In _Welkner's Peat Kiln_[30] (fig. 22) the peat, previously air-dried, is exposed to a stream of hot air, until it is completely desiccated, and the arrangement is such, that air-dried peat may be thrown in at the top, and the hot-dried fuel be removed at the bottom, continuously. In the cut, _A_ represents the section of a wooden cylinder about 10 feet wide and 6-1/2 feet deep, which surmounts a funnel of iron plate _A'_. The mouth of the funnel is closed by a door _n_; about 20 inches above the door the pipe _B_, which conducts hot air, terminates in the ring _a a_, through the holes in which, _e e_, it is distributed into the funnel filled with peat. The air is driven in by a blower, and is heated by circulating through a system of pipes, which are disposed in the chimney of a steam boiler. From time to time a quantity of dried peat is drawn off into the wagon _D_, which runs on rails, and a similar amount of undried peat is thrown in above. According to Welkner, a kiln of the dimensions stated, which cost, about $1800 gold, is capable of desiccating daily ten tons of peat with 20 _per cent._ of water, using thereby 2000 cubic feet of air of a temperature of 212° F. When the air is heated by a fire kept up exclusively for that purpose, 10 _per cent._ of the dried peat, or its equivalent, is consumed in the operation. At the Alexis Smelting Works, near Lingen, in Hanover, this peat kiln furnishes about half the fuel for a high furnace, in which bog iron ore is smelted. The drying costs but 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.