The Velocity of Sound in Hydrogen when Rotational Degrees of Freedom Fail to Be Excited

Abstract

932J. ELMER RHODES, JR. magnetization, and, therefore, in resistivity, it was necessary to separate this effect from the change in restivity due to domain orientation. Th£ separation was made by the method used by Englert, 19 by extrapolating the p vs. H curve, as illustrated in Fig. 12 for S3 percent nickel. The points for transverse magnetization lie on a straight line permitting easy extrapolation to the demagnetizing field corresponding to saturation; for the specimen of tape used this was small, (N/4:ir)B 8 = 0.047X9800 = 450. The same slope of p vs. H curve was used to extrapolate the longitudinal measurements to H=0.The velocity of sound in parahydrogen, normal hydrogen, and 50 percent para-50 percent orthohydrogen mixtures has been observed at several temperatures, and over a range of frequency to pressure ratio from one to 60 megacycles per atmosphere. Dispersion attributed to failure of the rotational degrees of freedom to follow the temperature associated with the translational degrees of freedom has been observed with all mixtures and at every temperature at which observations were made. Measurements at two different frequencies for similar samples at the same temperature indicate that frequency and pressure affect the velocity of sound only as the quotient, frequency/pressure, with the exception of small corrections C HANGES of sound velocity in some gases with variation of the frequency to pressure ratio have been known for a number of years. These have been attributed to failure of the internal degrees of freedom of the molecules to follow temperature changes in the sound wave. The first phenomenon of this type to be observed oersteds. The results are probably not accurate to less than 0.1 percent, but appear to lie on a smooth curve. The explanation of the shape of the curve is not apparent. On the one hand one might expect the effect to be large when the curie point is low, as it is at each end of the range of alloys studied, because there the change in spontaneous magnetization with field is relatively large. On the other hand, near 70 to 75 percent nickel the crystal anisotropy is zero, and order-disorder phenomena are observed, and there may be some connection, not now established, between these and the effect of spontaneous magnetization on resistivity.I am indebted to Dr. C. L. Dolph and Miss C. L. Froelich for assistance with the mathematics and computations involved in the solution of the energy equation. that must be applied because hydrogen is not a perfect gas. Experiments indicate that the dispersion occupies a greater range of frequency to pressure than would be expected if the rotational specific heat behaved as a simple relaxation phenomenon. It is shown that a simple relaxation phenomenon is not to be expected, and that the dispersion in parahydrogen can be characterized, approximately, by two relaxation frequency to pressure ratios, one for the rotational transition 0-2, and another for the transition 2-4. An expression for these relaxation frequency to pressure ratios, that rough...

Mössbauer Spectra of Tetrahedral Alkali Dithioferrates (III)

“…The existence of a high transition point for KFeS2 at -28° had been shown by Kerler et al 2 All the other compounds gave only the quadrupole split doublet spectra with no magnetic hyperfine splitting, down to liquid-nitrogen temperature. In order to decide the nature of transition involved in KFe~, the magnetic susceptibility vs temperature was studied in all these compounds.…”

On the Rarefied Gas Experiments

“…As in the case of heat conduction [ 23 ], the experimental results are considered as a benchmark problem in order to test the validity and feasibility of the corresponding generalized model. Here, one measurement performed by Rhodes [ 50 ] is discussed in detail. There are many other data in the literature [ 51 , 52 , 53 , 54 ], but this one is going to be sufficient to present all the necessary conclusions and difficulties arising in that field, i.e., how the scaling properties appear, the interpretation of the experiments and more importantly, the role of the material parameters.…”

“…A sonic interferometer [ 55 ] is used to measure the sound speed for various frequency-pressure ratios [ 50 ], see Figure 1 for typical data. The interferometer is placed in a dewar to maintain a constant temperature within.…”

“…It has to be emphasized that the frequency was constant as well in the experiments [ 50 ], i.e., the pressure is varied over the whole interval. More appropriately, it was the density that changed during the experiment when the constant temperature has maintained.…”

“…In Figure 1 , the results related to normal Hydrogen is presented. The measurement is also performed using pure para-Hydrogen and the 50–50 mixture of para-ortho Hydrogen [ 50 ]. Now choosing the curve from Figure 1 corresponding to K. Before making any advancement with the extended models, two essential aspects must be discussed.…”