May 9, 1895] 



NA TURE 



4i 



The plate E (Fig. 5) represents the behaviour of nickel-steel 

 armour. It will he 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 hath in France, while Captain Tressider ' had 

 perfected the use of the water-jet in England for the purpose of 

 rapidly cooling the heated jjlates. The princi]>le aflopted in the 

 design of the compound plates has been again utilised by Harvey, 

 who places the soft steel <ir nickel-steel plate in a furnace of suit- 

 able construction, and covers it with cariifjnaceous material such 

 as charcoal, and strongly heats it for a jieriod, which may be as 

 long as 120 hours. This is the old .Sheffield process of cementa- 

 tion, and the result is to increase the carbon from 0*35 P^"* cent, 

 in the body of the plate to o"6 per cent. , or even more at the front 

 .surface, the increase in the amount of carbon only extending 

 to a depth of two or three inches in the thickest armour. 



The carburi.sed face is then " chill-hardened," the result being 

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

 impact, unless they are t»f very large size as com]iared with the 

 thickness of the plate. The interesting result was observed 

 lately- of shot doing less harm to the plate, and penetrating less, 

 when its velocity was increased beyond a certain value, a result due 

 to a superiority in the power of the face of the plate to transmit 

 energy over that possessed by the projectile, which was itself 

 damaged, when a certain rate was exceeded. At a comparatively 

 low velocity the |)oint of the shot would resist fracture, but the 

 energ)' of the projectile is not then sufficient to perforate the 

 plate, which woukl need the attack of a much larger gun firing a 

 projectile at a lower velocity. 



Fic. 6. — Section of Barbette of the Majestic. 



The tendency to-day is to dispense with nickel, and to use 

 ordinary steel, "Harveyed ;"■' this gives excellent six-inch plates, 

 but there is some difference of opinion as to whether it is ad- 

 vantageous to omit nickel in the case of very thick plates. 

 and the pr<3l)Iem is now being worked out liy the method of 

 trial. Probably, too, the Harveyed plates will be much 

 improved by judicious forging after the prijcess, as is indicated 

 by .some recent work done in America. The use of chromium 

 in the plates may lead to interesting results. 



Turn for a moment to the '^ Majfslii- "' class of ships, the con- 

 struction of which we owe tt) the genius of Sir William White, 

 to whom I am indebted for a section representing the exact 

 size of the protection afliirded to the barlietle of the Maj,-s/ic. 

 [This sectiim was exhibited and is shown as reduced to the 

 diagram Pig. 6. J Her armour is of the Harveyed steel, which 

 has hitherto proved singidarly resisting to chromium projectiles. 



In this section, A represents a 14-inch Harveyed steel armour- 

 plate : n, a 4-inch teak backing; c, a ij-inch steel plate; D, 

 i-inch sieel frames ; and K, 4-inch steel linings. 



It will, I trust, have been evident that two of the rarer metals, 

 chromium and nickel, are playing a very important part in otir 



' Weaver, " Notes on .\rmour." Journal U.i^. .\rtillery. 

 p. 417. 

 - Hrassey"s .Vavai .Inniial, 1894. p. 367. 

 '* KiigineefiHg, vol. Ivii., 1894, pp. 465, 530, 595. 



Vol. iii. 1894, 



national defences ; and if I ever lecture to you again, it may be 



possible for me to record similar triumphs for molybdenum, 

 titanium, vanadium, and others of these still rarer metals. 



Here is another alloy, for which I am indebted to Mr. Had- 

 field. It is iron alloyed with 25 per cent, of nickel, and 

 Hopkinson has shown that its density is permanently reduced by 

 two per cent, by an exposure to a temperature of- 30°, that is the 

 metal expands at this temperature. 



Supposing, therefore, that a shi]i-of-war was built in our 

 climate of ordinary steel, and clad with some three thousand tons 

 of such nickel-steel armour, w-e are confronted with the extra- 

 ordinary fact that if such a ship visiteil the .Vrctic regions, it would 

 actually become some two feet longer, an<l the shearing which 

 would result from the expansion of the armour by exposure to 

 cold would destroy the ship. Before I leave the question of the 

 nickel-iron alloys, let me direct your attention to this triple alloy 

 of iron, nickel and cobalt in simple atomic proportions. Dr. 

 Oliver Lodge believes that this alloy will be found to possess very 

 reiuarkable projierlies ; in fact, as he U*\i\ me. if nature had 

 properly understood Mendeleef, this alloy would really have been 

 an element. As regards electrical projierties of alloys, it is im- 

 possible to say what services the rarer metals may not render ; and [ 

 would remind you that " platinoid," mainly a nickel-copper alloy, 

 owes to the presence of a little tungsten its peculiar property of 

 having a high electrical resistance which does not change with 

 temperature. 



One other instance of the kind of influence the rarer metals 

 may be expected to exert is all that time will permit me to give 

 you. It relates to their influence on aluminium itself. You 

 have heard much of the adoption of aluminium in such branches 

 of naval construction as demand lightness and portability. During 

 last autumn Messrs. Yarrow completed a torpedo boat which 

 was built of aluminium alloyed with 6 per cent, of copper. Her 

 hull is 50 per cent, lighter, and she is 34 knots fa.ster than a 

 similar boat of steel wi>uld have been, and, notwithstanding her 

 increased speed, is singularly free from vil)ration. 



Fn;. 7. — Half-section Mirlship of Aluminium Torpedo-boat 



Her plates are ^th inch thick, and Jth inch where 

 greater strength is needed. It reinains to be seen wdiether 

 copper is the best metal to alloy with alinniniimi. Several 

 of the rarer metals have already been tried, and among 

 them titanium. Two ])er cent, of this rare metal seems to 

 confer remarkable properties on aluminium, and it should do 

 so according to the views I have expre.ssed, for the cooling 

 curve of the titanium-aluminium alloy woulil certainly show a 

 high subordinate freezing point. 



Hitherto I have appealed to industrial work, rather than to 

 abstract science, for illustrations of the services which the rarer 

 metals may render. One reason for this is that at present we 

 have but little knowledge of some of the rarer metals apart from 

 their association with carbon. The metals viel<le<i bv treatment 



NO. 1332, VOL. 52] 



