96 



ANNUAL OP SCIENTIFIC DISCOVERY. 



INTERESTING EXPERIMENTS WITH GUNPOWDER. 



When ordinary small-grained powder is burned in a cannon, the 

 combustion is so rapid, and the gases are consequently so quickly de- 

 veloped and so highly heated, that an enormous pressure is produced 

 at the breech of the gun before the ball starts from its seat ; then, as 

 the gases expand, the pressure is rapidly reduced, so that the velocity 

 of the ball is small in proportion to the maximum pressure exerted 

 upon the gun. It occurred to Capt. T. J. Rodman, of the Ordnance 

 Department, U. S. A., that if the powder were made to burn a little 

 more slowly, the pressure would be less at the breech, and would fol- 

 low up the ball with more force during its passage out of the gun, 

 thus giving greater velocity to the shot with less danger of bursting 

 the cannon. 



The first plan that he tried for producing a slower combustion of 

 the powder was to make it in large grains, which were compressed 

 with great force, so that they could not be permeated by the gas, 

 and, consequently, could burn only by a gradual combustion com- 

 mencing on the outside and extending inward. Powder of the same 

 quality in every respect, except the size of the grains, was prepared 

 by the Messrs. Dupont, the grains in one sample being all three- 

 tenths of an inch in size, those of another four-tenths, of another five- 

 tenths, and of the last six-tenths. Capt. Rodman made a series of 

 fires with this powder in a 11-inch gun, using the same weight of 

 charge, 12.67 Ibs., and the same cylindrical shot, weighing 183.3 Ibs., 

 at every fire. Five fires were made with powder of each size of 

 grain, and the mean results are exhibited in the following table : 



The smallest-grained powder, three-tenths of an inch in size, pro- 

 duced a pressure at the bottom of the bore of 35,000 Ibs. to the 

 square inch; which was reduced to 6,700 Ibs. at 28 inches from the 

 bottom of the bore, giving a velocity to the shot of only 890 feet per 

 second; while the powder of largest grain, six-tenths of an inch in 

 size, though producing a pressure of only 21,000 Ibs. at the bottom of 

 bore, followed it up with 8,000 Ibs. at 28 inches, and gave a velocity 

 to the shot of 933 feet per second. 



The granular form, however, is not the best for cannon powder, 

 whatever the size of the grains. In order to give the greatest possi- 

 ble velocity to the shot, with such degree of pressure as may be safely 

 employed, the pressure against the shot should continue nearly uni- 

 form throughout its passage from the gun. It should be exactly uni- 

 form were it not for the fact that a less pressure will burst a gun if 



