MINERAL COAL. Bye 
MINERAL COAL.. 
Massive. Color black or brown; opaque. Brittle or im- 
perfectly sectile. .=0:5-2°5. G.=1°-2-1°80. : 
Composition. Carbon, with, some oxygen and hydrogen, 
‘more or less moisture, and traces also of nitrogen, besides 
some earthy mineral which constitutes the ash. ‘The car- 
bon, or part of it, is in chemical combination with the 
hydrogen and oxygen. 
Coals differ in the amount of volatile ingredients given 
off when heated. ‘These ingredients are moisture, and hy- 
drocarbon oils and gas, derived from the same class of 
insoiuble hydrocarbons that is the source of the oil of shales 
and other rocks. 
VARIETIES. 
1. Anthracite. Anthracite (called also glance coal and 
stone coal) has a high lustre, and is often iridescent. It is 
quite compact and hard, and has a specific gravity from 1°3 
to 1°75. It usually contains 80 to 93 per cent. of carbon, 
with 4 to 7 of volatile matter ; the rest consisting of earthy 
impurities. Burns with a feeble blue flame. 
Those yielding the most volatile ingredients are called 
free-burning anthracite. 
2. Bituminous Coal. Bituminous coal varies much in the 
amount of oil, coal-tar, or gas it yields when heated; and 
there is a gradual passage in its varieties through sem- 
anthracite to anthracite. It is of a black color, with the 
powder black, but it is softer than anthracite, and less 
Instrous. — Tlie specific eraviby does not exceed Io. “The 
volatile ingredients constitute usually between 20 and 40 
per cent. 
Caking Coal includes that part of bituminous coal which 
softens when heated and becomes viscid, so that adjoining 
pieces unite into a solid mass. It burns readily with a 
lively yellow flame, but requires frequent stirring to prevent 
its agelutinating, and so clogging the fire. Mon-caking coal 
resembles the caking in appearance, but does not soften and 
cake. ‘The chemical difference between caking and non- 
caking coal is not understood. 
3. Cannel Coal is very compact and even in texture, with 
little Iustre, and breaks with a large conchoidal fracture. It 
takes fire readily, and burns without melting to a clear yel- 
