Approximately 0.1 g
of sample was transferred into a weighed graduated 50 ml centrifuge
tube. Distilled water was added to give a total volume
of 10 ml. The sample in the tube was stirred gently by hand for
30 s at room temperature, and then heated at 60 C for 30 min.
After cooling to room temperature, the samples were centrifuged
for 30 min at 3000 rpm. The weight of sediment was
recorded