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By J. D. Runkie, A. G. Lyle, G. A. Gillies

Tar evaluation of data obtained by selective flotation from even a simple ore is a very difficult process, and when the ore tested is complex the process becomes extremely difficult and cumbersome The authors, in the course of an investigation into the selective behavior of various flotation reagents on nonmetallic minerals§ were confronted with an aggravated form of this difficulty, owing to the large mass of data that had accumulated over a period of years They finally devised a method whereby the results of the various flotation tests could be correlated and interpreted by means of graphs representing recoveries and rejections of the component minerals in the ore This method of graphical analysis proved so useful in nonmetallic flotation that it was afterwards applied to sulphide flotation, where it yielded equally satisfactory results Since this method of analysis leads to very definite conclusions as to the effect of changes in reagents and flotation procedure, it is felt that a wider application of the method might assist the industry by reducing the amount of test work required, and possibly increase the accuracy of the final analysis GRAPHS In Fig I, four curves are plotted on the same graph with cumulative percentages as ordinates and cumulative weights as abscissas In this instance the four curves are named, respectively the barite-recovery curve, the limestone-rejection curve, the silica-rejection curve, and the summation curve In these tests barite was the mineral concentrated, therefore a barite concentrate was produced Definitions Before explaining the curves in detail it might be advisable to define several new terms, such as "percentage rejection," "summation index," and "summation curve," as well as the word "test," which has been used in a special sense. A "test" will include all the operations performed upon a batch of ore from the time it is placed in the rod mill until the last product has been assayed Thus a test may be a comparatively simple procedure producing only one concentrate and a tailing, or it may be a very complicated procedure producing five or more concentrates of a specific mineral as well as a tailing The number of concentrates produced will depend entirely upon whether the collector was added to the pulp in the flotation cell in one lot or was added in five or more portions Percentage Rejection-The ability of a selective flotation collector to reject an undesired mineral is just as important as its ability to collect the desired mineral The percentage rejection curves shown on the graphs give this factor due consideration and its value is calculated as follows Suppose a concentrate contains 5 per cent of an undesired mineral This indicates

Jan 1, 1942

By R. R. Templeton

THE year 1924 was particularly notable in the petroleum industry of California as it was a period in which extensive town-lot drilling, with attendant overproduction and allied problems, virtually ceased and the industry returned to a nearly normal condition. Nearly all major field operations were conducted by large operating and marketing companies; in contrast to 1922 and 1923 field operations, when small promotion companies set the pace and forced the large companies to follow. The outstanding features of petroleum development were: 1. The three major fields of 1923, namely Huntington Beach, Long Beach, and Santa Fe Springs, declined from a production of 13,042,939 bbl., in January, to 6,764,417 bbl., in December, a drop of nearly 52 per cent: During this period, Huntington Beach declined 35 per cent., Long Beach 42 per cent., and Santa Fe Springs 63 per cent. 2. Methods of pumping deep wells were improved in some particulars; this contributed toward sustaining the productions of these three famous fields above what was predicted. 3. Of the fields producing previous to 1924, only three increased in production to any appreciable degree, during the year, as the result of bringing in new wells. These fields are Dominguez, Torrance, and Wheeler Ridge. Dominguez, discovered in September, 1923, produced 56,851 bbl. in January and increased regularly to a production of 1,641,042 bbl. in December. Torrance increased from a production of 972,261 bbl. in January, to 1,783,670 bbl., in May, and then declined to 1,393,215 bbl. in December. Wheeler Ridge, discovered in January, 1923, produced 23,254 bbl., in January, 1924, increased to a high of 33,678 bbl., in September, and declined to 27,430 bbl. in December. 4. Nearly all the production that had been shut-in during 1923 was opened in 1924, except some wells chiefly in Coalinga, Fullerton, and Santa Maria districts. The opening up of this shut-in production, combined with the increased productions from Dominguez and Torrance, were the chief factors that held the rate of decline for the state to a gentle slope.

Jan 7, 1925

By CYRIL W., William Campbell, Henry M. Howe

THIS paper gives the results of an investigation of the behavior of the argentiferous cobalt-nickel arsenides of Temiskaming, Ontario, in roasting, made in the metallurgical laboratories of the School of Mines, of Columbia University in the City of New York. The ore was kindly given by the owners of the La Rose and Trethewey properties at Cobalt, Ontario, and Mr. E. J. Hall, Tutor in Assaying in Columbia University, has helped us much. I. OBJECT OF THE INVESTIGATION. The object of the investigation was to learn:- 1. The temperature at which the arsenic is most rapidly expelled; 2. The thoroughness with which it is expelled by prolonged roasting at this temperature; 3. The effect of adding charcoal (a) near the end of the roast and (b) at the beginning of the roast. II. NATURE OF THE ORE. The important ores mined in the Temiskaming deposits are native silver-with small amounts of dyscrasite (Ag6 Sb), argentite (Ag2S), pyrargyrite (Ag3SbS3)-smaltite (CoAs2), chloanthite (NiAs2) and niccolite (NiAs). Mispickel (FeAsS) and cobaltite (CoAsS) also occur in smaller quantities. The average composition of the ore shipped from this district for the first six months of 1905 -was: silver, from 4.1 to 4.8 per cent.; cobalt, from 6.9 to 8.2 per cent ; nickel, from 3 to 4.7 per cent ; and arsenic, from 30.9 to 34.6 per cent. The ore which we treated consists chiefly of smaltite ; In our laboratory-work

Jan 1, 1907

By H. Rush Spedden, A. M. Gaudin

Although the number of minerals that are ferromagnetic‡ or highly paramagnetic is strictly limited, it has been known for some time that many minerals have slight but supposedly characteristic magnetic susceptibilities. With the exception of pyrrhotite, however, sulphides have been thought nonmagnetic. A new magnetic separator has been made available recently in limited quantity to research laboratories. This device, the Frantz Isodynamic Separator, has been used for the separation of various non-sulphides from each other. Its application to the separation of sulphides, however, does not seem to have been reported. In the Richards Mineral Dressing Laboratories, the success achieved through the use of this device in separating associated sulphides has been so startling as to lead us to believe that it constitutes a magnificent adjunct to heavy-liquid separation and to quantitative mineragraphy as a tool for the mineral investigator. The separator (Fig. I) consists of: 1. A powerful magnet, the strength of which can be adjusted by, means of a rheostat; 2. A vibrating chute of nonmagnetic metal on which the mineral to be separated is made to flow (Fig. 2); 3. A feed bin and adjustable feeder; 4. Receptacles for the collection of products; 5. Means for changing, setting, and accurately reading the two slopes of the chute; viz., the cross slope and longitudinal slope. The separator is made operative by the special shape of its pole pieces, which ensures a strongly converging field. It is said by the makers of the machine that the pole pieces apply a constant mechanical force to a particle of given susceptibility, regardless of its position in the operating space of the separators." Susceptible particles, therefore, behave as though of lower specific gravity than under ordinary circumstances. This effect, combined with the slopes of the chute and the action of the vibrator, causes a stratification not unlike thai obtainable on a shaking table. The chute is of rectangular cross section, and shallow; it is broadened toward the discharge end and divided longitudinally by a partition into two compartments that lead to the collecting receptacles. Although the separator probably can be used to make separations at fairly coarse

Jan 1, 1943

By H. Rush Spedden, A. M. Gaudin

Although the number of minerals that are ferromagnetic‡ or highly paramagnetic is strictly limited, it has been known for some time that many minerals have slight but supposedly characteristic magnetic susceptibilities. With the exception of pyrrhotite, however, sulphides have been thought nonmagnetic. A new magnetic separator has been made available recently in limited quantity to research laboratories. This device, the Frantz Isodynamic Separator, has been used for the separation of various non-sulphides from each other. Its application to the separation of sulphides, however, does not seem to have been reported. In the Richards Mineral Dressing Laboratories, the success achieved through the use of this device in separating associated sulphides has been so startling as to lead us to believe that it constitutes a magnificent adjunct to heavy-liquid separation and to quantitative mineragraphy as a tool for the mineral investigator. The separator (Fig. I) consists of: 1. A powerful magnet, the strength of which can be adjusted by, means of a rheostat; 2. A vibrating chute of nonmagnetic metal on which the mineral to be separated is made to flow (Fig. 2); 3. A feed bin and adjustable feeder; 4. Receptacles for the collection of products; 5. Means for changing, setting, and accurately reading the two slopes of the chute; viz., the cross slope and longitudinal slope. The separator is made operative by the special shape of its pole pieces, which ensures a strongly converging field. It is said by the makers of the machine that the pole pieces apply a constant mechanical force to a particle of given susceptibility, regardless of its position in the operating space of the separators." Susceptible particles, therefore, behave as though of lower specific gravity than under ordinary circumstances. This effect, combined with the slopes of the chute and the action of the vibrator, causes a stratification not unlike thai obtainable on a shaking table. The chute is of rectangular cross section, and shallow; it is broadened toward the discharge end and divided longitudinally by a partition into two compartments that lead to the collecting receptacles. Although the separator probably can be used to make separations at fairly coarse

Jan 1, 1943

By AIME AIME

THE Tuesday afternoon session", H. A. Bedworth chairman and T. S. Fuller, vice-chairman, was opened with D. J. McAdam, Jr.'s paper entitled "The Influence of Cyclic Stress on Corrosion." This paper dealt with the influence of cyclic stress on corrosion of alloy steels, corrosion-resisting steels, monel metal and aluminum alloys. The paper was discussed by T. S. Fuller, who pointed out that steels under stress corroded more than unstressed steels when subjected to steam.

Jan 1, 1930

By Louis W. Huber

The Liberty tunnels extend through a very steep hill in Pittsburgh (locally called Mount Washington) for a distance of slightly over a mile. The two tunnels parallel each other and are 59 ft. apart, center to center (Fig. 1) They are for vehicular traffic, and in each there is ample space for two lines of vehicles. Northbound traffic, toward downtown Pitts- burgh, is confined to the east tunnel and southbound traffic to the west tunnel. The South Hills residential district is separated from downtown Pittsburgh by Mount Washington, a steeply rising escarpment south of and adjacent to the Monongahela River. The Mount Washington district immediately south of the Monongahela River has been reached, for many

Jan 1, 1927

By Robert Maddin

THE application of electrolytic polishing of metals introduced a new technique for preparing surfaces, especially for single crystals. This procedure has generally been assumed to eliminate the strain introduced by mechanical polishing and to result in a more truly representative surface, particularly in the case of soft metallic materials. However, apparently little information is available concerning specific characteristics of a surface prepared electrolytically. The conventional method of mechanical polishing is known to produce a layer of distorted metal which is usually removed by a suitable chemical etchant. To what depth the strain introduced by mechanical polishing penetrates into the lattice is still obscure. The present investigation illustrates the apparently anomalous appearances of glide ellipses on electrolytically polished surfaces of aluminum single crystals. EXPERIMENTAL PROCEDURE AND RESULTS Aluminum single crystals, 99.975 pct pure, remaining from the investigation of Found,1 were polished electrolytically using a solution of fluoboric acid and a low current density. Laue back-reflection technique, interpreted after the manner of Greninger,2 was used to determine the orientation and the specimen axis rotation of the crystals. Three flat surfaces about 4 mm wide parallel to the specimen axis, one perpendicular to the theoretical slip direction and the other two 1200 apart, were polished mechanically and repolished electrolytically. A tensile load was applied using a Southwark-Emery tensile machine at a rate of about 40 lb per min. Elongation was measured by noting the initial and final gauge lengths. X ray diffraction was used to obtain the usual X and X values in order to calculate the elongation and shear by plotting stereographically the specimen axis rotation by means of the Schmid-Boas formula.3 In Table I may be found the value of the gauge diameter, measured elongation, calculated elongation and shear for the crystals investigated. Fig 1 shows the initial and final positions of the specimen axes of the crystals. [ ] At a low magnification the slip lines developed on specimen Al-I appeared straight and rather evenly spaced. However, at a high magnification, the slip lines were seen to be composed of small markings which were present throughout the length of the specimen (Fig 2). The distance between the markings was fairly constant and their directions all parallel to one another. Fig 3-5, photographed on different surfaces of the specimen, illustrate the interesting appearance of these lines. It may be noticed from Fig 4 that the markings, which present the appearance of

Jan 1, 1948

By Robert Maddin

The application of electrolytic polishing of metals introduced a new technique for preparing surfaces, especially for single crystals. This procedure generallv has been assumed to eliminate the strain introduced by mechanical polishing and to result in a more truly representative surface, particularly in the case of soft metallic materials. However, apparently little information is available concerning specific characteristics of a surface prepared electrolytically. The conventional method of mechanical polishing is known to produce a layer of distorted metal which is usually removed by a suitable chemical etchant. To what depth the strain introduced by mechanical polishing penetrates into the lattice is still obscure. The present investigation illustrates the apparently anomalous appearances of glide ellipses on electrolytically polished surfaces of aluminum single crystals. Experimental Procedure and Results Aluminum single crystals, 99.975 pct pure, remaining from the investigation of Found,' were polished electrolytically using a solution of fluoboric acid and a low current density. Laue back-reflection technique, interpreted after the manner of Greninger,2 was used to determine the orientation and the specimen axis rotation of the crystals. Three flat surfaces about 4 mm wide parallel to the specimen axis, one perpendicular to the theoretical slip direction and the other two 120° apart, were polished mechanically and repolished electrolytically. A tensile load was applied using a Southwark-Emery tensile machine at a rate of about 40 lb per min. Elongation was measured by noting the initial and final gauge lengths. X ray diffraction was used to obtain the usual x and X values in order to calculate the elongation and shear by plotting stereographically the specimen axis rotation by means of the Schmid-Boas formula.³ In Table I may be found the value of the gauge diameter, measured elongation, calculated elongation and shear for the crystals investigated. Fig I shows the initial and final positions of the specimen axes of the crystals. At a low magnification the slip lines developed on specimen Al-I appeared straight and rather evenly spaced. However, at a high magnification, the slip lines were seen to be composed of small markings which were present throughout the length of the specimen (Fig 2). The distance between the markings was fairly constant and their directions all parallel to One another' Fig 3-57 photographed On different surfaces of the specimen, illustrate the interesting appearance of these lines. It may be noticed from Fig 4 that the markings, which present the appearance of

Jan 1, 1949

By E. C. Bain

THE more familiar compositions of iron-carbon-chromium1 and the iron-carbon-tungsten2 systems have been investigated with a degree of thoroughness which has permitted the construction of their three-dimensional equilibrium diagrams; and it is probable that these equilibrium diagrams are sufficiently accurate for the present metallographic needs. Strangely enough, in spite of their importance, the alloys of iron, carbon and manganese apparently have not been investigated in the same systematic manner, and so far as is known, no three-component equilibrium diagram for this system is available. Even iron-carbon-nickel alloys3 have been studied rather more thoroughly; for these the solidus and liquidus surfaces have already been determined, but the solid transformations in this, as in the manganese system, have not been reported systematically. The present paper deals with the constitution at equilibrium of a series of 36 iron-carbon-manganese alloys of commercial purity limited by 1.5 per cent carbon and 15 per cent manganese, a range of compositions including most of the manganese steels. The temperature range of melting has not been determined, nor has the high-temperature (delta iron) ferrite equilibrium been included in the study, it being considered that the more important characteristics of the manganese steels are their ordinary transformations in the solid state. The delta iron region is almost certain to be a small tetrahedron not very different in magnitude or contour from that in the iron-carbon-nickel diagram. It is probably true

Jan 1, 1932

DETAILED programs for the Regional Meeting to be held at Boston, on Aug. 29, 30, 31, will be available on arrival at the Copley-Plaza Hotel, where registration will begin at 10 a. m. on Wednesday morning. The opening session will be non-technical in character and will be called to order at 11 a. m. Hector J. Hughes, Dean of the Graduate School of Engineering of Harvard University, and others will speak, and in the afternoon visits are to be made both to Harvard and Massachusetts Institute of Technology. Wednesday afternoon will be devoted mainly to the opening of an exhibit of geophysical instruments and methods at Tech. On the way back to the hotel a tour of Old Boston will permit the visitors to see many of the historic points of the city. A special meeting of the Board of Directors has been called to be preceded by the usual subscription dinner at the University Club at 6.30 p. m. Owing to limita-tions of room, invitations have been sent only to the usual list designated in the By-Laws, the Directors, past officers, chairmen of sections and of technical committees. The dinner and a brief business session of the Board will be followed by a technical session at the Copley-Plaza at 8 p. m. and this in turn by a buffet supper at the University Club at 10 p. m. Sep-arate entertainment is being provided for the women for the evening. Thursday will be devoted to technical sessions both in the morning and afternoon. If necessary to permit adequate discussion, an overflow session will be ar-ranged in the afternoon. In the evening, a subscription dinner will be given at the Copley-Plaza at which past-presidents John Hays Hammond and Robert H. Rich-ards will be guests of honor. It is promised that speeches will be short and dancing will be arranged for following. The women will be offered a luncheon and bridge party at one of the country clubs on Thursday, and Friday will be devoted to an all-day excursion for both men and, women. Members are asked to register promptly on arrival so that the various committees will know as early as possible for how many to provide. The major part of the technical program has been provided by the Committee on Geophysical Methods of Prospecting, and a series of papers of great value and interest in this new field has been brought together. Abstracts of substantially all of them are printed in this issue of MINING AND METALLURGY and the papers themselves will, with one or two exceptions, be avail-able in printed form at the meeting and later in the regular publications of the Institute.

Jan 9, 1928

By George A. Hill

WE of the oil industry, devoted to freedom of initiative, free competitive enter- prise, and free American institutions, applaud, with one voice, affirmation by the President of the national will and purpose to preserve and to protect, against all aggressors, "our American way of life with our individual and national freedom." We subscribe utterly and completely to this guiding declaration and seek its further definition as applied to the oil industry. Fortunately for all, the policy of the Government, after adequate study and deliberation, has been given precise definition. The National Defense Advisory Commission, with its patriotic, highly qualified, and distinguished personnel, has unanimously agreed to and adopted twelve general principles governing national defense contracts and also fair labor standard requirements. The President of the

Jan 1, 1940

By Zay Jeffries

Page Introduction............................. 474 Nature of Experiments ........................ 476 Materials Used in Experiments..................... 476 Description of Samples........................ 476 Details of Tests and Apparatus .................... 486 Determination of Elongation...................... 488 Determination of Reduction of Area .................. 488 Results of Tests........................... 489 Quantity and Arrangement of Amorphous Phase............. 497 Properties of Amorphous and Crystalline Phases............. 501 Intercrystalline Fracture........................ 530 Trans-crystalline Fracture....................... 531 Rupture ............................... 535 Explanation of Beilby's Results..................... 536 Mechanical Properties of Copper Wires................. 537 Mechanical Properties of Tungsten Wires................ 542 Mechanical Properties of Iron Wire................... 546 Effect of Diameter of Wire on Mechanical Properties........... 554 General Considerations on Properties of Metals at Very Low Temperatures .. 556 General Considerations on Physical Properties of Complex Alloys...... 557 Summary.............................. 559 Discussion.............................. 562 Introduction DuRing the period 1914 to 1916. the writer observed many times that tungsten wire could be drawn hot until it became brittle but on cooling to room temperature it became ductile again. In searching the literature for parallel cases. it was found that Beilbyl had produced hard-drawn wires of gold. silver. and copper that showed less than 1 per cent.

Jan 1, 1919

By William H. Shockley

There was an extensive mining and industrial exploitation of Russia, about 20 years ago, by Belgian, French and British capitalists; but the results were discouraging. It is said that the Belgian and French public together lost approximately $400,000,000, chiefly in the coal and iron industry of southern Russia. This loss is largely accounted for by the fact that most of the companies were formed, as usual in " boom" times, to sell stock; and that thorough investigations were not made. I11 1906, renewed interest was taken in Russian mines, especially in those of gold and copper, and a considerable literature is growing on this subject; but as yet I have seen no account of one of the large Russian mining estates. The following notes on such property, where the conditions are so different from those in the mining regions of the United States, should be of interest: This inadequate and probably somewhat inaccurate account is made up, partly from my own notes made on the ground, in the summers of 1904 and 1905, and partly from a volume on the geology and resources of the estate issued several years ago, containing surface- and mine-maps, and from a pamphlet published in 1904, giving a general account of the condition and prospects of the property. This pamphlet includes a report made in 1899 by Arthur L. Pearse, a member of this Institute. Both these books are in Russian, and were prepared by the Bogoslovsk Mining Co., which owns and operates the property. Articles in many other languages have appeared dealing with various matters connected with the estate; but I know of no other general account of it. In numerous books and articles on the Urals and Siberia, however, localities are described in which somewhat similar conditions prevail. Recent papers by

Jan 1, 1909

By T. S. Lundy, C. J. McHargue

HE diffusion rate of v48 in single crystals of bee vanadium has been determined at temperatures from 1002° to 1888°C. Standard techniques of lathe sectioning were used for specimens annealed above 1500°C while sectioning by grinding was used for specimens annealed at lower temperatures. As will be seen, the lower-temperature data is enhanced on an Arrhenius-type plot relative to values expected by extrapolation of the high-temperature data. Single crystals were obtained from Linde Co. In Table I the analysis supplied by the vendor is compared with an analysis at Oak Ridge National Laboratory of a sample after a diffusion anneal. The isotope v4' was prepared by the Isotopes Division of Oak Ridge National Laboratory. Proton bombardment of a titanium target in the 86-Inch ORNL Cyclotron was followed by a carrier-free chemical separation. Nineteen specimens, 1/2 in. diam and 3/8 in. long, were cut from the as-received vanadium single crystals. Each specimen was machined with the flat face perpendicular to the longitudinal axis. Specimens were polished through 1/0 emery paper and were etched with 25 pct HF-10 pct H2SO4-10 pct HNO3-55 pct H2O. The polishing and etching steps were repeated until a satisfactory surface finish was achieved. The isotope was electroplated onto the specimens from a neutral solution. Counting rates of the deposited layers were approximately 100 counts per sec. At temperatures above 1200°C specimens were annealed in a tantalum resistance furnace under an argon atmosphere. Temperatures were measured with a Pyro micro-optical pyrometer and a Pt-Pt 10 pct Rh thermocouple. At lower temperatures the specimens were sealed in evacuated quartz ampoules and annealed in Kanthal wire-wound horizontal tube furnaces. A severe reaction occurred at 1200°C between the quartz and the vanadium. This

Jan 1, 1965

By W. E. Wrather

DURING the war the mineral industry, and metal mining in particular, extended itself more than any other to attain the limit of its productive capacity. Likewise, probably no other industry went quite so far toward jeop¬ardizing its own economic future through depletion of material reserves. Once we looked to Europe for most of the manufactured goods we needed. Our own limited mineral requirements were easily supplied from mines near the Eastern seaboard. With expansion and industrialization, our mineral needs increased in proportion, and the centers of mining activity moved westward to Michigan, Wisconsin, Minnesota, and the Tri-State district, where seemingly inexhaustible high-grade deposits of iron, copper, lead, and zinc ores were opened and rapidly developed.

Jan 1, 1946

By C. K. Leith

THE resolution presented at the Annual Meeting of the A.I.M.E., calling on Congress to provide now for postwar accumulation of mineral stock piles under Government control, expresses, I think, the nearly unanimous view of the mining industry. As a result of the trying experiences of the first World War, Mr. Baruch, in his report of Dec. 24, 1919, to the President, urged that steps be taken at once to ensure adequate supplies of raw materials for future emergency. In the twenty years that followed, the same program was vigorously urged on Congress by many individuals and agencies, public and private, including the Secretaries of War and Navy, many members of Congress, the Bureau of Mines, the Planning Committee for Mineral Policy appointed by President Roosevelt, the A.I.M.E., the Mining and Metallurgical Society, and others.

Jan 1, 1943

By Henry Rawdon

THE RELATION between the course, or path, of the fracture of metals and alloys, produced in service or as a result of certain laboratory tests, and the crystalline units of which such materials are composed is of utmost importance. The fracture of normal material is, in general, intracrystalline, i.e., it consists of a break across the grains rather than of a separation between them. An intercrystalline fracture indicates either that the metal is of very inferior quality or that the break occurred under very unusual conditions, e.g., at a very high temperature. The usual mechanical tests, when applied to metals of the type that breaks with an intercrystalline fracture, merely measure the coherence of adjacent grains for one another and reveal little as to the real properties of the metal itself. Even such a soft plastic substance as lead, under suitable conditions, may be rendered so weak and brittle that the metal can be easily crumbled into powder by the fingers although the constituent grains have lost none of the intrinsic properties of lead. Various erroneous explanations of this behavior of lead have appeared in the scientific literature, the change being described usually as an allotropic one. The importance, in an industrial sense, of a proper explanation of this type of the corrosion of lead justifies the description of the type of metal deterioration that follows.

Jan 2, 1920

By W. C. Maurer

Although millions of feet of rock are drilled annually, the basic drilling mechanisms involved are not well understood. The primary reason for this lack of knowledge is because the basic principles of rock failure are not well understood and rock failure is the primary mechanism in drilling. A better understanding of the drilling mechanisms would enable a more scientific approach to the design and use of drills and bits. The paper reviews several models which have been proposed to explain various aspects of the different drilling methods. These models are described and their limitations and areas of application are discussed. Drilling rate relationships are developed and related to the basic rock failure mechanisms. TYPES OF MECHANICAL DRILLS There are three basic methods of mechanically attacking rock: 1) percussive action, 2) rotary action, and 3) combined rotary-percussive action. A percussion drill applies a force perpendicular to the rock surface and the bit moves into the rock perpendicular to the surface, forming a crater beneath it (Fig. 1). A rotary drill applies a constant thrust to the bit while a torsional force moves the bit parallel to the rock surface, breaking the rock ahead of it. A rotary-percussive drill applies both a rotary force and a percussive force to the bit which moves into the rock at an angle to the surface. The commonly used drills can be classified as: rotary-drag, diamond; percussive-hammer, piston, churn; and combination-rotary-percussive, roller.

Jan 1, 1967

By Clyde E. Williams, V. N. Krivobok, C. H. Herty

THE extreme effect of the depression on the steel industry is well illustrated by the fact that the amount of iron ore shipped from the Lake Superior district was the lowest in 47 years. Something over 3 1/2 million tons of ore was shipped in 1932, compared with over 65 million tons in 1929. It is not surprising then that practically no advancement in iron ore beneficiation has been made. Improved research and development work, however, was continued at the Michigan College of Mines in the survey of the lean iron ores of Michigan with reference to the possibility of their concentration; at the University of Minnesota in its large-scale jigging studies of Lake :Superior ores; and at Battelle Memorial Institute in the development of improved jigging of iron ores. The successful operation of the new Hadsel mill at a gold property in California gave such low grinding costs on a quartz ore as to give much encouragement in the iron ore industry for a cheapening of the cost of grinding lean ores for concentration.

Jan 1, 1933