COAL AND ITS CLASSIFICATION 265 
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has a less rectangular jointing than bituminous coal, and 
usually breaks into nodular lumps with curved surfaces. It 
has usually only from 3 to 5 per cent. of volatile material, 
and from 93 to 95 per cent. of carbon. Its thermal effi- 
ciency is from 14,500 to 15,000 B.T.U., which is less than the 
best bituminous coal owing to loss of heat during its slow 
kindling. The intense heat generated by its combustion, 
and freedom from smoke render anthracite especially suit- 
able for metallurgical and naval purposes, and slow combus- 
tion stoves. 
(GRAPHITE 
The complete removal of the volatile constituents of coal 
may leave a residue of fixed carbon as coke; where the 
removal of the volatile matter is due to rock pressure or 
earth-movements the residue forms graphite, which may 
occur in beds, veins, or masses. Its main use, owing to 
its softness and permanent colour, is in “lead ” pencils; 
fine scales are used as lubricant and polishing material. 
Graphite may result from the decomposition of inorganic 
hydrocarbons, but it is often the last stage in the coal series. 
The chief supplies are from Central Europe, Ceylon, Mada- 
gascar, and Korea. The price varies usually from 4d. to 8d. 
per lb. 
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SECTION II. SAPROPELIC COALS 
CanneL Coar—Cannel or candle coal is a bituminous coal, 
composed of sapropel, an organic mud. It varies in lustre 
from dull to brilliant ; it may be structureless or well-bedded, 
and it may have a less regular jointing than humic coal. 
It burns with a bright yellow flame, and is sometimes so 
rich in volatile matter that it can be ignited by a match. 
Large splinters were used for lighting houses, and it thus 
gained its name of candle coal, of which cannel is a modifi- 
cation. It is often called gas coal owing to its high gas yield; 
its gas is too smoky to burn with incandescent mantles, and 
is mainly used for gas enrichment for factories where the 
vibration is too great for mantles. Most if not all cannel 
coal has been deposited in water or swamps, and it usually 
occurs in lenticular patches which may pass into ordinary