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Discussion of the paper of PHILIP W. HENRY, presented at the New York meeting, February, 1915, and printed in Bulletin No. 97, January, 1915, pp. 23 to 30. C. ,E. GRUNSKY, JR., San Francisco, Cal. (communication to the Secret ary*).-The difference of opinion of engineers on the subject of depreciation is justified, to some, extent, by the many viewpoints from which such a subject can be considered when applied to properties of widely differing physical characteristics. Mr. Henry takes up the subject of depreciation as applied alone to oil properties, and in doing so makes a clear distinction between amortization and the repair or renewal requirement. After carefully reading the paper the purpose of its author in suggesting a "depreciation" reserve or fund to keep the property at a constant value does not seem clear. As shown by Mr. Henry, the depreciation element as compared with the operating expense per gallon of oil is very large because of the comparatively short life of the oil properties, and it is also evident that such a "depreciation" fund would in a short time contain a very large amount of money. It seems desirable and permissible in income-tax matters to take into account the depreciation of property and to separate from the income such money as is necessary to amortize the invested capital to an extent warranted by the depreciation. However, it does not seem either necessary or desirable to create a large fund which will in time approximate the entire invested capital and which may he invested by the directors, as Mr. Henry suggests, "in the property itself or in outside securities." This method seems cumberome and liable to offer in the reinvestment of such a fund temptations to a directorate that might show more devotion to its own interests than that of the stockholders. A reserve fund is very frequently desirable in mining and oil operations, but to keep up a fund of this magnitude or to reinvest it in outside securities does not seem desirable from a stockholders' standpoint. The. money withdrawn from the receipts to be placed in the depreciation fund (not including replacements and the drilling of new wells necessary to keep up the productiveness) should he returned to the stockholders of the company, not as dividends, but as an amortization of the invested capital.

Jan 5, 1915

By Gifford White

Considerable attention has been directed in recent years to methods of electric prospecting other than the conventional direct-current techniques. It has been extensively recognized that electrical data of a more general nature than that possible by direct-current methods might be useful in geophysical studies. To this end, a number of different types of electric currents have been employed, such as single-frequency alternating currents, square-topped periodic current waves,4 periodic surges of a less specific nature,s and suddenly applied direct current.1,2 Yet, to the author's knowledge, little analysis of these different types of driving currents has been made from the standpoint of network theory to determine just what typc of currents would give the most useful data, and, most important of all, to determine the relation of the data taken by one method to those of another. Without touching on the actual theoretical problem of how currents flow in the earth under specified boundary conditions, some very useful information can be obtained from the study of the fundamental integral equations of electrical networks, throwing light on the problem not ordinarily appreciated by the field worker. Some manipulation of the standard network equations will be made, with the sole purpose in mind of developing expressions leading to practical results. Suppose that four points in the earth have been located and it is wished to obtain the most useful type of electrical data by inserting current into two of them and measuring the potential developed between the other two. The first problem that arises is that of which pair of the four shall be chosen as current grounds. In the direct-current case, where only steady potentials are measured, the selection is of little consequence, but as soon as currents varying with time are used at the current grounds, a new effeet arises. The fact that a varying current is flowing in the current-carrying conductor between the current grounds means that magnetic and electric fields varying with time will be produced

Jan 1, 1940

By Gifford White

Considerable attention has been directed in recent years to methods of electric prospecting other than the conventional direct-current techniques. It has been extensively recognized that electrical data of a more general nature than that possible by direct-current methods might be useful in geophysical studies. To this end, a number of different types of electric currents have been employed, such as single-frequency alternating currents, square-topped periodic current waves,4 periodic surges of a less specific nature,s and suddenly applied direct current.1,2 Yet, to the author's knowledge, little analysis of these different types of driving currents has been made from the standpoint of network theory to determine just what typc of currents would give the most useful data, and, most important of all, to determine the relation of the data taken by one method to those of another. Without touching on the actual theoretical problem of how currents flow in the earth under specified boundary conditions, some very useful information can be obtained from the study of the fundamental integral equations of electrical networks, throwing light on the problem not ordinarily appreciated by the field worker. Some manipulation of the standard network equations will be made, with the sole purpose in mind of developing expressions leading to practical results. Suppose that four points in the earth have been located and it is wished to obtain the most useful type of electrical data by inserting current into two of them and measuring the potential developed between the other two. The first problem that arises is that of which pair of the four shall be chosen as current grounds. In the direct-current case, where only steady potentials are measured, the selection is of little consequence, but as soon as currents varying with time are used at the current grounds, a new effeet arises. The fact that a varying current is flowing in the current-carrying conductor between the current grounds means that magnetic and electric fields varying with time will be produced

Jan 1, 1940

By John D. Weibmer

A strong step towards acknowledgement of mining as a skilled trade has been taken by the Tintic Division of Kennecott Copper Corp. In May 2 ceremonies, a pilot program was signed into force which, possibly for the first time in US history, recognizes mining as an apprentice trade and grants journeyman status to those who complete the prescribed training sequence. The apprenticeship standards, hammered out after months of consultation between management, labor, and government, are presently limited only to underground hard-rock mining and only within Kennecott's Tintic Division, but the architects of the program are confident that the concept will spread-first to other underground operations where miners desire documented evidence of their special skills, then to open-pit and soft-rock operations.

Jan 6, 1977

By R. Webeler

In order to study the role of work hardening in the fatigue process, use was made of the great sensitivty of the resistivity of AuCu to cold work. A change of the resistivity of AuCu of the order of 1 to 2 pct at the temperature of liquid nitrogen was found to occur as a consequence of severe fatigue. ACCORDING to Orowan's theory,' the process of fatigue In metals 1s associated with the production of a number of small regions which have undergone strain hardening. This phenomenon is supposed to occilr even if the stress applied during fatiguing is always smaller than the yield stress. In an attempt to verity the existence of such regions, Welber and Webeler' undertook to detect the stored energy associated with severe fatigue in copper. Previous experiments" had shown that the energy stored in a sample of copper which has been cold worked by torsion is released in the temperature range between 150" and 250°C when the sample is heated from room temperature and that no more energy is released (or absorbed) between 250" and 450°C. In particular the stored energy amounted to 0.41 cal per g for a case in which the mechanical energy expended in twisting the sample was 11.9 cal per g. In the case of fatigued copper, however, no release of stored energy could be detected between 150" and 250°C, so that the experimental error of &0.02 cal per g represents an upper limit for the amount of energy stored in strain hardening., It seemed desirable to attack the problem in a new fashion. For this purpose, it was decided to make use of the fact that, if an alloy capable of undergoing the order-disorder transition is ordered and then cold worked, the resistivity, p, increases very greatly above the value for the ordered state even if the deformation is very small. Some insight into the nature of the fatigue process may be obtained then by measuring the resistivity of an ordered sample before and after subjecting it to fatigue. For reasons which will become apparent from the following remarks, considerably more can be learned by carrying out the resistivity measurements at two different temperatures. In the case of a material containing impurities, vacancies, dislocations, or other imperfections of essentially atomic dimensions, the resistivity, p, according to Matthiessen's rule, can be represented as a sum of two terms p = p, + p, where p, is the (temperature dependent) resistivity of the pure metal, and p, is the temperature independent contribution of the imperfections. Briefly, the physical basis for this rule is the following: The main contribution of the impurities in question to the resistivity results from the fact that they interrupt the periodicity of the lattice and thus scatter the conduction electrons with a probability which is almost independent of temperature. In order that this be the case, it is necessary that the' extension of the impurities be small enough—roughly less than one electron mean free path—so that their main effect on the resistivity occurs for the foregoing reason. If an alloy like AuCu is partly or completely disordered by quenching from an appropriate temperature, Matthiessen's rule also applies to a very good approximation* with p, representing in this case the resistivity po of the ordered sample and p, the additional (temperature independent) resistivity due to the disorder. In general, the disorder can be represented in terms of atoms which are displaced from their "proper" positions in the superlattice and which thus qualitatively represent the imperfections in the superlattice responsible for the term p,. Since the misplaced atoms are distributed at random throughout the super-lattice, their contribution to the resistivity still can be considered in terms of the scattering of conduction electrons by lattice defects. The situation is somewhat more complex in the case of an alloy disordered by cold work because the process of disordering here does not involve a random redistribution of the atoms; however, Matthiessen's rule also holds in this case. Whenever Matthiessen's rule does apply, the values of the quantity /3 = (p? — /(T, — T,), where p, and p, are the values of the resistivity at two fixed temperatures, T, and T,, respectively, is constant (independent of p,) for a given alloy or metal. In particular, if a sample of AuCu is subjected to ordinary cold work, the value of /3 remains equal to Po, the value for the ordered material. According to Orowan's theory,' as remarked before, a fatigued sample contains a large number of isolated severely cold-worked regions, which make up only a small proportion of the metal. Thus, if a sample of AuCu initially in the ordered state is fatigued, more or less disordered regions will be produced within the ordered material. If these regions are small enough so that Matthiessen's rule applies, then it follows from the previous discussion that /3 again will remain equal to Po. If the effect of fatigue is to produce cold-worked regions which are macroscopic—of the order of at least several electron mean free paths—the effective resistivity, p, has to be computed by use of the ordinary laws of large-scale electrodynamics. For the sake of simplicity, it will be assumed here that the cold-worked regions are completely disordered and have a resistivity, p,. For a given proportion A of disordered regions the effective resistivity, p, for the current in a given direction depends on the geometrical configuration of these regions. In any case, the value of p for such

Jan 1, 1956

By W. T. Thom

All engineering education is faced by certain basic problems, three of which seem to have particular present importance in geological engineering training in general, and in respect to training for oil field geo-exploratory work in particular. Problem i The first of these problems has to do with present and future educational objectives and with the numbers and qualities of the men who should be coming out of our geo-exploratory training programs. Before the war we needed ever-increasing numbers of graduates at the Bachelor's level and a very much smaller number of men who had reached the Doctorate degree. Now, with more difficult, more extensive, and more costly exploratory work; with a rapid expansion of company "staff" activities, and with the initiation of many new research organizations and laboratories; it is clear that men of exceptional ability will be more and more in demand, and that the schools will need to carry a greater proportion of their students through to the Ph.D, degree. Problem 2 Assuming that the mineral industries will need an increasing supply of well-qualified Ph.D.s for future geoexploratory work (staff, line and research), can the schools expect to provide this supply of able Ph.D.s merely by expanding the proportion of B.S. and B.A. majors who go on through to the doctorate stage of training? And the answer is definitely "No"—as the situation stands at present. Most A.B. graduates are years short of the preparations in basic science and elementary engineering prerequisite to effective graduate study in the geoexploratory fields (paleontology ex-cepted), and similarly many of the annual crop of B.S. graduates lack adequate training in English; in ancient and modern history; and in the modern principles of labor and public relations. Indeed, several basic problems of undergraduate curricular organization and integration remain to be solved before most recipients of a Bachelor's degree will have that sound and broad educational foundation prerequisite to graduate training on a really effective basis. It is for these reasons that we have continued to experiment with our geological engineering program at Princeton, in an endeavor to provide a pilot-plant demonstration of a suitably broad and flexible undergraduate curriculum. Problem 3 But assuming that the schools can and do get undergraduate curricula set up in proper phase and scale to meet needed enrollment quotas for graduate training, what about the most urgent part of our whole mineral-industry educational problem? What about finding and bringing into mineral-industry training those youngsters of superior ability who are, by potential or known inclination, especially well-qualified for geoexploratory work?

Jan 1, 1949

By Robert B. McCormick

WORLD WAR II has developed a use for the nonmetal mineral quartz crystal that was unknown in World War I. During the interim period of peace, experimental work in the radio field with the piezoelectric properties of quartz crystal resulted in the almost universal adoption of quartz-crystal radio oscillator plates to control frequency in radio broadcasting, police, commercial and amateur communications equipment. Telephone resonators and filters made from quartz crystal also were developed, which vastly improved the frequency control of long distance telephone circuits. EXPANSION OF THE INDUSTRY The sudden war demands of the armed services for radio equipment using quartz crystal for frequency control led to an unprecedented expansion of the manufacturing industry. It is estimated that the 1940 peacetime volume amounted to approximately $1,500,000, while today a vast new quartz-crystal industry supplies more than $150,000,000 worth of quartz oscillator plates to the Army and Navy each year. This demand has caused an enormous expansion not only of American manufacturing facilities but also of Brazilian mining output, virtually our only source of raw quartz crystal. Actual figures of imports and consumption cannot be cited, for security reasons, but certain comparisons have been made, which indicate the transformation of quartz crystal from a minor to a major nonmetal. Lends has shown that the value of quartz-crystal exports from Brazil is now about equal to that of phosphate rock produced domestically in 1941 and actually exceeds the combined value of crude feldspar, gypsum and fluorspar production in the United States in the same year. This great expansion under wartime pressure was not accomplished without some anxious moments, but all the demands of industry have been met and the Government has been able also to accumulate a substantial stock pile of material against future contingencies. INSPECTION AND GRADING OF QUARTZ CRYSTAL The swift growth of the quartz-oscillator industry necessitated the simultaneous evolution of methods and criteria for inspecting and grading quartz crystal. It has been found that, generally speaking, it is economically feasible to cut only crystals that are at least 30 per cent by volume free from major defects such as optical and electrical twinning, cracks and fractures. Blue needles, bubbles, "chuva" and other minor imperfections can be tolerated in the usable portion unless present in great excess. The present marketing system in use in both Brazil and the United States, as far as quality is concerned, depends solely on the "usability" of a crystal, which is defined in the Brazilian-American agreement2

Jan 1, 1945

By VILLIAN BRADEN

THIS paper is presented in the hope that it will be instructive in view of the future large expansion of the mining industry in the west-coast countries of South America. There is a more or less general impression that the Spanish-American workman is inferior to the American, but after some years of experience and observation I doubt the correctness of this view. Taking into consideration all the elements which make for efficiency of labor, it has been found, particularly in Chile, that under proper organization native labor yields as much, man for man, and more, dollar for dollar, than in the Western United States. If a manager is willing to accept unreservedly the c costumbres del pais, without combating intelligently and patiently the ones tending to inefficiency, he should expect no better results than he deserves. He must conscientiously insist that a " square deal " be given and exacted; that liquor be excluded from camp as far as possible; that comfortable quarters and other uplifting elements of life be provided; and that the costumbres del pais shall not be over-ridden roughshod. He should also insist upon the gradual and reasonable adjustment of these conditions to the exigencies of the work; and (by no means the least difficult of his tasks) he should select the most competent men to patiently direct and teach the natives in the several departments, and by their own example encourage self-respect and decency. While the Braden mine is by no means as yet operated on a large scale, according to modern rating, it will nevertheless be interesting to note what has actually been accomplished there. An illustrative description of the mines and mill of the\

Oct 1, 1909

By N. C. Nissen, J. A. Thomas, A. Illis, K. N. Subramanian

Successful miniplant and laboratory testwork has indicated that high purity selenium can be produced from copper refinery slimes. The recovery technique fits into existing unit operations, and the selenium recovery in the new process was close to 99%. This recovery virtually eliminated any selenium being processed through the smelting stage. In addition, miniplant tests conducted at Inco Metals Co.'s J. Roy Gordon Research Laboratory in Mississauga, Ontario, have demonstrated the reliability of the process with respect to extractions, product quality, filtration characteristics, and effluent disposal. Inco's copper refinery at Copper Cliff, Ontario, produces about 500 t/d of copper with the anode slimes fall typically averaging 0.5% of the throughput. Investigations relating to the treatment of slimes within Inco's R&D have been conducted on several occasions since 1959, when the available alternatives such as acid or alkaline pressure leaching, aqueous or high temperature chlorination, roasting, smelting, etc., were considered. Interest in slimes processing was revived recently to meet increasingly stringent environmental standards and to replace equipment of a relatively old plant.

Jan 11, 1978

By E. C. Lee

THE safety of mine workers has received more attention from both State and Federal law-making bodies than any other industry, a fact that shows clearly the hazardous nature of the industry. The last, but by no means the least, of the measures adopted for the protection of mine workers, is workmen's compensation legislation. This is proving to be a powerful instrument for greater safety in the industries, from the fact that special stress is laid not on how the accident happened or who may have been responsible for it, but on how badly the employee is hurt by it. The injured person does not have to employ lawyers to prove his case, because the mere fact of his employment is proof of his right to compensation. The immediate effect of such legislation is the certainty confronting the mine operator that he must pay out large sums for every accident, regardless of its cause, thus adding materially to the cost of the production of his coal. This fact furnished to the operator the strongest incentive to reduce the causes of accidents; not that the operator has ever lacked reasonable consideration for the welfare of his employees and a proper humane interest in their safety, but his engrossment in earning his daily livelihood has been so great that he has not felt that he had the time to devote to the safety of the operation. This time he must now find because of the actual-cash value of the prevention of accidents in his mines. This agency alone proved inadequate to bring about a material improvement because operators have always been willing enough to improve safety conditions when possible to do so within reasonable limits of their financial ability. The requirement in the Workmen's Compensation Laws of several of the States, that the mine operator shall insure as a guarantee of his ability to meet his compensation obligations, has furnished the needed incentive, moral and financial, necessary to the prompt and effective dissemination of a more general knowledge of the causes and

Jan 10, 1917

By M. S. Hunter, D. L. Robinson

An extremely fine subgrain structure found in aluminum and aluminum alloys is shown and a method for revealing this structure is described. The appearance and some of the characteristics of this structure are described and the possible significance of subgrain structure in terms of chemical, electrochemical, and metallurgical processes is considered. GRAINS and grain boundaries, which constitute the principal manifestations of the crystalline aggregates known as metals, play such an important part in determining the characteristics and properties of metals and alloys that their nature and behavior have long been of much concern to the met-allographer. Many investigators have speculated on the possible existence of a finer structure within the usual grain structure and, through X-ray diffraction and metallographic techniques, have revealed evidence that such finer structures exist. Among these structures are the mosaic blocks and domains described by Burgers1 and others in their contributions on crystalline structure and the dislocation theory, the small units associated with polygoniza-tion described by Cahn,2 and the intragranular blocks revealed more recently by Lacombe and Beaujard.3 his paper describes some novel methods for clearly revealing a very fine granular substructure within the usual grains of pure aluminum and aluminum alloys. It also compares the characteristics and behavior of this subgrain structure with those of the ordinary grain structure and gives some examples of the manner in which this substructure may influence the characteristics of aluminum alloys. Metallographic investigations of aluminum and its alloys have dealt extensively with the functions and behavior of grains and grain boundaries and have evolved a definite concept of the relation between grain structure, orientation and physical, mechanical, chemical, and electrochemical behavior. During the examination of etched samples, a roughening or mottling of the body of certain grains has occasionally been observed. Such roughening obviously represented differential attack by the etching solution, but its true significance was not at first realized. It is now known that this roughening probably rep- resented a subgrain structure, although the particular etching treatments used were not capable of revealing this subgrain structure clearly. Also, in practically all cases, the subgrains were apparently far too small to be resolved by the light microscope. Recently, a method has been developed for revealing clearly the subgrain structure of most aluminum alloys. This method is somewhat unique in that it eliminates much of the usual tedious mechanical polishing and the attendant danger of a surface layer of flowed metal and at the same time is simple, rapid, and effective. It involves the use of the Alcoa R5 Bright Dip, a patented chemical polishing treatment licensed by Aluminum Co. of America. This treatment produces a bright, highly polished surface at least the equal of any mechanical polish and also etches the subgrain boundaries as well as the ordinary grain boundaries to reveal both the grain and subgrain structure simultaneously. Metallographic specimens to be examined are taken through the customary grinding and polishing operations used for aluminum alloys.' The usual care required in the final polishing operation to prevent a flowed surface layer and to obtain a high polish is not necessary, however, because any flowed layer is eliminated and a high polish is produced by the final immersion in the Alcoa R5 Bright Dip. Depending on alloy type, this dip takes from a few seconds to about 3 min, after which the sample is rinsed well, blown dry, and is ready for examination. The substructure can be revealed by some of the usual metallographic methods such as electropolish-ing or mechanical polishing and etching but no method has been found which is the equal of the new chemical polishing treatment. Mechanical polishing followed by the usual metallographic etching is not entirely satisfactory for revealing this substructure, probably because of the flowed surface layer resulting from the mechanical polish. If the usual etching methods are prolonged sufficiently to remove this layer, the specimen surface becomes quite rough and the substructure is not defined clearly.

Jan 1, 1954

By D. P. Mitchell

Western Australia is the home of much that is new and interesting in the gold-mining industry. Some of the gold deposits are outranked for size and value by nothing yet discorered, while the value of the ores is, in many cases, rivaled only by their complex character. As in all parts of the world, many of the ore-bodies occur in ways which tax the skill of the miner in following them; and among these the writer considers the case of the East Murchison United more interesting than the average. This is one of the leading gold-mines of the colony in point of production, and is situated near the town of Lawlers, in the East Murchison district. The country for several miles around the mine is mainly granite, and the line of outcrop on which this mine is located can be traced for a long distance. As will be seen from the accompanying plan (Fig. I), there are, at the water-level, two nearly parallel veins running slightly north of west. Structural Features.—The most striking peculiarity of these veins, and the hardest to understand, is their tendency to send out horizontal stringers or side-veins. These vary in size from a veinlet an inch thick to a veil] several feet in width, and they extend with great persistence into the wall-rock on either side of the vein. This tendency is shown in Figs. 2 and 3. The usual signs of a movement of the wall-rocks, such as a ribbon-structure of the quartz and a well-defined gouge or seam of clay along the walls, are in many places lacking, while in other places they appear strongly marked. They seem more in evidence below water-level than above. It is a commonlly accepted idea that when a gold-bearing vein loses in width, it often gains in value. In this instance, however, the direct opposite is the case; for in many stopes it has been possible to leave the narrow portions of the vein to act as pillars, and to extract only the wide portions, which are

Jan 1, 1900

By L. Messulam, A. S. Appleton

Iwo major studies of the Fe-Cr-C system are available in the literature. The earlier one of Kinzel and crafts' forms the basis for the data most commonly quoted in works of reference (e.g., Metnls HandDook) though the later work of Bungardt el a1.' is more extensive and amenable to analysis in terms of isothermal sections and so forth. However it is evident from examination of either of these studies that the delination of phase boundaries on the basis of the data obtained can only be very approximate. Indeed in several instances the data are so inconclusive that this delineation is a matter of opinion. This note is to report an analysis of experimentally determined carbon activity data in this system, which, originally intended as a means of checking the self-consistency of the data for a number of alloys, enables some conclusions to be drawn concerning the 10503C isothermal section of the iron-rich corner of the system as deducible from the data of Bungardt

Jan 1, 1967

By Cornelius Kelley

I HAVE been asked to pay a tribute to the mining industry. It is appropriate to this occasion that a word upon this subject should be spoken to this assemblage; but to pay a tribute to the mining indus-try, one that would be worthy of its traditions and its accomplishment and that would outline what it has meant to the economic and social development of this nation, would carry me far beyond what must be the brief confines of this address. I wonder how many there are who have ever paused to reflect how different might have been the current history of the world had it not been that for nearly eighty years a never-interrupted stream of wealth has flowed from the storehouse of treasure in the mines of the West into the commercial and economic life not only of this nation but of the world. Truly it was a historic day that Marshall discovered in the runway at Sutter's mill the glistening particles that proved to be gold. That event was one of the most momentous events in its consequences that ever happened in the history of mankind. Without its occurrence this nation undoubtedly would have grown; it would have reached a position; of economic and social soundness; but certainly it could not have achieved the splendid and immediate results that have become our proudest heritage and established our unrivaled posi-tion in the industrial world. As the primal cause that led to one of the great migratory movements of man it stands alone, unequaled, without any precedent in the annals of history, comparable in its effect on the imagination, on the movement, and on the devlop-ment of a people. Nearly three-quarters of a century had passed since the banners of the Revolution had been furled and a new nation had come into existence. Beyond the boun-daries of the original colonies, and through the passes of the Alleghanies, hardy frontiersmen had cut their way, and the process of establishing what have become -great states in the Valley of the Mississippi was under way. An empire of virgin land beckoned to the home-seekers of the world; but scarcely had its occupation been begun when, true to the instinctive urge that meant the ultimate destiny of the nation, there began the movement to carry the Stars and Stripes westward to the Pacific. Within the boundaries of what was then Mexico, Americans fought and died in the Alamo, and the banner of the Texan had been raised in eager ex-pectancy that its Lone Star might be added to the grow-ing constellation on the American banner.

Jan 5, 1928

By C. C. Harris

The characteristics of some common size distribution equations are critically discussed. A generalized form of several well-known size distribution equations is obtained from a differential equation describing statistical distributions. The equation contains three parameters and can describe the major features of size distributions in the fine and the coarse size regions. A graphical method for its implementation is provided. The application of this and other equations to sets of data are compared both for the quality of fit and from a comminution kinetics viewpoint. If a narrow size range of a brittle material is broken sufficiently to obliterate the feed sizes, but not so severely that excessive secondary breakage occurs, a plot of cumulative fraction by weight undersize (Y) vs. sieve size (X) on a log log grid (sometimes called the Gates-Gaudin-Schuhmann plot)1-3 gives a straight line of slope ~ 1 over much of its range. On closer inspection, deviations in the extreme coarse range covering perhaps 10 to 30% of the total sample may be apparent (frequently, a change in slope from ~ 1 to a value different from unity) together with over-all slight irregular departures from a smooth line. One model of breakage postulates that the same fracture pattern persists throughout all size ranges.4 The fracture pattern is characterized by the slope of the line on a log log grid. Accordingly, a distribution of sizes broken in the manner specified earlier is expected to produce a size distribution having the same slope as that of a broken narrow size range. Additionally, the slight irregularities mentioned above should even out in the summation process, giving a smooth straight line of slope ~1 on a log log plot. This idealized state of affairs does not, however, describe the distribution of a multi-event process such as that for a tumbling mill product. On the average, these curves (plotted again log log) tend to have a slope in the fine region different from and usually less than unity,5 while the coarse size region curves with increasing slope for cases of mild reduction, and with decreasing slope when moderate or severe size reduction has occurred. In addition, there are usually slight irregular deviations from a smooth curve. Most curves display two distinct regions — fine and coarse — and a few curves show one or more intermediate regions. Feed size studies6,7 show an effect which theory is required to explain. For the same material, mill loading and other operating conditions, and the same time of grinding, plotting the dimensionless ratios Y vs. X/(feed size) does not reduce the size distribution data to the same curve. Y vs. X does not correlate the coarse region, but it can provide a crude correlation of the fine region which improves as size diminishes and as grinding time increases. The size distribution in the coarse region is somewhat more dependent on the feed size than is the distribution in the fine region wherein the degree of dependence diminishes as time proceeds; the distribution of sizes in the fine region are determined largely by the nature of the material and the comminution conditions. A comprehensive model of comminution must recognize that several different patterns or modes of breakage can occur in a mill; 5,8,9 that there can be some selection in that some size ranges are broken more than others; and that, while some particles may be the product of a single fracture event, or may even remain unbroken, others result from multiple rebreak-age. Thus, breakage in a tumbling mill is more complex than the Schuhmann4 model admits in that several different types of comminution micro-events* occur rather than just one type, and these events, though different in size scale, are of the same overall pattern as that which is visualized by the model. The concept of an average comminution micro-event has, therefore, a mathematical rather than a physical connotation, at least for tumbling milling. Equations with which to describe particle size distributions have been sought for over half a century.10-13 No equation presently in general use was first derived from an analysis of the statistical mechanics of breakage; whatever theoretical basis the existing

Jan 1, 1969

By M. C. Flemings, G. E. Nereo

General expressions are given to describe macro-segregation in castings and ingots which results from mass flow of solute-rich liquid to feed solidification and thermal contractions. Analytical solutions are given for solidification with planar isotherms (unidirectional and bidirectional heat flow). These solutions describe inverse segregation and centerline segregation. Numerical examples are given for A1-4.5 pct Cu alloy. In 1540, Vannoccio Biringuccio published one of the first references to macrosegregation, describing the problem of exudation and inverse segregation in the manufacture of bronze gun barrels.' Since then, a great many studies of macrosegregation have been reported. Recent work of particular engineering interest includes that of Marburg 2 and others:" on centerline segregation and other types of segregation in large steel ingots, and work of Adams,5 Scheil, 6 and Kirkaldy and youdelis7 on inverse segregation in nonferrous ingots. In most studies on this subject, the various types of macrosegregation have been treated as separate phenomena. For example, quite different mechanisms have been proposed for formation of centerline segregation, negative cone of segregation, inverse segregation, banding, and so forth. In this, and in several papers to follow, it is proposed that these as well as other types of macrosegregation result from the same basic mechanism and can be quantitatively described by the same basic equation. It has often been suggested that some types of segregation (such as centerline segregation and banding) occur as a result of buildup of solute at the tips of growing dendrites.2-4 ,8-10 As example, banding can be induced in centrifugal castings by mechanical vibration, and Northcott 10 suggests this might be due to the influence of the vibration on the boundary layer at the dendrite tips of the growing dendrites. However, in view of the extremely small boundary layer known to exist at the tips of the dendrites,11,12 any interpretation of macrosegregation based on this boundary layer is clearly incorrect. Note that experiment has shown that significant buildup of solute does not occur at dendrite tips in ingot solidification, but even if such buildup occurred the thickness of the enriched zone would only be the order of D/U where D is liquid diffusion coefficient and U is dendrite tip velocity. For usual casting or ingot solidification this solute-enriched layer is 10"3 cm, far too small to account, for example, for centerline segregation.11'12 It has also been suggested that convection in the bulk liquid (ahead of the advancing dendrites) might cause segregation by sweeping away the solute-rich boundary layer in front of the dendrites.3 However, since there is no significant boundary layer, this explanation must be incorrect. The convection might directly cause segregation by penetrating between the dendrite arms, and presumably in a rimming steel ingot it is sufficiently vigorous to cause some segregation in this way. Centerline segregation, however, cannot be interpreted as resulting from this convection since a sharply segregated zone is usually found near the centerline, with the bulk of the ingot being nearly of nominal composition. If convection in the bulk liquid were the direct cause, a gradual change in ingot composition over the entire cross section would be expected. It is known that sudden changes in convection of the bulk liquid during solidification can result in banding,14 but it is not clear that the banding results directly from the effect of convection on solute distribution. Changes in convection also affect thermal conditions in the liquid-solid region of a solidifying ingot. It will be seen later in this paper, and in a paper to follow, that macrosegregation is strongly influenced by these thermal changes. Recognizing that in some cases of ingot solidification (as in solidification of rimming steels) convection in the bulk liquid may have a direct effect on solute distribution, we neglect it in this paper and in the several to follow. We then derive general expressions describing macrosegregation which results from the mechanism of interdendritic flow of solute-rich liquid

Jan 1, 1968

By W. D. Forgeng, R. L. Folkman, D. C. Hilty

The solubility of oxygen in molten Fe-Cr alloys has been determined at 1550° , 1600°, and 1650°C for alloys containing up to alloyshasbeenabout 50 pct Cr and found to decrease as chromium increases to 6 pet and then to increase gradually. Phase relations in the Fe-Cr-0 system at steelmaking temperatures have been evaluated and two previously unreported oxides have been identified. OPERATIONS in the melting and refining of chromium steels are dependent to a major degree on the reactions of chromium and iron with oxygen and are primarily directed toward controlling and modifying these reactions to secure maximum advantage in the utilization of chromium. Although fairly effective practices have been developed empirically, understanding of the specific reactions is limited. Moreover, the ability of molten steel to dissolve oxygen that subsequently precipitates as oxide inclusions during solidification is well known, so that clarification of the effect of chromium on the nature and mechanism of formation of these inclusions is desirable. Study of the problem indicated that increased knowledge of the fundamental Fe-Cr-0 system is essential to further technical and economic improvement. Consequently, an investigation of the influence of chromium on the solubility of oxygen in molten iron and of phases and phase relations in the Fe-Cr-0 system was undertaken at the Metals Research Laboratories of the Electro Metallurgical Co. as part of a general program on the effective utilization of chromium in chromium steel production. Experimental Procedure All of the experimental runs made during this investigation were carried out in the rotating crucible induction furnace which has been described in detail in a previous publication.' In review, the principle underlying this furnace is that rotational forces in the crucible cause the molten metal to assume a concave shape in such a manner that the slag is contained in the molten metal cup, thereby minimizing slag/crucible contact and subsequent reaction. Practically all of the heats were melted in commercial-quality magnesia crucibles of the type usually furnished for laboratory induction furnaces. All of the runs were made under an argon atmosphere after the furnace chamber had been degassed. Bath temperatures were controlled by Pt—Pt-10 pct Rh thermocouples. The basic furnace charge consisted of a premelted 12 to 15 lb electrolytic iron slug which had been cast to a shape convenient for fitting into the rotating furnace crucible. A typical analysis of the electrolytic iron slugs is given in Table I. For certain runs, it was desirable to melt down charges containing high initial chromium contents. In these cases the chromium was added to the electrolytic iron during the premelting operations. Chromium was added to the rotating furnace bath in the form of electrolytic chromium of the analysis given in Table 11. In all of the constant temperature runs, the standard procedure was to melt down the electrolytic iron or alloy slug under vacuum, admit argon to slightly greater than atmospheric pressure, and adjust rotational speed to develop a well formed "cup" on the bath surface. The melt was then saturated with oxygen by an addition of ferric oxide and the temperature of the bath adjusted to within +5°C of the desired level. At this point the heat was permitted to come to equilibrium prior to sampling or further addition. This time interval was varied from 15 min to 2 hr but generally was about 20 min. After sampling, the desired chromium addition was made and the bath again equilibrated prior to subsequent sampling. This cycle of addition and sampling continued for the duration of the run which lasted from 4 to 8 hr. At the end of this period, power was shut off and the bath allowed to solidify in the furnace. Quenched metal samples were taken from the equilibrated melts by means of the "Taylor sampler" which has been described by Taylor and Chipman.' Before being submitted to chemical analysis, all samples were carefully examined for surface slag occlusions and cold shuts. Later in the study, each sample was radiographed and examined metal-lographically in cross-section to determine the presence of internal defects. On the basis of these examinations, sound and apparently clean specimens were selected from the Taylor samples for chemical analysis.

Jan 1, 1956

By D. H. Yardley

GEOCHEMICAL investigation of trace elements in surface materials was begun near Ely, Minn., in 1953 along the basal contact of Duluth gabbro with Giants Range granite (Fig. 1). This article presents data on the distribution of copper and nickel in till and in stream sediments in the area and proposes an explanation for the types of distribution found. The Duluth gabbro, one of the world's largest basic intrusives, intrudes rocks which range in age from Keewatin to middle Keweenawan. Within the test area the gabbro is in contact with granite except for short sections where it is in contact with remnants of iron formation. Sulfide mineralization occurs within the gabbro, near and parallel to the basal contact for a distance of several miles. Schwartz and Davidson' have described the geologic setting of the mineralization. The sulfides, believed to be syngenetic, include chalcopyrite, cubanite, pentlandite, pyrrhotite, and minor amounts of bornite. They occur disseminated in the silicates and as small interstitial masses. The ratio of copper to nickel is about 3.8:1, based on 66 chemical analyses of rock samples from various outcrops (Ref. 1, p. 702, and Ref. 2). Test Procedures: With specified exceptions, all nickel and copper tests were made by the chromo-graph method,:' which measures the intensity of a colored spot formed by a reaction between the metal being determined and special reagent paper. The intensity is then compared to the intensity of spots prepared from samples of known metal content. Details of the test procedure are outlined in another article (Ref. 4, pp. 77,78). All soil samples tested in this investigation to date have been weighed on an analytical balance. However, a volumetric scoop designed to provide about 0.1 g of soil adds to the speed and ease of testing and has been found to give satisfactory results (Ref. 5, p. 531, and Ref. 19). The size of the samples used for the tests was 0.1 g. Whenever such small samples are used there is some question as to whether they are representative of the several grams in the field sample. Many repeat tests of the samples used in this investigation demonstrated that results can be reproduced within the limits of accuracy of the method without formal mixing beyond that inherent in screening the soil fractions. Furthermore, the 0.1 g is probably as representative of the field sample as the field sample is of its area of influence. Hawkes and Lakin (Ref. 6, p. 291), who considered the general problem, compared ground and quartered bulk samples of 500 g with 5-g grab samples. They concluded that "there is no significant loss in accuracy of data by substituting grab samples for bulk samples." The term soil implies somewhat different things to the geologist, engineer, and soil scientist.' For convenience the term as used in this article refers to unconsolidated material (the mantle) overlying bed rock. Sampling Procedure: Samples were taken at 100-ft intervals along north-south traverse lines across the gabbro-granite contact. The soil (till) samples were taken at an average depth of 1 ft, which was below the high-humus surface layer and into clean till. Samples taken at 1-ft intervals down to ledge showed as high a metal content at 1 ft below the air-surface as at greater depths and in two instances were slightly higher. The till at 1-ft depth did not appear to differ from material at greater depths. Total depth to bedrock has been tested at only a few points and where measured varied from 1 to 10 ft. Aerial Distribution Contours and Profiles: Plotting of copper, nickel, and cobalt content in contour form (Fig. 2) shows that anomalous amounts of these metal ions occur in till over and closely adjacent to mineralized areas of the gabbro. Contouring nickel content alone, or the copper content, outlines the same target area. Contours of the copper content provide a more distinct anomaly than nickel because of the higher copper concentration. The traverses are rather widely spread for interpolation; however, drilling has confirmed the target area essentially as shown.

Jan 1, 1959

By Franklin J. Kay

Introduction The methods used in surface, mining vary throughout the world, depending on many variables such as: the types of over- burden materials, the depth of the overburden, the thickness of the seam, and other operational choices, both financial and functional. However, the stripping machines are typically draglines, stripping shovels, excavators, scrapers, loaders, and bulldozers. In all cases the economic feasibility of mining thin seams depends on the market needs, the market location, the equipment used, the mine management, the quality of the coal, and the labor market. Slight negative combinations of these parameters have closed many mines while positive combinations allow others to exist. The limited mobility or slow movement of large stripping shovels, draglines, and bucket wheel excavators make them more economically fitted to areas where large quantities of overburden are to be moved. This is necessary to keep the transfer and setup time between pits a negligibly small percent of the total operational time. Equipment such as the scrapers, loaders, backhoes, trucks, and bulldozers that are either very mobile or can be trailered is more versatile and can be used in the smaller area mines.* Mobile equipment is also more practical in areas with shallow overburden because of the constant movement required while removing overburden. In thin coal seams the equipment is usually paired such that the operational equipment can be listed as: (1) dragline-loader, (2) shovel-truck- loader, (3) scraper-loader. (4) loader-truck-loader, or (5) loader-loader. In these operations the overburden is removed with the first machine(s) of the pairing and the loader or loaders are used for coal production. Recent articles in Coal Age (Chironis, 1978) and Mining Engineering (Wiebmer, 1978) have discussed varying philosophies in mining similar seams of coal. One operator uses draglines for competitive mining while the other uses scrapers for the same purpose. Both cite strong cases sup- porting their choice of equipment as good sound economic decisions and their success supports their choices. The drag-line operation is adding new larger draglines to decrease the cost of mining, rather than to increase coal production. The scraper operation has also gone to more and larger scrapers for basically the same reasons. These operations and all

Jan 1, 1981

By Edward N. Trump

Extensive beds of rock salt occur in New York, Michigan, Kansas, and Texas. Wells are drilled through the beds, cased, and equipped with a suspended center tube. By circulating water through such a well, the soluble saline is dissolved and a brine produced. Operation of a well results ordinarily in the formation of an inverted conical cavity in the saline, inasmuch as the dissolving action of the fresh water is more rapid at the top of the bed than at the bottom. Under continued operations, the side wall of the cavity becomes so flat that a blanket of mud is deposited thereon and if the bed is overlain with shale or a soft rock caving follows. Three methods of operating wells have been employed—the "Tully plan," "the Detroit plan," and "the Trump plan." Both the Tully plan and the Detroit plan involve the formation of the aforesaid conical cavity with constant caving of shale above and deposition of mud on the side wall; the Trump plan was developed to avoid both these circumstances and thus materially prolong the life of a well. Details of the three plans follow. The Tully Plan In the Tully plan, the water passes down the annular space between the casing and the center tube, the brine rising in the center tube (Figs. I and 2). An inverted conical cavity is formed, the side wall of which relatively soon becomes so flat that it is blanketed by mud and impurities from the rock salt; this blanket limits dissolving action to the perimeter of the base of the cone, situated at the top of the saline bed. Caving of the overlying strata follows, and the total production of brine from the well is comparatively small. The Detroit Plan In the Detroit plan, the water passes down the center tube, the brine rising in the annular space between the center tube and casing (Figs. I and 2). Initially, this flow forms a pear-shaped cavity in the bottom of the salt bed, but this cavity soon changes in shape to that of an inverted cone, as under the Tully plan, with the attendant disadvantages inherent in that plan. Application of the Detroit plan is limited to salt beds 300 ft. thick as a minimum. This depth of bed is necessary to prevent fresh water of lower specific gravity than the brine from rising in the

Jan 1, 1948