PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 865 



as to produce an effect upon objects intervening its coursjp, almost, 

 or quite, as great as vvoulcl be from the projection of a solid body. 

 Therefore, the larger the boiler the more disastrous the effect, this 

 being as the cubical contents of the boiler multiplied by the 

 pressure. 



With the greatest care and skill in constructing wrought-iron 

 boilers, there are manj'^ features of weakness Avhich must unavoid- 

 ably occur. We have first the unseen defectibilities of the plates, 

 the liability to strain the iron in bending it cold, the impossibility 

 to punch the rivet holes so as to correspond, and have the rivets 

 always perpendicular to the plate, the necessary resort to the 

 drift pin, and strain in drawing the work together, the constant 

 Hse of the caulking tool to conceal defects, are some of the facts 

 well known to boiler makers. How often do we read of a boiler 

 exploding when first placed under steam, and the cause beyond 

 the reach of investigation ? 



The usual cold water test of a new boiler under high pressure 

 often induces injurious strains that afterward develop themselves, 

 while it affords no sign of security from unequal or irregular 

 expansion under heat, either of which may end in its destruction. 

 Such features of danger are beyond the reach of inspection of 

 officials or experts. 



An eminent writer says : "Steam boilers are not merely tanks 

 for boiling water, but great magazines in which tremendous power 

 is stored, the safe custody of which is of paramount interest to all 

 in the vicinity." And again: "The strength of any structure is 

 its weakest point." 



If the damage was confined to the boiler it would be of little 

 account to the public ; but with wrought-iron boilers it is rarely 

 unattended with other injuries — walls overthrown, timbers and 

 flooring broken, splintered and projected as if crushed l)y power- 

 ful artiilerj^ machinery ruined, and, among the ruins of all, the 

 coals of the furnace frequently complete the catastrophe — but 

 that other chapter — the dead, the scalded, and the maimed — call 

 for the exercise of all talent and effort for averting such horrible 

 calamities. 



In an ordinary boiler the heat may l)e so intense in the furnace 



as to burn or blister or crack the walls, and this may arise, not 



from the inability of the metal to transmit the heat, but, doubtless, 



often from such a rapid generation of steam as to overcome the 



[Am. Inst.] CCC 



