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By W. M. Bertholf

To establish the minimum or break-even efficiency of a preparation plant it is necessary to determine the ratio of production costs per ton of run-of-mine coal to sale price per ton of clean coal. This ratio is then divided by the percentage of plant recovery. Assume, for example, that washability data indicate that 80 pct of the run-of-mine coal may be recovered as clean coal selling for $5.50 per ton. If the same plant incurs $4.00 per ton mining costs and $0.25 per ton preparation costs, the cost to sale price ratio would be 4.25/5.50, or 77.3 pct. Since the plant is capable of recovering 80 pct of the run-of-mine coal the minimum plant efficiency would be 77.3/80, or 96.6 pct. If the plant efficiency were increased to 100 pct the limit on preparation costs would be increased to $0.40. Therefore, the washing operation must be accomplished at a cost of $0.25 to $0.40 per ton and the efficiency must be 96.6 pct or higher. By plotting a curve of efficiency vs preparation costs and taking into consideration the plant cost, feed rate, operating costs, and yields of the various flowsheets it is possible to select a financially sound process. Table I classifies preparation processes according to their nature of separation. It must be remembered that what is thought to be ideal does not always prove practical under actual operation. An outstanding example is the work done on the plunger-type jig. It was determined by the law of equivalence that this unit could treat satisfactorily only sizes differing by no more than a ratio of 2. Yet these same plunger-type jigs are successfully treating sizes considerably greater than this ratio.

Jan 12, 1957

By R. A. Bowen

The Montreal mine, operated by the Montreal Mining Co., is four miles west of Ironwood, Mich., in Iron County, Wisconsin. It is the westernmost producing property on the Gogebic Iron Range of the Lake Superior district. Its production is 4000 tons of hematite per day from an average depth of 2300 ft. This tonnage is hoisted through a five-compartment vertical shaft. Several mining methods are in use but in the larger orebodies the method is sublevel caving. ORE Occurrence and Chaeacteristics The main orebodies of the Montreal mine lie in eastward-pitching troughs formed by the intersections of intrusive dikes with impervious members of the iron formation. The formation has an average width of 425 ft., strikes east and west and dips north at approximately 62. The dikes dip south at 45° and bear north 20' from the strike of the formation, making the intersections with various members pitch east at 16°. The dikes are not continuous across the formation but are interrupted by a longitudinal bedding fault, which has a throw of 380 ft. vertically and 885 ft. horizontally. North of the fault zone the formation is called "hanging," south it is called "footwall" formation. The faulting has created two ore-bearing horizons; viz., at the intersection of banging dikes with the slate members and the foot dikes with the quartzite footwall. In each formation the main ore-bearing member consists of wavy beds of hard chert interlaid with hematite. In the most productive part of the mine, where the sublevel caving method is employed, a hanging-formation dike lies in juxtaposition with a footwall dike and the iron formation carries ore in certain sections from the quartzite footwall to the hanging dike. Here a horizontal section of the orebody may be 300 to 400 ft. wide for a length of 150 ft. or more and tail out lengthwise in both the foot and hanging formations. The footwall ore section is much longer than the hanging wall because of the orebody's greater height above the "pitching dike."

Jan 1, 1940

By Roy Neal

THERE are two main sources of the water that floods productive oil or gas sands. The water may rise from the lower depths of the producing stratum, or it may come from beds above or below the oil-bearing formation. Usually the recovery of oil is decreased by water entering the oil sands, and most oil-field waters, especially those of deep wells, tend to foster the formation of an emulsion, which is expensive to treat. This paper deals with a method of distinguishing between waters that encroach upon oil-bearing, beds from sources in the same stratum and waters .that reach the oil sands from horizons above. In order to remedy effectually water difficulties in oil and gas wells, it is absolutely necessary to determine the source of the invading water. Sometimes evidence such as the structural relations between the strata penetrated by neighboring wells and those found in the well under investigation is not adequate; also, data from drill logs and well records, from mechanical tests made on the wells by plugs, testers, drilling tools, etc., and from tests by chemical indicators such as eosin and Venetian red, may he unsatisfactory, for such data may fail to locate the source of the infiltrating waters. As a resort in such cases, the application of chemical analyses, that is, the comparison of an analysis of the water in, question with that of typical waters from the various water horizons in that particular district, has in certain instances proved of value. This method has been used to advantage in the Westside Coalinga field of California, where the source of water may be fairly definitely determined from its composition. The chief conclusions concerning the chemistry of the oil-field waters in California by G. S. Rogers1 are: "Oil-field water is not necessarily salty, as is generally believed, and may not be even slightly salty to the taste. The degree of concentration of chloride in such water is governed primarily by local conditions and is not affected by the position

Jan 1, 1919

By R. A. Bowen

The Montreal mine, operated by the Montreal Mining Co., is four miles west of Ironwood, Mich., in Iron County, Wisconsin. It is the westernmost producing property on the Gogebic Iron Range of the Lake Superior district. Its production is 4000 tons of hematite per day from an average depth of 2300 ft. This tonnage is hoisted through a five-compartment vertical shaft. Several mining methods are in use but in the larger orebodies the method is sublevel caving. ORE Occurrence and Chaeacteristics The main orebodies of the Montreal mine lie in eastward-pitching troughs formed by the intersections of intrusive dikes with impervious members of the iron formation. The formation has an average width of 425 ft., strikes east and west and dips north at approximately 62. The dikes dip south at 45° and bear north 20' from the strike of the formation, making the intersections with various members pitch east at 16°. The dikes are not continuous across the formation but are interrupted by a longitudinal bedding fault, which has a throw of 380 ft. vertically and 885 ft. horizontally. North of the fault zone the formation is called "hanging," south it is called "footwall" formation. The faulting has created two ore-bearing horizons; viz., at the intersection of banging dikes with the slate members and the foot dikes with the quartzite footwall. In each formation the main ore-bearing member consists of wavy beds of hard chert interlaid with hematite. In the most productive part of the mine, where the sublevel caving method is employed, a hanging-formation dike lies in juxtaposition with a footwall dike and the iron formation carries ore in certain sections from the quartzite footwall to the hanging dike. Here a horizontal section of the orebody may be 300 to 400 ft. wide for a length of 150 ft. or more and tail out lengthwise in both the foot and hanging formations. The footwall ore section is much longer than the hanging wall because of the orebody's greater height above the "pitching dike."

Jan 1, 1940

By C. C. Griggs

From its inception, a limestone quarry or mine should be under the direction of a capable engineer. Before it becomes a reality, he should outlinc the future results, plan the most economical methods for moving the materials and the most efficient equipment, and pilot the undertaking along the narrow pathway of success, avoiding the pitfalls of uneconomical production and the precipitous walls of scanty profits. Inspection of successful limestone properties shows that all have had difficult engineering problems, the solution of which have required keen engineering ability. In approaching a subject of this nature, it is logical to follow the progress of the limestone operation from its inception to the end, as reflecting the engineering required. There are four major divisions: Investigation, equipment, development, and operation. Investigation On the reliability of the engineer's estimates and the soundness of his judgment depend the success or failure of the enterprise. When one visits a prosperous concern, realizes that the limestone is of a constant chemical composition, sees the mechanical devices installed, and watches the output leave the plant in trains of railroad cars or fleets of vessels, he may overlook the fact that in the remote past this great creation was born in some man's brain and evolved through competent engineering. Many factors must be considered before a promoter could procure the money necessary to launch such an enterprise, for a conservative banker will only recommend a successful producer while the promoter must provide funds on his own and his engineer's judgment. An engineering investigation must be made preliminary to expenditure for actual operation, which, for a limestone deposit, would' naturally embrace such subjects as : ' Readily available. 1. Tonnage available........ Possibly available. Chemical analysis.

Jan 1, 1925

By Francois E. Heuze

The Crestmore Mine of the American Cement Company lies at the eastern end of the Jurupa Mountains, 50 miles east of Los Angeles. Originally, a quarry was opened in 1908 for "limestone" used in the manufacture of cement. The mining operations eventually went underground employing first a modified system of block caving and later the "room and pillar" scheme. The limestones are relatively small roof pendants preserved in an enveloping and intrusive quartz diorite. They occur as two irregular lenticular bodies roughly parallel at the top and tending towards convergence at depth. Their dip varies between 25 and 30 degrees E. The presently mined lower bed, Chino limestone, is typically composed of alternating bands a few inches to a few feet thick of medium to coarsely granular white crystalline limestone and somewhat yellowish limestone (brucite marble). A "room and pillar" scheme of mining is currently employed in the lower body of the Crestmore Mine. The levels are horizontal and access is provided by a spiraling road starting in the old quarry. The present depth of operations is an average 750 ft below the surface. Fig. 1 gives a three-dimensional general sketch of the mine. The long axis of the rooms is in an E-W direction, normal to the strike of the beds. Fig. 2 is a horizontal map of the 130 level, the deepest level mined presently. It is in this level that most of the in-situ investigations have been conducted. The present investigation was made possible by a non-restrictive grant of the American Cement Company to the University of California. The program included a series of in-situ tests using flat-jacks, plate bearing,

Jan 1, 1968

By C. D. King

DURING the 30-year period spanned by these annual Howe Memorial presentations, many lecturers could proudly claim a kinship either as a student or an associate of the man whose memory we honor. Although it has been my good fortune to have attended many of these annual lectures, it was not my privilege to have known Henry Marion Howe personally. However, his great repute as teacher and scientist was known to all undergraduates of my day and the later years have enhanced my appreciation of his wisdom and foresight. Those who knew him well have said he derived particular pleasure from speculations on the future world of metallurgy. For this reason, I feel that perhaps he would not be unsympathetic to a lecture in his honor which departs from the highly instructive scientific presentations made in the past by so many able Howe Memorial lecturers, and which is concerned more with the practical phases of various steelmak-ing processes and some speculations on their future form and relative importance. The word "revolutionary" is frequently applied to each seemingly important improvement in the production of steel ingots, but in retrospect these changes, impressive as they appear at the time, are merely steps of progress. In the hundred years from the inception of tonnage steelmaking, only three processes can be truly classified as revolutionary. They are the pneumatic process, known in this country as the bessemer process; the reverberatory method called the open hearth process; and, the electric furnace process. There have been many variations and combinations of the three fundamental methods, but they remain truly the only revolutionary methods in steelmaking since its early history. Everything else has been evolutionary, in effect. doing the same things that we have done in the past but doing them better, correcting our errors through experience, and slowly but inevitably reaching a higher state of accomplishment. It has often been said that coming events cast their shadows before, and the production of steel ingots is no exception. As a result of the unrelenting demands of World War I1 and the years that followed, truly impressive progress has been made in steel ingot production. The incessant pressure for immediate results during this period required the employment of initiative and daring, as in few past decades, and many developments were brought to fruition. Of equal importance is the possible effect on future steelmaking methods of the many ideas initiated but still in formative stages. Fig. 1 portrays ingot production in the United States by the three fundamental processes over a period of 75 years and is interesting because it poses some questions as to future trends. The early ascendancy of the bessemer, its replacement in importance by the open hearth process, the amazing growth of the latter, and the recent challenge of the electric furnace are evident from the chart. Management is fully aware of these changes, but is even more interested in the future trends. Our concepts of the relative importance of the more recent developments and their possible effect on future processes may perhaps be best exemplified by a specific, hypothetical problem. Let us assume management is contemplating a new ingot producing plant with an output of 100,000 net tons per month, located in an area where some purchased scrap may be obtained but where by far the largest component will be own-produced blast furnace iron. Management requires a process or combination of processes which will yield highly uniform quality characteristics in the ingot form, and represent the soundest selection in investment and operating cost. Under these conditions, the obvious selection for the past four decades has been the open hearth process but, in view of more recent developments, management may believe that it is no longer permissible to disregard other possibilities with impunity. Accordingly, to be assured of the best possible selection, they request that you review not only the possibilities of utilizing the conventional open hearth, duplex, bessemer, and electric furnace methods, but also the more recent developments, such as the turbo-hearth, the Linz-Donawitz method, the Perrin modifications, and other possibilities. With this background, one might then appraise the relative importance of these methods to meet a specific need, and concurrently speculate on the forms that future ingot processes will assume and the relative importance of these processes.

Jan 1, 1955

By R. V. Norris

The removal of mine-water by hoisting in tanks instead of pumping, while somewhat a reversion to the methods of the ancients, has come very rapidly into favor in the anthracite region of Pennsylvania during the past few years. In fact, so much so, that at the present time there are at least eight large collieries at which all the water is hoisted, and six more plants are in preparation. The particulars of the plants in operation and under construction, as far as decided on, are given in the tables on pages 107 and 108. Besides these, the Delaware, Lackawanna and Western R.R. Co. is constructing a hoist of large capacity for a depth approximating 500 feet, to be located in the Keyser Valley, near Scranton. The hoists will be driven by electric motors, geared directly to the sheaves. The Lehigh Valley Coal Company is planning a large hoist for the Packer collieries in the Shenandoah district, but no work has been done on this as yet. The earliest regular hoisting, I believe, mas done by means of semi-cylindrical tanks (Fig. 1) at the Nanticoke collieries of the Susquehanna Coal Company. These tanks were attached under the regular shaft-carriages, taking in water through six large clack-valves in the bottom, and discharging through an endgate opened by a lever which was operated by a guide-piece on the shaft head-frame. These tanks were designed July, 1880, by the late J. H. Bowden, one of the very early members of the Institute. Similar tanks are still used in emergencies at the Nos. 1, 2, 3 and 6 shafts of the company. The objections to. their use were: that water could only be hoisted during the night-shift, or when the shafts were not in use for hoisting coal, thus requiring a very large sump, and greatly limiting the water capacity of the plants; that the alternate wetting and drying

Jan 1, 1904

By D. H. Davis

HAND picking was the earliest form of coal preparation, first practiced to improve the outward appearance of the coal being loaded and to remove any pieces that might appear objection- able to the buyer. It is still extensively practiced on the plus 1-in. sizes, and particularly on the plus 4-in. and larger sizes. The percentage of ash reduction that can be obtained by hand picking depends entirely upon the amount of free impurity occurring in the coal. In a particularly dirty seam, where a considerable quantity of rock occurs with the coal as mined, hand picking produces sizable reductions in ash. If the coal is prepared clean at the working face hand picking is a final check; in some cases, on the smaller sizes, it is practiced only to show that an effort is being made to prepare a clean product. Because of the variety and different methods of handling coal, the early plants were not always adapted for efficient hand picking. At most mines an attempt is made to remove the visual impurities at one or more of the following places in the surface plant:2 (1) in the tipple during screening; (2) on picking band, belt, or shaking conveyors;. (3) during the loading of the coal as it goes into the railroad car. Whatever the physical arrangements of the plant may be, the usual practice is to run the coal over the screen, picking table or boom at such a rate that each-piece of impurity is exposed to the view of the picker. Coal should be uniformly sized and spread out on the table so as not to exceed one particle in depth. The flow should be even in tonnage and the speed of travel should be from 30 to 60 ft. per minute and not 'exceed 80 ft. per minute. The dirtier the coal, the slower the speed required for a fixed number of pickers. Actually, picking capacity depends on the number of particles per minute that can be picked out and-rejected. The percentage of impurity removed is determined by this and the average weight of piece rejected. Handling a mixture of sizes from nut to the largest lump over the same picking table or conveyor is not conducive to efficient separation by hand picking because the lump hides the smaller impurities. Picking tables should not exceed 5 ft, in width, so that a picker on either side will be able to remove impurities from the center of

Jan 1, 1943

By H. H. Hasler

THE mining and removal of coal from two or more beds, either simultaneously or consecutively, in vertically adjacent areas have always been matters of concern to mine operators from both operating and recovery points of view. However, with the progressive introduction and use of electrical and mechanical facilities, such problems assume even greater proportions. In this paper typical cases occuring in Cambia County, Pa., are given and procedures whereby such problems may be .greatly reduced, if not entirely eliminated, are suggested. Throughout a considerable portion of the Central Pennsylvania bituminous coal region, particularly in Cambria County (Fig. I), the portion of the region to which references in this paper are made, large areas are encountered where two or more beds of coal occur and have been mined extensively since the earliest days of mining in the county. Generally, operations were commenced in one bed of coal on a property, following which, as conditions appeared to warrant, operations were commenced in another bed or beds on the same property, in some instances by the same operator. Operating results by no means have been uniformly successful, as the following review of some typical cases indicates, partly because of lack of experience in earlier cases and in certain later cases to disregard for the experiences of earlier operators. It is suggested that repetitions of such failures may be reduced largely, if not eliminated entirely, by adherence to a few basic principles founded upon past experiences. Geology and Stratigraphy The geology, stratigraphy, and relief of almost all of Cambria County have been studied and reported at length by the U. S. Geological Survey in its Johnstown, Ebensburg and Barnesboro-Patton Folios and other publications, by the Pennsylvania Geological Survey and by various individuals. All exposed rocks occurring within the boundaries of the county are of sedimentary origin, consisting of alternate beds of sandstone, slate, shale, fireclay, coal, limestone, etc., and all have been classified by the U. S. Geological Survey as extending from the upper strata of the Catskill formation, Devonian system, to and including, in a few hilltop areas, the lower strata of the Monongahela formation, Carboniferous system. Included within that range is the Allegheny formation, Pennsylvania series, which embraces all of the commercially important beds of coal that occur in the county, viz., the A, or Brookville, to the E, or Upper Freeport, both inclusive, shown in Fig. 2. The measures are traversed by a series of anticlines and synclines, extending in a northeasterly and southwesterly direction, which form broad, gently sloping basins (flat to 15 pct pitch, exceptionally to 25 pct). However, the topography of the surface is such that long lines of outcrops of all beds of coal overlying bed B, and to a limited extent bed B also, occur over large areas, a factor which contributed to the early and extensive development of mining activities in the county. Earliest mining developments of commercial importance were made in B, C', D, and E beds of coal, and it is in these beds that the principal mining operations are being conducted. To a limited extent, mining operations also have been conducted in local areas in the A, B rider and C beds. Coal beds being mined today range in thickness from approximately 28 to 60 in. Intervals between the respective beds of coal are variable but conform somewhat to the following general averages: A to B, 60 to 100 ft.; B to C, 50 ft.; C to C', 70 ft.; C' to D, 45 ft.; and D to E, 45 ft. The following are typical mining cases obserced over a period of years in various parts of the county.

Jan 1, 1952

By Bernard Schneider

The diversity of methods available to engineers and geologists for studying rock masses is a reflection of the fact that, despite the rapid and encouraging progress made over the last few years, there is still no unified and comprehensive method which can be used to predict the over- all behavior of a foundation. Nevertheless, it is agreed that the fundamental characteristic affecting the engineering properties of rock is fissuration, and this paper de- scribes a few new or improved methods of studying fissuration and its influence on major engineering factors such as permeability, deformability, or internal stresses in the rock volume. TESTS ON SAMPLES Conventional tests on samples using thin slices can be improved by staining the slices before cutting with certain ionic dyes which have an affinity for certain types of surface. This shows up the microdiscontinuities. For example (quoted terms are French trade names) : "Turquoise Motylhne JSA" will show up porous alteration of basic feldspars. "Vert brillant SA" is used for acid feldspars. "Fushine ASA" will show up voids in all rocks. A mixture of "Turquoise" and "Rhodamine BSA" will show up zones of alteration in all types of feldspars. With this technique, it is easy to make an optical classification of the different structural types, e.g.: (1) rocks completely free from voids; (2) rocks with microfissures, which in turn can be subdivided into (a) rocks with microfissures secant to the mineral structure, (b) rocks with microfissures parallel to the mineral structure, and (c) rocks with ran-

Jan 1, 1970

By William A. Edmiston, R. E. Grace

A simplified model for the theory of reaction rates near equilibrium has been applied to the reduction of wustite. A linear relationship between the net rate of reaction and the Gibbs free-energy change, ?F, is predicted. The reduction of wustite in H2 -H2O gas mixtures was studied with a microbalance technique at temperatures from 850° to 950 °C. The predicted model was found to be valid to -?F/RT = 0.1 or approximately -200 cal per mole away from equilibrium. ThE theory of reaction rates near equilibrium has been developed by a number of authors. Prigogine, Outer, and Herbo1 have studied the catalytic hydrogena tion of benzene in an attempt to deduce some intrinsic connection between reaction rates near equilibrium and thermodynamics. Manes, Hofer, and weller2 have derived more general expressions for reaction rates near equilibrium from classical thermodynamics. Hollingsworth3,4 has commented briefly on the work of Manes et al. Benson5 has summarized in a general way the results of the earlier contributions. It is the purpose of this paper to apply the theory of reaction rates near equilibrium specifically to the reduction of wustite in H2-H2O gas mixtures. The basic premise is that the reduction of wustite proceeds by a surface reaction, rather than by solid-state diffusion ,or gaseous diffusion. Richardson and Dancy6 and Gellner and Richardson7 have suggested that the reduction of wustite may be governed by iron diffusion in wustite. Mckewan8-11 has proposed that reduced iron layers on various oxides are sufficiently porous to offer a negligible impedance to the reducing gas. The linear motion of interfaces reported by McKewan and discussed by Themelis and Gauvin12 indicates the lack of diffusive control during reduction. The reduction studies of magnetite reported by Quets, Wadsworth, and Lewis13 give additional evidence that reduction rates are linear when the reaction products are porous and nonprotective. The interpretation of measurements reported in this paper is predicated upon a surface-controlled reduction reaction, at least in the earliest stages of reduction when the reduced iron layer is thin.

Jan 1, 1967

By Edwin C. Eckel

The title of this study may fairly lead to misunderstanding unless its basal viewpoint is explained at the start. There is of course no chance of misunderstanding the term strategic minerals-for some years past it has been rather generally used to cover those mineral supplies, important for war use, which do not occur in adequate amount on the territory of the Power under consideration. Even here, however, I might add a note of warning. It is commonly understood that the list of strategic minerals will vary, according to what country we are considering; but it is rarely understood, even in Staff studies, that it varies equally according to the particular adversary we happen to be considering. In the present study I have stated the definition in the broadest possible terms, and have at this stage purposely avoided limiting it to any one country or war situation, with the express purpose of being free to bring out certain implications which are commonly, if not always, overlooked. The more important opportunity for misunderstanding is, of course, that my views on the phenomena war and peace do not coincide with those currently fashionable, particularly in advanced intellectual circles. For we must face the fact that for a decade past the natural reaction from war conditions has shattered the public mentality so completely that our public discussions of such questions have very little relation to fact; they are excursions into ideal rather than Realpolitik. And as such they serve merely to prevent public discussion or accept-

Jan 1, 1932

By K. C. Li

TITANIUM, because of its high strength, weight ratio, and high melting point, became the metal of the jet age. Zirconium, because of its low neutron cross section and high corrosion resistance to hot water, became an integral part of the nuclear era. Since both metals are very similar chemically, more or less the same process is used for their production. The sudden rise of this new industry of titanium and zirconium seems to have caused some uncertainty as to the future development of processes for making these metals. Although zirconium was discovered in 1789 and titanium in 1790, it was not until 1945, six years after W. J. Kroll patented his process, that F, S. Wartman of the U. S. Bureau of Mines perfected the technique of producing ductile titanium, and it was not until 1946 that Kroll perfected the technique of producing ductile zirconium in commercial quantities. Since then the Government and private industry have spent millions of dollars each year constantly searching for new methods, with the hope that some day titanium can be produced as economically as aluminum and magnesium or as cheaply as stainless steel.

Jan 11, 1957

By S. Korman, S. B. Tuwiner

Chalcocite flotation is affected by agitation intensity during conditioning. Sodium sulphide in minute quantity may activate or depress, depending on conditions. Oxygen is a depressant while oxygen and sulphide neutralize each other by re-action at the mineral surface. Diffusion across a stagnant film at the surface governs reaction rates, while film thickness is reduced upon increase of agitation intensity.

Jan 2, 1950

By W. W. Harvey, F. O. Dudas

Toward hot hydrochloric acid, the usual order of reactivities of the common copper sulfide and associated minerals is reversed, and the rates of H2S formation vary as [ ]. The iron component of chalcopyrite and bornite reports to the solution as ferrous chloride, while pyrite remains essentially unreacted. If a pressure of H2S is maintained in the reactor, copper solubilization is suppressed, and the primary copper sulfides are converted to finely divided secondary sulfides (principally covellite). The HCl leach reside then consists mainly of covellite, pyrite and acid-insoluble gangue. Copper can be selectively leached from this upgraded concentrate to yield a clean, strong copper sulfate solution for direct electrowinning. Preliminary analysis indicates competitive economics with respect to established hydrometallurgical processes. Other concentrate treatments based on an initial HC1 leach are proposed and relative advantages compared. The common denominator of the major process routes considered is the requirement to regenerate HC1 from an FeC12 solution. Five distinct concentrate compositions were employed in the experimental study, which included some attention to the fates of selected minor constituents of the copper concentrate, especially gold, silver, molybdenum, arsenic and selenium. Significant mineralogical features of reactants and products are described.

Jan 1, 1978

By Fred C. Bond

Many grindability tests have been made in the Allis-Chalmers laboratory since the tabulated results were last published.' The lists of standard ball-mill and standard rod-mill grindability tests are brought up to date in this paper, and considerable new material is added. This includes a tabulation of open-circuit grinding tests, with impact and compression-crushing tests. The standard ball-mill grindability tests (Table I) were made in a standard laboratory ball mill, 12 by 12 in. inside, running at 70 rpm, with a charge of 285 iron balls ranging from 1½ to 3/4 in. in diameter and weighing 20,125 grams. Seven hundred cubic centimeters of minus 6-mesh stage-crushed dry feed was used, and the circulating load was maintained constant at 250 pct by adjusting the number of mill revolutions for each grinding period. Tests were made at all mesh sizes from 28 to 200, and the grindability is the number of net grams of screen undersize produced per revolution. The table includes 479 tests. It has been calculated that the ball mill does 52.3 joules of useful work on the ore per revolution2 with 93 joules input to the mill. The standard rod-mill grindability tests (Table 2) were made in a laboratory tilting rod mill, 12 in. in diameter by 24 in. long inside, with a wave-type lining, running at 46 rpm. The grinding charge consisted of six I1/4-in. diameter and two 13/4-in. diameter steel rods, all 21 in. long and weighing 33,380 grams. The mill was rotated level for eight revolutions, then tilted up 5' for one revolution, down 5° for one revolution, and returned to level for eight revolutions. It was discharged by tilting downward at 45° for 30 revolutions. Feed consisted of 1250 cc of minus in. stone and the circulating load was maintained constant at 100 pct by adjusting the number of mill revolutions for each grinding period. Tests were made at all mesh sizes from 3 to 65, and the rod-mill grindability is the number of net grams of screen undersize produced per revolution. The table includes 105 tests. The impact and compression-crushing tests (Table 3) are given in a table that is an extension of a previous publication8 in which the method of testing was described in detail. Two equal hammers weighing about 30 lb each were arranged to strike simultaneous blows on opposite sides of the test specimen. Broken pieces of rock passing a 3-in. square and retained on a 2-in. square were set up with the smallest dimension between the hammers, and this distance was measured. The height of the hammers was increased slightly before each blow until the specimen broke, and the foot-pounds per inch of thickness was calculated. Ten pieces

Jan 1, 1949

By G. H. Enzian

THE effects of phosphorus and nitrogen on the properties and behavior of low carbon steels are important considerations to both the manufacturer and the user of such material. For one thing, these two elements are the principal points of distinction between the chemical compositions of Bessemer and open-hearth grades. Further, open-hearth steels themselves may vary considerably in nitrogen content depending on the raw materials and ..practice used. In addition, appreciable amounts of rephosphorized open-hearth steels are being used at the present time in some low alloy, high strength grades and in certain other cases. For these and other reasons, it was felt desirable to obtain more complete knowledge of the effects of simultaneous small variations in phosphorus and nitrogen content on such properties of low carbon steel as tensile strength, impact toughness, sensitivity to cold work, and strain aging. A long range investigational program designed to furnish such information, was carried out, and the present paper summarizes some of the data currently obtained. General Discussion The strengthening effect of relatively small amounts of phosphorus in steel has been recognized, and to some extent utilized, for many years. A number of investigators have pointed out, from time to time, that under proper conditions of control, phosphorus can be a useful alloying element in low carbon steels.1-3 Nevertheless, in spite of the volume of data on the subject, the use of phosphorus for this purpose has always been handicapped by widespread feeling that its presence makes the steel brittle, difficult to cold work, and unreliable at low temperatures. This belief on the part of some steel users is not entirely justified in many cases, and often stems from early experience with acid Bessemer steels which have appreciably higher phosphorus (and nitrogen) contents than basic open-hearth grades. Nitrogen in steel, and its effect on properties, has also received considerable attention in the literature.4 In 1906, Braune5 ascribed the brittleness of Bessemer rails to the nitrogen content, and proposed a schedule of nitrogen limits for steels for various uses. This was one of the first papers to recommend directly the use of nitrogen content as a quality control measure, but it did not meet with much favor or support; as a matter of fact, the Jernkon-toret was rather sharply criticized for publishing the paper. In the intervening years a number of papers have been published on the subject of nitrogen in steel. As a result, it is now generally recognized that nitrogen can have an important effect on the properties and behavior of steel and that the presence of this element should be considered in any systematic study of factors affecting steel quality. In 1932, Graham6 introduced the concept that the quality of various steels could conveniently be evaluated and compared in terms of "sensitivity", which was defined as "the characteristic reaction rate of a piece of steel toward brittleness or hardness." This concept formed the basis for a broad research program into factors causing variations in the quality of commercial steels. At an early stage of this work, it became apparent that the observed effect of either phosphorus or nitrogen on the sensitivity of steel depended, in no small measure, on how much of the other of these two elements was also present. Indeed, the combined effect of phosphorus and nitrogen in steel may often be more important than the specific effect of either. With a few exceptions, it is not possible to predict accurately the effect on steel properties of a change in the amount of either phosphorus or nitrogen in the steel without also specifying the approximate amount of the other element. It seems desirable, at this point, to discuss briefly the distinction between strain-sensitivity and strain aging as used in this paper. In the early stages of its development, the work-brittleness test7 (which will be described in more detail later) was used

Jan 1, 1951

By J. Weertman

High-temperature creep experiments were carried out on indium, lead, and on binary substitutional alloys of In-Pb, In-Sn, In-TI, In-Cd, In-Hg, Pb-Bi, Pb-Sn, Pb-In, and Pb-Cd. The stress at which the power law creep equution breaks down was found to be much smaller for indium and lead than for metals with larger elastic moduli. The exponent over the stress in the power law creep equation was found to decrease upon alloying from values close to 4.5 to values near 3. THIS paper describes a set of high-temperature creep experiments made on high-purity lead and indium and on lead-rich and indium-rich single-phase binary alloys of various metals. These ex- periments were carried out to check two predictions of some creep equations derived by us"2 from a dislocation creep model due essentially to Mott. This model is shown in Fig. 1. Here dislocation loops are emitted from sources, not shown, situated on different slip planes. As the loops expand they come into each others' stress fields and are stopped. However, at high temperatures, as Mott has pointed out.

Jan 1, 1961

W. R. CRANE, State College, Pa.-The use of mine models for instructional purposes, both in the classroom and for more general work, as in the engineer's office, is of so much importance that I was pleased to FIG. 1.-MODEL OF A TIMBERED STOPE. see Professor Stock's paper which supplements a fairly voluminous literature on the subject. I have been interested in model making for instructional purposes for nearly 20 years and have tried my hand at practically every phase of the work, and have also employed practically every kind of material that

Jan 1, 1918