Slag is the fusible compound formed by the reaction of flux with gangue present in the ore during smelting. Flux + Gangue → Slag If the calcined or roasted ore still contains gangue before the reduction with carbon, an additional substance called flux is added which combines with the gangue to form a fusible material called slag. It does not mix with the molten metal, but forms a separate layer and can be easily separated out.

The process in which metals are extracted from their molten chlorides or oxides by passing electric current through them is called electrolysis. The metals such as aluminium, sodium and potassium are extracted from their molten oxides and chlorides respectively by electrolysis method and this process is known as electrolytic reduction.

The layer of aluminium oxide on the surface of aluminium articles is made thicker by the process of electrolysis to give the articles more protection from corrosion. This process is called anodizing.