866 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



Tveight of»the water ai^ainst the plates, separating it therefrom by 

 a stratum of globules of steam, so rapidly replaced by others that 

 the water is borne up, even to the upper gauge-cock, thus deceiv- 

 ing the attendant. The extreme heat increasing and extending to 

 other parts of the boiler, the steam blowing off and still rising in 

 the gauge, the pump seems doing its duty well. The fire is slack- 

 ened, furnace doors opened, and safety valve raised to bring down 

 the steam. The plates ov.er the furnace, which may have become 

 nearly or quite red hot, now cool down to water contact, and 

 instantly flashing steam beyond the resistance of plates and rivets, 

 away goes the boiler, rattling down everything around it. 



Boiler explosions, and severe ones, are not rare in the works of 

 makers themselves, a great disaster of this kind not long since in 

 Philadelphia, and a more recent one in this State, are instances in 

 point. In both those cases the proprietors are eminent for skill 

 and prudential care. 



A coroner's jury in Philadelphia, upon the occasion of five 

 deaths from a boiler explosion in that city, after censuring the 

 proprietors of the works, find "The storage of gunpowder in our 

 city is prohibited by law, but any one may place a steam powder 

 magazine, with match burning, at our side or under our feet with 

 impunity ; such magazines undermine our crowded streets, and 

 unless properly cared for, will one day reveal their existence in 

 fearful disaster." 



A perfect provision against boiler explosions under ordinary 

 circumstances is simply impossible, whatever be the nature of the 

 material of which the boiler is made. The iron or the work may, 

 with the greatest care for perfection, be occasionally weak in some 

 of its parts, or the steam may, from accident or neglect, be 

 increased to a bursting pressure, when all else is right ; and. such 

 a condition is incidental to a majority of boiler explosions. 



It is, therefore, of primary importance Jhat the effects of such 

 accidents should, if possible, be confined t-o the boiler alone, that 

 no injury shall extend to other property, or the attendants be 

 harmed. 



Mr. Colburn, in the paper referred to, says: "Whatever the 

 bursting strength of a riveted wrought-iron cylinder, that of a cast- 

 iron sphere of like dimensions and thickness will be the same." 



And, in a paper upon boilers, read before the institution of 

 Mechanical Engineers, at Birmingham, England, May, 1864, he 

 said: "Although it cannot be said that cast-iron in itself, is a 



