Polytechnic Association. 765 



"We may conclude, then, from the result of Mr. Stevens' experi- 

 ments : 



"First, That 'low water,' although undoubtedly one cause, is not 

 the only cause of violent explosions, as is so commonly supposed, but 

 that a most violent explosion may occur with a boiler well supplied 

 with water. 



" This was shown on a small scale by the experiments of the com- 

 mittee of the Franklin Institute above referred to. 



"Second, That what is generally considered a moderate steam 

 pressure may produce the very violent explosion of a weak boiler, 

 containing a large body of water, and having all its flues well 

 covered. 



" This has never before, we believe, been directly proven by experi- 

 ment." 



The third result I have already read. 



Professor T. proceeded to give a calculation, roughly made, of the 

 force manifested in the explosion of one of the boilers, compared with 

 the pressure of the steam ; and continued : 



Mr. Stevens suggested that as this large boiler had been under 

 steam for a week at low pressure, there might, perhaps, be a portion 

 of that heat stored up, which was developed in the explosion ; but 

 the calculation, which I intend to repeat with more accuracy here- 

 after, shows that the work done in the explosion was not assisted by 

 any such superfluous heat. 



Dr. Richards — How do you explain the bursting of a boiler at a 

 pressure less than the hydrostatic test ? 



Professor Thurston-— I have very little doubt that the reason was 

 that the strain was thrown differently upon the braces, when heated 

 to the temperature of 300 degrees than when it was cold. I have no 

 doubt that Mr. "Wiard is correct in attributing many explosions to 

 unequal expansion ; but 1 would no sooner ascribe all explosions to 

 that cause than give one medicine for all diseases. I think we know 

 the causes of all explosions, and that with proper care and intelli- 

 gence on the part of those who design, those who construct and those 

 who manage boilers, explosions can be avoided, except in those 

 exceedingly rare cases in which accidents occur notwithstanding the 

 most careful management. 



Mr. J. K. Fisher suggested the bursting of a boiler by forcing air 

 into it, so that the rupture might take place at the temperature of 

 construction. 



Professor Thurston — It is proposed to explode one boiler by the 



