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Doctor David Yang has presented an important new flotation development in the area of fine particle flotation technology; at the same time Dr. Yang presents an explanation for the effectiveness of this improved new fine flotation system in terms of an optimum dispersion state. The same statement is made for the case of carrier flotation (ultraflotation), in the removal of anatase from kaolinite by addition of calcite (selective flocculation of the anatase - calcite system and dispersion of kaolinite). Dr. Yang's data and statements raise some important questions, and I will adress myself to the more fundamental aspects of this new flotation system. The addition of sodium silicate, well known as a good depressant-dispersant agent for siliceous gangue minerals, is proved to be greatly enhanced by the incorporation of polyvalent metal salts into sodium silicate prior to flotation, producing in this manner a condition, as described by Dr. Yang, of optimum dispersion, which in the case of fine-grained oxidized taconite can be described as selective flocculation (coagulation) of hematite and almost complete dispersion of siliceous gangue components. Dr. Yang recognizes that the main mechanism, while not completely understood at this time, seems to operate by modifying the surface characteristics of the gangue slime particles so as to prevent collector from bonding there to, and making the particles strongly hydrophilic so they will become fully dispersed and consequently will not float during froth flotation. At the same time it appears that the conditioning reagent also modified the surface characteristics of the floated minerals (hematite and spodumene in this case) so that they will aggregate and tend to more readily adsorb the collector, resulting in an improved flotation kinetics and selectivity.

Jan 1, 1979

By Benjamin Gildersleeve

Uniquely colored, thin-bedded quartzite is quarried between Crossville and Crab Orchard in Cumberland County, Tenn. It is produced in all sizes up to the limits of transportation from beds usually ranging in thickness from less than 1/2 in. to 6 in. The stone is very resistant to wear and weathering and is marketed throughout the country for many different purposes in exterior and interior construction. The annual production exceeds 36,000 tons, valued at nearly $1,000,000.

Jan 8, 1950

We regret to advise that, owing to unusual pressure of business at our printers, Volume TAX will not be ready for distribution so early as was announced in the last Bulletin. It will probably be distributed in November. Volumes LVII and LVIII were mailed during the month of August to all members whose dues were paid on Aug. 1; members who failed to receive their Transactions within a reasonable time are requested to notify the Secretary. In the case of members who have recently changed their addresses, the Transactions Were sent-to addresses on record on Aug. 19; those who did not notify .us of change of address until after Aug. 19 will find their Transactions at the old address.

Jan 10, 1918

By Guy R. Johnson

In working brown iron-ore mines on the system employed at Longdale, namely, stoping from the top down, the usual procedure is to drive a succession of upraises from the lowest adit to the highest, or to the top of the deposit, as the case may be. These up-raises are usually driven 120 feet apart., along the strike of the vein,. As the work goes on, they are connected by levels, 10 feet spa* (vertically), and then serve as chutes. A transit is useless in surveying these chutes, and the writer has for several years made use of a hanging compass. The method of using this instrument, described in a former paper (Trans., xx.,.105), embracing as it does the use of a cord and several strips. of wood,

Jan 1, 1894

By John E. O’Rourke, Kevin M. O’Connor, Pamela H. Rey

INTRODUCTION The resurgence of coal mining activity in the United States, brought on by the spiraling costs of fossil fw1 energy in the Seventies, has come at a time of intense public concern for the quality of the environment. Notwithstanding pressure on our economy to develop alternate sources of fue1 energy to the import of oil, the legislatures of several states have reacted to public concern over the environment by passing strict regulations aimed at con- trolling the subsidence effect s of underground mining. Agencies of the federal government charged with assistance to the mining industry, including the Department of Energy and the Bureau of Mines, have sponsored a number of instrumentation and field measurement projects aimed at the development of subsidence prediction models that can aid the mine operator's task of subsidence control. There are good empirical models developed in Europe for subsidence prediction, but they were made possible by a large body of mining-induced subsidence data collected there over a long period of time. No com- parable subsidence data base exists in the United States, and consequently empirical modeling of subsidence is not a realistic approach for our near term needs. Moreover, the geologic and topographic diversity of the several coal regions in the United States is expected to necessitate the development of several empirical models, each one expected to be relevant to its own region. Because of the time and costs that are likely to be involved in an empirical modeling approach, it is considered more expedient and cost effective to develop a general, mechanistic model for subsidence prediction purposes. In order to develop such a model, it is necessary to investigate and quantify the mechanics of the subsidence process from the mine level up to the ground surface. The series of projects discussed in this paper are designed to achieve this objective and include the following work: (1) the identification of geotechnical instrumentation that will pro- vide mine level overburden and surface subsidence data. (2) a field demonstration of selected instruments, and (3) documentation of case histories for complete subsidence mechanics, using the demonstrated and preferred instruments. An identification of feasible instrumentation and monitoring techniques was completed by Woodward-Clyde Consultants (WCC) in 1977 (O'Rourke and others). This paper discusses a demonstration of those instruments at a mine in Utah, and at two subsequent projects, currently underway at longwall mines in Colorado and West Virginia. 'he latter two projects when complete will provide documented case histories of subsidence mechanics. The process of optimizing subsidence instrumentation and monitoring techniques to the conditions encountered during installation and monitoring for these underground mines is shown to be an evolving one, and one which has had some notable successes to date. INITIAL DEMONSTRATION The initial design and demonstration of selected monitoring systems was carried out at the SUFCO No. 1 mine, near Salina, Utah. The instrumented panel was approximately 152 m wide. 640 m long. and was 290 m to 320 m deep. The mined height of coal. seam averaged 2.4 m. The mining method was room and pillar using continuous mining machines. This method allowed some monitoring of the supported condition during development, and eventually allowed monitoring of a caved system when both chain pillars and room pillars were extracted on retreat. The two instrument systems shown on Table 1 were selected from the earlier feasibility report for demonstration at SUFCO No. 1. Collectively, the two systems, one for a fully-supported mining method and the other for a fully-caved method, incorporate most of the instrumentation to be found within all five systems listed in the earlier feasibility report. The instrumentation includes surface, subsurface and mine monitoring installations. All of the SUFCO instruments selected to meet the specifications of the general instrument types listed on Table 1 were manually operated. That is, data from the installed system could only be obtained while a person was there to physically observe or operate the system readout. Automatic data recording equipment was available for some installations, but the objectives were to keep the systems as simple as possible for the demonstration project. A complete description of the surface, sub- surface and mine level instruments, and the demonstration project results are given in WCC (1982), and selected features are discussed in this paper.

Jan 1, 1982

By T. Wasson

Midland and Isabella counties have been the centers of activities for the year 1932. The major part of the 6,967,000 bbl. produced during the year was obtained from the old Mt. Pleasant field and the Eastern Extension field. The total production to the end of 1932 for Michigan, from all fields since discovery, is 20,679,600 bbl. Production in the Eastern Extension field was obtained from Dundee limestone of Devonian age, at a depth of about 3600 ft. As a result of the year's activity in this area, the limits of the Eastern Extension have been defined. No new fields have been discovered. A number of prospective areas have been drilled and condemned by dry holes. Probably the most outstanding development of the year was the discovery of oil on the Yost farm, in sec. 35 of Greendale Township, Midland County, by the Pure Oil Co., in the early part of December. Production is from the Dundee limestone similar to that in the Eastern Extension but is 4 miles south of that area. The first well has averaged about 500 bbl. per day since completion. It is near the center of a solid block held by the Pure Oil Co., so that rapid development due to competitive drilling is not expected. During the early part of the year the Midland-Isabella area was under proration, but on May 17 proration restrictions were discontinued and remained so until the end of the year. While the Eastern Extension saw the principal activity, some work was done in other fields of Midland and Isabella counties, but very little new production was added. The Vernon field on the north showed a slight increase in production over 1931. The Leaton field decreased. The well in Porter Township, Midland County, is still kept in the production ranks but very little drilling was done in that area. The old Saginaw field, Saginaw County, still remains the only spot in the state where commercial production is obtained from the Berea sand. It showed a slight decline over 1931 with no new producers for the year. The Muskegon field on the west side of the state showed a considerable decline over 1931, but owing to the rejuvenation of some wells by the use of acid this drop was not as great as might have been expected. Only two new producers were drilled in that area.

Jan 1, 1933

PRESIDENT ARTHUR DWIGHT District 0 NEW YORK, N Y PAST PRESIDENTS EDWIN LUDLOW District 0 MINNEAPOLIS, MINN HERBERT HOOVER, District 4 WASHINGTON, D C FIRST VICE-PRESIDENT JVC REYNOLDS NEW YORK, N Y

Jan 1, 1923

By Henry J. Kaiser

A few months ago I had the honor of addressing the Society of Mining Engineers annual banquet in Sun Francisco. I have since been asked to amplify some of the remarks I made at that time concerning the management policies of the Kaiser organization and various aspects of our corporate thinking. This is a difficult task for an insider like myself. I look at the different companies, and the men who run them, and it is hard to think of these men in terms of policy or procedure. Actually I prefer the term management philosophy to either policy or procedure. My father, Henry J. Kaiser, is not only the founder but the guiding spirit of our organization. His philosophy, and in turn that of the organization, centers around two concepts, service and accomplishment.

Jan 1, 1960

By K. N. Clark, N. B. Carter, C. G. Thomas, V 7. 0 / 300 dpi

A statistically designed, experimental study showed how gangue minerals, flux additions, fineness of grind, firing temperature, and time affect the properties of acid pellets made from a Western Australian hematite ore. Alumina has less effect than silica and lime, but interactions between the six variables occur, which influence abrasion index, reducibility, and cold compression strength. Finer grinding has little influence on reducibility but improves the other two properties. The major variable is firing temperature, which interacts with all other variables to affect pellet properties. Calculations based on the data show the implications for straight-grate pellet plants and optimum hood temperature ranges.

Jan 1, 1982

By S. C. Dhara

A process of solvent extraction and separation of platinum group metals (PGM) and gold using primary, secondary, tertiary, and quarternary organic amines has been briefly described. The effects of amine structures; the use of diluents; the principle of synergism and antisynergism in the mixed extractants; the oxidation states of metal ions are explained in the amine extraction process of precious metals.

Jan 1, 1984

By J. F. Smith

ELASTIC constants of yttrium and eleven of the rare earth elements have been measured. This has been accomplished by measuring the propagation velocities of ultrasonic pulses. The velocity measurements were made by noting the elapsed time between an applied pulse and the appearance of successive echoes. The pulse-echo technique has become relatively common, and the basis of the measurement is outlined in several standard tests, e.g., Heuter and Bolt.1 Two important assumptions are made when using this method for the determination of elastic moduli. First, the pulse is assumed to propagate as a plane wave. To justify this assumption, the cross section of the test specimen should be large compared to the wave length of the transmitted pulse. For these measurements on the rare earth elements the minimum cross section wave length ratio was about 20. A second assumption which must be made when using polycrystalline specimens is that the grains are sufficiently numerous and randomly oriented so that the specimen may be approximated as elasti-cally isotopic. The grain size in the as-cast specimens which were used is believed to be sufficiently fine for this approximation, and the degree of preferred orientation is believed to be small. Supporting this viewpoint is the fact that elasticity measurements by the pulse-echo technique on as-cast specimens of other metals give results which are in satisfactory agreement with values obtained by other techniques. Hence, it is believed that the measured elasticity values for the rare earth elements are not apt to be seriously in error due to the assumption of elastic isotopy. The apparatus used in this determination was a modified Sperry Reflectoscope with a precisely calibrated time base circuit. Piezoelectric transducers were used both to generate the pulse and to detect the echoes. X-cut quartz crystals were used for the longitudinal modes, and Y-cut quartz crystals were used for the shear modes. Frequencies of 2.25 and 5 megacycles per sec were employed. Most of the specimens were 2.5 to 5.0 cm in length. Results Table I is a tabulation of the measured propagation velocities of longitudinal waves and of shear waves, together with densities obtained by Sped- ding, Daane, and Herrmann2 from lattice parameter measurements. The shear modulus, Poisson's ratio, and Young's modulus were calculated from the data in Table I through use of the following relationships: µ = pv32 [1] s=2-(vb/vs)2/2[1-(vb/vs)2] [2] and Y= 2µ(l+s) [3] where s is the shear modulus, Y is the Young's modulus, s is Poisson's ratio, p is the density, V0 is the longitudinal wave velocity, and v, is the shear wave velocity. The calculated quantities are shown in Table 11. Compressibility values can be computed from the relationship and the computed values may be compared with measured values obtained by Bridgman.8 Table III lists the data for such a comparison. The agreement is satisfactory, being particularly good for neodymi- um and gadolinium, poor for samarium, and intermediate for the other elements. Some variation is expected since Bridgman's measurements are isothermal, whereas the present measurements are adiabatic. In addition there may be some effect due to small variations in purity. Though most of the rare earth metals measured by Bridgman and all of the metals used in the present measurements were prepared at this laboratory, minor purity variations might exist since the samples came from different lots. Also, any imperfections such as dislocations, vacancies, voids, grain boundaries, microcracks, etc., should contribute to the volume change of a com-

Jan 1, 1958

By Robert Anderson

ROUGHLY, a crack in a casting may be considered, for the moment, to be due to fracture of the alloy resulting from the stress set up by the contraction in volume on passing from the liquid to the solid state. Cracks may be external or surface, internal or deep-seated, or incipient or so-called strain cracks. Draws may appear as depressions, unevenness, and "pinching in" of the surface of a casting. Roughly, draws are due to contraction in volume and are governed largely by the same factors as cracks. A casting may be cracked, however, without being drawn. Shrinkage is a foundry term; it connotes the contraction in volume of a metal or alloy on passing from the liquid to the solid state. Pattern-makers' shrinkage is the total contraction in volume (including liquid, solidification, and solid shrinkage) that occurs when an alloy is poured into a mold. The contraction in volume of aluminum is one of the principal factors affecting the occurrence of cracks, as will be shown later, and the question of shrinkage and its control requires careful study in any treatment of cracking in castings. In the case of, sand and die castings, cracks have been attributed to a number of causes, but in the case of most light aluminum alloys, they are due to the large contraction in volume on freezing and the lack of its regulation or control. The most important factors are: (1) Contraction in volume; (2) composition of alloy; (3) quality of melting charge; (4) design of casting; (5) method of molding; (6) hardness of ramming; (7) method of gating; (8) hardness and characteristics of cores; (9) chills; (10) risers; (11) melting temperatures; (12) furnace used for melting; (13) pouring tempera-tures; (14) inclusions in alloys; (15) hot shortness of alloys; and (16) physical properties of alloys at high temperatures. Of these, the first, second, third, and eleventh to sixteenth involve ascertainable metallurgical facts; the remainder are largely matters of opinion, judgment and technical knowledge of men experienced in the production of castings.

Jan 10, 1921

By C Gunther

The purpose of this book is to present the practical side of economic geology concisely and in convenient form; established facts and the applications of accepted views are emphasized; theoretical discussions and questions of genesis are avoided. Coal, iron, and placer deposits are omitted; they are subjects of specialized study that are fully and concisely treated in other works. The reader is assumed to possess a knowledge of mineralogy, petrography, and elementary geology. The arrangement adopted is based on Kemp's theory of magmatic waters, on Lindgren's conclusions on hydrothermal and secondary alterations, and on the theories of secondary enrichment enunciated by Emmons and Weed. No general classification of ore deposits is attempted, nor is any attempt made to fill by hypothesis the wide gaps, nor to explain the apparent contradictions that rank economic geology among the most inexact of sciences. The present knowledge of the subject is too incomplete to warrant such broad generalizations. The demand for good properties generally exceeds the supply. While mines of the first rank will undoubtedly be discovered from time to time, it is probably true that a great proportion of deposits having outcrops of commercial grade or of evident promise have been recognized and explored. A review of mining conditions over long periods shows that the rich discoveries belong to pioneer days, and that as time goes on the more important developments are the result of lower working costs, improved metallurgical processes, and an increasing knowledge of economic geology. As engineers in search of developed mines no longer expect to find properties having positive ore of greater net value than the price asked, so those in search of prospects should not expect to

Jan 1, 1932

By Walter R. Crane

Operators of diamond drills have long been familiar with threadlike markings or riflings on cores but apparently have given but little serious thought to the conditions that are responsible for their production. The opinion generally held by those who have observed the phenomena is that the riflings are produced directly or indirectly by vibration, but so far as the writer is aware no systematic attempt has been made to demonstrate the fact. A careful search through the literature on diamond-drilling practice has been rewarded by only one reference to such markings of cores. J. N. Justice1 writes, "Of the peculiarities met with in the core, I will mention only one. The core from the "H" drill, at about 360 ft. came out rifled and pentagonal. The change from the circular to the pentagonal was sudden, and for 9 ft. this structure was maintained, when suddenly it returned to the circular. I have not been able to find any one who can explain the cause of this change of form. The drill men marveled at it and suggested vibration, six-stone bits, and several other hypotheses which need not be mentioned." The writer became interested in the matter of core riflings some 10 years ago while in the Flat River lead region of Missouri, where many remarkable examples of "rifled" cores were observed and collected. Since that time similar phenomena have been observed in various localities throughout the United States and Canada, and samples have been gotten together illustrating a large number of variations in form. After a careful study had been made of the material at hand it seemed desirable that certain data should be obtained from the experience of others regarding the normal action of diamond drills in forming cores, portions of which are occasionally rifled, before an attempt was made to draw any conclusions as to their cause. About 20 letters were addressed to diamond-drill companies, operators, and engineers actively engaged in drilling operations, with a

Jan 1, 1917

By Ralph Schilthuis

SEVERAL investigators1-8 have reported evidence of the existence of native or connate water in oil-and-gas-bearing strata. Both water and salt have been detected in cores of oil sands that yielded oil and gas exclusively when produced. Electrical logs often reveal unexpectedly low resistivity through oil and gas sands, indicating the presence of some material that is a considerably better conductor of current than oil and gas. Furthermore, calculations9 of the oil and gas content of reservoirs based upon production and reservoir-pressure decline data indicate appreciably lower values than are arrived at under the assumption that the pore space is occupied completely by oil and gas. ORIGIN AND OCCURRENCE OF CONNATE WATER IN OIL-AND-GAS-BEARING FORMATIONS The view has been expressed,10-15 and is generally agreed upon, that the expulsion of oil and gas material from source beds and the subsequent migration and accumulation occurred in the presence of salt water. As the strata that usually form reservoirs for oil and gas were laid down by, or in the presence of, ancient seas, the pore space within the strata must have been saturated with salt water before the entrance of the oil and/or gas. Thus, the accumulation of oil and/or gas in the upper regions of structures suitable for reservoirs must have required displacement of the connate water therefrom. In the absence of any forces other than gravitational, it would be expected that the displacement of the connate water out of the zones finally occupied by gas and oil would be complete, and that the vertical distribution of gas, oil, and water in a reservoir would be strictly in the order of their densities. Apparently, however, surface and interfacial forces that will not permit complete segregation of the fluids are active within the capillary spaces comprising a reservoir. The effects of these forces on both accumulation and production of oil and gas have been the subject of study by a number of investigators. 16-37

Jan 1, 1938

By Hans Conrad, W. D. Robertson

FORMAL theories of yielding and flow have been developed to describe thermally activated plastic flow in metal crystals.'-" hey are all based on Becker's' original idea that thermal fluctuations aid the applied stress in overcoming internal barriers to flow and lead to the following relation. where j is the strain rate; C is a constant which includes a frequency factor, the entropy, the number of flow units, and the amount of strain associated with each successful fluctuation; E(T) is the activation energy associated with flow, and is a decreasing function of the applied stress, 7; k is Boltzmann's constant; and T is the temperature in OK. The various theories differ mainly in the model chosen and in the nature of the relationship between the applied stress and the activation energy. Beckerl and Orowan' suggest a relationship of the form E a(Ti — t)2, where .ri represents the stress required for flow without the aid of thermal fluctuations; Kauzmann,3 Cottrel1,5 and Seeger6,7 suggest E a(t — t) ; Fisher8 suggests E while Cottrell and Bilby4 suggest a more complex relationship between E and 7. Additional data are needed to test these various theories., esweciallv- in view of Dorn's9 ork. which indicates that the activation energy for creep is independent of the stress and strain. The present paper presents the stress-strain data derived from incremental loading of magnesium single crystals in tension and direct shear, in the temperature range of 78" to 364°K. Incremental loading was employed in order that the creep component of the strain could be determined. Stress-strain curves of aluminum10-13 and copper" single crvstals. derived from incremental loading tests, have been found to be in agreement with those obtained by the more conventional constant strain rate or loading rate tests. Two types of tests were conducted in the present investigation: 1) tests in which the temperature was maintained constant throughout the entire

Jan 1, 1958

By William Crane

OPERATORS of diamond drills have long been familiar with thread-like markings or riflings on cores but apparently have given but little serious thought to the conditions that are responsible for their production. The opinion generally held by those who have observed the phenomena is that the riflings are produced directly or indirectly by vibration, but so far as the writer is aware no systematic attempt has been made to demonstrate the fact. A careful search through the literature on diamond-drilling practice has been rewarded by only one reference to such markings of cores. J. N. Justice1 writes, "Of the peculiarities met with in the core, I will mention only one. The core from the "H" drill, at about 360 ft. came out rifled and pentagonal. The change from the circular to the pentagonal was sudden, and for 9 ft. this structure was maintained, when suddenly it returned to the circular. I have not been able to find any one who can explain the cause of this change of form. The drill men marveled at it and suggested vibration, six-stone bits, and several other hypotheses Which need not be mentioned." The writer became interested in the matter of core riflings some 10 years ago while in the Flat River lead region of Missouri, where many remarkable examples of "rifled" cores were observed and collected. Since that time similar phenomena have been observed in various localities throughout the United States and Canada, and samples have been gotten together illustrating a large number of variations in form. After a careful study had been made of the material at hand it seemed desirable that certain data should be obtained from the experience of others regarding the normal action of diamond drills in forming cores, portions of which are occasionally rifled, before an attempt was made to draw any conclusions as to their cause.

Jan 5, 1916

By Gerhard Derge, Harold Markus

The introductory paper1 of this series described the potential behavior of tin in sodium carbonate and bicarbonate solutions whose pH ranged from 8.4 to 11.2 and demonstrated that significant and reproducible results could be obtained by proper attention to experimental technique. In examining the corrosion of tin under such conditions, it is desirable to know the effects of anions, aside from carbonate, that are likely to be present in commercial materials packaged in tin. Therefore, in this paper the potential behavior of tin in carbonate solutions to which sodium fluoride, chloride, bromide, iodide, sulphate, nitrate, monobasic phos-phate, dichromate, perborate and acetate have been added will be dcscribed. For most of the additions, solutions containing 0.001 and 0.01 moles of the added material were studied. The experimental procedure was exactly the same as that described in the first paper; the pH of the electrolyte was controlled by adjusting the ratio of carbonate to bicar-l,ol~ate as follows: pH 0.1 M NaHC0............................................ 8.4 2 parts 0.1 M XaHCOr, 1 pa.rt 0.1 M NaZCO?................. 9.5 1 part 0.1 M NaHCOs, 2 parts 0.1 M iVa.,C03. ................ 10.0 0.1 M Na2C0............................................. 11.2 The reagents used were all of C.P. grade. The anions studied may be divided into three groups: (1) anions that had little or no effect upon the potential curves—sulphnte, nitrate, and acetate; (2) those that helped to prevent corrosion at low pH only -fuoridc, chloride, bromide, and iodide; (3) those that helped to prevent corrosion at high pH also—phosphate, pcrborate, and chromate. Potential Measurements f The time-potential curves represntative of group 1 are shown in Fig. 1. These are the curves for 0.005 M sulphate ion and their similarity

Jan 1, 1939

By Harold Markus, Gerhard Derge

The introductory paper1 of this series described the potential behavior of tin in sodium carbonate and bicarbonate solutions whose pH ranged from 8.4 to 11.2 and demonstrated that significant and reproducible results could be obtained by proper attention to experimental technique. In examining the corrosion of tin under such conditions, it is desirable to know the effects of anions, aside from carbonate, that are likely to be present in commercial materials packaged in tin. Therefore, in this paper the potential behavior of tin in carbonate solutions to which sodium fluoride, chloride, bromide, iodide, sulphate, nitrate, monobasic phos-phate, dichromate, perborate and acetate have been added will be dcscribed. For most of the additions, solutions containing 0.001 and 0.01 moles of the added material were studied. The experimental procedure was exactly the same as that described in the first paper; the pH of the electrolyte was controlled by adjusting the ratio of carbonate to bicar-l,ol~ate as follows: pH 0.1 M NaHC0............................................ 8.4 2 parts 0.1 M XaHCOr, 1 pa.rt 0.1 M NaZCO?................. 9.5 1 part 0.1 M NaHCOs, 2 parts 0.1 M iVa.,C03. ................ 10.0 0.1 M Na2C0............................................. 11.2 The reagents used were all of C.P. grade. The anions studied may be divided into three groups: (1) anions that had little or no effect upon the potential curves—sulphnte, nitrate, and acetate; (2) those that helped to prevent corrosion at low pH only -fuoridc, chloride, bromide, and iodide; (3) those that helped to prevent corrosion at high pH also—phosphate, pcrborate, and chromate. Potential Measurements f The time-potential curves represntative of group 1 are shown in Fig. 1. These are the curves for 0.005 M sulphate ion and their similarity

Jan 1, 1939

By William A. Longacre

IN a previous paper1 the author discussed the problem described by the title of this paper, outlining and reviewing the Gish-Rooney method, with comparison and brief analysis of the interpretation techniques of Roman2 and Tagg.3 Some aspects of the simple type of two-layer system were reviewed from various sources.4,5,6 THE TWO-LAYER PROBLEM For the configuration shown in Fig. I, and for any electrode separation A, the apparent resistivity is a function of the relative depth [HA], the overburden resistivity pi, and a factor K defined by the equation [ ] where p2 is the resistivity of the lower bed, Thus, by the known theory of electrical images, [ ] THE MULTILAYER PROBLEM As the number of isotropic, homogeneous, horizontal layers increases, the difficulties of interpretation multiply. The theory becomes much more involved, and in view of the state of our knowledge, the general problem is virtually impossible of exact solution. However, certain types of [ ] multilayer problems can be worked out in terms of two-layer theory. Hummel,7 Pirson,8 Tagg,3 Watson,9 and others have pointed out the possibility of building up approximations of multilayer resistivity curves with suitable combinations of two-layer curves. Many three-layer curves can be constructed in this way to a good degree of accuracy, and special types of four-layer curves can be approximated. It is very likely that as the number of layers increases, the method of combination will not give good approximations except in very special cases, In the analysis of actual field data, the author has found that many obviously multilayer curves can be solved partially with a good degree of accuracy, using the theory that thin adjacent beds may be considered as one layer or zone, and applying two-layer theory to the extremities of the field curve. MODIFIED TAGG METHOD OF INTERPRETATION Tagg's second method, though superior to his first, necessitates a large number

Jan 1, 1941