PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 



405 



re-eiiforce would be the result, as 

 shown in the diagram. As the 

 heat expands the metal in the 

 direction of the diameter also, its 

 effect in this direction also must be 

 considered. The expansion of 

 length, however, is of most conse- 

 quence in considering the probable 

 direction of fracture. 



That the fracture almost always intesects the vent, has been heretofore 

 referred to the weakness resulting from drilling away part of the metal; 

 but on page 355, Major Wade's Reports on Metals for Guns, we find that 

 after a gun had been put to extreme proof, and exhibited signs of fracture, 

 a hole was drilled one inch forward of the base ring, and four inches from 

 the line of the vent, to a depth of four inches, and of the diameter of one 

 and a quarter inches. The gun was then fired with double charges of 

 power, and with a bore full of balls and wads, eleven times, to bursting. 

 Although the piece burst into more then twelve fragments, one of the frac- 

 tures intersecting the vent, it did not split through the large hole, showing 

 that the gun had strength to resist the pressure of the powder, but burst, 

 notwithstanding the drilling away of so large a part of the metal, from the 

 communication of heat. The true cause, px-obably, of the intersection of 

 the vent by the fracture, was the communication of heat to the surface of 

 the vent, thereby expanding the column of metal about it; for it should be 

 recollected that the passage of a large quantity of gases through the vent 

 would communicate more heat to its surface than would be communicated 

 if there was no current, but the capacity of the vent only filled; in that 

 case not much heat would be supplied to the surface, because the quantity 

 contained within the vent would be small. 



But in this example, as in all others, as is well known to ordnance 

 inspectors, the fracture began to exhibit itself on the interior surface of 

 the bore. 



It is often noticed as a curious phenomenon when large guns burst, that 

 notwithstanding the chase or forward part of the gun, several feet in 

 length, may be thrown many feet end over end, the shot passes through the 

 chase the length of the bore without being diverted from the direction of 

 its aim. This fact corroborates the theory under consideration, as it is evi- 

 dent that the shot is not projected by the same force that bursts the gun — 

 the communication of heat to the inner metal of the gun requiring a longer 

 interval of time, and gun metals being comparatively non-conductors of 

 heat. In Rodman, plate II., fig. 2, is shown the interior line of fracture of 

 a 10-inch columbiad. Here a thin 

 bit of metal, indicated by the line 

 marked [ET", is shown, which seems 

 nearly to envelop the bore. Nearly 

 one-half the re-enforce was broken 

 off this gun in the same manner as 

 chips break off a stone door cap when a building is burning, but in this 

 example the outside of the stone is first heated while the inside remains 



