recording to the nearest 0.1 g. Spread the sample evenly to a
depth of no more than 25 mm [1.0 in.], preferably less for
shorter drying time, unless the coal is subbituminous C or
lignite rank (Classification D388), or the rank is not known,
and the nominal top size is 2.36 mm (No.8) in which case,
spread the sample evenly (using a strike plate) to a depth less
than 19.1 mm [0.75 in.] but no less than 12.7 mm [0.50 in.]
(1).3 Place both the pan containing the sample and emptied
sample container in the air-drying oven that has been adjusted
to maintain temperature no more than 10°C [18°F] above
ambient temperature for easily oxidized coals or no more than
15°C [27°F] above ambient temperature for other coals.
Ambient air can be used with no heating. Air changes in the
oven must be at the rate of one to four per minute. (The sample
may be stirred gently from time to time to promote uniform and
quicker drying.) Continue drying until the coal surfaces appear
to be dry. Remove the pan and container from the oven and
weigh together. Carefully transfer residual coal from the dried
sample container to the sample in the pan. Weigh the empty
container and subtract its weight from the combined weight of
pan, sample, and container recorded both before and after the
first air-drying period. Calculate the percent weight loss of the
sample. Return the pan or pans with sample to the oven and
continue drying. Weigh at 1- to 2-h intervals until the weight
loss drops to a level near the 0.1 %/h target (about 0.2 to
0.3 %/h). Complete the air drying at ambient temperature,
allowing the sample to reach equilibrium (0.1 % loss per hour
or 0.05 % loss per half hour) with both ambient temperature
and humidity before the final air-dry weight is recorded (Note
3). When this point is reached, record the final air-dry weight.
Calculate the percent air-drying loss. Strictly observe the
cautions of Section 7.