86 ANNUAL OF SCIENTIFIC DISCOVERT. 



immediately converted into steam at a slightly lower temperature and 

 lower pressure, and this, in the same way, is followed by other steam 

 at still lower temperature and pressure, and so on till the temperature 

 is -reduced to 212 Fahr. "and the pressure to 0. Then there remains 

 in the boiler a portion of water at the boiling point, the other portion 

 having gone off in the shape of steam of continually diminishing pres- 

 sure. From this it is evident that the destructive energy of the steam, 

 when a certain pressure is shown by the steam-gauge, is proportional 

 to the quantity of water in the boiler. By the assistance of Prof. Mil- 

 ler and George Biddell, Esq., the author has been able to obtain a re- 

 sult which he believes to be worthy of every confidence. He first 

 stated, as the immediate result of Mr. Biddell's experiments, that when 

 there were in the boiler of a small locomotive twenty-two cubic feet of 

 water, at the pressure of sixty pounds per square inch, and the fire was 

 raked out, and the steam was allowed gently to escape, with perfect 

 security against priming, the quantity of water which passed off before 

 the pressure was reduced to was 2f cubic feet, or one eighth of the 

 whole. In regard to the use made of Prof. Miller's theory, Prof. Miller 

 had succeeded in obtaining a numerical expression for the pressure of 

 steam at twelve different measures of the volume occupied by water 

 and steam, which expression the author had succeeded in integrating 

 accurately and had thus obtained an accurate numerical expression 

 for the destructive energy of steam. In regard to the use of General 

 Didion's experiments, these experiments gave the velocity of the ball, 

 in cannon of different sizes, produced by different charges of powder. 



Wu 2 



The author found, by trial with the formula - -^, ^ , , 



2g x weight ot powder 



which of these experiments exhibits the greatest energy per kilogramme 

 of powder, and had adopted it in the comparison. The result is as fol- 

 lows : the destructive energy of one cubic foot of water, at sixty 

 pounds pressure, per square inch, is equal to the destructive energy of 

 two English pounds of gunpowder in General Didion's cannon experi- 

 ments. General Didion's experiments were made, as the author under- 

 stood, with smooth-bored cannon. It cannot be doubted that much 

 energy is lost in the windage ; some also from the circumstance that 

 the propelling power*ceases at the muzzle of the gun, before all the 

 energy is expended ; and some from the coolness of the metal. If we 

 suppose that, from all causes, one-half of the energy is lost, then we 

 have this simple result : the gauge-pressure being sixty pounds per 

 square inch, one cubic foot of water is as destructive as one pound of 

 gunpowder. In one of Mr. Biddell's experiments, the steam-valve was 

 opened rather suddenly, and the steam escaped instancy with a report 

 like that of a very heavy piece of ordnance. This is not to be won- 

 dered at ; it appears from the comparison above that the effect was the 

 same as that of firing a cannon whose charge is forty-four pounds of 

 powder. 



ILLUSTRATION OF THE ACTION OF THE SO-CALLED " GIFFARD'S 



INJECTOR." 



The paradoxical and apparently impossible action of Giffard's in- 

 jector, employed instead of a feed pump in charging steam-engine 

 boilers, was illustrated in a remarkable manner by the Abbe Moigno, 



