The residue left after the burning of coal is known as ash. It is generally composed of inorganic substances. The total sulphur content of coal can be determined gravimetrically by the Eschka method. In this method, a coal sample is heated with the Eschka mixture (2:1 calcined magnesia and anhydrous sodium carbonate by weight) in an oxidizing atmosphere. This removes majorly all combustible matter and converts all forms of sulphur (pyritic’ and ‘organic, sulphur) to sulphate