HOW GUN-BARRELS ARE MADE. 213 



" The great advantage derived in this instance from 

 air-furnace welding is a chemical one ; for while the 

 small pieces of steel are fusing on the bed of the air 

 furnace, the oxygen is extracting the carbon, and leaves 

 the resulting metal mild steel, or iron of the densest 

 description; while the succeeding hammering and 

 rolling and re-welding produce the mechanical arrange- 

 ment of making the whole of an extremely fibrous de- 

 scription. The polishing secures a clean metal ; in- 

 deed, so free from specks are the generality of barrels 

 thus made, that it is scarcely possible to imagine clearer 

 metal. When contrasted with the best of ordinary 

 iron, by a powerful microscope, the closeness and 

 density of grain are strongly apparent. 



" To such an extent has this been carried, that I can 

 produce specimens of a considerably increased specific 

 gravity. The barrels made of this metal, in general, 

 beat all tried against them ; with this great advantage, 

 that the finer the polish in the interior the better they 

 shoot, and continue longer free from lead. The only 

 difficulty is in the working ; as the boring, filing, &c, 

 are more difficult. Moreover, greater care is required 

 to see that they are not annealed, when in the hands 

 of the borer or filer ; for in such case they would be 

 considerably injured, though not to the same extent as 

 barrels of a softer nature. I tested a great variety of 

 bars by drawing them asunder longitudinally by the 

 testing machine, and the average strength of a rod of 

 6-i6ths broad by 5-i6ths thick and 12 inches long, 

 containing 1.40625 solid inches of iron, was equal to 

 a tension of 11,200 lbs. This furnished a barrel 



