Dissolution: the crude salt solid is gray, and the liquid obtained by adding water is turbid.

Filtration: the filtrate is a colorless transparent liquid and the residue on the filter paper is black.

Evaporation: the amount of liquid in the evaporating dish decreases as it is heated; when it evaporates to a certain extent, a solid precipitates from the bottom of the dish. The solid obtained by evaporation is white in color.