Unit conversion problem

[GeertD]

Hi,

Two issues regarding units.

Unit conversion for ionic species:
The methods: sol.total(), sol.total_element(), sol.activity() all allow to convert the units:
sol.total('C', units='mg')

This works great, but fails for ionic species:
sol.total('CO3-2', 'mg') >> ERROR

It looks like the convert_units() method called, cannot handle the valence at the end.
This works fine, and return the right value:
sol.total('CO3', 'mg')

I would suggest to change the convert_units() so it can handle ionic species as well.

Volume and weight specific units:
PhreeQC calculates with absolute amounts of components (mol) and solution (kg water, kg solution, L solution).

Typically, a solution will have 1.0 kg water (default), unless specified otherwise.
Therefore, sol.total(species) returns unit: mmol. Most likely equal to: mmol/kgw.

To be sure about the concentration units, one would have to do:

m_water = sol.mass		>> kg water (not kg solution)
m_sol = sol.density * sol.volume		>> kg solution
sol.total(species)/m_water		>> unit: mmol/kgw
sol.total(species)/m_sol			>> unit: mmol/kgs
sol.total(species)/sol.volume	>> unit: mmol/L

Same for other units (umol, mol, mg, g, ... ).

As a user, we typically want the concentration, not the absolute amount.
It would be very handy if the convert_units() method (called by sol.total(species)) could also convert to units like: mmol/kgw, mmol/kgs, mmol/L and the other ones (umol, mg, g, ... ).

Best regards,
Geert