7. If sample is not completely white, moist ash with a few drops of water or diluted acid
(4N nitric acid) or petroleum ether. If the water is used, evaporate on water bath and repeat
heating in the muffle furnace for 30 – 60 min until constant weight is obtained.
8. Decrease the temperature of the furnace to 180ºC and transfer the crucibles into a
desiccator, cool for 30 min and weigh (W3).
NOTE: If ash samples are to be used for mineral analysis, temperature of the furnace should not
exceed 450oC. Too high a temperature may cause the volatilisation of certain elements
particularly Fe, K, Na, S, Cl & P. It may also cause the mineral matter to fuse and melt.
9. The ash content is determined as the equation written below
Ash content (g/100g) = (W3-W1)/(W2-W1) × 100
where: W1 = weight crucible
W2 = weight of crucible + sample
W3 = weight of ash
Duplicate results should not differ by more than 5% of the mean.