708 



STEAM-BOILER INSPECTION AND EXPERIMENTS. 



New York on board that vessel, -with great destruc- 

 tion of property and life. This box was 6 feet long, 

 4 feet high, and 4 inches wide, all over. The two 

 side-plates were of the best flange fire-box iron, T S 

 of an inch thick, manufactured by the " Abbott Iron 

 Company." The plates were held together by a 

 single row of rivets at their edges, passing through a 

 frame made of wrought-iron bars, mitred at their 

 ends, and having the same outside dimensions as 

 the box. These bars were 3t inches wide, 2 inches 

 deep, and perforated at the centre line by the holes 

 for the rivets. The side-plates were braced together 

 every 8$ inches one way and 9 inches the other 

 way of their surface, by bolts of H inch diameter, 

 with threads cut upon each end and screwed into 

 corresponding threads cut in the plates over which 

 both ends of the bolts were slightly (and but very 

 slightly) riveted. The box was placed on one edge 

 upon an 8-inch-thick brick wall, and was enclosed 

 with side-walls of brick masonry, with the exception 

 of a strip 15 inches deep at the top and 12 inches 

 wide at one side, which protruded into the air, and 

 to which the gauges were attached. The enclosed 

 portion of the box was heated by two small furnaces 

 without intercommunication, the fire-grates of each 

 being 27 inches long and 14 inches wide. The fuel 

 was wood, and the products of combustion were dis- 

 charged through two sheet-iron pipes. The surface 

 of the box exposed to the fire was 19i square feet, 

 and was all water-heating surface, as the box was 

 filled with water to within 9 inches of its top. Of 

 the total interior -height of the boiler, therefore, 37 

 inches were occupied by water and 7 inches by 

 steam. The fires being brought to steady action, 

 and steam raised to the atmospheric pressure, the 

 opening for the escape of the latter was closed, and 

 the pressure rose gradually, in 33 minutes, to 165 

 pounds. 



When the pressure reached 165 pounds to the 

 square inch, the box exploded with a loud report, 

 completely demolishing the brick-work by which it 

 was enclosed. The two sides were hurled in exactly 

 opposite directions^ and to about equal distances, at 

 right angles to their surfaces. The fracture had oc- 

 curred in one plate only, and was along the whole 

 riveted seam joining it to the frame. For a large 

 part of the length of the seam, this plate was torn 

 out between the rivets, and for the remaining part 

 the rivets were sheared. The other plate was not 

 fractured, nor were the bars of the frame broken ; 

 the plate and the frame remained riveted together, 

 but not uninjured all the bars of the latter being 

 bent considerably inward, forming an irregular 

 curve of from 4 to 6 inches versed-sine. Both plates 

 were bulged out irregularly, so as to be about 9 

 inches' dishing, and the bulging took place near tho 

 bars. Not one of the bolts was broken, and neither 

 the threads upon their ends, nor the threads in the 



Slate, were stripped or injured, but the slight rivet- 

 ig over of the ends of the bolts was broken off in 

 all of them. 



The fact that the plates did not rupture at the 

 centre, under their great amount of bulging (and 

 only one of them tearing off at t'he line of rivets 

 alonof its edge), shows the excellence of the inetal 

 which endured this great, almost instantaneous, and 

 permanent stretching without fracture ; and to this 

 same extensive stretching must be attributed the 

 escape of the screw-threads on the ends of the bolts, 

 and in the plates, from injury. The plate, by stretch- 

 ing, simply enlarged the diameter of the hole in 

 which the threads were cut, until the bolt, thus left 

 free, slipped through without injury to its threads, 

 only breaking off the slight riveting over of its ends. 

 Had these bolts been secured by nuts on the outside 

 of the plates, the box would have borne an enor- 

 mously greater pressure than that which exploded 

 it. Between the bol|s there was a small permanent 

 stretching of the plates, giving eaoh space between 

 th.e bolts a slightly dishing or bulged form, in addi- 



tion to the general bulging of the plates, thus form- 

 ing a system of secondary bulges, as it were ; and 

 around every bolt both plates were strongly marked 

 by a congeries of circular crispations. 



The conclusions from this experiment are: That 

 a gradually-accumulating steam-pressure in a boiler 

 can produce a true explosion, violently^ hurling its 

 fragments, with a loud report, to a considerable dis- 

 tance, even though 84 per cent, of its capacity be 

 filled with water ; and that screw-bolts should not 

 be used in boiler-construction without nuts, or hav- 

 ing, as an equivalent, a large portion of their ends 

 formed into massive rivet-heads ; because the stretch 

 of the plates is sufficiently great, under a much less 

 pressure than will fracture the bolts or strip their 

 threads, to allow the latter to slip through unin- 

 jured. 



Previous to this experiment, the box had been 

 subjected to a hydrostatic pressure of 138 pounds per 

 square inch, and to a steam pressure of 102 pounds 

 per square inch, without fracture. 



The third experiment was made on November 23d. 

 The boiler exploded during this experiment was 

 built by T. F. Secor in 1845, and taken out of the 

 steamboat Bordentown in August last, after having 

 been twenty-five years in use. When taken out, the 

 inspector's certificate allowed it to be worked with a 

 pressure of 30 pounds per square inch. It was a 

 horizontal fire-tube boiler, with the tubes returned 

 immediately above the furnace and combustion- 

 chamber. 



It had but one furnace, and that was 11 feet 5 

 inches in width, with grate-bars 7 feet in length. 

 The top of the furnace and the top of the combustion- 

 chamber were flat, and braced to the flat top of the 

 shell above th.em by rectangular braces 2 inches by 

 i inch in cross-section, placed 17 inches apart cross- 

 wise the boiler, and 12 inches apart lengthwise the 

 boiler, each brace holding a flat surface of 204 square 

 inches, to which it was attached by crow-feet so ar- 

 ranged that the flat surface between the sustaining 

 rivets was 12 inches square. The flat water-spaces 

 wei'e braced at intervals of 8 inches in one direction, 

 and 12 inches in the other, by 1 inch diameter screw- 

 bolts, each of which held a flat surface of 96 square 

 inches. The iron plates of the boiler were a large i 

 inch thick. The tubes were of iron, and 384 in num- 

 ber, arranged in 8 r6ws vertically and 48 rows hori- 

 zontally. Each tube was 2 inches in outside diam- 

 eter and 12 feet in extreme length. The total height 

 occupied by the tubes, from the lower side of the 

 lower tube to the upper side of the upper tube, was 

 22 inches. The tubes were divided into sixteen 

 groups, and the groups were separated by water- 

 spaces 2rV inches wide in the clear vertically, and H 

 inch wide in the clear horizontally. From the lower 

 side of the lower row of tubes to the top of the fur- 

 nace and combustion-chamber, was a space 6 inches 

 in width for water-circulation. The bridge-wall and 

 the bottom of the combustion-chamber were of brick. 

 The furnace had no water-bottom, but its side-lei: H 

 of 4i inches' width rested in a pan which covered 

 the entire area beneath its furnace. 



The shell of the boiler was rectangular, with the 

 exception that the vertical sides were joined to the 

 flat top by quadrantal arcs of 37 inches' radius. All 

 the seams were single riveted. Upon the centre of 

 the boiler was a cylindrical steam-drum of 6 feet 

 diameter and 8 feet 8 inches height. The flat water- 

 space at the front of the furnace was 41 inches wide, 

 and that at the back end of the boiler was 5 inches 

 wide, including thicknesess of metal. The width of 

 the boiler was 12 feet 2 inches, its length was 15 feet 

 5 inches, and its height, exclusive of the steam-drum, 

 was 8 feet 6 inches. The shell was braced very un- 

 equally. Each upper horizontal brace, 1} inch large 

 in diameter, sustained the pressure upon a surface 28 

 by 12 inches, or 336 square inches ; and each rectan- 

 gular vertical brace adjacent the sides, 2 inches by I 

 inch in cross-section, sustained the pressure upon a 



