7G4 Transactions of the American Institttie. 



" In the first experiment, we probably have an illustration of by far 

 the most usual behavior of steam boilers, when yielding to over-press- 

 ure. The pressure gradually rising, ruptured the boiler at its weakest 

 point, which happened to be a spot of merely local weakness ; the rent 

 extended toward stronger portions, but soon became large enough to 

 discharge the steam as rapidly as it was made. The strength of the 

 metal in the direction of the line of fracture being sufficient to resist 

 further extension at the maximum pressure attained, no greater injury 

 was done. The spot being patched, the boiler is still probably capable 

 of doing good service for a considerable length of time. 



"When boilers give way from excessive weakness or' from steam 

 pressure, they very generally do so in the manner described. The 

 explosion is the exceptional case, and the frequency with which old 

 boilers " blow out " in every part, though usually about the stayed 

 surfaces, and the apparent impunity with which they are kept at work 

 after being frequently patched, has probably been the most influential 

 cause of the existence of the belief, which is, unfortunately, wide- 

 spread among engineers, that the mere pressure of steam cannot cause 

 explosions, and that, if the boiler contains a sufficient quantity of 

 water, it is perfectly safe, except against sundry mysterious forces, 

 which are probably, like the fairies and ghouls of earlier times, existent 

 only in the imaginations of tlTose whom they terrify. 



"'In the second and third experiments, we have illustrations of the 

 comparatively rare cases in which explosions actually occur. 



" The second was a perfectly new construction, in which corrosion 

 had not developed a point of great comparative weakness, and the 

 fracture occurring simultaneously, and very equally on all sides, the 

 two halves were completely separated and thrown far apart with all 

 the energy of unmistakable explosion, although there was an ample 

 supply of water, and the pressure did not exceed that frequently 

 reached in locomotives and on the western rivers, and although the 

 boiler itself was quite diminutive. 



" The unexpected circumstance of the drawing out of the stay-bolts, 

 without breaking and without stripping their threads, was one of the 

 most interesting points of the experiment. 



" In the third experiment, as in the second, it is probable that the 

 weakest part extended very uniformly over a large part of the 

 boiler, either in lines of weakened metal, or over surfaces largely 

 acted upon by corrosion. Immediately upon the giving way of its 

 braces, fracture took place at once in many different parts. 



