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By AIME

Burton J. Westman-Besides decreasing the diamond size, there appear to be two other approaches open to overcome excessive diamond loss and, more particularly, the rapid diamond polish that took place in this quartz-feldspar rock. First, however, a short discussion of the diamond characteristics should be made in order to discuss the situation more clearly. The West African diamonds which we can assume were used. for this drilling have two disadvantages when drilling hard, exceptionally fine-grained rocks. These are rapid polishing and, if .the bit isn't "drilled in" carefully, a tendency to damage, resulting in excessive diamond loss. The normal wear resistance of any diamond is inversely proportional to the compressive strength of the diamond, therefore only the highest grade, of diamonds free from insipient fractures should be employed. Using upwards of 90 diamonds per carat instead of the20 to 30 per carat not only decreases the total projected area of the cutting points but increases the stress per point which, in turn, causes greater depth of penetration into the rock. Considering this depth of penetration, therefore, suggests an approach other than increasing the, number of diamonds per carat and that is to decrease the actual number of diamond points (also the carat weight per bit) so that the penetrating force on an individual diamond is increased. This penetration increases the chipping or rock shearing action.

Jan 1, 1950

By R. W. Raymond

The absence of a convenient glossary- of terms connected with mining and metallurgy has long been felt by the general public. It is to meet this want, not to furnish a technical manual for experts, that the following glossary has been prepared. It originated in an attempt on my part to revise for publication the manuscript of a compilation prepared from the appendix of Yale's work on Mining Titles and one or two other sources, to serve as an appendix to a new work on mining law, about to be published by Mr. H. N. Copy, of Washington, D. C. This revision soon assumed, contrary to my original intention, the proportions of a reconstruction; and with the consent of Mr. Copp, and for the purpose of receiving from my fellow-members valuable aid, I presented my still incomplete work as a paper at the Lake Superior meeting of the Institute, inviting from any quarter suggestions of new terms or better definitions to be incorporated in the glossary before its final publication. This invitation was so widely and generously responded to, that I cannot undertake to make in this place individual acknowledgments to those members of the Institute, and professional colleagues outside of it, who have favored me with assistance and advice. The labor bestowed upon this paper since its presentation at the Lake Superior meeting has considerably exceeded that of its first preparation, as

Jan 1, 1881

By Dr. O’Neil Thomas J., Donald W. Gentry

"We can easily represent things as we wish them to be..” -Aesop INTRODUCTION The first eight chapters of this book have primarily addressed the concepts and fundamentals associated with project valuation, particularly as they apply to mining-related projects. Specific emphasis was placed on the engineering and economic parameters and estimates necessary for quantifying line items in pro forma income statements and the subsequent calculation of net annual cash flows. Given these estimates of relative benefits, costs, and annual cash flows for a project, it then becomes necessary to convert these estimates into measures of relative desirability or attractiveness. The criteria and techniques typically utilized to determine project acceptability or desirability are, then, the topics of discussion in this chapter. Before proceeding it may be advantageous to put the problem of project evaluation into proper perspective by reiterating some of the fundamental concepts developed in Chapter 1. The basic premise set forth in this book is that the objective of the firm should be to maximize its value to its owners (stockholders' wealth). This value or wealth is represented by the market price of the firm's common stock; consequently, the primary objective of the firm can be restated as one of maximizing the value (price) of the firm's common stock in the marketplace over the long term. This price, in effect, is an indicator or index of the market's perception of the company's progress and a reflection of the investment, financing, and dividend decisions made by corporate management. These three major decisions are inter- related and jointly impact the market price of the firm's stock. Therefore, if the objective of maximizing the value of the firm to its stockholders is to be achieved, an optimal combination of the three decisions will be necessary. It is important to emphasize that maximizing stockholder wealth is not the same as profit maximization or even the maximization of earnings per share. Corporate managers making decisions based on the objectives of maximizing profits and/or earnings per share must recognize that these objectives do not consider: (I) the timing or duration of expected returns, (2) the business and financial risks of the promised earnings, or (3) the dividend policy of the firm. Obviously all of these factors are of concern to the company's stockholders and will have an effect on the market value or price of the firm's common stock. Maximizing market price per share, or wealth maximization, is therefore the appropriate corporate objective and

Jan 1, 1984

By E. M. Wise

IN a previous communications the improvement in strength, harden-ability and color, occasioned by replacing gold in a typical gold-silver-copper alloy by various amounts of platinum, or palladium, was discussed. In the present paper the results of further studies upon the constitution and the nature of the hardening transformation in these alloys are pre-sented. This research may be summarized as follows: 1. The liquidus and solidus have been determined for the alloys of the palladium and platinum series. Cooling curves were utilized for deter-mining the liquidus of the palladium alloys but this method proved unsuitable for the platinum alloys so that a, novel quenching method was utilized for the latter. Both the liquidus and solidus of the palladium alloys increase steadily with the palladium content. The liquidus of the platinum alloys increases rapidly with the platinum content, while the solidus temperature increases with the platinum content up to about 14 atomic per cent platinum, but suffers no further increase with additional increments of platinum up to 20 atomic per cent at least, owing to a peritectic reaction. 2. Palladium, and even more effectively platinum, reduces the rate of grain growth. Owing to this fact and to the increase in the solidus temperature, "overheating" does little or no damage to alloys containing reasonable quantities of these elements. This is confirmed both by tensile tests and metallographic examination. 3. The excess phase present in one of the high-platinum-content alloys has been isolated and chemically analyzed and was found to consist almost wholly of platinum, gold, and copper, evidently derived from the compound AuCu, by the partial replacement of gold by platinum.

Jan 1, 1933

By Herbert Clark Hoover, Lou Henry Hoover

DIGGING of veins I have written of, and the timbering of shafts, tunnels, drifts, and other excavations, and the art of surveying. I will now speak first of all, of the iron tools with which veins and rocks are broken, then of the buckets into which the lumps of earth, rock, metal, and other excavated materials are thrown, in order that they may be drawn, conveyed, or carried out. Also, I will speak of the water vessels and drains, then of the machines of different kinds,1 and lastly of the maladies of miners. And while all these matters are being described accurately, many methods of work will be explained. There are certain iron tools which the miners designate by names of their own, and besides these, there are wedges, iron blocks, iron plates, hammers, crowbars, pikes, picks, hoes, and shovels. Of those which are especially referred to as " iron tools " there are four varieties, which are different from one another in length or thickness, but not in shape, for the upper end of all of them is broad and square, so that it can be struck by the

Jan 1, 1950

By M. A. Scheil

Austenitic stainless alloys are susceptible to stress-corrosion cracking which may occur under certain corrosion environments irrespective of their susceptibility to intergranular corrosion. Test samples are described for investigating stress-corrosion susceptibility of alloys for industrial equipment. A laboratory test using a solution of magnesium chloride boiling at 309 F. was found to produce transgranular cracks in several alloys investigated and in types 347 and 316 stainless steel tubing a residual stress of the order of 10,000 psi. was observed to initiate cracking. The susceptibility to stress-corrosion cracking as judged by the boiling magnesium chloride test indicates that alloys may be selected which will withstand a high stress in service Stressed specimens of stainless alloys included in a corrosion testing program will aid in determining the acceptibility of these fabricated alloys, when stressed, to the service conditions.

Jan 1, 1945

By Edward Steidle

NOTHING stands still. We go forward or backward. As a distinct group of educators, our immediate concern is with the preparation of young men and women for participation in the mineral industries on a professional basis. I am going to have the temerity to state emphatically that for a long time as a whole we have remained in a static position. We are now confronted with the choice of advancement or retrogression. We are still in a position to make a choice and our ultimate fate will depend upon the course of action we elect to follow. Wars always have been great catalysts and social and scientific advancements mature under military stimulus in a fraction of the time normally consumed. We are now in the midst of a conflict whose duration or final effects cannot be estimated. However, the record already demonstrates that this war as never before is a mineral war in which incentive, strategy, and outcome are directly related to the distribution and utilization of minerals. The inevitable result is a drain upon our resources now reflected in our record production and a growing public consciousness of the importance of minerals in the role of human affairs. It is evident that we must seek new mineral frontiers beyond the borders of the United States and take every other precaution to forestall a "have-not" position in the world.

Jan 1, 1943

Since the comprehensive review of the Persian fields presented by Sir John Cadman last year, operations have proceeded normally. No developments of especial importance fall to be recorded and it remains only to bring up to date the full information given at the beginning of 1933. Controlled production from the Masjid-i-Sulaiman and Haft Kel fields has been maintained at slightly higher rates than during 1932. The figures for the past five years are as follows: These represent crude oil and products piped to the coast but exclude products reinjected into the reservoir, a process that has been in continuous operation at Masjid-i-Sulaiman during the period under review. The systematic delimitation of the Haft Kel field has been continued during the past year and results have been sufficiently encouraging to justify the inception of a wider scheme for distribution of production. Drilling has been resumed recently in the Persian sector of the Naft Khaneh field, and preliminary survey work is in progress for the selection of a site for a refinery at Kermanshah arid the construction of a connecting pipe line. Investigations in connection with the scientific control of reservoir were dealt with in considerable detail in last year's review. This work has been steadily pursued during 1933 and certain of the investigations have been the subject of papers presented to the World Petroleum Congress held in London in July of last year.

Jan 1, 1934

By T. S. Lundy, J. I. Federer

A graphical method has been developed and tested for separating the effects of grain boundary and lattice diffusion in polycrystalline materials. The method is based on the assumptions that for unidirectional diffusion from a plane source of radioactive material, the penetration of activity far into the specimen from the source is due solely to grain-boundary effects, and 2) pure grain-boundary penetration is described by a linear plot of log activity vs the perpendicular distance x from the source. The former is based on the fact that at any temperature the grain-boundary diffusion coefficient is always very large relative to the lattice diffusion coefficient; and the latter is based on the derivation of Fisher.1 Using these criteria along with appropriate penetration data (in this case, data for the diffusion of Cb95 in pressed and sintered UO2) one first plots the data as log activity vs x2 and as log activity vs x, as shown by curves 1 and 2, respectively, in Fig. 1. A tangent line to curve 2 for large x (curve 3) is then transferred to the x2 plot as curve 4. The subtraction of curve 4 from curve 1 yields curve 5 which represents only lattice diffusion and may therefore be related to the diffusion coefficient by using the appropriate solution to Fick's second law. It should be noted that the method has inherent inaccuracies for small and large values of x2 and only the subtraction at intermediate values can be used. For the illustrated specimen the calculated diffusion coefficient is 3.4 X 10-11 sq cm per sec at1445°C while data using a single crystal of UO2 at the same temperature yielded a value of 2.9 x 10-11 sq cm per sec.2 The same method of subtracting grain-boundary diffusion effects to obtain lattice diffusion coefficients has been successfully used to determine self-diffusion coefficients of Th230 in polycrystalline thoria.

Jan 1, 1962

By D. I. Cameron

A graphical method has been developed and tested for separating the effects of grain boundary and lattice diffusion in polycrystalline materials. The method is based on the assumptions that for unidirectional diffusion from a plane source of radioactive material, the penetration of activity far into the specimen from the source is due solely to grain-boundary effects, and 2) pure grain-boundary penetration is described by a linear plot of log activity vs the perpendicular distance x from the source. The former is based on the fact that at any temperature the grain-boundary diffusion coefficient is always very large relative to the lattice diffusion coefficient; and the latter is based on the derivation of Fisher.1 Using these criteria along with appropriate penetration data (in this case, data for the diffusion of Cb95 in pressed and sintered UO2) one first plots the data as log activity vs x2 and as log activity vs x, as shown by curves 1 and 2, respectively, in Fig. 1. A tangent line to curve 2 for large x (curve 3) is then transferred to the x2 plot as curve 4. The subtraction of curve 4 from curve 1 yields curve 5 which represents only lattice diffusion and may therefore be related to the diffusion coefficient by using the appropriate solution to Fick's second law. It should be noted that the method has inherent inaccuracies for small and large values of x2 and only the subtraction at intermediate values can be used. For the illustrated specimen the calculated diffusion coefficient is 3.4 X 10-11 sq cm per sec at 1445°C while data using a single crystal of UO2 at the same temperature yielded a value of 2.9 x 10-11 sq cm per sec.2 The same method of subtracting grain-boundary diffusion effects to obtain lattice diffusion coefficients has been successfully used to determine self-diffusion coefficients of Th230 in polycrystal- line thoria.

Jan 1, 1962

By O. T. Berge

Development and production from open cut mines continued its vigorous growth trend during the year 1968. Material handling and transportation were again exposed to the use of larger equipment with shovels, trucks and front end loaders leading the way. Highlights of World Mining Activities Africa: The Anglo American Corp. opened a new high-grade copper mine in Zambia during the year. In Angola, the Companhia Minera do Lobita planned a 3 million ton iron ore production for 1968 from new mines which will ultimately produce 5 million tons per year. A feasibility study of Bethlehem Steel Co., for the development of large high- grade iron ore reserves in Gabon, was in final stages of completion this year and Pickands Mather and Co. continued its investigation of iron ore deposits along the Ivory Coast.

Jan 2, 1969

By Vsevolod Krivobok

THE re-crystallization of metals has been the subject of much scientific investigation, some of which has resulted in a better understanding of this extremely important and interesting phenomenon. Unfortunately, while many have propounded theories of re-crystallization, but a few have presented experimental evidence as to how it takes place. If this can be determined the question, why re-crystallization occurs, may be answered more definitely. Re-crystallization in single phase metals consists of a complete rearrangement and re-sizing of the grains, of which the structure is composed, while the type of structure remains the same. That is to say, if the structure before re-crystallization is composed of a number of polyhedral grains of different shape and size, a particular spot after re-crystallization will be seen to consist of grains in no way different from the original except in size and shape. The re-crystallized grains may be smaller or larger, depending on the treatment received; and, while the re-crystallization may be brought about by means of heat treatment only in passing through a critical range, yet it is common knowledge that single phase metals subjected to cold working are possessed of a tendency toward re-crystallization, even if the heating does not reach critical range. The study of re-crystallization would, of course, be much easier if we had single crystals of any metal as the original material with which to study the phenomenon of re-crystallization, since it would permit the observation of structural changes at what amounts to enormous magnification, by changing the scale of the specimen. In metals of more normal grain size the crystal boundaries introduce complications, but the process, it may be assumed, is essentially the same. Such an opportunity

Jan 2, 1926

By Frank G. Snyder

The Precambrian of Midcontinent United States includes a metamorphic belt of probable Middle Precambrian age, a belt of Keweenawan volcanics and sediments, and widespread igneous activity that extended from Iowa to Texas. Most of the present structural configuration of the Midcontinent was developed by epeirogenic movements during the Paleozoic. The dominant elements are basins and arches. Three major metallogenic provinces occur in the Midcontinent. They include the Missouri Precambrian iron ores, the Lake Superior copper ores, and the Mississippi Valley lead-zincbarite- fluorite deposits. Several large iron deposits, occurring in rhyolite and andesite host rocks, are known. Both discordant massive bodies and replacement- type bodies occur. The iron deposits are believed to have been formed during the period of igneous activity. They are essentially the same age as the volcanics and older than the granites that intrude the volcanics. The Lake Superior copper ores include two established districts, the Keweenawan district and White Pine, and the copper-nickel deposits in the Duluth gabbro. The lead-zinc-barite-fluorite deposits include four major districts, Southeast Missouri, Upper Mississippi Valley, Tri-State, and Illinois-Kentucky, and at least eight minor districts. Ore may occur in stratiform deposits and in veins. The major districts all contain stratiform deposits, but several have produced appreciable quantities of vein ore. Only vein deposits are known in some of the smaller districts. The major features of all districts can be catalogued in terms of host rocks, structural patterns of districts, types of ore-bearing structures, and mineralogical characteristics. From these features, a Mississippi Valley type ore body, in its type area, can be defined.

Jan 1, 1968

By A. H. Geisler

The correlation of property changes during precipitation with structure has progressed, sometimes rapidly but other times more slowly, since the fundamental discovery of Merica, waltenberg and Scott.1 The predominent factor that hampered the progress has been limitations imposed by the various detection methods. Refiments in x ray diffraction tech-niques and in metallographic methods, which have been extended by the electron microscope, have contributed new information within the last few years. These permit an extension of the theory as proposed by Mehl and Jetter in 1940'2 Now that a sufficient number of alloys has been investigated to establish a general mechanism of the precipitation process, a correlation of the facts into a generally applicable theory of age-hardening is both warranted and desirable. The purpose of the paper is to provide an orderly correlation of the phenomenological facts of precipitation hardening. Speculation 011 mechanism of hardening will be confined to that consistent with existing theories of hardening, Age-hardening accompanies the formation of a new structure, the precipitate, as provided by a11 alloy system ill which solid solubility decreases with decreasing temperature. Upon this premise alone all such systems would be expected to include age-hardenable alloys. Alas, this is not always the case. Few attempts have been made to explain the variable degree of age-hardening among different alloys or to explain the influence of small alloying additions upon the hardening. Dispersion hardening as originally postulated3 is not adequate.* Coherency hardening—the term that will be used to distinguish the properties of a two-phase mixture in the unique and unstable transition state at which the phases are strained into precise atomic registry (continuity or coherency) in planes

Jan 1, 1949

Jan 1, 1888

By Peter R. Morris, Alan J. Heckler

THREE angles are required to specify the orientation of a crystallite with respect to a physical reference frame. The distribution of crystallite orientations in a polycrystal is thus a function of three angular variables. The most widely used experimental techniques for studying orientation in polycrystals lead directly to the pole figure representation, i.e., the distribution of the poles of certain crystallographic planes in terms of two angular variables. In recent years1-5 methods have been developed which permit determination of the (three-angle) crystallite orientation distribution from several (two-angle) pole figure distributions. In this work Roe's method has been applied to the study of orientation in hcp materials. The method is illustrated for commercial purity titanium sheet (Ti-70) which was cold rolled (65 pct reduction), annealed at 1450°F for 3 min, and air cooled. The grain shape was observed to be equiaxed after this treatment. EFFECTS OF PHYSICAL, CRYSTALLOGRAPHIC SYMMETRY In Roe's method the crystallite orientation distribution, w(?,?,F), is expanded in a series of generalized spherical harmonics 11(?,?,F) = E E E W^Zirmtye-tote-in* [l] 1=o ,,,=-I ,,=-I where { = cos 8. The set of Euler angles employed here is illustrated in Fig. 1. The axis for each rotation is denoted by a double arrowhead. The positive sense of each rotation is that of a right-handed screw advancing in the direction of the double arrowhead. The X, Y, and Z directions correspond to the rolling direction, cross direction, and normal direction, respectively. In the initial orientation (10.O), (12.O), and (00 . 1) planes are perpendicular to the X, Y, and Z directions, respectively. The IC/ rotation about the Z axis is carried out first by rotating X into X', Y into Y', and leaving 2 unchanged, i.e., Z' = Z. The 8 rotation about the Y' axis is carried out second by rotating X' into X", 2' into Z", and leaving Y' unchanged, i.e., Y" = Y'. The I$ rotation about the Z" axis is carried out last by rotating X" into X"', Y into Y"', and leaving 2" unchanged, i.e., 2"' = 2". Any specified orientation of the X'", Y'", and Z'" crystal-fixed axis system relative to the X. Y, and Z physical axes (rolling direction, transverse direction, and sheet normal direction, respectively) can be obtained by appropriate IC/, 8, and (F rotations. The Zl,, of Eq. [l] are the Jacobi polynomials, augmented by the square root of the weight function. The Zl,, are symmetric in m,n, i.e., Zl,,= Zlnm. For orthotropic physical symmetry and hexagonal crystallographic symmetry, the coefficients, W!,,, of the series are all real, W!mn = Wzfi, = Wlm~ = Wlfi~, 1 and m are even and n is restricted to 6k, where k = ...,-2,-1, 0, 1, 2, .-.. The determination of the Wlmn from pole figure data has been previously described.'~~ The Zl,, may be written in multiple angle form

Jan 1, 1970

By F. J. Plecity, J. T. Michalak, W. C. Leslie

W. M. Williams (McGill University)-The authors are to be congratulated on completing this detailed investigation of recrystallization behavior. The present writer has recently completed some research at the University of Toronto on the recrystallization and grain growth behavior of a number of "pure" irons, and he would like to take issue with the authors' contention that recrystallization cannot be followed by means of hardness measurements. Two series of specimens of Ferrovac E, a com- mercially available iron, were annealed to complete recrystallization at 525" and 620" C, measurements being made both of Rockwell hardness and of volume percent recrystallized as a function of annealing time. Good correlation was found between these two quantities and, following the earlier practice of Cook and Richards for copper, hardness measurements were used in an extensive investigation of recrystallization. No anomalous behavior was observed as a result of this practice. Specimens which showed complete softening always showed, (metallographically and by X-rays), completely re-crystallized structures. These observations do not, of course, detract in the least from the results of the work under discus-

Jan 1, 1962

By A. J. Stosick, J. R. Hoffman, E. Rudy, St. Windisch

The binary alloy system Mo-C zoas investigated by means of X-ray, metallog/aphic, thermoanalytical, and melting-point techniques on chemically analyzed specimens. The system, Fig. 39, is characterized by three congruently melting, intermediate phases, Mo2C, n MoCi-x, and aMoC1-,, of which only Mo,C is stable at temperatures below 1650°C. Substoichio-metrzc (~32.5 at. pct C) dimolybdenum carbide undergoes a homogeneous sublattice order-disorder transformation at temperatures of approximately 1400°C, whereas hyperstoichiorrletric compositions undergo a discontinuous Phase change. The order-disorder transitions in the Me, C phases are discussed in terms of the structural changes involved in the transformation processes and the absence of long-range sublattice coherency in stoichiometric or hyperstoiclziomet-ric compositions attributed to the impossibility of obtaining long-range order in a linear chain of alternating carbon atoms and vacancies. From the experimental phase relutionships and the known thermody-namic data for Mo2 C, limits for the free energies of formation for the high-temperature phases r) MoC1-, and aMoC1-, are deriued and found to be in good agreement with data previously obtained from phase equilibria in ternary metal-carbon systems. IN the course of studies of the high-temperature phase relationships in ternary systems of refractory transition metals with carbon,' a number of inconsistencies found in previous work necessitated a reex-amination of some of the related metal-carbon binaries. A reassessment of the binary system data also seemed

Jan 1, 1968

J. H. HEGINBOTHAM, a, metallurgist of the General Engineering Co., talked on "Current Milling Practice at Kirkland Lake," at the December meeting of the Utah Section. The ore is enough alike through the whole district so that some generalizations and comparisons may be made. The question as to whether or not the flotation process should be used in the flowsheet for extracting gold by cyanide solutions is still being vigorously debated, and it will seemingly need some years for a definite answer to be given. Most of the gold is either free, though much of it is finely dispersed in quartz, or occurs with pyrite. At times there may be 2 per cent of telluride compounds in the ore, but the amount of gold telluride present is small and has not been definitely established. It has been shown by Dr. Haultain and others that though gold tellurides may be so finely disseminated that it is necessary to grind the ore exceedingly fine, the compounds themselves are not difficultly soluble. (An increase in temperature helps to dissolve tellurides, and also to settle pulps.) It is likely that if the ore were ground through 400 mesh, practically all of the gold would be soluble. As it is, with 96 to 98 per cent of the ore ground to minus 200 mesh, and some 70 per cent minus 325, the cost of

Jan 1, 1934

By John Griffen

This paper records over twenty years' experience with the use of the Rheolaveur system in the United States, showing its ability to meet changing conditions caused by the dirtier mine output of present-day mechanical mining methods. Data are given on size ranges handled, number and capacity of units installed, maintenance experience, and operating results on two-product and three-product separations. IT is not the purpose of this paper to discuss the principles employed in the Rheolaveur system of fine-coal cleaning as these have been fully covered in the technical literature of the Institute."2 Rather, our purpose will be to record the highlights of over 20 years' experience in the United States with Rheolaveur fine-coal launders, which will indicate their capabilities and costs of cleaning and their adaptability to meet the changing conditions caused by present-day mechanical mining methods. Rheolaveur fine-coal launders are used in the United States to treat a wide variety of size ranges of fine coal, the coarsest being 1/2 in. to 0 and the finest about 1/8 in. to 0. In Europe feeds as coarse as 5/8 in. and as small as 1/2 mm (28-mesh) to 0 are being cleaned. The size ranges usually handled in this country are 3/8 to 1/4-in. round to 0. Thirty five units with a combined hourly feed capacity of 3200 tph have been installed in the United States. Individual units are cleaning as little as 25 tph, while others are cleaning as much as 200 tph. Rheolaveur fine-coal launders offer cleaning units of high capacity and are outstanding in requiring a minimum of building space per ton of input. Experience has shown that maintenance costs are low. Several installations were made in the Pittsburgh district from 1928 to 1930, and since that time operation has been largely two shifts per day. Minor repairs to liner plates and Rheo boxes have been required during the intervening years, but no major replacement of launders was required until 1947 and 1948. At one of these plants, launders operated for 17 years before they were replaced and during that period over 26,000,000 tons of —5/16-in. coal were cleaned. The effect of the much dirtier raw coal produced by mechanical loading of the Pittsburgh seam is shown by the following tests. The data in table I summarize the performance of a Rheo fine-coal unit when cleaning hand-loaded raw coal. The —4-in. raw coal fed to the cleaning plant analyzed only 8.16 pct ash and 1.31 pct sulphur and contained 4.6 pct sink, 1.55 sp gr. Two years later, in 1945, mechanically-loaded coal from the same mine was cleaned in the same plant. The feed, —4 in., then analyzed 20.10 pct ash and 1.53 pct sulphur and contained 20.2 pct sink, 1.55 sp gr. The performance of the Rheo fine-coal unit when cleaning this coal is given in table 11. It will be noted that the +48-mesh coal is cleaned almost as thoroughly as in table I. The large amount of high-ash slimes produced from the dirtier feed are responsible for the higher ash of —--48-mesh washed coal in table 11. In this plant the Rheo fine-coal unit did not get the full load of refuse resulting from mechanical

Jan 1, 1951