If this last is
required the increase in weight multiplied by 0.111 gives its amount.
COALS.
The determination of the actual carbon in coals and shales is seldom
called for; if required, it would be performed in the way just
described.[118] The ordinary assay of a sample of coal involves the
following determinations--moisture, volatile matter, fixed carbon, ash,
and sulphur. These are thus carried out:--
~Determination of Moisture.~--Take 3 grams of the powdered sample and
dry in a water-bath for an hour or so. The loss is reported as moisture.
Coals carry from 1 to 2 per cent. If the drying is carried too far,
coals gain a little in weight owing to oxidation, so that it is not
advisable to extend it over more than one or two hours.
~Determination of Volatile Matter.~--This determination is an
approximate one, and it is only when working under the same conditions
with regard to time, amount of coal taken, and degree of heat used, that
concordant results can be arrived at. It is a matter of importance
whether the coal has been previously dried before heating or not, since
a difference of 2 per cent. may be got by working on the dried or
undried sample. Take 2 grams of the powdered, but undried, sample of
coal, place in a weighed platinum crucible, and support this over a good
Bunsen burner by means of a thin platinum-wire triangle.
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