The effect of pressure to several hundred kilobars has been measured on the compressibilities of seven substances having the NaCl (fcc) or CsCl (sc) structure. These include NaCl, KCl, CsCl, MgO, CaO, CaS, and TlI. For the first four crystals a Born—Mayer treatment involving the Madelung energy, van der Waals' terms, and an exponential repulsion (with constants evaluated from initial volume and compressibility) gave a quantitative fit throughout the range. CaO has a measurable lower compressibility at high pressure than predicted from the theory. This effect is exaggerated in CaS. An interesting feature of the behavior of TlI is that although it exhibits metallic conductivity above 160 kbar, there is no measurable discontinuity in the compressibility near this point.

The effect of pressure up to several hundred kilobars has been measured on the lattice parameters of a number of hep metals and alloys including magnesium and six dilute alloys, cadmium and two alloys, two alloys of silver with indium and two with antimony, and the rare-earth metals holmium, erbium, and thulium. For magnesium and its alloys the x-ray data combined with resistance data give rather clear evi dence for a transition at high pressure from hep to dhep (ABABAB---to ABACABAO ••)• Electrical resistance measurements on pure cadmium indicate a similar event. No transition is noted for the cadmium alloys. All four silver alloys underwent a similar transition at high pressure. The rare earths show a highpressure transition accompanied by an increase in the lattice parameter с with increasing pressure, which may be related to those appearing in the group II metals and the silver alloys.T HE effect of pressure to several hundred kilobars has been measured on the lattice parameters of 17 metals and alloys having the hexagonal-close-packed structure (hep) at 1 atm and 25 °C. The materials studied include magnesium and six dilute alloys of mag nesium, cadmium and two alloys, four alloys of silver, and three rare-earth metals. The magnesium and alloys were obtained from C. S. Smith of Case Institute of Technology and from R. S. Busk of Dow Chemical Company. The cadmium, silver, antimony, and indium were 99.99% material from A. D. Mackay. The cad mium alloys with silver were prepared by melting mixed powders of the two in vacuo in a resistance furnace at 650°C. The alloys were annealed for 21 days at 300°C. The samples were filed and the filings reannealed for 48-72 h at 290°C. The silver alloys were prepared by melting in an argon atmosphere in an induction furnace, annealed in vacuo for 23 days at 550°C. The filings were reannealed for 72 h at 550°C. All alloy samples were checked for weight loss at each stage. The compositions of the alloys, the electron to atom ratios, and the one atmosphere lattice parameters for both pure metals and alloys are summarized in Table I.

An apparatus has been developed which permits x-ray powder patterns to be obtained to over 500 kilobars presure. The apparatus is derived in part from the supported tapered piston electrical resistance apparatus in use in this laboratory, but the x rays are transmitted through a thin layer of LiH with suitable platinum collimation. The pressures are established by measuring the change of lattice parameter of a suitable marker mixed with the sample. These changes are then compared with volume changes obtained in shock wave work. Usual markers used to date include silver, rhodium, and palladium. Typical data for sample pressure versus average applied pressure for these metals are given. Also included is the change in lattice parameter with pressure for CsCl to 500 kilobars. The results are compared with the extrapolation of Bridgman's data.

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