1. Instrument and equipment
(1) drying box:  it is provided with automatic temperature control device, and one up-draught blower installed inside, the drying box can keep the temperature in the range of 105 ~ 110 ℃.
(2) the weighing bottle glass: Diameter of 40 mm, 25 mm high, with an inner grinding cover.
(3) Up-draught drying box:  Built-in color silicone or granular anhydrous calcium chloride.
(4) Electronic scale: Sensitivity of 0.0001 g.
2.Measuring methods：
(1) Use the previously dried and weighed (accuracy is 0.0002 g) weighing bottle to weigh the air dried base coal sample of1±0.1g with particle size below 0.2mm, and to accurate the weight to 0.0002 g, and flat it in the weighing bottle.
(2) Open the weighing bottle caps and put into the drying box that has been up-draught dried and heated to 105 ~ 110 ℃ .Under the condition of continuously up-draught, the bituminous coal has been dried for 1 h and the anthracite coal has been dried for 1 ~ 1.5 h.
Note : Up-draught blowing in advance  is to make the temperature uniform in. Before putting the weighing bottle containing coal sample into the drying box, the up-draught blowing is started.
(3) Remove the weighing bottle from the drying box,  immediately cover it, and put it in the dryer for cooling to room temperature (about 20 min), then weigh it again.
(4) Take inspecting drying, the drying will last 30 min every time, until the reducing weight of the coal samples that has been dried for two times consecutively doesn't exceed 0.001 g or the coal weight is increased. .In latter case, the weight of the coal before weight increasing shall be adopted as the calculation basis of mass. With moisture of coal samples under 2% ,the inspecting drying is no necessary..
3.The results of calculation:
                      G1
        Mad=                ×100
                       G
where:
Mad -moisture content of air dried-basis coal sample, %.
G1 - mass reduced of coal sample after being dried, g.
G - the mass of the coal sample, g
Precautions: When weighing the coal sample on balance, the action shall be fast. After the coal sample has been weighted, the weighing bottle shall be well covered ,in order to prevent the moisture from being affected by the outside world.

4. Precision of moisture measurement   

 The repeatability of moisture measurement is shown in the table: