THE EARER METALS AND THEIR ALLOYS. 511 



offered more effective resistance to steel shot (see lower part of Plate 

 0, fig. 1, PI. XXVI). 



It appears that Berthier recognized, in 1820, the great value of 

 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 2,000 feet 

 per secoud ' (see lower part of Plate D); and unless the armor plate is 

 of considerable thickness, such projectiles will even carry bursting 

 charges of explosives through it. [The behavior 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 tough- 

 ening and hardening the plates so as to resist the chrome-steel shot. 

 About the year 1888 very great improvements were made in the pro- 

 duction of steel plates. Devices for hardening and tempering plates 

 were ultimately obtained, so that the latter was hard enough through- 

 out their substance to give them the necessary resisting power without 

 such serious cracking as had occurred in previous ones. But in 1889 

 Mr. Kiley 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 represents the behavior of nickel-steel armor. 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. 



Xow, as to the hardening processes. Evrard had developed the use 

 of the lead bath in France, while Captain Tressider 3 had perfeeted 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 utilized by Harvey, who places the soft-steel or 

 nickel-steel plate in a furnace of suitable construction, and covers it 

 with carbonaceous material, such as charcoal, and strongly heats it for a 

 period, which may be as long as one hundred and twenty 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 0.0 per cent or even 

 more at the front surface, the increase in the amount of carbon extend- 

 ing to a depth of only 2 or 3 inches in the thickest armor. 



The carburized 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 3 of shot doing 



'Journal United States Artillery, 1893, Vol. II, page 497. 



2 Weaver. Notes on Armour, Journal United States Artillery, Vol. Ill, 1894, page 417. 



3 Brassey's Naval Annual, 1894, page 367. 



