The pressure inside the chamber was measured by a 100 Ω manganin sensor calibrated using a dead weight piston gauge with a relative uncertainty of 0.05% (Rostocki, Urbański, Wiśniewski, & Wilczyńska, 2005). The manganin sensor resistance was measured using a linear unbalanced resistance bridge (Rostocki & Wiśniewski, 1977). Constant temperature in the chamber (±0.1 °C) was maintained by a thermostatic water bath and a precision thermostat (Julabo Labortechnik, Germany). A copper–constantan thermocouple was placed inside the high-pressure chamber.