306 Mr. Mallet on the Physical Conditions 



ment by combustion and abrasion will be greater as the weight of powder is so, 

 and will be greater for chambered guns with elongated cartridges, which ignite 

 more slowly, and hence give a longer period of issuing flame before the shot 

 moves, than with cylindric bores or quicker igniting powder. The practice 

 with any recorded example of wrought-iron guns has been scarcely sufficient to 

 enable proof as to durability to be drawn from it. We have, however, the 

 following from Major Talcott (Report to the American Minister of War in 

 1832) upon a wrought-iron 6-pounder, which fired sixty-three rounds with one 

 shot and 1| lbs. of powder, at Watervleid Arsenal : — 



" The iron seems of good quality, tolerably hard for forged iron, and the 

 inequalities of the shot have made very little impression upon the bore, — nothing 

 like the effect that would have been produced upon a brass gun subjected to 

 the same trial." 



The wrought-iron 32-pounder made some years since in one solid piece of 

 wrought-iron, under the direction of Captain (now Colonel) Simmons, R.E., is 

 understood to have suffered no perceptible injury in this respect by the practice 

 carried on with it at Shoeburyness. Whatever this objection to wrought-iron 

 may be worth, it has certainly been much overstated. 



314. The extent oiballotage depends not only upon the material of the gun, 

 and the other conditions above stated, but upon the amount of windage, which, 

 as it is greater, allows more play to the shot in its passage, and lets it strike the 

 sides of the chase alternately at a greater angle. But as wrought-iron guns 

 have the advantage in point of strength, so the windage may be diminished in 

 them with safety, and thus, while this evil may be reduced, greater accuracy 

 of aim, and either longer range or economy of powder, secured. 



315. 5°. That the rapid corrodibility of wrought-iron by air and moisture, 

 and by the residue of the powder, is such, that wrought-iron guns 

 would rapidly become iinserviceable, through enlargement of the 

 bore, by mere corrosion. The comparative relations of the four 

 metals has been already made (Chap. 32, Tables xvl-xvil) on accu- 

 rate data, and this objection shown to be perfectly groundless. 

 The degree of corrosion, from any, or all, of these causes, will be 

 quite the same upon a square inch of surface, of the exterior or 



