During the progress of test the coal should be regularly sampled for the
purpose of analysis and determination of moisture.
Select a representative shovelful from each barrow-load as it is drawn
from the coal pile or other source of supply, and store the samples in a
cool place in a covered metal receptacle. When all the coal has thus
been sampled, break up the lumps, thoroughly mix the whole quantity, and
finally reduce it by the process of repeated quartering and crushing to
a sample weighing about 5 pounds, the largest pieces being about the
size of a pea. From this sample two one-quart air-tight glass fruit
jars, or other air-tight vessels, are to be promptly filled and
preserved for subsequent determinations of moisture, calorific value,
and chemical composition. These operations should be conducted where the
air is cool and free from drafts.
[Illustration: 3460 Horse-power Installation of Babcock & Wilcox Boilers
at the Chicago, Ill., Shops of the Chicago and Northwestern Ry. Co.]
When the sample lot of coal has been reduced by quartering to, say, 100
pounds, a portion weighing, say, 15 to 20 pounds should be withdrawn for
the purpose of immediate moisture determination. This is placed in a
shallow iron pan and dried on the hot iron boiler flue for at least 12
hours, being weighed before and after drying on scales reading to
quarter ounces.
The moisture thus determined is approximately reliable for anthracite
and semi-bituminous coals, but not for coals containing much inherent
moisture. For such coals, and for all absolutely reliable determinations
the method to be pursued is as follows:
Take one of the samples contained in the glass jars, and subject
it to a thorough air drying, by spreading it in a thin layer and
exposing it for several hours to the atmosphere of a warm room,
weighing it before and after, thereby determining the quantity
of surface moisture it contains.[68] Then crush the whole of it
by running it through an ordinary coffee mill or other suitable
crusher adjusted so as to produce somewhat coarse grains (less
than 1/16 inch), thoroughly mix the crushed sample, select from
it a portion of from 10 to 50 grams,[69] weigh it in a balance
which will easily show a variation as small as 1 part in 1000,
and dry it for one hour in an air or sand bath at a temperature
between 240 and 280 degrees Fahrenheit. Weigh it and record the
loss, then heat and weigh again until the minimum weight has
been reached. The difference between the original and the
minimum weight is the moisture in the air-dried coal. The sum of
the moisture thus found and that of the surface moisture is the
total moisture.