und which is the same in chemical constituents
as the poisonous gas which we and all animals exhale. But there is this
to be said. Probably in the far-away days when the diamond began to be
formed, the tree or other vegetable product which was its far-removed
ancestor abstracted carbonic acid gas from the atmosphere, just as do our
plants in the present day. By this means it obtained the carbon wherewith
to build up its tissues. Thus the combustion of the diamond into
carbonic-anhydride now is, after all, only a return to the same compound
out of which it was originally formed. How it was formed is a secret:
probably the time occupied in the formation of the diamond may be counted
by centuries, but the time of its re-transformation into a mass of coky
matter is but the work of seconds!

There is another form of carbon which was formerly of much greater
importance than it is now, and which, although not a natural product, is
yet deserving of some notice here. Charcoal is the substance referred to.

In early days the word "coal," or, as it was also spelt, "cole," was
applied to any substance which was used as fuel; hence we have a
reference in the Bible to a "fire of coals," so translated when the
meaning to be conveyed was probably not coal as we know it. Wood was
formerly known as coal, whilst charred wood received the name of
charred-coal, which was soon corrupted into charcoal. The
charcoal-burners of years gone by were a far more flourishing community
than they are now. When the old baronial halls and country-seats depended
on them for the basis of their fuel, and the log was a more frequent
occupant of the fire-grate than now, these occupiers of midforest were a
people of some importance.

We must not overlook the fact that there is another form of charcoal,
namely, animal charcoal or bone-black. This can be obtained by heating
bones to redness in closed iron vessels. In the refining of raw sugar the
discoloration of the syrup is brought about by filtering it through
animal-charcoal; by this means the syrup is rendered colourless.

When properly prepared, charcoal exhibits very distinctly the rings of
annual growth which may have characterised the wood from which it was
formed. It is very light in consequence of its porous nature, and it is
wonderfully indestructible.

But its greatest, because it is its most useful property, is undoubtedly
the power which it has of absorbing great quantities of gas into itself.