of the upper shell, and the other was similarly placed near the after end. The lower shell was 71 inches in exterior diameter and 15 feet in extreme length. The upper shell was 68 inches in exterior diameter and 13 feet in extreme length. The ends of the shells were flat and vertical, and the after ones of both shells were in the same vertical· plane, the forward or furnace end of the lower shell projecting 24 feet forward of the corresponding end of the upper shell. The two shells were entirely inclosed in brick masonry, which formed exteriorly a parallelopipedon 19 feet long, 10 feet wide, and 13 feet 4 inches high above the level of the fire-room floor. The back and side walls were 21 inches thick, the front wall was 12 inches thick, and the flat top was supported beneath by brick arches resting on iron beams of H cross-section. The least thickness of the top was 4 inches, and its greatest thickness was 8 inches. In addition to the above brick walls, there was another which may be called the partition wall. It was entirely within the other walls, and vertical, with its after face in the vertical plane of the after ends of the two shells. This wall was six inches thick, and extended wholly across the inclosure formed by the exterior walls, and from its bottom to its top completely dividing it into two separate parts, one of which was 24 inches long in the clear, lengthwise the shells, and formed the channel for the gases of combustion in their passage from the after end of the lower to the after end of the upper shell. The remaining part was 12 feet long in the clear, lengthwise the shells, and formed the chamber containing the two shells. This chamber was filled with the gases of combustion which, after emerging from the forward end of the upper shell, enveloped the cylindrical parts of both. At the bottom of the back wall was an elliptical man-hole with diameters of 14 and 18 inches, to give admission to the after chamber or channel. In the upper part of the front wall was a rectangular opening opposite the forward end of the upper shell, closed by doors, and of sufficient size to allow the sweeping of the tubes and entrance into the large chamber containing the two shells. The two ends of the lower shell were supported on the front and partition walls of masonry, and on, equispaced between them, two iron castings. The upper shell was supported from the lower shell by their two vertical connecting pipes, and its after end also rested on the brick partition wall. Neither shell had any side supports. The lower shell contained two horizontal cylinders extending from one end of it to the other, and having their horizontal diameters in the plane of the horizontal diameter of the shell. These cylinders were 2-3622 feet in inside diameter and 15 feet in extreme length. In the forward portion of each cylinder, with a dead-plate 12 inches long between the forward end of the cylinder and the forward end of the grate, was placed a grate 6.5618 feet long, slightly inclining downwards toward the back. The bridge-wall was of fire-brick supported on an iron casting. The front end of the upper side of the grate was on a line with the horizontal diameter of the cylinder, and the back end was four inches below that line. The top of the bridge-wall was eight inches above the upper side of the grate at its back end. The upper shell contained seventy horizontal wrought iron firetubes of 4 inches external and 33 inches internal diameter, with an extreme length of 13 feet. These tubes are arranged, vertically, in seven rows, the horizontal diameters of those of the third row from the top being in the plane of the horizontal diameter of the shell. In the top row there are ten tubes, in the next three rows twelve each, in the next row there are ten tubes, in the next row eight, and in the lowest row six. The least spaces between the tubes, both vertically and horizontally, are 0.8 inch in the clear. The tubes are placed vertically, one immediately over the other. The normal water-level was 3 inches above the upper row of tubes, leaving 17 inches for the greatest height of steam room in the shell. On the top of the upper shell and at the middle of its length was placed, vertically, a cylindrical steam-drum with a curved top. The exterior diameter of this drum was 23 feet and its extreme height above the top of the shell was 23 feet. The steam from the shell was admitted to the drum through two perforated dry-pipes, which extended horizontally along the upper side of the shell. The steam-pipe connecting the boiler with the engine was bolted upon the top of the steam-drum. The chamber enclosed by the brick masonry and containing the shells extended 16 inches deep below the lower side of the lower shell, and from this lower part, and at the back end of the shell, the gases of combustion were carried to the chimney through a horizontal flue of masonry lying beneath the floor of the boiler-house. From the foregoing description it will be seen that the gases of combustion after crossing the bridge-walls in the lower shell, pass horizontally through the cylinders behind them into the channel or back chamber of the masonry; thence they ascend vertically, enter the tubes in the upper shell, and, passing horizontally through them, debouche into the front chamber of the masonry, where they spread out and completely envelop both shells as they descend vertically to the bottom of the chamber and enter the horizontal brick flue which conducts them to the chimney. The direction of the gases is thus changed, first from horizontal to vertical, then from vertical to horizontal, and finally from horizontal to vertical, before they leave the heating surfaces; the distance they travel from the centre of the furnaces to the horizontal flue leading to the chimney is about 40 feet. The surface of the steam room in the upper shell is steam superheating surface. The following are the principal dimensions and proportions of the boiler, namely: Extreme length of brickwork, Extreme breadth of brickwork, 19 feet. 10 feet. Extreme height of brickwork above bottom of chamber, 14 feet. 3 inches. 4 inches. 13 feet. 5.3689 sq. ft. 2.8000 sq. ft. Aggregate cross area for draught over the bridge-walls, walls, Heating surface in back ends of the two shells, ft. Heating surface in the tubes, calculated for inside di 893.3925 sq. ft. 10.6387 sq. ft. 141.6616 sq. ft. Heating surface in the front end of the upper shell, Total steam superheating surface in the boiler, Steam-room in the boiler, 249-4903 sq. ft. 1506.2813 sq. ft. Square feet of water-heating surface per square foot of grate surface, Square feet of steam superheating surface per square foot of grate surface, Square feet of grate surface per square foot of draught area above bridge-walls, Square feet of grate surface per square foot of draught area through tubes, COAL. 75.8000 sq. ft. 497-2077 cu. ft. 111.0882 cu. ft.. 48.5897 2.4451 11.0714 5.7740 The fuel consumed during the experiment was a good quality of semi-bituminous coal of the kind in daily use at the establishment, and it was burned just as received from the mine. A special analysis of this coal gave the following for its centesimal composition: |