Experiments on two varieties of Iron. 105 



ing alone diminishes it, while the structure is thereby rendered 

 more uniform. 



Our next remark is, that between the ordinary and the hammer 

 hardened state of No. 1, there is a difference in tenacity of 11.7 

 per cent, of the strength in the former condition ; and that for 

 No. 2, this difference amounts to 13 per cent. The Enghsh ca- 

 ble bolt iron, above mentioned, manifested a difference of 20 per 

 cent., under similar diversity of treatment. The difference be- 

 tween the tenacity of No. 1, when annealed, and that when ham- 

 mer hardened, is 23.3 per cent, of the strength when annealed, 

 and for No. 2, this difference is 17.6 per cent. 



Now as we have already proved, that hammer hardening di- 

 minishes the extensibility of a bar, it must follow, that stiffness 

 as well as strength, is essentially augmented by this treatment. 



It may be farther remarked, that by thirteen trials, the stronger 

 variety of Mclntyre iron, had a specific gravity of 7. 728, and by 

 twelve trials, that of the weaker kind was found to be 7.676, the 

 difference .6 of one per cent. — and that the mean specific gravity 

 of other kinds of bar iron formerly tried, was found by seventeen 

 trials to be 7.725. The Russian iron above mentioned, had by 

 the mean of ten trials on separate portions of the same bar, a spe- 

 cific gravity of 7.801, the highest being 7.8702, and the lowest 

 7.7586. These facts in connexion with the increase, both of 

 strength and specific gravity by hammer hardening, appear to fa- 

 vor, though perhaps they do not establish the supposition, that 

 whether from chemical constitution, or from m^echanical treat'?nent, 

 a deficiericy in specific gravity, is ati ijidication of inferiority in 

 the strength of iro7i. I am aware of some apparent exceptions to 

 this rule. 



In conclusion it may be observed, that the great amount of 

 much worse iron which finds its way into the American market, 

 will render even the Mclntyre iron, No. 2, an object worthy of 

 the attention of the consumers of this article. But as a large 

 and increasing demand for good iron'prevails in the United States, 

 in proportion to the increase of finished and accurate machinery, 

 requiring superior materials as well as workmanship, there can be 

 no doubt, that any quantity which could probably be produced, 

 if possessing the properties of No. 1, would command a ready 

 market, and the best of prices. 



Vol. xxxvi, No. 1.— Jan.-April, 1839. 14 



