40 
odour. When heated in closed vessels it yields olefiant 
gas (carburetted hydrogen — C 2 H 2 ), empyreumatic oil and 
tar, also ammonia and watery vapour, and leaves a black, 
porous slag of metallic lustre, which is called burned coal 
or coke. Water, acids, and oil do not dissolve any part of 
it, but with sulphuret of carbon a small quantity of brown 
resin is given off. The composition generally is 70—80 
per cent of carbon, 3—21 per cent of hydrogen, 2—7 per 
cent of nitrogen, 6—24 per cent of oxygen, so that it may 
be said that the coals of each district have a different com¬ 
position. Thus a few, especially coarse and earthy coals, 
yield very little olefiant gas; on the other hand, others, 
such as the slaty and all cannel coals, gfve double and 
triple as much. 
The following descriptions of coal are distinguished by 
their structure :— 
1. Slate-coal , with distinctly foliated fracture, and a 
highly resinous lustre, sometimes tarnished in various 
colours, of T27—1*34 specific gravity. It is the most 
abundant kind of common coal, which is found especially 
where large beds of common coal occur, as at Ruhr, Saar 
in Silesia, Belgium, France, England, North America, and 
Australia. Fig. 10 represents a bit of slate-coal from 
Planitz in Saxony. 
2. Splint-coal. —Compact, slightly lustrous, pitch-black, 
of a thick slaty structure and uneven fracture. It is found 
in subordinate beds sometimes with slate-coal, as, for in¬ 
stance, in Saxony, Moravia, and Silesia. It presents in 
the fracture a strong fatty lustre, so that it is also known 
popularly as pitch-coal. The specific gravity varies from 
1*45—1-60. ' 
3. Parrot or Cannel-coal. —Greyish or brownish-black, 
slightly lustrous, of flat conchoidal, almost even fracture, and 
compact slaty segregation ; but slightly friable, and burns 
with a clear flame. It has the very low specific gravity 
of 1*21—1*27, and leaves as residue of combustion a loose 
coke. The principal localities for it are in England and 
Scotland, at Wigan in Lancashire, at Lesmahagow in 
Lanarkshire, and West Wemyss in Fife ; it has lately 
been found near Saarbriick, as seen in Plate XII., Fig. 9. 
It is applied with great advantage to the manufacture of 
gas; it leaves, however, a small very porous coke, and 
loses about 44 per cent in weight. As it is extremely 
compact, and may be made into boxes, buttons, knife- 
handles, etc., it also takes on a very handsome polish. In 
burning, of all coals it leaves the smallest amount of ash, 
which sometimes only amounts to \ per cent. 
4. Earthy Goal , or pulverulent coal , Jiusskohle of German 
authors.—Greyish-black, pulverulent, dim or glimmering, 
readily giving off colour, easily inflammable, generally 
found in small layers between the slate-coals, and only ex¬ 
ceptionally in separate beds, as at Ganitz. The fine powder, 
under the microscope, presents distinct cells and vessels, 
as they occur in the stems and leaves of the lower vascu¬ 
lar plants ; this structure is only partially destroyed by 
coking. Technically we distinguish between caking coal , 
coking coal, and sandy coal. The first comprises those coals 
which are easily melted aud leave a loose coke, the last 
such as are perfectly incapable of being melted and yield a 
brittle coke, while coking-coal is a compact, tough coal, 
which leaves the best coke. The splint-coal of Belgium 
yields 81, that of Essen on the Ruhr 79'5, that of Saarbriick 
66, and the English cannel coal only 51*3 per cent of coke. 
Common coal is not only highly valued for the manufac¬ 
ture of gas, but especially useful as fuel, for 100 pounds of it 
produce exactly as much heat as 230 pounds of dried wood ; 
and indeed it may be said that the greater part of modern 
industry, and the application of steam-power to machinery, 
railways, and steam-boats, have only been made possible 
by the help of coal, so that it is now in extensive demand, 
and produced in great quantities. Luckily the coal-fields 
of many countries are so considerable, that many of them 
still possess a sufficient supply for a thousand years. 
The geological occurrence of real common coal is 
limited to the older stratified rocks; the peculiar coal for¬ 
mation is confined to certain basins and cavities in the 
neighbourhood of the oldest stratified and primary rocks. 
Yet there are black coals in the course of the Alps, and in 
the middle and even in the upper stratified rocks, although 
in smaller quantity, which resemble the old slate coal. 
Coal occurs generally in turn with slaty clay, contain¬ 
ing vegetable remains, in layers, from a few inches to 
three and six, and exceptionally to as many as 30 feet 
in thickness, imbedded in the carboniferous sandstone. 
In Silesia and Saxony there are generally found only 
from 4—12 beds, in England 12—40, in the Saarbriick 
60—170, in Belgium as many as 200—300 beds, with 
a total thickness of 50—375 feet. In North America, 
the greatest coal-field extends over Pennsylvania, Ohio, 
and Virginia, with a surface of 2500 German square 
miles; there are 10—15 seams, from 8—50 feet thick, of 
the finest coal. In Illinois and Michigan there are also ex¬ 
tensive coal-fields, and it has been reckoned that the total 
superficial area of the coal formation, in the twelve prin¬ 
cipal coal states alone, amounts to 133,132 square miles, or 
a quarter of their entire area; the Pennsylvanian bed alone 
has an area of 15,437 square miles, or one-third of its en¬ 
tire area. The coal land in Great Britain and Ireland has 
an area of 11,859 square miles, or about one-tenth of the 
whole surface. In the year 1855 the total produce of coal 
in this country amounted to 64,453,070 tons, whereof 
4,760,000 tons were exported. The smelting of iron an¬ 
nually consumes about 10,000,000 tons of coal, or nearly 
four tons of coal for every one of iron produced. Extensive 
coal-beds have also of late years been found in the East 
Indies and Australia, in Borneo, Sumatra, and the Celebes. 
Jet. 
This name is applied to a compact, highly lustrous 
coal, of a perfectly black to a pitch-black colour, with a 
fracture of resinous lustre, and sometimes with a distinct 
wood-like structure. It is perfectly compact, and difficult 
to work, of L29—L35 specific gravity, and 2*0 to 2‘5 
hardness, capable of polish, and burns a long time without 
smell, leaving only from 2—3 per cent, of ash. It is 
principally formed in the lias and tertiary formations, and 
it is used partly for fuel, and partly for the manufacture of 
small objects of art and ornament. It occurs most abun¬ 
dantly in this country at Whitby, in Yorkshire, where the 
value of the jet manufactured in 1855 amounted to £20,000. 
Figs. 11—13. —Brown Coal, Lignite. 
Brovm coal is the name generally applied to the coals 
