<336 Transactions of the American Institute. 



I have endeavored to burst a boiler by over-pressure, and in one 

 case I subjected the boiler to a pressure of 650 pounds to the square 

 inch. Before it gave way it was so stretched that it was two inches 

 larger in circumference at the center than at the ends; and it did not 

 give way until the leaks were so great that we could not get more 

 pressure upon it. There was evidence in every pant of that boiler 

 of the extraordinary pressure that had been applied. 



As to the weakening by the water-test of foity-eight pounds, so 

 that afterward a less pressure will cause a rupture, it is only necessary 

 to suggest that after the water-test the boiler is subjected to a pres- 

 sure of forty-seven pounds, forty-six, and so on, pound by pound down 

 to the ordinary pressure at which it was to be worked. 



The theory was advanced, that in applying the water-test the boiler 

 was strained by the momentum of the water flowing into it. We 

 must remember that, although the water itself is incompressible, the 

 iron is so elastic that ten or -twelve gallons may be put into a boiler 

 after it is full, the iron stretching to receive it, and afterwards return- 

 ing to its original size. The elasticity of the iron makes up for the 

 want of elasticity in the water. 



As to the theory of too little water exposing the upper tubes to 

 the steam, we must remember, first, that the perpendicular tubes 

 were always exposed to the steam ; and, next, that even a tempera- 

 ture of 500° or 600° would not materially injure the iron. Further- 

 more, we find in practice that boilers of this form are just as apt to 

 explode with the proper amount of water in them as without it. 



Superheated steam cannot have caused the explosion. It is sup- 

 posed that the surplus heat of the steam might be communicated to 

 the water, generating an increased quantity of steam and causing an 

 increased pressure. That is now known by engineers to be impossible. 

 There being a given number of units of heat in the steam and water 

 contained in a boiler, it makes no difference whether the water is 

 cold and the steam is at 1,000°, or whether the two are mixed ; the 

 pressure is the same. I have tried repeated experiments to determine 

 this ; and I have superheated the steam up to 1000°, heating the iron 

 red hot, while the water was about 300° ; and upon mixing them, 1 

 have found only the increase of pressure which could be directly 

 traced to the heat in the boiler iron. 



There is a theory of the decomposition of steam, that the oxygen 

 leaves the steam and unites with the iron, at a high temperature, 

 forming an explosive gas. It would be impossible that the gas should 

 explode without a new supply of oxygen, or without being raised to 



