The heat is
continued until no further quantity of gas comes off and burns at the
mouth. This takes only a few minutes. The cover is tightly fitted on,
and when cold the crucible is weighed. The loss in weight, after
deducting the moisture, gives the "volatile matter," and the residue
consists of "fixed carbon" and "ash."
~Determination of Ash.~--The coke produced in the last operation is
turned out into a porcelain dish and ignited over a Bunsen burner till
the residue is free from particles of carbon. Calcination is hastened by
stirring with a platinum wire. The operation may be done in a muffle,
but this gives results a few tenths of a per cent. too low. The dish is
cooled in a dessicator, and weighed. The increase in weight gives the
amount of "ash," and the difference between this and the weight of the
coke gives the "fixed carbon."
The assay is reported as follows:--
Moisture at 100° C. ---- per cent.
Volatile matter ---- "
Fixed carbon ---- "
Ash ---- "
contains sulphur ---- per cent.
~Determination of Sulphur.~--The sulphur exists in the coal partly in
organic combination, partly as metallic sulphide (iron pyrites,
marcasite, &c.), and, perhaps, as sulphate. So that the sulphur
determination must be separately reported, since a portion will go off
with the volatile matter, and the remainder would be retained and
weighed with the coke.
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