MECHANICS AND USEFUL ARTS. 69 



" la the best double-flued and double-furnaced English boilers, 

 about one square inch of permanent air-opening, behind the 

 bridge, is necessary for every square foot of grate-bar, — air pass- 

 ing as usual through the grate-bars from the ash-pit, and often 

 through holes in the furnace door. In the 'Amory' furnace, a 

 three to six-inch pipe is ample, (!onve3ing heated air to the cavity 

 of the curves, the ash-pit door (and the holes in the furnace 

 door, if necessary) being closed, after the fires have been well 

 kindled, — a very much less open air-space than in the best Eng- 

 lish furnaces. With an insufficient amount of air, if l)ituminous 

 coal or pine wood be used, the too-compact fire being suj^plied 

 only thi'ough the grate-bars, the gases pass quickly and uncon- 

 sumed through the flues, with a thick volume of dark smoke by 

 the chimney. Enough air only should be admitted to convert the 

 carbon of the fuel into carbonic acid by its oxygen, the hydrogen 

 being converted into water in the shape of vapor. In this con- 

 dition of a furnace, the products of combustion become invisible, 

 so that we may justly conclude that smoke is the measure and 

 gauge of imperfect combustion. 



"Some turnace-makers admitted air through the furnace-doors 

 by a few large, or many small openings ; others, behind the bridge ; 

 but, in every case, cold air. In the ' Atiiory ' furnace, at a proper 

 distance from the fire, is placed a coml)ustion, or reverberating 

 chamber of concavo-convex hollow iron curves, concave toward 

 the fire, when a single one is used, and the length of grate-bars is 

 sufficient to admit the loss of so much fire-surface ; the curve on 

 the level of and just behind the fire; — concave toward each 

 other when two are used, above and at a greater or less distance 

 from the fire. Between the curved iron plates (best made of 

 boiler-plate one-eighth or one-sixth of an inch thick) is a hollow 

 space, communicating underneath with each, into which air is 

 received, heated b}^ passing through a pipe introduced through 

 the boiler, or otherwise, the air communicating with the fire- 

 chamber by several openings on the concave surfaces. It is also 

 necessary that the anterior curve be lower than the posterior, 

 to insure and facilitate the revolving of the gases in the chamber. 



*' The principles of this furnace have for several years been 

 applied to locomotive, stationary, house, and steamboat furnaces, 

 with the most satisfactory results, as the testimonials appended 

 will show ; and it is confidently recommended to engineers, ma- 

 chinists, and builders, as meriting all that is claimed for it in 

 the saving of fuel and the consumption of smoke. 



" This "furnace neither draws the air through the fuel by the 

 production of a partial vacuum behind it from high temperature 

 and rarefaction in the chimney, nor forces air through it by com- 

 pression, or other mechanical contrivance, before the fuel, — the 

 first exceedingly wasteful, and the second inconvenient and un- 

 necessary; but it secures a most perfect combustion and free- 

 dom from smoke, by the retention and reverberation of the gas- 

 eous products in a circular chamljcr, in which a due amount of 

 heated air is introduced, converting, in this way, much carbonic 

 oxide (usually escaping by the chimney) into carbonic acid gas, 

 and thus saving a great amount of caloric. 



