POLTTECHXIC ASSOCIATIOX. 725 



original position of the boiler, crushing several trees in their fall. 

 Two other large fragments fell at less distances, while smaller ones 

 were thrown much farther. Almost the whole of the boiler was lit- 

 erally torn into shreds, which were scattered far and wide, the only 

 portion remaining where the boiler had been being the tubes. These, 

 though considerably distorted, were otherwise uninjured. Both tube- 

 plates had been blown from the tubes in opposite directions, and at 

 the same moment, for nearly all the tubes were found lying in a heap 

 on the ground immediately beneath the place they had occupied in 

 the boiler, the riveting of their ends over the plates having been 

 simultaneously stripped. The top of the furnace and the top of the 

 combustion chamber, which, in the boiler, were immediately beneath 

 the tubes, had entirely disappeared into debris, as had also the sides 

 and ends of the shell. The boiler seems to have first yielded by the 

 fracture of the upper row of horizontal braces. The loud report 

 heard, when the pressure attained fifty pounds per square inch, was 

 probably caused by their breaking. The larger masses were all thrown 

 in one direction — at right angles to the side of the boiler ; but the 

 smaller fragments were projected radially in all directions, as from a 

 center. Two heavy bomb-proofs, constructed of large timbers and 

 sand for the protection of the other boilers, were dislodged, and a 

 part of the fence of the inclosure was destroyed by the impact of the 

 flying fragments. The crow-feet, in most cases, remained firmly 

 attached to the shell, and the braces had parted — probably in the 

 welds — leaving the ends still secured to the crow-feet. The screw- 

 bolts, which braced the flat water-spaces, had slipped from their fast- 

 enings in the plate without injury to the screw-threads either upon 

 them or in the plate. The latter was permanently bulged or dished 

 between the bolts, and this stretching of the metal had, by its enlarge- 

 ment of the holes, allowed the screw ends of the bolts to draw out 

 without injury to the threads either on the bolts or in the plates. 



The ground beneath, and for a considerable distance around where 

 the boiler stood, was saturated with the water of the boiler; in fact, 

 made into mud, and the adjacent grass and small shrubbery were so 

 drenched that an ordinary boot was wet through by walking among 

 them. At seven minutes before the explosion took place, the water- 

 gauge on the boiler was examined and found to indicate the water- 

 level fifteen inches above the top of the tubes. 



The conclusions to be' drawn from this experiment are the follow- 

 ing : 



1st. An old boiler, containing a large mass of water above the 



