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THAM, 0.3 M, protected mice from the CNS symptoms of oxygen toxicity at 4 atm. This was shown by the prolonged time required before onset of seizure activity. The same concentration of THAM did not protect at 6 atm. Addition of low concentrations of KCl and NaCl appeared to reverse this protection. A mixture of THAM, 0.6 M, and 0.15 M KCl is lethal to mice.

By inelastic scattering of neutrons, the origin of diffuse X‐ray scattering along [ζ00] directions has been investigated. Phonon frequencies are found to be anisotropic and especially low for the [ζ00] direction. Phonons with low frequencies cause enhanced X‐ray scattering in pronounced diffuse streaks. It is probable that this occurs because a soft optic phonon, which drives the α‐β transition and which has been investigated at q = 0 by other authors, becomes soft very predominantly for the [ζ00] direction and forces down an acoustic dispersion branch. The measured phonons are strongly damped at 560 °C (13° below the transition) so that there is a remarkable tail at zero energy transfer, but elastic scattering as expected from static disorder was not observed. The dispersion for deviations from the [ζ00] direction shows a steep valley, which explains the width of the diffuse scattering perpendicular to the [ζ00] direction. Die Ursache von diffuser Röntgen‐Streuung in [ζ00]‐Richtungen wird mit unelastischer Neutronenstreuung untersucht. Die beobachteten Phononen‐Frequenzen sind anisotrop und in der [ζ00]‐Richtung besonders niedrig. Sie führen zu ausgeprägten diffusen Streifen in der Röntgen‐Streuung und haben ihre Ursache wahrscheinlich darin, daß eine optische Mode, die den α‐β Übergang treibt, vorzugsweise in der [ζ00]‐Richtung weich wird und dabei einen akustischen Dispersionszweig mitnimmt. Die gemessenen Phononen sind bei 560 °C (13° unterhalb des Übergilngs) stark gedämpft, so daß ein merklicher Ausläufer sich bis ω = 0 erstreckt. Rlastische Streuung, wie für statische Unordnung zu erwarten, wird dagegen nicht beobachtet. Außerhalb der [ζ00]‐Richtungen yeigt die Streufläche zu diesen Richtungen hin ein steiles Tal. Das erlrlärt die Breite der diffusen Röntgenstreuung senk‐recht zur [ζ00]‐Richtung.

Die Volumenpolarisation, die man durch die Einwirkung von elektrischen Feldern mit einer Feldstärke bis zu 106V/cm berechnet, sind so klein, daß man nur geringfügige Polarisationen und Verschiebungen der Atome erhält. Sie sind aber mit modernen Meßmethoden der Rüntgen-Streuung an Einkristallen nachweisbar. Im Falle des LiF wird gezeigt, daß die gemessene relative Atom-verschiebung ca. 4·10-3Å beträgt und etwa eine Größenordnung höher liegt als der theoretisch berechnete Wert.

Diffuse streaks have been found in x-ray scattering especially for the [ξ00] directions by H. ArnoId1 and by R. Comes et al2. Preliminary inelastic neutron scattering near the α-β phase transition by K. W. Bauer et a1.3 has shown that these diffuse streaks are due to an anisotropic softening of the phonon branches. Now we have mapped branches in [ξ00] (Г-M) and in M-K directions for energies below 7 THz. In this region there are three optic and three acoustic branches. The highest branch is that which at the Г-point connects to the soft mode (A1; at room temperature 6.3 THz). This soft mode has the eigenvector of the displacement at the α-β phase transformation.4 This optic branch shows a temperature dependence for 0 ≤ q < 0.3, whereas for 0.2 < q ≤ 0.5 (M-point) the two lowest acoustic branches soften. The other branches remain rather unchanged. The dispersion of the temperature dependent modes is measured at (To-T) = 555; 280; 130.5; 60.5; 30.5; 18.5, 7.9, 2.5, -8.5. Along the [ξ00] direction the softening clearly produces a deep valley in the dispersion surface, which explains the diffuse streaks seen in x-ray scattering. Model calculations by T. H. K. Barron and C. C. Huang5 describe the room temperature dispersion curves sufficiently well. For the lowest branch at the M-point we measured the intensity at room temperature at 56 different positions in reciprocal space and found very good agreement with the dynamical structure factors calculated from the eigenvector of the model by Barron and Huang. The frequency of the lowest branch of M (T2-mode) has the same temperature dependence as the lattice expansion ΔL.H. Grimm6 has shown that the lattice expansion is proportional to the order parameter squared; the order parameter δ being a rotation of the SiO4- tetrahedra. Including results of U. T. Höchli and J. F. Scott7 one finds[image omitted] with To - Tc ≊ 10°C. This is the same analytical form as used for Tb2(MoO4)3 by B. Dorner et al, Applying a formulaδ ∼ (T*c - T)βwhere T*c To, we find β = ⅙ for quartz as well as for Tb2(MoO4)3