August 27, 1891 



NATURE 



405 



lead-tin alloys polymerization may take place after the alloys 

 liave become solid, and it seems to be admitted that the same 

 cause underlies both polymerization and allotropy. The pheno- 

 menon of allotropy is dependent upon the number of the atoms 

 in each molecule, but we are at present far from being able to 

 say what degree of importance is to be attached to the relative 

 distance between the atoms of a metal or to the "position of one 

 and the same atom " in a metallic molecule, whether the metal be 

 alloyed or free, and it must be admitted that in this respect organic 

 chemistry is far in advance of metallurgic chemistry. I cannot, 

 as yet, state what is the atomic grouping in the brilliantly- 

 coloured gold-aluminium alloy, AuAl.,, which I have had the 

 L;ood fortune to discover, but, in it, the gold is probably present 

 111 the same state as that in which it occurs in the purple of 

 cassius. 



Much valuable information on the important question of allotropy 

 in metals has already been gathered by Pionchon, Ditte, Moissan, 

 Le Chatelier, and Osmond, but reference can only be made to 

 the work of the two Inter. Le Chatelier concludes that in 

 metals which do not undergo molecular transformation the 

 electrical resistance increases proportionally to the temperature. 

 The same law holds good for other metals at temperatures aVjove 

 that at which their last change takes place ; for example, in the 

 case of nickel above 340', and in that of iron above 850°. 



It is probable that minute quantities of foreign matter, which 

 profoundly modify the structure of mas-es of metal, also induce 

 allotropic changes. In the case of the remarkable action of im- 

 purities upon pure gold I have suggested that the modifications 

 which are produced may have direct connection with the periodic 

 law of Mendeleeff, and that the causes of the specific variations 

 in the properties of iron and steel may thus be explained. The 

 question is of great industrial importance, especially in the case 

 of iron ; and Osmond, whose excellent work I have already 

 brought before the members of this Association in a lecture 

 <lelivered at Newcastle in 1889, has especially studied the in- 

 fluence upon iron exerted by certain elements. He shows that 

 elements whose atomic volumes are smaller than that of iron 

 delay, during the cooling of a mass of iron from a red heat, the 

 change of the &, or hard variety of iron, to the a, or soft variety. 

 On the other hand, elements whose atomic volumes are greater 

 than that of iron tend to hasten the change of ;8 to a iron. It 

 i--, however, unnecessary to dwell upon this subject, as it was 

 dealt with last year in the address of the President of the 

 Association. 



It may be added that the recent use of nickel-steel for armour- 

 plate, and the advocacy of the use of copper-steel for certain 

 purposes, is the industrial justification of my own views as to 

 the influence of the atomic volume of an added element on the 

 mechanical properties of iron, and it is remarkable that the two 

 bodies, silicon and aluminium, the properties of which when in 

 a free stale are so totally different, should, nevertheless, when 

 ihey are alloyed with iron, affect it in the same way. Silicon 

 and aluminium have almost the fame atomic volumes. 



The consequences of allotropic changes which result in 

 alteration of structure are very great. The case of the tin 

 regimental buttons which fell into a shapeless heap when ex- 

 posed to the rigorous winter at St. Petersburg, is well known. 

 The recent remarkable discovery by Hopkinson of the changes 

 ill the density of nickel-steel (containing 22 per cent, of nickel) 

 which are produced by cooling to - 30°, affords another instance. 

 This variety of steel, after being frozen, is readily magnetizable, 

 although it was not so before; its density, moreover, is per- 

 manently reduced by no less than 2 per cent, by the exposure to 

 cold ; and it is startling to contemplate the effect which would 

 be produced by a visit to the Arctic regions of a ship of war 

 built in a temperate climate of ordinary steel, and clad with some 

 ihree thousand tons of such nickel-steel armour; the shearing 

 which would result from the expansion of the armour by ex- 

 posure to cold would destroy the ship. Experimental compound 

 armour-plates have been made, faced with 25 per cent, nickel- 

 steel, but it remains to be seen whether a similar though lessened 

 effect would be produced on the steel containing 5 to 7 per cent, 

 of nickel, specially studied by J. Riley, the use of which is 

 warmly advocated for defensive purposes. Further information 

 as to the molecular condition of nickel-steel has within the last 

 few weeks been given by Mercadier, who has shown that 

 alloying iron with 25 per cent, of nickel renders the metal 

 isotropic. 



The molecular behaviour of alloys is indeed most interesting. 

 W, Spring has shown, in a long series of investigations, that 



alloys may be formed at the ordinary temperature, provided that 

 minute particles of the constituent metals are submitted to great 

 pressure. W. Hallock has recently given strong evidence in 

 favour of the view that an alloy can be produced from its con- 

 stituent metals with but slight pressure if the temperature to 

 which the mass is submitted be above the melting-point of the 

 alloy, even though it be far below the melting-point of the mou 

 easily fusible constituent. A further instance is thus afforded of 

 the fact that a variation of either temperature or pressure will 

 effect the union of solids. It may be added that B. C. Damien 

 is attempting to determine what variation in the melting-point of 

 alloys is produced by fusing them under a pressure of two 

 hundred atmospheres. Italian physicists are also working on 

 the compressibility of metals, and F. Boggio-Lera has recently 

 established the existence of an interesting relation between the 

 coefficient of cubic c )mpressibility, the specific gravity, and the 

 atomic weight of metals. 



Few questions are more important than the measurement of 

 very high temperatures. Within the last few years H. Le Cha- 

 telier has given us a thermo-couple of platinum with platinum 

 containing 10 per cent, of rhodium, by the aid of which the 

 problem of the measurement of high temperatures has been 

 greatly simplified. A trustworthy pyrometer is now at hand for 

 daily use in works, and the liberality of the Institution of 

 Mechanical Engineers has enabled me to conduct an investiga- 

 tion which has resulted in the adoption of a simple appliance 

 for obtaining, in the form of curves, photographic records of the 

 cooling of masses of metal. A report on the subject has already 

 been submitted to a Committee, of which the Director-General 

 of Ordnance Factories is the Chairman ; and Dr. Anderson, to 

 wTiom I am indebted for valuable assistance and advice, intends 

 to add this new method for obtaining autographic curves of pyro- 

 metric measurements to the numerous self-recording appliances 

 used in the Government factories which he controls. It has 

 proved to be easy to ascertain, by the aid of this pyrometer, what 

 thermal changes take place during the cooling of molten ma-ses 

 of alloys, and it is possible to compare the rate of cooling of a 

 white-hot steel ingot at definite positions situated respectively 

 near its surface and at its centre, and thus to solve a problem 

 which has hitherto been considered to be beyond the range of 

 ordinary experimental methods. Some of the curves already 

 obtained are of much interest, and will be submitted to the 

 Section. It is probable that the form of the curve which repre- 

 sents the solidification and cooling of a mass of molten metal 

 affords an exceedingly delicate indication as to its purity. 



Prof. H. E. Armstrong holds that the molecules of a metal 

 can unite to form complexes with powers of coherence which 

 vary with the presence of impurity. Crookes, by a recent 

 beautiful investigation, has taught us how electrical evaporation 

 of solid metals may be set up in vacuo, and has shown that even 

 an alloy may be decomposed by such means. We may hope 

 that such work will enable us to understand the principles on 

 which the strength of materials depends. 



Before leaving the consideration of questions connected with 

 the molecular constitution of metals, I would specially refer to 

 the excellent work of Heycock and Neville, who have extended 

 to certain metals with low melting-point Raoult's investigations 

 on the effect of impurity on the lowering of the freezing-point of 

 solids. With the aid of one of my own students, H. C. Jenkins, 

 I have further extended the experiments by studying the effect 

 of impurity on the freezing-point of gold. Ramsay, by adopting 

 Raoult's vapour-pressure method, has been led to the conclusion 

 that when in solution in mercury the atom of a metal is, as a 

 rule, identical with its molecule. The important research on 

 the liquation of alloys has been extended by E. Matthey to the 

 platinum-gold and palladium-gold series, in which the manipula- 

 tion presented many difficulties ; and E. J. Ball has studied the 

 cases presented by the antimony copper-lead series. Dr. Alder 

 Wright has continued his own important investigation upon 

 ternary alloys ; and A. P. Laurie has worked on the electro- 

 motive force of the copper-zinc and copper-tin and gold-tin series, 

 a field of research which promises fruitful results. 



In no direction is advance more marked than in the mechani- 

 cal testing of metals, in which branch of investigation this 

 country, guided by Kirkaldy, undoubtedly took the leading 

 part, and in connection with which Kennedy and Unwin have 

 established world-wide reputations. I would also specially 

 mention the work which has been carried on at the Government 

 testing works at Berlin under Dr. Wedding, and the elaborate 



NO. II 39 VOL. 44] 



