The pressure, P, and their temperature derivative (partial derivative P/partial derivative T)(V), of binary mixture 0.7393H(2)O + 0.2607NH(3) has been measured in the near- and supercritical regions. Measurements were made in the immediate vicinity of the liquid-gas coexistence curve (one- and two-phase regions) using a high-temperature, high-pressure, nearly constant-volume adiabatic piezo-calorimeter. Measurements were made along 40 liquid and vapor isochores in the range from 120.03 kg m(-3) to 671.23 kg m(-3) and at temperatures from 403 K to 633 K and at pressures up to 28 MPa. Temperatures at the liquid-gas phase transition curve, Ts(p), for each measured density (isochore) were obtained using the quasi-static thermograms technique. The expanded uncertainty of the pressure, P. and temperature derivative, (partial derivative P/partial derivative T)(V), measurements at the 95% confidence level with a coverage factor of k = 2 is estimated to be 0.05% and 0.12-1.5% (depending on temperature and pressure), respectively. The direct measured pressures. P, and temperature derivatives, (partial derivative P/partial derivative T)(V), has been used to calculate the internal pressure (or energy-volume coefficient) as (partial derivative P/partial derivative T)(T) = T(partial derivative P/partial derivative T)(V) - P. We also measured the temperature derivatives of the internal energy (partial derivative P/partial derivative T)(V) = C-V (isochoric heat capacity) using the same apparatus. The measurements were made at isochoric heating of the system at quasie-quilibrium conditions. The effect of pressure, temperature, and concentration on the internal pressure was studied. The measured values of pressure (P-S), temperature derivative, (partial derivative P/partial derivative T)(VS), temperature (T-S) and density (rho(S)) at the saturation curve together with isochoric heat capacity measurements were used to calculate other thermodynamic properties of the mixture at the bubble-and dew-pressure points curves. Some unusual "appendix type shape" behavior of the (partial derivative P/partial derivative T)(V) and internal pressure, P,, near the critical and maxcondetherm points (in the retrograde region) was found. (C) 2010 Elsevier B.V. All rights reserved.