A. Van Itterbeek

Measurements of the Velocity of Sound in Liquid Argon and Liquid Methane

The ultrasonic velocity in liquid argon and methane has been measured between their boiling and melting points and the ratio of specific heats calculated. The compressibilities and degrees of association have also been calculated and compared with the results obtained for other liquefied gases (hydrogen, helium).

Quelques mesures sur des films minces de nickel

Summary In this paper the results of a research on the properties of thin nickel films formed by cathodic sputtering are given. We specially measured the electrical resistance of these films between 37 °K and 650 °C after the resistances have been sintered during 24 hours. The thickness of these films varied between 30 mμ and 700 mμ. Down to a thickness of 200 mμ the temperature coefficient α = 1/R 0 × dR/dT still showed a sudden drop at the Curie point (360 °C). Fig. 3 gives the dependency on temperature of α for different thicknesses of the films. In fig. 4 is shown how a depends on thickness before and after sintering. From this fig. can be seen that α becomes negative for films thinner than 40 mμ. Figure 5 represents the specific resistance ρ at 0 °C as a function of thickness before and after sintering.

The velocity of sound in liquid argonand liquid nitrogen at high pressures

DURING the last few years we have carried out some measurements on the velocity of sound in liquid argon, liquid oxygen, and liquid nitrogen I-3 in order to obtain thermodynamic data. The earlier experimental arrangement, consisting of an interferometer with variable path length, limited the allowable pressure to about 75 kg/cm 2. In that range the pressure dependence was nearly linear. In order to extend this pressure range appreciably we developed a new apparatus with a fixed path resonator, and new measurements were carried out in liquid nitrogen and liquid argon. These results are compared with those obtained by other authors.

Measurements on the dielectric constant of carbon dioxide as a function of pressure and temperature

Abstract The dielectric constant is measured by using an electrostatic method, on carbon dioxide between 1 atm. and 16 atm. at 0°, 11°, 25°, 40°, 50° and 100°C. The accuracy for the polarisation is 0,01%. Our experimental results agree very well with those obtained by Michels and Kleerekoper, who measured in the high pressure region from 25 atm. We found that the polarisation would possess a maximum at 40°C. Measurements are also made on gas mixtures: CO 2 ue5f8 O 2 , CO 2 ue5f8 CO and O 2 ue5f8 H 2 . Our previous measurements are confirmed.

Measurements on the electrical resistivity of thin nickel films

Dans une publication antérieure, nous avions signalé que le coefficient de température de la résistance électrique des films en nickel était négatif en dessous dune certaine épaisseur critique (40 mµ). Au-dessus de 40 mµ, la courbe «Résistance en fonction de la température» présentait un minimum aux basses températures. A la suite de nouvelles expériences, nous avons constaté que ce phénomène est accompagné dune déviation de la loi dOhm: la résistance diminue quand le courant de mesure augmente. Nous avons pu conclure que ces deux particularités ne sont quindirectement provoquées par la minceur des films. La cause principale est leur état de cristallisation imparfaite. En effet, après avoir subi un échauffement à 150° C pendant plusieurs heures, le coefficient de température négatif change de signe (le minimum disparaît) et la loi dOhm est respectée.

Mesures sur la résistance électrique de films minces en cuivre, en argent et en plomb

Sommaire Nous avons mesure la resistance electrique de films minces (de 10 a 100 mμ) en cuivre, en argent et en plomb. Ces films furent obtenus par decharge cathodique. Leur resistance fut mesuree entre la temperature ordinaire et le point debullition dhydrogene. Nous avons trouve que le coefficient de temperature des films en cuivre et en argent est beaucoup plus petit que celui du metal normal et deviendrait meme negatif pour une epaisseur de 3 mμ. pour le cuivre et de 4,5 mμ pour largent. Le coefficient de temperature des films en plomb est presque egal a celui du metal normal et ne change presque pas en fonction de lepaisseur. La resistance specifique des films en cuivre et en argent peut etre representee par la formule etablie par Hamburger: log ρ = A . log D + B dans laquelle A est egal a — 1,0 et B = −3,3 pour le cuivre et —0,6 et —4,1 pour largent. La regle de Matthiessen fournit des valeurs satisfaisantes pour la resistance residuelle des films en cuivre et en argent, mais ne satisfait pas pour les films en plomb.

Chapter XVII Velocity and Attenuation of Sound At Low Temperatures

Publisher Summary The chapter describes accoustical measurements at low temperatures in different fields. As for the solids, the measurements were concerned with the study of the elastic constants of metals and crystals at low temperatures, and their relation to the temperature variation of the specific heat. Furthermore, measurements were carried out on the velocity and the attenuation of sound in superconductors for the purpose of checking whether a discontinuity appears at the transition point. Measurements on the other condensed gases were done to obtain experimental data about the equation of state of the liquid and also about the calorimetric and thermodynamic quantities like the isothermal- and the adiabatic compressibility coefficient, the ratio of the specific heats, and so on. Furthermore, from measurements on the attenuation of sound in gases like hydrogen and deuterium at low temperatures information could be obtained concerning the relaxation time for the transfer of translational- into rotational energy corresponding to the lowest levels.