1862.] and its Resistance to Projectiles at High Velocities. 497 



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 0-23 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 although 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 veloci- 

 ties. It is also found that wrought-iron, which exhibits a fibrous 

 fracture when broken by bending-, presents a widely different aspect 

 when suddenly snapped asunder by vibration, or by a sharp blow from 

 a shot. In the former case the fibre is elongated by bending, and be- 

 comes developed in the shape of threads as fine as silk, whilst in the 

 latter the fibres are broken short, and exhibit a decidedly crystalline 

 fracture. But, in fact, every description of iron is crystalline in the 

 first instance ; and these crystals, by every succeeding process of ham- 

 mering, rolling, &c., become elongated, and resolve themselves into 

 fibres. There is, therefore, a wide difference in the appearance of the 

 fracture of iron when broken by tearing and bending, and when broken 

 by impact, where time is not an element in the force producing rupture. 



If we examine with ordinary care the state of our iron manufacture 

 as it existed half-a-century aj^o, we shall find that our knowledge of its 

 properties was of a very crude and most imperfect character. We have 

 yet much to learn, but the necessities arising from our position as a 

 nation and the changes by which we are surrounded, will stimulate our 

 exertions to the acquisition of knowledge and the application of science 

 to a more extended investigation of a material destined, in course of 

 time, to become the bulwark of the nation. It is, therefore, of primary 

 importance, that we should make ourselves thoroughly acquainted, not 

 only with the niechanical and chemical properties of iron, but we should 

 moreover be able to apply it in such forms and conditions as are best 

 calculated to meet the requirements of the age in which we live. 



Entertaining these views, I cheerfully conmienced with my talented 



