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By Portland P. Fox, Berlen C. Moneymaker

The development, within recent years, of core drills capable of drilling holes up to 72 in., or even more, in diameter, has made possible an entirely new and valuable method of geologic exploration. Although little used until recently as an exploratory tool except in the United States, by the Tennessee Valley Authority and the Corps of Engineers of the U. S. Army, for the exploration of damsites, the large-diameter core drill may be used to good advantage in other types of geologic exploration. Its principal utility is that of supplementing, rather than replacing, other means of exploration. Although core is frequently recovered intact, the greatest advantage of large-diameter drilling is that the holes produced are large enough to be entered by the geologist and engineer, and thus afford an excellent means of examining undisturbed rock. The walls of the holes are smoothly cut, and in some rocks nearly or quite polished, so that the most minute details of structure and stratigraphy are clearly disclosed. Such features as faults, joints, bedding planes, weathered "seams," and beds or layers of soft materials, which are not always amenable to disclosure by cores recovered from small-diameter holes, are conspicuously displayed in the walls of large holes. Frequent reference to the drilling of large-diameter holes is made in engineering literature, but comparatively little emphasis has been placed on their value in geologic investigation. It is, therefore, intended that the present paper acquaint the geologist, as well as the engineer, with the large-diameter core drill and the technique involved in its use, and also with its advantages, disadvantages and limitations as an implement of geologic exploration. The Equipment The equipment generally employed in the drilling of large-diameter holes consists of a trunnion-type drill head mounted on a sliding base, which allows it to slide clear of the hole and thus permit the introduction

Jan 1, 1941

By G. D. Van Arsdale

This paper describes a series of experiments leading to the development of a method for leaching the mixed ores of the Inspiration Consolidated Copper Co., containing chalcocite and silicates of copper, by the use of solutions acidified with sulfuric acid and carrying ferric sulfate. Iron is added to the solutions and ferric iron is regenerated electrolytically to a percentage high enough to act as an effcient solvent. The decreased yield is partly compensated for by a higher current density. An important problem in modern copper metallurgy, particularly in the Southwest, has been to obtain good recoveries from what are commonly known as mixed ores; that is ores in which the copper occurs partly as oxide and partly as sulfide compounds. The dividing line between mixed ores and ores commonly accepted as concentrating is not definite. In other words, much ore now being concentrated carries considerable copper in non-sulfide form, on which recoveries are not so good as on ores carrying less of these constituents. While treatment by concentration may be commercially profitable on ores carrying oxide copper within certain limits, there are large deposits for which the application of concentration could not be considered, and yet which have not been considered amenable to leaching because they carried too much sulfide. The Inspiration Consolidated Copper Co. has large amounts of such mixed ores, and this paper is an account of the experimental work by which a method was developed for their treatment, and for which a large plant is now being erected by the Inspiration Co. It is not claimed that the method is a general solution of the problem of mixed-ore treatment but it is apparently well adapted for leaching the ores of the Inspiration Co., for which it was designed. The work done has covered preliminary laboratory and test-plant investigation, and a pilot-plant run, extending from March to the middle of December, 1923. Thoroughly consistent and satisfactory results were obtained continuously for more than six months in the pilot plant; and it is believed that the results and probable costs that can be had on a large scale have been definitely proved. The method, however, was designed for local conditions; and while the basic principles are general, there are ores on which it will not work and other ores for which considerable modification may be required.

Jan 1, 1926

By Bruce N. McIver, Leo Casagrande

Similarities are noted in the practices and problems of constructing dams to impound mine tailings, fly ash, and chemical wastes. The comparison of a typical tailings dam with a conventional water-retaining earth dam shows that the former is inherently less stable and can be susceptible to cracking, liquefaction, erosion, and frost action, as illustrated by examples. Several methods are presented for building safe tailings dams using either the coarse fraction of the tailings or local soils, the important factor in each method being proper compaction of the material. The safety of existing tailings dams can be improved by flattening the overall slope, preferably by adding berms, or by decreasing the height. Where neither remedy is possible, the installation of electro-osmotic tie-backs is suggested. Dumps of mine spoil can be stabilized economically by compacting the material in layers along the toe to form a dam.

Jan 1, 1971

By FREDERICK W. BRADLEY

MINING methods are evolved rather than devised; and the process is slow. The advance in no particular year is phenomenal, but progress is un- questionably being made constantly in several directions: (a) better adaptation to given conditions of various "systems" of mining; (b) better utilization of mechanical equipment ; (c) improvement in working conditions so as to promote the health, safety and efficiency of the workers. During the year 1930 operations were commenced at a number of important new mines. Methods adopted are not new, except in minor detail, but the fitting of methods to conditions is interesting, because, as the engineers presumably started from scratch, they have selected the methods that experience under similar conditions has indicated as being the best.

Jan 1, 1931

By T. B. Massalski, Horace Pops

The occurrence and the temperature dependence of the athermal martensitic transformation in bcc Cu-Zn ß-phase alloys have been studied by cold-state microscopy, differential thermal analysis, and electrical -resistivity measurements. CinenzatograpJzic studies have shown that in the majority of alloys the transformation occurs in two stages. A thermoelastic phase, having a 'needlelike" uppearance, forms initially at the MS temperature and grows relatively slowly, chiefly in the edge (lengthwise) direction. With further cooling, an additional martensitic phase forms in rapid bursts at a lower temperature, MB, Both martensitic phases appear to have the same cry stallographic habit hut their modes of formation and growth are different. For the composition range studied, between 38.55 and 41.49 wt pct Zn, the habit planes determined are close to the (2.17 ,12) plane of the matrix, in general agreement with the prediction of the phenomenological theory of martensite formation. Thermal cycling through the MB temperature produces permanent plastic deformation in the 0 matrix and gradutally eliminates the typical burst phenomena. Thermal cycling only through the MS temperature produces no noticeable deformation effects. THE bcc Cu-Zn ß-phase alloys tend to become unstable at low temperatures and undergo a martensitic transformation,'-3 but the details of the transformation have not been completely determined. Following earlier metal log raphic and X-ray work1 Tichener and ever' determined by means of electrical-resistivity measurements the temperature range of the martensite transformation during continuous cooling. The transformation temperature was found to decrease with increasing zinc content, becoming about -130°C for an alloy containing 40.04 wt pct Zn. Hull and Garwood3 made a metallo-graphic study of Cu-Zn 0 brasses at temperatures down to -160°C, and determined the habit plane of the transformation product for an alloy containing 38.88 wt pct Zn. No metallographic studies below liquid-nitrogen temperatures have been reported. The martensitic transformation in ß-brass alloys can also be induced by deformation.1,4 The MD temperature corresponding to the appearance of the strain-induced martensite is some 300°C higher than that observed without strain, and hence the transformation can be strain-induced in alloys containing a higher percentage of zinc. Massalski and Barrett4 found that alloys containing as much as 51.89 wt pct Zn could be transformed into a faulted hcp structure by cold working at liquid-helium temperature. Because the details of the MS temperature and morphology reported in the literature are somewhat incomplete, a further study has been made of some of the above features. A design of a cryogenic stage for optical metallography5 has permitted the examination of specimens at temperatures down to 4.2oK, and the use of a cinecamera has permitted a study of the morphology on cooling and heating. The particular aim of the present work was to examine the transformation temperatures, the habit planes, and the growth morphology over a wide composition range in the ß-phase field. The effect of thermal cycling upon the subsequent transformation was also examined.

Jan 1, 1964

By D. J. Barrett, M. A. Sochocky

INTRODUCTION Summary of Factors Influencing Comminution Circuit Design The selection of an appropriate comminution circuit for a specific ore is one of the most important decisions in the design of a processing plant. The importance is related to the fact that the capital and operating costs for crushing and grinding plant generally represent, as is well known, the major portion of the plant costs. This chapter will, therefore, identify as many as possible of the factors which influence the selection of a comminution circuit. The number of factors which will have to be considered for any comminution project will depend, among other things, on the type of project. If, for example, the project is an entirely new mining development, then most, if not all, the factors identified will have to be analyzed. If the project is an expansion of a developed mining operation or if the new orebody is adjacent to a viable operation, then the existing operation will influence the choice of factors or design constraints which need to be considered. The existing infrastructure or supporting systems may be quite adequate to accommodate the requirements of any expansion or new development. Hence, those factors may not have to be considered. To cover, however, the widest spectrum of projects, the factors which have been identified in this chapter are those which will have to be considered for the most complex of projects, that of developing an entirely new mining operation. The range of factors is as broad as the range of different ore types. Thus, each development must be treated with individualized care. The most important step in the development is the analysis and understanding of the ore characteristics. The hardness of the ore, its abrasiveness, friability, moisture content, grade, mineralization including gangue mineralization, liberation size, chemistry, and other characteristics should be the first to be analyzed in the investigation. The next should be the determination of factors such as plant size, throughput, location, climate, accessibility, and availability of water. The selection of samples for initial bench scale work and bulk sampling (when needed) for further

Jan 1, 1982

By J. J. Jakosky

A REVIEW of the progress in applied geophysics during the recent depression years reveals marked advances "over the methods employed several years ago. Of late, geophysical work has been curtailed to a con-siderable extent in the fields of oil and base-metal exploration, its especial domains a few years ago. Greater attention has been directed toward the use of geophysical technique in other engineering problems. Constantly maintained research programs have developed new instruments and per-fected better field, laboratory and interpretation techniques based on experience and skill acquired from years of application in the older geophysical field. During the past two years, geophysical methods have been employed in problems that required information on thickness of fill materials and subsurface bedrock contours. Considerable success has been attained, with subsequent drilling checking the predicted depths within one to five per cent. In general, these problems were similar as far as the fundamen-tal physical and geological conditions were concerned, but they have varied widely in specific detail and in engineering aspects. Character-istic of the different problems are: (1) yardage and bedrock profile in gold-placer mining; (2) water supply, involving underground drainage and storage conditions; (3) bedrock contours in dam-site and other structural investigations; (4) gravel and fill yardage, and other structural features along rights of way and in rock and gravel quarrying. Of particular interest, perhaps, to mining men are the problems of gold placer deposits and water supply. Geophysical work on gold placers is of especial interest because of the present expanded activity in all phases of gold mining. The development of a suitable water supply at, an economical cost is often of prime importance in insuring a successful mining venture. Particularly is this true in the arid Southwest. How-ever, the use of geophysical work in water supply is not confined to the needs of mining development.

Jan 1, 1933

Jan 1, 1902

By D. A. Munro, G. P. Contractor

Fourteen 50-lb laboratory melts were investigated to determine the effect of uranium on the tenpering characteristics of loo-carbon (0.06 to 0.1 pct C) steels. It was found that uranium additions, particularly in the range 0.30 to 0.45 pct, enhanced the hardness and both ultimate and yield strength of the experivzental steels in the quenched and tempered condition. The structural and morphological chazges indicated that uranium retarded tempering of the tnartensite, thereby hindering the normal formation of polygonal ferrite formed in the late stages of tempering. The effect of this was to make possible the re-tension of the acicilar ferritic structure in the uranium-bearing' steels. The iraniuin-bearing steels also showed IVidnzanstatten-type growth of ferrite plates and had large prior austenite grains containing assenzblies of fine ferrite grains, mainly acicular in geometry. The fine-grained ferrite structure and the presence of more numerous and apparently smaller precipitates in the uranium-bearing steels are thought to he principally responsible for the itnproved tensile strength and hardness of the experinzental uranium-bearing steels. At ternperirzg temperatures above 455% (850'F) the ferrite in the higher-uraniun steels nzaintained acicularity and, hence, its strength and resistance to tempering. Uranium did not produce a secondary hardening peak. However, it retarded softening during the third stage of tempering because of its effect of inhibiting the grouth of cementite particles and of retaining the acicularity of ferrite plates. The resistance to coalescence accounted for the slow grocth of the ferrite grains in the uranium-modified steels and, hence, fov the persistence of the acicular ferrite structure. IT had been found previously1 that uranium additions up to about 0.45 pct had no significant effect on the tensile properties of low-carbon steel (0.06 to 0.10 pct C) in the as-rolled and normalized conditions, Fig. 1. On the other hand, it was observed that uranium in excess of about 0.30 pct had an embrittling effect as revealed by Charpy V-notch impact results. It was also noted that, as the uranium content increased, the morphology of pearlite changed from lamellar to feathery and the ferrite grains showed an etching effect resembling striated or dashed markings, suggestive of precipitation. The sharp drop in the impact properties shown in Fig. 2 warranted an assumption that the uranium content of about 0.30 to 0.45 pct may produce some secondary hardening reaction on tempering, analogous to that associated with a Cr-Mo-V steel, which shows very poor CVN toughness at the secondary hardness peak in the tempering curve.1' With this background and the reported findings of Hasegawa and noda that low-carbon uranium-treated steel showed signs of secondary hardening, the present investigation was undertaken to determine the effect of uranium additions on the mechanical properties of 0.10 pct C steels. No attempts were made to investigate in detail the mechanisms of hardening, although some suggestions based on the experiments are made. MATERIALS AND PROCEDURES A series of 50-lb induction-furnace melts was made using AISI 1008 rimming steel billets as the melting stock. The melting, forging, and rolling techniques proven satisfactory in previous projects'-3 were employed as a guide for this investigation. The steel was deoxidized with aluminum (2 lb per ton) prior to the addition of high-purity uranium. The analysis of each melt is given in Table I. Properties were evaluated as a function of heat treatment and are presented in terms of hardness and tensile strength vs tempering temperatures. The variation of hardness with the tempering temperature was studied on the quenched and tempered specimens, some of which measured 0.50 by 0.25 in. diam and the others 0.40-in. cubes. Before quenching, the specimens were vacuum-sealed in glass tubes and normalized at 900°C (1650°F) for 20 min. Following this treatment, the sealed specimens were hardened by austenitizing at 955°C (1750°F) for 20 min and water quenching, and then tempered for 1 hr in the range 150 to 730°C

Jan 1, 1967

By Carl F. Dietz, Dyke V. Keedy

The problem of drying ores is one that most mill-engvineers are sooner or later called upon to meet, and it may be timely to point out some of the difficulties resulting from such operations from purely a metallurgical and economic standpoint. We mean, in the following pages, to discuss primarily the effect of such operations on the ore. itself, without particular reference to the mechanical or cost features of the subject. That an appreciable tonnage of the ore fed to the usual form of drier, either rotary or stack, is lost, is fairly well appreciated, but we believe that only a few mill-managers know just what their drier-losses amouilt to, and we have found that in most cases they console themselves with the fact that the drier-smoke is not very much discolored, and it is generally believed that the draft is not sufficient to carry away more than a negligible percentage of the values.

Jan 1, 1913

By J. E. Ostberg, G. Phragmen, A. Hultgren, S. Wohlfahrt

Detailed study was made of a number of rimming ingots, both low and high carbon, and especially upon effects of superimposed air pressure. Requirement to suppress core bubbles is between 10 and 15 atm; at 6.5 atm freezing was in semikilled manner and at 3 atm, steel was of rising type. Probable mechanism of freezing under various conditions is discussed. AN earlier paper' reported an investigation made by a committee for studying rimming steel ingots appointed by Jernkontorets in Stockholm. The present paper is the outcome of some further work done by the same committee. Since the characteristics of ordinary rimming steel are connected closely .with the amount of gas liberated during freezing and since this amount of gas is governed by the pressure, it was considered of interest to ascertain in what manner and to what extent definite pressures applied to the top of the liquid steel in the mold would affect the solidification process and the consequent structure of a rimming steel of ordinary composition. The experiments were made at the Domnarfvets Steel Works. The steel was made according to normal practice in a 4-ton Rennerfelt electric furnace. Ferromanganese was added in the furnace; no aluminum was added, with one exception. Analyses of the four heats are given in Table I. The top-poured ingots measured about 12 in. sq x 48 in. and weighed about 1300 lb. One or two ingots of each heat were allowed to solidify under pressure, using a special device for admitting compressed air to the upper closed part of the mold, as shown in Fig. 1. A heavy plate sealed with asbestos was bolted to the top of the mold. The plate had a tapered aperture for pouring. Immediately after pouring the hole was closed by a wedged plug, and compressed air was admitted through a hole in the plug. Because of some delay in applying the plug, full pressure was not reached immediately. The pressure was adjusted to the desired value as indicated by a manometer. In order that the interior of the ingot might have the benefit of the pressure, the freezing of the top crust was delayed by a refractory lining applied to the top part of the mold, Fig. 1. Ingots were also cast from each heat without applied pressure, and with and without refractory lining at the top. Axial sections of ingots were cut either of the whole ingot or of some part of it of special interest; sections were polished and usually etched.' To facilitate description of structures the following terms may be used for different types of ingots solidified under gas evolution: 1. Box-hat or boot-leg ingot: Abundant gas evolution during casting and during rimming; no rim holes. 2. Normal rimming ingot: Lively gas evolution during rimming; usually rim holes in lowest part of

Jan 1, 1952

By E. H. Sellards

Phosphate rock like other mineral substances is found in nature in varying degrees of purity.

Jan 1, 1915

By Arthur Knapp

The practical application of mud-laden fluids in wells has been the subject of many papers.' However, there seems to have been little investigation of what actually happens when mud-laden fluids are applied to a loose porous sand. The assumption is that the fluids penetrate the sands and that there is some plastering action. The degree of penetration and the relation of plastering action to wall stability is not generally known. This paper describes a series of experiments made in an attempt to observe, in laboratory apparatus, the action of mud-laden fluids under conditions simulating those to be found in a well. For the purposes of this discussion all fluids containing solid matter in suspension are mud-laden fluids. Series I: Penetration of the Pores of Uncemented Sands The subject of the penetration of porous formations by water is discussed in detail in Water-Supply Paper No. 67 of the U. S. Geological Survey. No attempt was made to repeat the experiments described therein. The results of the first experiment of this series are given simply to show the capacity of the apparatus used. The conditions in this first experiment were maintained throughout the remainder of this and the second series, except where noted. The experiments of Mills, McCoy, and others on subsurface flows, adjustments, migrations, etc., deal with the oil, water or gas within the porous beds.V he experiments described herein deal with the conditions immediately surrounding the bore hole.

Jan 1, 1923

By Arthur Knapp

The practical application of mud-laden fluids in wells has been the subject of many papers.' However, there seems to have been little investigation of what actually happens when mud-laden fluids are applied to a loose porous sand. The assumption is that the fluids penetrate the sands and that there is some plastering action. The degree of penetration and the relation of plastering action to wall stability is not generally known. This paper describes a series of experiments made in an attempt to observe, in laboratory apparatus, the action of mud-laden fluids under conditions simulating those to be found in a well. For the purposes of this discussion all fluids containing solid matter in suspension are mud-laden fluids. Series I: Penetration of the Pores of Uncemented Sands The subject of the penetration of porous formations by water is discussed in detail in Water-Supply Paper No. 67 of the U. S. Geological Survey. No attempt was made to repeat the experiments described therein. The results of the first experiment of this series are given simply to show the capacity of the apparatus used. The conditions in this first experiment were maintained throughout the remainder of this and the second series, except where noted. The experiments of Mills, McCoy, and others on subsurface flows, adjustments, migrations, etc., deal with the oil, water or gas within the porous beds.V he experiments described herein deal with the conditions immediately surrounding the bore hole.

Jan 1, 1923

By T. W. Guy

IN approaching the problems of sampling coal, a brief statement of certain facts that are more or less taken for granted may be helpful: 1. The coal-mine operator needs reliable data as to the physical and chemical characteristics of his coal in order to plan and control intelligently its mining, preparation, and marketing. The consumer needs such data in order to select the equipment and the coal best suited to meet his requirements, to check the quality of fuel delivered, and the efficiency of its use. Various government control agencies require such data as a basis for classifications and establishment of limits, for use in carrying out the requirements of federal, state or municipal laws. 91. All such data must be obtained by analyses, measurements, or tests made on samples, which are taken to represent the coal tested. It is now becoming generally recognized that, in accordance with statistical laws, test results from samples are not expected to represent the exact qualities of the lot or lots from which they are taken, except within statistical, or "expected limits. Such limits are definitely specified by some present standards of the American Society for Testing Materials and the British Standards Institution. 3. Samples that give ash within satisfactory limits are usually assumed to be sufficiently accurate for other analyses, except under special condi¬tions such as meeting close specifications for coals showing wide variability in sulphur, fusibility of ash, or other quality. 4. In modern coal sampling the increment is recognized as the basis for taking samples. For a given accuracy the number and weight of increments specified are increased with: (a) the expected ash, and (b) the top size designation of the lot to be sampled. 5. It is extremely important that every sampler recognize that: the specified number and weight of increments are minimums, and that the precautions to be used in order to take them properly are also minimums; that in the reduction of the gross sample the sizes specified for the coal after each stage of the crushing are maximum; that the quantities specified to be taken after each crushing stage are minimum; that any short cuts or failures to meet the requirements specified will reduce the statistical accuracy of the results, although it is possible that one or two checks on a few results may seem to show otherwise.

Jan 1, 1943

Jan 1, 1920

By Paul A. Beck

It is well known that the hardness of metallic single crystals, like that of polycrystalline metals, increases during deformation (hardening by cold-work). It is also known that, as a consequence of deformation. the metallic material acquires an evident thermodynamic instability, revealed, for example, by the fact that the increased hardness gradually decreases with time, especially at elevated temperatures (softening by annealing). The temperature at which the stabilizing process begins is different for various metals, and for any metal it depends on the amount of deformation. Such stabilization of deformed metals may proceed in two different ways: through recovery, and through recrystallization. The former process allows the unstable deformed metal body to approach stability gradually and without visible change in the grain structure; the latter process, like an allotropic transformation, yields directly the undeformed stable "phase" in the form of new undeformed crystals, which, starting out of a certain number of nuclei, grow into and " consume " the deformed hard material. The extent of stability attainable through recovery is limited, especially if the deformation of the metal crystal or crystals involves not only the gliding along slip planes, but also the bending of the slip lamellae, or at any rate the bending of comparatively large parts of the crystal lattice. In such cases, for instance in bent single crystals or polycrystalline metals subjected to any deformation, recovery will not as a rule be able to restore the "istraight" undeformed lattice, and stability can be attained only by recrystallization; that is, by the consumption of the bent crystal lattice parts by new, undeformed crystals—a much more drastic process. It is evident that the part of the surplus free energy stored in deformed crystals, which is present in the form of the elastic energy of the bent lamellae, is in these instances not considerably involved

Jan 1, 1937

By J. P. Timmons, J. H. Moran, G. K. Miller, M. A. Coufleau

A prototype equipment has been designed and built for the digital recording of well logs on magnetic tape at the same time that the regular film recording is made. The format of the digital tape produced is such that it can be used directly at the input of the ZBM 704, 7090 or other models of ZBM computers which accept digital magnetic tape. This apparatus has been used for the experimental field recording of dipmeter tape logs which were subsequently computed by means of an ZBM 704 or 7090. In this paper the equipment and the digital tape are described briefly, and their application to the computer-interpretation of dipmeter data is discussed. A principal element in the interpretation of the dipmeter log is the correlation of the three microresirtivity dipmeter curves to determine the depth displacements between them. Several correlation methods for computer use are considered, with particular attention to their sensitivity to error and their consumption of computer time. The tape data were used to compute information content of the dipmeter microresistivity curves in terms of their frequency spectra. The results show that the sampling rate used in recording the digital information is quite adequate and illustrate a use of the digital tape in evaluating the characteristics of new tools. Some examples of field results are shown. It can be foreseen that, when digital tape recording becomes available for general field use, a whole new realm of possibilities will be opened up for the processing of other well logs through computations, which hitherto were not feasible because they were too laborious and time-con.sunzing. INTRODUCTION The last few years have seen a revolution in the design and production of data-processing equipment. Stored-pro-gram digital computers have progressed from a research curiosity to the basis of a major industry. There are now hundreds of such machines in daily use in the United States. With the acceptance of a technique that was, in fact, already clearly described by John von Neumann in 1945, the last decade has seen great strides in the development'of components, reliability, programming systems and, most spectacularly, in the sheer number of machines built and in use. In 1957 there were enough digital computers available to the oil industry to justify the suggestion that it would be worthwhile to investigate the possibility of using these machines in processing well log data.' The first result of this investigation was the appearance of what may be referred to as the input-output bottleneck. Well logs are customarily recorded on film. To get these data into a machine required then (and still does): a time-consuming semi-automatic reading of the film; conversion of the log data to digital form; and recording these digital data in some medium acceptable for computer input, such as cards, magnetic tape, or punched paper tape. However, the recording, reading, and re-recording could only result in deterioration of the data. Therefore, it was concluded that the fist step should be the development of a new, more direct recording technique supplemental to the film recording, which would provide easy access to the digital computer. There are many solutions to the problem of recording log data in an easily recoverable form. After careful consideration it was decided to adopt the boldest solution which, it was felt, was also the most elegant. It was decided to record well logs directly, in the field, on magnetic tape in such a way that this tape could be used without further modification as an input to the IBM 704 or 7090 computer. To realize practical field recording of magnetic tape logs, it became necessary to develop in a rather small package, an analog-to-digital converter, a tape recorder, and the necessary multiplexing and control circuits to allow the simultaneous recording of a multiplicity of logging signals. The magnetic tape recording was to be made simultaneously with the conventional logging operation in such a way as not to interfere with it. Along with the development of hardware, it was necessary to begin development of interpretation techniques and machine programs that would exploit the power of the digital computer. Here, again, there is a long list of possible applications. After much consideration it was decided to concentrate on the interpretation of the dipmeter log as a first application. It is the object of this paper to describe in some detail the developments sketched in the last three paragraphs.

By AIME AIME

The following changes of address of members have been received at the Secretary's office during the period of Mar. 1 to May 1, 1908. This list, together with the list in Bi-Monthly Bulletin, No. 20, March, 1908, therefore, supplements the annual list of members corrected to Jan. 1, 1908, and brings it up to the date of May 1, 1908. The names of Members who have accepted election during March and April, 1908 (new members), are printed in italics., By a simple method of cutting out these names and addresses, and pasting them directly over the corresponding names in the annual list of members, the record can be kept practically up to date and the value of the list correspondingly increased. For this purpose the changes of address have been printed only on one side of the page. The names of new members, being in italics, are readily distinguished from the others, and can be pasted in approximate alphabetical order on the margins of the pages of the list.

Jan 5, 1908

By G. R. Gardner, D. H. Davis

INCREASING realization of the importance of dust control, and the recommendations of various agencies, have led the mining industry to become actively concerned with this problem. The background and necessity for adequate dust-suppression measures have been discussed in a number of publications, including those of the U. S. Bureau of Mines, and the use of spray water to reduce dust at the face and on roadways has been recommended. The problem resolves itself into obtaining adequate dust reduction at a reasonable cost. Inasmuch as the term "adequate dust suppression" has never been clearly defined, nor have permissible limits of dustiness (in terms of dust count) been established, it is apparent that any method selected may be required to meet additional demands. Until the industry has been given some indication of permissible limits of dustiness, no permanent solution is possible. Progress will be somewhat handicapped until such information is available. In addition, dust reduction must be obtained without the addition of any excessive moisture to the coal, since consideration must often be given to: I. Quality standards, particularly reduction in heat value. 2. Handling characteristics, particularly in regard to unloading from railroad cars and bins. 3. Application of dry methods of coal cleaning. 4. Necessity for fine screening within specified limits of oversize and undersize. Little detailed information is available as to the advantages and disadvantages of the several methods of water distribution, the location and protection of sprays, operating data on pressure, quantity of water, and so forth, and results obtained. In 1940 an investigation was undertaken to determine and evaluate the principal factors involved. This paper constitutes a progress report on this work and cannot in any way be regarded as complete on any one of the several phases. CLASSIFICATION OF DUST SOURCES The various sources of underground dust may be classified as primary or secondary. A primary source is one associated with appreciable degradation of size, that is, where the greater part of the actual fines capable of becoming air-borne dust are produced. A secondary source may be considered as one in which the greater part of the fines have been produced at some previous operation and are in such condition that they can be dispersed as air-borne dust. These conceptions appear to be of practical significance, as experience indicates that when dust is controlled at the primary sources the importance of secondary sources is minimized. For these reasons, investigations to date have been concerned principally with the primary sources of dust, and this paper is concerned particularly with one of these-namely, undercutting. In accord with the foregoing definitions, the sources to which the following opera-

Jan 1, 1942