336 MM. H. Sainte-Claire Deville and Troost on the 



metres ; and, with the charge of powder 0*825 kilog., the velocity 

 of the issuing ball was 400 metres per second. Applying the 



Wx V 2 



formula ■ Q . _ , the energy of 1 kilogramme of gunpowder 



(as fired in a cannon) is found to be 



56656, 

 and that of an English pound of gunpowder 



25700, 



the units being in all cases the metre and the kilogramme. 



17. Comparing this with the numbers found in art. 14, we 

 have, 



The destructive energy of 1 cubic foot of water at the tempe- 

 rature which produces the pressure 60 lbs. to the square 

 inch, surrounded by hot iron, is precisely equal to the 

 destructive energy of two pounds of gunpowder as fired in 

 a cannon. 



18. The destructive energy of the hot water, however, abstract- 

 ing the effect of the surrounding hot iron, is considerably less 

 than the number used in this comparison ; and the destructive 

 energy of the gunpowder, abstracting the effects of windage, cold 

 iron, and short barrel, is considerably greater than the number 

 used for it. Without pretending to form an accurate estimate 

 of these effects, I think that their combination with that affect- 

 ing the energy of the water may have diminished the apparent 

 proportion of the energy of gunpowder by one-half. In that 

 case 



The destructive energy of 1 cubic foot of water at the tempe- 

 rature which produces the pressure of 60 lbs. to the square 

 inch is equal to that of 1 pound of gunpowder. 



Royal Observatory, Greenwich, 

 September 3, 1863. 



XL VIII. On the Measurement of High Temperatures. 

 By MM. H. Sainte-Claire Deville and Troost*. 



IN the experiments which chemists have constantly to make at 

 very high temperatures, they are frequently stopped by the 

 difficulty of finding suitable vessels. Platinum vessels appear at 

 first sight perfectly suitable ; but we have always discarded them, 

 from the mistrust with which we are inclined to regard a metal 

 that is generally considered as having the property of condensing 



* Comptes Rendus, vol. lvi. p. 977 (May 25, 1863). 



