Safety Appai^atus for Steam Boats. 317 



-descent metals, coals, and furnaces, to mark the melting point of 

 metals, to verify the results presented by other instruments employed 

 in similar operations, and to answer some other practical and scien- 

 tific purposes. As the instrument would require a drawing in order 

 to be fully understood, a description of it is postponed to a future oc- 

 casion ; several series of experiments on other points of the subject 

 are likewise deferred. 



Art. XV. — Safety Apparatus for Steam Boats, being a combina- 

 tion of the Fusible Metal Disk tvith the common Safety Valve ; 

 by A. D. Bache, Professor of Natural Philosophy and Chemistry 

 in the University of Pennsylvania. 



- (Extracted from the Journal of the Franklin Institute for April, 1831.) 



Among the causes which produce the explosions of steam boilers, 

 no one stands more prominent, whether we have regard to the fre- 

 quency of the explosions caused by it, or to their violence when they 

 occur, than a defecdve supply of water within a boiler when in ac- 

 tion. When the supply of water afforded to a boiler, is insufficient 

 to compensate for the water which is converted into steam, the level 

 of the fluid within is lowered ; the boiler itself becomes heated, of- 

 ten intensely, and the steam partakes of this temperature without, 

 from an insufficient supply of moisture to give the density correspond- 

 ing to that temperature, having a corresponding elastic force. Of 

 the existence of such a state of things within a boiler, the ordinary 

 safety valve gives no indication, the tension of the steam within is 

 not sufficient to overcome the weight with which the valve is loaded; 

 it not only ceases to deserve the name of safety valve, but the open- 

 ing of it, by hand, may be the very means of producing an explosion : 

 for the escape of steam, thus permitted, relieves the water within the 

 boiler 'from pressure ; the fluid rises in foam ; and being thrown into 

 contact with the heated sides of the boiler, (or, as is supposed by 

 some, being projected into the hot and unsaturated steam,) is flashed 

 into steam, too considerable in quantity to find a vent through the 

 valve, and of an elastic force sufficient to defy the controlling power 

 of the materials used in the construction of the boiler. The raising 

 of this valve is not necessary to the production of an explosion in 

 the circumstcinces supposed, a supply of water suddenly introduced 



VoT. XX.~No. 2. 41 



