Search Documents

By F. W. Maclennan

ORE production from the property of the Miami Copper Co. began early in 1911. Until 1925 this ore came from the so-called high-grade orebodies, which contained a little over 2 per cent. copper. This ore was mined by the following methods. 1. Top slicing after mining the peaks by square setting, which produced 4,524,347 tons, including ore from square setting. 2. Shrinkage stoping with sublevel caving of the pillars, which produced 2,230,577 tons. 3. Undercut caving with hand tramming, which, produced 15,427,672 tons. Estimating December tonnage, the total ore mined to the end of 1929 will amount to slightly more than 43,000,000 tons. The first method was described by E. G. Deane1 and the second by D. B. Scott,1 and the third, together with a general, description of the mine, by J. H. Hensley, Jr.1 The geology of the district has been worked out by. Dr. F. L. Ransome.2

Jan 1, 1930

By Edgar Kidwell

To any one acquainted with the practical conditions surrounding the mining engineer and mine-manager, especially in this country, the presentation to the American Institute of Mining Engineers of a paper on the above subject will need no explanation. The members of this profession are continually called upon to design and erect, both above and underground, structures which involve the use of beams. Not to mention the various buildings connected with large mining operations, I need only refer, in support of this statement, to trestles, derricks, headworks, etc., on the surface, and to timbered stations and other spaces of large span in the mine-workings. Notwithstanding the rapidity with which iron and steel are replacing wood in the construction of large buildings, there will always be cases in which the use of metal will be unadvisable. Especially will this be true in districts remote from large cities. Works of temporary character will continue to use timber. High freight-charges, the liability of delays in delivering iron, and the temporary character of many of the structures, will for many years to come make it advantageous for the mines west of the Mississippi and on Lake Superior to construct their buildings almost exclusively of wood. The timber-resources of the country are decreasing so rapidly that already the engineer finds difficulty at times in obtaining beams of large size. This difficulty will steadily increase, and will force the constructor to resort more frequently to built-up beams, such as have long been used in Europe, owing to the difficulty of obtaining there such large sizes of timber as have

Jan 1, 1898

By Forrest W. Kinsey

The use of pellets in North American blast furnaces has made the mixes used in the associated sinter plants unique. These mixes generally contain a high percentage of fine waste oxide materials as the principal iron bearing portion of the mix, with iron ores and concentrates added in minor amounts only. Additionally, the sinter basicity is always above one and can be three or higher. This paper will discuss the large body of knowledge and experience developed by one company on this type of sinter mix. Results of laboratory tests will be used to illustrate how mix composition and feed preparation affect sinter productivity and quality.

Jan 1, 1977

By Donald A. Dahlstrom

The selection and sizing of filters depends on the characteristics of the type of filter and the feed slurry. In addition, the rate functions of cake formation, cake washing and cake dewatering must be determined in order to design the filter station on the basis of desired performance. This chapter discusses the applied theory used to determine the rate functions and illustrates how to incorporate these into the filter cycle to obtain the required objectives. This also permits the sizing of the filter and auxiliaries as well as the selection of the proper type of filter.

Jan 1, 1978

Alder, John W., Student, Mass. Inst. of Tech Cambridge, Mass. '38 Allen, Charles F Mines McFarland, Cal. '34 Anderson, Norman John, Student, South Dakota School of Mines Rapid. City, S. D. '32 Ansel, Gerhard, Student, Mass. Inst. of Tech Cambridge, Mass. '34 Arakelian, Haig Mark, Student, Inst. of Tech Cambridge, Mass. '34 Archer, George K., Student, Colorado School of Mines Golden, Colo. '34 Arnot, Paul H. 608 S. Acacia St., Compton, Cal. '31 Asel, Philip R., Student, Colorado School of Mines Golden, Colo. '32 Augenthaler, Robert L., Student, New Mexico School of Mines Socorro, N. M. '32 Augustine, Robert W. Address Wanted. '32. Austin, Robert B., Student, Univ. of Idaho Moscow, Idaho. '34

Jan 1, 1934

By R. W. Smith, K. H. Lee Discussion by Fred C. Bond

Fred C. Bond (Tucson, Ariz.) — This is a valuable paper presenting much well directed research testing. It describes a practical method by which the long and relatively accurate Bond closed-circuit grindability can be adapted to a known ore so that results of comparable accuracy can be obtained on the same ore from much shorter batch grinding tests. This can be very useful in control work. In large mills a routine batch grinding test on the head sample can be made each day, or even each shift, to check grinding performance by comparison of the work index from each mill grinding section with that obtained from testing. However, it would be well to re-standardize the batch test against a Bond test, perhaps once a week at

Jan 1, 1969

By James W. Baxter

Underground mining of limestone is becoming increasingly practicable in Illinois. Most quarries are near rivers on the western and southern borders where competition for land use is intensive. Increasing demands for stone can be met by expanded mining with access by adits in existing quarries and by inclines and shafts at downdip sites. Geologic, hydrologic, and engineering conditions indicate that deep mines in the Ste. Genevieve, Salem, Ullin, and basal Burlington limestones of Mississippian age and in the Moredock member of the Dunleith formation of Ordovician age are particularly feasible, but development will require prudent exploration and planning to ensure that the product will be of good quality.

Jan 1, 1981

By Donald Ingvoldstad, Harold E. Lee

At Bunker Hill the original charge storage and preparation system was installed in 1917 to accommodate lead-silver gravity mill products. Only minor tonnages of wet fines such as vanner and flotation concentrates were received. Charge flux and diluent requirements were provided by an ample supply of siderite middlings and coarse limerock. While oversize material was crushed through Y4-in., the use of roll crushers in series resulted in a more or less granular, free-running charge of adequate porosity. Under such conditions, receipts could be proportioned directly from receiving bins, and suitable blending was obtained by passing the resultant layered composite through a small Stedman disintegrator. This elementary system served well for production and smelting of an extremely lead-rich sinter, in the low column blast furnace. Here sinter physical quality is less critical, and appreciable quantities of raw flux and oxidized ore may be charged directly to the blast furnace without seriously impairing furnace capacity.

Oct 1, 1956

By J. C. Irvine

Meramec Mining Co., a joint venture of Bethlehem Steel Corp. and St. Joe Minerals Corp., mines and pelletizes iron ore at the Pea Ridge mine. The Pea Ridge property is located near Sullivan, Miss., about 113 km (70 miles) southwest of St. Louis. The ore body was delineated in the mid-1950's by St. Joe during a lead exploration program. The first test holes drilled on the Pea Ridge magnetic anomaly revealed the presence of a large magnetite deposit; further drilling in 1956 and 1957 confirmed that the ore body was mineable. Meramec Mining Co. was incorporated in 1957 and shaft sinking began late in the year. Production began in April 1964. The ore body is overlain by about 400 m (1300 ft) of flat-bedded sediments. It is tabular, about 800 m (2600 ft) long and up to 180 m (1600 ft) thick. It dips about 80° and is of unknown depth. The ore is mainly high-grade magnetite with small zones of specular hematite. The wall rock is a Precambrian rhyolite porphyry.

Jan 9, 1976

NEW MEMBERS The following list comprises the names of those persons who became members during the period Feb. 10 to Mar. 10, 1915: Members BANKS, HAROLD PURDY, Min. Engr 61 Broadway, New York, N. Y. BARAGWANATH, JOHN G., Min. Engr., Morococha Mining Co.; Morococha, Peru. BEESON, JOSEPH JOSIAH, Min. Geol Stanford University, Cal. CALLOWAY, ALFRED W Pres., Davis Coal & Coke Co., Cumberland, Md. DEETRICK, JAMES W., Mgr., Republic Iron & Steel Co., 826 Pennsylvania Ave., Youngstown Ohio.

Jan 4, 1915

By K. C. Mills, E. T. Turkdogan

The results on the rates of vaporization of Fe-Ni alloys, levitated by an electromagnetic field in a stagnant atmosphere of helium, are shown to be in close agreement with those predicted theoretically. AS shown in Part I of this series of papers, the rates of vaporization of metals enhanced by convection currents are increased further by the process of condensation of metal vapor when there is a steep temperature gradient in the boundary layer. At the time this theoretical work was completed one of the authors (K. C. Mills) had already carried out some experimental work on the rates of vaporization of molten Fe-Ni alloys. The experimental work was done under conditions which make it possible to compare the experimental rate data with those predicted on theoretical grounds. EXPERIMENTAL The object of the experiments was to evaluate the activities in a number of binary metal systems. The details of the experimental technique are given in another paper by Mills, Kinoshita, and Grieveson,2 and, for the present purpose, a brief mention of the relevant features of the experimental method will be adequate. Using an induction coil, the metal weighing about 1 to 1.5 g was levitated by the electromagnetic field in a stagnant atmosphere of pure helium. The helium was freed from oxygen and water vapor in the usual manner, and its pressure in the vaporization chamber was maintained at 1 atm through a bleeder device. The vaporization chamber consisted of a pyrex tube, 2.8 cm diam, with a side arm connected to the helium bleeder. The bottom of the tube, shaped conical, was surrounded by the induction coil, and the top was sealed with an optical flat for the purpose of measuring the melt temperature with a two-color optical pyrometer. By suitable adjustment of the high-frequency power input, the metal was brought to the desired temperature in about 30 sec of levitation. After a specified vaporization time, e.g., 3 to 4 min, the alloy was quenched by switching off the power. The amount of metal vaporized was determined from the difference between the initial and final weights of the sample. During the vaporization time, temperature fluctuations of about ±10°C were observed. COMPARISON OF EXPERIMENTAL DATA WITH THEORETICAL VALUES The experimental results are given in Table I. As already mentioned, the attainment of the vaporization temperature took about 30 sec from the moment of levitation. Therefore, the times recorded in Table I are 30 sec less than the total time; this is considered to be a reasonable estimate of actual vaporization times.

Jan 1, 1964

By L. A. Weitzenkamp, N. M. Bashara

A study of the electrical conductivity of gold films less than 200 in thickness indicates a negative temperature coefficient of resistance and a thermal actiuatlon energy of less than 0.25 ev. The films consist of discrete metal islands of linear dimensions from a few angstroms to 1000A. Films were able to withstand applied fields up to 60,000 v per cm before breakdown occurred. A model for the conduction mechanism is proposed which involtes a Potential barrier due to work junction, irriage forces , and an electrostatic potential arising from separating an electron from a neutral island leaving behind a positively charged metal island. Activation energies of less than 0.25 ev ave consistent with this model, which includes a tunneling andor Thermal mechanism for conduction between the separate metal islands. An apparent satuvation effect in conductivity at high fields is observed experimentally. The saturation effect may be explained by the influence of the electrostatic contribution to the potential barriers for the transition through several islands adjacent to the original island which was activated to give up an electron. The proposed model gives Poor quantitative agyeement for the intermal electrical field between islands. ThIS paper will relate the structure of discontinuous metal films to the electrical properties and will emphasize the following topics: 1) the relation of the conduction mechanism to particle size and a comparison of particle size from electrical measurements with electron-microscope studies; 2) the saturation of the conductivity at high electric fields; and finally, 3) a comparison between the external field applied and the apparent field between particles. che- latter comparison points to a need for a modification in the model for the conduction mechanism first proposed by orter' and expanded by Neugebauer and webb2 which will be dealt with in the discussion. The paper is based on results on gold films on glass microscope slides. The clms were vacuum-evaporated and were about lOOA thick, thickness being measured by interferometry. It has been observed that metal films of this thickness do not exhibit bulk metallic conduction. Films thinner than some critical thiclmess, depending upon substrate temperature and other factors, have conductivities which increase with increasing temperature with thermal activation energies of less than 0.25 ev. Electron-microscope studies3 have shown that these films consist of discrete metal islands having linear dimnsions from a few angstroms to approximately 1000A. When the metal is being vacuum-deposited on the substrate, islands on the order of a few angstroms appear first. As the deposition continues the islands may tend to agglomerate into larger particles and may eventually grow together into a continuous film,3''' In our tests the conductivity of the gold films was found to be about ten orders of magnitude less than the bulk conductivity of gold. When oxygen was introduced into the test chamber the conductivity decreased by a factor of about one-third. This can be related to an increase in work function for gold caused by adsorption of oxygen, as reported by Oullet and Rideal.s Exposure to an atmosphere of water vapor caused an increase in conductivity by a factor of 2 or 3 when a low field was applied. When the films were exposed to water vapor under a high field the conductivity increased by as much as two orders of magnitude. The activation energies measured were much less than the work function for gold, 0.25 ev or less, with the smaller activation energies observed for thicker films. It will be shown that the activation energy is a function of particle size and spacing. In general the model for the potential between metal islands would include the effective work function, the image force, the applied field, and an electrostatic term. The electrostatic contribution arises from the potential required to separate an electron from a conducting sphere. According to Neugebauer and webb2 the maximum potential due to the field and the electrostatic term only is

Jan 1, 1967

By T. G. Digges, C. L. Vold, M. R. Achter

A study was made of the effect of the growth conditions on the perfection of single crystals of niobium (columbium). Dislocation densities, determined by means of double-crystal diffractometer measurements , were not greatly affected by the method of crystal preparation but could be reduced by annealing treatments. However, the size, sharpness, and tilt angles of the substructures, observed with X-ray reflection macrograph, were sensitive to variations in growth procedures as well as to subsequent thermal treatments. Although the dislocation density was the same in both types, there were more low-angle bound-aries in crystals grown by zone melting than in those prepared by strain anneal. Mechanisms to account for these observations are discussed in terms of dislocation movements. A planned study of the structure-sensitive properties of refractory metals required the use of single crystals of a high degree of structural perfection and, for ease of handling, of large cross section. It appeared that the strain-anneal technique could satisfy both of these requirements. First, crystals grown in the solid state have been reported to be more perfect than those obtained from the melt.' Second, the diameters of rods which may be produced by zone melting should have a theoretical limit determined by specific gravity, thermal conductivity, and surface tension, while the diameter of strain-annealed rods is limited only by practical considerations. Previously it was shown that niobium (columbium) single crystals of 1 in. diam2 may be grown by strain anneal, compared to the 0.5 in. maximum diameter achieved by zone melting, as reported for molybdenum by Belk.3 The current research was undertaken to investigate and optimize the effect of various process variables on the perfection of 1/4 and 1/2-in.-diam niobium single crystals grown by strain annealing and to compare their perfection to those grown by zone melting. Characterization of these crystals was more conveniently accomplished by means of X-ray than by metallo-graphic techniques. EXPERIMENTAL PROCEDURE Specimen Preparation. Zone-melted crystals of 1/4 in. diam were produced by the standard electron-beam zone-melting technique. The swaged and cleaned rods were outgassed, in the solid state at a temperature near its melting point, at a rate of 12 in. per hr, and single crystals were grown by making two molten passes at 2 in. per hr. By maintaining a zone length of 4 to % in., very uniform single crystals several inches long were obtained. For the strain-annealed crystals, an induction heater was used, in preference to other types of heating, to take advantage of the good penetration of large sections. A five-turn coil, 1 in. long, operating at 10 kc and powered by a motor generator, was contained in a vacuum chamber. The rod, suspended from the upper end, was raised through the coil for both recrystallization and crystal growth. In preliminary work single crystals of the same material were also grown with single and multiturn coils powered by a 450-kc generator. A vacuum of 2 X 10-6 Torr was maintained at temperatures up to 2400°C. Starting with electron-beam-melted ingots of 21/2 in. diam, the analysis for which is given in Table I, the material was cold-swaged to the desired cross section of 1/4 and 1/2 in. diam and then recrystallized. The rods were then strained in a tensile machine and converted to single crystals by passing through the induction coil. As with zone melting, control of orientation is possible by the use of special procedures. Other investigators, see for example Williamson and smallman,4 have reported that orientation control may be achieved by a bending technique. In the present work the strained rod is partially lowered through the coil to start the growth of the crystal. Then it is removed and bent at a point in the poly crystalline portion. Finally, it is returned to the chamber and growth is continued "around the corner". This procedure has certain limitations. If the bending operation exceeds the critical strain, recrystallization may take place. Also, the amount of bending which can be imparted to the rod is limited by coil geometry, and up to now has been 10 deg. However, by repeating the bending and growing operations it should be possible to attain any desired orientation. In preparation for X-ray examination, single crystals were sectioned and planed by means of the spark-erosion technique. To obtain the maximum reflected intensity, the (110) plane was exposed for examination. They were then etched 3 to 5 min in a mixture of con-

Jan 1, 1967

By M. P. Tixier

In several log interpretation methods, water saturation is evaluated by use of the ratio of the readings of a short spacing resistivity device and a long spacing resistivity device plus information on the mud filtrate and connate water resistivities, which is often derivable from the SP. These methods are valid over a certain range of conditions, usually specified by moderate invasion and R.. greater than R,. Since these methods involve no explicit evaluation of the formation factor, F, the saturafiion so found may be used in the standard Archie equation to derive a computed formation factor which, as a check, may be compared with the formation factor known from other independent measurements. Discrepancies in the two values of formation factor generally indicate that the ratio method is not within its range of applicability. If the computed F is too low, the corresponding S, is too low; if the computed F is too great, the corresponding S, is too great. By means of this "porosity balance" check, and some knowledge of the probable conditions of invasion, the interpretation can often be improved. The poqosity balance check is discussed for the cases of the Induction-Electrical Log Interpretation Method, the Rocky Mountain Method, and the R.,/R, Method. For the first method, a discussion is also given for the case of shaly sands. INTRODUCTION Al though many logging tools are available to obtain a practical value of porosity, the only logging method reflecting the water saturation is electrical logging. Water saturation is commonly computed from electrical log data by means of the basic Archie formula, Where F is the formation factor, R, the resistivity of the formation water, and R, the true resistivity of the formation. One difficulty in this procedure is a possible error in the evaluation of R, from the logs— for example, in the case of very deep invasion. There is no possibility, inherent in the procedure, which would provide a check of the accuracy of R, and, hence, of the computed saturation. Other approaches have been proposed which are based essentially on the ratio of the readings made with two dzerent devices: one device, with a short radius of investigation, provides a value close to the resistivity of the invaded zone; the second device, with a long radius of investigation, gives a value close to the true resistivity of the bed. By these methods, the determination of saturation is made independently of any direct knowledge of the formation factor. Therefore, if the formation factor (or porosity) is known from other sources (core analysis, neutron log, MicroLog . . .), it becomes possible to take advantage of this additional information in order to check the value of saturation derived from these latter methods. Inasmuch as this proposed check procedure relies on a knowledge of the value of formation factor or porosity, it has been deemed appropriate to call this verification a porosity balance. The purpose of this paper is to discuss the principle and the application of the porosity balance, depending on the method of interpretation being used. Basis of the Method There are in existence three interpretation methods by means of which the water saturation can bc found without a knowledge of the formation factor (or porosity). As just stated, they are based on the fact that the ratio of the two resistivities (one measuring the resistivity close to the hole, the other measuring the resistivity far from the hole) is independent of the formation factor since it affects the two resistivity measurements in the same way. Chronologically, the resistivity ratio methods are: (1) the Rocky Mountain Method, which has been used since 1943 and was explained in a paper in 1949;' (2) the R../R, Method or Shaly Sand Method, presented in 1954, which permits the calculation of the water saturation in both clean and shaly sands2; and (3) the Induction-Electrical Log Method, presented in 1957 for the interpretation of the induction-electrical log combination." Each method requires certain definite conditions in order for the interpretation to be reliable. The porosity balance method will let us know whether these conditions are fulfilled. In clean formations we know that the fundamental Archie relation (Eq. 1) must always be verified. This relation can be rewritten:

By J. J. Beeson

The second part of the paper includes a detailed account of the processes of secondary-enrichment which have been effective in producing the disseminated ores. While both parts present new features, it is hoped that the discussion on secondary chalcopyrite and bornite may be of interest to those who are engaged in the study of secondary processes in other districts. The excellent work' Economic Geology of the Bingham Mining District, by J. M. Boutwell, was published in 1905. Since that time the extensive development work-surface cuts and underground drifting-of the Utah Copper Co. has made possible the collecting of samples for more detailed microscopic study. The writer has taken advantage of this fact and presents the following work, not as a criticism, but as a' continuation of the work which was begun by Mr. Boutwell. b. Acknowledgments.-The present study was undertaken at the suggestion of Dr. A. F. Rogers; to him, and to Prof. C. F. Tolman and Prof. S. W. Young, the writer wishes to express his thanks for criticism in the preparation of this paper. The writer also expresses his thanks to D. C. Jackling, Vice-President and Managing Director of the Utah Copper Co., for permission to publish this paper, and to William Spencer, D. W. Wadleigh, T. S. Carnahan, J. A. Caulfield, Percy Dayer, and Edward Norsefall, for the courtesies extended to him while a co-worker in the mines.

Jan 11, 1915

By J. H. Nead, J. W. Halley

The new low-alloy high-strength steels are obviously here to stay. With 75 per cent higher yield strength and 50 per cent higher tensile strength than plain carbon structural steel, they permit 20 to 40 per cent weight savings and 10 per cent or more increase in pay load in the construction of railroad cars, buses, trucks, and a great variety of material-handling equipment. Their cost is low enough so that the extra cost of the new lighter construction over that with carbon steel offers an attractive self-liquidating investment; in some instances new construction with these low-alloy steels may even be as cheap as with plain carbon steel. A considerable and rapidly growing demand for the low-alloy steels has already sprung up. The many steel compositions that have appeared on the market lately18, 27, 28, 29, 30 to meet this demand would seem to indicate that no single composition is uniquely fitted for the purpose. However, no doubt some compositions are more suitable than others. The purpose of this study was, therefore, to compare the effects of the various alloying elements that might be used in the low-alloy steels in order to choose the metallurgically most logical composition, paying due regard, of course, to the economic aspects involved. Properties Desired in Low-alloy Steel A distinction between the new low-alloy steels and the common alloy steels is that the latter are generally used in the heat-treated (that is, quenched and tempered) conditions, whereas the new low-alloy steels are not only not heat-treated but are not susceptible to heat-treatment in the ordinary sense of the term. In this lies one of their chief advantages. Their properties can be obtained in the as-rolled, air-cooled, or annealed condition, just as with mild plain carbon structural steel. There is no need for heat-treating. Such steels can be readily formed hot or cold, and their properties are not appreciably changed by hot

Jan 1, 1936

By J. H. Nead, J. W. Halley

The new low-alloy high-strength steels are obviously here to stay. With 75 per cent higher yield strength and 50 per cent higher tensile strength than plain carbon structural steel, they permit 20 to 40 per cent weight savings and 10 per cent or more increase in pay load in the construction of railroad cars, buses, trucks, and a great variety of material-handling equipment. Their cost is low enough so that the extra cost of the new lighter construction over that with carbon steel offers an attractive self-liquidating investment; in some instances new construction with these low-alloy steels may even be as cheap as with plain carbon steel. A considerable and rapidly growing demand for the low-alloy steels has already sprung up. The many steel compositions that have appeared on the market lately18, 27, 28, 29, 30 to meet this demand would seem to indicate that no single composition is uniquely fitted for the purpose. However, no doubt some compositions are more suitable than others. The purpose of this study was, therefore, to compare the effects of the various alloying elements that might be used in the low-alloy steels in order to choose the metallurgically most logical composition, paying due regard, of course, to the economic aspects involved. Properties Desired in Low-alloy Steel A distinction between the new low-alloy steels and the common alloy steels is that the latter are generally used in the heat-treated (that is, quenched and tempered) conditions, whereas the new low-alloy steels are not only not heat-treated but are not susceptible to heat-treatment in the ordinary sense of the term. In this lies one of their chief advantages. Their properties can be obtained in the as-rolled, air-cooled, or annealed condition, just as with mild plain carbon structural steel. There is no need for heat-treating. Such steels can be readily formed hot or cold, and their properties are not appreciably changed by hot

Jan 1, 1936

By Larry D. Hartzog

PANELISTS Paul Chamberlin, Nerco Minerals Jim Gourdie, Goldfield Mining Corp. Roger Leonard, Cyprus Northumberland Mining Co. Eric Daniels, Tenneco Minerals John Dasher, Consulting Metallurgist Bob Shoemaker, San Francisco Mining Associates Larry Hartzog, Bechtel Civil and Minerals, Inc.

Jan 1, 1984

By K. N. Han, H. Lee, M. C. Fuerstenau

An investigation of the recovery of finely-divided cassiterite and silica particles less than 1 µm (1200 mesh) in size has been carried out using packed and fluidized beds. The bed particles used included cassiterite and silica particles ranging from 44 to 210 µm (325 to 70 mesh). Effects of various system parameters on the recovery and selectivity of cassiterite fines were investigated. System parameters included pH of the slurry solution, superficial velocity, slurry concentration, and bed particle sizes. High recoveries of cassiterite fines were obtained at pH 4.0 and slow slurry flow rates. In a packed bed system, recovery of cassiterite fines was greater than 95%, while that of silica fines under the same conditions was about 35%. Although the total recovery per pass is not as good as the packed bed, the fluidized bed system exhibits good recovery in general and an excellent selectivity of cassiterite fines. There is an optimum superficial velocity, vo, for the rate of fine particle uptake and the apparent rate constant has the form of Kvo1/2- K'vo, where K and K' are system constants.

Jan 1, 1985

By Irwin Roman

IN a previous paper,1 a method was suggested for determining the depth to a bed in the simple case of a uniform overlying layer of constant thickness. The main purpose of the present paper is to show how a slight modification of that method has been used to interpret specific data obtained in the upper peninsula of Michigan by the staff of the Depart- FIG. 1.-THE TECTONIC CONFIGURATION. ment of Mathematics and Physics of the Michigan College of Mining and Technology. The method of Tagg2 has also been used on the same data, thus furnishing a comparison of the e two methods, as well as a method of using the two methods jointly. The method of measuring the apparent resistivity is that suggested by Wenner,3 and illustrated in Fig. 1. A current I enters the earth at the positive pole C and leaves it at the negative pole D. The potential V of the high electrode A, with respect to the low electrode B is measured by suitable means. The separation of the collinear points in the order shown, DBAC, is 1, the same. for each interval.

Jan 1, 1934