762 Transactions of the American Institute. 



The President — Might not unequal heating tend to burst the 

 boiler ? 



Mr. D. Blanchard — The heat would reduce the strength a little. 

 Mr. T. D. Stetson — It has been asserted that heat increases the 

 strength of iron up to 500° Fahr. 



Dr. D. D. Parmelee — On a question like this, we want practical 

 facts. John Matthews, the soda-fountain man, told me, a few weeks 

 since, that some years ago he had the brilliant idea of making 

 steel receivers to hold carbonic acid; for steel would be light, and 

 give a great amount of strength. He brazed them, and subjected 

 them to 150 pounds pressure. His father suggested to him to keep 

 up the pressure for a while, for they might burst. They were allowed 

 to stand, and the pressure gradually diminished until ultimately it 

 came to about half that pressure, when the receiver exploded with 

 great violence. "Why was this ? The theory is this : there is no 

 alloy of two metals the molecules of which have the same cohesion 

 those of pure metals have. Probably the molecules of different metals 

 tend to roll around each other. When the hydrostatic pressure is 

 first applied, it does not move them at first, because they require 

 time to move. You may put millions of tons upon a glacier, without 

 moving it, and yet it is constantly progressing. In the boiler, you 

 apply the pressure and see no-result. You afterward apply a lower 

 pressure, continuously, and the atoms continue to move, the joints 

 becoming gradually weaker, until at last the weakest point gives way, 

 and you have an explosion, although a pressure equal to the hydros- 

 tatic pressure may have never been reached since the original test. 



Among the causes of boiler explosions, I have met with one in my 

 own practical experience, which I have never heard mentioned among 

 all the theories advanced ; for I had a boiler which was accidentally 

 left, in the winter, filled with water, and cold, instead of heat, burst 

 the boiler. (Laughter.) 



Mr. D. Blanchard — I do not deny that chemical causes may 

 weaken a boiler, after the hydrostatic test ; but I object to the glamour 

 of the supernatural in the theory that a boiler which will stand a 

 certain test to-day, will to-morrow, without any change, explode at a 

 materially lower pressure. 



Prof. R. H. Thurston — Yery fortunately I received to-night the 

 proof-sheets of an article I prepared for the Journal of the Franklin 

 Institute, upon this subject, and I will read a portion of it : 



" Third. That a steam boiler ma} 7 explode, under steam, at a 



