boiler is 14 feet mean diameter outside, and 20 feet long, and has eight furnaces 36 inches least internal diameter.

Grate-surface. - Total grate-surface in four boilers is 624 square feet.

Grate-bars.-The grate-bars are of wroughtiron, in two lengths, of approved pattern. The furnace-fronts, bridge-walls, and bearers are properly fitted to support the bars.

Tubes.-Each boiler contains nine hundred and sixty-four lap-welded wrought-iron tubes. Every third tube, vertically and horizontally, is a stay-tube, and is No. 8 B. W. G. thick and 24 inches external diameter. The other tubes are No. 12 B. W. G. in thickness, 24 inches external diameter.

The stay-tubes are screwed into both heads, the ends at front heads to be swelled. They are expanded into both heads and beaded over at combustion-chamber ends.

Boiler-shells.-The shells are of plates 1% inches thick, the longitudinal joints are doublestrapped and double-riveted each side of seams. The circular joints are lap-jointed and doubleriveted.

Tube-sheets.-The tube-sheets are inch in thickness, and are accurately drilled for the. tubes.

Boiler-heads and Braces.-The upper portion of the heads are % inch thick and the lower

portion inch thick. The upper portions of heads are braced by three rows of steel stays 22 inches diameter in the body, 17 inches between centers horizontally, and 13 inches vertically. Jaw-braces are of iron. The tops of combustionchambers are stayed to shell by 134-inch iron braces with crowfeet on top of the chambers, placed 64 inches apart in length of boiler and 13 inches in the diameter. All steel braces are without welds in length or eyes. The through braces are made with nuts on both sides of boiler heads, having raised threads on ends.

Furnaces.-The furnaces are of the best steel, welded at joints, and corrugated. They are 36 inches diameter at the inside of corrugation, 1⁄2 inch thick, and are single-riveted at their junction with front heads and combustion-chambers. Ash pans of 4 inch wrought-iron are fitted in all furnace-flues reaching from front to bridgewall.

Bridge-Walls.-A bridge-wall of approved pattern is fitted in each furnace. The upper part is finished with fire-brick. The bridgewalls are easily removable.

Combustion-Chambers. The combustionchambers are 54 inches deep; the sides, tops, ends, furnace-plates and tube-sheets inch thick. The sides stayed by steel screw staybolts 14 inches diameter, spaced 65% inches from

center to center.

Smoke-Boxes and Uptakes.—The smoke-boxes and uptakes are made with single shell, covered with an approved non-conducting substance and protected by an outside shell. The inner shell is secured to boilers by 21⁄2-inch angle-irons. Both shells are made of iron inch and 1⁄2 inch thlck, respectively.

The connection doors are made of wroughtiron with double shells, and fitted with hinges and catches of wrought-iron. The outside shell is,& inch thick, and the lining % inch thick.

Furnace fronts. The furnace-fronts are of wrought-iron 3% inch thick, with cast-iron perforated liners.

Furnace-doors. The furnace-doors are of wrought-iron 14 inch thick, with cast-iron perforated liners.

Ash-pit Doors.-The ash-pit doors are of wrought-iron inch thick, flanged 1 inch deep, and fitted to place so as to thoroughly close the ash-pits, and fit lugs on bulkhead when not in

use.

Saddles.-Each boiler is to rest on three saddles, which are built in and form part of hull. The boilers are secured by double angle-irons riveted to saddles and bolted to boilers.

Smoke pipes.-There are two smoke-pipes 60 feet in total height above the upper grates. They are 6 feet 9 inches in diameter, made of wrought-iron plates; the lower course No. 7

B. W. G. thickness, the upper ones No. 8. The pipe is stiffened by flat bands on the inside, at top and bottom, and by a band 4 inches wide and I inch thick on outside at top. The pipe is inclosed its entire length by a jacket, leaving an annular space of at least 3 inches. The jacket is of wrought-iron, No. 13 B. W. G. thick, and covered by a hood for the escape of hot air. The pipe and jacket are made with strapped buttjoints. The smoke-box and breeching inclosed by a jacket made of No. 16 iron. The pipe is provided with stays, eyes and shackles, and is supported in such a manner as to relieve the uptakes of its weight. A pivoted damper is fitted in each smoke-pipe.

Dry pipes. -Each boiler has a perforated tinned-brass dry pipe of reduced diameter at the internal end, but of same diameter at front end as the steam-pipe with which it is connected. It is placed as high as possible, and extends nearly the length of the boiler.

Its upper surface is pierced with holes 3% inch in diameter, spaced equidistant, their aggregate area to be twice that of the cross-section of the pipe.

Boiler Clothing.-The boiler shells and fronts are covered with approved material, which is protected by a galvanized-iron covering, the joints of which are lapped and bolted.

Safety-valves.-Each boiler has two automatic

spring safety-valves 6 inches in diameter, adapted to a maximum pressure of 160 pounds per gauge, and fitted with proper levers and approved mechanism for working them from the firerooms. The chests, valves and stems are of composition, and seats of nickel.

The chests are bolted to stop-valve chambers, and connected by copper pipes to the escapepipes, which are also of copper. The seats of all safety-valves are at least 1⁄2 inch above the bottom of their chests.

Sentinel-valves.—There is a sentinel-valve of 1⁄2 square inch area attached to the front of each boiler, fitted with movable weight and notched lever, and weighted to close tightly against a boiler pressure of 175 pounds per square inch.

Water-gauges.-Each boiler has two composition water-gauges carrying glasses 16 inches in exposed length, and with outside pipe-connections to top and bottom of boiler, the bottom of glass being 1 inch below the highest heating surface. The water-level is marked on brass plate on outside of boiler.

There are four gauge-cocks on each end of boiler, placed 4 inches apart, the lowest cock 4 inches below the highest heating surface of the boiler.

Salinometer-pots.-There is a salinometer-pot of approved pattern for each boiler, fitted in an accessible position and suitably connected,