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By J. B. Knaebel, M. W. Von Bernewitz

OUTSTANDING FACTORS that have largely induced the current great interest in the reopening of old mines and the search for new deposits are the increased relative value of gold, the certainty of a market for it, and the decreased activity and poor profits in other lines of endeavor. It is easy to understand why a miner out of a job and unable to find any other means of livelihood would naturally take to the hills with his pan, pick, and shovel; but never before have inexperienced, would-be prospectors and placer miners materialized from the factories and farms, the haberdasheries, and the oil and gasoline supply stations, in such numbers as the last couple of years have witnessed, except when rich strikes of the proportions of a Klondike have been made. What, may one ask, has occasioned this condition? Unemployment has put these men in a receptive frame of mind, and newspaper and magazine articles have done the rest-- The Gold Miner of Los Angeles (a new weekly), The Mid- Week Pictorial (New York) for Sept. 3, 1932, and Popular Science Monthly for August, 1932, for instance. Even the Saturday Evening Post had an article on a promising part of Colorado. Stories that good wages may be had for the panning in nearly every western state have been featured by daily papers, popular "scientific" magazines, and quasi- technical journals. These tales have been eagerly grasped by thousands of people whose ignorance of mining has only served to increase their enthusiasm.

Jan 1, 1932

By Arthur F. Taggart

A general awakening of interest among mill men concerning the mechanical efficiencies of their crushing machines is evident from a perusal of the recent files of mining publications. Considering the large part of the power bill which must be debited to the crushing department, such interest is natural. When, however, the articles on the subject are read, the only statement upon which the writers agree is that fine grinding consumes a large amount of power, and that the machine which, from a concentration standpoint, offends as a slime producer is, for that reason, a serious offender in wasting power. When the mill man attempts to find a method for measuring the power wasted, or to compare the efficiency of one machine with that of another for the same work, he is confronted with a choice of methods which lead to conflicting results. There are two reasons why the work of crushing is not more generally understood. In the first place, experimental data are difficult to obtain; and in the second place, before these data can be put in general form certain assumptions must be made. A difference in these assumptions by different investigators has led to conflicting conclusions. This conflict has resulted in the proposal of two laws. The first of these is the so-called Rittinger's law, which is variously stated as follows: "The work of crushing is proportional to the reduction in diameter."—R. H. Richards: Ore Dressing, p. 304 (1903). "The work required to crush rock is very nearly proportional to the reciprocals of the diameters crushed to."—A. Del Mar: Engineering and Mining Journal, vol. xciv, No. 24, p. 1129 (Dec. 14, 1912). "The work done in crushing is proportional to the surface exposed by the operation, or better expressed for this purpose, the work done on a given mass of rock is proportional to the reciprocal of the diameter of the final product, assuming that all the mass has been reduced to one exact size, which is only theoretically possible."— A. 0. Gates: Engineering and Mining Journal, vol. xcv, No. 21, p. 1039 (May 24, 1913). ' ' " Of this law as variously stated above H. Stadler says (Grading Analyses and Their Application, Author's Reply to Discussion, Transactions of the Institution of Mining and Metallurgy, vol. xx, p. 426 [1910-111):

Jan 1, 1915

By Takahide Wakamatsu, Douglas W. Fuerstenau

Contact angles on alumina are related directly to the adsorption of alkyl sulfonates at the solid-water interface and thus are strongly controlled by the pH of the solution, the concentration of surfactant, and the number of carbon atoms in the alkyl chain. As the pH of the solution is increased above the point of zero charge, sulfonate adsorption ceases and alumina remains hydrophilic. However, in neutral and acidic solutions, contact angles increase markedly in magnitude when the adsorbed sulfonate ions form hemimicelles at the solid-water interface. Under a wide variety of solution conditions, a limiting value of the contact angle is attained at the point of reversal of the zeta potential. Finally, contact angle phenomena are empirically correlated with the sulfonate adsorption density through the work of adhesion.

Jan 1, 1974

By MARK H. LAMB

(Canal Zone Meeting, November, 1910.) THE recent growth of a sentiment among cyanide-plant designers against the use of gravity-stamps for the crushing preliminary to cyanidation may be said to date from the almost simultaneous perfection of the ribbed tube-mill liner and of the tall, air-agitation tank. The first step in the resulting change of practice was the universal adoption of the tube-mill for fine-grinding and the use of coarse screening oil the battery. This was the beginning of the surrender of supremacy by the gravity-stamp ; since merely the single fact that it was a more economical machine for crushing fine had retained it in favor as compared with ball-mills, rolls, or steam-stamps. The surrender, however, is not yet complete. It is the universal practice to use rolls where a relatively small tonnage is to be crushed coarse, as, for example, when coarse concentration is included in the plan of treatment. Power, attendance, repairs, and first-cost are smaller for the rolls, under such circumstances, than for stamps; and it is becoming daily more apparent that, with no concentration to provide for, the use of rolls and tube-mills, without the complication of trommels and elevators required by concentration, is rapidly gaining favor in the eyes of the leading designers. The next step was the use of the rapid-running Chilean mill between the gravity-stamps and the tube-mill, which again narrowed the field of operation of the gravity-stamp while radically widening its screen-aperture. Such a combination of stamps and Chilean mill offers advantages when fine concentration is necessary, since the reduction in the Chilean mill call be adjusted easily and governed by varying the screen-mesh. But even concentration is now looked at askance. One of the leaders of this metallurgy has abandoned the separation and

Jul 1, 1910

By A. P., Svenningsen

ECONOMICAL handling of a minimum of 25,000 tons of minus 3/4-in. ore per day, grinding it to 2 per cent on 65 mesh, and effecting a high recovery of the copper at the lowest possible cost were the principal aims in the design of the new Morenci concentrating plant. Dealing with a tonnage of this magnitude, it is obvious that lost motion cannot be tolerated. When ore is carried on a conveyor an unnecessarily long distance or elevated to a greater height than necessary, or when pulp flows in a launder by a circuitous route thereby losing elevation and distance, we have lost motion which is always costly both from the standpoint of construction and operation. In addition to the 25,000 tons of ore which must be handled, 100,000 tons of water per day has to be carried through the plant in the treatment of the ore. Though water is not so difficult to handle as the ore, the combined tonnage represents a figure which could easily run into a considerable monetary loss per day if all phases of the design were not carefully followed with the idea of eliminating any unnessary handing of materials.

Jan 1, 1942

By P. Somasundaran Discussion by Knut L. Sandvik

Knut L. Sandvik (Mining Engineer, Mineral Dressing Laboratory, Technical University of Norway, Trond-heim, Norway) — The discovery that adsorption at solid-liquid interfaces is influenced by adsorption at other interfaces may prove very fruitful in the further development of flotation theory. Having reached the same conclusions as P. Somasundaran in some experiments with amine hydrochlorides, I would like to offer more direct evidence of the interfacial adsorption mechanism based on surface tension measurements and adsorption studies.' This evidence was derived from flotation tests carried out in a Hallimond tube at neutral pH and 60°C. The amount of amine solution and quartz surface were chosen to insure measurable concentration changes during flotation due to adsorption. Adsorption data for

Jan 1, 1969

By E. A. Anderson

THIS seems to be the year for superlatives in A.I.M.E. meetings. The programs of the various Divisions and Institute committees offered an abundance of interesting and valuable information in the form of technical papers, symposia. and lectures to large and interested audiences. The Institute of Metals Division may hold up its head with pride for its own program. With six technical sessions, three full-day symposia, and the annual I.M.D. dinner, four meeting days were not enough and many simultaneous sessions were required. The quantity and quality of the paper were equaled by the numbers and interest of those attending.

Jan 1, 1944

By Clyde E. Williams

MUCH has been said recently concerning the depletion of the Lake Superior iron ore re- serves. Estimates given indicate a total life of the present known reserves of twenty to thirty years. Some argue that there is no need to concern ourselves about the possible depletion of the Lake Superior iron ore supply because foreign ores can be brought in to this country at a lower price than rich agglomerated ore can be produced from the lean domestic ores. Some fear, as a result of this, a displacement of the steel business from present districts to the Atlantic seaboard. Others show that foreign ores will be brought to interior points via the projected Great Lakes-St. Lawrence waterway. Others believe that the South, given better freight rates, will extend its iron and steel market into northern territory.

Jan 1, 1931

By P. K. Koh, L. S. Birks, J. M. Siomkajlo

Direct identification in situ of x and a phase precipitates in stainless steel is possible with the electron probe microanalyzer. Although particles in the 1 p size range are too small to yield absolute percent composition, the relative % Crfi Mo ratio can be used to distinguish the two phases with better than 95 pct confidence. Wet chemical analysis of extracted residues gives Cr/Mo ratios in good agreement with electron probe results extrapolated to the 4 to 5 p size range. WHEN stainless steels are subjected to extended heating in the temperature region around 1600°F, precipitation of the brittle 0 or x phases may occur and impair the properties of the material. Identi-

Jan 1, 1961

By W. C. Elli, M. E. Fine

YOUNG'S modulus of elasticity in metals ordinarily decreases with rising temperature. The range of the thermoelastic coefficient at room tem- 1/E dE/dT perature (temperature coefficient of modulus, is illustrated1 by the values for tungsten and hard-drawn aluminum, —95 and —1220x10-6 eg C-1. However, a nearly zero thermoelastic coefficient is observed in some ferromagnetic alloys over a limited temperature range. In these alloys, as the temperature is raised, an increase in modulus arising from loss of ferromagnetism compensates the normal decrease. Iron-nickel alloys containing 36 to 52 pct Ni behave in this manner. In the present investiga- tion, the dependence of the modulus and thermo-elastic coefficient on cold working and annealing were studied in iron-nickel alloys in this range of nickel. Although these alloys, when fully annealed, have a coefficient near zero over a very small temperature interval, the temperature range of low coefficient can be extended greatly by straining and then stress-relief annealing. The modulus of face-centered cubic iron-nickel alloys annealed at 1000°C does not vary linearly with composition at room temperature but, as shown by the solid line of fig. 1, from Koster,' is minimum at 40 pct Ni and maximum at 87 pct Ni. The modulus increases with applied magnetic field but retains the minimum near 40 pct Ni. Schematic change of modulus with temperature for three compositions is shown in fig. 2.'. ' With increasing temperature, the slope becomes less negative, goes through zero (temperature of minimum modulus for the alloy), becomes positive, and resumes its normal negative value above the Curie

Jan 1, 1951

By A. W. Schlechten, R. F. Doelling

Parkes' process crusts were vacuum distilled using a shortened Pidgeon retort. Zinc was effectively removed below 800°C and recovered as a zinc sheet easily stripped from the furnace liner. Lead dasdistillationazinc required about 950°C and the resulting lead condensate tillationtended to stick to the thin metal liner. Final purity of residue is limited only by nonvolatile metals such as copper. THE successful commercial application of vacuum distillation for the removal of zinc from lead, as described by W. T. Isbell,' raises the question of whether or not a similar method can be used for other metal separations. Preliminary laboratory experiments on the vacuum distillation of Parkes' crusts by one of the authors' gave such encouraging results that it was decided to make a series of tests with large scale equipment to determine the results that might be expected in plant operation. The pilot-plant test results are reported in this paper. The great advantages of vacuum dezincing are its simplicity, the relatively low temperature of operation, and the fact that the zinc is recovered in the metallic state ready for use again in the desilveriza-tion of lead bullion. These same advantages and others would be realized from the vacuum distillation of the zinc-lead-silver crusts made in the Parkes' process. Zinc readily will distill over at temperatures of 800" to 900 °C as contrasted with the 1200°C or more used in the Faber du Faur furnace. Furthermore, the recovery of zinc as metal is practically perfect since there is no loss by oxidation or fuming. If the vacuum distillation is continued and hastened by raising the temperature to around 1000°C, the lead will distill over at an appreciable rate and deposit in a warmer zone of the condenser. This lead will contain a small amount of silver, but it can be returned to the desilverizing kettles and there is not the chance of loss that there is in disposing of the rich litharge from cupelling. The lower temperatures required will mean a saving of fuel and less wear on the equipment. One further point is that the vacuum distillation could be run on a small scale practically continuously, so as to avoid the accumulation of large amounts of silver-rich material and the need of assembling a large crew for special cupellation runs. It should be pointed out here that the final purity of the silver residue will depend on the copper or iron content of the crusts, as these and other metals with low vapor pressure will not be eliminated. The idea of treating the silver-zinc-lead crusts from the desilverization of lead bullion by vacuum distillation is not a new one, but such experiments have not been reported, as far as can be determined. In 1912, T. Turner presented a paper3 before the Institute of Metals on the vacuum distillation of brass, and a member of the audience suggested that he try his method on Parkes' crusts. In 1935, W. J. Kroll, noted for his discovery of debismuthiz-ing lead by calcium additions, published a paper' on vacuum distillation of metals and pointed out possible applications in the lead industry. Principles of Separation The successful separation of two or more metals by distillation depends upon an appreciable difference in the effective vapor pressures of the metals in the alloy to be treated. The vapor pressures of the common metals have been determined with considerable accuracy; for example, at 800°C the vapor pressures of the individual metals which are of particular interest in this paper are about .as follows: Zn, 241 mm; Pb, 0.0553 mm; and Ag, 0.0000276 mm. Unfortunately,, data are not available on the activities of the components in the ternary system Zn-Pb-Ag, but it can be estimated that on the basis of the vapor pressures of the individual metals a good separation can be made by distillation. The preliminary laboratory tests previously mentioned' supported this assumption. The pilot-plant size vacuum distilling furnace is shown in Fig. 1. It consisted of an abbreviated Pidgeon retort, 5 ft long with an ID of 8 in., heated by six silicon carbide elements placed symmetrically

Jan 1, 1952

By J. H. Bechtold

Tensile properties of annealed molybdenum were investigated from 1000" to—200°C. In the vicinity of room temperature a well-defined transition in tensile properties occurs. Reduction in area decreases from over 80 pct to 0 pct and, simultaneously, the yield strength increases about 60,000 psi. MOLYBDENUM, tungsten, iron, and many other metals and alloys with the body-centered cubic and hexagonal close-packed crystal structures change from ductile to brittle behavior over some relatively narrow temperature range. The temperature at which this transition in ductility occurs depends on chemical composition, microstructure, and method of testing. When fine grained, completely recrystallized molybdenum of commercial purity is tested in uniaxial tension at a slow strain rate, the transition occurs at slightly below room temperature.' Iron2 and tungsten3 tested under similar conditions become brittle at temperatures close to the boiling point of nitrogen, — 195°C and at about 200°C, respectively. A sharp change in ductility is uncommon in metals with the face-centered cubic crystal structure, however, a relatively sharp transi- tion in notched bar impact properties has been observed below room temperature in a face-centered cubic copper-antimony alloy.4 A transition from ductile to brittle behavior is usually explained by the concepts originally developed by Ludwik,5 and discussed and elaborated on by others including Orowan,6 Hollomon and Jaffe,7 and Gensamer8 In brief, there are two aspects to strength, first the resistance to flow and second the resistance to fracture. Both are functions of temperature, strain, strain rate, stress system, composition, and microstructure. With decreased test temperature the flow stress required to initiate plastic deformation increases more rapidly than the fracture strength and brittle fracture occurs at that temperature where the yield strength equals or exceeds a brittle fracture strength. This investigation was conducted to determine the effects of temperature, strain, and rate of straining on the flow and fracture strengths of molybdenum above, through, and below the ductile-to-brittle transition. Other variables were held constant during testing. This information is believed to show

Jan 1, 1954

By JAMES QATLEY

THE atmosphere, which plays such an important part in the manufacture of iron and steel, is the most variable element involved in its several processes; and particularly is this true of the blast-furnace process, which consumes air in large quantities. At no time since the blast-furnace became an important and widely used apparatus-even when it was operated in the most crude manner-have the variations in composition of the raw materials used been as frequent and as great as the variations in humility of the atmosphere. Important, improvements have been made in the blast furnace and its accessories, such as the hot-blast stoves, the increase in size and change in the shape of the furnace, more efficient blowing engines, the increased protection given to the bosh walls, and the careful preparation of' the raw material, all of which have exerted a pronounced influence on the furnace-operations from a metallurgical standpoint. But during the past eight years little advance has been made in this direction; the fuel-consumption has not diminished, nor has there been any material increase in production. Within that period, however, there has been witnessed the greatest development in appliances for the economical handling of material. So complete has been the work in this direction, that, except in isolated cases, in this country at least., a further extension does not hold out much promise of a satisfactory return on the investment required. It seemed that, with the exception of the gas-engine, we had about reached the limit, for like a strong wall, the atmosphere, with its humility as variable to-clay as when first blown into a primitive blast-furnace, appeared to stand as a Barrier to

Jan 1, 1905

By JAMES J. PURDY

The great majority of stokers used in residential heating installations are of the clinkering type. Because of inherent characteristics of the under- feed combustion process as it occurs in these small stokers, and because of the wide range of operating conditions encountered in residential heating schedules, not all bituminous coals can be used successfully in residential underfeed units. The problem of providing consumer satisfaction has been attacked by the joint efforts of the stoker manufacturers and the coal industry; the stoker manufacturers have been concerned with improving their product to permit the use of a wider range of coals, and coal operators have made every effort to market selected and better prepared coals. In view of the wide range of physical characteristics and chemical properties of bituminous coals, the problems are real and are receiving increased attention.

Jan 1, 1949

By O. E. Kiessling

THE Committee-on Production Control, at its meeting held during the last annual session in February, 1930, evidenced great interest in problems of stabilization affecting all mineral industries. . No immediate program of activity for the Committee as a- unit was decided on, however,, and efforts during the past pear have consisted lirgely of further stressing the economic aspects of mineral production and of the action by committee members, :.serving in their individual capacities, in sponsoring constructive changes, in specific, industries. Of greatest interest to the general subject of production control in 1930 was the very definite advance toward better coordination of demand and supply in the petroleum industry. Furthermore, since opinion both within and without the oil industry now favors a constructive program, and with a gradual change in legal precedents, it seems not unreasonable to expect greater progress in the near future.

Jan 1, 1931

By V. Balasubarmanian, Rajendra Kumar

ISOTHERMAL formation of martensite in a copper-aluminum-nickel alloy was previously reported by Hull and Garwood.' In the present work an attempt has been made to investigate some of the character- istics of the formation of isothermal martensite in binary copper-aluminum alloys containing 14.00 and 14.50 pct Al, respectively. Chill-cast alloys were prepared from OFHC copper and aluminum of greater than 99.5 pct purity. They were homogenized for 24 hr at 950° C. Polished samples were soaked at 1000°C and quenched in water to retain the p phase untransformed; martensite did not form during the quench. The surface was then repolished for isothermal microscopic studies at room temperature. The salient features of the martensitic transformation in copper-aluminum alloys observed in this investigation are: a) The transformation progresses (i) by nuclea-tion at new sites and (ii) by simultaneous slow isothermal growth of existing martensite plates. Slow isothermal growth of martensite has previously been observed by Holden2 in an uranium-chromium alloy and by Hull and Garwood in copper-aluminum-nickel alloy. b) Martensite plates nucleate preferentially at the pin holes formed during the casting of the specimen, Fig. 1. c) Some of the martensite plates pass right through other plates lying in their path, Fig. 1. d) Martensite plates cross grain boundaries without any change in the direction of growth. e) An irregular network of markings, Fig. 2, appears simultaneously with the formation of martensite. It was less prominent in the case of 14.5 pct alloy. The markings may arise due to spontaneous deformation under the lattice strains of the martensitic transformation. Crossing of martensite plates was first observed by Kulin and cohen3 when a high-nickel steel was cooled to 77°K. They suggested that the rapidly advancing plates atquire considerable kinetic energy and strike the obstructing plate with a momentum so as to nucleate the process on the other side of the plate. This, however, fails to explain the present observation where the slow isothermally growing martensite plates cross each other. Such plates would not possess large momentum to bodily displace the obstructing plate. Fig. 1 shows the martensite plates crossing each other without body displacements. This should be contrasted with Fig. 3 of Kulin and Cohen's paper where crossing of plates is accompanied by shearing or body displacements of the plates. The present observations can, how-

Jan 1, 1961

Jan 1, 1925

By AIME AIME

HOLDING the annual dinner-dance of the Institute at the Waldorf-Astoria had become such a tradition that there was widespread regret when it became known that the demolition of the building to make way for a huge office structure would perforce bring to an end the long and enjoyable series of gatherings our Institute had held there. This year the . Commodore was the place at which it was held and the commuters on the New York Central and the New Haven railroad systems, at least, found it a more convenient place for them. Except for the famous "Hoover" dinner, which will probably set a mark for all time, it was the largest dinner the Institute held, 1000 being present, and it taxed the facilities of the hotel to the utmost.

Jan 1, 1930

By J. P. BONARDI, William F. Boericke

BOULDER COUNTY, Colorado, ranked during the war years and until the end of 1918 as one of the foremost tungsten-producing districts of the world. In 1919 production fell off drastically, due to heavy importations of foreign ores from China, Burma and South America. So large were the imports that even after the enactment of a protective tariff in 1922 of 45c. per lb. on tungsten metal, equivalent to $7.14 per unit (201b.) of tungstic acid? (WO,), the stocks of metal in this country were extensive enough to supply the demands of industry, and prevent general resumption of mining by domestic producers. Even today there are only two producers in the Boulder district though at one time as many as twenty separate companies were in operation. About the same ratio holds for other tungsten-producing districts in the country, including California and Nevada. Total consumption of tungsten concentrate in terms of 60 per cent WO2 in the United States amounted to approximately 3790 tons in 1928, according to Frank L. Hess.' Of this amount, domestic mines contributed 1290 tons, and the rest, 2500 tons, was imported. Yet in 1917, with tungsten concentrate selling at $20 per unit, the Boulder district alone produced 2707 tons, indicating the effect of enhanced ore price upon production. It is believed by American tungsten miners that, given a sufficiently high tariff, all the demands of industry can be met by domestic production without placing a prohibitive burden on consumers. For instance, in steel manufacturing the percentage of tungsten entering into the manufacture is so small that, ?regardless of cost, it can constitute but a small fraction of the cost of steel to the buyer.

Jan 1, 1929

By Donald H. McLauqhlin

ITEM expressed in billions of dollars have become so commonplace these day- that a mere statement of the latest figures for the country s gold reserve scarcely conveys m adequate sense of the immensity of the commitment the nation has made in building up its huge stock, two-thirds of which is now stored at Fort Knox. Kentucky. Only by measuring it against quantities that mean something tangible to a particular group can an adequate comprehension of its magnitude he rained; consequently, to mining engineers, a comparison with the value of output from well-known mining districts might best serve to give some degree of reality to the astronomical figure at which the country gold is now valued.

Jan 1, 1941