548 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



Upon the inner metal was about 95,000 of pounds on each side, or a whole 

 pressure of 190,000,000 of pounds. 



38. I acknowledge this to be a somewhat exaggerated statement, if refer- 

 ring to the finished gun, as the cast block was longer by the length of the 

 sinking head than the gun, and part of the outside metal in a state of ten- 

 sion is turned off along the chase. 



39. Since the above was written another 15-inch gun has burst sponta- 

 neously at the Pittsburgh foundry. The fissures were somewhat different 

 to those in the first, some of them being nearly transverse around the gun, 

 behind the trunnions, and opened about one- inch wide on the outside, 

 showing the skin of the gun was too small. The perfection of the state 

 required by the advocates of the " initial tension" theory. It can be seen 

 that if these guns should not burst spontaneously before they are used 

 that but little heat would be necessary, communicated to the inside by the 

 powder when they are fired rapidly, to insure rupture. 



UNEQUAL COOLIXG OF WROUGHT IRON MASSES. 



40. The initial strains of large cylindrical forgings are, to some extent, 

 deranged by a cause that operates so unfavorably in solid cast-iron 

 guns — the cooling of the exterior first, and the consequent stretching of 

 the interior. 



FISSURES IN THE MONSTER MALLET MORTAR. 



41. The masses for this mortar were forged from puddled slabs of man- 

 ageable size, " by slabbing up two or more large flat pieces, laying these 

 upon each other, and welding them together into a rude sort of square 

 prison, which was afterwards partially rounded down, at the corners, 

 under the hammer. (See figs. 4 and 5.) 



42. Mr. Mallet gives the following facts and illustrations as to the cause 

 of fissure : Two masses, about two and a half feet in diameter and eight 

 feet long, were forged for two 36-inch mortars, which was constructing 

 for the British government. They were slightly tapered, and at one end 

 there was a collar projecting six inches all round, and about twelve inches 

 wide in the line of the axis, presenting laterally the general form shown 

 in the cut. 



43. These pieces were welded together, apparently, perfectly sound, but 

 after they had betiome cold they were invariably found, upon borings being 

 made into the centre, to have large rents internally, with jagged crystal- 

 line, irregular surfaces * * * * At first it seemed probable that the 

 rents due to cooling, now to be described, were found in the direction of 

 the broad planes of the slabs; but more careful and exact examination 

 proved that in more than one case, at least, these rents had undoubtedly 

 been found across, or at right angles to those planes. The opposite faces 

 of those rents were counterparts, and presented distinct evidence of having 

 been torn asunder by contraction, from the center towards the circumfer- 

 ence, as the mass cooled." 



44. One of these rents are shown in figure 6. " The limits of the 

 fractures, as seen perpendicularly to their plane, were found to be gene- 

 rally as shown by figure seven. The ascertainable extent was from 

 two to three feet along the axis, and usually rather more than half the 



