Determine separately the sample moisture by heating in an oven at 105 °C to constant weight. Cool in a desiccator.
Weight accurately 1 g about of grinded sample (1 mm about) approximately with 1 mg. ==> W1
Add 1.25% sulfuric acid up to the 150 ml notch, after preheating by the hot plate in order to reduce the time required for boiling.
Add 3-5 drops of n-octanol as antifoam agent.
Boil 30 minutes exactly from the onset of boiling.
Connect to vacuum for draining sulfuric acid.
Wash three times with 30 ml (crucible filled up to the top) of hot deionized water, connecting each time to compressed air for stirring the content of crucible.
After draining the last wash, add 150 ml of preheated potassium hydroxide (KOH) 1.25% and 3-5 drops of antifoam.
Boil 30 minutes.
Filter and wash as point 7.
Perform a last washing with cold deionized water aimed to cool the crucibles and then wash three times the crucible content with 25 ml of acetone, stirring each time by compressed air.
Remove the crucibles and determine the dry weight after drying in an oven at 105 °C for an hour or up to constant weight. Let cool in a desiccator. This weight (W2)represents the crude fiber plus ash content in comparison to initial weight