permanent influence on metallurgy, and only tentative views can be put forward. One result, however, stands out very clearly. This is, the effort which several nations had made to become self-supporting in regard to all essential supplies, and particularly in regard to metals. This applies particularly to England and France, but the more distant dominions, such as Australia and S. Africa, have displayed the same tendency while there is a strong effort to develop metallurgical industries in India. Some of these efforts, which had been stimulated either by urgent necessity or by the lure of exceptionally high prices resulting from the difficulties of import, were not likely to lead to permanent results. Thus the efforts to introduce a zinc-smelting industry on a large scale into England, or to re- open the tin-production of Cornwall, or the copper mines of Alderley Edge, were apparently destined to collapse on the return of more normal prices, and on the withdrawal of financial support from the State. In England particularly, a very strong reactionary tendency had set in, strictly limiting, if not entirely abolishing, State assistance for any but a very few " key " indus- tries, which were still looked upon as vital from the military point of view. In other countries also there was a marked ten- dency for the excision of the less profitable ventures which high war-time prices had either revived or brought into being. While this was likely to prove a healthy tendency in the long run, it inevi- tably led to difficulty and confusion for the time. This was fur- ther increased by the world-wide " slump," resulting in 1920-1 partly from wide-spread economic exhaustion and partly from the excessively high cost of production arising from inflation of various charges chiefly wages beyond the reasonable eco- nomic limit. One consequence, for example, was that there were in July 1921 not more than two copper refineries at work in the whole of America.
IRON AND STEEL. Prior to 1914, iron and steel metallurgy showed a definite tendency towards the development of very large plants and larger individual units, both in regard to fur- naces and rolling-mill equipment. The tendency towards in- creased size made itself felt in the blast furnace, particularly in American practice; progress, however, also included the de- velopment of practice in the direction of furnaces with thin walls and external water-cooling, such furnaces being driven very hard.
Pre-war Progress. In the period prior to 1914, considerable atten- tion was given to the importance of drying the blast, and it seemed at one time that this would become universal practice. Under war conditions development in that direction seems to have been checked at all events in England, and it has not been resumed with any degree of vigour since 1918. On the other hand, increased attention has been given to the utilization and cleaning of the blast furnace gases. This became particularly important in England during the war on account of the shortage of potash, a substantial recovery of this material being obtainable from the flue-gases of furnaces in which the charge included potash-felspar bearing material. At the same time it has been found that satisfactory cleaning of the gas very much increases the efficiency of its application 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 electro-static deposition of the dust by the method first developed by Lodge and latterly exploited in America by Cot- trell. The other method depends upon mechanical 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 hope to compete with the pro 1 net of Continental mines, yet cleaning of blast-furnace gas will doubtless be continued. There is the further possibility that the dust itself may be utilized for the recovery of the iron contained in it. This has actually been done successfully by briquetting the dust by a mo of the Schumacher process, in which a weak solution of ferrous sulphate is used as binder. A further proposal is to concen- trate the iron-content by some adaptation of the flotation process.
The actual application of flotation processes (see below) tt> finely divided iron-ores has not yet been found necessary or practicable, 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 finely divided carbon and pressed into briquettes, which are then heated to a moderate temperature. A partial reduction 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 at one time appeared likely to displace the Bes- semer converter entirely. More recently, however, the converter appears to be holding its own to a certain extent, although the steady increase in the application of basic open-hearth steel tends to give the large open-hearth furnace, particularly when working one of the continuous processes, a very great advantage.
War Period. The effect of war conditions on metallurgical prac- tice in the iron and steel industry has been profound. In the first place it became necessary, particularly in England, to make use of ores and other materials very different from those for which partic- ular furnace plants had been designed, while the supply of operative labour became very difficult. In consequence of these and other dif- ficulties, relaxation of quality became inevitable, particularly in regard to those grades of steel which were required in eaormous quantities. Thus specifications which, at the outset, demanded sul- phur and phosphorus contents of less than 0-035 % were gradually relaxed until, in the case of shell steel, the limits were raised to 0-08 % and similar concessions were made in regard to railway material and other grades of steel. This, of course, rendered available large bodies of ore which could not otherwise have been used by the acid process. At the same time, material made by the basic process began to be admitted for many uses for which acid steel had formerly been exclusively specified.
While these relaxations were undoubtedly justified and, on the whole, eminently successful for war purposes, the question has since arisen whether there should or should not be a return to the former more stringent specifications now that war conditions have ceased to exist. It is contended on one side that there have been no serious cases of failure resulting from the wider specifications and that, at the same time, the after-effects of war still make it practicably im- possible for British steel-makers to comply with the specifications of pre-war stringency. On the other hand, it is urged that the experience of the war is far too brief to justify full confidence in the steels of lower purity and that much longer experience is embodied in the older specifications. Finally, the British Engineering Standards Assn. has adopted a compromise, leaving the new limits for sulphur and phosphorus for most of the better grades of steel (particularly railway material) at 0-050 per cent.
Apart from the demand for enormous supplies of steels of the more ordinary grades, war conditions also brought with them unprece- dented demands for steels of the highest possible 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 partic- ularly in nickel-chrome steels. Reversion to the use of a simple nickel-steel for such purposes followed, but it must be admitted that 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 connexion 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 very 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 number of fur- naces, mostly of the arc-resistance type, were installed, particularly in Sheffield. Their great value lay in the super-refining of steel, some- times produced in a basic open-hearth furnace, sometimes obtained by the direct remelting of alloy-steel scrap. Probably the power of the electric steel furnace to deal satisfactorily 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 disappeared, with the result that the greater number of the electric furnaces, both in England and America, are now idle. None the less, there can now be no doubt that there must be, in the future, a definite use and function 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, particularly 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, as a rule, consists of quenching in oil, or more rarely in water, from a temperature above the critical range of the steel, followed by a " tempering " or re-heating to a temperature considerably below the critical range. In the majority of steels, the rate of cooling subse- quent to such 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. Considerable difference of opinion still prevails as to the cause and nature of such brittleness. One investigator (Andrews) connects it with the presence of phos- phorus in the steel, and states that such steels containing very little phosphorus are free from the trouble. Further, acute controversy
