RESISTANCE OF IRON PLATES TO PROJECTILES, 



281 



ascertained as a covei'ing for the sides of shrps of war. The very powerful 

 resistance of iron to projectiles at high velocities has directed most of the 

 maritime powers of Europe to the advantage of armour-plating ships for the 

 purpose of protecting them from the destructive effects of shot ; and it has 

 uow been proved that a sheathing of plates 4| inches thick, covering the 

 sides of a ship, extending to a depth of six feet below the water-line, is a 

 sufficient protection against existing guns of the heaviest calibre. It is true 

 that more powerful ordnance may be successfully tried against plates from 

 6 to 02 inches thick, but they are too heavy for general use on board ship ; 

 and as vessels of the present tonnage are not calculated to carry plates of 

 greater thickness than 4g or 5 inches, it is more than probable that the 

 country must be content with such protection as plates of these dimensions 

 can afford. 



Much, however, depends on the quality of the material of which they are 

 composed ; and the object of this communication is to furnish not only data 

 for the manufacture of them, but to point out their mechanical properties 

 and the best mode of attaching them to the ship. 



There are two descriptions of vessels to which armour-plates may be applied, 

 namely, those of iron, and the present existing vessels, composed entirely of 

 wood. In the present state of our knowledge, it is desirable that all vessels 

 of war should be formed of iron ; but the transfer is a work of time, and the 

 question now for consideration is, how to make our present wooden ships invul- 

 nerable, and how to apply the material to effect a maximum power of resistance 

 to shot. This is the great question for solution, and the Admiralty, fully alive 

 to the importance of the change, has instituted a long and laborious series 

 of experiments to determine these results. 



It is well known that all substances of a brittle nature are easily broken 

 by impact, and the best kind for resisting blows is a tenacious, tough, and 

 ductile material. To secure all these properties is a desideratum in the 

 manufacture of iron plates, and one which never ought to be neglected. In 

 submitting the following results obtained from the experiments, it may be 

 interesting to show the chemical compositions of some of the best irons ex- 

 perimented upon, and those marked with the letters A, B, C, and D, when 

 carefully analysed, were found to contain the following ingredients : — 



Comparing the chemical analysis with the mechanical properties of the 

 irons experimented upon, we find that the presence of -023 per cent, of carbon 

 causes brittleness in the iron ; and this was found to be the case in the ho- 

 mogeneous 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 velocities. It is also found that wrought iron, 

 which exhibits a fibrous fracture when broken by bending, presents a widely 



* Homogeneous iron is that description of iron or steel which is not rolled or manufac- 

 tured from piled bars, but obtained by the boiling process from the furnace, where the amal- 

 gamation is complete ; or, in other words, it is obtained from cast ingots according to the 

 Bessemer process, or direct from the bloom as it leaves the puddling furnace. 



