Ash fusion temperature of coal

The ash of coal is analyzed for the oxide composition.

Let the % age of different oxides is denoted as

SiO₂ = Si

Al₂O₃ = A

Fe₂O₃ = F

Na₂O =N

CaO = C

MgO = M

SO₃ = S

K₂O = K

Ash fusion temperature of coal in degree centigrade is calculated as AFT