Search Documents

By M. A. Dayananda

Based on the Kirkendall frame of reference, a method is proposed for the determination of atomic mobilities of all the diffusing species in a multicorn-ponent system with a single diffusion couple. The method is based on an atomic mobility model developed on the concept of negligible interactions among the intrinsic fluxes. It is shown in the model that mobilities can be obtained directly from the cumulative intrinsic fluxes past the Kirkendall interface. The proposed method replaces the need for a prior determination of interdiffusion coefficients far the calculation of mobilities. Relations between intrinsic diffusion coefficients and mobilities are derived and the mobility calculations are illustrated with diffusion data in Cu-Zn-Mn alloys at 850°C. ThE concept of "intrinsic flux" with respect to a fixed lattice was introduced "i Darken1 to explain toa Kirkendall effect2 demonstrated by the motion of inert markers during isothermal diffusion in single-phase binary solid solutions. Based on this concept, intrinsic diffusion studies have been made in various binary metallic systems3,4 employing such a lattice frame of reference, commonly referred to as the Kirkendall interface. Similar approaches, both theoretical and experimental, have been presented5"10 to study intrinsic diffusion in multicomponent systems. Based on the direct integration of Fick's law extended to multicomponent diffusion, Philibert and Guy8 proposed a method for the determination of intrinsic diffusion coefficients. For an n-component system, this procedure requires an experimental study with (n — 1) diffusion couples, all having their Kirkendall interfaces at the same compositio;, where n(n — 1) intrinsic diffusion coefficients are defined. This technique has been employed for ternary diffusion studies by Dayananda and Grace" and Guy and Leroy.11 A different approach is recommended by Ziebold and Cooper,12 who have derived relations between interdiffusion coefficients and atomic mobilities employing fluxes referred to the local center of volume. Their analysis is based on the simplifying assumption of negligible interactions among intrinsic fluxes. This assumption has been considered satisfactory for dilute solutions.5"7 The use of this analysis for the calculation of mobilities requires an initial determination of interdiffusion coefficients with a set of diffusion couples having intersecting diffusion paths. It is the purpose of this paper to propose a method that would permit a direct determination of mobilities of all components of a multicomponent system from a single diffusion couple. This method is based on a mo- bility model developed with diffusion fluxes referred directly to the Kirkendall interface, generally identified by inert markers. gen erall, like that of Ziebold and Cooper,12 employs the simplifying assumption that the flux of each component relative to a fixed lattice is caused only by the driving force of its own chemical potential gradient. THE KIRKENDALL INTERFACE Inert markers are employed in diffusion couples to locate experimentally the position of the Kirkendall interface. They are initially placed at the weld interface for "sandwich" couples, or at the original vapor-solid interface for vapor-solid couples. Studies of marker motion in binary systems3'4 with both types of couples indicate that markers remain in a plane of constant composition and move with this plane para-bolically with time. Parabolic marker movements were also observed in ternary Cu-Zn-Mn couples by Dayananda and Grace.10 It is reasonable to expect a similar marker behavior even for diffusion couples with a higher number of components.

Jan 1, 1969

By H. L. James

This paper presents the results and analysis of field trials of various magnetic instruments over anomalies ranging from 20 to 5000 gammas of vertical intensity. The following instruments were used: Askania vertical magnetometer, Wolfson vertical magnetometer (model M-I), Hotchkiss Superdips (used both parallel to and normal to the magnetic meridian, with several settings of the "sigma" angle), Lake Superior dip needle, and the dipping circle for measurements of inclination. The change in inclination over the measured anomalies ranged up to 4"; this caused pronounced changes in sensitivity of the Hotchkiss Superdip oriented parallel to the magnetic meridian. The variable sensitivity not only gives apparent displacement of crests of anomalies, particularly at high sensitivities, but also makes the data difficult or impossible to use in preparation of iso-anomaly maps. This weakness in field performance of the Superdip is shown to be eliminated by orienting the instrument normal to the magnetic meridian and measuring vertical intensity only, which in the latitude of upper Michigan is equal to 97 pct of the total intensity. The dip needle is seen to be relatively ineffectual for location of anomalies of less than 400 gammas. Introduction The U.S- Geological Survey, in cooperation with the Geological Survey Division of Michigan Department of Conservation, has for the past three years been engaged in a restudy of the Iron River-Crystal Falls iron mining district of upper Michigan. The bedrock in a large part of this area is covered with glacial deposits as much as 500-ft thick, and, inasmuch as some of the rocks have moderate to high magnetic permeability, extensive magnetic mapping has been done to assist in unraveling the complicated structure of the area. Several types of instruments have been used, and the major purpose of this paper is to present comparative data on the field performances of some of these instruments so as to aid others who face similar problems elsewhere to evaluate and choose the instruments best suited for the work. The paper is directed primarily to geologists and engineers rather than to geophysicists, although some familiarity with the instruments is presumed. The geology of the area consists of a complexly folded series of weakly metamorphosed sedimentary rocks, including the iron formation, which rests on older greenstones. Although the iron formation itself is only locally magnetic, some of the beds stratigraphically above the iron formation are rather strongly so. By tracing these hanging wall magnetic anomalies valuable information is obtained from which the structure and distribution of the iron formation can be inferred. Critical anomalies range from 25 to 6000 gammas of vertical intensity. Many anomalies can be traced in part with the common dip needle, but detection of others requires more sensitive instruments.

Jan 1, 1949

By H. L. James

This paper presents the results and analysis of field trials of various magnetic instruments over anomalies ranging from 20 to 5000 gammas of vertical intensity. The following instruments were used: Askania vertical magnetometer, Wolfson vertical magnetometer (model M-I), Hotchkiss Superdips (used both parallel to and normal to the magnetic meridian, with several settings of the "sigma" angle), Lake Superior dip needle, and the dipping circle for measurements of inclination. The change in inclination over the measured anomalies ranged up to 4"; this caused pronounced changes in sensitivity of the Hotchkiss Superdip oriented parallel to the magnetic meridian. The variable sensitivity not only gives apparent displacement of crests of anomalies, particularly at high sensitivities, but also makes the data difficult or impossible to use in preparation of iso-anomaly maps. This weakness in field performance of the Superdip is shown to be eliminated by orienting the instrument normal to the magnetic meridian and measuring vertical intensity only, which in the latitude of upper Michigan is equal to 97 pct of the total intensity. The dip needle is seen to be relatively ineffectual for location of anomalies of less than 400 gammas. Introduction The U.S- Geological Survey, in cooperation with the Geological Survey Division of Michigan Department of Conservation, has for the past three years been engaged in a restudy of the Iron River-Crystal Falls iron mining district of upper Michigan. The bedrock in a large part of this area is covered with glacial deposits as much as 500-ft thick, and, inasmuch as some of the rocks have moderate to high magnetic permeability, extensive magnetic mapping has been done to assist in unraveling the complicated structure of the area. Several types of instruments have been used, and the major purpose of this paper is to present comparative data on the field performances of some of these instruments so as to aid others who face similar problems elsewhere to evaluate and choose the instruments best suited for the work. The paper is directed primarily to geologists and engineers rather than to geophysicists, although some familiarity with the instruments is presumed. The geology of the area consists of a complexly folded series of weakly metamorphosed sedimentary rocks, including the iron formation, which rests on older greenstones. Although the iron formation itself is only locally magnetic, some of the beds stratigraphically above the iron formation are rather strongly so. By tracing these hanging wall magnetic anomalies valuable information is obtained from which the structure and distribution of the iron formation can be inferred. Critical anomalies range from 25 to 6000 gammas of vertical intensity. Many anomalies can be traced in part with the common dip needle, but detection of others requires more sensitive instruments.

Jan 1, 1949

By J. W. Spretnak, D. A. Chatfield, G. W. Powell, J. R. Eifert

In nzost cases, the driving force for a lattice transformation is produced by supercooling below the equilibriunz transformation temperature. The interfnce reaction in isothermally annealed, multiphase diffusion couples may involve a luttice transformation which also requires a driving force. Direct experinzental evidence has been obtained for the existence of the driring force in the form of a supersaturated phase at the aocc)-0@cc) interface in Cu:Cu-12.5 ult pct A1 couples; the super saturation is equivalent to an excess free energy of approximately 3 cal per mol at 905. A tentatiue interpretation of the dynanzic situation a1 the interface based on the free energy-composition diagram is proposed. THE presently accepted theory of diffusion in multiphase couples1 states that there will be a phase layer in the diffusion zone for every region which has three degrees of freedom and which is crossed by the diffusion path in the equilibrium phase diagram. For binary systems, this restriction excludes all but single-phase fields and, for ternary systems, only one- and two-phase fields are included. In addition, Rhines"~ as well as other investigators3 6 have reported that the compositions of the various phases adjacent to the interfaces are, for all practical purposes, the compositions given by the intersections of the diffusion path with the solubility limits of the single-phase fields of the equilibrium phase diagram. Some studies of the rate of thickening of these intermediate diffusion layers indicate that the thickness of the layer changes para-bolically with time, or: where x is the position of the interface relative to an origin xo, t is the diffusion time, and k is a temperature-dependent factor. crank7 shows mathematically that, if the compositions at an interface are independent of time and the motion of the interface is controlled by the diffusion of the elements to and from the interface, then the segments of the concentration penetration curve for a semi-infinite step-function couple will be described by an equation of the form: hence, Eq. [l] follows from Eq. (21 if the interface compositions are fixed and if the motion of the interface is diffusion-controlled. Although the concept of local equilibrium being attained at interfaces has assumed a prominent role in the theory of diffusion in multiphase couples, experimental evidence and theoretical discussions which challenge the general validity of this concept have been reported in the literature. arkeen' has stated that strict obedience to the conditions set by the equilibrium phase diagram cannot be expected in any system in which diffusion is occurring because diffusion takes place only in the presence of an activity gradient. Darken also noted that it is usually assumed that equilibrium is attained locally at the interface although the system as a whole is not at equilibrium, the implication being that the transformation at the interface is rapid in comparison with the rate of supply of the elements by diffusion. ISirkaldy3 indicates agreement with Darken in that he believes the concept of local equilibrium is at best an approximation because the motion of the phase boundary requires that there be a free-energy difference and, hence, a departure from the equilibrium composition at the interface. Seebold and Birks9 have stated that diffusion couples cannot be in true equilibrium, but the results obtained are often in good agreement with the phase diagram. The initial deviation from equilibrium in a diffusion couple will be quite large because alloys of significantly different compositions are usually joined together. Kirkaldy feels that the transition time for the attainment of constant interface compositions (essentially the equilibrium values) will be small, although in some cases finite. Castleman and sieglelo observed such transition times in multiphase A1-Ni couples, but at low annealing temperatures these times were quite long. Similarly, ~asing" found departures, which persisted for more than 20 hr, at phase interfaces in Au-Ni and Fe-Mo diffusion couples. Braun and Powell's12 measurements of the solubility limits of the intermediate phases in the Au-In system as determined by microprobe analysis of diffusion couples do not agree with the limits reported by Hiscocks and Hume-Rothery13 who used equilibrated samples. Finally, Borovskii and ~archukova'~ have stated that the determination of the solubility limits of phase diagrams using high-resolution micro-analyzer measurements at the interfaces of multiphase couples is not an accurate technique because of deviations from the equilibrium compositions at a moving interface; diffusion couples may be used to map out the phase boundaries in the equilibrium diagram, but the final determination of the solubility iimits should be made with equilibrated samples. The purpose of this work was to investigate the conditions prevailing at an interface in a multiphase diffusion couple and to compare the interface compositions with those associated with true thermodynamic equilibrium between the two phases. Microanalyzer techniques were used to measure interface compositions in two-phase Cu-A1 diffusion couples annealed at 80@, 905", and 1000°C for various times.

Jan 1, 1969

By J. G. EVANS

It is with a certain amount of trepidation that a man considers gathering his family of six, traveling across a continent, two oceans and a sea, and going to live in a foreign land. But "pioneering" is still possible, and a nation is "foreign" only until one has lived in it. We've had eight years of pleasant experiences in South Africa on which to base that contention. It was in January 1938 that my brother first extolled the virtues of South Africa to us, and just three months and a thousand small problems later my wife, two daughters, three sons and I were boarding a ship in New York, bound for Cape- town. We arrived in May, and within a week had found a furnished home with beautiful lawns, tennis, court, a garden, and everything needed for family comfort. The children were soon located in school, and I settled down to the task of entering the importing business, as had been my original intention. The importing business started out slowly but was coming along nicely when on Sept. 3, 1939 the war started in Europe and a declaration of war by the Union of South Africa was made on the following day. With the declaration came import and export controls. In fact we were controlled completely out of business in one stroke. Liquidating the business, I went to Johannesburg intending to find work in one of the mines. Government health and safety regulations require that all underground mine employees have a red ticket from the Miners Phthisis Bureau certifying that they are not susceptible to silicosis, the scourge of the Witwatersrand gold mining industry. I made application to the Bureau, completed a form covering my whole past life, and was given a complete physical examination. The following day I was startled to find that I had not only been refused a red ticket but had been classified with a green ticket which for- ever bars one from working underground in any scheduled mine in the country, and all this in spite

Jan 1, 1949

By PAUL DYER MERICA

PAUL DYER MERICA, who has been awarded the James Douglas Gold Medal for his achievements in non-ferrous metallurgy, is a Hoosier, having been born at Warsaw, Ind., in 1889. His father, a clergyman and educator, was president of the University of Wyoming from 1908 to 1913. After graduating from the University of Wisconsin in 1908, young Merica (not yet twenty years of age) went to China, where he was professor of chemistry in Chekiang Provincial College, Hangchow, until 1911. He then went to Germany to s t u d y and was fortunate enough to receive his Ph.D. from the University of Berlin just a few months before the outbreak of the World War in 1914. Returning to America, his first position was as special investigator at the En¬gineering Experiment Station of the University of Illinois, but before the year was out he joined the staff of the U. S. Bureau of Standards as associate physicist. Since 1918, he has been superintendent of research for the International Nickel Co. His work during those years is excellently summarized in the following quotation from the statement of Zay Jeffries recommending him for the award.

Jan 1, 1929

By Ta M. Li

Recent economic and environmental setbacks have not slowed Occidental Oil Shale, Inc.'s program aimed at the commercialization of oil shale. In fact, the firm expects to have a 795 MI (500C) bbl) per day production unit working by the end of 1976. The key to Occidental's ambitious program is an in situ method that extracts the valuable oil by retorting the shale in place. The process will require practically no water and will leave the spent shale in place underground. Additionally, all plant operations are to be located within the mine. These factors thus serve to make the operation attractive from an environmental viewpoint, in contrast to proposed conventional schemes which call for extensive underground mining, crushing and grinding at the surface, and construction of a massive surface retorting facility.

Jan 12, 1976

By J. Holms Pollok

The determination of specific gravity dates from such antiquity, and the various published methods of determining it are so numerous, that one may well be skeptical as to the value of a new means of obtaining so well-known a quantity. I make no claim to any great novelty for the little device here described, the principles, though not the convenient details, of which are more or less embodied in the publications of Mr.

Jan 1, 1900

By M. C. Flemings, R. Mehrabian, G. E. Nereo

Analytical expressions derived previously are used to describe quantitatively effects on macrosegregation of some solidification and mold design variables. Al-4.5 pct Cu alloy is used as example. It is shown that abrupt changes in heat transfer rate result in solute-rich or solute-poor "bands". Severe solute-rich bands accowzpany "reheating" that can result, for example, from abrupt formation of an air gap at a mold-metal interface. With planar isotherms, solute-poor regions also result from reduction in cross section through which fluid flow to feed shrinkage takes place. It is suggested that the negative "cone" of segregation often found at the base of large ingots results from this reduction in cross section for feeding. Consideration is given to the positive and negative segregation to be expected in laboratory ingots in association with changes in ingot cross section. Under-riser positive segregation is considered and it is concluded this segregation results when vertical temperature gradient is low in the region of the riser; the segregation is accentuated by the temperature gradient reversal which can occur in inadequately insulated risers ("'hot tops"). Finally it is shown for Al-4.5 pct Cu alloy that the assumption of constant k and p in analytic solutions gives calculated results close to those obtained for the case of ziariable k and 0. A basic "local solute redistribution equation" was derived earlier' for calculation of macrosegregation resulting from flow of solute-rich liquid to feed solidification shrinkage, thermal contraction, and/or other contractions occurring during solidification. This expression relates fraction liquid, g~, to liquid composition, CL, at a given position x, y, z, in a solidifying Eq. [I] is for the general case of three-dimensional heat and fluid flow assuming constant solid (but not necessarily liquid) density during solidification, negligible net solute change from diffusion, and no pore formation. In this paper we first demonstrate application of this equation for calculation of macrosegregation in several examples involving one-dimensional heat and fluid flow. Specifically considered are examples in which segregation results from sudden changes in heat flow conditions. Next, Eq. [I] is used to describe segregation in examples where isotherms remain planar but where fluid flow is no longer one-dimensional. Application of this expression illustrates the type of segregation to be expected in unidirectionally solidified ingots of gradually or abruptly varying cross section. For segregation calculations, A1-4.5 pct Cu alloy is employed with constant k and p Vz = 0.172, 4 = 0.055), eutectic composition (CE = 33 pct Cu). In all examples, fraction eutectic is neglected in velocity calculations; this was previously shown to introduce little error.' A linear distribution of fraction liquid in the liquid-solid zone is assumed. In a concluding section it is shown that the assumption employed of constant k and /3 gives results close to those obtained when the actual (variable) values of k and 0 are employed.

Jan 1, 1969

By M. E. Wadsworth, R. C. Peterson, W. M. Fassell

The temperature and pressure dependence of the reaction of tantalum in oxygen were investigated from 500° to 1000°C at pressures from 10 mm Hg to 600 psi total oxygen pressure. Tantalum was found to oxidize linearly under the above conditions. Three distinct regions of temperature dependence were found with different energies of activation. From 500° to 600°C the rate of oxidation of tantalum was found to be essentially independent of the oxygen pressure at the pressure investigated. The oxidation rate increases rapidly with an increase in pressure from 600' to 800°C. The dependence of the oxidation rate on the bulk concentration may be expressed by V = k'?, where k' is the specific rate constant and ?=k1Co2/(l + K1Co2), where k, is the equilibrium constant for the adsorption of oxygen on tantalum. ONLY a limited amount of data has been presented in the literature on the oxidation behavior of tantalum metal. Some values of its oxidation rate were reported in the Corroston Handbook' and by McAdams and Geil.' The first extensive investigation of tantalum was the work of Gulbransen and Andrews." They determined the reaction rates of tantalum in O2 and N2. Their results indicate that this metal follows the parabolic law in the temperature range of 250" to 450°C in O2 at pressures of 7.6 cm Hg with an activation energy of 27,400 cal per mol. In nitrogen, the metal follows the parabolic law from 500" to 800°C at 7.6 cm pressure. All experimental determinations were of 2 hr or less duration and deviations from the parabolic rate conceivably could occur at longer times. A spectrophotometric study of the oxidation of tantalum by Waber, Sturdy, Wise, and Tipton' indicated good agreement between this method and the microbalance technique. The experiments were conducted in air from 220" to 350°C. The metal was found to follow the logarithmic law up to 320°C and the parabolic law at higher temperatures. The activation energies in the logarithmic region were reported as 12.57 kcal per mol and 12.0 kcal per mol, respectively, for the microgravimetric and spectrophotometric methods. In the parabolic region the activation energy was found to be 27.2 kcal per mol, in good agreement with the value of Gulbransen and Andrews." The present paper is concerned with the behavior of tantalum from 500" to 1000°C in oxygen at pressures ranging from 1/2 to 40.8 atm pressure. Earlier preliminary data by McKewan5,6 indicated the following facts concerning the behavior of tantalum: 1—At temperatures from 500" to 600°C, the metal followed the linear law. 2—At 575°C the rate of oxidation was found to increase with O2 pressure. 3—The Arrhenius plot in this temperature region was nonlinear. The nonlinearity of the Arrhenius plot was indicative of a more complex behavior than originally suspected for this metal.

Jan 1, 1955

By WILKES BARRE

AS PREVIOUSLY announced, the semi-centennial meeting of the Institute is to be held at Wilkes-Barre, Pa., on Sept. 12, 13, 14, and 15. An interesting program of technical sessions and excursions is now being prepared by the Local Committee. At the time of going to press the program had not been completed in sufficient detail to permit its being pub¬lished in this number. The detailed program will be published in the September MINING AND METALLURGY, which will be printed in time to be distributed before the Wilkes-Barre Meeting. It may be said in advance, however, that the Com¬mittee has progressed so far in its work that we are assured of one of the -most notable meetings the Insti¬tute has held and that members will miss a rare .treat if they do not attend. The many trips and excursions, as well as the banquet, will be -given to the members as a compliment from the members of the Local Com¬mittee. . . The paper by Howard Eavenson on the Lynch Plant of -the United States Coal and Coke Co. will be illustrated by lantern slides and moving pictures. One of the most appropriate discussions will be that opened by Prof. J. F. Kemp on the Stratigraphy of the Anthracite Region; this also will be amply illustrated.

Jan 1, 1921

By Frances H. Clark

IN wartime, the fabrication and use of metals assumes increased importance, for a modern war of sizable proportions cannot be undertaken with- out a vast supply of this material. Light alloys of aluminum and magnesium, which were comparatively unknown in the last war, will play an important role in this one. Due to research on a vast scale in the interim of years, industry is today well equipped to fabricate metals on an enormous scale. Research for the past year has been most productive and a comprehensive survey in the space of this article would be impossible. It is hoped that the stressing of a few items here and there out of a great quantity of able work will indicate in a small way the advances made within recent times. Specific references to the literature will be omitted at the Editor's re- quest but some authors of papers that I have found of special interest are mentioned.

Jan 1, 1940

By H. F. Beardmore

PETROLEUM consumption during 1946 broke all previous records and further increases are expected during 1947. U. S. consumption amounted to an average of 5,280,000 bbl a day, of which 4,745,000 bbl was domestic crude oil, with the rest from natural gasoline production and crude oil imports. World consumption during the past year, excluding Russia, is estimated at 7,200,000 bbl daily. Forecasts for 1947 indicate a U. S. consumption of 5,425,000 bbl daily of petroleum products. This is expected to be made up of 4,655,000 bbl of domestic crude oil production, 340,000 bbl of natural gasoline production, 400,000 bbl of crude oil imports, and the rest from stocks. Petroleum's principal use is still as a fuel. The field remains highly competitive, but petroleum has been continuously progressing. Less than fifty years ago, oil supplied only one twentieth as much of the nation's total energy as coal, but today it supplies over half as much.

Jan 1, 1947

By Albert Brokaw

THE so-called ?paraffin dirt" of the Gulf Coast oil fields has been con¬sidered an indication of the possible presence of oil and gas, and not a few wells have been brought in solely on the basis of such evidence. In a sense, it may be empirically justified as evidence of the presence of oil or gas, though it cannot be said to be infallible. If the writer is correctly informed, its association with oil and gas was pointed out by Lee Hager some years ago, and while it is commonly mentioned by geologists and operators in conversation, no discussion seems to have found its way into print. The present interpretation is based on laboratory study rather than on field investigation, and is put forth with the hope of stimulating discussion which shall lead to more complete understanding. The term "paraffin dirt" has been applied to soils with a peculiar texture, which has been described' as "curdy" or "rubbery." When moist, the material breaks much after the fashion of "green" cheese. It is rubbery under compression, but does not resemble rubber in tenacity or cohesion. When dry, the material ranges from hard clods to a horny mass of high tensile strength. The shrinkage in drying is very great, especially in the hornlike matter. The moist material ranges in color from dark brown in the specimens rich in organic matter to grayish in specimens containing more inorganic matter. All of the specimens studied were readily attacked by molds, which in some cases grew in great profusion on the samples. Samples exhibited a rather characteristic "swampy" or "mucky" odor when wet, and a characteristic odor of humic soils when moist.

Jan 4, 1918

By W. F. Boericke

THE recent completion by the United States Aluminum Company of a $4,000,000 addition to its plant at Massena, N. Y., consisting of a large blooming mill and structural mill, gives this organization, a subsidiary of the Aluminum Company of America, the distinction of possessing the largest aluminum rolling mill in the world, as well as the first mil1 in this country to roll aluminum exclusively. The plant is located near the international boundary line between Canada and the United States, about 3 miles from the St. Lawrence River, to take advantage of the development of cheap hydroelectric power which is needed not only for the manufacture of structural shapes from the ingots, but in the reduction of alumina to the metal by the well-known Hall process as well. A power canal from the St. Lawrence River to the power house on the Grasse River at the plant provides for the waterflow, which, coupled with a drop of 47 ft. in 2% miles, generates 80,000 hp. through vertical turbines. An additional 60,000 hp. is purchased.

Jan 1, 1930

By Robert Williams

A description is given of a double heat treatment of 60-40 brass. Photomicrographs are included to show the changes that take place in the microstructure on reheating the water-quenched specimens. A wide variation in the mechanical properties may be obtained by the described heat-treatment method. ON SEVERAL occasions, when 60-40 brass is first obtained in the beta condition by quenching at about 825° C. and is then reheated, the writers have noticed that recrystallization will take place in the form of twin crystals at the grain boundaries of the original beta crystals. It was, therefore, thought that interesting results would be obtained if this twinning process was studied further, especially as to the temperature at which it first occurs. The material used in the investigation was a bar of extruded muntz metal, 1/2 in. in diameter, and of the following composition: Copper, 60.21 per cent.; zinc, 39.73 per cent.; lead, trace; iron, trace; tin, nil. Specimens I in. in length were sawed from this bar and a hole was drilled into the side of each specimen until it reached the center, and the tip of a platinum-platinum rhodium thermocouple was inserted. A small Hoskins' resistance-type electric furnace was used for heating the specimens. The specimens were first heated at 840°C. for 2 hr. and then quenched in cold water, in order to get the material entirely in the beta state. In every case, in the reheating process, the furnace was brought to the desired temperature before the specimen was introduced. The time occupied in preheating was from 20 to 30 min. By sawing back 1/4 in. on each side of the hole, two parts were obtained from each specimen

Jan 3, 1924

By J. E. Tobey

BECAUSE of the wide-spread publicity given to Nylon yarn as being made from ?coal, air, and water,? the general public has become conscious of the nonfuel uses of bituminous coal. Some of these uses are as filler for fertilizer, carbon for the absorption of orders, for water supply, and for the bedding of cattle. Spectacular as are these accomplishments the fact is that only a small amount of coal is used for nonfuel purposes. It is on the utilization of coal as fuel that the industry depends. Practically all the coal mines for years to come will be used for making coke for the generation of heat. Recently much attention has been paid to the significance of ash in coal. Another study worthy the interest of metallurgists in the iron and steel industries if that of Dr, Lowry of the Carnegie Institute of Technology relative to the percentage of sulphur in coal and coke.

Jan 1, 1941

By W. J. O'CONNOR

THE production of lead in the United States for the period from 1720 to 1912 was 10,432,668 tons valued at $924,600,000. The average price during this period was 4.4c. a pound, although lead sold at times below 3 cents. We know that in the early days of lead smelting in Montana lead was deliberately lost in the slag and only enough reduced as bullion to collect the silver. This bullion was freighted by ox team to Corinne, Utah, the terminus of the railroad at that time, and shipped to Swansea or Omaha, Neb., for refining. The slag from some of the above mentioned operations contained as much as 15 per cent lead and has since been resmelted. Since 1921 the production of lead has increased each year and the price and tonnage have been as follows :

Jan 1, 1926

By Charles L. Elliot

Data on mining applications of geophysical activity in the Free World in 1964 have been made available to SME again this year by the Society of Exploration Geophysicists. Worldwide data were collected as part of an annual service to the mining industry by the Committee for Geophysical Activity of SEG. Data are taken from 245 voluntary responses (53%) to questionnaires circulated to 463 company, government and university organizations engaged in mining geophysical operations and research all over the world. WORLD ACTIVITY Worldwide manpower utilization totalled 9323 professional man-months and $14.5 million was reported spent in mining geophysical activity in 1964. This is up from 9078 man-months and $12.6 million in 1963 and 8065 man-months and $12.8 million in 1962. Worldwide geophysical activity in terms of manpower utilization and expenditures is presented in the accompanying table.

Jan 9, 1965

By Victor M. Braschi

The railroad history of Mexico began with the first presidential term of General Diaz. Concessions for the building of railroads had been granted in former years; indeed, an exclusive privilege was granted, August 22, 1837, to Francisco de Arrillaga for the construction of a railroad from Mexico to Vera Cruz, with a branch to Puebla, and other concessions were granted from then on at various periods; but the year 1877 was the real beginning of the regular and constant decelopment of the railways of Mexico. The programme laid out at that time by the new government, and responded to by the nation, was to develop its natural ele-

Jan 1, 1902