ON THE CONSTRUCTION OF HOOPED CAXXON. ;V.» 



iron, the direction of the fibres being in the circumference of the -nm and 



e more- 



over not perfectly integrated with the cast-iron as making one piece with it, it 

 becomes necessary to consider the resistance to cross-fracture. 



By a recurrence to the former Memoir, it will be seen thai the castriron I 



Mil 



alone, if possessed of a tensile strength of 30,000 pounds per inch, may he relied 

 upon for preserving the gun from cross-fracture. But I cannot say thai I hav< 

 always been without some shade of doubt, whether the cast-iron, when exposed 

 to the crushing force between the fired powder and the hoops, would exhibit 

 the same resistance to cross-fracture that it would when free from this condition 

 It was in some degree to guard against any defect that might possibly arise (torn 

 this source, that I proposed that the hoops be made in two layers, and be 

 fitted to the body and to each other, by a screw-thread. In this case the 



screw was not to exercise its usual function of a mechanical power; but to 



serve, by the interlocking of the threads upon the body with those of the 

 hoops, to so cramp the two together, that the body could not he fractun 1 

 crosswise without either stripping the thread through a space equal to at least 

 half the length of the hoop, or fracturing the hoop crosswise before or at the 

 instant when the body gave way. Now, to strip the thread of a screw throu li 

 half the length of the hoop would require a force sufficient to make a shear 

 cut, through a section of metal equal to at least one-third the internal sur- 

 face of the hoop. The inner surface of the inner hoop, being 28X^14 = 88 

 inches in circumfrence and 15 inches long, gives a surface of l,'52l> inch< , 

 one-third of which is 440 inches. To strip or cut through a screw-thread form- 

 mg a section of this magnitude, taking each inch to require but even 30,000 

 pounds, demands a force of 13,200,000 pounds, while, as is shown in the former 

 Memoir, the whole force of the charge tending to produce cross-fracture is but 

 4,896,000 pounds, being the pressure of 32,000 pounds per square inch upon 153 

 inches, — the area V the caliber. The other alternative, that of fracturing one 

 °f the hoops at its weakest point, that is, where it breaks joint with two of the 

 hoops of the other layer, and where, of course, one thickness alone gives its 

 support against cross-fracture, furnishes the following computation : The area of 

 the cross-section of the inner and smaller hoop, contains 346 square inches, 

 which, giving the iron, in this its weakest direction, a tensile strength of 40,000 

 Pounds per inch, shows that a force of 13,840,000 pounds will be required to 

 tear the hoop asunder. 



