Tests are made comparing the results of EC (HaltaFall)
with those of PhreeqC version 3
  https://www.usgs.gov/software/phreeqc-version-3
using either the Davies eqn. or the SIT to calculate
activity coefficients.

For the Davies eqn. the same equilibrium constants are
used (mostly from the Wateq4 database).

For the SIT, the same epsilon values and equilibrium
constants are used:
  Thermodynamic database ANDRA/RWM - THERMOCHIMIE-TDB
  (www.thermochimie-tdb.com)
  Version 9b0
