ON RIFLED GUNS. 



13 



in which 



P\ = F (»/); 



and we should have all the data to ascertain with certainty whether the results, as regards 

 intensity of action, furnished by the plug experiments of Major Rodman, are true estimates of 

 the expansive energy of the gas within the gun. Unfortunately, the experiments thus far 

 have not been sufficiently numerous nor conducted in a way to evolve this desirable law. Nor 

 will its precise mathematical expression be matter of easy attainment, since so much 

 depends, not only upon the devices of the experiments, but also upon the nature and char- 

 acter of the powder as regards the proportions of its chemical ingredients, the size and com- 

 pactness of its grains, and the mode of manufacture. 



(16) — But we are not without the means of a fair proximate test of Major Rodman's 

 results. Take at random any one set of them, say the first, on page 196, as given by a -Im- 

 pounder, smooth bore, with a cylindrical missile, of which the weight was 75.44 pounds, the 

 charge of powder being 5.13 pounds, viz: 



Initial velocity 904 feet. 



Pressure in pounds at different distances from bottom of the bore on square iuch. 



At bottom 

 36420 lbs. 



14 in. = If, 1660 

 15850 



28 in. =21,3333 

 8370 



42 in. =3f,5000 

 6470 



56 in. =4f, 6666 , 70 in. =5f,8333 

 6850 8050 



84 in. =7f.0000 

 6720 



In the Ordnance Manual, page 18, we find the diameter of the bore to be 7 inches = f ,5833; 

 the length of the bore 110 inches = 9 f , 1666; and, at page 288, the length of the cartridge for 

 each pound of powder 0,98 inch. The length of the cartridge will be 5,13x0,98 = 5,0274 

 inches=0,419 feet; and the path over which the gas worked on the projectile 9 f , 16G6 — 

 0,419= 8 f , 7476. The table gives the intensities of this action at the beginning, then at a 

 point whose distance from it is 1,1666 — 0,419 = 0,7476, and then at equal intervals of 1,1666 

 of a foot to the distance 7 feet. At the mouth of the piece it will be assumed that the 

 pressure is 6000, suggested by the apparent law of decrease. The work, denoted by Q, will 

 come from 



36420 + 15S50 



\ 



Q = *.r. 2 iu{ + 



-X 0,7476 



(15850 



6720 



8370 + 6470 + 6S50 + S050 )x 1,1666 



) 



+ 



6720 + 6000 



X 1,7476 



in which 



whence 



0.5S33 



= f ,2916; 



Q = -. (,? 144^ 26135X0,7476X41025X1,16066 + 6360X1,7476 > 



(325) 



