These boxes being piled one upon another, and all in contact, like bricks in a wall, form the front and back walls of the boiler for the height occupied by the tubes. These fixed boxes are connected on their outside, vertically, by movable cast iron boxes, rectangular in cross section, and held in position by cross-bars secured by bolt and nut after the manner of securing manhole plates in a boiler. Every Method of connecting Tubes. two vertically adjacent fixed boxes, at front and rear of boiler, are connected by one movable box, which being taken off with the same degree of labor required for removing a manhole plate, exposes the interior of two tubes for examination and cleaning. In outer crosssection, the movable boxes are 4.13 inches wide and 3.86 inches deep; least thickness of metal, ğ inch. The joints between the fixed and movable boxes are made by means of a wrought iron thimble 31 inches long and 3:39 inches inner diameter, the outer side of the thimble forming two frustra of cones united at their bases. The holes in the boxes for receiving these thimbles being made of corresponding bevel to the frustra, the cross-bar, bolt and nut force the beveled surfaces into metallic contact, and thus form a joint water-tight under the boiler pressure. By means of these combined fixed and movable boxes, the water ascends from the lower horizontal cast iron box of 10 inches square cross section and 9 feet 2 inches length to the upper horizontal cast iron box of the same dimensions, by passing alternately forwards and backwards through the intervening tubes, ascending simultaneously each vertical row of tubes. The combined fixed and movable boxes answer exactly the same purpose as the cast iron bends with ordinary steam-heaters for rooms, with the advantage of easy separation. All the tubes are roofed over by a brick vaulting 23 inches thick, supported on iron girders of H cross section. This vaulting extends from the front to the back wall, and between the side walls of the boiler, thus completing the entire enclosure of the tubes and furnace. A horizontal wrought iron conduit carries the gases of combustion from the top of the back end of this enclosure to the chimney. Immediately above the vaulting is a large horizontal wrought iron cylinder, with segments of spheres for ends. The cylindrical part is 41 inches in external diameter and 11 feet in length. The axis is in the vertical plane passing longitudinally through the centre of the boiler; and the cylinder, with the exception of the front end, is encased in brick masonry the outside of which is rectangular. At the front end of this large horizontal cylinder and upon its top is a small vertical wrought iron cylindrical steam-drum of 311⁄2 inches diameter and 271⁄2 inches height, with a flat top, from which the steam is taken to the engine. Only the lower portion of this steam-drum to a small extent is cased in masonry. The object of carrying up this small steam-drum was to obtain height of steamroom to insure a supply of dry steam. The interiors of both cylinders are in common and constitute the steam-room, which was of very great capacity proportionally to the capacity of the engine cylinder and its speed of piston. A small portion of the lower part of the large cylinder is occupied by water, which, entering at the front end with the steam, passes out at the back end by a pipe to be described. The large horizontal cylinder communicates on each side of its forward end, on the level of its horizontal diameter, with the two ends of the upper horizontal cast iron box of 10 inches square cross section and 9 feet 24 inches extreme length, by means of curved pipes 9 inches in diameter, through which the cylinder receives the steam generated on the tube surfaces, and any water that may come with it. At the bottom of the back end of the large horizontal cylinder a pipe of 10 inches diameter and 12 inches length communicates with the centre of a horizontal pipe of 8 inches diameter, lying upon the top of the back wall of the boiler. This horizontal pipe has a length equal to the breadth of the boiler, and from each extremity a vertical pipe of 8 inches diameter descends to the corresponding extremities of the lower horizontal cast iron box of 10 inches square cross section and 9 feet 2 inches extreme length, thus completing the circulation of the water. In order that the gases of combustion may pass over the entire tube surface, instead of taking a straight course from the grate to the chimney outlet, two diaphragm plates of wrought iron are introduced horizontally betweeu the tubes, one above the other, in such manner as to equally divide the tubes. Both diaphragms extend entirely across the boiler, with one end touching either the front or back wall of the boiler, and leaving between the other or free end and the front or back wall, as the case might be, a sufficient space for the passage of the gases. The lower diaphragm leaves this space between its free end and the back wall of the boiler 2 feet 3 inches; the upper diaphragm leaves this space between its free end and the front wall of the boiler 1 foot 5 inches; so that the gases, after passing over the lower four horizontal rows of tubes in a direction from front to back, returns from back to front over the next four horizontal rows, and, finally, takes their original direction from front to back over the remaining four rows. From the foregoing description of the boiler will be seen that unusual precautions were taken to keep the current of the gases of combustion thoroughly broken up and mixed, and to compel it to pass. over the whole of the heating surface: the zig-zagging of the tubes, their position in the current which had to pass over them in a direction at right angles to their length, as well as in the direction of their length, and the deflections produced by the diaphragms, causing the whole of the gases to pass in succession over only one-third of the tubes at a time, must have accomplished very completely the purpose. The following are the principal dimensions and proportions of the boiler: Length over all, including masonry, Height from bottom of ashpit to top of large hori 13 feet 8 inches. 9 feet 2 inches. 15 feet 4 inches. Length of grate, Grate surface, Number of tubes at sides of furnace, Exterior diameter of tubes at sides of furnace, nace, 36. . 5 inches. Length of the remaining 24 tubes at the sides of the furnace, Number of tubes immediately over the grate, Exterior diameter of tubes immediately over the grate, Interior diameter of tubes immediately over the Length of the tubes immediately over the grate, calculated for half their inner circumference, Aggregate area of heating surface, calculated for outer circumference of the tubes, Aggregate cross area between tubes horizontally, 51⁄2 inches. 7 feet 10 inches. 9 feet 6 inches. 144. Cross area between lower diaphragm and back wall of boiler, Cross area between upper diaphragm and front wall of boiler, Length traversed by the gases of combustion from Steam-room, Square feet of heating surface per square foot of grate surface, calculated for inner circumference of tubes, Square feet of heating surface per square foot of grate surface, calculated for outer circumference 2.2017 sq. ft.. 1.3863 sq. ft. 22 feet. 269 square feet. 226.1 cub. feet. 102.5 cub. feet. 46.6424. of tubes, 49.1153. Square feet of grate surface per square foot of open- 18.3832. 29.1960. COAL. The coal consumed during the experiments with this boiler was semi-bituminous, from the mines of Monceau-Fontaine. It was an excellent steam-coal, and before being used had its dust separated by screening. Analyses were made of two specimens, with closely agreeing results, of which the following are the mean : |