378 Mr. Mallet on the Physical Coiviitions 



The breech-ring was forged on solid to the gun, but the trunnions had been forged 

 separately and screwed into the body of the gun, into holes prepared with a slight rein- 

 force of metal round each, the screw-threads being of sharp or angular form, and nearly an 

 inch pitch. The gun was stated to have been formed by laying together longitudinally 

 some ten or twelve voussoir-shaped heavy bars, previously forged out to form, and welding 

 these together by continuous longitudinal weldings, the breech being also welded in; the 

 whole was then bored out and turned. 



To the eye, both externally and internally, it presented an appearance of entire soundness 

 and perfection of material, and the result of its trial very much surprised the majority of 

 those who were present. 



The proof-charge fired consisted of 28 lbs. of powder, and two spherical 8-inch shot. 

 The gun was split nearly in half longitudinally, with other secondary longitudinal frac- 

 tures, and by diagonally transverse ones, turning out through one, and near to the other, 

 of the places of the screwed-in trunnions. Upon examination, after the rupture, I found the 

 wrouo-ht-iron of a quality so fine, as to answer to what is called technically " over-worked." 

 Its fracture was everywhere confusedly crystalline, the average sizes of the facets not being, 

 however, very large, though in some places reaching the surface of a silver penny, say, 

 f-inch across ; fragments were capable of being broken off, from bevilled edges of the 

 ruptured masses, by blows, almost with the facility of cast-iron, and with the same short, 

 crystalline fracture, although bending a little more before finally giving way. 



Along the face of the principal longitudinal fracture, and commencing at 1 foot 4 inches 

 from {he bottom of the chase, or very nearly opposite the seat of the shot, was the smooth, 

 bright, uneven (" slickenside" sort of) surface, that is, the evidence, in heavy forging, of a 

 false weld. This extended for nearly 4 feet in length, or almost up to one trunnion; it 

 reached all along, and opened right into the chase, and extended in depth into the sub- 

 stance of the gun about 3 inches, leaving some 5 inches or thereabouts sound (in some 

 places less); practically, therefore, the caliber of the gun, as respects the moment of strain, 

 was enlarged, at all the points of maximum distress, to at least 11 inches diameter, and the 

 effective thickness of metal was reduced to less than 5 inches. 



One of the most remarkable features presented, however, was the trace discoverable of 

 the place of nearly every longitudinal weld, by a marked alteration of character in the frac- 

 ture and colour of the iron at those places. The metal along these lines, which several of 

 the fractures followed, and most markedly along the edges of the false weld, was of a silvery 

 white colour, and arranged in large, brilliant, smooth, flat, crystalline plates, some as large 

 in surface as a half-crown piece, say Ij to 1^ inches across, through whose planes of cleavage 

 (all lying parallel, or nearly so, to the plane of the welding between two original voussoir 

 bars), the fractures had taken place in most instances. 



The crystals had followed in their arrangement the general law given in the text ; and 



