SUPPLIED IN FORGINGS, CASTINGS, ᏟᎪᎢᎻᏟᎪᎡᎢ G. & J. WEIR, LTD. Monel Dept. GLASGOW G. R. G. R. MINISTRY OF MUNITIONS. BY DIRECTION OF THE DISPOSAL BOARD (PLANT AND MACHINERY SECTION). FOR SALE BY PUBLIC TENDER. Two MOULDING MACHINES FOR HOLLOW T.N.T. Machines fitted with two driving plates and arranged for Lying at 1HE Works of Mr. E. COWLES, IVY ROAD, CIRCULATING KIER-High pressure 6 ft. diam. x 6ft. CONVEYOR, in dismantled condition, complete with about Lying at No. 6 NATIONAL FILLING FACTORY, CHIL WELL. MISCELLANEOUS PLANT. Tanks of different sizes C.I, W I. and wood suitable for oil and water storage. Liquor Distributors, consisting of 1. cocks and piping, &c. Filter Pr sses, 24 chambers, 3 sq., compete with feed pipes and wash- ut arrangements, reversible ratchet capstan, pressure up to 80 bs per sq. inch. No. 1 Kestner Film Evaporator complete with pre-heater collandria with steam tubes, co denser. &c., with supporting steel stage. Washing Machines, celt driven, brass revolving cylinder, F. and L. pulleys and automatic reversing gear, capacity 150 shirts. C.Í. Geared Fusion Pots, 5 ft. o in. diameter by 7 MINISTRY OF MUNITIONS. BY DIRECTION OF THE DISPOSAL BOARD (PLANT AND MACHINERY SECTION). FOR SALE BY PUBLIC TENDER. MEASURING TANKS. Large number of Measuring Tanks, sizes as follows:- Horizontal lead lined, 5 ft. 6 ins long. STORAGE TANKS. 5 ft. 6 in. diam. by 4 ft.; 5 ft. diam. by 6 ft. C.I. PANS, EARTHENWARE TANKS. Tenders CLOSE DECEMBER 4th. Ref. G 651 F. Full particulars and permits to view, together with Tender Forms, can be obtained from the Controller, D.B. 1 (E.), Embankment Buildings, Cha ing Cross, W.C. 2. NOTE. -For particulars of other Government Property for sale see SURPLUS,' price 3d. at all bo kstalls, or by quarterly subscription of 2/- post free payable in advance to the Director of Publicity Ministry of Munitions Whitehall Place, London, S w I. G. R. MINISTRY OF MUNITIONS. BY D'RECTION OF THE DISPOSAL BOARD (PLANT AND MACHINERY SECTION). FOR SALE BY PUBLIC TENDER. CHEMICAL AND ENGINEER'S PLANT. -- Mild Steel Vessels of in. plate. Platform Weft 3ins, dechines. TENDERS are invited for the following: Air Receivers. various sizes. Multiple Cylinder Air Compressor, 4 Closing NOVEMBER 26. Lying at H.M. FACTORY, SUTTON OAK. AMMONIA COMPRESSORS by the Lightfoot Refrigeration Co., Brine Cooling Tanks for above, 4 ft. 6 ins. diam. by o ft. high; one for each compressor, complete with steering gear and triple cooling coils. Sets of Evaporative Condenser Coils. provided with water catchment sump. Brick built Skeleton Furnace of Firebricks, complete with doors, firebars, &c. Gasometers, 9 ft. diameter by 8 ft. high, single lift, large number of accessories, including Piping, Valves, Cocks, Belting, &c. Closing NOVEMBER 24. Lying at Messrs. ARDOL'S FACTORY, SELBY. LAUNDRY PLANT. COMPLETE PLANT, su ta le for installing in Works, consisting of the usual type of standard machinery. Particulars of above and permits to view can be obtained from the Controller D.B.I. (E), Embankment Buildings, Charing Cross, London, W.C. 2. For particulars of other Government Property for sale see "SURPLUS," price 3d., at all Bookstalls; or by quar terly subscription of 2/- post free, payable in advance, to the Director of Publicity, Ministry of Munitions, Whitehall Place, London, W.C. I. 31 Donkey Cooler Channel Stanchions, az ft. 3 ins. long. 2.0 Donkey Cooler Trays, nearly new. 30 Donkey Cooler Trays, not used. 25 Donkey Cooler Trays, partly prepared. 230 End Plates for same. KESTNER MATERIAL. 6 Large type Separators, with 3-in. pipes and bends. 6 Small type Separators, with pipes and bends. 2 Sets triple-effect Condensers, with brackets. 3 Sets double-effect Condensers. 4 Sets 9-in. Vapour Collecting Mains, with 5-in. branches. 4 Sets 12-in. Ascension Pipes. 4 ft 9 in. pipes with 12 ft. by 5 in. branches. 24 13 in. Safety Valves. 24 ft. 5 in. Sluice Valves. 24 5 in. Pipes, 2 ft. 7 ins. long. Ref G. 421 M.K., No. 13840 to 51. Above lying at Messrs. BRUNNER, MOND, and Co., Ltd., Sandbach Works, NORTHWICH. Permits to view and Tender Forms can be obtained on application to the Controller, D.B. 1 (E), Embankment Buildings, Charing Cross, London, W.C. 2. sale see NOTE - For particulars of other Government Property for "SURPLUS," price 3d. at all bookstalls or by quarterly sub cription of 2/- post free, payable in advance to the Director of Publicity, Ministry of Munitions, Whitehall Place, London, S. W. 1. THE AND JOURNAL OF PHYSICAL SCIENCE Edited by Established in the Year 1859. (WITH WHICH IS INCORPORATED THE "CHEMICAL GAZETTE "). Published Weekly. Annual Subscription. free by post 1 Entered at the New York Post Office as Second Class Mail Matter. Transmissible through the Post-United Kingdom, at Newspaper rate; Canada and Newfoundland, at Magazine rate. Vol. 119.-No. 3110 [Copyright Friday, November 21, 1919 reserved. NOTICES OF Books NOTES...... M-RTINGS FOR THE WERK PAGE ..... 235 .... 238 .. 240 240 241 242 242 243 243 244 244 Registered as PRICE 4d. Required, a capable Analytical Chemist as Assistant in Laboratory in large Works in South Americe. Age 25 to 35. Good prospects -Write, giving fullest details of exCAPPER PASS & SON, Lim., perience, qualifications, age, and salary required, to " A. C.." care of Street's, 30, Cornhill, E.C. 3. BEDMINSTER SMELTING WORKS BRISTOL, are buyers of LEAD ASHES, SULPHATE OF LEAD, LEAD SLAGS, ANTIMONIAL LEAD, COPPER MATTE, TIN ASHES, &c., ORES, DROSS, or RESIDUES containing TIN, COPPER, LEAD, and BEDFORD COLLEGE FOR WOMEN. (UNIVERSITY OF LONDON). The Council invite applications for the Post of DEMONSTRATOR in the Department of Inorganic Chemistry, vacant from January, 1920. Candidates must have taken an Honours Degree or its equivalent in Chemistry. Applications must be sent in by SATURDAY, NOVEMBER 2`. WHATMAN Note a few of our later specialities: No. 42-"ASHLESS." Double Acid-washed and extremely close of texture. For use wit THE ASH OF A 125 cm. CIRCLE WEIGHS 000089 grm. No. 43-"ASHLESS." Double Acid washed, but also FAT-FREE. Specially recommended for any purposes where a fat-free paper is required. No. 44-"ASHLESS." Double Acid-washed, of thinner substance than the above. Recommended for use when the greatest possible degree of accuracy in quantitative work is required. THE ASH OF A 12 5 cm. CIRCLE WEIGHS 00008 grm. THE ASH OF A 12 5 cm. CIRCLE WE GHS 00015 grm. No. 50-Hardened by treatment with Nitric Acid. Very tough, it will resist great pressure, and can be used repeatedly. Can also be supplied in the form of Filter Cones, for use with Filter Pump, as a substitute for Platinum Cones. SOLE MANUFACTURERS: W. & R. BALSTON, LTD., MEDWAY MILL, MAIDSTONE, KENT. FIND OUT ALL ABOUT OUR COMPLETE RANGE FROM OUR REVISED BOOKLET AND PRICE LIST. In case of difficulty in obtaining Free Samples, write the Sole Mill Representatives H. REEVE ANGEL & CO., 9, BRIDEWELL PLACE, LONDON, E.C. 4. THE THE next it passes to the hands of the smith, who forges it by CHEMICAL NEWS hand and fashions the tool to shape. During this operation VOL. CXIX., No. 3110. HARDENING OF STEEL.* By Prof. H. C. H. CARPENTER, F.R.S. THE capacity of steel for hardening by being quenched from a bright red heat in water is the most important property possessed by any metallic substance. This property is utilised practically in the arts in a great variety of ways, and is the basis of all modern engineering work. To take two types of application only (1) It is utilised in the great variety of tools which are employed in modern engineering work, for machining metals and alloys to a high degree of accuracy so that they may constitute a given part of one of the thousand and one machines employed in the mechanic arts of modern civilisation, e.g.. the locomotive, turbine, gas engine, electro motor, &c. (2) The razor, the balance spring of the chronometer, the knife, the needle, the pair of scissors, the surgeon's lancet, and the dentist's twist drill are instances of the utilisation of this property in the finished steel as well, and they depend upon the capacity of such material to retain its hardness in the absence of stress indefinitely at the ordinary temperatures. Not only, however, is this property of the greatest practical import, but of the highest scientific interest, inasmuch as the search for the explanation of the capacity of steel for hardening has given rise to a large number of scientific investigations, which have done more than any. thing else to throw light on the constitution of steels and metallic alloys generally, and have helped to establish the modern science of metallography. My object this evening is to trace rapidly the history of some of the salient features of this scientific work, and to bring to your notice the most modern views as to the scientific explanation of this wonderful property of steel. I must preface my remarks, however, with this warning that within the compass of an hour's lecture it is not possible to attempt a complete exposition of the theories relating to the great variety of steel alloys that are now used in the arts, and I shall be obliged to confine my thesis to one of the simplest, albeit the best known of these materials—namely, what is called the pure carbon steel turning tool. Let us begin by considering the manufacture of the tool itself, and afterwards the conditions under which it is put to work and what follows then. some Although even the purest iron containing only the merest trace of carbon can be hardened to extent by quenching from a high temperature, a certain minimum percentage of carbon is necessary before the hardening is sufficiently marked to confer what may be called practical hardening properties on the steel. This minimum is about o'7 per cent, and the cutting tools used in the arts range from this figure up to 15 per cent. For reasons which will be subsequently apparent, it is simplest to consider the case of a steel tool containing o'g per cent carbon. The operation of manufacture of such a tool is briefly as follows: In the first place, a charge designed to give the correct composition is melted down in a crucible in a furnace whose temperature ranges from 1500°-1600° C. The steel is cast from the correct temperature into a metallic mould, giving what is called an ingot, e.g., a rectangular bar about 2 inches square and 2 feet long. The ingot is subsequently forged down to a bar, say, 1-1 inch in diameter; it is then cut up into lengths suitable for the dimensions of the tool itself, and A Lecture delivered at the Royal Institution, March 7. 1919. it is of the greatest importance that the composition of the steel should be altered as little as possible by oxidation of the carbon, otherwise the tool will not harden properly or evenly. Then follows the actual hardening operation, in which the nose of the tool, as it is called, is carefully heated to a given temperature in the neighbourhood of 800° C., withdrawn either from the smith's fire, or, better still, the hardening bath, and quenched outright in a bath of cold water at the ordinary temperature. This is an operation requiring the utmost skill. If the surface of the metal has been decarbonised in heating and scale has formed on the surface, the rapid transference of heat from the metal to the bath will not take place, imperfect hardening will result, and very likely cracks will be formed. If, however, the tool, as in the best modern practice, is heated up in a bath of fused salts, no loss of carbon takes place, and when it is removed from the bath it is covered with a thin film of fused salt. This dissolves almost instantaneously in the water, and the necessary rapid transference of heat from the metal to the water takes place. The best quenchings always have a peculiar "bite," accompanied by a dull, albeit sharp, sound, as the large bubbles of steam generated by the heat are absorbed in the surrounding water. The steel thus hardened, although possessing the neces sary hardness, is too brittle to be used as a tool. Accordingly the tempering process follows, in which it is heated to a moderate temperature depending on the work to which it is to be put. This temperature varies usually from 200°-300° C. This tempering process, while it withdraws some of the hardness produced by quenching, confers a most valuable property on the tool-namely, toughness-by means of which it stands up to its work, at any rate for a time, without cracking. Then comes the last stage, namely, the grinding of the tool on the grindstone, whereby a clean cutting edge of the required shape is produced. The tool is then ready for use, Let us suppose that it is to be used in taking a cut from a cylindrical bar of an unhardened steel. The latter is fixed in a lathe and rotated at an appropriate speed (Fig. 1). The tool. held in a tool-holder, actuated by suitable mechanism, is gradually brought up to the end of the rotating bar and a given rate of feed maintained. For an instant there is actual contact between the cutting edge of the tool and the bar. The moment, however, that this happens a chip is formed and a shearing stress is set up, as a result of which the work fails, not on the actual edge of the tool, but on an area inside. If the metal which is heing machined is ductile, it is cut away in long shavings, whose thickness depends on the feed; if, on the other hand, it is brittle, it breaks off into short chips. The effect of this friction between the two metals and the pressure of the shaving is to generate heat and to raise the temperature of the tool to a much greater extent than that of the bar which is being machined, and deterioration of the tool sets in; its hardness gradually diminishes, and pari passu wear of the tool itself by abrasion occurs. Eventually a stage is reached at which the cutting operation has to be discontinued, and the tool requires re-hardening or regrinding. The carbon tool of which I have just spoken cannot be used for taking the heavy cu's of which the modern alloy tools are capable, but they retain their preeminence even to-day in all machinery work where the highest degree of accuracy attainable is desired. A complete theory of the action of such tools must account for both the hardening and toughening of the steel, and its gradual loss of these properties by the operations I have described. Before attempting this, however, it may be interesting to refer briefly to the methods of hardening which chiefly occupied the attention of early workers. The Greek alchemical manuscripts give various recipes, from which it is clear that in the early days the nature of the quenching liquid was considered to be all-important. |