MECHANICS AXD USEFUL ARTS. 



95 



Constant Weight of Projectile, and Increasing Charges. 



Weight of Charge. 



3 

 4 

 5 



Pressure per Sq. In. 

 Pounds. 

 11,319 

 17,483 

 10,983 

 18,811 

 19,551 



Wt. of Charge. 



8 



9 



10 



11 



12 



Pressure per Sq. In. 

 Pounds. 

 24,146 

 28,972 

 3-2,0.38 

 37,463 

 38,961 



Constant Weight of Charge with increasing Weight of Projectile. 



Weight of Charge. 

 Pounds. 

 5 

 5 

 5 

 5 

 5 

 5 

 5 

 5 

 5 

 5 

 5 



Weight of Projectile. 

 Pounds. 

 35 

 40 

 45 

 50 

 55 

 60 

 65 

 70 

 75 

 80 

 85 



Pres. Square Inch. 

 Pounds. 

 16,733 

 17,503 

 24,226 

 27,323 

 28,632 

 34,966 

 32,797 

 34,886 

 36,964 

 a8,462 

 41,120 



" The points most worthy of note in these results are the very 

 marked increase in pressure of gas as the diameter of bore increases, 

 and that the indications of pressure are greater at 56 inches, 70 inches, 

 and 84 inches than at 42 inches, especially in the 9-inch and 11-inch 

 guns. The cause of the difference of pressure developed in these 

 guns of different diameters of bores is believed to be mainly due to the 

 great heat developed by the combustion of the larger mass of powder 

 in the large than in the smaller calibre ; and perhaps, also, to the dif- 

 ferent products of combustion formed under this increased temper- 

 ature and pressure, and partly to the greater cooling surface in pro- 

 portion to the weight of charge in the smaller than in the larger 

 calibre." 



The highest pressure observed in a cannon was 100,000 pounds to 

 the square inch, but this was greatly exceeded in a shell. A very 

 strong shell was cast ; the exterior diameter being twelve inches, and 

 the interior a little less than four, with an orifice only one-tenth of an 

 inch in diameter, this orifice being the only outlet for the gas. The 

 cavity was filled with powder, which was fired, when the instrument 

 indicated a pressure of 185,000 pounds to the inch. 



The following are some of the contusions to which Capt. Rodman 

 was led by experiments which we have not space to describe in de- 

 tail : 



u Time is required for the rupture of any mass of iron, though the 

 rupturing force may be greatly in excess of the resistance of that 

 mass. And in the ordinary discharge of cannon the gun is subjected 

 at each discharge to a force which would inevitably burst it, if per- 

 mitted to act for any appreciable length of time ; so that it may be 

 said that cannon do not burst because they have not time to do so be- 

 fore the bursting pressure is relieved." 



" Pressure increases in a higher ratio than that of the volume of 

 powder; it being, for the larger charges, almost as the squares of 

 the volumes." 



