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By John J. Reed

The mines of southeast Missouri's Lead Belt have been in operation since 1864, almost 100 years. During this period about 10 pct of the total ore available has been left in place as pillars, and this now represents the best ore reserve left to the older mines. St. Joseph Lead Co. has been investigating various plans of pillar recovery for several years. The example to be described is only one possible approach under a specific set of conditions. Conditions vary greatly in the different areas within the Lead Belt, and the same approach would be entirely in- adequate in certain other areas, but there are important sections where this system is clearly applicable.

Jan 7, 1959

By Paul G. Hoffman

A survey of the role of the United Nations Special Fund in the field of mining and metallurgy. An aircraft, manned by Canadians and crammed with modern scientific instruments, crisscrosses over the dense rainforests of tropical Surinam at Y4 kilometer intervals, prospecting for valuable mineral deposits. Mill head samples of Burmese lead and zinc ores arrive at a Colorado laboratory for analysis and experimentation to determine the best milling and ore-dressing techniques. At the new Institute for Applied Geology in Manila, Philippine mining engineers receive instructions from a Finnish petrologist. These scenes illuminate only a fraction of the exciting work in the mining and metallurgical fields being carried out by the United Nations Special Fund.

Jan 8, 1963

By J. Mark Gronseth

The instantaneous shut in pressure often times is not a well defined feature of pressure-time records from in situ stress determinations by hydraulic fracturing. As the applications of in situ stress data become more sophisticated, the grea5er the need for an unambiguous method with which to identify the instantaneous shut in pressure becomes. Controlled experiments suggest that the instantaneous shut in pressure should be equated with the pressure at the inflection point of the pressure-time record following shut in. A method for determining this value is presented. Often times the minimum instantaneous shut in pressure determined after several pressurization cycles is the best estimate of the stress acting perpendicular to the fracture plane.

Jan 1, 1982

By C. D. Dolman

SINCE the outbreak of the war we have discovered in the United States minerals of which there was no general knowledge, and which compared very favorably with anything that could be found in any foreign country. One of these was magnesite, or the carbonate of magnesium as it occurs in nature. This mineral crystallizes in the rhombohedral form, has a specific gravity of 3.00, molecular weight of 84 4, molecular volume of 28.1, and a hardness of 3.5 to 4.5.1 Had it not been for the development of the California deposits of this mineral and the discovery of immense new deposits in Stevens County, Wash., the production of steel during the war would have been more seriously handicapped than it was. Now, that the war is over, we face the possibility of competition' with the cheap Austro-Hungarian magnesite; and while that may not he so cheap as it was before the war, adequate protection should be given the producers in this country to insure the full development of our own resources. The consumption of magnesite in the United States in 1913, the year preceding the war, was 172,591 tons of calcined and 22,872 tons of crude magnesite. Less than 3 per cent. of this amount was produced at home. At the present time, practically all of the magnesite used in the United States is produced at home. Expensive plants have been constructed, extensive exploration work done, and production pushed to the utmost to supply the necessary requirements of the war. Thus a considerable industry has been built up within our borders. Some magnesite has been imported from Canada and Mexico, but the Canadian ore was of an inferior grade and could not be used satisfactorily. During the year 1918, production decreased in both the United States and Canada; the production in the United States was 225,000 tons in 1918 as against 315,000 in 1917, and in Canada 39,365 tons in 1918 as against 58,090 in 1917.

Jan 8, 1919

By Ralph M. Hunter

Until recent years, maintenance of surface coal handling facilities was a relatively simple task. Equipment consisted principally of conveyors, screens and crushers of comparatively simple construction. Electrical equipment consisted of motors and starters, with little, if any, interlocking. In most cases failure of any component affected only the grades of coal loaded so that even a prolonged breakdown did not affect mine operation materially. However, with the introduction of modern cleaning plants, the picture has changed. The equipment is much more complex and therefore more difficult to maintain. In many cases failure of any component of the plant prevents loading of coal. Even if provision is made to bypass, the quality of coal loaded is lowered, affecting markets. In the case of plants designed to permit full seam mining, marketable coal cannot be loaded without operation of the cleaning plant. Under these conditions it is apparent that considerable thought and effort toward better maintenance are justified. In order to assure continuous, efficient and economical operation, maintenance should receive consideration, not only after the plant is in operation, but while it is being designed. It is hardly necessary to say that the designer should strive for sturdi-ness and wearing qualities. It is sometimes not realized, however, that even the best parts will sooner or later require replacement or repair. The designer should, there- fore, give consideration to accessibility. Anyone who has had to do with cleaning plant maintenance is familiar with installations where several hours are required to get at a part that can be repaired or replaced in a few minutes, once it is accessible. As in most cases, experience is the best guide. The men who operate and maintain this equipment know the problems encountered. Whenever available, the opinions of these men should be sought and heeded. As an example, we might consider the refuse elevator on a Chance Cone. Our company is now operating three of these cones, the first of which was installed in 1941, and the latest in 1946. Exact records are not available, but well over 50 pct of delays charged to the Chance Cones have been caused by the refuse elevator. This elevator receives refuse from the cone and carries it to a point above the water level of the cone, discharging onto a dewatering and desanding screen. Since the elevator operates under water and necessarily has close clearances in the lower boot, it tends to jam on large pieces of refuse or tramp iron. The chain, buckets and boot are also subjected to the action of water, sand and refuse, which accelerate normal wear. In case of jamming or chain-breakage it is necessary to drain the elevator and the cone so that even a minor fault in the elevator causes a considerable loss of time for the cone. In our new plant, which will contain two Chance Cones, the refuse elevator has been eliminated. This was accomplished by raising the cone so that the refuse gates could discharge directly onto the dewater-

Jan 1, 1949

By P. D. I. Honeyman

CHANGING trends in concentration, involving regrinding with the subsequent production of a finely divided, high-grade flotation product, presents a real problem to the modern copper smelter. In the treatment of such a material, handling difficulties are numerous and potential possible losses may be very great. In many plants, of course, preliminary roasting of the furnace charge remains an economical necessity. Under such circumstances, the operator has no alternative except to follow orthodox roaster reverberatory practice, though taking all possible precautions to avoid excessive dust losses and bad working conditions. In other plants, roasting is not only unnecessary but would be highly undesirable, and at best the charge would be merely dried before entering the reverberatory furnace. In the latter case the possibilities of raw charging loom large. The Miami plant of the International Smelting Co. handles the entire output of concentrates of the several mining companies operating in the Globe-Miami district. All of these companies produce a flotation concentrate which, at the Miami Copper Co. particularly, is all reground and is high in grade. In addition, the Inspiration Copper Co. ships a substantial tonnage of high-grade cement copper to the smelter from its leaching plant. Following the flow sheet of the original plant, all such material received was bedded, dried in Wedge furnaces and smelted in reverberatory furnaces. At times during the history of the plant it has been necessary to carry the drying operation further, to a partial roast, before reverberatory smelting. Since the charge contained over 80 per cent flotation concentrates, the handling of which in a dried condition was at best a dusty job, unusual precautions were taken to cut down dust losses. The Wedge furnace plant was equipped with a Cottrell treater and all hoppers and calcine cars were carefully designed to cut down dust loss in transferring the so-called calcine from hoppers to car and from car to furnace. In the furnace itself the dusting problem was a severe one. Arch erosion was very rapid and flues and waste-heat boilers rapidly filled up with a partly smelted flue dust.

Jan 1, 1932

Planning for a surface coal mine includes selecting the best means and equipment for uncovering the coal, loading it, and transporting it to the preparation plant. The machines and methods that will ensure optimum production will depend upon the location and characteristics of the seam to be mined. Stripping Techniques The choice of stripping units is influenced primarily by the system of mining, such as contour or out-crop mining as contrasted to mining in a region of rolling terrain with relatively flat upland surfaces. Factors such as the life of the mining operations production requirements, types of overburden, local and regional dip of coal, and land reclamation are other important considerations.

Jan 10, 1967

By Ivor Jenkins

Processes employing 'controlled at-mospheres in the heat-treatment of metals and alloys are now well established on an industrial scale, and the general principles involved and the advantages to be gained in the use of the technique have received considerable publicity over a period of years. During this time the greatest emphasis has been on the establishment of the process in industry, the main effort being devoted to development work on various types of atmospheres, their useful fields of application and the design of suitable heat-treatment furnaces in which they are to be used. The various types of controlled atmospheres are fairly well standardized, but there still remains a considerable field for the investigation of related problems, in connection with both the gas-generating equipment and the surface chemistry of the heat-treatment of metals, especially in complex controlled atmospheres. This paper describes certain investigations of this nature that were carried out in England up to 1939. The development of processes employing controlled atmospheres has been asso-ciated to a very large extent with the heat-treatment of steels, both because of the major importance of steel in industry and the many diverse and dificult prob-lems of surface chemistry involved when steels of such a wide range of composition are heated in the presence of active gases. Controlled atmospheres such as disso-ciated and burnt ammonia or charcoal gas are used in the heat-treatment of low-carbon and high-carbon steels, but from certain points of view a suitable atmosphere generated by the partial combustion of city gas is to be preferred. Both the ammonia derivatives are comparatively expensive, and even if the burnt ammonia is regenerated, thereby reducing operating costs, the capital expenditure of the gas plant may make it prohibitive for the smaller type of furnace installation. Charcoal-gas generators are not without their operating difficulties especially those associated with the quality of the charcoal, clinker formation and the removal of carbon dust from the generated gas. City gas has the advantage of being comparatively cheap and "on tap" in most if not all industrial centers. The use of raw city gas as a protective atmosphere in the heat-treatment of steels has been described,' but it presents certain difficulties because of its complex composition and its explosive nature when mixed with air. These factors, together with the tendency toward sooting at elevated temperatures, arising mainly from the hydrocarbon gases present, all militate against its use as a protective atmosphere in industrial furnaces. The following analysis, based on the analyses of city gas in different localities in Great Britain, indicates the wide limits existing

Jan 1, 1948

By Ivor Jenkins

Processes employing 'controlled at-mospheres in the heat-treatment of metals and alloys are now well established on an industrial scale, and the general principles involved and the advantages to be gained in the use of the technique have received considerable publicity over a period of years. During this time the greatest emphasis has been on the establishment of the process in industry, the main effort being devoted to development work on various types of atmospheres, their useful fields of application and the design of suitable heat-treatment furnaces in which they are to be used. The various types of controlled atmospheres are fairly well standardized, but there still remains a considerable field for the investigation of related problems, in connection with both the gas-generating equipment and the surface chemistry of the heat-treatment of metals, especially in complex controlled atmospheres. This paper describes certain investigations of this nature that were carried out in England up to 1939. The development of processes employing controlled atmospheres has been asso-ciated to a very large extent with the heat-treatment of steels, both because of the major importance of steel in industry and the many diverse and dificult prob-lems of surface chemistry involved when steels of such a wide range of composition are heated in the presence of active gases. Controlled atmospheres such as disso-ciated and burnt ammonia or charcoal gas are used in the heat-treatment of low-carbon and high-carbon steels, but from certain points of view a suitable atmosphere generated by the partial combustion of city gas is to be preferred. Both the ammonia derivatives are comparatively expensive, and even if the burnt ammonia is regenerated, thereby reducing operating costs, the capital expenditure of the gas plant may make it prohibitive for the smaller type of furnace installation. Charcoal-gas generators are not without their operating difficulties especially those associated with the quality of the charcoal, clinker formation and the removal of carbon dust from the generated gas. City gas has the advantage of being comparatively cheap and "on tap" in most if not all industrial centers. The use of raw city gas as a protective atmosphere in the heat-treatment of steels has been described,' but it presents certain difficulties because of its complex composition and its explosive nature when mixed with air. These factors, together with the tendency toward sooting at elevated temperatures, arising mainly from the hydrocarbon gases present, all militate against its use as a protective atmosphere in industrial furnaces. The following analysis, based on the analyses of city gas in different localities in Great Britain, indicates the wide limits existing

Jan 1, 1948

By John M. Bostwick, James C. Bradbury

Bitumen is a general term for a group of materials composed of mixtures of hydrocarbons that are fusible and soluble in carbon disulfide. Included in the group are petroleum, asphalts, asphaltites, and mineral waxes. Asphalt is a dark-colored, cementitious solid or semisolid, which generally softens on heating and resumes a more viscous or solid state when cooled. It is found in native form in fissures and pore spaces in rocks and as lakes. It is also obtained from the residues produced in petroleum refining. Asphaltites are black, naturally occurring solid bitumens. They are generally shiny and break with a conchoidal fracture. Common asphaltites are gilsonite (uintahite), grahamite, and glance pitch. Mineral waxes are solid or semisolid, relatively nonvolatile bitumens of various colors, having an unctuous feel and waxy luster, Of the native waxes, ozokerite is the best known. Montan wax is also classed as a natural wax, although it never occurs in the pure state and must be extracted from lignite or cannel coal (Ladoo, 1920). Mineral waxes may also be obtained by pyroprocessing of petroleum, lignite, and peat. Pyrobitumens are dark-colored, solid hydrocarbons that are infusible and relatively insoluble in carbon disulfide. They are so-called because they will yield liquid and gaseous hydrocarbons only when heated. Asphaltic pyrobitumens are defined as "substantially free of oxygenated bodies" and include wurtzilite (elaterite), albertite, and impsonite (Thrush, 1968). Nonasphaltic pyrobitumens contain oxygenated bodies; examples are coal and peat. The nonasphaltic type will not be discussed further. Petroleum Asphalts Asphalts refined from crude petroleum have almost completely replaced the native types. Refineries can produce asphalts in every desirable grade more economically and in greater quantity than the native types and with a variety of properties that meet the requirements of the various manufacturers using them. For all practical purposes, it is estimated that more than 95% of the asphalts consumed in the United States are refined from crude petroleum (private communication). Native Asphalts Native asphalts are dark brown or black, semisolid or solid substances that, in theory, formed by slow, natural fractionation of crude petroleum at or near the surface of the earth (Goulston, 1938). They are colloidal systems of high molecular weight components dispersed in a medium consisting of low molecular weight components (Pracy, 1954). Native asphalts may occur as lakes, as impregnations of rock (rock asphalt) or as deposits consisting of mixtures of natural asphalt and mineral matter in various proportions (Stern, 1960). Practical use of native asphalt dates to about 3000 B.C. It was mined from surface pits or lakes and used, then as now, for masonry mortar, waterproofing aqueducts and tunnels, binders for road construction, and as an article of commerce (Miller, 1938). Generally the native asphalts find little commercial use today except where they are geographically abundant, easily mined and transported, or have specific or special application. Petroleum-refined asphalt is produced by unusually economical techniques and is much less costly to use. The largest and best known of the lake deposits is that on the Island of Trinidad, where the lake covers an area of 114 acres and is 285 ft deep at its center (Stem, 1960). The lake asphalt is refined by heating to evaporate in-

Jan 1, 1983

By R. F. Hehemann, Darrell W. Smith

The kinetics of alloying- in W-5 rot pct Re powder compacts were investigated at temperature about the upper limit for the formation of the x phase, such that a single intermediate phase was involved in the process. The rates and directions of motion of the a-o and o-b interface were assessed as functions of tinze at the sintering teri7peraticve by quantitative izetallog-ralhic techtziques. The iiotion 01 these interjuces could be specified approxitnate1.y by u Parabolic )-ate law and deviations from this ,rate law were attribuled to a complex interaction between surface dif'fusion and volume diffusion during the initial stages of sintering. WHEN binary or more complex alloys are produced by sintering compacted blends of elemental powders, a complication is encountered which does not arise in the sintering of pure metals. In addition to concern for grain size and densification, the rate of inter diffusion of the component elements must be considered. The general problem of alloying during sintering has been treated by numerous investigators.'-7 These investigations have been concerned only with systems that form continuous series of solid solutions and a concentric-sphere diffusion model4 provides a useful description of homogenization in these stems.' Some controversy remains, however, over the contribution of surface and grain boundary diffusion to the homogenization process. Heckel% ePorts that homogenization can be described by volume diffusion at all temperatures, whereas other invetiators'' recognize the importance of surface and grain boundary diffusion, particularly at lower temperatures. Analysis of the homogenization process in partially miscible systems is complicated by the motion of the interfaces separating the individual phases. A simple analytical solution does not exist for such finite systems with spherical symmetry. It was the purpose of this work to examine the kinetics of the formation and dissolution of an intermediate phase in a binary system through an assessment of the motion of the interfaces separating this phase from the terminal solid solutions. PROCEDURE The W-Re system is an example of a partially miscible binary system and was selected for study because of its current importance in refractory-metal technology. The equilibrium phase diagram, Fig. 1, shows that the o phase will be formed by interdiffu-sion between tungsten and rhenium. At temperatures between approximately 2125" and 282O°C, the o phase will appear as the only intermediate phase in the diffusion system. In this work, a mixture of elemental powders containing 5 pct Re was employed. In such a mixture, the rhenium particles will be distributed randomly in a tungsten matrix. During sintering, a o-phase layer will form at the W-Re interface. The development and subsequent disappearance of the o phase are controlled by the relative rates and directions of motion of the 0-0 and a-p interfaces. The motion of these interfaces can be inferred from quantitative metallographic measurements of the average radii of the o shells surrounding rhenium particles. Elemental tungsten and rhenium powders of commercial purity were employed in these investigations. The rhenium powder was spheroidized from +200 mesh agglomerates by plasma-arc spraying and was then classified to yield a powder composed of essentially

Jan 1, 1967

By G. M. Gay, R. L. Perrine

This paper describes a method of numerical computation for three-dimensional, unstable, miscible displacement behavior useful for heterogeneous systems, as well as for more ideal conditions. In the method, flow equations are first linearized by a perturbation approach. The basic flow process is separated and a solution for its behavior readily obtained. The remaining problem of deviations from the basic flow caused by non-ideal conditions is then subjected to numerical analysis. Results obtained from use of the method are also presented. Although conditions assumed in the test cal-culations were severe, results show the type of dispersing flow expected and appear quite satisfactory. The method has eliminated or reduced in importance problems of oscillating values near steep fronts, excessive computer smoothing, etc. A unique advantage of the method is that the source of variations from ideal behavior can be observed. ,The one serious drawback results from the algebraic complexity of the perturbation approach, and the need for second-order terms to be retained in calculations of interest. Fewer array points are available and more computer time is required than would be desired. However, these difficulties are also experienced with other approaches to the solution of three-dimensional dispIacement problems. INTRODUCTION Prediction of behavior of the miscible displacement process within a porous medium for any system of engineering importance is plagued by a number of difficulties. With typical fluid properties the displacing fluid has the lower viscosity, and there is a natural tendency toward flow instability. The problem of predicting instability is compounded by the fact that every real system is heterogeneous. Permeability will vary from point to point — not entirely systematically, and yet not in a random fashion leading to a readily defined average. Furthermore, permeability is unlikely to be isotropic. These permeability properties, which are characteristic of any real porous medium, accentuate the effects of flow instability. Another factor to be considered is that flow dispersion accompanies the displacement process in a porous medium. Mechanistically, dispersion is due to the fact that flow between any two points in the medium follows multiple tortuous paths, each characterized by slightly different flow properties. The fact that the coefficient characterizing dispersive properties of the real medium JS a tensor with variable elements complicates matters. Further difficulties arise because the parabolic influence, while not negligible, is small. Thus, there is a tendency toward steep and uneven displacement fronts along which dispersion smoothing must be represented accurately. Yet frequently used numerical analysis schemes may tend toward either instability, oscillation or excessive smoothing, none of which gives the desired accurate picture of flow behavior. Thus, while many experimental and analytical studies of the process have been made, predictions of actual performance are still subject to considerable uncertainty and possible improvement. This paper reports on part of a study which attempts to develop improved methods for solution of the flow equations describing the miscible displacement process. Of necessity, the calculations were performed on a large digital computer. A three-dimensional system is represented, and the coefficients defining dispersion and permeability can be varied in a manner representative of a real system. Because the differential equations are nonlinear, a first step is to linearize them using a perturbation approach. Objective of this approach has been to separate the basic flow which would occur in an ideal system and for which predictions are readily made. Then the numerical analysis, which is necessarily complex, is directed toward solution of the perturbation equations. These equations state how the basic flow is modified

Jan 1, 1967

By Y. C. Liu, G. A. Alers

Using X-ray pole-figure information and the single-crystal elastic constants, the angular variation of an elastic modulus in a polycrystal can be calculated and compared to measured clalues. This procedure has been used in the past to provide supporting ecidence for a particular choice of ideal orientations in the description o the X-ray pole figure. Since it is well-known that the absolute value oj an elastic modlus oj a poly crystal cannot be acczrralely calculated from the single-crystal elastic constants, there exists a serious question about the reliability oj this modulus method in the study of textures. This paper deriz-es sez3eral simple fornzulae for the ntzgular lariatiion of Young's modulus in the plane o a rolled sheet sing the same ssuinptions which lead to the lack oj detinztion of the absolute c'alre OJ the elastic ,nodulus. The vesults show that, although the absolute isallre oj Young's modulus depends strongly on the assumptions made, the shape of the modulus vs angle curve is not very sensitive to the assumptions and thus can be used reliably in texture studies. Exatzples oj' using this criteriotz are illustrated in the text. NeARLY all poly crystalline materials have some preferred orientation in the arrangement of their grains and hence exhibit anisotropy in their properties. This preferred orientation is usually measured and studied by X-rays which yield detailed information on the statistical distribution of grain orientations in the form of pole figures. The usefulness of these pole figures in theories of texture formation and in predictions of properties has come to depend almost entirely on the characterization of the pole figure by one or more ideal orientations. Unfortunately, this characterization is not unique and different authors often present different ideal orientations to characterize a given pole figure. In order to distinguish between these different choices of ideal orientations, it is necessary to go beyond X-rays and consider other physical properties which reflect the texture' simply because any choice of ideal orientations must predict correctly the observed anisotropy in all physical properties. The most common example of this procedure has made use of the angular variation of Young's modulus with respect to the rolling direction in the plane of a rolled sheet.3 4 Here the anisotropy can be measured easily and it can also be calculated from the single-crystal elastic constants and the chosen ideal orientation. Unfortunately the methods used to calculate this anisotropy were chosen for their simplicity rather than for their mathematical rigor so that there exists a serious question as to the validity of conclusions reached by this modulus method. It is well-known5 that the absolute value of the Young's modulus of a polycrystalline aggregate cannot be calculated very accurately because different mathematical averages over the grains yield different results. It is one purpose of this paper to examine the effect of different averaging procedures on the calculated anisotropy of Young's modulus in the rolling plane of rolled sheets in order to see if this property can be used reliably in texture studies. This particular modulus and type of material were chosen because the modulus is easily measured and rolled sheet is technologically important. The results show that, although different averages yield different absolute values for Young's modulus, the shape of the modulus vs angle curve is not very sensitive to the averaging procedure and thus can be used as a criterion to check the various ideal orientations used to characterize the X-ray pole figure. Examples of this checking procedure are given in the final section. Another purpose of this paper is to examine the possibility of using the anisotropy of Young's modulus as an indicator of texture without reference to pole figures or ideal orientations. Such a use would require that different textures yield quite different shapes for the modulus vs angle curve so that the distinction between textures would be quite clear. The experimental results presented in the final section indicate that there is easily enough variation in shapes to allow modulus measurements to be useful texture indicators, par-

Jan 1, 1967

By George W. Riter

(Canal zone meeting, November, 1910.) A DISTINGUISHED engineer, the active head of a large mining company, has said that surveying attains the dignity of a profession only in the hands of a few men-the few who know how to keep notes that will be understood by even a novice without further word of explanation. Of all mine-records, survey notes are perhaps the most important. The maps made from them serve as a working-guide, and as framework for other data ; and when, from any cause, access to underground workings is shut off, the surveyor's record often becomes invaluable. So seldom does a surveyor have a chance to check underground surveys by making a closure, that he is compelled to rely on the precision of each step of his work for the accuracy of the final result. When data are fully recorded on the spot, the notes, even in the hands of second parties, become evidence of the care and precision with which the surveying was done. It is worth a great deal to be able to pick up the work of a former surveyor where it was left o$; and to be able to carry it forward without retracing from the beginning. The purpose of this paper is to describe the survey-note system of a mine now under my direction, in which underground surveys had to be relied upon entirely for the proper division of rich ore-bodies between neighbors, thereby placing a premium on accurate surveying and permanent records. In survey-work, it soon turns out that paper is the least item of expense, and that little is gained by trying to economize note-book space. For many purposes it is best to record notes on cards or loose-leaves, which may be left in the office at the end of the day's work, and need not be carried into the mine again, there to become smeared with grime and grease. With the loose-leaf or card system, all notes relating to the same local-

Apr 1, 1911

(Under this heading will he published notes sent too the Secretary of the Institute by members or other persons introduced by members.) Management or superintendency desired by member, graduate mining engineer of large practical experience in the details of mining, milling, concentration and cyaniding. Experienced in the efficient mechanical equipment and operation, and in the general business management of a mining property. No. 444. Metallurgist and operator who has specialized in the hydrometallurgy of. gold and silver, particularly stamp milling and cyaniding, desires change from present position. Ten years' experience in Western U. S. Thirty-six years old, married, in best of health and will go. anywhere. Available in 30 days. No. 445.

Jan 4, 1918

By A. Patton

Introduction THE use of roll scale in the Bessemer process dates back, to the "best of our knowledge, at least 20 years. It was first used by the Ohio Steel Co.; Youngstown, Ohio (now the Ohio Works of the Carnegie Steel Co.) under the direction of Sam, MacDonald, Superintendent of the Bessemer Department at these works. Two 10-ton vessels and one blowing engine capable of blowing one heat at a time were employed. The object of using the scale was to -shorten the length of the blow; or in other words, to increase the production with the same equipment. Various means were tried out for introducing the roll scale into the bath of molten iron: It was shoveled into the vessel before the heat was charged, so that the metal would flow over the scale; it was shoveled into the bath after the vessel was turned up; it Was dumped into the empty iron ladle by the wheelbarrow-load, and at times wars dumped on top of the molten metal in the iron ladle. But the practice of introducing the scale into the iron ladle had to be abandoned on account of danger from explosions and of skulling the -ladles. It was soon learned that the proper place to charge the scale was in the empty vessel, so that when the molten iron was poured into the vessel it flowed over the scale, causing a considerable reaction to take place before the heat was turned up. Eventually, cylindrical chutes similar to those now in use were installed. Into these chutes the scale is dumped and carried into the empty vessel. Before this convenient means of introducing the scale was adopted, the Ohio Works had satisfactorily demonstrated that roll scale would increase production, by blowing 107 heats in one 12-hr. turn (1,087 tons) with one blowing engine, blowing one heat at a time; whereas, prior to the use of scale, the best practice at these works was about 80 heats under the same conditions.

Jan 2, 1917

By Frederick J. McGarry, Parviz F. Rad

Although tunneling machines have attained very high advance rates in medium-hard rocks, the need for frequent repairs has slowed their use in very hard rocks. Laser- assisted tunneling is expected to improve tunneling machine performance by improving either specific energy or amount and quality of muck. The beneficial effects of lasing are the initiation and growth of microcracks from differential thermal expansion of grains, and overall spalling in the vicinity of the lased area. Using a constant thrust rock cutting device with disk cutters, the effects of cutter geometry, cutter diameter, thrust, and speed variations on specific energy and muck were explored and the improvement in performance of disk cutters caused by lasing was evaluated. It was found that the improvement depends on beam power and density, beam speed, pattern of heating, and cutting pattern and procedure. A focused beam slightly offset from the cutter path gives the most improvement both when cutting on a smooth surface and when cutting in previously cut grooves.

Jan 1, 1971

By William B. Plank

ENGINEERING students to the number of 73,269 had been enrolled in United States and Canadian schools on Nov. 5, 1945, but, as shown in the following tables, even this sizable number will not greatly remedy the 150,000 deficit reported by Vannevar Bush, director of the U. S. Office of Scientific Research and Development, to exist in the engineering and scientific man-power supply. These figures were received in advance from the Society for the Promotion of Engineering Education, and are given in detail in the January 1946 issue of the Journal of Engineering Education. Although the enrollment on Nov. 5 was an increase of 76% over the low of 41,632 in 1944-45, it was still 36% below the peak enrollment in 1941-42 of 115, 228. These figures include both undergraduate students and graduate students in the schools of the United States and Canada and are therefore comparable. As was to be expected, almost half of this enrollment is in the first or freshman year and 25% of the total are veterans. Also, 1,850, or about 2.5%, are women. A measure of the seriousness of the engineering graduate supply in these two countries is indicated by the trend of the number of first degrees that have been conferred during this period of scarcity:

Jan 1, 1946

Nippissing Mines Co., Ltd., a Ventures subsidiary, has bought into the, Vermont Copper Co. Inc. which operates a copper mine in Vermont producing 700 tons daily. The Vermont Mining Co. has been in operation since 1943 under the present management. When present owners wanted to convert their holdings to cash, the Ventures people saw possibilities in the area which, has been little explored but has a sizable production record. Final approval of the Anaconda-Harvey project for a 72,000 ton aluminum reduction plant at Kalispell, Mont., has been announced by Defense Production Administration. After considerable discussion in the past few weeks regarding Anaconda's entrance into the aluminum field, the approval stated "clearly the best arrangement."

Jan 1, 1952

The Institute maintains for the use of members (and especially for the use of out-of-town members) a reading and writing room, where all usual office facilities are available, including telephone, telegraph, receipt, forwarding and care of mail and express packages, etc. A file of current magazines is also maintained in this room, and the Institute's staff will lend its best efforts to serving the members in connection therewith. The Institute also maintains for the use of its members free dressing rooms, library research department, etc. Attention is called to these facilities at the present time in the belief. that they may be especially useful to out-of-town members in connection with the Meeting.

Jan 5, 1918