Conductivity of Sodium-Ammonia Solutions

Abstract

has reported the occurrence of superconductivity in quickly frozen solutions of sodium in ammonia. In view of the fact that all other superconductors have transition points of the order of 5°K, corresponding to an excitation energy of 5X10~4 ev, the appearance of superconductivity at very much higher temperatures (about 200°K) is somewhat unexpected.We have repeated Ogg's conductivity experiment on a number of concentrations ranging from 0.7N to 2N and noted in agreement with his work that the resistance drops very appreciably on freezing. However by making a current and potential measurement we found that the small residual resistance was caused by the solution itself, and not as Ogg suggests by a contact resistance at the electrodes.It might be mentioned that Ogg's interpretation of the observed magnetic moment in a ring is not necessarily as conclusive as may appear at first sight. If a ring is frozen in a magnetic field and the field subsequently switched off, a magnetic moment due to paramagnetic regions within the material which have lost their ability to reorientate themselves could be mistaken for a persistent current. A more conclusive test is to freeze a ring in zero magnetic field and to attempt to induce a current by switching on and off a strong magnetic field. However, in a considerable niimber of experiments on rings with the concentration range stated above, we were unable to observe a residual magnetic moment with either technique of inducing a persistent current. Richard A. Ogg, Phys. Rev. 69, 243 and 544 (1946 I N a recent Letter to the Editor on the above subject, K. Sun 1 has pointed out that if Bethe's 2 calculation of the mass of the neutron is repeated, using Mattauch's 3 more recent values for the H^-D mass difference and the H 1 mass, a slightly lower neutron mass results. The value he obtains is 1.008 92 db0.000 04 as compared to Bethe's 1.008 93=b0.000 05. In the calculation, however, Sun used the same value as Bethe for the deuteron binding energy, namely 2.17±0.04 Mev, the uncertainty in this quantity being the main source of uncertainty in the neutron mass.The binding energy of the deuteron is now known more accurately than the above figure indicates and the more recent results should be used in the calculation. Wiedenbeck and Marhoefer 4 give 2.185 ±0.006 Mev for the deuteron binding energy. This latter value, together with Mattauch's 0.001 539 ±0.000 0021 mass unit for the H2 X -D difference, give the neutron-proton mass difference directly as 0.000 807±0.000 0068 or 751 ±6.3 Kev. Using the H 1 mass of Mattauch (1.008 130±0.000 0033), we then get a neutron mass of 1.008 93 7 ±0.000 0075. Thus the final mass, instead of being about 9 Kev lower than Bethe's value, and with an uncertainty of 37 Kev, is 6.5 Kev higher, with an uncertainty of only 7 Kev. i K. Sun, Phys. Rev. 69, 240 (1946). 2 H. Bethe, Phys. Rev. 53, 314 (1938). s J. Mattauch, Phys. Rev. 57, 1155 (1940).

Low temperature physics

“…A similar relation had already been obtained for the helium film by Bijl, de Boer and AIichels (1941) and by Gogate and Rai (1944). Daunt and Mendelssohn (1946a) have pointed out that this relation appears to be a direct consequence of a diffusion of the superfluid constituent under its zero point momentum. An experiment designed to prove the existence of such a mechanism has given a positive result (Daunt and Mendelssohn I946 b).…”

“…I n the latter type of experiment the film flow is always limited by this critical rate which, on the other hand, is independent of the level difference. I n order to determine the differencein gravitational potential at the ends of the film, Daunt and Mendelssohn (1946b) employed a device in which the flow occurred at less than the critical rate, Under these conditions it was found that within the limit of accuracy the potential difference at the ends was zero; it was less than 15 times smaller than the level difference required to accelerate the helium to the observed velocity by free fall. -4tkins (1948) has found a film flow of a higher rate than that previously observed ; this also depended on the liquid level when, instead of a beaker, a bulb with a narrow neck was used.…”

Highly conducting states in metal–ammonia solutions

“…The Ðrst to report on an apparent superconductivity was Ogg,2 who observed long-lasting ring currents in the classical Kamerlingh Onnes experiment with frozen MAS. The e †ect was subsequently conÐrmed by Hodgins3 and Verkin et al,4 but could not be reproduced by Boorse et al, 5 Daunt et al 6 and Giulotto and Gigli. 7 No evidence of Ñux expulsion or of truly persistent currents was obtained.…”

Conductivity of Sodium-Ammonia Solutions

“…1 A graybody comparison, in the spectral region occupied by the band, approximately 9 mu to 10 mu, is then made between the radiation intensity of the earth's surface (thermocouple) to space and the return radiation intensity of the ozone layer. 1 The method is a promising one, for even the preliminary, very low resolution spectra yield essentially correct temperatures. The temperature of the ozone layer is found to be -44°C and -53°C for the evenings of September 5, 1941 and November 3, 1941, respectively-8…”