If the precipitate settles readily, the supernatant liquor may be decanted through the filter paper, more water added to the precipitate and again decanted.
The decanted ley deposits on standing a 70% potassium chloride, which is purified by washing with cold water.
This powder is then lixiviated with hot water, the liquor decanted, and the alum allowed to crystallize.
Every twenty-four hours or so the flow of juice may be conveniently stopped, and, after all the impurities have subsided, the superincumbent clear liquor may be decanted by a cock placed at the side of the cone for the purpose, and the vessel may be washed out.
Water is added, and as soon as the gangue and copper particles have settled the clear solution is decanted, and the residue washed several times in the same way.