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7. Determination of ash The ash temaining following ignition of medicinal piant materials is determined by three different methods which measure total ash, acid-insoluble ash and water- soluble ash. The total ash method is designed to measure the total amount of material remain- ing after ignition. This includes both “physiological ash”, which is derived from the plant tissue itself, and “non-physiological” ash, which is the residue of the extraneous matter (e.g. sand and soil) adhering to the plant surface. Acid-insoluble ash is the residue obtained after boiling the total ash with dilute hydrochloric acid, and igniting the remaining insoluble matter. This measures the amount of silica present, especially as sand and siliceous earth. Water-soluble ash is the difference in weight beeween the total ash and the residue after treatment of the total ash with water. Recommended procedures Total ash Place about 2-4 of the ground air-dried material, accurately weighed, in a previ- ously ignited and tared crucible (usually of platinum or silica). Spread the material in an even layer and ignite it by gradually increasing the heat to 500-600°C until it is white, indicating the absence of carbon. Cool in a desiccator and weigh. If carbon- free ash cannot be obtained in this manner, cool the crucible and moisten the residue with about 2 ml of water or a saturated solution of ammonium nitrate R. Dry on a water-bath, then on a hot-plate and ignite to constant weight. Allow the residue to cool in a suitable desiccator for 30 minutes, then weigh without delay. Calculate the content of total ash in mg per g of air-dried material. Acid-insoluble ash To the crucible containing the total ash, add 25 ml of hydrochloric acid (~70g/1) TS, cover with a watch-glass and boil gently for 5 minutes. Rinse the watch-glass with 5ml of hot water and add this liquid to the crucible. Collect the insoluble matter on. an ashless filter-paper and wash with hot water until the filtrate is neutral. Transfer the filter-paper containing the insoluble matter to the original crucible, dry on a hot- plate and ignite to constant weight. Allow the residue to cool in a suitable desiccator for 30 minutes, then weigh without delay. Calculate the content of acid-insoluble ash in mg per g of air-dried material. 28 
