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When burning, the inorganic impurities in the sample are relatively stable (such as sodium chloride, potassium chloride, sodium sulfate, etc.), if not due to burning and evaporation, this method can be used to determine the ash in the sample.

[Determination Method] Put the ceramic crucible cover (or nickel crucible) on a high temperature electric furnace (i. e., ver furnace) or gas flame, burn to a constant weight of approximately (about 1 hour), move it to a calcium chloride drier and cool to room temperature. The crucible lid was then weighed together on the analytical balance and set to G1 g.

In already weighed crucible, take appropriate sample (depending on the ash in the sample, generally called 2-3 grams), said to 0.0002 grams, the crucible lid mouth about three quarters, with low fire slowly heating crucible, make the sample gradually carbonization, after the crucible in electric furnace (or gas flame), not less than 800℃ burning to approximate constant weight (about 3 hours), moved to the calcium chloride drier, cooled to room temperature, weighing. It is best to burn after 2 hours, cool, weigh, and then burn for 1 hour, then cool, weigh, such as two weighing successively, the weight is almost unchanged, then means that has been burned completely, if the weight is reduced after the second burn, then must be the third burn, burn until similar to the constant weight, set G grams.

(G-G1) / sample weight x100= grey%

[Note] - -The sample size can be determined according to the amount of ash in the sample, less ash sample, can be called about 5 grams of sample, more ash sample, can be called about 2 grams of sample.

2. The duration of burning depends on the weight of the sample, but the burning is similar to the constant weight.

3. The weighing difference that burns twice successively had better be in 0.3 mg below, maximum difference cannot exceed 1 mg, regard as approximate in constant weight namely.