Char a quantity of the substance, representing about 2 grams of the dry
material, and burn until free of carbon at a low heat, not to exceed
dull redness. If a carbon-free ash can not be obtained in this manner,
exhaust the charred mass with hot water, collect the insoluble residue
on a filter, burn till the ash is white or nearly so, and then add the
filtrate to the ash and evaporate to dryness. Heat to low redness, until
ash is white or grayish white, and weigh.