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By Gerald F. G. Sherman

The ore deposits of the Warren district, in which the mines of the Copper Queen Consolidated Mining Co. are situated, have been described in a number of technical publications, and will not be discussed here in detail. Certain of their characteristics, however, control methods of underground transportation and hoisting of ore. In the Copper Queen mine, the majority of the ore has occurred in a zone encircling the west boundary of the porphyry intrusion of Sacramento Hill. It has a width varying from 800 to 1,200 ft., and a thickness of about 400 ft. It reaches the surface in the older part of the mine to the northwest, but dips to the southeast, where it is reached at 1,400 ft. below the Czar collar, in its farthest extension at present developed on Copper Queen ground. There is one major extension from the northwest end of the zone toward the west along the Czar fault, and others of minor importance. Individual orebodies are scattercd through the zone in an eccentric manner, only matched by their own irregularities of form and size. Their most gencral characteristics are the softness of the ore and their grcat horizontal rather than vertical extent. It has been estimated that the average vertical thickness of ore in the Czar and Lowell divisions is between 30 and 35 ft. It is calculated by assuming it to be uniformly distributed over its horizontally projected area. In this zone, and for some distance above it, the ground has been subjected to intense alteration and intense but irregular oxidation. It has resulted in an enormous quantity of earthy or clayey material, which may be either ore or waste, which when wet is both heavy and tenacious. Below alteration, the ground is fairly hard, and the limestones contain primary ores differing from those heretofore considered typical of the camp, and which have not yet been thoroughly exploited. The mine production has been drawn from many orebodies spread over a great area.l A diagram map (Fig. I), of haulage drifts and loading stations, illustrates the situation in 1914.

Jan 1, 1916

By Joseph Chalmers, J. S. Desmond, R. Van A. Mills

[Because of the limited space in this volume and the fact that a description covering the oil recovery buildings and equipment (see page 4, Technical Publication No. 144) will be given in a forthcomnig U. S. Bureau of Mines publication, and because the paper was published in detail as Technical Publication No. 144, and is available as a separate at the Institute, it is impossible to include here more than the following brief extract.] Problems Being Studied The selection of the first problems to be studied was based largely upon the following very practical questions asked by several of the largest operators in the Mid-Continent field. 1. What are the causes for the formation of excessive amounts of bad thick oil on properties that are being repressured with compressed air and how can this trouble be prevented? 2. Why, in some areas, does the oxygen in the air injected into an oil sand during repressuring operations apparently change to carbon dioxide? Is carbon dioxide formed by the oxidation of some of the oil in the sand'? How can the formation of inert or low B.t.u. casinghead gas, loaded with nitrogen, carbon dioxide and oxygen, be prevented? 3. What percentage of the oil originally present in an oil sand can be recovered by the ordinary methods of operation when the gas originally dissolved in the oil is the main propulsive agent? 4. What percentage of the amount of oil produced by ordinary methods can be recovered under average conditions by repressuring a so-called depleted oil sand? 5. What are the relative propulsive efficiencies of compressed air and natural gas in repressuring operations? 6. What are the practical advantages of pressure maintenance and early repressuring as compared with late repressuring?

Jan 1, 1929

By M. T. Worley

This paper reports investigative work conducted to develop a method of estimating the groundwater influx from a homogeneous permeable formation into a vertical mine shaft during sinking. A method of analysis was developed using data obtained from pumping tests and a modification of the Theis non-equilibrium interpretation technique. Excess influx of groundwater into mine shafts has long been one of the more important problems encountered in the development of a mining property. Much work has been done on methods of preventing such influx and on pumping schemes to control inflow if preventive measures fail. The fundamental aspects of the problem, on the other hand, seem to have been neglected. The purpose of this paper is to review the fundamentals of groundwater flow and to propose a rapid method of analyzing hydrologic data in order to estimate influx from a homogeneous permeable formation into a mine shaft. Such an estimate of the quantity of water to be encountered is of value in planning grouting, pumping and other programs designed to control that influx. It is emphasized that the proposed method of analysis should be regarded only as a tool to be used in evaluating the problem before investing the capital necessary to begin development of a property. FUNDAMENTALS OF GROUNDWATER FLOW In order to effectively approach the problem of estimating influx into a mine shaft, a knowledge of the fundamentals of fluid flow through a porous medium is necessary. Darcy, in 1856, developed an empirical relationship to explain the flow of water through sand filters. This relationship V = k (dh/dl), is the basis for all other flow formulae. It has been shown that Darcy's relation is a solution of the Laplace equation and thus is analagous to other natural phenomena such as heat flow. Theis, using the analogy of heat flow by conduction, developed an expression for determining the transient or time-dependent groundwater flow through a homogeneous, isotropic medium. The resulting equation Was also derived by Jacob using hydrologic considerations alone.' The individual terms in the equation are described in Table I. It is important to understand the assumptions upon which this equation is based. 1) The medium through which the fluid flows is infinite in areal extent, homogeneous and isotropic. 2) The well into which the fluid discharges completely penetrates the medium. 3) The characteristics of the medium remain constant at all times. 4) The initial pressure surface is horizontal. 5) The confining media are impervious and horizontal. 6) Fluid is removed from storage instantaneously by a decline in pressure. 7) The diameter of the discharge well is infinitesimal with respect to the drainage radius of the medium.

Jan 1, 1962

By F. F. Sharpless

ARRIVING at Davis Junction, after leaving Portland, we expected to wait for an hour and a half, but found the superintendent of motive power of the Southern Pacific, Mr. Williams, waiting for us with a car, and were immediately taken aboard this and whisked off to Sacramento. After dinner, we were taken to the railroad shops to see their work in reclaiming scrap steel. We saw them draw off the slag from the electric furnace, and later make a casting. At about 11 o'clock, we took the train for Reno. A delegation of the Nevada Section, with Mr. Kirchen and Mr. Rives at its head, met us at the station. Immediately after breakfast, we started for the property of the Comstock Mines Co., where General Bulkeley Wells was to be our host. We had a de-lightful ride out to the mines and through the old city of Virginia, or through what was left of that old city, reaching General Wells' camp at about 10:30. This contains the newest thing in cyanidation and a remarkably fine iron and concrete mill building. After a trip underground, we were called to luncheon, where about 250 sat down. The afternoon was spent in the mill, and we were taken to Gold Hill, which is a part of Virginia City, for dinner, again as the guests of General Wells, who made a consummate toastmaster. Governor Emmet Boyle was the first speaker; he was followed by President Dwight, and then came President William Sproule of the Southern Pacific. A song, "The Engineer," was followed by Senator Key Pittman, Professor Jones of the State University, Mayor Stuart of Reno, and ex-Senator Charles Hend-erson. The president of the Western Pacific and the president of the Pacific Coast Line were there, also many notable operators of Nevada and California.

Jan 11, 1922

Executive ARTHUR S DWIGHT, Chairman B THAYER CHARLES F RAND P MATHEWSON J V W REYNDERS Membership WILLIAM H BASSETT, Chairman W Y WESTERVELT Vice-chairman P MATHEWSON H G MOULTON F T RUBIDGE Finance WALTER H ALDRIDGE, Chairman GEORGE D BARRON GALEN H CLEVENGER

Jan 1, 1923

Washington has been the largest coal producing state of the Pacific Coast, and the only one producing coke commercially. With the exception of the few estimated figures, the tonnages in Table 71 are from Goodyear and other sources as shown. [ ]

Jan 1, 1942

By J. M. Weehuizen

Complete details are given of the drilling method by which two shafts were sunk at the new Beatm'x mine of Staatsmijnen in the Netherlands. The nature of the rock strata in the Dutch mining district determined choice of the drilling rather than the freezing method. Data for each step and details of the equipment used are given in the illustrations. Staatsmijnen was founded in 1902 with government financial backing, but it is run as a private enterprise, on a commercial basis, with the normal fiscal obligations. The company now has four mines in operation with annual outputs amounting to 7 1/2 million tons of coal. In 1952 it was determined that a new mine—the Beatrix—would be opened. Details of the shaft-sinking operation are described in this paper. SHAFT LOCATION The coal-bearing carboniferous rock in the Dutch mining district is overlain almost completely by soft water-bearing strata, which at the site of the new shafts are about 1600 ft thick. The sinking of the new shafts through this soft water-bearing overburden (Fig. 1) is a costly and time-consuming affair. From the two availaible sinking methods: 1) Poetsch's well known freezing method or 2) the drilling method of Honigmann-de Vooys, the latter was preferred, not only because of its relative cheapness, under the prevailing conditions, but primarily because by using the drilling process, a special type of shaft lining of steel, concrete, and bitumen could be used. The new shafts, located 330 ft apart, have an inner diameter of 18 ft, 4 1/2 in. The boreholes, which have a diameter of 25 ft and which were drilled through nearly 1600 ft of overburden and some 100 ft of carboniferous, each contain more than 29,000 cu yd—by far the largest in the world. DRILLING METHOD The drilling method is based on the use of mud-flush—a thin mixture of clay and water—to keep the borehole filled during the entire drilling period and during insertion of the lining (Fig. 2). The pressure of the mudflush against the borehole wall is greater than that of the water in the surrounding

Jan 1, 1961

By A. B. Parsons

NOT every organization on reaching the relatively ripe age of three score and fifteen can say with truth that its purpose and objects remain precisely the same as prescribed by its founding fathers. Of course, constancy of purpose may be something else than unalloyed virtue. It could merely reflect slavish worship of tradition, intellectual stagnation, or sheer inertia. On the other hand, it could establish the fact that the founders were men possessed of broad outlook, of prophetic vision, and of an acute sense of direction. In addition to charting the course with precision, the founders of the A.I.M.E. surely showed a flair for expressing clearly in a few words what others might say obscurely in many words. To quote verbatim from the "call" for the meeting, in 1871, the proposed organization was to have: "two great objectives: "First, the more economical production of the useful minerals and metals. "Second, the greater safety and welfare of those employed in these industries." This text underwent some refining on several subsequent occasions but today the ultimate product, as set forth in the Constitution reads: "to promote the arts and sciences connected with the economic production of the useful minerals and metals and the welfare of those employed in these industries by all lawful means." The original call was dated "Wilkes-Barre, Pa., April, 1871," and was signed by Eckley B. Coxe, of Jeddo, and by R. P. Rothwell and Martin Coryell, both of Wilkes-Barre, each of the three subscribing himself as "mining engineer." The authors proceeded to explain briefly just how it was proposed to achieve these objectives: "In European countries, where the arts of mining and metallurgy have long been the subject of the most careful study, no means have been found so effectual in attaining the end above proposed, as the free interchange of experience among those actually engaged in these industries; and this object has been accomplished mainly through the medium of `Institutes,' `Associations,' or `Societies,' composed of those engaged in these occupations, and by the periodical publication of `essays' or `papers' communicated to such societies by their members. "It must be evident to all practical men that the interchange of the varied experience

Jan 1, 1947

By J. E. Ryan

TRONA, Calif., is a miniature urban community of some 3500 people, located on the northwest shore of dry Searles Lake in the extreme northwest corner of San Bernardino County, approximately 186 miles north and east of Los Angeles. Since it is situated on the Mojave Desert, a typically desert climate prevails with wide variations in temperature between day and night, extreme daytime summer heat, and cool to cold winters. Rainfall averages somewhat less than 4 in. per year, and dust storms are common. The rate of evaporation, .however, is great, amounting to 6 to 9 ft of water per year. The extremely low humidity makes the summer heat of 110°F tolerable with only a mild, temporary discomfort. Nature of Deposit During the periods when Searles Basin was flooded, the waters that passed through Indian Wells Valley spread out to form a broad, shallow lake providing, in effect, a settling basin for suspended sediment. The drainage into the deeper and more isolated Searles Basin thus was clarified to a great degree before concentration began. Today, the elevation of the dry surface of Searles Lake is 1618 ft, and the salt deposit measures 5x7 miles. At the eastern and northeastern margins of the main playa zone and just at the foot of the alluvial slope of sand and coarser wash from the Slate Range mountains, a rim of crusted salts rises a few feet above the level of the flat. The deposit is a saline efflorescence composed of salts that were presumably brought up with rising ground waters to be deposited at the surface by solar evaporation. This deposit consists chiefly of trona, and it is after this Trona Reef that the town Trona was named. Strip mining operations have been conducted in the past at infrequent intervals for the recovery of crude trona salts. The main focal point of interest in Searles Lake from a commercial standpoint is the main salt body located almost centrally in the basin. The exposed portion of this porous saline deposit covers approximately 12 sq miles and averages 71 ft deep. Its interstitial voids, which constitute 50 pct of the total volume, are permeated with a brine, which is in equilibrium with the soluble salt deposits. The brine is the raw material for the operations of the American Potash and Chemical Corp. plant at Trona, shown in Fig. 1. The soluble salt deposits are of interest for their potential values in future technologic development. The brine, which is stratified according to slight differences in density, stands usually within 6 in. of the surface of this exposed, firm, salt body. The surface is usually dry and will support the weight of heavy mobile units and drilling equipment. Occasionally, however, surface waters from the higher watersheds encroach upon the main salt body during infrequent periods of precipitation on the surrounding mountains. This water dissolves surface salt, becomes a dilute brine, and has been observed to stand as high as 18 in. above the salt surface when undisturbed. Windstorms will shift the water back and forth across the lake surface. The exposed salt body is surrounded by additional submerged areas of commercial soluble salt deposits covering some 20 sq miles, hidden from view by marginal playa mud. These vary in depth up to as much as 30 ft. Thus, the outline of exposed and submerged salt deposits of commercial value is estimated to cover a total area of 32 sq miles, which is roughly circular but slightly elongated from northwest to southeast. It has been estimated that each square mile contains about 100 million tons% f alkali salts. The results of drill borings in the past 15 years have brought to light the interesting fact that the main salt body lies superimposed on an impervious mud deposit from 10 to 15 ft thick containing relatively little soluble salt. Under this deposit lies a second soluble salt body 35 ft deep. The lower salt body is interspersed with numerous insoluble mud lenses and its composition is considerably different from that of the primary, or main salt deposit. Recent drill borings have not penetrated beyond 300 ft. They have, however, revealed that underlying the lower salt body, the mud sediments carry deposited minerals of trona, nahcolite, mirabilite and much less soluble carbonates or sulphates of calcium and/ or magnesium. This structure is shown in Fig. 2. Current Lake Survey Program Several hundred holes have been drilled in the deposit. However, to carry out a thorough and carefully correlated study of the composition of the soluble salts and other minerals in the dry lake basin, a drilling program was inaugurated recently and is now nearing completion. In this survey, pattern drill holes are sunk at regular lh-mile intervals to a depth of approximately 150 ft. Drilling equipment consists of a No. 51 C. P.

Jan 1, 1952

By R. G. Davies

THE effect of ordered structures upon steady state creep has not been extensively studied although it has been demonstrated that the brass,' ie,' and Fe3Al3 superlattices increase the creep resistance. Suzuki and Yamamoto observed an acceleration in the creep rate of Ni3Fe below the critical temperature for order, (T, - 505"), for both the ordered and disordered states, and that the activation energy for creep was independent of the applied stress. They concluded that a dislocation climb creep mechanism was operative down to 300°C which is - 1/3 TM where TM is the absolute melting temperature. This is quite remarkable in that it is usually observed that climb controlled creep in both pure metals and alloys ceases below - 1/2 TM (590" for ie). With this anomaly in mind it was decided to reinvestigate creep in a 75 at. pct Ni-25 at. pct Fe alloy. The creep apparatus and operating conditions have already been decribed. Since Ni-Fe alloys order very slowly, it is possible to have a disordered alloy at a temperature below T,. A long anneal at a temperature just below T, produces considerable long-range order;5 the ordering treatment in the present investigation was 150 hr at 485°C which gives an antiphase domain size of-SOW

Jan 1, 1963

Benjamin B. Thayer was elected as representative of the Institute on the John Fritz Medal Board of Award vice Albert Sauveur, whose term expires. Robert M. Raymond was confirmed as member of the, Engineering Foundation Board for two years in accordance with the By-Laws of the United Engineering Society. The following preambles and resolutions were passed: WHEREAS, the Chamber of Commerce of the United States is taking a vote, through the Chambers of Commerce, Boards of Trade and other constituent members of the National Chamber situated throughout the country, on the question whether or not the primary natural resources, comprising timber, the ores and deposits of useful metals, and' the deposits of minerals, which are a source of heat, light and power, should he exempt through remedial Congressional legislation from the restrictive limitations of the Anti-Trust Acts, and WHEREAS, a Committee of the National Chamber, the Chairman of which is a Past President of the American Institute of - Mining Engineers, has recommended favorable action upon this question, and

Jan 2, 1917

By Rudolph G. Wuerker

The scarcity of values of tensile strength of rocks has been explained by the lack of successful testing procedures. In the case of mine rock a description is given' of the difficulties encountered in testing a cylindrical specimen, such as a core, by conventional methods. Over a period of years the following method has given definite and reproducible results with the weakest as well as with the strongest rocks. It does not completely supersede the use of cores with special fixtures but is a supplement in all cases where cores cannot be obtained, as from soft rocks, or in cases where it is less expensive to prepare test specimens by cutting them out of the rock instead of drilling cores.

Jan 2, 1955

The recent dedication of Magma Copper Co.'s San Manuel, Ariz., electrolytic copper refinery and rod casting plant marks the culmination of a three year, $250 million expansion-modernization program. The new facilities will eventually permit an annual production of 200,000 tons of marketable copper for direct sale to fabricators. The Newmont Mining Corp. subsidiary will produce and market continuous cast 5/16 in. copper redraw rod, full plate cathode copper and sheared cathode plate under its own brand name. Among the four largest in the nation, the new refinery and plant, was built at a cost of $34 million and will be fully automated. In addition, all materials used in the plant will be recycled and no waste, discard or emissions will occur.

Jan 3, 1972

By R. A. Conkling

DORSET HAGER, Tulsa, Okla. Recently we have, been doing a little work along the same lines Mr. Conkling has outlined iii his paper. I am not prepared to say that Mr. Conkling is not correct but our results do not agree with his. I think it is a question of difference in correlation and interpretation of the well records. Our cross-section of the Cushing pool does not agree with that of Mr. Conkling and we find instead of the beds thickening in the syncline, there is a tendency to thicken on top of the anticline. We took the north dome of the Cushing field, and are now trying to get all the records. It will probably be another month before we have all the data complete but our results at present do o not agree with those of Mr. Conkling at all.

Jan 4, 1917

By C. H. Li, R. J. Stokes, T. L. Johnston

A portion of the Ni3Cr-Ni3Al phase dzagram has been investigated, including the precipitation of 1 (Ni3Al) as well as the existence of ordered Y (Ni matrix), Extensive metallographic studies by electron microscopy have been carried out and X-ray diffraction diagrams have been taken at both elevated and ambient temperatures, No long-range ordering of the phase was found above 893°C (1639°F) in the compositional range investigated. The high rate of formation of the ordered ?1 phase upon quenching has been confirmed, a phenomenon which up to the present Lime has retarded the understanding of this phase diagram, Specimens with controlled amounts of ?1 exhibited up to a six-fold improvement in yield and creep strength compared with single-phase Ni-Cv-A1 alloys. MOST of the important high nickel heat-resistant alloys are related to the nickel-chromium-aluminum system. One of the important functions of the aluminum, often accompanied by titanium, is to produce a precipitate of the very fine ?1 phase (Ni3A1, X) where X may be Ti, Cr, or other elements. A number of investigators1-" have demonstrate the presence of y' in these alloys but most of their materials contained large amounts of other elements resulting in appreciable amounts of con- fusing phases such as carbides. Further clouding of the precise role of y' has been the suspected existence of an ordering reaction in the y matrix itself, ro-3,12-17 It appeared from these investigations that aluminum in Ni-Cr alloys would raise the ordering temperature of the matrix from 540°C at NisCr to 1300°C at Ni,Al. In support of this possibility, the matrix phase in the parallel Ni-Fe-A1 system is ordered to very high temperatures.1 OBJECTIVES OF THIS RESEARCH From this survey of the literature it appeared desirable to conduct an investigation of the simple Ni-Cr-A1 system using the alloys of the highest available purity to avoid the complication of foreign phases and thereby isolate the structures in the Ni-Cr-A1 system. Procedures were developed to study ? - ?o and ? - ?1 equilibria. Preliminary mechanical tests at elevated temperatures were also conducted.

Jan 1, 1962

By J. B. Austin

IN developing a consistent picture of the thermal expansion of the commercial chromium steels, which cover a range of carbon contents, it is desirable to know the expansion in the limiting case of the binary, carbon-free, iron-chromium alloys. We have, therefore, determined the thermal expansion of a series of five special alloys, ranging in chromium content from 3 to 10.5 per cent, with not more than 0.03 per cent carbon, over a temperature range extending beyond the transformation region; this low carbon content enables us to draw reasonably reliable conclusions as to the behavior of the carbon-free system. Moreover, the measure-ments serve to determine the beginning and the end of the alpha-gamma transformation; and they emphasize once more the fact that a transforma-tion temperature determined by any method in which the specimen is cooled at an appreciable rate is apt to be seriously in error, particularly if the metal contains a transformation-retarding element such as chro-mium or managanese. The lag, or undercooling, observed at the ? - a transformation is explained in terms of the influence of temperature on transformation velocity; the rather unusual shape of the ? loop is attributed to a change with temperature and with composition of the distribution of chromium between the alpha-iron and gamma-iron solid solutions. The exact composition of the alloys which were obtained through the courtesy of Dr. W. Rohn, of the Heraeus Vakuumschmelze A-G., is given in Table 1. Determinations of the linear thermal expansion and of transformation temperature were carried out in the vacuum dila-tometer previously described,1 using a rate of heating and of cooling of 3.0° to 3.5° per minute unless otherwise stated. Magnetic susceptibility, which was measured in studying the rate of transformation, was determined with a magnetic balance, which also has been described.2

Jan 1, 1935

By J. B. Austin, R. H. H. Pierce

IN developing a consistent picture of the thermal expansion of the commercial chromium steels, which cover a range of, carbon contents, it is desirable to know the expansion in the limiting case of the binary, carbon-free, iron-chromium alloys. We have, therefore, determined the thermal expansion of a series of five special alloys, ranging in chromium content from 3 to 10.5 per cent, with not more than 0.03 per cent carbon, over a temperature range extending beyond the transformation region; this low carbon content enables us to draw reasonably reliable conclusions as to the behavior of the carbon-free system. Moreover, the measurements serve to determine the beginning and the end of the alpha-gamma transformation; and they emphasize once more the fact that a transformation temperature determined by any method in which the specimen is .cooled at an appreciable rate is apt to be seriously in error, particularly if the metal contains a transformation-retarding element such as chromium or managanese. The lag, or undercooling, observed at the ?-a transformation is explained in terms of the influence of temperature on transformation velocity; the rather unusual shape of the ? loop is attributed to a change with temperature and with composition of the distribution of chromium between the alpha-iron and gamma-iron solid solutions. The exact composition of the alloys which were obtained through the courtesy of Dr. W. Rohn, of the Heraeus Vakuumschmelze A-G., is given in Table 1. Determinations of the linear thermal expansion and of transformation temperature were carried out in the vacuum dilatometer previously described,1 using a rate of heating and of cooling of 3.0° to 3.5° per minute unless otherwise stated. Magnetic susceptibility, which was measured in studying the rate of transformation, was determined with a magnetic balance, which also has. been described.2

Jan 1, 1935

By A. G. Guy

IN the course of a research on steady-state diffusion it became necessary to make diffusion calculations for a finite solid. This problem was found to be sufficiently different from the corresponding problem for the semi-infinite solid for an entirely new approach to be necessary in obtaining a useful solution. The assumption of an exponential variation of the diffusion coefficient with concentration' was no longer a practical necessity, so that the new solution offered the possibility of handling diffusion in semi-infinite solids for arbitrary variations of the diffusion coefficient with concentration. In discussing the principle on which this method of calculation is based, it is convenient to consider the relatively simple problem of one dimensional diffusion into a matrix that initially contains none of the diffusing substance. The solution of the set- ond Fick Law,?C/?t=D0?2C/?x2, for diffusion into a semi-infinite solid is3 C/C=1-F(x/2vD0t [1] where C is the concentration of the diffusing substance at a depth x cm below the surface after dif- A. G. GUY, Member AIME, and M. GOLOMB are Professor of Metollurgicol Engineering and Professor of Mathematics, respectively, Purdue University, Lafayette, Ind., A. S. YUE, formerly with Purdue University, is now with the Research Laboratory, Dow Chemical Co., Midland, Mich. TP 4505E. Manuscript, July 18,1956. fusion has occurred for t seconds; C, is the concentration of the diffusing substance at the surface of the matrix; Do is the diffusion constant, expressed in sq cm per sec; and + represents the Gauss error function. The corresponding solution for diffusion into a finite solid of thickness, 1, is conveniently written for the change in concentration, C+, at a point midway through the matrix and for times, t, great enough for the following equation to be used4 c1/2/C1=(1/2-2/?e-?2D0t/l2) [2] In Eqs. 1 and 2 the diffusion coefficient is represented by the symbol Do (rather than by D) to emphasize that these equations are valid only for constant values of D. To understand how these equations can be modified to take account of actual variations of D, such as that shown in Fig. 1, first consider the fact that for a given time of diffusion theconcentration at a given point is determined, not by the D value alone, but by the ratio x/vD0 in Eq. 1 and by a similar ratio, l2/D0 in Eq. 2. Even though in fact D varies, it is possible to keep this ratio constant by using a special coordinate system, x,, that varies with D in the appropriate manner. The necessary character of this special coordinate system can be easily visualized by imagining that

Jan 1, 1958

By F. W. Bloecher

DETERMINATION of the surface area of finely divided minerals is of interest to mineral engineers engaged in flotation, comminution, and de-watering studies. In the industrial minerals field, many materials are classified as to fineness according to their specific surface (surface area per unit weight). A method of surface area determination has been tested and used in the Richards Mineral Engineering Laboratories at M.I.T. It involves low temperature krypton adsorption measurements using the technique described by Beebe.' During the past fifteen years a number of new surface measurement techniques have been developed. Those that are broadly applicable to materials dealt with by mineral engineers include the permeability method in which a gas or liquid is passed through the sample, and the low temperature gas adsorption methods first described by Brunauer, Emmett, and Teller."" Efforts to make surface determinations from size distribution curves have long been attempted"."." but because of the uncertainty of sub-sieve size distribution and inaccuracies in screen analyses, the method is at best only a rough approximation. The most widely used gas adsorption method utilizes nitrogen gas." Nitrogen adsorption, however, is not particularly suited as a tool for most mineral engineers because the method is not applicable for surface determinations on coarse materials, that is, materials coarser than approximately 150 to 200-mesh. Other gases have been used in mineral engineering studies, particularly ethane."' lo The use of ethane gas, however, involves .a technique that is too sensitive for most mineral engineering work. The permeability method of surface area determination has the disadvantage of not being sensitive enough to detect the surface represented by minute cracks, the so-called internal surface of a particle. The low temperature krypton adsorption method described by Beebe1 utilizes apparatus and techniques that are essentially the same as those used in the ethane adsorption method."1° The surface area is calculated by the B.E.T. method."-' The krypton adsorption technique is particularly suited to the needs of the mineral engineer because: (1) The method can be used for making surface area measurements of rather coarse materials (35 to 48-mesh), as well as extremely fine materials, such as clays or colloidal slimes with specific surface that might be as high as 20 to 30 mb er g. (2) The use of krypton gas offers the advantage of low saturation pressures (2-3 mm) at the conveniently obtained liquid nitrogen temperature. Therefore the krypton vacuum system need not be designed to measure or withstand internal gas, pressures above one atmosphere as is the case with the nitrogen gas method. (3) The krypton technique offers the safety feature of employing liquid nitrogen, as contrasted to the ethane technique in which liquid oxygen is required. Furthermore, ethane vapor pressure at liquid oxygen temperatures is low (about 10 microns), and a high sensitivity McLeod gage is required for pressure readings. (4) The measurement technique with krypton gas is much simpler and faster, and the apparatus is less elaborate than that required with either nitrogen or ethane gases. Apparatus A krypton surface measurement apparatus like that used at M.I.T. is shown in Fig. 1. It is constructed of pyrex glass. A vacuum is maintained by two mercury diffusion pumps in series backed by a mechanical vacuum pump."' The vacuum thermocouple gage is used for checking the vacuum within the system. This type of gage is quite sensitive down to a pressure of 1 micron of mercury," but may be used to indicate pressures much lower than that

Jan 1, 1952

By L. D. Jaffe, J. H. Hollomon

THE effect of tempering temperature and time upon the properties of quenched steel is clearly a subject of great practical importance, as well as of considerable theoretical interest. It would be very desirable to be able to predict the properties of a quenched steel when given any selected tempering cycle, with a minimum of experimental work upon that heat or even type of steel. Two problems are involved: one consists of relating the structure obtained to the physical properties, and will not be discussed here; the other, with which this paper deals, involves the relations of time, temperature and composition with the structure obtained on tempering. Indentation hardness is perhaps the most convenient quantitative measure of the tempered structure, or of what might be called the "degree of tempering." Undoubtedly, it is not an exact measure, and in some cases (as when temper-brittleness occurs) pieces of the same quenched and tempered steel may have widely differing properties at the same hardness. However, hardness has the advantage of being simple to determine and is certainly the most widely used indication of the degree of tempering. Moreover, for fully quenched steels that are not temper-brittle and do not contain retained austenite when quenched, it appears that, in general, if the hardness of the steel is the same, the tensile and impact properties will also be identical, whether a high or a low tempering temperature is used. The tempering charts available in the metallurgical literature usually give the hardness as a function of tempering temperature for only one tempering time. However, in practice, tempering times frequently vary, and a method of converting tempering curves for one time to tempering curves for some other time would be very valuable. It is also advantageous, in determining the tempering treatment necessary for a given part, not to have to temper samples at several temperatures for the time used for the commercial tempering operation. A more satisfactory procedure would be to employ times of the order of 10 to 30 min., rather than 5 or 10 hr., and if possible to use only one temperature. Furthermore, it is frequently desirable, for reasons such as temper-brittleness,* to obtain a given hardness with short times at relatively high temperatures, and it would be convenient to be able to compute without tests the time required to produce this hardness. Remarkably few quantitative studies of the hardness of quenched steel tempered over wide ranges of temperature and time

Jan 1, 1945