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By R. W. Baldwin

As used in geophysical exploration, the term overvoltage applies to secondary voltages set up by a current into the earth which decay when the current is interrupted. These secondary effects may be measured by pick-up electrodes. The term induced polarization has often been employed to describe this same phenomenon. In its own operations Newmont Exploration Ltd. commonly uses the word pulse. The basis of this method in prospecting is that metallic particles, sulfides in particular, give a high response, whereas barren rock, with certain exceptions, gives a low response. Overvoltage has been tried in searching for many types of mineral occurrence but has been most successful in outlining the widespread disseminated mineralization associated with porphyry coppers. History:' Newmont Mining Corp. has been interested in overvoltage since 1946, when Radio Frequency Laboratories of Boonton, N. J.. drew the company's attention to phenomena observed in the laboratory. At the instigation of A. A. Brant further model studies were undertaken, and the first tests were performed in 1947. Tests at San Manuel, Ariz., in 1948 were very encouraging, clearly demonstrating that the method could be used to distinguish scattered sulfides at depth. H. 0. Seigel followed up the San Manuel work with a study to determine the phenomena involved.'

Jan 1, 1960

By C. P. Watson

Economics has been defined as the useful application of wealth or material resources. The search of alchemists in the Middle Ages for s formula by which base metals might be transmuted into gold was no more intensive than has been the search by all branches of the oil industry for methods whereby the rnatcrial resources of West Texas in the nature of sulfur-bearing oil might be usefully applied. The purpose of this paper is to present in brief space developments that are conceded to possess economic significance. History The first discovery of oil in commercial quantities in the Permian Basin of West Texas was the Westbrook field in Mitchell County in 1920. Three years later the discovery well in the Big Lake field was cornpleted as a small pumper (70 bbl.) at a depth of 3028 ft. In 1925, discovery of the Powell or World pool in Crockett County stimulated activities in the Permian Basin, further establishing the importance of the Permian limestones as sources of production. The years 1925 and 1926 were marked by a period of extensive leasing and drilling activities. At the close of 1926 more than 7,000,000 acres had been leased and discovery wells completed in the Hurdle, Hendricksand Yates fields, definitely establishing the importance of the Permian Basin as a source of production from free-flowing wells. Review of Fields The producing fields in the Permian Basin are grouped on three distinct lines of folding. These may be separately identified as the Big Lake-Powell fold; the Yates, Hurdle, and Church-McElroy area and the Winkler County development. Production is derived from a porous limestone stratigraphically uniform, encountered at depths varying from 900 to 3100 ft. Lenticular sand bodies above the lime in Howard County have resulted in the

Jan 1, 1928

By P. Somasundaran, D. W. Fuerstenau

Adsorption isotherms for dodecyl sulfonate on alumina were determined at 45°C and 25°C and the data was used for calculating the partial molar heat and entropy of adsorbed ions under various concentrations. Changes in OH and AS observed at certain concentrations agree with the postulate of interaction of surfactant ions to form two-dimensional aggregates at the solid-liquid interface. Values of the total OH and AS for the aggregation process calculated using the Clausius-Clapeyron equation is used to interpret the interactions of surfactant ions with each other as well as with the solvent molecules.

Jan 1, 1973

By M. T. Simnad, G. Derge, Ling Yang

STUDY of diffusion in molten substances is important in at least two respects. Diffusion data, combined with thermodynamic and kinetic information, throw light on the structure of the liquid state. Moreover, a knowledge of diffusion coefficients and their temperature dependence is useful in ascertaining the controlling step in many metallurgical reactions. Although diffusion measurements have been made on a number of molten salts, slags, metals, and alloys,'-'" the results available are still limited and widely scattered, especially for the high temperature melts. It is the purpose of this investigation to establish reliable procedures for the measurement of self-diffusion coefficients in high temperature melts and to use these procedures to determine the self-diffusion coefficients of iron in molten Fe-C alloys of different carbon contents. Experimental Measurement of self-diffusion coefficients in high temperature melts is usually carried out by using one of two methods. In the first, diffusion takes place between two cylindrical samples of the same material, one of which is made radioactive. The diffusion coefficient is calculated from the radioactivity penetration curve in the solidified sample after the diffusion. In the second method, samples contained in capillaries of an inert substance are immersed in an infinite reservoir of the same material. Either the material in the capillary or that in the reservoir is made radioactive and the diffusion coefficient is calculated from the change of the radioactivity of the sample in the capillary after the diffusion. The second method is simpler because a radioactivity penetration curve is not needed for the calculation of the diffusion coefficient; however,.it is valid only when no convection has occurred in the capillary during the diffusion. A radioactivity penetration curve is therefore always useful in indicating that the required conditions for the diffusion are ful- filled. Towers and Chipman" recently studied the self-diffusion of calcium and silicon in CaO-Al,O,-SiO, melts by using the capillary method. Instead of measuring the change of the radioactivity of the sample in the capillary, they autoradiographed the sample after the diffusion and calculated the diffusion coefficient from the intensity distribution of the autoradiograph. Their method is useful when the radioactive isotopes are weak ß-emitters, but is very difficult, if not impossible, to apply to cases involving strong ß or y-emitters. For such cases, sectioning of the sample according to the method of Morgan and Kitchener' may be used for the construction of the radioactivity penetration curve. The self-diffusion of iron in molten Fe-C alloys has been studied in this manner and the experimental procedures are described as follows: The diffusion apparatus is shown schematically in Fig. 1. The bath consisted of about 200 g of an Fe-C

Jan 1, 1957

By A. G. H. Anderson, Eric R. Jette

During the period from 1910 to 1920, there was a lively interest in the subject of grain growth and many papers were published, followed by interesting discussions. Questions dealing with the fundamentals of grain growth—why and how it occurs—were treated in papers by Howe,' .Jeffries,² Sauveur,² Chappell,4 Beilby,5 Mathewson and Phillips,6 Mc Adam,7 Carpenter and Elam,8 Stead and Carpenter,9 Ruder,l0 as well as others. Since that decade, much indeed has been done regarding the practical control of grain size, and it is now possible to order material having a size sperified in the American Society for Testing Materials classification. Also, one hears the term "spliced boundaries" used in connection with certain tungsten lamp filamentsl1 wherein it is important to prevent "sagging" between consecutive turns of the helix.12 This practical use of a certain knowledge as to the things that influence or even control grain growth should not be taken as an indication that the subject has been thoroughly explored and that nothing more can be learned from fundamental studies. It is with this thought in mind that a report of some observations and experiments on abnormal grain growth is believed justified. Abnormal grain growth is met with in heat-treating high-carbon steels in the austenitic range,'? in the hardening treatments of high-speed steels,14'15 and in the low-temperature annealing of strained low-carbon steels as in sheet and wire material. Entirely aside from these instances of exaggerated grain growth, which some might consider as freakish, it is thought that abnormal growth is simply a case where the growth forces and the forces tending to prevent growth are almost, but not quite, evenly balanced. Information relative to grain-growth characteristics in general may be obtained from a study of abnormal growth conditions, which may be looked upon as vantage points. Reflection will show at once that if growth forces are great in comparison to inertia or resistance to growth, many crystals start to grow and, for that reason, none becomes very large, whereas if inertia is

Jan 1, 1938

By Eric R. Jette, A. G. H. Anderson

During the period from 1910 to 1920, there was a lively interest in the subject of grain growth and many papers were published, followed by interesting discussions. Questions dealing with the fundamentals of grain growth—why and how it occurs—were treated in papers by Howe,' .Jeffries,² Sauveur,² Chappell,4 Beilby,5 Mathewson and Phillips,6 Mc Adam,7 Carpenter and Elam,8 Stead and Carpenter,9 Ruder,l0 as well as others. Since that decade, much indeed has been done regarding the practical control of grain size, and it is now possible to order material having a size sperified in the American Society for Testing Materials classification. Also, one hears the term "spliced boundaries" used in connection with certain tungsten lamp filamentsl1 wherein it is important to prevent "sagging" between consecutive turns of the helix.12 This practical use of a certain knowledge as to the things that influence or even control grain growth should not be taken as an indication that the subject has been thoroughly explored and that nothing more can be learned from fundamental studies. It is with this thought in mind that a report of some observations and experiments on abnormal grain growth is believed justified. Abnormal grain growth is met with in heat-treating high-carbon steels in the austenitic range,'? in the hardening treatments of high-speed steels,14'15 and in the low-temperature annealing of strained low-carbon steels as in sheet and wire material. Entirely aside from these instances of exaggerated grain growth, which some might consider as freakish, it is thought that abnormal growth is simply a case where the growth forces and the forces tending to prevent growth are almost, but not quite, evenly balanced. Information relative to grain-growth characteristics in general may be obtained from a study of abnormal growth conditions, which may be looked upon as vantage points. Reflection will show at once that if growth forces are great in comparison to inertia or resistance to growth, many crystals start to grow and, for that reason, none becomes very large, whereas if inertia is

Jan 1, 1938

By Joseph W. Richards

THIS method of briquetting flue-dust, or flue-dust mixed with fine ores, or, in a few exceptional cases, coke-dust, has come into large commercial use in Europe, and a small plant is already in operation in the United States. It promises to become of such great importance to the iron industry of the United States that the following description will certainly interest the majority of our pig-iron producers. Discovered in 1908, the process rests upon the observation of Dr. Schumacher that blast-furnace flue-dust, while possessing of itself no binding or cementing properties, acquires strong cementing properties if mixed with a very small amount of certain salt solutions, the amount of which is so small that the resulting cementation appears to be rather by catalytic action of the salts added than by the mass-action of such chemicals. To be more specific, fresh blast-furnace flue-dust mixed with from 5 to 10 per cent. of its weight of magnesium chloride or calcium chloride solution-that is to say, with from 0.25 to 2 per cent. of its weight of magnesium chloride or calcium chloride-acquires the property of setting within a short time, from 15 to 60 min., and forming a hard cemented briquette. Alkaline solutions appear to have no action such as described, and they even interfere, if present, with the action of the magnesium and calcium solutions. When treated in this way the flue-dust briquette sets very hard, apparently from pure excess of cementing- and setting-power. It is, therefore, possible to . mix with the flue-dust a considerable proportion of inert ore or like material, which has no setting-power by this process, and thus to make a compound briquette containing large quantities of ore mixed with flue-dust, but in which the flue-dust may be regarded as the cement or binding-material. A particularly strongly cementing flue-

May 1, 1912

By B. C. Wonsiewicz, G. Y. Chin

THE presence of deformation bands in cold-worked metals is known to influence the development of deformation textures1 but has not been considered in any theoretical treatments. At the present time the most rigorous theory of deformation textures appears to be based on Taylor's concept of homogeneous deformation of a crystal within a polycrystalline aggregate.' For each crystal the Taylor theory allows the operation of several equivalent combinations of five or more slip systems. Hence deformation bands can arise from the operation of a separate combination of slips in each of several portions within a crystal. On the other hand, a second type of band may occur as a consequence of slip on systems other than those selected on the basis on homogeneous deformation. This type appears to be associated with crystals of symmetrical orientations, such as the [loo] and [lll.] axial orientations in drawn wires of fcc single crystals studied by Ahlborn.3 In this note we propose a simple mechanism of deformation banding of the second type, and compare the theoretical results for wire drawing of [loo] and [Ill] with Ahlborn's observations. In outlini the model requires that the work to accomplish a given overall shape change by banding be less than or equal to the work to accomplish the same change by homogeneous deformation. While the work by homogeneous deformation, WH = ?T ;dri, can be calculated exactly by the equivalent methods of Taylor2 or of Bishop and Hill,4 the work by banding, WB, is less certain. The latter consists of 1) Wi, work by slip within a band, 2) Wb, work associated with formation of a boundary between bands, and 3) Wc, work to correct the difference in shape change arising from banding and homogeneous deformation. The Wi term can be evaluated explicitly for a band with an assumed set of slip systems, but a satisfactory analysis of Wb and Wc has not been obtained. Since WB = Wi + Wb + Wc WH, for banding to occur, however, a necessary condition is Wi = WH . Hence it seems reasonable to choose a band with the lowest value of Wi among competing bands consistent with Wi = WH, and then minimize Wb and Wc by arranging the physical configuration of the selected band. Wc is minimized by combining neighboring bands such that their net strain matches the macroscopic strain as closely as possible, and Wb is minimized by enforcing strain compatibility across the boundary between two neighboring bands, similar to the case of a grain boundary.5 It is realized that this procedure is not completely satisfactory, but it does seem to explain Ahlborn's observations reasonably well. The procedure is now outlined for the two corner orientations. a) [l00]. Fig. 1 shows a (100) stereographic projection. The results of the Taylor analysis for axi-symmetric flow by homogeneous deformation6 show that, while [loo] itself is unstable, the rotation of the tensile axis will nevertheless be confined to within about 15 deg from [loo]. Alternatively, less work may be expended by banding with slip on a pair of systems with primary-conjugate relationship, e.g., (ll1)[10l.I + (li1.)[110]. The latter represents minimum Wi for all possible bands.* Since there are four symmetrically

Jan 1, 1970

By George J. Conroy, James H. Green

Results of a long-term program of electrical parameter measurement in underground coal mine working sections, performed by The Pennsylvania State University under US Bureau of Mines (USBM) sponsorship, are utilized as the basis for an analysis of the electrical energy requirements during operation. A model section is hypothesized, developed from the average or most representative characteristics as determined from tabulations of the measurements. Performance factors of the model section's machine complement are then analyzed, particularly with regard to the energy required per ton of raw coal cut and delivered from the section. Results are given in kilowatt -hours per ton.

Jan 1, 1980

By A. S. Michaels, M. C. Porter, A. Stancell

Previous laboratory studies have demonstrated that the injection of small quantities of reverse wetting agents during water displacement can increase oil recovery from unconsolidated porous media.9 In the present investigation, an attempt has been made to determine more fully the effects of reverse wetting treatments and to clarify the mechanism by which increased oil recovery is effected. Water-oil displacements were performed in beds of 140-200 mesh silica sand. Hexylamine slugs (injected after 0.25 pore volume of water throughput), when adequate in size and concentration, were effective in promoting additional oil recovery. Their effectiveness increased with the quantity of amine injected. However, slugs of sufficient size and concentration to stimulate oil production at water flow rates of 34 ft/day did not do so at 4 ft/day. Visual studies in a glass grid micromodel have shown that the stimulation of oil production, via ayueous hexylamine, is a result of transient changes in the oil wettability of the pore walls. if the amine slug is of sufficient size and concentration to induce significant changes in the adhesion-tension, large continuous oil masses will be formed. if the superficial water velocity is high enough to result in rapid desorption of the amine, a favorable "wettobility gradient" may be established across the masses; under such conditions, high oil mobility is observed, and increased oil recovery results. INTRODUCTION It is generally agreed that the efficiency of oil displacement by water in porous media is limited in part by capillary forces which cause the retention of isolated masses of oil — resulting in the so-called "irreducible minimum oil saturation". Recent estimates10 indicate that there are about 220 billion bbl of petroleum in United States reservoirs which are not economically recoverable with present techniques (such as water flooding). This amounts to almost five times the known recoverable reserves. It has been recognized for some time that a suitable alteration in the water-oil interfacial tension and/or the contact angle, as measured between the water-oil interface and the solid surface, should result in better displacement efficiency. Surface active agents can be used as interfacial tension depressants to accomplish this objective,1,2,7 but unfortunately, the additional oil recovery is seldom commensurate with the treatment cost. In contrast to interfacial tension depressants, the effect of contact angle alterations on water-oil displacements has received relatively little attention in the literature. It is known that the wettability affects the displacement process.3,4,11 Displacements in water-wet systems generally result in lower residual oil saturations than those in oil-wet systems. The effect of "'transient" wettability alterations concurrent with the displacement process have been investigated by Wagner, Leach and coworkers,4,11 wherein it has been demonstrated that the establishment of water-wet conditions during water flooding of oil-wet, oil-saturated porous media is accompanied by significant increase in oil displacement efficiency. Michaels and Timminss studied the effects of transient contact angle alterations resulting from chromatographic transport of reverse wetting agents through unconsolidated sand. It was demonstrated that chromatographic transport of short-chain (C4 through C8) primary aliphatic amines can improve oil recovery and that the recovery increases with the quantity of amine injected (i.e., with either the amine concentration or the volume of the slug injected). Circumstantial evidence indicated that the increased displacement efficiency resulted primarily from transient changes in wettability of the porous medium. In the Present investigation. additional information has been obtained on the effects of reverse wetting treatments and the mechanism by which increased oil recovery is accomplished. Hexylamine slugs of varying size and concentration were chromato-

Jan 1, 1965

By Samuel M. Cassidy

The exact date of man's first use of coal is lost in antiquity. The discovery that certain black rock would burn was undoubtedly accidental and probably occurred independently and many times in the world over thousands of years. It is quite likely that these independent discoveries were made when primitive man chanced to build camp fires on exposed ledges of a black rock, then was amazed when it caught fire. The Chinese recorded the use of coal 1100 years before the Christian Era and from the Bible we learn that King Solomon was familiar with coal in what is now Syria. In Wales, there is evidence that the Bronze Age people used coal for funeral pyres, and it is known that the Romans used this fuel. There are other ancient references. So the knowledge that coal would burn, and even some uses of that knowledge, go back thousands of years. However, practical and consistent use of coal seems to date to England in the Middle Ages. COAL IN AMERICA In the Americas, there is evidence here and there of occasional use by the Indians. However, the first recorded discovery of coal, in what is now the US, was by French explorers, who reported an outcrop exposure on the Illinois River in 1679. Following this, other discoveries were made by French and British explorers, but the first recorded actual usage was in Virginia in 1702, where a French settler was granted permission to use coal for his forge. Earliest recorded commercial mining was in 1750, from the James River coalfield near Richmond, VA, a deposit now abandoned. Besides local consumption from this field, shipments were made to Philadelphia, New York, and Boston. During the Revolution this coal was of importance in the manufacture of shot and shell; so important, in fact, that the British sent an expedition in 1781 to destroy the iron works and

Jan 1, 1981

By Frank G. Snyder

INTRODUCTION Numerous deposits of lead and zinc sulfides, often accompanied by barite and fluorite, occur in carbonate host rocks throughout central and eastern United States. So similar are the deposits in broad general characteristics that they long have been classified as Mississippi Valley type. They differ widely, however, in details such as metal ratios, age of host rock, type of ore-bearing structure, and probable time of mineralization. The theories developed to explain the source and transport of the metals are many and are known to all. The deposits have been termed telethermal on the basis of their presumably shallow occurrence and the attempt to relate the metals to the classic hydro- thermal sequence. 1t is now recognized that deposits of this type can occur at any depth; the only depth limitation is thickness of the sedimentary section. Ideas on the source of the metals also have changed, A rapidly growing body of evidence suggests that the metals were brought by concentrated brines from nearby sedimentary basins. The hypothesis preferred today by many geologists postulates that the metals were deposited during the course of normal sedimentation in depositional basins of miogeosynclinal or orthogeosynclinal type. At some time after deposition of the sediments, the metals were carried out of the basins by migrating brines; the brines moved laterally and upward into structurally high areas; they entered any reservoir-like structure, either primary or secondary in origin, that happened to be available; in this reservoir, possibly in a sulfur-rich environment, the metals were precipitated as ore minerals.

Jan 1, 1970

By H. Foster Bain

FROM time to time geologists and mining engineers, impressed by the heavy demands made on our mineral reserves' by modern industry, and particularly by the steadily mounting rate of production necessary to meet that demand, have issued warnings as to the danger of exhaustion. There can be no dispute as to the fact that mineral deposits are exhaustible. New mineral, is not created to replace that taken from the earth and when a crop of mineral is once harvested another cannot be grown in the same area. The evidence of exhaustion 'of particular oreshoots, deposits, or even of whole districts is familiar to all who have mined. If one were to judge solely from the abandoned mills and prospect holes he would rightly conclude that mining is but a short-lived industry. If one were, furthermore, to assemble the data as to known reserves of almost any of the commonly used minerals, and divide them by the annual tonnage mined, he would come to the same conclusion. If, again, one were to consider the most carefully made estimates of competent men seeking to measure the earth's reserves of minerals and plot against them a projection of the curve of past consumption, he would be justified in viewing the situation with alarm.

Jan 1, 1930

By F. G. Cottrell

AS previously announced, Van. H. Manning has resigned as director of the Bureau of Mines, effective June 1, to become director of research with the newly organized American Petroleum Institute. Doctor Manning has been connected with the Department of the Interior for 34 years, having been civil engineer with the Geological Survey, from 1885 to 1910, previous to his connection with the Bureau of Mines which was organized in the latter year. Doctor Manning was appointed to an administrative position in the new Bureau under Joseph A. Holmes, its first director, and on Jan. 1, 1911, was made assistant director. On Jan. 1, 1914, when Doctor Holmes had to relinquish active

Jan 1, 1920

By AIME AIME

A COMMITTEE of the American Railroad Association, consisting of Samuel Rea, president of the Pennsylvania System, Chairman; F. D. Underwood, president of the Erie Railroad; A. T. Dice, president of the Philadelphia & Reading Railroad; E. J. Pearson, president of the New York, New Haven & Hartford Railroad; and C. H. Markham, president of the Illinois Railroad (who was represented at the meeting by J. F. Porterfield of his system), met at the headquarters of the American Institute of Mining and Metallurgical Engineers, New York, on April 6 to assist in the Coal and Coke Committee's attempt to solve the bituminous coal problem. There was a full discussion of the questions of seasonal freight rates and the purchase by the railroads during the slack months of their winter's supply of coal. As the question of fuel supply for the railroads is in the hands of the Railroad Association, as well as the coal operators, it was vital that it should be represented at this important conference. The situation from the point of view of the mine operators was presented very thoroughly. No seasonal rates were considered necessary for the year 1920, and, as this matter requires considerable thought, it will be given thorough study and worked out in detail at a subsequent meeting.

Jan 1, 1920

By R. E. Sabaski

Total grinding mill system life is dependent upon the original selections and specifications of its components: the mill, its drive, drive motor, motor control, and power system. This paper discusses the complex considerations involved and the critical decisions which must be made by the buyer, the mill manufacturer, and by the gear vendor during the proposal and ordering stages. Interrelations between the mill manufacturer and the gear vendor, application of ACMA standards, how drive standards and specifications are refined through steady-state and computer-simulated torsional analyses are included, along with correlational field testing, as demands for larger sizes challenge the current state of the art.

Jan 1, 1984

Jan 1, 1917

By M. R. J. Wyllie, Walter D. Rose

The use of electrical well logs for the quantitative determination of such reservoir parameters as connate water saturation, formation permeability and connate water salinity has recently been attracting the attention of a number of workers1,2,3,4,5. While the theory of the determination of connate water salinity from the self potential S.P. log has received rather detailed treatment, relatively little attention has been paid to the theoretical aspects involved in the quantitative interpretation of resistivity data. It is clear that if electrical well logs can be used for the quantitative evaluation of physical characteristics of reservoir rock, they will provide a valuable tool to supplement cheaply information obtained by more laborious core analysis. In certain cases it is conceivable that the coring program could be considerably curtailed if the electric log could be relied upon to give reasonably accurate quantitative information. It is our object in this paper to examine the theoretical basis of quantitative log interpretation as expressed in such well-established logging concepts as formation factor and cementation factor. It is also our object to investigate the physical aspects of the rela- tionship which is presumed to exist between resistivity index and brine saturation in reservoir rock. In particular, we will endeavor to draw attention to the fact that it is possible to express these logging concepts in terms of capillary pressure-saturation relationships, permeability and tortuosity, parameters which we will consider in this paper to be fundamentally indicative of rock texture. The probability of being able to obtain from log recordings alone the data theoretically essential to permit quantitative log interpretatiou will be examined, and consideration will also be given to the problem of formulating simple semi-empirical relationships for use in the field. THEORETICAL CONSIDERATIONS The concept of formation resistivity factor, or as it is now commonly called, formation factor, appears to have been introduced by G. E. Archie",". Formation resistivity factor as defined by Archie is the resistivity of a rock 100 per cent brine-saturated divided by the resistivity of the brine. This relationship had previously been used by physical chemists and the concept is, for example, implicit in an early treatment by Fricke7 of the conductivity of aqueous slurries. Archie was able to establish the fact that although the relationship between formation factor and porosity did not change too greatly for different rock textures, the relationship between formation factor and permeability was markedly dependent on rock texture. The relationship found by Archie between formation factor and porosity was expanded by H. Guyod8. Archie had suggested that the formation factor, F, could be expressed in terms of the porosity, F, as follows: F =F-m .... (11 where, F = effective porosity fraction of the sand, and, m = an exponent greater than about 1.3. Guyod introduced the term cementation factor for the exponent, m, since it may be qualitatively shown that formation factor for any given porosity tends to increase as the sand becomes more cemented. It would appear that the concept of m as an exponent representing the cementation in a sand is strictly only of qualitative value, since the quantitative estimation of m by means other than the determination of F and F has not been possible. Guyod suggests that m can be estimated from a visual examination of a sample of rock, but this method appears to be both arbitrary and unreliable. It can be said, however, that in intergranular reservoirs of practical interest, the range of m is from about 1.4 to 3.0. A possible explanation for the fact that m is found to lie between these limits will be offered below. The determination of formation factor is an essential preliminary to the

Jan 1, 1950

By Robert H. Richards

This truly remarkable machine was built on a preliminary scale in May, 1895. The first full-sized table was built by Mr. A. R. Wilfley, and was used in his own mill in Kokomo Colo., in May, 1896. The first table sold for installation was placed in the Puzzle mill, Breckinridge, Summit county, Colo., in August, 1896. The mill enthusiasts at first hailed it as the cure for all the ills that flesh is heir to in the milling line. A little later it was found to make losses which were serious, and on this account the table succeeded only to a limited extent in displacing the vanners of the gold-mills. Still later, mill-men in a number of districts throughout the country made special studies of the faults of the machine, and devised a number of ways of grouping supplementary machines to overcome as far as possible the losses, and at the same time retain the benefit of the extraordinarily large capacity accompanied by the production of clean concentrates for which the machine has become so justly famous. I hope to make an exhibit of some of these methods in an appendix to my book on ore-dressing which is now in preparation. These experimenters have not written up the subject, and if they possess all the facts they have not given them out for the benefit of the mining profession at large. The object of this paper is to obtain the facts and to present them so clearly that their bearing can be seen by all. To this end two complete series of tests have been planned. One (the present paper), to study concentration of galena in presence of quartz; the other (to follow shortly), to study concentration of chalcopyrite in presence of quartz. Some authorities claim that the table does its best work when treating natural products; by this phrase I mean products which have been crushed to pass through a limiting

Jan 1, 1908

By W. B. Hall, Joy D. Lewis

Mine-run ore is received at Vitro in gondola cars and fed directly to a Cedar Rapids impact crusher. Following screening, the undersize travels through a recently installed three-stage sampling plant where successive cuts are executed by conventional Geary-Jennings type cutters to produce a final sample of 1 lb per ton of raw ore fed. Crushed ore is transported to one of three storage silos or to stockpile, depending upon grade and type of amen- ability. This permits the blending of a mill feed with some degree of consistency. Final grinding is accomplished in one of two closed circuit ball mill-classifier systems allowing simultaneous processing of two basic types of ores. High acid consumers may be leached separately in the required environment. Part of the free acid remaining can then be utilized by an ore stream entering later whose component ores require much less free acid for leaching.

Jan 11, 1958