A new method of determining the pressure dependence of the Grüneisen parameter is described. The measurements were carried out on NaCl to 33 kbar at room temperature using an end-loaded piston-cylinder apparatus. A fluid cell arrangement with Bridgman unsupported area seals was used. Changes of sample temperature associated with small adiabatic pressure changes were measured and the Grüneisen parameter could be calculated from the thermodynamic relationship γ = (KsT)(∂T∂P)s where Ks is the adiabatic bulk modulus. Our results are in excellent agreement with those reported by Roberts and Ruppin [1] who calculated the pressure dependence of γ from thermodynamic and ultrasonic data and in excellent agreement with those reported by Hardy and Karo [2] who carried out a lattice-dynamical calculation.

The thermal diffusivity of Teflon, sodium chloride, quartz, and silica glass was measured at 40° C to pressures of 35, 18, 30, and 36 kbar, respectively. A transient line source method was modified for use in a piston-cylinder high-pressure cell. Pressure gradients were determined by experiments with bismuth foils. The pressure dependence of the thermal diffusivity at 40°C for the substances studied may be represented as follows (κ in square centimeters per second, P in kilobars): for the low-pressure phases of Teflon, Teflon I-II, P < 5.5 kbar, κ = 0.0012 + 3.6 × 10−5P; for the high-pressure phase, Teflon III, 5.5 kbar < P < 35 kbar, κ = 0.0012 + 8.0 × 10−5 P; for polycrystalline halite, P < 18 kbar, κ = 0.0031 + 9.5 × 10−4 P; for quartz, perpendicular to the c axis, P < 30 kbar, κ = 0.031 + 5.3 × 10−4 P; for silica glass, P < 36 kbar, κ = 0.0068 — 6.7 × 10−6 P. The diffusivity of silica glass decreases with pressure, in contrast to the diffusivity of its crystalline counterpart, quartz, which increases with pressure. In addition to the diffusivity the thermal conductivity of Teflon was determined by measuring the power applied to the heater wire. The thermal conductivity of a Teflon I-II mixture is approximately constant at 0.0075–0.0078 cal/cm s °K to 5.5 kbar. Above 5.5 kbar the conductivity of Teflon III is given by K = 0.0062 + 4.0 × 10−5P. The specific heat of Teflon decreases with pressure and decreases discontinuously by 15% across the Teflon II-III phase change, in good agreement with the decrease predicted from thermal expansion and compressibility data.

A high-temperature cell has been developed in which a weak salt such as NaCl is used as a pressure medium. This cell exhibits extremely low friction. The behavior of the cell was studied in detail by observing the melting temperature of metals by dta over the range 10–60 kbar and 300°–1400°C. Melting temperatures determined on compression and decompression strokes coincide. Friction corrections are eliminated. Transition pressures determined in this cell agree with those determined in gas apparatus over the range of overlap. Comparison with other cells indicates systematic overestimation of pressure in the other dta cells studied. Applicability to geologic phase studies is discussed. Over the range 10–60 kbar the precision of pressure determination in this cell is ±(0.3–0.5) kbar. Absolute accuracy is estimated to be ±(1% + 0.5) kbar.

Isothermal compression data derived from shock-wave and static-compression measurements on metals exhibit a nearly precise linear relation between the logarithm of the bulk modulus and the specific volume up to volume changes of 40%. As a result, solid isotherms can be accurately fitted or extrapolated in this range by means of two parameter functions of either a Birch or a modified Tait form.

The volume compressions of lithium, sodium, potassium, and rubidium, have been determined in a piston cylinder apparatus to 45 kbars pressure. The results are at considerable variance with Bridgman's 1948 measurements. The bulk moduli and some of their pressure derivatives have been estimated by fitting a Murnaghan equation to the pressure volume data, and the results are compared with values obtained from ultrasonic measurements. The static compressions have also been compared with isothermal compressions calculated from the shock Hugoniot measurements.

A differential technique has been used to measure the absolute effect of pressure on the emf of Chromel-Alumel and Pt-Pt10Rh thermocouples. The experiments were conducted in a solid pressure medium piston-cylinder apparatus to 35 kbar and 1000°C. Extrapolation of these data shows Chromel-Alumel to read as much as 28°C high at 50 kbar and 1200°C and Pt-Pt10Rh as much as 28°C low at 50 kbar and 2000°C. Graphs are presented which show correction voltage versus temperature for various pressures.

The Bi III–V and IV–V equilibrium boundaries were studied by monitoring electrical resistance changes. Extrapolation of the III–V data to 25°C yields an equilibrium transition pressure of 77.5 ± 1.0 kbar. The extrapolation also agrees within experimental error with the pressure of 78.2 kbar determined in a separate experiment at 22°C. The use of the transition as a calibration point is discussed, and a procedure for estimating the compression-stroke transition pressure from the equilibrium transition pressure is proposed. This involves adding 2 kbar to the equilibrium pressure at room temperature.

The pressure of the barium I-II transition has been determined in a modified single-stage piston-cylinder apparatus to be 55.0±0.5 kbar at 22°C. Three barium samples of different purity were used and no significant variation of the transition pressure found. The temperature coefficient of the transition pressure is 0–0.015 kbar/°C near room temperature. The effect of the presence of dissolved hydrogen on the transition pressure is discussed.