Dependence of the optical induction on the mechanism of the photochemical thietane formation

The photochemical thietane formation from $\text{3a}$ and $\text{1}$ or $\text{5}$ proceeds with 3 to 4.5 times higher optical purity via the T₁ state of the thiones than via the S₂ state.     

Catalytic—kinetic determination of iodide,manganese and molybdenum with the use of an absorptiostat

The kinetic—catalytic determination of several catalysts by use of an absorptiostatic method is described. The determination of iodide in the range 0.5–5.0 $\text{μg}\text{45 ml}$ is based on its catalytic action on the cerium(IV)-arsenic(III) reaction. The catalytic action of manganese(II) on the reaction of malachite green with periodate was used for its determination in the range 1–10 $\text{μg}\text{45 ml}$. The determination of molybdenum(VI) in the range 10–100 $\text{μg}\text{40 ml}$ is based on its accelerating action on the oxidation of iodide with hydrogen peroxide.     

Gradient expansion of the atomic kinetic energy functional

It is demonstrated that the ground-state atomic kinetic energy functional T[?], where ? is the electron density, can be computed to surprising accuracy from the truncated gradient expansion: T[?] = + T₂[?] + T₄[?], with T_o[?] = $\text{3}\text{10}$(3π²)$\text{2}\text{3}$ ∫ ?$\text{5}\text{3}$ d_τ, T₂ [?] = $\text{1}\text{72}$ ∫ (??)²?^?1 d_τ, and T₄ [?] given by the formula of Hodges. Calculations of T₀, T₂ and T₄ are reported for He with ? both the Hartree—Fock and a very accurate density, and for Ne, Ar and Kr with ? the Hartree—Fock density. For Kr, T₀ + T₂ + T₄ is within 0.3% of the exact Hartree—Fock T, with T₂/T₀ = 0.05, T₄/T₂ = 0.17.     

Dosage de l'histidine: Étude polarographique et dosage du dinitrofluorobenzene

After polarographic study and determination of dinitrofluorobenzene at varying pH and determination of a number of electron exchanges (n), standardization curves have been constructed at pH 5 and 10. They allow the estimation of DNFB to a concentration of 1γ/ml with a precision of 4–7%. The curve shows 2 or 3 leaps, according to pH.. The E_{$\text{1}\text{2}$} of the first two are less than 1 volt.     

The surface tension of liquid copper

The surface tension of liquid copper of 99.999 mass per cent purity has been measured by the sessile drop method in the temperature range 1373 to 1861 K. The least-squares equation expressing the surface tension σ as a function of temperature T is:

$\text{σ(}\text{Cu}\text{)/}\text{mN m}{}^{\mathrm{?}}\text{= (1552±35) ? (0.176±0.023)T/}\text{K}$

The linear correlation of excess surface enthalpy $\text{H}{}^{\mathrm{\sigma }}\text{A}{}^{\mathrm{\sigma }}$ and excess surface entropy $\text{S}{}^{\mathrm{\sigma }}\text{A}{}^{\mathrm{\sigma }}$ per unit area among σ(T) from the literature is also demonstrated. Estimation of $\text{S}{}^{\mathrm{\sigma }}\text{A}{}^{\mathrm{\sigma }}$ via the statistical electron-gas theory of Zadumkin and Pugachewich yields an equation for the calculation of recommended values for the surface tension of molten copper as a function of temperature:

$\text{σ(}\text{Cu}\text{)/}\text{mN m}{}^{\mathrm{?}}\text{= 1497 ? 0.174(T/}\text{K}\text{)}$

.     

The determination of molybdenum and tungsten in sea and surface water

A simple method for the determination of molybdenum and tungsten in sea and surface water is presented. Molybdenum and tungsten are concentrated on activated charcoal by adsorption as the ammonium pyrrolidine dithiocarbamate complex; the optimal pH for adsorption is 1.3. Mo and W are then determined by thermal neutron activation, forming ⁹⁹Mo (T_{$\text{1}\text{2}$} = 66.7 h) and ¹³⁷W (T_{$\text{1}\text{2}$} = 23.8 h), respectively. The ^99mTc daughter of ⁹⁹Mo is measured as soon as the equilibrium between ^99mTc(T_{$\text{1}\text{2}$}= 6 h) and ⁹⁹Mo is established. The detection limits are 0.05 μg Mo l^-1 and 0.05 μg W l^-1 (or 0.001 μg W l^-1 after a simple chemical separation).     

Synthese et proprietes d'oligomeres presentant un nombre variable de fonctions acides

Materials with various contents of grafted acid groups have been prepared by radical addition of thiols to the double bonds in polybutadiene. For their determination, a method involving NMR and determination of $\text{Mn}$ is prepared. The glass transition temperature increases with the content of grafted acid groups. Intermolecular hydrogen bonds have been found by i.r. and viscosity studies. Relations between the ratio of free to bonded carbonyl groups and temperature and between log η₀ and (temp.)^?1 are linear for all samples with a change of slope between 120° and 140°C. This effect is found also for non-functional samples of polybutadiene; it is discussed in terms of the liquid-liquid transition T₁₁ and it is probably due to change in chain conformation.     

An improved absorption correction based on a Gaussian ionization distribution model for electron probe microanalysis

The electron range equation R, employed in a Gaussian absorption correction, is optimized making use of f(χ) values which were calculated from ionization distributions determined experimentally by Brown and Parobek. A new expression of R[R = $\text{(1 + 2}\text{h}\text{)}\text{(1 +}\text{h}$)2.59 × 10^?5(E^1.3₀ ?E^1.3_c)] g cm^?2 is proposed in this paper.The absorption correction using the new electron range equation R is applied to oxygen determination in several silicates and sulfates with greater accuracy than other methods. This equation also predicts one of the most accurate mean depths of ionization at an accelerating voltage of 25 kV for Zn and Cd tracers in Al, Cu, Ag and Au matrices.     

Melting-point purity determinations: Limitations as evidenced by calorimetric studies in the melting region

Typical melting curves, chosen from the results of more than 125 melting-point studies, are presented to illustrate both the reliability and the inherent limitations of the calorimetric method of purity determination. It is shown that this method usually is one of the best means of accurately determining small concentrations of impurity. However, analysis of anomalous melting curves leads to the conclusion that pseudo-equilibrium curves are often obtained as a result of inhomogeneous distribution of impurity in the liquid phase or of non-equilibrium distribution of impurity between the solid and liquid phases. Evidence is given to support the contention that solidsolutions were formed in as many as half of the samples studied and that for this reason, impurity values calculated for perhaps $\text{1}\text{3}$ of the samples are in error by 200% or more. Although these large uncertainties in impurity values usually correspond to less than 0.1 % uncertainty in purity values, modified procedures are proposed to minimize such errors.     

An evaluation of the alkaline p-hydroxybenzoic acid hydrazide procedure for the determination of reducing sugars

The use of alkaline p-hydroxybenzoic acid hydrazide (HBAH) for the determination of reducing sugars in extracts of plant tissues offers an attractive alternative method to those currently employed. The procedure has good selectivity for reducing sugars, a broad temperature range for maximal colour development, tolerance for ethanol concentrations in the sample up to 40% ($\text{v}\text{v}$), and interferences limited to chloroform and to high protein and calcium concentrations. Further, the range of the method is easily adjusted so that reducing sugar determinations may be performed on a macro- or micro-scale.     

Temperature dependence of cage processes in the photofragmentation of phenyl acetate

It was found that the ratio of initial yields of o-hydroxyacetophenone and phenol in the photodecomposition of phenyl acetate in hexane is a linear function of ηT^{$\text{1}\text{2}$} between 224 and 330 K. The observed temperature dependence is ascribed to the competition between combination and disproportionation of acetyl and phenoxy radicals rather than to geminate combination and escape from the solvent cage.     

The isothermal Joule-Thomson coefficient of acetone and of chloroform

Using a flow calorimetric apparatus, measurements of the isothermal Joule-Thomson coefficient of acetone and chloroform have been made over the range 313.15 to 373.15 K. Values of ($\text{B-}\text{T}\text{d}\text{B}\text{d}\text{T}$) obtained from the measurements are found to be consistent with measurements of the second virial coefficient B. For acetone the measurements are also found to be consistent with values of $\text{T}{}^2\text{d}{}^2\text{B}\text{d}\text{T}{}^2$ obtained from the pressure derivative of the heat capacity. Best-fit equations are given, and parameters for the Stockmayer potential are found.     

A method for obtaining potential parameters for helium from T1 measurements

The temperature dependence of T₁ for ³He gas in the range 0–4°K is calculated for a Lennard-Jones (12,6) potential. The relaxation of the nuclear spins is assumed to be due to a dipolar interaction between the nuclei. A minimum value in the relaxation time, T_1,min, is found to occur at a temperature denoted by T_min. By repeating the calculation for different pairs of values of the potential parameters ? and σ, we have found that for a density of 10^?2 g/cm³,σ²T_min = 13.0?1.12 × 10³ ?σ², T_1,min/σ²(T_min)^{$\text{1}\text{2}$} = 17.4?6.56 × 10² ?σ², with ?, σ, T_min and T_1,min in eV, Å, °K and minutes, respectively. From measurements of T_min and T_1,min, ? and σ can be determined.