t little, since half the requisite heat is obtained from the waste
heat of the furnace itself.

[Illustration: Fig. 22.--WELKNER'S PEAT DRYING KILN.]

The advantages of this drying kiln are, that it is cheap in construction
and working; dries gradually and uniformly; occupies little ground, and
runs without intermission.

Other drying ovens are described in Knapp's _Lehrbuch_ der _Chemischen
Technologie_, 3. Aufl. Bd. 1, Theil 1, pp. 178-9; _Jahrbuch der
Bergakademien Schemnitz_ und _Leoben_, 1860, p. 108, 1861, p. 55;
Wagner's _Jahresbericht der Chemischen Technologie_, 1863, p. 748;
Zerrenner's _Metallurgische Gasfeuerung in Oesterreich_; Tunner's
_Stabeisen- und Stahlbereitung_, 2. Auflage, Bd. I, pp. 23-25.

15. _Peat Coal, or Coke._

When peat is charred, it yields a coal or coke which, being richer in
carbon, is capable of giving an intenser heat than peat itself, in the
same way that charcoal emits an intenser heat in its combustion than the
wood from which it is made.

Peat coal has been and is employed to some extent in metallurgical
processes, as a substitute for charcoal, and when properly prepared from
good peat, is in no way inferior to the latter; is, in fact, better.

It is only, however, from peat which naturally dries to a hard and dense
consistency, or which has been solidified on the principles of
Challeton's and Weber's methods, that a coal can be made possessing the
firmness necessary for furnace use. Fibrous peat, or that condensed by
pressure, as in Exter's, Elsberg's, and the Lithuanian process, yields
by coking or charring, a friable coal comparatively unsuited for heating
purposes.

A peat which is dense as the result of proper mechanical treatment and
slow drying, yields a very homogeneous and compact coal, superior to any
wood charcoal, the best qualities weighing nearly twice as much per
bushel.

Peat is either charred in pits and heaps, or in kilns. From the
regularity of the rectangular blocks into which peat is usually formed,
it may be charred more easily in pits than wood, since the blocks admit
of closer packing in the heap, and because the peat coal is less
inflammable than wood coal. The heaps may likewise be made much smaller
than is needful in case of wood, viz.: six to eight feet in diameter,
and four feet high. The pit is arranged as follows: The ground is
selected and prepared as for charcoal burning, and should be elevated,
dry and compact. Three stout poles are firm