282 



Mr. Mallet on the Physical Conditions 



Table XVUI. 

 Experiments on the Strength of Wrought-Iron Tubes. 



It will be recollected that these tubes are rolled chiefly to resist external 

 pressure, that the fibre of the iron in them, is all parallel to the axis, or longi- 

 tudinal, and the line of welding in the same direction ; hence, their conditions 

 of manufacture are the most unfavourable possible for effective resistance to 

 internal pressure : and yet, their powers are enormovis. The actual static pressure 

 withstood by a tube of about the caliber of a 6-pounder, and of only a quarter 

 of an inch thick., being, perhaps, about half the maximum pressure produced 

 by discharge upon that gun. The causes of this superiority have been already 

 fully developed (chaps. 22, 23, and 24), and are dependent on the simple fact, 

 that these tubes are rolled, and not hammered, and if such results are obtained 

 with a very inferior and almost careless mode of manufacture, what might not 

 be produced were its objects directed, not merely to tubes sufiiciently good to 

 resist the moderate pressures, to which their marketable uses alone expose them, 

 and to their production at a moderate market price, — but to the production of 

 rolled tubes of large caliber and thickness, of the finest and toughest iron, and 

 whose fibre should be uniformly arranged spirally round the axis, like the twist 

 barrel of a fowling-piece (sect. 218), and specially prepared for cannon. 



271. There can be no doubt, therefore, that by suitable modifications of the 

 rolling process, and a judicious selection of the iron, tubes could be rolled for 

 forming guns of all calibers, up to 12-pounders at least, possessing enormous 

 resisting powers, great extensibility within the elastic limit, and hence, great 

 safety in service, and at a cost perfectly insignificant as compared with any 



