fraction of the whole working
capability out of coal, the actual amount of energy dormant in this
substance cannot but strike us as being prodigious. It has already been
said that a pound of coal on complete combustion gives out 13,890 heat
units. This quantity of heat corresponds to over 10,000,000 foot-pounds of
work. A horse-power may be considered as corresponding to 550 foot-pounds
of work per second, or 1,980,000 foot-pounds per hour. Thus our pound of
coal contains a store of energy which, if capable of being completely
converted into work without loss, would in one hour do the work of about
five and a half horses. The strangest tales of necromancy can hardly be so
startling as these sober figures when introduced for the first time to
those unaccustomed to consider the stupendous powers of Nature.

If energy is indestructible, we have a right to inquire in the next place
from whence the coal has derived this enormous store. A consideration of
the origin of coal, and of its chemical composition, will enable this
question to be answered. The origin of coal has already been discussed.
Chemically considered, it consists chiefly of carbon together with smaller
quantities of hydrogen, oxygen, and nitrogen, and a certain amount of
mineral matter which is left as ash when the coal is burnt. The following
average analyses of different varieties will give an idea of its chemical
composition:--

-------------------------------------------------------------------
Variety of Coal. | Carbon. | Hydrogen. | Oxygen. | Nitrogen. | Ash.
-------------------+---------+-----------+---------+-----------+-----
S. Staffordshire | 73.4 | 5.0 | 11.7 | 1.7 | 2.3
Newcastle (Caking) | 80.0 | 5.3 | 10.7 | 2.2 | 1.7
Cannel (Wigan) | 81.2 | 5.6 | 7.9 | 2.1 | 2.5
Anthracite (Welsh) | 90.1 | 3.2 | 2.5 | 0.8 | 1.6
---------------------------------------------------------------------

There are in addition to these constituents small quantities of sulphur
and a certain variable amount of water (5 to 10 per cent.) in all coals,
but the elements which most concern us are those heading the respective
columns.

From the foregoing analyses, which express the percentage composition, it
will be seen that carbon is by far the most important constituent of coal.
Carbon is a chemical element which is found in a crystalline form in
nature as the diamond, and wh