Distribute the gross moisture sample over the required
number of tared pans. Weigh each pan with sample as it
is filled from the gross sample. Place in an 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 (oven temperature not to exceed 40°C). Ambient air may
be used with no heating. Maintain air circulation through the
oven at a rate of one to four air exchanges per minute, but in
no case should it be sufficiently high to blow fine particles from
the pans. Gently stir the sample from time to time to ensure
uniform drying throughout the sample. Continue drying with
intermittent stirring until the coal surfaces appear to be dry.
Remove from oven, weigh, and record the weight. Return the
pans with sample to the oven and continue the operation.
Calculate the percent weight loss. Repeat the drying and
weighing process at 1- to 2-h intervals until the weight loss is
less than 0.1 %/h (Note 1). Allow the sample to reach equilibrium
with ambient temperature and humidity before the final
air dry weight is recorded. Avoid excess drying.