40 



NATURE 



[May 9, 189; 



of weakness, but always confer some property which is precious in 

 industrial use. How these rarer nictals act, why the small 

 quantities of the added rare niclals (>eniieale the molecules, or, 

 it may be the atoms, and strengthen the metallic mass, we do not 

 know : we arc only gradually accumulating evidence which is 

 aflbrded by this very delicate physiolwjical methoil of investiga- 

 tion. 



As regards the actual temperatures represented by points on 

 such curves, it will lie rcmemberetl that the indications afforded 

 by the recording pyrometer are only relative, and that gold is one 

 of the most suitable metals for enabling a high, fixed jK>int to be 

 determined. There is much trustworthy evidence in favour of the 

 adoption of 1045° as the melting point hitherto accepted for 

 gold. The results of recent work indicate, however, that this 

 is too low, and it may prove to be as high as io6i"7, which is 

 the melting point given by Heycixrk and Neville' in the latest 

 of their admirable series of investigations to which reference 

 was made in my Friday evening lecture of 1891. 



It may be well to [xjint to a few instances in which the 

 industrial use of such of the rarer metals, as have been available 

 in sufficient quantity, is made evident. Modem developments in 

 armour-plate and projectiles will occur to many of us at once. This 

 diagram ( Fig 5 ) affords a rapid view of the progress which has been 

 made, and in collecting the materials for it from sarious sources, 

 I have l)een aided by .\Ir. Jenkins. The effect of projectiles of 

 approximately the same weight, when fired with the s:ime velocity 

 against six-inch plates, enables comparative results to be studied, 

 and illustrates the fact that the rivalry l)etwcen artillerists who 

 design guns, and metallurgists who attempt to produce lx)th 

 impenetrable armour-plates and irresistible projectiles, forms one 



layer of steel of an intermediate quality ca,st between the tw- 

 plates. Armour-plates of this kind differ in detail, but the 

 principle of their construction is now generally accepted as 

 correct. 



•Such plates shown by plate B, resisted the attack of large 

 Palliser shells admirably, .as when such shells struck the jilate 

 they were damaged at their piints, and the remainder of the 

 shell was unable to perforate the armour ag.unst which it wa^ 

 directed. .\n increase in the size of the projectiles letl, however, 

 to a decrea.se in the resisting i>ower of the jilates, jHirtions of the 

 hard face of which would at times be detached in flakes from the 

 junction of the steel and the iron. An increase in the toughness 

 of the projectiles by a substitution of forged chrome-steel for 

 chilleil iron (see lower |«rt of plate B), secured a victor)- for the 

 shot, which was then enabled to impart its energy to the plate 

 faster than the surface of the plate itself couUl transmit the 

 energy to the l)ack. The result was that the plate was overcome, 

 as it were, piecemeal : the steel surface was not sufficient to resist 

 the blow itself, and was shattered, leaving the prttjectile an ci-sy 

 victor)' over the soft liack. The lower part of plate, H (in Fig. 5). 

 represents a similar ])late to that used in the Nettle trials of 

 18S8.' It must not be forgotten in this connection, that the 

 armour of a ship is but little likely to \k strtick twice by heavy 

 projectiles in the same place, although it might be by smaller 

 ones. 



Plates made entirely of steel, on the other hand, were found, 

 prior to 1888, to have a considerable tendency to break up 

 completely when .struck by the .shot. It was not possible, on that 

 .account, to make their faces as hard as those of compound plates : 

 but while they did not resist the I'alliser shot nearly so Hell a'^ 



Attack of 6-incii Arxiour-I'Uxtfs uv 4. 72. inch Shei.us, wkighing 57.2 lbs. 



'4l aJ ^ 

 111 



*f 



Wrought iron. Compound plate. Siccl. Steel. Nickcl-slecl. H.irvcycd, iiickti-slci-l. 



■ 888. 1888. 1888. 1894. 1894. 1894. 



Fic 5.— The upper serio of projectiles are P.illiser chilled-iron shells, and the lower .ire chrome-steel. In e.ich c.-im; the velocity of the projectile is 



.-ipproximately 1640 foot-seconds, and the energy' 1070 foot-tons. 



of the nuist interesting [lagcs in our national history. When 

 metallic armour was first applietl to the sides of war vessels, it 

 was of wrought irrin, an<l proved to l)e of very great service by 

 al>solutcly preventing the pa.s.sage of ordinary cast-iron shot into 

 the interior of the ves-scl, as was demon.strate<l during the 

 .\merican Civil War in 1866. It was found to be necessary, in 

 order to pierce the plates, to employ bariler and larger proj'jctiles 

 than those then in ii.'te, and the chilled cast iron shot with which 

 Gilonel I'alliser's name is identified proveil to l>e formidable and 

 effective. The pfjint of such a projectile was sufficiently hard to 

 retain its form under im|«act with the plate, and it was only 

 necessary to im|>art a imxlerate velocity to a shot to enable it to 

 |ia.ss through the wr<iught-iron armour (A, Fig. 5). 



It s<H)n l)ecame evi<lent that in order to resist the attack of 

 such projectiles with a pbte of any rea.sonable thickness, it 

 would lie necessary lo make the plate harder, so thai the jMiint 

 of the projectile should lie rlamaged al the moment of first 

 contact, and the reaction to the blow distributed over a consider- 

 able area of the pl.ate. This object couM lie attained by either 

 luing a steel pl.ate in a more or less hardened condition, or by 

 employing a iilate with a very hard face of steel, and a less hard 

 but tougher Inck. The authorities in this country during the 

 decade. lS.So-90, h.ad a very high opinion of plates that resisled 

 attack uilhoul the development of through-cracks, and this led 

 to the priKluction of the coin(xiund [ilale. The lacks of these 

 plates (n, Fig. 5) are of wrought iron, the fronts are of a more 

 or less hard variety of steel, either cast on, or welded on by a 



' "Trail*. Crhem. Soc.," vol, Ixvii., 1895, p. 160. 



NO. 1332, VOL. 52] 



the rival comixiund plale, they olicrcd more eflective resistance 

 to steel shot (see lower pari of plate c. Fig. 5). 



It appears that Kerthier recognised, in 1S20, thegre.1t value of 

 chromium when alloyed with iron : but ils use for projecliles, 

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

 projecliles now cominonly coiUain from I "2 to I '5 per cent, of 

 chromium, and will hold logelher even when ihoy strike steel 

 plates at a velocity of 2000 feet per second.-' (see lower pari of 

 pl.ate n) : and unless the armour-plate is of considerable thick- 

 ness, .such projectiles will even carr)' bursting charges of explo- 

 sives through it. [The behaviour of a rhromium-.sleel .shell, made 

 by Mr. Iladfield, w.as dwelt upon, and llie shell was exhibited.] 



It now remained to Ik' seen what could be done in lite way of 

 toughening and hanlening ihe plates so as to resist the chrome 

 steel shot, .\boul the year 1S8S, very great improvements were 

 made in ihe production of steel plales. Devices for hardening 

 and lenijK'ring plates were ulliinately obtained, so that the latter 

 were hard enough throughout their substance to give Ihem the 

 necessary resisliiig |viwer wiihoul such serious cracking as had 

 occurred in previous ones. Hul in 1X89, .Mr. Riley exhiliiled, at 

 the meeling of the Iron and Sleel Instilule, a ihiii plale that 

 owed ils remarkable toughness to the |>resence t»f nickel in the 

 sleel. The iininediate result of this was that jilales could lie 

 niaile lo contain more carbon, and hence be harder, without al 

 the .s;ime lime having increa.sed briltleness ; such plales, indeed, 

 could be water hardened and yet not crack. 



' I'rotetttines Insliliition of Civil KnKineers, 18B9, vol. xcviil, p. \,et stq.. 

 '-' /i^ut-nnt \. .S. .\rlillcrv. i8oi. Vol. .p. .107 



