574 TRANSACTIONS OF THE 



carried to a high degree, as the strength of the metal usually em- 

 ployed in the construction of boilers, and especially copper, is 

 rapidly diminished by raising the temperature much above that 

 which it attains while producing steam of the elastic force now 

 commonly used for working a steam engine. The danger in this 

 case would arise not from any increase of pressure caused by the 

 overheated metal, but solely from the diminished ability of the 

 overheated part to sustain the pressure previously existing. 



This being the State of things, that is, some portion of a boiler 

 or flue becoming overheated in consequence of a deficiency of 

 water, it is contended that to commence supplying the boiler with 

 water, is to incur the risk of an explosion, because the water 

 sent in under such circumstances, will be suddenly, in fact, in- 

 stantaneously, converted into steam of great elastic tbrce. 



The writer once heard tlie master of a steamboat, who now 

 commands one of the vessels in the Collins line, remark to a 

 person with whom he was conversing upon the subject of -explo- 

 sions, that it was " dangerous, very dangerous indeed, to turn 

 the feed into a boiler suddenly." 



This opinion deserves an examination; if it is well founded it 

 ought to be known to all engineers, and should guide their prac- 

 tice in managing the water supply to their boilers; if it is un- 

 founded or fallacious, its ftillacy should be shown, in order that 

 it may no longer be relied upon as accounting for results with 

 which it may have little if any connection. 



The quantity of water required to be evaporated to furnish 

 steam for working an ordinary steam engine, is about one cubic 

 foot and a quarter per hour for the power of each horse; and it 

 is not common in any other than locomotive boilers to allow a 

 smaller proportion of water surface than two and a half square 

 feet per horse power of the engines to which they are applied, 

 (some engines have as much as six square feet,) but taking two 

 and a half which is probably the minimum allowance, the depth 

 evaporated per hour will be six inches. In other words, if a 

 steam engine furnished with a boiler in which the water surface 

 was two and a half square feet for the power of each horse, should 

 be worked one hour without using the feed pump, the surface of 

 the water in the boiler would be found lowered six inches. The 

 feed pump is generally made somewhat larger than is necessary, 

 if constantly worked, and all things in perfect order, to replace 

 the quantity of water evaporated; this is in order to provide, 

 when necessary, for the waste caused by leaks in the boiler, in 

 the pipes, valves, and other parts of the engine. 



