The most splendid phenomenon of this kind is the combustion of charcoal
points. Pointed pieces of the residuum obtained from gas retorts will
answer best, or Bunsen’s composition may be used for this purpose. Put
two such charcoal points in immediate contact with the wires of your
battery; bring the points together, and they will begin to burn with
a dazzling white light. The charcoal points of the large apparatus
belonging to the Royal Institution became incandescent at a distance of
1/30th of an inch; when the distance was gradually increased till they
were four inches asunder, they continued to burn with great intensity,
and a permanent stream of light played between them. Professor Bunsen
obtained a similar flame from a battery of four pairs of plates,
its carbon surface containing 29 feet. The heat of this flame is so
intense, that stout platinum wire, sapphire, quartz, talc, and lime
are reduced by it to the liquid form. It is worthy of remark, that no
combustion, properly so called, takes place in the charcoal itself,
which sustains only an extremely minute loss in its weight and becomes
rather denser at the points. The phenomenon is attended with a still
more vivid brightness if the charcoal points are placed in a vacuum,
or in any of those gases which are not supporters of combustion.
Instead of two charcoal points, one only need be used if the following
arrangement is adopted: lay the piece of charcoal on some quicksilver
that is connected with one pole of the battery, and complete the
circuit from the other pole by means of a strip of platinum. When
Professor Peschel used a piece of well-burnt coke in the manner just
described, he obtained a light which was almost intolerable to the eyes.