Appendix 13.
The German "Treppen-Rost" or Step-Furnace for the Burning of Brown Coal.^*

Construction (See Fig. 1-4, No. IX.)—Above an opening of 45 centimeters in width, communicating with the ashpit, lies a slide-frame S, with massive slides of 10-12 millimeters in thickness, the whole resting in front, for the sake of solidity, upon a cast-iron plate a, 13 centim. broad, and 4-5 centim. thick. Upon the slide-frame S is placed a cast-iron double T support, 24 centim. in height, 13 centim. broad, and 12 millim. thick, and upon this lies a second slide-frame S. The slides of this frame being 25 millim. thick, are, however, perforated or broken longitudinally, in order to form a grating; or better, movable fire-bars 5-7 centim. thick, are used instead of the broken slides, which are liable to crack. Upon the slide-frame S lies a second cast-iron plate c, of the same dimensions as a, and at suitable height a third cast-iron bar B, 9 centim. high and 6 centim. broad, is fixed into the side walls of the furnace. The length it is let into the walls is about 15 centim., whilst a and c, and the slide-frames S and S enter the walls only about 8 centim, with their ends. Upon the, what may be called, cross-supports B and c, rest now, with their ends the cast-iron cheeks W in such a manner that they may be freely shifted broadways, and carry step-like (hence the name of the furnace) the several fire-bars of which the upper one p is about three times broader than the rest. Above p is fixed the cast-iron supply funnell F serving for the receipt of the fuel, and which is sometimes furnished with a slide for regulating the supply of fuel into the furnace. The fireplace is fixed between two stone-walls, and covered by a fire-proof arch, which is either inclined and smooth, or, as indicated by the dotted lines, broken step-like for the purpose of offering to the combustible gases more heated surface on which they strike, and are set burning. The cheeks W are 25 millim. thick, and 10-12 centim. broad, and placed at 0-4 to 0-6 meter distance from each other. The whole length of the furnace is generally 2 meters or smaller, the breadth equal to, or less than 1-3 meter; and the inclination of the cheeks W is most advantageously at an angle of 30° (i.e., for the burning of brown coal, for which these furnaces are most suitable, and nearly exclusively used).

The most approved connection of the fire-bars, with the cheeks W is shown in figures 3 and 4. Their thickness is 1-12 millim., page 236the vertical distance between two bars 19-20 millim., the distance between their surfaces 27-32 millim., their breadth 118-120 millim., and they project one over the other about 47 millim. The working of such a furnace requires much less strength and intelligence than that of the common plane fireplace. The funnel F is filled with the fuel, and, according as the latter burns off the steps (which is easily seen), the fireman pushes a fresh lot from top downwards by means of a spade-like tool, introduced between the lower edge of the funnel F and the top bar p. The gradually accumulating ashes are from time to time removed from the fire-bars by means of a flat piece of iron, which is moved hither and thither over the latter. In order to remove cinders and ashes from the upper slide S’—(S being always kept a little open to let draught in for perfect combustion) — the slide S is first shut, then S’ opened to let the ashes and cinders drop upon S; then S’ is shut again, and fuel stoked down to cover it, and now, finally, S is opened so that the ashes, etc, can fall down into the ash-pit. In this manner the detrimental introduction of a large amount of cold air into the furnace is entirely avoided. The chief advantage of this furnace consists in the steady, nearly continuous, burning of the fuel, and that with proper regulation of the draught the combustion can be rendered close upon perfect, whilst all the smoke is consumed. To this has to be added another great advantage, namely, that during the supply of fuel no unnecessary amount of cold air is introduced into the furnace, and that, as previously mentioned, a common workman is able to serve the latter easily and well, and without being exposed to any strong heat bursting into his face. The furnace has also, however, some drawBacks, viz., that no coal can be burned in it that bakes or clogs, and that the fuel rests upon a larger area of iron, being, therefore, much more cooled, and for a larger surface extent prevented from burning, than in the common plane furnace.