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The heat liberated by isothermal compression permits the determination of the thermodynamic properties of liquid water−heat capacity, compressibility, and expansivity. The results, as a function of pressure and temperature, have been extrapolated as far down as −40 °C. They confirm the existing data in the region of the supercooled liquid and also the existence of a divergence of the measured properties. This could be explained as a lambda transition occuring at −45 °C on isobars p = 0. The abnormal heat capacity which characterizes this transition is well described as a function of the temperature by a formula with critical coefficients as already suggested by others.

A large optical-aperture membrane diamond anvil cell designed for infrared spectroscopy is described. The cell offers definite advantages compared to existing systems. Other possibilities concerning x-ray diffraction analyses with the cells are mentioned. 0 1995 American Institute of Physics.

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