Glass marbles were placed on top
of each test tube to prevent loss of water through evaporation.
Then the tubes were placed in a boiling water bath for 10 min,
and then it was removed and cooled. A reagent blank was prepared
by taking 1 ml of water and 4 ml of anthrone reagent in
a tube and treated similarly. The absorbance of blue–green
solution was measured at 620 nm in a colorimeter.