G.J. Van Den Berg

The electrical resistance of gold, copper and lead at low temperatures

Summary The resistance curve of the gold wires measured (not very pure) has a minimum. The copper resistances measured show, that it is impossible to apply Matthiesens rule for these resistances. The calculated “ideal” resistance of lead calculated (by means of Matthiesens rule) follows Blochs formula at low temperature. The transition point of lead is 7.20°K.

The magnetization of some nickel alloys in magnetic fields up to 15 kOe between 0°K and 300°K

Abstract The magnetizations of three Ni-Cr alloys (with 0.9, 5.6 and 9.1 at. % Cr), three Ni-Mn alloys (with 2.1, 5.6 and 11.3 at. % Mn) and five Ni-Cu alloys (with 40, 50, 60, 70 and 80 at. % Cu) were measured in magnetic fields (H) up to 15 kOe at temperatures obtained with liquid helium, hydrogen, nitrogen and ethylene, and at room temperature. A dynamic ponderomotoric method was used, in which the magnetization could be determined by measuring time intervals. For the Ni-Cr alloys the slopes of the magnetization versus field curves were at low temperatures different from zero and increased with increasing Cr-content. For the Ni-Mn alloys the slopes of the spontaneous magnetization versus temperature curves increased at low temperatures with increasing Mn-content. The magnetization at 0°K of Ni-Mn 5.6 at. % was nearly equal to that of Ni-Mn 11.3 at. %, which confirmed the occurrence of a maximum in the magnetization at about 9 at. % Mn as observed by Marian. Although the accuracy was rather poor for deciding between a Bloch T 3 2 -law or a T2-law as a description for the temperature dependence of the spontaneous magnetization at low temperatures, there was a tendency for obeying the Bloch T 3 2 -law. The Ni-Cu 60 at. % alloy seemed to have a small spontaneous magnetic moment at helium temperatures, which suggests the presence of holes in the 3d- band above 60 at. % Cu. This can be fitted in a simple band theory picture, which predicts a vanishing of the 3d holes at about 70 at. % Cu, though ferromagnetism might already disappear below this copper content. The magnetizations of the Ni-Cu alloys with 60 and 70 at. % Cu were found to be the same function of H/T at all temperatures except the lowest ones. The anomalous paramagnetic and caloric behaviour of the Ni-Cu alloys with more than 60 at. % Cu could not be explained from the very small, if present, number of Bohr magnetons in the 3d band of the homogeneous alloy, but was attributed to variations of the local Ni concentration (clustering) which gives rise to a superparamagnetism.

Glutamic acid production byArthrobacter globiformis

Two hundred and fiftyArthrobacter strains were tested in a basal salts-glucose medium for their ability to produce glutamic acid; 50 strains produced small amounts of glutamic acid and alanine, as well as traces of other amino acids. Five biotin-dependent strains produced extraordinarily large amounts of glutamic acid. One of these, which was identified asA. globiformis, was selected for further study. Glutamic acid was only produced by this organism at biotin levels suboptimal for growth; maximal production (0.45 moles of glutamic acid per mole of glucose consumed) occurred at a biotin level of 10−5 µg/ml. Other factors which markedly influenced glutamic acid production were temperature, (NH4)2SO4 concentration, and pH of the growth medium.The taxonomy of glutamic acid-producing bacteria and the correlation between biotin deficiency and glutamic acid production are discussed.

STRUCTURE AND ZEEMAN-EFFECT IN THE SPECTRUM OF THE TANTALUM ATOM Ta I

Abstract The analysis of existing wavelength data of the Ta I spectrum results in the detection of 6 ground levels and numerous higher terms, in addition to those reported by previous investigators. The total number of classified lines is now 687. They correspond to combinations between 19 even ground levels and 98 odd high levels. The Z e e m a n-effect is investigated in the region 2500–8500 A and of practically all levels the g-values can be determined. The low terms belong to the configurations 5 d 3 6 s 2 and 5 d 4 6 s ; no levels of 5 d 5 could be detected. The odd levels originate in the configurations 5 d 2 6 s 2 6 p , 5 d 3 6 s 6 p and 5 d 4 6 p , the most important multiplets of which can be identified.

Measurements of the viscosity of He-gas at liquid helium temperatures as a function-of temperature and pressure*

Synopsis Measurements are carried out on the viscosity coefficient of heliumgas at liquid helium temperatures as a function of temperature and pressure. Three different types of apparatus based on the oscillating disc method have been used. The experimental values obtained for the viscosity coefficient as a function of temperature are approximately 10% too high as compared with the theoretical values calculated by De Boer (Physica 10 (1943) 348). The rate of change in the viscosity as a function of pressure agrees very well with the rate of variation found by Ubbink (Physica 13 (1947) 659) for the heat conductivity.

The electrical resistance of gold and silver at low temperatures

Summary In accordance with the earlier measurements 1) the resistance curves of the gold wires measured show a minimum. The “ideal” resistance calculated by means of Matthiessens rule, without taking into account the points below the temperature of the minimum, grows proportionally to T4.2. The minimum shifts to higher temperatures, when the residual resistance grows. One of the samples of pure silver shows a minimum too. The “ideal” resistance, calculated in the same way as for gold, grows proportionally to T4.1.

STRUCTURE AND ZEEMAN-EFFECT IN THE SPECTRUM OF THE TANTALUM ATOM Ta I. PART II

Synopsis The analysis of the Ta I-spectrum is continued. A few ground levels and a great number of high odd levels are found in addition to those given previously. Moreover a group of high even levels is discovered from which the ionization potential is found to be (7.77 0.10) Volt. The total number of classified Ta I-lines is now 1262, corresponding to transitions between 22 even ground levels, 182 odd levels and 8 high even levels. All newly classified lines and Zeeman-effect data are presented. The interpretation of the detected energy levels is revised and extended. Configuration calculations concerning the low even levels, using the method of Racah, are helpful in locating and interpreting a number of them. Typical perturbations are pointed out.

Magnetic susceptibility of some Au-V alloys

Abstract The magnetic susceptibility of some Au-V alloys (0.2, 0.3, 0.5, 1.0, 2.0 and 10.0 at.% V) has been measured from 2 K to 293 K. The temperature dependence of the impurity susceptibility of the most dilute samples (0.2 and 0.3 at.%V) can be described, for T

Measurements on the viscosity of mixtures of helium and argon

Synopsis The coefficient of viscosity of a mixture of helium and argon was determined by the method of the oscillating disc at 291.1°, 230°, 193°, 90°, 81° and 72°K. The maximum in the “viscosity coefficient-concentration of helium” curve appears to shift to higher He-concentrations at decreasing temperatures. The curve calculated with the help of the formula and tables of Hirschfelder, Bird and Spotz (Lennard-Jones 12-6 model) does not quite agree with the experimental curve, but gives less deviations than that calculated by Wilke and Bock.

Measurements on the viscosity of liquid helium by means of the oscillating disc method

Measurements by means of the oscillating disc on the viscosity of liquid helium were done above, around and below the λ-point, in order to clear up the discrepancy between earlier measurements made in the laboratory. Our measurements required preparative measurements on the constant of the oscillating system, on the value of the penetration depth in the liquid, and the accuracy of the determination of the temperature. The viscosity was approximately constant between 4.2 and 2.6°K, contrary to earlier measurements. Between 2.6 and 1.8°K the value diminishes from 28 to 5 micropoises. The passing of the λ-point does not result in a discontinuity of the viscosity. Between 1.8 and 1.3°K the viscosity decreases from 5 μP to 1.3 μP, if the density ρ of the liquid as a whole is used in the calculations and not the density ρn of the “normal” fluid. Below the λ-point a rather good agreement is found for the uncorrected viscosity coefficients between our measurements and those obtained by Keesom and MacWood and by Andronikashivili.