74 



ANNUAL OF SCIENTIFIC DISCOVERY. 



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 stati- 

 cal 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 be- 

 tween 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 let- 

 tered A, B, C, D, with the exception of C. The iron of plate E 

 contained less phosphorus than either of the three, A, B, D, and it is 

 clearly established that phosphorus is an impurity which tends in a 

 remarkable degree to render the metal "cold short," i. e. brittle 

 when cold. 



The following table shows the chemical composition of these irons : 



Comparing the chemical analysis with the mechanical properties 

 of the irons experimented upon, we find that the presence of 0.023 

 per cent, of carbon causes brittleness in the iron ; and this was found 

 to be the case in the homogeneous iron plates marked C ; and al- 

 though it was found equal to A plates in its resistance to tension and 

 compression, it was very inferior to the others in resisting concussion 

 or the force of impact. It therefore follows that toughness combined 

 with tenacity is the description of iron plate best adapted to resist 

 shot at high velocities. It is also found that wrought iron, which 



