fine, and both were of good quality. In starting fires, but a very small quantity of pine wood was used with either. The grate bars were — inches thick, with inch air spaces between. Bracing of the Boilers.-The bracing of this kind of boilers at the flues is peculiar; it is represented in fig. 2. The flat flues it will be observed are braced in the fire spaces, and not in the flat spaces, as in ordinary boilers. These braces are studs of wrought iron, with a collar on the inside abutting against one side of the flue; this side of the flue is punched, and the outer end of the stud passed through it and riveted over; the opposite side of the flue only abuts against or touches the other end of the stud, as the force to be withstood is that of compression solely. Of course, with this system, it is absolutely necessary to fit the boilers with an air valve opening inward by the atmospheric pressure, or a vacuum valve, as it is commonly called. It is obvious on inspection, that the sides of the boilers cannot be braced from, or stayed to the sides of the side flues, because of the unbalanced pressure that would result on those flues; for the studs communicate the pressure from one side of the flue to the other, and if this other be again stayed to the side of the boiler, it is plain the pressure on one side of the Alue and on the side of the boiler will be in the same direction; and these two pressures will only be resisted by the pressure on the other side of the flue. Now, as the pressures on each side of the flue balance each other only, it would leave the pressure on the side of the boiler wholly unbalanced. To brace the sides of the boilers, then, it is necessary to tie them across above and below the flues by heavy tie rods, and as this leaves the flat side for more than the depth of the flue unsupported, that side must be stiffened by a heavy vertical bar of wrought iron fastened to the side at the usual intervals for braces by lugs. These vertical bars are placed lengthways the boilers at the usual intervals for braces, and the heavy tie rods are fastened to the bars at top and bottom, unless the flues descend to nearly the bottom of the boiler, when that bottom becomes itself the tie rod. Of course, each pair of these rods must be sufficiently strong to sustain the pressure on the whole surface comprised longitudinally between the centres of the vertical bars and vertically between the centres of the tie rods. The system is shown in fig. 3. Trial Trip. On the 30th December, 1852, an engineer's trial trip was made from the Navy Yard at Washington down the Potomac river to Fort Washington and back. The Hon. Mr. Kennedy, Secretary of the Navy, and Commodore Shubrick, Chief of the Bureau of Construction, with a number of other gentlemen, were on board. The time occupied in running between the given points was accurately noted. The brick work of the boiler was as shown in fig. 1; the 7 inches high brick wall being under the hanging bridge, and the brick work in the top part of the front end of the flues being 22 inches down. The hinged hanging plate marked 6 inches, and depending below the hanging water bridge, was not on. The water was perfectly smooth. In running from the Navy Yard to the Fort, the tide, which is here without much influence at the strongest, was at the flood; the gentle southerly breezes were unfavorable. On the return, the tide was ebbing fast, but the same breezes as before were now favorable. The distance from the Arsenal (14 miles below the Navy Yard) to the Fort and back to the Arsenal, including turning, traversed by the vessel, is 21 miles. Time occupied in running it, 110 minutes; mean draft of the vessel 7 feet; immersion of the lower edge of the paddle, 2 feet 11 inches. The consumption of coal was ascertained by careful measurement. The speed as given by the chip log was large 9 knots per hour, or 10.944 statute miles. It is well known that when the speed of a vessel exceeds 8 knots per hour, the indications of the chip log become too low. Speed of vessel in statute miles per hour, 11.4545 25 Slip of the centre of pressure of the paddles in per cents. of its speed, 24-63 18 pounds. 36 or 2 feet 2 inches. 666 pounds. 6.252 Steam cut off at from commencement of stroke of piston, 66 66 66 1919-521 0:383 10.918 19.4 pounds. 194-78 Trip from Washington to Baltimore.-On this trip, the brick work of the boiler was as shown in the large engraving. The vessel drew 9 feet 5 inches forward and 8 feet 5 inches aft; mean draft 8 feet 11 inches, having 120 tons of Lackawanna anthracite on board, with full stores, &c. Immersion of lower edge of paddles, 4 feet 7 inches. The vessel was very badly trimmed, being a foot by the head. Left the Arsenal on the 15th January, 1853, at 7 hours 5 minutes, A. M., and steaming down the Potomac river, was abreast of Point Lookout at 7 hours 56 minutes P. M., the same day. Time 12 hs. and 51 m., from which there is to be deducted 1 hour and 10 minutes for stoppages to repack cut-off dash ports, leaving the running time 11 hours and 41 minutes. Distance by Chart 102 statute miles; smooth water and light fair winds. No blowing off done. Slip of the centre of pressure of the paddles in per cents. of its speed, 8.730 18.264 21:39 11.3 pounds. 62 or 3 feet 8 inches. 631 pounds. Steam cut off at from commencement of stroke of piston, Mean effective pressure on piston per square inch, by indicator, After rounding Point Lookout, the Water Witch proceeded up Chesapeake Bay to Baltimore, against about half a gale of wind and considerable sea, and at 9 hours 50 minutes A. M., January 16th, stopped the engines and anchored in Baltimore harbor; distance from Point Lookout, 97 statute miles; time, 13 hours 54 minutes. During this half of the trip steam was carried as high as possible, and the performance of the boilers may be considered their maximum. No blowing off done. RESULT. Speed of the vessel in statute miles per hour, 6.978 18.508 Slip of the centre of pressure of the paddles in per cents. of their speed, 37.98 by indicator, 22.3 pounds. Steam cut off at from commencement of stroke of piston, 59 or 3 feet 6 inches. Consumption of Lackawanna anthracite per hour, 909 pounds. Pounds of steam evaporated per hour, from brackish water, with tem- 2486.080 0.497 14.902 Pounds of steam evaporated per hour, from brackish water, with tem- 66 66 66 66 66 Mean effective pressure on piston per square inch by indicator, 25.7 pounds. 191.02 Trip from Baltimore to Norfolk.-On the arrival of the Water Witch at Baltimore, the grates were altered so as to be 7 feet instead of 6 feet long. This alteration involved no others, and the rest of the boilers remained as before. This change made the grate surface 71 square feet instead of 61 square feet. The vessel left Baltimore on the 19th Jan., 1853, at 11 hours 45 minutes, A. M., and anchored off the Navy Yard, Norfolk, at 7 o'clock A. M., Jan. 20th. On the passage several stoppages occurred from causes not connected with the machinery, involving a loss of one hour and a quarter, making the running time 18 hours. Distance by Chart, 190 statute miles; moderate wind and sea on the port quarter, but no sail set. The counter being out of order, the revolutions of the wheels were noted at regular intervals by the watch. Draft of vessel, 8 feet 9 inches forward, and 8 feet 10 inches aft; immersion of lower edge of paddles, 4 feet 5 inches. No blowing off done. RESULT. Speed of the vessel in statute miles per hour, Slip of the centre of pressure of the paddles in per centums of their Initial steam pressure in cylinder per square inch above atmosphere, Pounds of water evaporated per hour, from bay water, with tempera- 1090 pounds. 3.313 pounds. 5.566 During the above trip the heat in the lower part of the smoke chimney was sufficiently great to burn off the paint. For the sake of ready comparison, I have collected the results of the foregoing trips into one table, an examination of which will show the effect produced by the various modifications of the boilers, and by the different drafts of vessel, immersion of paddles, &c. 11.4545 8.73 6.978 10-556 18.264 18.508 22.4 24.63 21.38 37.98 22.48 11.3 22.3 18.3 Speed of the vessel in statute miles per hour, 18 From the foregoing results it will be perceived that these boilers only gave an average performance, and the reason must be looked for principally in the cross area of the flue, compared with its length and surface. The heated gases passed out before their temperature was sufficiently reduced, and they were not brought in contact with the heat absorbing surfaces for the proper length of time. The thickness of the flue iron was a scant quarter of an inch; that of the other heat absorbing surface,ths of an inch. The flues were also too deep, probably 21 inches too deep, for the gases to diffuse over, and the main current of hot gas, and consequently, the principal heating portion of the flues, were to a great extent comprised between the dotted lines in the large engraving. The net cost of the boilers complete, was 13 cents per pound. By an examination of the table of results, it will be perceived that just in proportion as a greater amount of coal was burned, the evaporative result decreased. But the maximum amount burned per square foot of grate surface per hour, was only 15-352 pounds, with a proportion of heating to grate surface of 25.8 to 1.0, a proportion larger than sufficient to absorb the heat generated, had it been brought in contact with it; consequently, had all the heat absorbing surface been effective, the evaporation with anthracite would have been as high economically with the combustion of 1090 pounds, as with that of 631 pounds; but if the effective heat absorbing surface be considered greatly reduced, it is plain why the combustion of a less amount of coal in the same time should give a higher result. During the preceding trips, there was always a great amount of back pressure in the condenser, owing principally to the arrangement of the air pump, which was inclined, and had a solid piston. The engine never made what is called "a good vacuum." The indicator cards show the condition of the valves; Nos. 1 and 2 were taken in quick succession from the top and bottom of the cylinder, working full stroke at the Dock; revolutions of the wheels, 11 per minute. Nos. 3 and 4 were similarly taken during the trial trip, the cut-off remaining the same in both; revolutions of the wheels, 26 per minute. On the Arrangement of the Materials in the Blast Furnace, and the Application of the Waste Gases. By MR. SAMUEL H. BLACKWELL.* The use of the waste gases given off from the top of the blast furnace, has been long known and adopted in many of the Continental iron works. The higher cost of fuel, and the greater attention paid to a scientific knowledge of the most important process of manufacture, led to the use From the London Journal of Arts and Sciences, January 1853. |