Sulphur Ash and Clinker.

The sulphur in coal is usually united with iron in the iron pyrites. The sulphur burns out but the iron is left behind and tends to run together forming clinker. Clinker, of course, as all firemen know, spreads across the fire-bars and if not removed prevents the air from passing up through the fire-grate, and steam is not produced. Some coals do not clinker, but fall into the ashpan in a state of powder. This ash is of an earthy nature and consists principally of silica, aluminium, calcium and magnesium.