If the "meth water"
in the Erlenmeyer flask is far too acidic (e.g. 10 drops of hydrochloric acid too much), generous amounts of sodium hydroxide are poured in until all the meth in the water becomes "free base" again and is completely converted into toluene. The water layer is discarded and new distilled water comes in, it is neutralized with hydrochloric acid until all the meth is gone
has passed into the new water, and the PH value is close to neutral THIS TIME. Abi