code: def lg_solubility_ratio(electrolytes, gas, units=None, warn=True):
      
      if units is None:
          M = 1
      else:
          M = units.molar
      if warn and 'F-' in electrolytes:
          warnings.warn("In Schumpe 1993: data for fluoride uncertain.")
      return sum([(p_gas_rM[gas]/M+p_ion_rM[k]/M)*v for k, v in electrolytes.items()])
docs: Returns the log10 value of the solubilty ratio
  
      Implements equation 16, p 156. from Schumpe (1993)
  
      Parameters
      ----------
      electrolytes : dict
          Mapping substance key (one in ``p_ion_rM``) to concentration.
      gas : str
          Substance key for the gas (one in ``p_gas_rM``).
      units : object (optional)
          object with attribute: molar
      warn : bool (default: True)
          Emit UserWarning when 'F-' among electrolytes.