496 



3Ii\ W. Fairbuirn on the Properties of Iron^ [May 9, 



Remarks. — The specimens subjected to compression gradually 

 squeezed down to one-half their original height, increasing at the same 

 time in diameter till they attained 90 tons on the square inch. 



In these experiments, four descriptions of iron were selected, 

 marked A, B, C, D : the two first and last were taken from rolled and 

 hammered iron plates, excepting C, which was homogeneous, and gave 

 higher results to tension and dead pressure than the others. 



In density and tenacity they stood as follows r-^- 



Here it will be observed, that the strengths are in the ratio of the 

 densities, excepting only the B plates, which deviate from that law. 



On the resistance to compression, it will be seen that in none of 

 the experiments was the specimen actually crushed ; but they evidently 

 gave way at a pressure of 13 to 14 tons per square inch, and were con- 

 siderably cracked and reduced in height by increased pressure. 



From the experiments on punching, we derive the resistance of 

 A, B, C, D plates to a flat-ended instrument forced through the plate 

 by dead pressure, as follows : — 



Here may be noticed, that the difference between the steel plates of 

 series C, and the iron plates of series A, is not considerable, though in 

 all the others the steel plates exhibit a superiority in statical resistance. 



Having ascertained, by direct experiment, the mechanical resist- 

 ance of different kinds of iron and steel plates to forces tending to 

 rupture, it is interesting to observe the close relation which exists 

 between not only the chemical analysis as obtained by Dr. Percy, but 

 how nearly they approximate to the force of impact, as exhibited in the 

 experiments with ordnance at Shoeburyness. 



Dr. Percy, in his analysis, observes, that of all the plates tested at 

 Shoeburyness, none have been found to resist better than those lettered 



