cp calculation according to Driesner 2007 et al: 0-1000degC; 0.1-500MPa (doi:10.1016/j.gca.2007.05.026)
function specificHeatCapacity_pTX_Driesner input SI.Pressure p; input SI.Temp_K T; input SI.MassFraction X_NaCl "mass fraction m_NaCl/m_Sol"; output SI.SpecificHeatCapacity cp; end specificHeatCapacity_pTX_Driesner;