38 ANNUAL OF SCIENTIFIC DISCOVERY. 



26,000 Ibs., the bar being suspended in a vertical position, left free 

 all around. A stout mill-hand, armed with a billet of one and a half 

 inches in diameter and two feet long, then struck the sample horizon- 

 tally a number of blows, hitting the reduced section as hard as he 

 could. The blows were counted and continued until rupture took 

 place. Care was taken to maintain a tension of 26,000 Ibs. during 

 this test, by screwing up the lever, while the sample kept stretching. 

 Other means for producing vibration were attempted, but none proved 

 so effective as the hitting with an iron bolt. I would remark here, 

 that most of these irons would support from 70,000 to 80,000 Ibs. per 

 square inch; and that good samples of three-quarters of an inch 

 square Avould support a strain of 26,000 Ibs. for a whole week, with 

 no visible stretching, provided all vibration and jarring was avoided. 

 But the least jar would produce a permanent elongation. 



Without going into the details of these interesting and instructive 

 experiments, I will only state that the number of blows which the dif- 

 ferent samples resisted, when encased in ice, ranged from three to 

 one hundred and twenty. Inferior qualities of a crystalline texture 

 would break at the third or fourth blow. Good samples of refined 

 puddled bar resisted very well, and went up to sixty blows, while the 

 better qualities of hammered charcoal irons supported up to one hun- 

 dred and twenty blows, stretching and drawing all the time. Indeed, 

 it seemed a wire-drawing process on a rough scale. On the tension 

 being reduced to 20,000 Ibs., some good samples resisted the almost 

 incredible number of three hundred blows before breaking. 



Such qualities of iron may be depended upon for the construction 

 of wire cables and car-axles. They will be safe at the North Pole, 

 while inferior qualities may answer very well in warmer latitudes. 



Well observed facts of the durability of irons, when exposed to ten- 

 sion and vibration, are of more value than speculative opinions. I 

 will here record a few more facts, experienced by myself. 



In 1844 I removed the old timber aqueduct over the Alleghany 

 River at Pittsburgh, the heaviest work of that description in the 

 United States, consisting of seven spans of one hundred and fifty feet 

 reach. It had stood fourteen years. All the suspension bars taken 

 out of the old trusses and arches, and originally made of good pud- 

 dled iron, on being tested and worked up into bolts for the new wire 

 suspension aqueduct, proved of good quality, as good as such irons 

 generally are. 



During the great fire at Pittsburgh, in 1845, the old Monongahela 

 Bridge, of eight spans, a heavy Burr structure, burned down. I con- 

 tracted to put up a suspension bridge, and accepted all the old mate- 

 rials, which were not consumed, including about thirty tons of ham- 

 mered charcoal iron of excellent quality. This iron, after a severe 

 usage for over thirty years, was found so good that I had it all drawn 

 into wire. Every bar was good for 60,000 Ibs. per square inch, as 

 strong and tough as it ever could have been before going into the 

 bridge. The old structure was loose and limber, producing consid- 

 erable vibration on all vertical bars. 



On excavating for the southern anchorage between the old wing- 

 walls of the old Monongahela Bridge, a number of round bars of one 

 and a quarter inches diameter, about forty feet long, good puddled 



