4) Determination of ash content [68] Weigh accurately. 3g sample to be measured (accurate to 0.001g), put it into a crucible, carbonize with an electric furnace, burn the crucible to a constant weight, place the crucible containing the sample in a horse In a furnace, set the heating temperature to 550 ° C and burn at this temperature for 10-15 hours. Take out after burning, put into a desiccator, cool to room temperature, and weigh. After repeated burning to constant weight of the sample, calculate the ash content in the sample.