uminous coal is softer than anthracite, contains more volatile
hydrocarbons, kindles more easily and burns more rapidly. It is
ordinarily free burning, has a high calorific value and is of the
highest order for steam generating purposes.

Bituminous coals are still softer than those described and contain still
more volatile hydrocarbons. The difference between the semi-bituminous
and the bituminous coals is an important one, economically. The former
have an average heating value per pound of combustible about 6 per cent
higher than the latter, and they burn with much less smoke in ordinary
furnaces. The distinctive characteristic of the bituminous coals is the
emission of yellow flame and smoke when burning. In color they range
from pitch black to dark brown, having a resinous luster in the most
compact specimens, and a silky luster in such specimens as show traces
of vegetable fiber. The specific gravity is ordinarily about 1.3.

Bituminous coals are either of the caking or non-caking class. The
former, when heated, fuse and swell in size; the latter burn freely, do
not fuse, and are commonly known as free burning coals. Caking coals are
rich in volatile hydrocarbons and are valuable in gas manufacture.

Bituminous coals absorb moisture from the atmosphere. The surface
moisture can be removed by ordinary drying, but a portion of the water
can be removed only by heating the coal to a temperature of about 250
degrees Fahrenheit.

Cannel coal is a variety of bituminous coal, rich in hydrogen and
hydrocarbons, and is exceedingly valuable as a gas coal. It has a dull
resinous luster and burns with a bright flame without fusing. Cannel
coal is seldom used for steam coal, though it is sometimes mixed with
semi-bituminous coal where an increased economy at high rates of
combustion is desired. The composition of cannel coal is approximately
as follows: fixed carbon, 26 to 55 per cent; volatile matter, 42 to 64
per cent; earthy matter, 2 to 14 per cent. Its specific gravity is
approximately 1.24.

Lignite is organic matter in the earlier stages of its conversion into
coal, and includes all varieties which are intermediate between peat and
coal of the older formation. Its specific gravity is low, being 1.2 to
1.23, and when freshly mined it may contain as high as 50 per cent of
moisture. Its appearance varies from a light brown, showing a distinctly
woody structure, in the poorer varieties, to a black, with a pitchy
luster