318 Safety Apparatus for Steam Boats, 



will produce the same dreadful effect. That such ch'cumstances 

 have frequently occurred, and have as frequently caused the results 

 above described, is fully shown by the various authentic accounts of 

 explosions on record. 



The memoir of M. Arago, a translation of which is contained in 

 the Journal of the Franklin Institute,* furnishes proofs of this fact ; 

 and the explosion of the boiler of the Chief Justice Marshall, during 

 the last summer, has, I conceive, been fairly referred to the occur- 

 rence of similar circumstances. 



The French Academy, when called upon, in 1823, to report to 

 their government, the precautions to be used to prevent the explo- 

 sions of steam boilers, satisfied of the insufficidncy of the common 

 valve to insure safety, required that in addition to two safety, valves 

 of the ordinary construction, one at the disposal of the engineer, the 

 other under lock and key, there should be two plates of fusible 

 metal covering apertures in the boiler ; the one having its melting 

 point at 18° F. above the temperature of the steam, which, accord- 

 ing to the statement of the proprietor, made when his engine was es- 

 tabhshed, was required to be used in the engine, the other at 18° 

 above the fusing point of the first : the fusing point of each is thus, 

 even in a high pressure engine, much below the temperature to which 

 the boiler being heated there would be danger of explosion. f Now 

 whether the steam be very elastic or not, so soon as it, or the boiler, 

 arrives at the temperature requisite to fuse these plates, they melt, 

 and the steam is discharged -, this, too, below the limit of tempera- 

 ture at which such a discharge of steam would, according to the 

 statement made in the former part of this article, be attended with 

 danger. 



These plates are made of alloys of bismuth, tin, and lead, in pro- 

 portions varied according to the temperatures at which they are re- 

 quired to melt ; by covering each with a piece of fine wire-gauze, it 

 is prevented from swelling out by the effect of softening as it verges 

 towards the fusing point. 



Experience has shown that these plates can be relied on, confi- 

 dently, to answer the ends proposed. In the stationary engine we 



" Vol. V.^ No. 6, and Vol. VI. No, 1, 1S30. 



I Iron at a dull red heat has a temperature of f)47° F. while steam of eleven at- 

 mospheres corresponds according- to (he late detei'mination of Arago and Diilong; )o 

 a temperature of 367 54° F 



