1874.] Zub [Cresson. 



ence to the time-table, that' the engine would have to remain upon the 

 siding until an expected passenger train had passed. The engineer then 

 left the engine, having first stopped off the steam-blower and observed a 

 steam pressure of about 90 lbs. per square inch. 



The boiler exploded between ten and twenty minutes after the engineer 

 had left it. The fireman, who had been cleaning the valves of the sand- 

 box, was at work upon the engine when the explosion took place, and 

 when last seen was standing upon the left side of the engine near the 

 donkey-pump, which was used to supply the boiler with water when the 

 engine was upon the siding. The portion of the boiler immediately over 

 and back of the crown-sheets of the fire-box, and including the back 

 dome, was blown off bodily, the line of fracture passing indiscriminately 

 through the seams and across the sheets. 



The seams not torn apart were strained in some places as much as ^ of 

 an inch and opened. The fire-box was blown backwards, carrying with 

 it the back tube-sheet. The remaining portion of the waist of the boiler 

 and the engine were driven forward along the track, the tubes remaining 

 fast in the forward tube-sheet. An examination of the fire-box showed 

 the crown-sheet to have been forced violently downwards, one edge crush- 

 ing the side-sheets of the fire-box, the other edge and the ends of the 

 crown-sheet remaining nearly in place. 



Every stay that was displaced was either fairly broken or drawn 

 through the sheets. There were no signs of undue pressure upon any 

 joint or part of the remaining waist of the boiler, excepting at the line 

 of rupture. 



The iron in every part of the boiler appeared in good condition, without 

 signs of burning or heating, except in one lower corner of the fire-box, 

 which part, however, was not ruptured or affected by the explosion. Trial 

 pieces of the iron cut from several parts of the fire-box and waist-sheets 

 exhibited good fracture, the lowest tensile strength found was 51,000 lbs. 

 to the square inch. 



After a careful examination of the wreck, and of the results of my own 

 experience, I have arrived at the conclusion that the explosion of this 

 boiler was caused by the projection of water upon the heated crown-sheet. 

 The crown-sheet of the furnace was most probably heated to a tempera- 

 ture of between 500° and 600° Ft., in consequence of a neglect to keep 

 the water in the boiler at the proper height. 



This temperature, not sufficient to produce a spheroidal state of the 

 water thrown upon the crown-sheet, allowed of enough heat to be stored 

 up and given out suddenly to cause steam of very high pressure to be 

 instantly generated, so that the rear portion of the boiler was blown to 

 pieces before a sufficient time had elapsed to allow of the distribution of 

 the expansive force throughout the waist. By reference to the results of 

 experiments detailed in the following paragraphs, it will be seen that an 

 average of ^-^-^ of an inch of depth of water over the crown-sheet could 

 readily be converted into steam in one second of time, and would produce 

 A. p. S. — YOL. XIV. 2h 



