-------+

Water in coal.

The amount of water present in freshly raised coals varies very
considerably. It is generally largest in lignites, which may sometimes
contain 30% or even more, while in the coals of the coal measures it
does not usually exceed from 5 to 10%. The loss of weight by exposure to
the atmosphere from drying may be from 1/2 to 3/4 of the total amount of
water contained.

TABLE III.--_Composition of Fuels (assuming Carbon = 100)._

+------------------------------+-------+---------+---------+-----------+
| | | | |Disposable |
| |Carbon.|Hydrogen.| Oxygen. | Hydrogen. |
+------------------------------+-------+---------+---------+-----------+
| Wood | 100 | 12.18 | 83.07 | 1.80 |
| Peat | 100 | 9.85 | 55.67 | 2.89 |
| Lignite | 100 | 8.37 | 42.42 | 3.07 |
| Thick Coal, S. Staffordshire | 100 | 6.12 | 21.23 | 3.47 |
| Hartley Steam Coal | 100 | 5.91 | 18.32 | 3.62 |
| South Wales Steam Coal | 100 | 4.75 | 5.28 | 4.09 |
| American Anthracite | 100 | 2.84 | 1.74 | 2.63 |
+------------------------------+-------+---------+---------+-----------+

Origin of Coal.

Coal is the result of the transformation of woody fibre and other
vegetable matter by the elimination of oxygen and hydrogen in
proportionally larger quantity than carbon, so that the percentage of
the latter element is increased in the manner shown in Table III., given
by J. Percy, the mineral matter being also changed by the removal of
silica and alkalis and the substitution of substances analogous in
composition to fire-clay. The causes and methods of these changes are,
however, not very exactly defined. According to the elaborate researches
of B. Renault (_Bulletin de la Societe de l'Industrie minerale_, 3 ser.
vol. xiii. p. 865), the agents of the transformation of cellulose into
peaty substances are saprophytic fungi and bacterial ferments. As the
former are only active in the air while the latter are anaerobic, the
activity of either agent is conditioned by variation in the water level
of the bog. The ultimate term of bacterial activity seems to be the
production of ulmic acid, containing carbon 65.31 and hydrogen 3.85%,
which is a powerful antiseptic