152 ANNUAL OF SCIENTIFIC DISCOVERY. 



liminaries, let us see how the explosions called fulminating are to be 

 explained. 



These explosions take place only when the machine has been for a 

 greater or less time at rest, and generally at the moment when they 

 are about to resume the movement of the machine, and the boiler by 

 its complete quietness gives no indication of the event. It is enough 

 to open the throttle-valve, or one of the gauge -cocks, or the door of 

 the furnace or ash-pit, or, in fact, any disturbance of the unstable 

 equilibrium which has been established, to decide the catastrophe. It 

 has also been remarked that, before the explosion, the pressure in 

 the boiler is rather low than high. What, then, has taken place ? 



When the machine was stopped, the pumps were also stopped; 

 the furnace and ash-pit doors were closed, as were all the escapes for 

 steam or water. The ebullition continued, the safety-valve acted, 

 and the water which had recently been pumped in was purged from 

 air. Then, when the activity of the fire had fallen sufficiently, the 

 valve fell into its seat, and the apparatus assumed a state of repose. 

 If the atmosphere was calm, the draft null, and the escapes of water 

 and steam hermetically closed, the apparatus (allow me to use the 

 figure) has gone to sleep, and the molecules of water being at rest, 

 the temperature has gradually been raised to a point notably above 

 that of evaporation under the existing pressure. As the water pro- 

 duces no steam, that pressure may be and may keep below that neces- 

 sary for the action of the safety-valve. Things being in this condi- 

 tion, let any cause whatever disturb the equilibrium of the molecules, 

 and all the heat stored up in the liquid mass is instantly employed in 

 producing an enormous volume of steam, while the mass of water not 

 evaporated falls to the temperature corresponding to its pressure. 



Figures will easily account for the violence of the explosion which 

 takes place. Let us suppose, in fact, that the pressure in the boiler, 

 before the explosion, was four atmospheres, and that the temperature, 

 in the quiescent state of the water, was only 170 Cent. (338 Fah.) 

 As at four atmospheres the temperature of the water and steam is 145 

 Cent. (293 Fah.), each kilogramme of water in the boiler contains 

 25 units of heat above its normal quantity. Therefore, the moment 

 this heat was liberated, it must have converted into steam 



25 



606.5-1-0.305X145145' 



or nearly -^th of a kilogramme 'of water ; that is, about one-twentieth 

 of the mass of water in the boiler was suddenly converted into steam. 



Now, if we suppose that the volume of water in the boiler was 

 double that of the steam, a quantity of water equal to one-tenth of 

 the volume of the steam is suddenly vaporized ; and as, at a pressure 

 of four atmospheres, one volume of water produces four hundred and 

 seventy-seven volumes of steam, the volume of the steam will be in- 

 creased forty-seven times, and the pressure will be one hundred and 

 eighty-eight atmospheres. It will be conceived that against such 

 generations of steam the safety-valves are of no effect, and that the 

 explosions are really fulminating. 



This manner of looking at the phenomenon leads to the suggestion 

 of the following precautions : to prevent the torpor of the water, let 



