factors for mixtures of water vapor and CO₂-free air have been made at -20, -10, and +70 °C. The results, coupled with previous experimental enhancement data, have been used to calculate the second interaction virial coefficients, B _aw , for water vapor air mixtures from -50 to +90 °C. Within this temperature range, an error analysis shows that the uncertainties in B _aw are between 6 and 10 percent. The calculated B _aw · values are used in deriving enhancement factors at 10 °C intervals for -50<t<90 °C, at varying pressure intervals from 0.25 to 100 bar. The associated uncertainties are shown as a function of pressure and temperature. The enhancement factors are extrapolated to -80 °C.

There are several glasses and glass-ceramics available today which have low coefficients of thermal expansion - some near zero. For this reason they often serve as substrates for massive mirrors in orbit. In order for such a mirror to enjoy a lifetime of 5 years or more of diffraction-limited service, the substrate must be dimensionally stable and thereby preserve the original figure. Early in l967, it was decided that the National Bureau of Standards and Corning Glass Works would undertake a joint effort to measure the lengths of small samples of such materials over a period of years. These measurements were completed in 1971. The average length changes in parts per million of the four materials selected are as follows: Corning Code 9623 a glass ceramic- 0.30Corning Code 7971 a titanium silicate- 0.37Corning Code 7940 a vitreous silica- 0.47Corning Code 9622 a glass-ceramic- 1.03.

An analysis of Cu iii based on observations from 500 to 6900 Å is presented. The low structures 3d ⁹ and 3d ⁸4s are complete, including the rarely, if ever before, found 3d ⁸(¹S)4s ²S. The 3d ⁷4s ² includes ⁴F, ²F, ²G, and ²H but the ⁴P, ²P, a ²D, b ²D have eluded all attempts to find them. The ionization potential calculated from 4s, 5s, 6s ⁴ ${}^4{\text{F}}_{4^{1/2}}$ is 296 980 cm_-1 but by a comparison with Ni II which has a longer series an approximate value of 297 140 can be estimated. The 3d ⁸4d group is complete, except for one level, as is 5dbased on ³F and ¹G, the other 5d groups being incomplete. 3d ⁸(³F)4f is complete and 26 levels based on ¹D, ³P, ¹G are known. 3d ⁸(³F)5g is incomplete and a few levels based on ¹D and ¹G have been found. A discussion of the validity of the analysis of Cu iv by J. F. Schröder and Th. A. M. Van Kleef is given.

The enthalpies of combustion and formation of one sample of ortho- and two samples of parafluorobenzoic acids have been determined by combustion in an oxygen-bomb calorimeter. The data obtained by other investigators are discussed briefly. The values obtained and their estimated uncertainties are as follows: [Table: see text] where ΔHc° corresponds to the reaction: ${\text{C}}_7{\text{H}}_5{\text{O}}_2\text{F}\left(\text{c}\right)+7{\text{O}}_2\left(\text{g}\right)+48{\text{H}}_2\text{O}\left(\text{liq}\right)\to 7{\text{CO}}_2\left(\text{g}\right)+\left[\text{HF}+50{\text{H}}_2\text{O}\right]\left(\text{liq}\right).$.

The enthalpy of combustion of cholesterol was measured in an adiabatic, rotating-bomb calorimeter capable of high precision with relatively small samples. The random error for the experimental measurements was 0.006 percent which may be compared with approximately 0.3 percent for prior investigations on this substance. The results obtained for the enthalpy of combustion and the derived enthalpy of formation together with the estimated overall uncertainties are: $\Delta H{c}^{°}\left({25}^{°}\text{C}\right)=-16524.0\pm 3.9\text{kJ/mol}$ $\Delta H{f}^{°}\left({25}^{°}\text{C}\right)=-674.8\pm 4.1\text{kJ/mol}$ The results of prior investigations are discussed briefly.

The enthalpies of combustion of acetanilide and urea have been determined in an oxygen-bomb calorimeter. The following values and their estimated uncertainties were obtained. [Table: see text].

Accurate measurements of the thermal conductivities of Ar and He agree with the theoretical value of 2.5 ϕηc _v (η = viscosity, c _v = specific heat capacity at constant volume ϕ is a number slightly greater than 1 depending upon the intermolecular potential). Measurements of the thermal conductivities of N₂ at 9.6 and 75 °C as a function of pressure up to 2.53 × 10⁷ Pa help to appraise the validity of other measurements of the thermal conductivities of dense gases. The excess conductivity of nitrogen (the additional conductivity resulting from pressure) is shown to be a function of only the density of the nitrogen from 0 to 700 °C and pressures up to 1.3 × 10⁸ Pa.

Heat capacities of two polyethylene samples, one linear with a density of 0.973 g cm^-3 and one branched with a density of 0.91 g cm^-3, have been determined by adiabatic calorimetry from 5 to 360 K in a different experimental arrangement then employed for studies of other polyethylene samples in this series. The heat capacity behavior of these two samples confirms expectations for samples with corresponding densities.

A formal formulation of the differential cross section for x-ray inelastic scattering is given for a real solid, in particular, in terms of the polarization propagator and the inverse dielectric function. The differential cross section is related to the causal functions of electron properties rather than those retarded functions.

The coefficients in van der Poel's equation for calculating the shear modulus of a particulate composite have been greatly simplified, making the calculation much less unwieldy. Approximate solutions of van der Poel's equation are also derived, and it is shown that one of the low order approximations is Kernels equation, or Mashin and Shtrikman's equation for the highest lower hound. The Kerner approximation is often too low in value when the volume fraction of filler exceeds 0.2, but it can he used to provide further simplification in van der Poel's equation, or it can be used as a first approximation in a Newton's method of solution.