OZZETO DI MA-TA

Potassium nitrate could also be obtained from store-bought black powder,
simply by dissolving black powder in boiling water and filtering out the sulfur
and charcoal. To obtain 68 g of potassium nitrate, it would be necessary to
dissolve about 90 g of black powder in about one litre of boiling water. Filter
the dissolved solution through filter paper in a funnel into a jar until the
liquid that pours through is clear. The charcoal and sulfur in black powder are
insoluble in water, and so when the solution of water is allowed to evaporate,
potassium nitrate will be left in the jar.