1895. J on the Barer Metals and their Alloys. 515 



chromium when alloyed with iron ; but its use for projectiles, 

 although now general, is of comparatively recent date, and these 

 projectiles now commonly contain from 1*2 to 1*5 per cent, of 

 chromium, and will hold together even when they strike steel plates 

 at a velocity of 2000 feet per second * (see lower part of plate D) ; 

 and unless the armour-plate is of considerable thickness, such pro- 

 jectiles will even carry bursting charges of explosives through it. 

 [The behaviour of a chromium-steel shell, made by Mr. Hadfield, 

 was dwelt upon, and the shell was exhibited.] 



It now remained to be seen what could be done in the way of 

 toughening and hardening the plates so as to resist the chrome-steel 

 shot. About the year 1888, very great improvements were made in 

 the production of steel plates. Devices for hardening and tempering 

 plates were ultimately obtained, so that the latter were hard enough 

 throughout their substance to give them the necessary resisting 

 power without such serious cracking as had occurred in previous 

 ones. But in 1889, Mr. Eiley exhibited, at the meeting of the Iron 

 and Steel Institute, a thin plate that owed its remarkable toughness 

 to the presence of nickel in the steel. The immediate result of this 

 was that plates could be made to contain more carbon, and hence be 

 harder, without at the same time having increased brittleness ; such 

 plates, indeed, could be water-hardened and yet not crack. 



The plate E (Fig. 7) represents the behaviour of nickel-steel 

 armour. It will be seen that it is penetrated to a much less extent 

 than in the former case ; at the same time there is entire absence of 

 cracking. 



Now as to the hardening processes. Evrard had developed the 

 use of the lead bath in France, while Captain Tressider f had per- 

 fected the use of the water-jet in England for the purpose of rapidly 

 cooling the heated plates. The principle adopted in the design of 

 the compound plates has been again utilised by Harvey, who places 

 the soft steel or nickel-steel plate in a furnace of suitable con- 

 struction, and covers it with carbonaceous material such as charcoal, 

 and strongly heats it for a period, which may be as long as 120 

 hours. This is the old Sheffield process of cementation, and the 

 result is to increase the carbon from 0*35 per cent, in the body of 

 the plate to 0*b' per cent, or even more at the front surface, the 

 increase in the amount of carbon only extending to a depth of 

 2 or 3 inches in the thickest armour. 



The carburised face is then "chill-hardened," the result being 

 that the best chrome-steel shot are shattered at the moment of 

 impact, unless they are of very large size as compared with the 

 thickness of the plate. The interesting result was observed lately J 

 of shot doing less harm to the plate and penetrating less, when its 



* ' Journal U.S. Artillery,' 1893, vol. ii. p. 497. 



t Weaver, " Notes on Armour," ' Journal U.S. Artillerv,' vol. iii. 1894 

 p. 417. 



+ Brassey'd * Naval Annual,' 1891, p. 307. 



