oms,
it will be seen that the tale of waste is still more deplorable. But we
are at present rather concerned with what we actually do get from coal
than with what we ought to get from it, and here, when we come to deal
with the various material products, we shall have a better account to
present.

If instead of heating coal in contact with air and allowing it to burn, we
heat it in a closed vessel, such as a retort, it undergoes decomposition
with the formation of various gaseous, liquid, and solid products. This
process of heating an organic compound in a closed vessel without access
of air and collecting the products, is called destructive distillation.
The tobacco-pipe experiment of our boyhood is our first practical
introduction to the destructive distillation of coal. We put some powdered
coal into the bowl of the pipe, plaster up the opening with clay and then
insert the bowl in a fire, allowing the stem to project from between the
bars of the grate. In a few minutes a stream of gas issues from the
orifice of the stem; on applying a light it burns with a luminous flame,
and we have made coal-gas on a small scale.

In the destructive distillation of organic substances, such as wood or
coal, there are always produced four things--gas, watery liquid, and
viscous products known as tar, while a residue of coke or charcoal is left
in the retort. This is a very old observation, and was made so long ago
that it becomes interesting as a point in the history of applied science
to know who first submitted coal to destructive distillation. According to
Dr. Gustav Schultz, we must credit a German with this observation, which
was made towards the end of the seventeenth century (about 1680) by a
chemist named Johann Joachim Becher. The experiment is described in such a
quaint manner that the exact words of the author are worthy of being
reproduced, and the passage is here given as translated by Dr. Lunge in
his work on _Coal Tar and Ammonia_--

"In Holland they have peat, and in England pit-coals; neither of them is
very good for burning, be it in rooms or for smelting. But I have found a
way, not merely to burn both kinds into good coal (coke) which not any
more smokes nor stinks, but with their flame to smelt equally well as with
wood, so that a foot of such coal makes flames 10 feet long. That I have
demonstrated with pit-coal at the Hague, and here in England at Mr.
Boyles', also at Windsor on the large scale. In this conn