The coal residues were then treated with alkali
(0.5 mol L−1 NaOH). The water soluble salt of HA
thus formed was dissolved into a solution which was
filtered through What man No. 42 filter paper through
vacuum suction to separate it from insoluble organic
residues. The solution was evaporated to dryness on a
water bath (Hai and Mir, 1998) and stored until use in
the laboratory.