  Liquid water exhibits anomalous behavior in the supercooled region. A popular
hypothesis to explain supercooled water's anomalies is the existence of a
metastable liquid-liquid transition terminating at a critical point.
  The hypothesized phase transition is not directly accessible in a bulk
experiment because it is expected to occur in "no-man's" region below the
kinetic stability limit of the liquid phase at about 235 K, the temperature of
homogeneous ice formation. Therefore, verifications of this hypothesis are
usually based on extrapolations from the experimentally accessible region.
  In this work, we present the results of high-resolution adiabatic calorimetry
measurements of cold and supercooled liquid water in the range from 294 to 244
K, the lowest temperature of water's supercooling achieved so far in a bulk
adiabatic-calorimetry experiment. The resolution of the measurements is also
record-high, with the average statistical (random) error of about 0.1 %. The
data are consistent with adiabatic-calorimetry measurements of supercooled
water earlier reported by Tombari et al. [Chem. Phys Lett., Vol. 300, P. 749
(1999)] but significantly deviate from differential-scanning calorimetry
measurements in emulsified water reported by Angell et al. [J. Phys. Chem.,
Vol. 86, P. 998 (1982)] and by Archer and Carter [J. Phys. Chem B., Vol. 104,
P. 8563 (2000)]. Consequences of the new heat-capacity data in interpretation
of the nature of water's anomalies are discussed.
