Boiler Explosions. 161 



quantity In any boiler in common use, yet fifty pounds of coal 

 are required to cause it, and the imparted heat is equal to the 

 amount expended to convert about 430 pounds of water at common 

 temperature to steam. By a too sudden release of pressure, this 

 latent heat might all be released in one or two seconds, and there- 

 by cause an explosion. The idea quite generally prevails that all 

 boiler explosions are due to low water. That might cause such 

 a disaster, but that alone I think seldom does. Often, no doubt, 

 boilers are seriously injured by the plates being burned. Burned 

 plates lose about one-half their strength. Eepeat the operation 

 often enough and it is only a question of time, and a raiher lim- 

 ited time, too, when the boiler will be ruined. 



Several years since, the United States government squandered 

 about $100,000 at Sandy Hook and Pittsburg, trying to determine 

 the cause of boiler explosions. The experiments were under con- 

 ditions which were almost totally different from those under which 

 boilers are used. Hence, practically, they were nearly failures. 

 Two things were discovered, however ; one, that a boiler will not 

 explode when you want it to, and that water, pumped in on plates 

 red hot, would all run out through the seams, which were caused 

 to open from the rapid contraction, or else escape through the 

 safety valve as steam. This operation was repeated three times 

 to produce an explosion. 



Boiler plates are burned oftener from incrustation than from low 

 water. Wherever this formation is thick enough to prevent the 

 water from coming in close contact with the iron, that must be 

 the result, and if from this cause the plates when in use become 

 Fig. G. sufficiently hot to weaken the ten- 



sile strength in a place of any large 

 area, a rupture will surely follow. 

 Fig. 6 shows a section of a feed 

 pipe filled with lime in the short 

 space of three months. A few years 

 since I had an opportunity to exam- 

 ine a case of this kind. The boiler 

 was of the locomotive type, and 

 was not under cover. The plate over the fire had been forced 

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