Remove zero-concentration ions from solutions.

ionize/Solution/__init__.py

@@ -111,8 +111,12 @@ def __init__(self, ions=[], concentrations=[]):
             else:
                 ion = copy.copy(ion)
             ion.context(self)
-            assert concentration >= 0, 'Concentrations must be positive.'
-            self._contents[ion] = concentration
+            if concentration == 0:
+                continue
+            elif concentration <0:
+                raise ValueError('Concentrations must be positive.')
+            else:
+                self._contents[ion] = concentration
 
         self._hydronium = database['hydronium']
         self._hydroxide = database['hydroxide']
@@ -206,6 +210,8 @@ def __sub__(self, other):
                 ion, concentration = other
                 new_contents = dict(self._contents)
                 new_contents[ion] = self.concentration(ion) - concentration
+                if new_contents[ion]==0:
+                    del new_contents[ion]
                 return Solution(new_contents.keys(), new_contents.values())
             except:
                 raise TypeError('Solutions add to other Solutions or to an'

ionize/Solution/titrate.py

@@ -77,7 +77,8 @@ def equilibrate_CO2(self, partial_pressure=atmospheric_CO2):
 
     def min_func(concentration):
         new_sol = self + (CO2, concentration)
-        deionized = concentration * (1-sum(new_sol[CO2].ionization_fraction()))
+        with CO2.context(new_sol):
+            deionized = concentration * (1-sum(CO2.ionization_fraction()))
         return deionized - eq
 
     with warnings.catch_warnings():

ionize/__version__.py

@@ -1 +1 @@
-__version__ = '1.0.3'
+__version__ = '1.1.0'