METALLURGY

progress in metallurgy after torr was profoundly affected by the world war. modern war- fare is so entirely dependent upon the products of metallurgy that the effort to secure military victory to some extent resolved itself into a struggle for supremacy in metallurgical output, in regard to steel products such as guns and shells, ship-plates and armour, etc., to copper and its alloys, to zinc, to lead and anti- mony, and, in a special degree, to aluminium. during the war period, therefore, the progress of metallurgy became mainly a relentless struggle for output in which, in some directions, quality was sacrificed and heavy ‘‘ war risks’’ were cheerfully taken, after the termination of the war, industria! con- ditions became extremely unsettled and difficult; the shortage of ships was followed by acute industrial disturbances, particularly in england. the continental nations only slowly resumed their norma! activities, and were gravely hindered on all sides by the direct and indirect economic consequences of the treaty of versailles. as the result of continued political and financial uncertainty, recovery in the metallurgical industries remained slow, except perhaps in belgium, until 1925. towards the end of that year, following the improved atmosphere resulting from the locarno pact, signs of im- provement began to sect in. meanwhile, however, the metallurgical industries of america experienced a period of special prosperity, and the relative rate of devclopment in metallurgical practice in the eastern and western hemispheres must be in part ascribed to these factors. divisions of the subject the whole period under review thus falls into three main divisions: prior to 1914, the war period and the post-war period. the intlu- ence of the war has left important traces in certain directions but the line of development appears to be tending towards a simple continuation of pre-war lines, thus, very great efforts in england and in certain of the british dominions to render those countries metallurgically self-supporting were made either as the result of direct governmental encouragement and support or on account of the abnormally high prices ruling for some of the metals. this led to the development of propertics and processes which were, under more normal conditions, uneconomical, and these—with govern- mental support unavoidably withdrawn and prices at a less abnor- mal level, have necessarily been abandoned. an important exception is the great development in the zinc industry in great britain and australia, in which, thanks to real metallurgical advances, permanent economic success has been achieved. in a totally different direction, however, war conditions led to a relaxation of the severity of specifications, particularly for steel products. after the war, stecl makers claimed that their difficultics were almost as great as ever. it was suggested that the relaxed specifica- tions had led to no disastrous results and that, therefore, they might be safely continued. the british engineering standards associa- tion adopted a compromise course and, while rejecting the extreme relaxations accepted under war conditions, also refrained from a return to full pre-war severity. it has resulted that ‘‘ war time products ” are looked upon with grave suspicion. a steady tendency towards increasing stringency in specifications, particularly in the 879 direction of higher requirements as to the purity of metals and alloys, is now (1926) making itself felt. a similar tendency appears to exist also in america, but the methods of applying specifications and tests in that country are so widely different from those adopted in england that direct comparison is liable to be misleading. another effect of the war, and of the subsequent strong move- ment towards disarmament, has been the need for industrial re- arrangements and reconstructions on a large scale. at the end of 1918, the metallurgical and allicd industries were entirely devoted to armament and munitions and had then to find different outlets for their activities. ‘phe enginecring reconstruction work required in the devastated regions of fkurope proved no adequate outlet and in many cases, particularly in england, great works had to close down. in america, with an enormous home market the conversion of armament and munition works to peaceful output was carried through successfully on a large scale. consequently, the industrial ‘slump " in that country was comparatively slight and brief, i. iron and steel prior to 1914 iron and steel metallurgy showed a tendency towards the development of very large plants and larger in- dividual units, both in regard to furnaces and rolling-mills. the tendency towards increased size made itself felt in the blast furnace, particularly in american practice; progress, however, also included development in the direction of furnaces with walls and external water-cooling, such furnaces being driven very hard. pre-war progress-—in the period prior to ror4, considerable attention was given to drying the blast, and it seemed at one time that this would become universal practice. under war conditions this development was checked, at all events in england, and has not been resumed since 1918. increased attention has, however, been given to the utilisation and cleaning of blast furnace gases. this became particularly important in england during the war on account of the shortage of potash, a substantial recovery of this matcrial being obtainable trom the flue-gases of furnaces in which the charge included potash-felspar. at the same time satisfactory cleaning of the gas very much increases its efficiency in stoves and under boilers, owing to the absence of fouling with dust. on the other hand, a degree of cleaning which will render the gas fit for direct use in gas-engines is a much more expensive matter, and not so obviously economical. the cleaning processes adopted are mainly of two kinds; one of these depends upon the electrostatic deposition of the dust by the method first sug- gested by lodge and developed in america by cottrell (see fume precipitation). the other method depends upon filtration of the gas through fabric bags which are kept in a state of agitation, as in the halberg-beth system. although, under normal conditions, pot- ash recovered from flue-dust could not compete with the product of continental mines, yet cleaning of blast-furnace gas will be continued. the dust itself may be utilised for the recovery of iron con- tained in it, by briqueting the dust by a modification of the schu- macher process, in which a weak solution of ferrous sulphate is used as binder. a further proposal is to concentrate the iron-content by some adaptation of the hotation process. the application of flotation processes (sce below) to finely divided iron-ores had not been found necessary or practicable up to 1926, but methods dealing with finely divided ores (both ferrous and non- ferrous) have been considerably developed. in addition to the schumacher process already mentioned, reference must be made to the dwight-lloyd process, in which the ore is mixed with a small proportion of fincly divided carbon and pressed into briquettes which are then heated to a moderate temperature. a partial reduc- tion of the ore takes place, leading to a sintering of the briquette which thus acquires the necessary strength. in the production of steel, the open-hearth furnace has made very great progress and appears likely to displace the bessemer converter, although the latter seems to be holding its own to a certain extent. the steady increase in the application of basic open-hearth stecl tends to give the large open-hearth furnace, particularly when working one of the continuous processes, a very great advantage. war pertod.—in the first place it became necessary, particu- larly in england, to make use of ores and other materials very different from those for which particular furnace plants had been designed, while the supply of operative labour became very dificult. in consequence of these and other difficulties, relaxation of quality, already mentioned above, became inevitable, partic- ularly in regard to those grades of steel which were required in very large quantities. apart from the demand for enormous supplies of steels of ordinary grades, war conditions also caused great demands for 880 steels of the highest quality for special purposes. the production of guns was one of these, and much difficulty was. encountered both in england and america with defects—known as “ snow flakes’ or “ gun measles ”—occurring particularly in nickel- chrome steels. reversion to the use of a simple nickel-steel for such purposes followed, but this entailed a serious disadvantage, if only on account of the greater difficulty experienced in securing satisfactory heat-treatment. this difficulty was also encountered in connection with the gearing used for the propelling machinery of turbine-driven ships. high-quality steels, mainly alloy steels, were also required in relatively very large quantities for purposes of air-craft construction, principally for the working parts of aero-engines. this demand led to a great development in the production and treatment of alloy steels. here, and generally in the production of the better grades of steel, the electric furnace played a remarkable part. a large num- ber of furnaces, mostly of the arc-resistance type, were installed, particularly in sheffield. their value lay in the super-refining of steel, sometimes produced in a basic open-hearth furnace, some- times obtained by the direct remelting of alloy-steel scrap. probably the power of the electric steel furnace to deal satisfac- torily with such scrap, even when in the form of workshop swarf, constituted its greatest value during the war. since the end of the war, however, the demand for such steel has almost disap- peared, with the result that the greater number of the electric furnaces, both in england and america, became idle. none the less, there must be, in the future, a definite use for a certain number of electric furnaces in steel metallurgy. alloy steels —in regard to alloy steels, while nickel-chrome and nickel steels have found by far the widest application, par- ticularly for war purposes, other alloy steels have also assumed importance. nickel-chrome steel in particular, in addition to the difficulties already mentioned, has been found to be subject to a defect known as ‘‘ temper brittleness.’’ alloy steels, in order to assume their most desirable physical condition, require specific heat-treatment, which, asa rule, consists of quenching in oil, or more rarely in water, from a temperature above the critical range of the steel, followed by “ tem- pering "’ or reheating to a romper ate considerably below the critical range. in the majority of steels, the rate of cooling subse- quent to tempering is of little importance, but in a certain number of nickel-chrome steels slow cooling after tempering leads to a form of brittleness which is entirely removed if the steel is cooled very rapidly (quenched) after tempering. the cause of temper-brittle- ness has received much investigation, and the results indicate that it is due to a change or “ transformation " which occurs in the steel at or near 300° c.; it appears to be favoured by certain impurities, notably phosphorus. further, acute controversy has arisen as to the importance or otherwise of such ‘‘ temper brittleness ”’ on the ground that it can only be detected by a particular form of test—the “‘ notched bar impact test.’”” hatfield has repeatedly suggested that this test measures a property of no practical importance, and that therefore temper brittleness is only “ apparent ”’ and not “real.” this view, however, has not been generally accepted, since a number of in- vestigators (rosenhain, greaves and others) have found a very distinct correlation between a low value under the notched bar impact test and cases of actual failure in service. chromium steels.—for certain purposes, where simple nickel steels are not found adequate, a chrome-vanadium steel has been extensively used. the fact that vanadium plays a really im- portant rele in such steels has come to be recognised, but there are still difficulties in its metallurgical applications. for quite a different range of purposes a steel containing relatively large amounts of chromium (about 13°, brearley) has found wide applications. its best-known application is to the production of “ stainless ’’ cutlery, which has proved extremely successful in practice, and in spite of the relatively high cost has come into extensive use as a labour-saving device (see rustless steel). some difficulty was at first experienced in hardening this ma- terial satisfactorily; it requires a higher quenching temperature than cutlery-hardeners have been accustomed to employ (hat- field), and, as a consequence, the earlier products were insuffi- ciently hardened, and gave rise to the complaint that such cut- lery would not keep its edge. later practice has overcome this defect, although the fact still remains that “stainless”? knives, metallurgy not being automatically sharpened by daily polishing, require careful sharpening from time to time. new applications of this steel to other purposes where resist- ance to corrosion is important are being found almost daily. incidentally, it was found that this steel is capable of resisting the severe conditions which occur in the service of an exhaust-valve in aeroplane engines, although a high-tungsten steel (18% tungsten) has been found to be slightly better. more recently, special alloy steels for use at high temperatures have been de- veloped both in england and in germany. these contain con- siderable proportions of both nickel and chromium, while in some cases tungsten ts also present. unlike the simple chromium steels, these new materials retain a considerable degree of strength at temperatures well above 700° c., particularly if tested in tension at ordinary rates of loading. testing under prolonged loading—known as “creep stress testing ’’—has, however, been developed to furnish more reliable data where material is exposed to continued load at high temperatures, and it is as yet difficult to find any material which shows a higher “creep stress’ than two tons per sq. in. at 800° centigrade. this figure is attained both by some of the steels just mentioned and by a non-ferrous nickel-chromium alloy (80% nickel, 20% chromium}. this whole subject 1s attracting much attention in view of the tendency towards the use of higher temperatures and pressures in both steam and internal combustion engines. while the simple chromium steels of the “ stainless” type still hold the field for cutlery and similar purposes where hardness is essential, their powers of resisting corrosion have been surpassed to a surprising degree by the recently developed alloy steels containing considerable proportions of both nickel and chromium, with, how- ever, very little carbon. these are “ austenitic” steels, ¢.e., they consist mainly of what is known as ‘‘gamma”’ iron, are non- magnetic and very tough and ductile. they cannot, however, be hardened by quenching, although they frequently exhibit a tendency to harden very markedly under the action of cold working. the manganese steel of sir robert hadfield, which proved so valuable as a material for shrapnel-proof helmets during the war, is an extreme example of this kind, as this stcel becomes intensely hard when subjected to cold working, even if this only takes the form of surface abrasion. the high nickel-chromium steels do not harden to anything like the same extent, but sufficiently so to make them difficult to machine. like mangancse stcel in the quenched or “ toughened ”’ condition, they are non-magnetic, but their outstanding feature is resistance to corrosion. the best of them remain unaffected by most liquids, in- cluding sea-water, solutions of magnesium chloride and even strong nitric acid. strong hydrochloric acid alone attacks them. ‘these remarkable materials have only recently (1925) become com- mercially available, but their application is already developing rapidly. their good physical properties, combining high strength and great ductility, make them desirable materials for many kinds of structural work, but applications on the very large scale are still hindered by their relatively high cost. high-speed steels —in the metallurgical progress of the period under review, the development of high-speed cutting steels occupied an important place, their possibilities having been steadily exploited to an increasing extent, their development being naturally accompanied by an evolution of machine-tools capable of utilising the high cutting powers of the new steels. under war conditions the great demand for tool-steels of this kind created a relatively enormous demand for tungsten, and considerable developments in the mining and production of tungsten took place. efforts to replace tungsten by other metals were also made, and very great claims were advanced for a high- speed steel in which molybdenum in combination with vanadium was used in place of tungsten (arnold), the action of cutting tools has received careful study by a number of investigators, largely under the auspices of the cutting tools research com- mittee of the institution of mechanical engincers. in connection with high-speed steels, mention may here be made of a type of alloy which has been used, with considerable success, in place of such steel. this, known as “ stellite,’’ consists, according to a reliable analysis, mainly of cobalt 56°, chromium 34 %, tungsten 9°%, carbon 1°%. tests with this material have shown that it is capable of cutting rather faster than the best tungsten steel, pro- vided that the cut is smooth and regular, but that for roughing cuts, where the tool is subjected to sudden shocks and jars, the alloy is unsuited, as it is too brittle and the tool frequently breaks off. metallurgy these alloys, originating in america, have received much attention and development in germany. in england the hardness and in- corrodibility of these alloys has led to their use as a substitute for platinum for such purposes as standard weights. cobalt steel.—the great development of cobalt production at sudbury in canada has made this metal available and has at- tracted interest to its possible uses. a high-speed tool-steel, containing cobalt has been produced in sheffield, which has been successful in general use and has the remarkable property that it does not undergo distortion during hardening. great difficulty existed under war conditions in the production of accurate parts —such as those of shells and fuses—which were required to be strictly interchangeable. this difficulty extended back to the gauges and master-gauges used for the checking of such parts and ultimately in many cases to the cutting-tools used in their production. in other cases, the steel of which the gauges them- selves were made gave much trouble owing to distortion during hardening, requiring considerable adjustment by “ lapping ”’ of the hardened article. a cobalt steel has also become important for permanent magnets. made in the first place of hardened carbon steels, the requirements particularly for the magnetos used for ignition pur- poses in aircraft engines led to the use of special steels containing about 6° of tungsten. a japanese invention, based upon ex- tensive researches carried out in that country (hondo), has produced a cobalt magnet steel which, in its best examples, gives surprising results, combining an exceptionally high coercive force with a relatively large remanence. by the use of this steel a much smaller and lighter magnet suffices for a magneto of given power. the steel is expensive, and when supplied in quantity appears to vary in quality, while there is also some difficulty in its workshop manipulation. | case hardening—processes for the surface hardening of tough steel have come into increasing use, and methods for securing full hardness of the case, with a tough core and good gradation between the two, have been developed. more recently a method of surface hardening has been worked out in germany (krupp) which entirely avoids the necessity for quenching and its attend- ant distortion. a special steel, containing both chromium and aluminium, is employed, and the surface is hardened by the formation of a layer of intensely hard nitride, produced by pro- longed heating at about 500° c. in a gas consisting mainly of ammonia. w'elding.—one of the most remarkable developments (metal- lurgical in the wider sense) during the period under review has been that of autogenous welding, (¢.v.) both by the oxyacetylene flame and by the electric arc, both these processes afford a relatively cheap and simple means of making joints in metal, particularly in iron and steel, and as the joint consists of ‘ the same metal ” as that which is being joined there is a specious suggestion that the joint is “ perfect " in the sense of being as good as the unjointed material, although it is quite possible to obtain welded test-pieces which break, under a tensile test, away from the actual joint, the joint itself can never be regarded as equal in strength and toughness to the unjointed steel. the reasons are that the material in the weld itself has solidified from fusion and is at best equal in properties to the same steel in the cast condition, while the rest of the plate itself has been immensely improved in quality by forging and rolling and possibly by heat-treatment. further, adjacent to every such weld there is a region of steel which has either been severely overheated or —a little farther away—which has been heated to a temperature just below the critical range. jn both these regions the steel is seriously weakened, and it is in the latter that test-pieces generally break. the most serious difficulty, however, is that of being sure that any autogenous weld is truly sound. examination of many welds has shown that complete soundness js difficult to secure, and that it 1s the exception rather than the rule, even in careful practice. also, it is not possible to ascertain by any external examination of a weld whether it is sound or not. examination by the aid of a powerful x-ray installation can sometimes be employed to assure the sound- ness of an important weld, but as a rule this is not feasible. it would seem, therefore, that there is grave doubt whether welded joints can be relied upon to carry severe working stresses or whether they should be employed in vital parts unless an exceptionally heavy factor of safety can be allowed. experience in aeroplane construction supports these doubts, and a construction in which steel tubes are joined together by pinned and 881 soft-soldered joints has been found more reliable than autogenous welding, provided that the working stress on the solder is kept toa low value. on the other hand, the welding processes afford a ready means of making joints and effecting repairs where no other process could be used, and under war conditions particularly rapid repairs were frequently executed with great success. at the same time, welded joints should not be compared with the unjointed material but rather with joints made in other ways, such as riveting; and there the comparison is much more favourable except for the serious element of uncertainty. the application of welding, and particularly of electric arc welding, to such purposes as ship construction, has, however, found considerable acceptance. cast iron.—this metal has received much attention, both on the practical and the research sides. in germany this is strongly indicated by numerous patents and scientific papers and in great britain by the formation and growth of the cast [ron research association. one of the most striking developments 1s that of so-called ‘‘ pearlite ” iron, in which the rate of solidifica- tion is adjusted, by suitable preheating of the sand moulds, to the thickness of the casting and the silicon content in such a way as to secure desirable (pearlitic) microstructure and specially good physical properties. special furnaces suitable for the pro- duction of cast irons low in total carbon, or specially desulphur- ised, have also been developed. in america the production of malleable castings on a jarge scale has progressed, with the introduction of electric furnace melting for the iron and malleable-annealing in continuous fur- naces of the tunnel-kiln type. the casting of grey iron castings in permanent metal moulds has also been developed,the chilling etlect of the iron mould being avoided by the interposition of a hard layer of relatively non-conducting refractory material. the exposure of cast-iron to increasingly high temperatures has re- vived the problem of the “ growth” of this metal, particularly on repeated heating and under the influence of superheated steam. the view that growth is essentially due to oxidation occurring in the graphitic pores of the iron is still held, but it is recognised that this action is not solely due to silicon and that it may be as much dependent upon the treatment of the iron and its con- sequent structure as upon its chemical composition. uw. non-ferrous metals flotation process —the outstanding feature in the progress of non-ferrous metallurgy is summed up in the one word “‘ flota- tion.” published scientific research (langmuir, sulman and pic- ard, edser) has gone far towards the explanation of this process which has made enormous progress and has revolutionised the practice of the extraction of many non-ferrous metals, particu- larly those occurring in the form of sulphide minerals, such as galena, zinc-blende and the various pyritic copper ores. its effects have been direct in superseding most gravitational methods of separation, and indirect in view of the fact that flota- tion deals primarily with very finely divided material, including the ‘slimes ” which were the greatest difficulty of the pre-flota- tion. metallurgist. not only has this affected ore-grinding and handling practice, but it has brought about a great change in smelting practice also. thus the treatment of copper concentrates is being carried out to a rapidly increasing extent in the rever- beratory furnace to the steady exclusion of the blast furnace. the principles of the process——the principles of flotation do not appear to be entircly understood, as there is considerable divergence of opinion whether flotation phenomena are the result of purely “ surface tension '’ forces or whether electrical forces play the most important part. the operations involved are, however, sufficiently clearly defined and consist essentially of three steps which may over- lap or merge into one another. the first of these may be described as the ‘oiling ’’ process, which consists in adding to the pulp or mixture of finely ground ore and water some “ oiling” reagent. this may be either an essential oil or one of a great range of chemical substances, generally organic in character. only a very small amount of such a reagent is used, since the addition of larger quan- tities produces entirely different effects due to the formation of oil films of appreciable thickness. | the minute amount of oi] reagent, on the other hand, appears to produce some change on the surfaces of certain minerals having a metallic or semi-metallic character—zine-blende being a_ typical example—which makes them less readily ‘‘ wetted "’ by the liquor of the pulp, or, put in another way, increases the angle of contact 882 between these surfaces and the liquid. the gangue of the ore is less affected or not at all affected by the oiling reagent, but in many cases it is necessary artificially to increase the difference between mineral and gangue by the addition of some “ gangue modifying reagent '’ which renders the gangue more readily wetted by the aqueous liquid of the pulp. these ‘ gangue modifiers " are as a rule alkalis or mineral acids. the third step in the process consists in adding to the pulp some substance which causes the ready production of a stiff and lasting froth when air is introduced, either by agitation or by blowing or drawing it through the liquid in a finely divided state. very fre- quently the “ oiling reagent’ also serves as the froth-produccr. when the pulp thus prepared is treated so as to produce a froth, the oiled mineral particles adhere to the air-buhbles very firmly, the mineral-air surfaces evidently being the seat of less potential energy than the mineral-water surfaces and consequently the buoyancy of the combined bubble with its mineral burden causes it to float to the surface, where it accumulates as a very stiff mineralised froth which can be mechanically separated in various ways. a further action appears to take place, which is related to the flocculation of the min- eral particles by the oil emulsion in contact with air-bubbles, this results in the attachment to cach bubble of the finest mineral par- ticles in large and heavy agglomerations, thus greatly increasing the efficiency of the whole process, the flotation process has found its largest application in the con- centration of various types of sulphide ores, and, on this ground alone, has attained very great industrial and technical importance. its application to other minerals has, however, been actively pur- sued and in a great many cases with considerable success. minerals having a more or less metallic character are particularly suited for flotation, so that native metals constitute an obviously promising application. for the treatment of finely divided gold-bearing ores the older cyaniding processes in their modern forms continue to hold their own, but a few large mines have adopted flotation. in some cases, where graphite has interfered with cyaniding, a little agitation with oil is serviccable in rendering the graphite harmless. application to minerals of the oxidised type is less simple, and here it seems to be necessary, in many cases, to submit the ore to a previ- ous “ activating ’’ treatment. considerable success in the treatment of ores of this kind has been attained by the use of sodium xanthate as a flotation reagent. preliminary roasting in a reducing atmos- phere in the hope of producing a more or less metallic surface coating upon the ore particles has been tried, while ‘ sulphidising " by ex- posing the finely ground ore to the action of hydrogen, ammonium or organic sulphide has also been used with great effect in some cases. another problem is that of “ differential flotation " for the purpose of ope: different metalliferous minerals in a complex ore, such as the separation of zinc-blende or sphalerite from galena. in acertain number of cases, oiling reagents have been found which act differentially upon different flotable minerals, but every particu- lar case still requires extensive rescarch which does not always lead to a satisfactory industrial solution. smelting —beyond its immensely important direct effects in rendcring possible the economic concentration of a number of ores and in cheapening the concentration of others, the develop- ment of flotation has also profoundly affected smelting practice, since the product of flotation, being very finely divided, differs widely from the product of gravity concentration, the concomi- tant progress of the reverberatory furnace has been accompanied by the development of the use of powdered coal as fuel, which has attained very wide extension. extremely finely divided coal is blown or otherwise forced into the combustion-space of the furnace, where it burns with a flame very similar to that of a jet of gas. the obvious advantages of such a system are that the loss of heat involved in the gasification of coal in producers is saved, together with the labour and the technical diff- culties involved, while most of the advantages of gas-firing can also be secured by burning powdered coal. as against this must be sect the cost of grinding the coal sufficiently fine and of injecting it into the furnace, while disadvantages also attach to the fact that the ash of the coal is introduced into the furnace and thence into flues, regenerators, etc. the question of the manner in which the coal is to be powdered and conveyed into the furnace receives rather differ- ent treatment in different forms of the process, but it is coming to be recognised that extremely fine grinding is advantageous, and in one process the coal is made into an “ emulsion ” of coal-dust and air which is said to flow and to be capable of being pumped like a dense liquid. the coal particles appear to become coated with a closely adherent (probably ‘' absorbed ’’) layer of air, and as soon as the temperature becomes high enough very rapid combustion takes place. the use of coal-air mixtures or ‘ emulsions,’’ however, implics the introduction into the furnace of a relatively large amount of cold air, and this materially affects the question of regeneration or recu- peration of the heat of the waste gases of the furnace. this is also affected by the presence of the fine ash-dust which tends to clog or even to flux the tubes or chequer-work. in some furnaces, where an metallurgy extremely high temperature is not required, the problem can be solved by dispensing with regeneration or recuperation entirely and utilising the heat of the waste gases for raising steam, etc. another d0int to be borne in mind is that a suspension of coal-dust in air may pe a powerful explosive and must be treated with the care due to such substances. the use of oil fuel for fring metallurgical furnaces has also assumed large dimensions, and rivals the extension of powdered coal firing, 1t possesses many advantages in regard to the points just discussed, so that the relative merit of the two processes becomes mainly a question of cost. in the methods for the extraction of non-ferrous metals, dur- ing the period under review, there has also been an important development in an entirely different direction. this is the great advance in hydrometallurgical processes, such as direct leaching and electrolytic treatment of ores. the elimination of the ger- man zinc smelters during the war, so far as supplies of zinc ores from the british empire and the allied countrics were con- cerned, undoubtedly supplied a stimulus to this development, which has been particularly marked in connection with the extraction of zinc from its ores. the treatment of many other ores has also come within reach of “ wet way ”’ methods, and these promise to play a large part in metallurgical extraction. iil-copper the effect of notation, powdered-coal firing and the advance of hydrometallurgical methods on the metallurgy of copper have already been referred to, but mention may be made of the leaching of alkaline ores with solutions of ammonia and am- monium carbonate which has been developed at the calumet and hecla mines. leaching methods are employed by the largest individual producer of copper—in the belgian congo. in regard to the metal itself, there is an increasing tendency for the exclu- sive employment of electrolytic copper. in part, this arises from the increased supplies of this quality of metal, but more from the increasing demand for high purity. “ best selected ”’ and ‘‘ tough”’ (arsenical) copper are still in demand for some purposes, par- ticularly for locomotive fireboxes and stays. the value of the arsenic has been found to lie in a certain neutralisation of the effects of oxygen; where more complete deoxidation is possible the value of arsenic is more doubtful. with regard to finished copper, much attention has been paid to certain anomalies which occur during severe cold-working, such as wire-drawing, while the effect of heating the metal in a reducing atmosphere has also been further studied. a particularly interesting case of failure in copper when heated ina bath of fused sodium chlo- ride has been studied by the bureau of standards at washington. this material became brittle and broke with a typical inter-crystal- line fracture. it was shown that this arose from an electrolytic effect produced by the contact of the copper with the iron containing- vessel in the presence of the fused electrolyte (rawdon). metallic sodium is formed in contact with the copper and appears to pene- trate between the crystals of the metal. a case has also been de- scribed where molten solder (lead-tin) acted in a similar manner when in contact with a particular kind of brass, the so-called ‘ man- ganese bronze ” (dickenson). copper alloys ——with regard to copper alloys, some progress has been made in the difficult question of nomenclature. a com- mittee appointed by the institute of metals has issued a no- menclature report which defines the old terms ‘“‘ brass’ and “bronze.” the former is defined as any alloy of copper with zinc containing more than 50% of copper; if other elements besides zinc and copper are present, they are to be named as a prefix to the term “ brass.” thus an alloy containing 2% tin, 28% zinc and remainder copper would be termed a “ tin brass.” bronze on the other hand is defined as implying an alloy of copper with tin, containing more than 50% of copper, with the same convention in regard to additional elements. thus an alloy con- taining 10% tin, 2% zinc, and remainder copper would be called a zinc bronze. an attempt is also made to systematise nomencla- ture of more complex alloys. so far as brass and bronze are concerned, these two terms are now rarely used except within the definitions named. | an immense amount of experiment and research has been devoted to copper alloys. a considerable number of special alloys are now known, cach possessing valuable properties. the aluminium man- ganese copper alloys have been very fully described in the ninth metallurgy report to the alloys research committee of the institution of mechanical engineers; these include alloys capable of attaining tensile strengths as high as 52 tons per square inch. other copper aluminium alloys—known as aluminium bronzes—with or without the addition of iron, have found considerable industrial application in america, mainly as forgings, sometimes of considerable size. in great britain small die-castings of such alloys are used for parts of electrical switch-gear. other alloys of special strength have been launched under various proprietary namas. for war purposes a most important part was played by the cupro- nickel alloys, containing either 15 or 20% of nickel, remainder cop- per. the production of this alloy on the very large scale required for the war revealed difficulties arising mainly from casting-defects in the slabs used for rolling. the remarkable power of this material to undergo severe cold-working, without becoming excessively brittle, suggests that it is likely to have other useful applications beside bullet envelopes, but for industrial purposes these alloys have not been widely exploited. on the other hand, the much more expensive monel metal has been widely pushed and has found considerable practical application, mainly on account of its valuable combination of great strength with great resistance to corrosion. this alloy is manufactured “‘ direct "' by the reduction of ores from the sudbury district in canada, and special virtue is claimed on the ground that it is a “natural” alloy and has not been melted together in the foun- dry. it has been shown that such a claim cannot be substantiated. corrosion.—in connection mainly with copper alloys, a large anount of study has been devoted to corrosion, under the auspices of the corrosion research committee of the institute of metals. the results have been embodied in a series of extensive reports, and serve to throw new light on the corrosion, partic- ularly, of marine condenser tubes. this is ascribed, essentially, to the formation on the surfaces of the tubes of an adherent, but by no means impervious, deposit of basic salts. by restricting the circulation of water in contact with the metal under these deposits, they lead to the formation of solutions containing a fair- ly high concentration of cupric chloride, and such a solution rapidly attacks brass, with the resulting formation of pits and ultimately of holes. it is considered that the brass as a whole is dissolved under these deposits, but that in certain conditions the copper is redeposited as a spongy mass, thus leading to the apparent ‘‘ dezincification ” of the brass at such points. the problem is there to prevent such adherent deposits. the production of protective coatings on metals as a means of preventing corrosion has received much attention, the use both of cadmium and of chromium plating for this purpose having been de- veloped. cadmium plating is used chieily for the protection of aluminium, but chromium 1s applicable alike to steel, copper, brass and other metals. the deposition takes place from an electrolyte of chromic acid and requires a high current density. the deposit is bright, has a bluish white lustre and remains untarnished in the air and in many vapours. owing to its great hardness as well as its chemical inertness, chromium plating is much superior to nickel or silver plating. the finish, however, is not yet quite as good. the theoretical aspect of corrosion has also received much attention, and special research on this subject has been initiated. already, however, a new theory of electrochemical corrosion has succeeded in uniting the views of those formerly advocating divergent views (bengough, evans, bancroft). the scope of the researches undertaken by the above-mentioned committee has been extended to include fresh-water (land) condenser plant, and a special sub-committee has been formed to study the whole question of the corrosion of aluminium alloys, while a parallel investigation into atmospheric corrosion has been undertaken by the non-ferrous metals research association. in regard to the corrosion of alumintum alloys and its prevention, important progress has been_made by the development of the “ anodic oxidation "’ process. the metal is suspended as anode in an electrolyte and rapidly becomes covered with an oxide or hydroxide coating which stops the passage of the electric current. this coating is strong and flexible and serves as an excellent protection against corrosion, the protective effect being further enhanced by allowing the surface to absorb a coating of lanoline. the treated metal and alloys resist both fresh and salt water and a salt spray. the coating can be applied to alloys of aluminium so long as they do not contain much more than 4% of copper. iv. platinum, zinc, aluminium, etc. platinum.—the metallurgy of the noble metals has not under- gone any striking development during the period under review either in regard to extraction or uses. 833 the cyaniding process has undergone a series of more or less minor improvements, and it was at one time thought that aluminium dust would replace zinc-dust as the precipitant for pregnant solutions. zinc-dust, however, still predominates, and the same remark applies to the proposed method of precipitating the metal electrolytically. in regard to platinum, there has been an ever-increasing scarcity, enhanced by the complete upheaval in russia. the russian supply, however, is potentially the largest in the world, and production has slowly increased. some new discoveries of platinum have been made in the waterberg and lydenberg districts in south africa. here some 60% of the metal is too fine to be caught on corduroy strakes, and some other method, such as flotation or smelting with lead, will ultimately have to be used. another source of platinum whose im- portance tends to increase is the refining residue of copper and nickel, the great rise in the price of platinum has led to the study of pos- sible substitutes, and a number of such materials have been put forward. thus for the ' breaks" used in the magnetos of internal combustion engines, tungsten sparking points have been substituted for platinum. for chemical purposes various alloys, some containing gold and palladium, have been tried, but only with partial success, since none of them really possess the combination of properties— chemical resistance and very high melting point-—which renders platinum so valuable. a number of special alloys, in which tungsten and chromium generally play an important part, also exhibit great chemical resistance, but in these cases the hardness and brittleness of the material are generally a serious difficulty. for use in chemical work on a large scale, however, a considerable number of alloys have been produced which attain a fair measure of success. silicon itself has many a:lvantages for some of these purposes, but in the impure form, generally met with, it is relatively weak and brittle. platinum itself has been prepared of much higher purity than was formerly attainable, owinz to contamination by calcium derived from the lime crucibles in which it was melted. zinc.—the metallurgy of zine received much attention during the war. reference has been made above to the general questions relating to zinc extraction, but mention may be made here of the growth of the enormous electrolyte plant at risdon, near ho- bart, tasmania, where 33,000 h.p. are employed in dealing with the products of the australian smelters, producing zinc 99-95% pure, as well as over 150 tons yearly of cadmium. there has also been great development at the united states centre at picher, oklahoma. efforts are being made in norway and germany to obtain high recoveries of zinc from lowgrade and complex ores by electro-thermic smelting with a silicide reducing agent. on the allied side during the war there was at one time consider- able shortage of zinc, and substitute alloys were studied for all pur- poses which should avoid the use of zinc. the shortage then dis- appeared, and at a later stage alloys consisting mainly of zinc were tried as substitutes for brass and for certain aluminium alloys. some of these zine alloys proved to possess remarkable properties, tensile strength exceeding 20 tons per sq. in. being obtained in cast alloys containing about 3% of copper and 7% of aluminium, re- mainder zinc. [it was further found that these alloys could be ex- truded and, under certain conditions, rolled. unfortunately, alloys of this type, when they contain both aluminium and copper, are unstable and undergo serious changes of volume, accompanied by great loss of strength, even at the ordinary temperature if kept for any considerable time. on the german side, while there was never any shortage of zinc, this metal and its alloys were extensively employed as substitutes for other metals. pure zinc was widely used in place of copper for: electrical purposes, while zinc alloys with copper and aluminium were also largely used. apparently, cases of failure due to the instability of these materials passed unnoticed under the stress of war; at all events, german metallurgists have described these ‘‘ war bronzes "’ without mention of such deterioration with time, except as the result of corrosion. it may be mentioned, however, that alloys rich in zinc, which contain cither copper alone or aluminium alone, do appear to be free from the trouble in question. aluminitum.—aluminium and its alloys have played a par- ticularly conspicuous part and have undergone remarkable de- velopments since rgro. prior to the outbreak of war, aluminium itself had become relatively very cheap (below f100 per ton), and this fact stimulated interest in its use. during the war, on the other hand, while the metal itself became scarce and very dear, its applications for military purposes grew very much in importance and raised its alloys for the first time to the rank of important materials of engineering construction. its uses arose mainly in connection with aircraft, and became increasingly important in the closing years of the war. this rapid development of aluminium alloys under war conditions was to a considerable extent the result of progress which had been 884 made prior to 1914. one step in this progress was marked by the section on light alloys contained in the ninth report to the alloys research committee (rosenhain and lantsberry), published in 1909; but the discovery, by wilm of berlin, of the possibility of hardening aluminium and its alloys, when a small percentage of magnesium had been added to them, led to the next and most important forward step. the application of this discovery to the best of the alloys, described in the above-named report, led to the production of the now widely known and used alloy “‘ duralumin.” this contains from 3 to § °> of copper, about i “> of manganese and about 0-5 °% of magnesium. as rolled, this material has a tensile strength of about 18 tons per sq. in., but if heated to a temperature of 480° c. to 500° c. and quenched, it gradually acquires much greater strength—rising to about 26 tons per sq. in., the ductility remaining the same at about 16 to 18° elongation on two inches. such a material, possessing the strength of a very mild steel com- bined with a density as low as 2-8, constituted a remarkable advance in wrought aluminium alloys. at quite an early stage in its history this alloy was employed for the construction of zeppelin airships. the manufacture of the alloys was taken up in england under li- cence from the german patentee, and the alloy has been extensively used in the construction of british rigid airships. its use has, how- ever, not been free from difficulties and disadvantages, and great efforts have been mace to arrive at better alloys by research in great britain. as a result, a serics of new aluminium alloys for use in the wrought form have been developed. the most important of these 1s one developed at the national physical laboratory and known as “ alloy y,”’ having the composi- tion: copper 4°, nickel 2°%> and magnesium 13%. this alloy, when quenched from a temperature of 530° c. after previous cold-rolling, can be made to attain a tensile strength of 28 tons per sq. in. com- bined with an elongation of 20°; on two in.; its density is 2-8, and it possesses two very important further properties, viz., remark- able resistance to corrosion, and a relatively very high resistance to fatigue (repetition stresses), particularly at slightly elevated tem- peratures. forgings of this alloy have heen successfully used as connecting-rods in high-speed internal combustion engines, and it is finding a constantly widening range of engineering uses. more recently, a german alloy —‘“ lautal ’’—in which the alloying ele- ments are copper and silicon, has been produced industrially. it is not superior to alloy y or duralumin. aluminium alloys.—important as are the results achieved with the wrought alloys just described, results of more immediate importance have been achieved with casting alloys of aluminium. at first these were employed mainly on more or less subsicliary castings, such as crank-cases, and for that purpose an alloy con- taining from 12 to 14% of zinc and about 2} °% of copper (general- ly known by the number of the british air board specification as “l 5’) was very widely used. efforts were soon made, however,,. to employ light-alloy castings for more important parts in aero- plane engines, viz., cylinders and pistons. here the value of these materials lies not so much in their specific lightness as in their high thermal conductivity. in the case of the cylinder castings of air-cooled engines particularly, this is valuable in preventing distortion arising from unequal cooling of the windward and lec- ward sides, while in the pistons it reduces the temperature of the compression space and thus increases the density of the indrawn charge, and at the same time allows of the employment of higher ‘compression ratios. the effect of these advantages is to increase very appreciably the power output of an engine of given size and weight, while also reducing the petrol consumption (sce aero engines). the alloys first and most extensively used were those of aluminium with copper, a 12‘) alloy being particularly popular. another widely used alloy contains 7°, of copper with 1% of zinc. these alloys, although initially not as strong as some of those containing zinc, do not lose their strength so rapidly when heated, so that at the working temperature of an aluminium-alloy piston (about 250° c.) they are stronger than such an alloy as ‘' l5.” even these alloys, however, are relatively very weak when hot—they register a tensile strength of about six to seven tons per sq. in. at 250° centigrade. recently, researches at the national physical laboratory have shown that the alloy already referred to above as ‘“y "---containing copper 4%, nickel 2°,, magnesium 13 %o—is particularly strong at high temperatures, even in the cast state. it is, further, amenable to hardening by quenching and ageing even in the form of castings, and when thus treated attains a tensile strength as high as 26 tons per sq. in. at the ordinary temperature and 13 tons per sq. in. at 250° centigrade. many important applications are opened up as the result of the remarkable properties of this alloy. an important development in aluminium alloys is the advent metallurgy of the “ modified ” alloys of aluminium with silicon, known as “alpax,” “silumin,” ete. it has been found that an alloy of aluminium with from ro to 14% of silicon solidifies with a rather coarse, nearly eutectic, structure containing some primary crys- tals of silicon. if, however, just prior to casting, the alloy is treated either by the addition of a small amount of metallic sodium or by reaction with a flux containing sodium compounds, such as the fluoride or the hydrate, the resulting structure is profoundly altered; the eutectic structure becomes exceedingly fine and the alloy now shows primary aluminium—1i.e., the eutectic concentration appears to have been altered. the “modified ” alloy shows physical properties much superior to the untreated material, particularly in regard to an exceptional degree of ductility. the alloy yields castings having very good, clean, bright surfaces, although the avoidance of internal un- soundness is not always easy. for castings in which good appear- ance, ductility and absence of porosity is important, while strength is a lesser consideration, these aluminium silicon alloys offer great advantages. important progress has also been made in improving the soundness of aluminium alloy castings and ingots by the recognition of the fact that gases, and particularly hydrogen, dissolved in the molten metal give rise to pin-holing and unsoundness in castings, particularly when cooled at moderate rates. it has been shown (archbutt) that most of the deleterious gas escapes from the metal if it is allowed to solidify very slowly, as for instance by cooling in the furnace. sub- sequent rapid remelting does not allow it to reabsorb much gas, and castings can then be made from it of exceptional soundness. similar observations in regard to copper were made simultaneously by edwards and prytherch. a less expensive method of removing hydrogen or other deleterious gas is that of bubbling nitrogen through the molten metal prior to casting (rosenhain). this process has proved as successful as presolidification and is coming into use. an important process for the electrolytic refining of aluminium was worked out in 1925 by edwards and his collaborators in america. molten aluminium, to which copper has been added to raise the density, lies at the bottom of the bath; upon it floats the molten cryolite electrolyte, and on this again floats the pure aluminium. the lowest layer is anode and the top layer cathode, and by electrolysis the top layer of high purity metal increases at the expense of the bottom layer. aluminium has in this way been obtained of more than 99-95% purity, and the properties of this high purity metal are distinctly different from those of the purest commercial metal previously obtainable (99-7 °%). magnesium.—during the latter part of the period under review, this metal began to acquire technical importance. high price and great corrodibility had formerly prevented its use, but the price has been much reduced and, if the demand increases sufliciently, this may become lower than that of aluminium, as satisfactory raw materials are plentiful and the reduction process could be rendered equally economical. as regards corrosion, the production of metal of higher purity, and especially free from chlorides derived from the electrolyte, shows much better resist- ance 10 atmospheric corrosion than the older material. the mechanical strength of magnesium and its alloys never ap- proaches that of the better aluminium alloys, but their greater light- ness offers some advantages. magnesium and some of its alloys have been successfully used, particularly in france, for pistons of internal combustion engines and for other special purposes. the thermal conductivity of these materials, however, is decidedly inferior to that of aluminium alloys, and this is likely to lessen the advantages to be gained from extreme lightness, as further improve- ments are made, however, magnesium alloys are likely to prove of increasing technical importance. berylium or glucinum metal has been produced in reasonable quantities, although still at a very high laboratory cost. the combination of great lightness, considerable resistance to cor- rosion, high strength and high melting point found in this metal may render it technically interesting provided that the cost can be made reasonable and that it can be produced in a malleable form. the latter has not, so far, been done. nickel.—this has received a wide range of new applications, partly as the result of the need of the nickel industry to find new uses when the principal older use—for armament purposes— came practically to an end after the washington conference. metallurgy among the more important developments are the alloys for use at very high temperatures, alloys of nickel and chromium containing various amounts of iron and manganese have been known for a con- siderable time as “‘ nichrome,’’ and proved valuable for such uses as electric resistance heaters for temperatures not much above 1,000° centigrade. more recently these have been improved upon by a high-purity alloy consisting solely of nickel and chromium (80% ni, 20% cr.), and this alloy also exhibits remarkable strength at high tempcratures (up to 800° centigrade). in this respect, however, it 1s not appreciably superior to the best of the special “ steels which have been developed for use at very high temperatures. these usually contain large amounts of both nickel and chromium, to which tungsten is sometimes added, the proportion of iron in some cases falling as low as 54°. the increasing use of very high temperatures in engineering practice lends special importance to these materials. other metals.—developments in the remaining metals are mostly of a minor nature. progress has been made in connection with cobalt. its use in steel and in certain special alloys has already been men- tioned, but it has also been shown to give a more adherent and more durable electro-plate coating than nickel, and it is important to note that its resemblance to nickel is not nearly so close as was previously supposed. in regard to /ead and its alloys, a remarkable develop- ment has been that of alloys with the rare-earth metals, particularly calcium and barium. these confer a remarkable degree of hardness on lead, and a special alloy of this kind is finding application as a bearing metal. v. physical metallurgy side by side with, and to a great extent furnishing the basis for, the development in the treatment and use of metals and their alloys, there has been a very great development of metallurgical science in the direction of ‘‘ physical metallurgy.” alloy systems —a very large amount of work has been de- voted to the further and more detailed study of the constitution of alloy systems. a number of the somewhat rough preliminary determinations of the equilibrium diagrams of most binary alloy systems previously made, have been revised and rendered more accurate. in ferrous alloys, the iron-carbon system has received much further study, particularly in regard to the critical points of iron itself. important work at the bureau of standards, u.s.a. (burgess and crowe), has firmly established the three well- known critical points, ai, az and as, and has shown that pre- vious attempts on the one hand to discredit the very existence of a. (carpenter), and on the other to show that it was a double point (arnold) were based on experimental error. on the other hand, german investigators (ruer, hanemann) have estab- lished the existence of a higher critical point, which in pure iron occurs at a temperature very close to 1,400° centigrade. in connection with the critical points, considerable attention has been devoted to the whole question of allotropy. a dutch school of investigators (cohen) have sought to show the existence of numerous allotropic transformations in many metals, but their conclusions are based on extremely slight evidence derived from determinations of minute irregularities in density changes. on the other hand, the japanese school (iiondo) seek to show that the az transformation in iron is not allotropic in character, and this view is confirmed, to a certain extent, by strong evidence that the passage through this point docs not involve any change of crystallisatton—evidence which has recently been confirmed by x-ray methods. the matter, how- ever, turns upon the definition of allotropy. in addition to the iron-carbon system, the iron-nickel, iron- chromium, the manganese-carbon and nickel-carbon systems have been carefully investigated. the systematic study of the alloys of iron, in the first place free from carbon, has been begun at the national physical laboratory under the auspices of a special com- mittee. the production of iron, chromium, manganese and silicon in a very high state of purity and a study of the iron-oxygen system are some of the results already obtained. in non-ferrous alloys, considerable attention has been given to the alloys of zinc, a portion of the ternary system copper-aluminium-zinec (alloys rich in zinc) having been very fully worked out (haughton, bingham). the allotropy of zinc itself has also been very thoroughly studied (benedicks, bingham) and the reality of the transformations estab- lished. great advances have been made in the knowledge of the equilibria of several of the important alloy systems in which alu- minium is the predominant metal. the ternary systems aluminium- zinc-copper, aluminium-iron-silicon and aluminium-magnesium- silicon (jlanson, gayler) have been fully worked out so far as the alloys rich in aluminium are concerned. for the representation of the results of such investigations a new type of model has been devised (rosenhain) in which the various equilibrium surfaces are repre- sented by systems of wires coloured to indicate the phases concerned in each transformation. 885 the aluminium-magnesium-silicon system.—the study of the aluminium-magnesium-silicon system has proved particularly important, throwing light on the age-hardening properties which are found in many aluminium alloys containing magnesium. the magnesium in these alloys 1s present as a compound mg.si, which is more soluble in solid aluminium at high temperatures than at the ordinary temperature. quenching such an alloy from a tem- perature just below its solidus retains the compound in solid solution and in this state the alloy is soft. gradually, however, at the ordinary temperature and more rapidly at slightly higher temperatures, this super-saturated solid solution deposits the excess of dissolved compound in an extremely finely divided condition, accompanied by a gradual hardening of the alloy. this process is strictly analogous to that which can be brought about in certain alloy steels which can be rendered (or kept) completely ‘‘ austenitic’? (homogeneous solid solution) by quenching; they are then soft and ductile, and do not undergo hardening while at rest at the ordinary temperature. if the temperature is raised so as to bring about “ tempering ”’ the solid solution breaks down in precisely the same way as indicated above and the stecl becomes hard (and also magnetic). it would thus seem that hardening as the result—direct or indirect —af quenching is due to the separation from solid solution, in a state of extremely fine division, of a phase the formation of which had been suppressed by quenching. according to the theory of amorphous metal (see below) each of the minute crystallites of the phase thus separated will be surrounded by a zone of amorphous metal, which is itself very hard. if the minute crystals thus separated are sufficiently small and numerous, the result will be that a considerable proportion of the whole alloy will be thrown into the amorphous state, extreme hardness resulting. on this view, the martensite of hardened steel should consist mainly of minute crystallites of alpha-iron embedded in an amorphous matrix consisting of iron and carbon (or carbide) in solution in it. this suggested con- stitution of martensite readily accounts for its hardness and for the fact that it is magnetic, ancd—in view of the intimate manner in which the minute crystallites of alpha-iron are embedded in unyielding and un-magnetisable amorphous metal—accounts also for the magnetic hardness of the martensitic steel. this view is further confirmed by the observation that the chemical behaviour of quench-hardened steel is in certain respects closely similar to that of the same stecl hardened by cold work and thus rendered partially amorphous (whiteley). finally, it has re- cently been shown by x-ray methods that the space lattice typical of alpha-iron is present in martensitic steel (westgren). theory of amorphous mctal—the theory of amorphous metal just mentioned has played an important part in scientific metal- lurgical thought during the period under review. the conception that metal could be rendered amorphous by mechanical disturbance of its crystalline structure was originated by beilby, in the first instance, to account for the phenomena ob- served by him and others in connection with the polishing of metals and other substances. beilby further applied the conception to ex- plain the hardening which metals undergo as the result of plastic deformation (cold work) by suggesting that layers of amorphous metal are formed on the surfaces on which internal slip occurs during plastic straining. both these theories are widely but not universally accepted in england and america, but find opposition on the conti- nent. more recently rosenhain has brought forward a conception which has already been present in the minds of many other inves- tivators (notably osmond) in a less definite form, that a film or thin layer of amorphous metal exists in the inter-crystalline boundaries of all metals, quite apart from any effects of strain. this view has been vigorously contested, but experimental evidence in its confirmation has been steadily accumulated. the most striking series of facts supporting the ‘‘ amorphous cement " theory is connected with the behaviour of the inter-crystal- line boundaries under stress. jn normal circumstances these bound- aries are stronger than the crystals themselves, so that fractures of metals generally occur by breaking through the crystals and not by pulling them apart. it has, however, been shown that at a high temperature near to, but definitely below, the melting point, pure metals can be easily caused to break with a perfectly inter-crystalline fracture (rosenhain and ewen). this is ascribed to the greatly de- creased viscosity at such temperatures of the inter-crystalline amorphous metal, which is regarded as possessing the properties of a 886 viscous under-cooled liquid. the actual viscosity, however, depends very much upon the nature of the metal and upon the temperature — the farther a metal is below its normal melting-point the higher the viscosity of the amorphous phase. accordingly, in some of the softer metals and alloys the amorphous material is sufficiently mobile to allow ot sensible movement in rela- tively short times. thus, an alloy of zinc with copper and aluminium has been discovered which, in the cold-worked state when it is par- tially amorphous, behaves very much like pitch; it will bend to any desired extent if allowed to do so gradually, but breaks short if rapid bending is attempted. similarly, the inter-crystalline cement in cer- tain metals and alloys, although it proves stronger than the crystals when the metal is loaded at any normal rate, appears to be capable of giving way by some form of viscous or visco-elastic movement under very prolonged loading such as that due to internal stresses. season cracking.—much attention has been devoted to the study of fractures occurring in various metals as the result of the application of internal or other prolonged stresses. in brass these phenomena have become known by the misleading term “ season cracking,” but strikingly similar phenomena have been found in a number of other metals, including certain alloys of alu- minium, platinum and steel (rosenhain and archbutt). in the case of brass, steel and aluminium alloys, certain types of chem- ical reagents which act preferentially upon the material in the crystal boundaries contribute to the occurrence of such fractures, which are typically inter-crystalline (aloore and beckinsale). at the same time in the case of the aluminium alloys at all events such chemical action serves to accelerate the fractures, but is not essential to it since it occurs, although more slowly, in high vacuum or in an atmosphere of pure dry hydrogen (rosenhain and archbutt). in the case of brass it scems probable that “ season cracking ” can occur without the intervention of any chemical action. similar types of cracking which have been discovered in mild stecl, however, appear to be very closely associated with the effects of certain chemicals, such as concentrated solutions of alkalis, fused ammonium nitrate, etc. while there are still some metallurgists who refuse to think in terms of an amorphous inter-crystalline cement (hatfield, tammann), the great ma- jority of investigators are agreed that, directly or indirectly, this conception serves to explain the occurrence not only of inter- crystalline fractures under prolonged loading but also a number of other phenomena associated with the crystal boundaries. intimately connected, also, with the nature of inter-crystalline boundaries are the important phenomena of recrystallisation and crystal growth, which are of fundamental importance with all annealing and heat-treatment operations, and have been studied in great detail. one of the most striking features is the relatively rapid formation of large crystals in certain conditions. thus in an oblong piece of metal which has been severely strained, and is then heated in such a way as to be well above the usual tempcrature of recrystallisation at one end and well below it at the other, a zone is found in which very large crystals are formed; this may occur either as the result of a temperature-gradient being applied to a uniformly strained piece of metal or of the application of a suitable uniform tempcrature to a piece of metal in which there is a strain-gradicnt. the explanation appears to be that for a given degree of previous plastic strain there is a temperature most favourable to rapid crystal growth (jeffries). an interesting practical applica- tion of the ideas derived from the study of these phenomena 1s the production of wires of certain metals, notably tungsten, which have been so treated as to consist, for considerable lengths, of single long crystals. this result is achieved by drawing the cold-worked wire into an annealing furnace at a suitable tem- perature, at precisely the right rate. the tungsten wire thus pro- duced is particularly valuabic for the manufacture of electric lamp filaments (see elecrric licutinc), and it has also been shown to possess interesting elastic propertics (wartenberg) which are readily accounted for by the absence in such material of any amorphous inter-crystalline material the viscous or visco- elastic propertics of which affect the behaviour of the wire. much study has also been devoted particularly to the recrystal- lisation of aluminium after cold-working, and as a result very metallurgy large single crystals of aluminium have been produced (car- penter and elam). this has opened the way for the study of single crystals under strain (taylor and elam) and under fatigue (gough and hanson), (see fatigue of mertats). it has also given the impulse for the production and study of single crystals in other metals (davey, bridgeman, czochralski). the general result emerges that in most respects single crystals behave very much like aggregates, but possess greater duc- tility and, in the case of copper, have an appreciably higher conductivity. their mode of deformation under strain and fa- tigue is found to confirm the original theory of deformation by slip on crystallographic planes (ewing and rosenhain), but extensive research on fatigue phenomena both in single crystals and crystal aggregates (moore, jasper, mcadam, gough, jen- kin) has as yet failed to produce a satisfactory explanation of fatigue failure. the fatigue range, however, has been dissociated from the “ elastic limit ” and found to be related rather to the ultimate strength. the application of x-ray methods of crystal analysis to the study of the atomic structure of metals has received much attention. the normal crystal lattices of almost all the known metals have been worked out, as well as those of a number of alloys (w. h. and w. l. bragg, hull, bain, wyckof, westgren, debye, scherrer, wever, owen and preston and many others). (see crystallography; x-ray.) the majority of metals have either a face-centred or body-centred cubic lattice; a few (zine cadmium, etc.) have a close-packed hexagonal structure, while the more brittle metals show structures of lower symmetry. the lattice structures of solid solution alloys are found to be those of the parent or solvent metals often either expanded or contracted by the addition of the dissolved metal. on the basis of this structure a general theory of the properties and behaviour of solid solutions has been worked out (rosenhain) which affords satisfactory explanations of their behaviour on melting and freezing, their hardness and electrical conductivities and the powcr of different metals to form solid solutions. x-ray methods have also been used, as already mentioned, in very important work on the behaviour of metal under strain and fatigue. the effect of cold working on the atomic structure has been particularly fully investigated, and it has been shown (polanyi, mark, kerber, sachs) that cold working, such as cold rolling, not only elongates the crystals of a metal and sets up disturbances of the lattice structure, but sets the crystals in an orientation which tends to place one of their axes in the direction of rolling. annealing, although it rapidly brings about recrystal- lisation into equi-axed crystals, does not necessarily abolish the oriented structure, probably because the newly formed crystals tend to assume the orientation of their predecessors. ‘the directional structure—called by german workers the “ fibre ” structure of cold worked metal—is completely removed only by annealing at very high temperatures. vi. organisation of the industry certain institutions and organisations have attained impor- tance as factors in metallurgical progress. the imperial min- eral resources bureau, merged in the imperial institute, has published a large amount of information, mainly in regard to the mineral resources of the british empire. the continued progress and growth of the institute of metals has becn a marked feature of metallurgical activity; this body has now attained a member- ship of over 1,700. in america an institute of metals has been formed on different lines, as part of the institute of mining and metallurgica] engineers. the british engineering standards association, formerly the engineering standards committee, exerts a powerful influence on the metallurgy of those metals which form the materials of engineering. the issue of standard specifications for a large number of non-ferrous metals has been undertaken. in connec- tion with the british government department of scientific and industrial research, a non-ferrous metals research associa- tion has been formed and has carried out important researches, particularly in connection with copper, brass, aluminium, the mitals—meteorology jointing or metals, die-casting, etc. the british cast iron research association has been mentioned. this brief summary of the developments of metallurgical science deals only with a few points of outstanding interest. bibliography.—for iron and steel metallurgy, industrial as well as scientific, the journal of the iron and steel institute, london, should be consulted for original publications and abstracts which cover the literature of the whole world on this subject. in addition, excellent abstracts will also be found in the metallurgical section of the journal of the society of chemical industry, and in such journals as stahl und eisen, the revue de metallurgie and the metallurgist (supplement to the engineer). in addition the iron age, the lron and coal trade review and similar journals may be mentioned. for general metallurgy, see the annual volumes of afineral industry and the journal of the institution of mining and metallurgy. for the non-ferrous metals, sce the journal of the institute of metals (ab- stracts as well as original papers), revue de metallurgie and several german journals, zetischrift fiir metallkunde, metall und erz, zeit- schrift fiir anorganische chemie, and the appropriate section of the american institute of mining and metallurgical engineers (ameri- can institute of metals). the publications of the u.s. bureau of standards (washington) and of the national physical laboratory (teddington, england) are important. the faraday society (lon- don) has published in its transactions several “ gencral discussions,”’ including particularly one on the fatlure of metals under internal and prolonged stress, another relating to metallurgical microscopy, one on the application of x-rays and one on the physical chemistry of steel making. (w. ry.) metals: see aluminium; antimony; copper; fatigue of metals; lead; manganese; mica; nickel; tin; zinc. metcalf, willard leroy (1858-1925), american artist (see 18.257), died in new york city march 9 1925.