1. Instrument and  equipment
(1)the muffle furnace :
 Muffle furnace can maintain the temperature of 815 + 10 ℃.The furnace hearth has enough constant temperature zone.
(2) Porcelain cupel: Rectangle, underside 45 mm in length and 22 mm in width , 14 mm in height .
(3) Up-draught drying box Built-in color silica gel.
(4) electronic platform scale: Sensitivity of 0.0001 g.
2.  Measurement method; Slow ashing method
(1)Use the cupel that has been burnt to mass constant cupel, to weigh the air dried 1± 0.1g coal samples with particle size under 0.2 mm, with accuracy 0.0002 g, and evenly flat it in cupel, in order to make its mass not to exceed0.15 g per square centimeter.
(2) Put the cupel into the Muffle furnace with temperature not exceeding 100 ℃ , shut the furnace door to make the door have 15 mm gap or so. With the time not less than 30 min, slowly heat the furnace to about 500 ℃, and keep it under this temperature for 30 min. Continuously heat the furnace to 815±10℃, and under this temperature, burn the coal sample for 1 hour.
(3) Take the cupel from the furnace and put it on the heat-resistant porcelain plate or asbestos board, to cool it in the air for about 5 minutes, then move it into the dryer for cooling (about 20 min), then weigh it.
(4) Take inspecting burning, the drying will last 20 min every time, until the changing mass of the coal samples that has been burnt for two times consecutively doesn't exceed 0.001 g. Take the last time mass after burning as the calculation basis. With ash of coal samples under 15% ,the inspecting burning is no necessary.
Measurement method of quickly ashing:
(1)Use the cupel that has been burnt to mass constant cupel, to weigh the air dried 1± 0.1g coal samples with particle size under 0.2 mm, with accuracy of 0.0002 g, and evenly flat it in cupel, in order to make its mass not to exceed 0.15 g per square centimeter. Put the ash cupel of coal sample on the on the shelf for cupel in advance.
(2) Heat muffle furnace to 850 ℃, open the furnace door,  slowly push the cupel shelf out with cupel heap into the muffle furnace, firstly ash the first row ash cupel. After 5 ~ 10 min, when the coal samples will no longer burn, push the ash cupelts of Row No.2, No.3 and No. 4 into the hot part inside in the furnace in sequence (if the coal samples fired and exploded, the test shall be invalid).
(3) close the furnace door, burn it under the temperature of 815 + 10 ℃  for 40 min.,
(4) Take the cupel from the furnace and put it  in the air for cooling for about  5 minutes, then move it into the dryer  for cooling (about 20 min),  then weight it .b5 Take inspecting burning, the drying will last 20 min every time, until the mass changing of the coal samples that has been burnt for two times consecutively doesn't exceed 0.001 g.Take the last time mass after burning as the calculation basis.In case the results of inspecting burning is not stable,  this method shall be changed to slowly  ashing method for  measuring again.With ash content of coal samples under 15% ,the inspecting burning is no necessary.
3.The results of calculation:
                       G1
        Aad=                ×100
                       G
where:
Mad -ash content yield of  air dried-basis coal sample, %
G1 - mass of the residual after combustion, g.
G - the mass of the coal sample, g.
4.Precision of ash content measurement 

The repeatability and reproducibility of ash content measurement is shown in the table