involved in the Construction of Artillery. 391 



Nothing can more strikingly show the deteriorating effect of forging into large 

 masses (however done) upon the tenacity of wrought-iron, than the facts of the preceding 

 Report, nor the uncertainty of the process, as respects welding. That the latter difficulty 

 may be greatly mitigated (though it cannot be removed), by pre-eminent skill on the part 

 of the hammer-man, is proved by the success of the Mersey Steel Company, in the dupli- 

 cate perfected by them of the gun which failed for the " Princeton," and still more in the 

 stupendous and apparently perfect forging they have now almost finished into a gun for 

 Government, — no doubt by far the largest ever made in one piece, being 13^ feet length of 

 chase, 13 inches caliber, 14 or 15 inches thick at the charge, and about 9 inches at the 

 muzzle; a solid shot of which will weigh 300 lbs. 



Note R.— (Sect. 214.) 



See Note Q. Late experience has shown me, that in very large cylindric masses of forged 

 wrought-iron (i.e., of 3 feet diameter, and upwards), amongst the other abnormal circum- 

 stances involved in their production, is that of their frequently rending or tearing, inter- 

 nally, in planes nearly parallel with and about the axis, though not always in it,— 

 presenting characters similar to those described in Section 217; and the cause appears to 

 be, that in the progress of cooling of such a mass, the exterior cools first, and becomes rigid, 

 while the internal portions are still red-hot and soft. The external parts would contract as 

 they cool; but they already grasp, in perfect contact, the still hot interior; the exterior, 

 therefore, cannot contract fully, but becomes solid under constraint oircumferentially, — 

 partly itself extended, in virtue of its compressing the still hot and soft interior; the latter 

 at length, also, becomes cold and rigid; but its contraction is now resisted by the rigid arch 

 of the exterior, with which it is surrounded. The contraction of the interior, therefore, is 

 limited to taking place radially outwards from the centre ; and thus the mass rends itself 

 asunder in some one or more planes parallel to the a.xis of the cylinder. 



In a cylindric mass of forged iron, varying from 24 to 36 inches in diameter, rents of 

 18 inches in width across a diameter were found, with jagged counterpart surfaces, clearly 

 torn asunder, and about |ths of an inch apart at the widest or central part ; and the fact is 

 most instructive as to the enormous internal strains that must exist, from like causes, in 

 cast-iron guns and mortars of large size. 



It is probably from this cause that more or less hollowness is found in the centre of 

 almost every large forging, greater in proportion as it is larger. The difficulty is one not 

 easily overcome: very slow, and, as far as possible, uniform cooling of the whole mass in 

 an annealing oven, suggests itself as one ; but this has disadvantages, in enlarging tlie 

 crystalline development of the metal; or providing a central cylindric opening, so as to 

 cool both the circumference and the centre together. 



3e 2 



