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By S. WHINERP

(Cleveland Meeting, October, 1912.) I AM indebted to L. E. Bryant, of Danville, Ky., President of the Virginia Mining Co., operating coal-mines in Scott county, Tenn., for the following information relating to the existence of the Clinton iron-ore under the NW. slope of the Cumberland Plateau in Kentucky and Tennessee. During the past 15 years quite an important oil-field has been developed in a region having Wayne county, Ky., as its center, and a large number of wells have been drilled in that and adjacent territory in the search for oil. Many of' these wells have been carried to considerable depths below the recognized oil-bearing horizon, and one of them was drilled by Mr. Bryant at Pine Knot, a station on the Cincinnati, New Orleans & Texas Pacific railroad, a few miles north of the point where that road crosses the Kentucky-Tennessee State-line. The elevation of the surface at the crossing is about 1,400 ft. above sea-level. The railroad is located on the dividing ridge between the Cumberland river and Big South Fork. At a depth of 1,720 ft. below the surface the drill reached and passed through a formation which the drillers called " red rock," but which Mr. Bryant classified as Clinton iron-ore, as its geological position corresponded to that formation. The ore at this point was 6 ft. thick and appeared to be of uniform quality throughout. An analysis of the drillings gave : Fe, 33; Mn, 0.25; Si02? 3 ; Al203, 2 ; CaO, 13; MgO, 7 ; P,05, 0.333 per cent. ; S, trace. This analysis seems to confirm the belief that the ore is Clinton, and that it is of a quality equal to the average of the deep or unbleached Clinton ores in Tennessee and Alabama. This discovery led Mr. Bryant to make further examinations and inquiries, and he found that the stratum called " red rock " by the drillers had been passed through and noted in the great majority of the wells carried down to the same geological hori-

Oct 1, 1912

By W. F. Holbrock

IN a previous paper1 a method for the measurement of the compara-tive desulphurizing power of slags was described and data, were presented covering the range of likely slags containing up to 10 per cent MgO. In the present work the range is extended to include Tags containing up to 20 per cent MgO, and the effect of temperature on 5 per cent and 15 per cent MgO sings over the range 147.5° to 1525° C. is included. The method used was that described in the previous paper except that some of the temperature measurements were made with a noble-metal thermocouple instead of a tungsten-graphite thermocouple. Twelve-gram charges of 0.S per cent sulphur-metal and 5-gram charges of slag were subjected to heating for 30 min. at a prescribed temperature. The charges were analyzed for sulphur content. For purposes of comparison, desulphuriz-ing power is defined as the ratio of the percentage of sulphur found in the slag to that found in the metal. Six slag and metal charges were made coincidentally in holes in a section of all electrode graphite rod. One slag and metal charge was used as a control by means of which adjustment in the desulphurization value could be made for small varia-tions in temperature and other factors. For convenient presentation of the data, the slags are arranged in groups -in each of which one of the four main slag components is constant. Thus, the 15 per cent MgO slags are presented separately from those containing 20 per cent MgO.

Jan 1, 1938

By William M. Newton, John E. Sherborne

The value of the electric log as a means of interpreting underground structures has been increasingly demonstrated by its almost universal present-day use. It becomes important, therefore, to be able to evaluate the factors that affect the values obtained. By far the greatest number of electric logs are measured today in boreholes filled with rotary mud, the properties of which may exert an important influence on the electric log. In an effort to establish what the order of magnitude of such effects might be, a series of investigations was made in the laboratory and the field. Apparatus suitable for either field or laboratory use was designed and a procedure established for determining the factors that affect the resistivity of drilling muds over a wide variation in mud condition. Five muds representative of the types of clay-base muds employed in California were tested and the following observations were made: 1. The effect of raising the temperature from 8o° to i8o°F. is to decrease the resistivit~ of the mud or filtrate approximately 50 per cent. 2. The resistivity of the mud in most cases closely approximates that of its filtrate. 3. The change in the resistivities of muds caused by the addition of chemical is not the same function of the amount of chemical added for each mud. 4. The effect produced by increased sodium chloride content is to reduce markedly the resistivity of the mud and its filtrate. 5. Weighting materials, such as baroid and limestone, tend to increase the resistivity of drilling mud. 6. Cement and counteracting reagents reduce mud resistivity. The results of the investigation indicate that the mud resistivity is materially affected by the addition of electrolytes whether these are added for the purpose of conditioning the mud or enter the mud when salt beds or highly saline structures are penetrated. It should be observed, however, that the magnitude of the effect produced upon the electric log by changes in mud resistivity is also dependent upon the relative salinity of the water en. countered in the formation being logged. The laboratory data are supplemented by field data, which indicate that both the self-potential and resistivity curves are influenced by mud resistivity.

Jan 1, 1946

By John E. Sherborne, William M. Newton

The value of the electric log as a means of interpreting underground structures has been increasingly demonstrated by its almost universal present-day use. It becomes important, therefore, to be able to evaluate the factors that affect the values obtained. By far the greatest number of electric logs are measured today in boreholes filled with rotary mud, the properties of which may exert an important influence on the electric log. In an effort to establish what the order of magnitude of such effects might be, a series of investigations was made in the laboratory and the field. Apparatus suitable for either field or laboratory use was designed and a procedure established for determining the factors that affect the resistivity of drilling muds over a wide variation in mud condition. Five muds representative of the types of clay-base muds employed in California were tested and the following observations were made: 1. The effect of raising the temperature from 8o° to i8o°F. is to decrease the resistivit~ of the mud or filtrate approximately 50 per cent. 2. The resistivity of the mud in most cases closely approximates that of its filtrate. 3. The change in the resistivities of muds caused by the addition of chemical is not the same function of the amount of chemical added for each mud. 4. The effect produced by increased sodium chloride content is to reduce markedly the resistivity of the mud and its filtrate. 5. Weighting materials, such as baroid and limestone, tend to increase the resistivity of drilling mud. 6. Cement and counteracting reagents reduce mud resistivity. The results of the investigation indicate that the mud resistivity is materially affected by the addition of electrolytes whether these are added for the purpose of conditioning the mud or enter the mud when salt beds or highly saline structures are penetrated. It should be observed, however, that the magnitude of the effect produced upon the electric log by changes in mud resistivity is also dependent upon the relative salinity of the water en. countered in the formation being logged. The laboratory data are supplemented by field data, which indicate that both the self-potential and resistivity curves are influenced by mud resistivity.

Jan 1, 1946

By B. R. Banerjee

MATERIAL used throughout this investigation was high-purity aluminum (99.998 pct). The 1/2-in. cubes were cut out of a cold-rolled slab and annealed at 550°C for 1 hr before deformation. The single crystal specimen was 1 in. in diam x 0.33 in. thick, cut from a cylindrical crystal produced by cooling at about 55°C per hr in a furnace which had a convenient gradient of about 10°C in every 4.5 in. vertical crucible length. Specific data on the ten specimens studied are summarized in table I. Three types of deformation were employed: (I) compression in a hand-operated hydraulic press; (2) impact with a 7-lb sledge hammer; and (3) rolling, using a wedge-shaped specimen' to obtain a gradient of deformations varying from 0 to 50 pct along the length of the wedge. Specimens were either deformed at room temperature, or first cooled in a freezing mixture of dry ice and ether at a temperature of —72°C and then deformed between steel blocks cooled with dry ice. The specimens deformed at the low temperature were ground and polished through 000 emery paper and wheels impregnated with alundum and alumina No. 1. During this entire procedure the specimens were dipped frequently in the freezing mixture of dry ice and ether in order to maintain constantly a frosty surface as insurance against overheating. All specimens were given a final electrolytic polish, using two different electrolytes* to insure that the surface effects observed were not char- acteristic of the polishing technique. With both electrolytes, the annealed specimens gave even surfaces with good polish. Several standard etchants were tried without success. The best results were obtained with an immersion etchant, developed in this connection, containing: hydrofluoric acid, 4 parts; nitric acid, 1 part; glycerine, 3 parts. Discussion of Results Typical strain markings have been observed within deformation bands, as shown in figs. 1, 2, and 4. By stereographic plotting of metallographic measurements, the strain markings within a deformation band in a single crystal of aluminum deformed by compression were found to be traces of (111) planes within a maximum scatter of 6". The edges of the deformation band were found to be traces of the (100) planes also within the maximum scatter of 6" (in agreement with previous workers). At 30 pct deformation, this scatter was considered quite normal because of the fragmentation and rotation of the crystal. This solution, based on the traces on one plane of observation is not unique, but as the planes were observed to be those normally and logically to be expected, further work in this regard was not felt to be necessary. The study of strain markings in a wedge-shaped specimen, rolled to obtain a gradient of deformation from 0 to 50 pct, revealed prominent strain markings at 25 pct reduction in thickness (fig.5). Faint and weak strain markings were visually observable up to a minimum reduction in thickness of about 12 pct. Since strain markings have been observed in other face-centered cubic metals after much smaller deformations;1, 2 and since the rate of recovery in aluminum is high, it is believed that, at lower deformations, self-recovery removes the localized strains at the slip interfaces, thus removing the source of the etching effects that give rise to strain markings. At high magnifications, strain markings sometimes seem to appear as very thin, light-banded re-gions bounded by a pair of dark edges. This so-

Jan 1, 1951

By Dae S. Young

A new probabilistic approach is introduced for slope stability analysis including adverse impact of blasting vibrations. The material strength within a slope area is randomized in this bi-variate joint probability analysis. To be a completely general engineering method, the new probabilistic approach employs the random variable transformation technique: the Hermite model of the Gaussian transformation function, which transforms the experimental histogram of strength values to the standard Gaussian variables. Because bi- normal joint probability is analyzed on the true probability region projected on the Gaussian transformed variable plane, it is an exact solution of slope stability based on the available sample data. Details of the probabilistic approach are given through a case study on an iron ore mine. The case study demonstrated that the probabilistic approach is effective and simple enough to be a routine engineering practice for slope analysis.

Jan 1, 1984

By F. E. Rizzo, L. R. Bidwell, D. F. Frank

THE use of galvanic cells for the determination of oxygen activities has spread rapidly since the suitability of calcia-stabilized zirconia as a solid electrolyte material was first demonstrated by Kiukkola and Wagner.' In many of these investigations:-7 including several at ARL, the free-energy changes for various oxidation-reduction reactions involving the oxides FexO, NiO, and Cu2O have been measured as a means of assuring that a cell apparatus is functioning properly. As a result, a large quantity of data pertinent to the calculation of the high-temperature standard free energy of formation (?GO) of these oxides has been accumulated. AGFexo has been carefully measured in many independent investigations, using a variety of techniques, and consequently is accurately known. chipmans has used this informa-

Jan 1, 1968

By John W. Langley

In the summer of 1888 it was the fortune of the writer to present the subject of the desirability of establishing a set of samples of steel, which should be analyzed with extreme care, in order that they might become standards to which scientific and commercial analyses of iron and steel could be subsequently referred; also, that greater uniformity in the results of analyses might be brought about, since these standards would bear towards analytical methods somewhat the position which the original units of weight and length, the gramme and meter, or the pound and yard, preserved in Paris, London, and Washington, do to the mechanical arts. The plan met with hearty co-operation, with the result that com mittees were appointed in Sweden, Germany, France, England, and America, to receive the material and to see that the necessary au alyses were executed. In England, the British Association for the Advancement of Science appointed a committee, which subsequently published a plan

Jan 1, 1891

Herewith are transmitted the joint report of the Treasurer and Finance Committee for 1934 and the reports for the same year of the Chairmen of the following Committees: Admissions, Membership, Papers and Publications, Library, and MINING AND METALLURGY. TO these reports you are referred for details of the year's activities. Finances.-Income for 1934 from all sources totalled $134,967 com- pared with $121,689 in 1933. The increase is accounted for principally by four items: $6000 increase in initiation fees and dues of new members; $1800 in current dues; $4000 in "back" dues; and $2800 in the sale of publications, including TRANSACTIONS volumes and technical papers in the form of "separates." In passing, it may be remarked that income from back dues during 1935 will be less than in 1934, for the obvious reason that the total amount of dues in arrears has shrunk and consequently there is less to draw from. Income from

Jan 1, 1934

By E. Peters

As in other fields of Extractive Metallurgy, Hydrometallurgy is preoccupied with separation processes and with oxidation-reduction processes. The physical chemistry of each type of process can be described in terms of thermodynamic equilibria and in terms of reaction kinetics. Reaction kinetics are much more important at the low temperatures limiting hydrometallurgical processes than in com- parable pyrometallurgical operations and the number of cases in which the kinetics can be described by simple liquid-phase mass-transfer models are sharply limited. It is convenient to subdivide the applicable rate phenomena into processes in which (a) interface reactions control the rate,(b) mass transfer processes control the rate, (c) solid state process affect the rate, (d) thermodynamically predicted phase changes or molecular reactions fail to take place, (d) metastable substances or supersaturated phases persist, and (elchomogeneous reactions in solution affect the chemistry and the kinetics. Examples are drawn from the unit steps of leaching, cementation, hydrogen reduction, and electrowinning.

Jan 1, 1973

By C. A. Schempp

STUDY of the adaptability of Tintic Standard ores to concentration dates back to somewhat before January, 1921, when the chloridizing mill at Harold, Utah, was put into operation. The operation of this mill has been fully covered in the TRANSACTIONS (Vol. 73). The process consisted essentially of a chloridizing roast followed by a percolating leach with a nearly saturated solution of common salt, acidified with sulfuric acid; precipitation of silver on sponge copper, and of copper and lead on tin-plate cuttings. This mill was built to treat the low grade siliceous ores having an average content of

Jan 1, 1933

By H. H. Wade, N. F. Schulz

The large quantities of iron-bearing materials, including taconite, semi-taconite," and other low-grade ferruginous materials occurring in Minnesota and elsewhere, constitute an important potential source of iron. Satisfactory grade and recovery of iron ore concentrate cannot ordinarily be obtained from these ferruginous materials by simple methods of beneficiation. Iron is distinctive in that the free metal and two of its oxides [magnetite (Fe,O,) and maghemite (gamma-Fe,O,) ] are strongly ferromagnetic. The successful magnetic separation of natural magnetite from taconite has already been established on a commercial scale. The iron in semi-taconite, how- ever, occurs largely as goethite (Fe,Os.H,O) and hematite (Fe90,) which do not respond to ordinary magnetic separation methods. Magnetic roasting converts these iron oxides to magnetite, which can, after liberation, be magnetically concentrated.

Jan 11, 1960

(The following list contains the names of those members of the Institute of whose connection with military service. we have only recently become acquainted; it also includes the names of a few who have recently been promoted or transferred. A complete list was published in the Year Book, issued as a supplement of the Bulletin for March, 1918.) ADAMS, HENRY, Major, Assistant to Department Engineer, North-eastern Dept. ALINE, P. A., Co. C, 316th Supply Trains. * Low-cost cottage construction in America; a study based on the housing collection in the Harvard Social Museum, by Winthrop A. Hamlin. Cambridge, Mass., Harvard University, 1917. (Publications of the Department of Social Ethics, No. 7.) 30 pp., 4 charts. Illus.

Jan 5, 1918

By Barbara A. Thompson

A previously reported high-resolution method for the location of boron-rich areas in metallurgical and biological specimens was been adapted for general use on a routine basis. The rnetlzod utilizes neutron activation and autoradiograpizy. Alpha-particles emitted by boron nuclei upon neutron capture are recorded on a photographic emulsion. The resulting a-particle tracks show the location of boron-rich areas. Experimental techniques, interferences, and limitations of the method are discussed in detail. The method is most useful where there is marked segregation of boron. In this type of sample, the segregation can be observed when the nominal boron concentration is as low as 0.0006 pct. THE positive identification and location of boron-rich areas in metals is frequently of great interest in metallurgical work. Unequivocal identification is often difficult to make by conventional metallo-graphic methods. Recently, a method has been described which accomplishes this objective by neutron activation and autoradiography.l-3 The method can be described briefly as follows. Upon neutron capture, a -particles are emitted by boron nuclei according to the following reaction: ,Blo + n - ,a4 + 3Li7 + 2.4 mev The energy is dissipated as kinetic energy of the products. By irradiating a boron-containing sample in contact with a photographic emulsion and subsequently developing this emulsion, a-particle tracks are obtained whose location corresponds to the location of boron-rich areas in the sample. Two factors combine to make the reaction extremely specific for boron. The first is the unusually high (755 barns) cross section of boron for thermal neutron capture. The second is the higher neutron energy required to produce (n, a ) reactions in essentially all other nuclei except lithium. These two factors make the method specific for boron by six to seven orders of magnitude when a predominantly thermal neutron source such as the Brookhaven reactor is used. The reported limit of detection of this method is of the order of 0.01 pct B., The present work was originally undertaken to determine whether this limit could be lowered by use of a thinner emulsion. However, initial experiments showed that in order to use the method at all, it was necessary to reestablish the optimum experimental conditions in terms of the available irradiation facilities. It is the purpose of this paper to describe these experimental conditions in detail, to discuss the factors influencing sensitivity, and to evaluate several techniques for increasing sensitivity. EXPERIMENTAL A) Preliminary Experiments—The first measure-ments were made using samples of crystal oriented silicon steel containing various concentrations of boron. In the later experiments, samples of various high-temperature alloys such as M-252, hcoloy 901, Nichrome V, and so forth, were used. Faraggi, et al.,2 reported that the lower limit of sensitivity in this type of sample was about 0.01 pct B using nuclear emulsions of 50- u thickness. but that it should be possible to extend this limit by the use of thinner emulsions. Accordingly, we first used Kodak Auto-radiographic Stripping Film (Permeable Base) which has an emulsion thickness of only 5 µ. This was mounted on the metallographic specimens according to the technique described by Boyd.4 The emulsion remained in contact with the metal surface throughout exposure and development. Since the emulsion is transparent after development, the autoradiograph and metal surface can be viewed simultaneously and any correlation between film blackening and structure of the metal can be made directly with no problems of realignment. Because the silicon steel is readily attacked by moisture alone, it was necessary to apply a protective coating to the metal surfaces before mounting the emulsion. The coating was made extremely thin in order to absorb as few a-particles as possible. Boyd4 and Gomberg5 have discussed various plastics used for this purpose; however, none was sufficiently impermeable to prevent chemical attack of the steel during the developing process. This attack resulted in the production of gross chemical artifacts in the emulsion. It was, therefore, necessary to use the method of Wolfsberg and John6 as follows. A very thin (approximately 1 µ) coating of Plexiglas II was applied by dipping the sample in a 2 pct solution of Plexiglas II in dichloroethylene. Then, because the emulsion will not adhere to Plexiglas 11, a thin coating of Parlodion was applied in a similar manner using 2 pct Parlodion in iso-amyl acetate. No protective coating was necessary with the high-tem-

Jan 1, 1961

By W. Mostowitsch, H. O. Hofman

In our investigation of the Behavior of Calcium Sulphate at Elevated Temperatures with Some Fluxes,' we incidentally studied the decomposition of ferric oxide when heated in a current of dry air. We found that at 1,500° C., with 15-min. periods of heating, Fe²,O³, hardly changed in weight, the greatest loss being 0.23 per cent., and we therefore concluded that the compound remained unchanged at 1,500° C. in a current of dry air. In a more recent experiment we heated Fe²,O³, in a current of dry air and found that there was a decided loss in weight. A new investigation upon the behavior of Fe², O³, using a larger amount of substance and heating for a longer period of time, revealed the fact that a measurable dissocia-

Jan 1, 1910

By Robert E. Green, Edmund G. Henneke

The velocities of the three possible modes of elastic wave propagation have been calculated for single-crystal copper at 1-deg intervals throughout the standard stereographic triangle. The results are presented as isospeed contours. The deviations between the direction of maximum energy flux and specimen axes are presented as arrows drawn on stereographic projections. The orientation factors associated with dislocation motion on the primary slip system only and also on all twelve slip systems have been calculated for all three elastic waves. The orientation factors associated with a longitudinal standing wave resonant specimen have also been calculated. The results of these calculatians are compared with earlier calculations on aluminum crystals and the relevance of these results to ultrasonic attenuation measurements is discussed. GREEN and inton' have recently outlined a procedure for determining the orientation factors for dislocation damping in single crystals. The stress field associated with a given mode of elastic wave propagation is resolved on the slip systems in which it is assumed the dislocations are vibrating due to this stress field. Since, at room temperature, slip has been observed on a limited number of systems in fcc and hcp metal crystals, it is assumed that these systems are the appropriate ones to use for the resolving process. This procedure has been applied to aluminum crystals by Hinton and hreen' and to zinc crystals by Henneke and Green.3 In the present paper the modes of elastic wave propagation have been calculated for copper crystals possessing orientations at 1-deg intervals throughout the standard stereographic triangle. The deviation of the energy flux vectors from the specimen axis have been calculated for each mode. The stress field associated with each mode has been resolved on the (111)(110) slip systems in order to determine the orientation factors for dislocation damping. MODES OF ELASTIC WAVE PROPAGATION For any direction in a linear homogeneous aniso-tropic material three elastic modes can be propagated. In general, each of these modes has both longitudinal and transverse particle displacements associated with it and thus are not "pure" modes. However, there is always one component which is greatest in either a longitudinal or transverse direction and hence the mode may be referred to as quasi-longitudinal or quasi-transverse, accordingly. For certain axes of high symmetry pure modes may be propagated. The phenomenon of refraction of the energy flux vector is also exhibited by elastic wave propagation in ani-

Jan 1, 1969

By William D. Klopp, Joseph R. Stephens

ThE phenomenon of high ductility associated with a phase transformation, termed super plasticity, has been reported for a number of alloy systems. Abnormally high ductility has been observed during tensile testing of cast eutectic alloys of Pb-Sn and Mg-cu.1 Brasses of Cu-37 at. pct Zn and Cu-40 at. pct Zn elongate up to 180 pct when tested near their transformation temperature.' Enhanced ductility was also observed in Cu-47 at. pct Zn tested near the order-disorder transformation temperature. The most remarkable super-plastic effect reported to date is for the eutectoid alloy A1-60 at. pct Zn, where elongations up to 1000 pct have been reported.3 underwood4 has recently summarized the conditions that normally accompany the superplastic effect which are: 1) a phase transformation or allotropic change or order-disorder transformation; 2) an externally applied stress; 3) presence of an interface between two phases; and 4) a metastable structural condition. In addition, higher ductility is observed when the specimen is tested at slow deformation rates rather than under impact. The purpose of this note is to present evidence of the superplastic effect in a Cr-30 at. pct Co alloy. In addition, low-temperature bend ductility data are given for the alloy in the quenched, metastable, single-phased condition and in the slow-cooled, two-phased, near-equilibrium condition. Sixty-gram alloy ingots were prepared by noncon-sumable arc melting of iodide chromium and electron-beam-melted cobalt. These were cast into rectangular ingots and fabricated to 0.035-in. sheet by rolling at 2300°F. Attempts to roll at slightly lower temperatures invariably resulted in severe cracking, apparently due to presence of the brittle a phase below the transformation temperature of 2230°F. Tensile specimens with a 0.25 by 1.0 in. reduced section were cut from the sheet by electrical discharge machining. The specimens were heated at 2400°F for 1/2 hr to obtain a recrystallized, bcc, single-phased structure. Temperature of the specimens was subsequently raised or lowered to the desired test temperature and held for 10 min prior to testing at a crosshead speed of 0.01 in. per min. Fig. 1 shows the chromium-rich side of the Cr-Co phase diagram.6 The alloy composition investigated is near the point of maximum solubility of cobalt in chromium, and the alloy is two-phased when in equilibrium at temperatures below 2230°F. The results of tensile tests conducted at temperatures indicated by X's in Fig. 1 are summarized in Figs. 2, 3, and 4. Tensile elongations shown in Fig. 2 increase from 11 pct at 1900°F to a maximum of 160 pct at 2250°F. The elongation then decreases to 44 pct as the test temperature is further increased to 2600°F. The proximity of the temperature of highest elongation and the solvus temperature suggests that a superplastic effect is present in Cr + 30 at. pct Co similar to that observed for other alloys that show anomalous ductility. The variation of upper yield stress with temperature is shown in Fig. 3. A small peak in yield stress occurs at 2250"F, coincident with the maximum in

Jan 1, 1967

By R. C. Mahon

During the early history of the Lake Superior district, tamarack timber was used almost exclusively in the wines. It had the strength and lasting qualities necessary for a satisfactory mining timber. But about fifteen years ago the tamarack trees were attacked by a blight which killed nearly all of them so today no tamarack timber is available. Hemlock, spruce, and poplar have neither the necessary strength nor the lasting qualities for mining timber, but a large supply of maple and birch is available. These have ample strength but, when placed underground, fail by decay in about three years. This means that, instead of replacing the timber sets once in fifteen years, it must be done five or more times in the same space of time which involves not only incraesed timber costs but more important, an increased labor cost.

Jan 1, 1949

By J. F. Abel, F. T. Lee

Subsidence is controlled by a complex com¬bination of mining and geologic factors. For example, a compilation of worldwide data shows that, as the percentage of shale in the overlying rock mass decreases and the amount of sandstone increases, the angle of draw (and the area affected by subsidence) decreases. Limestone in the over¬burden appears to cause a more than twofold decrease in the angle of draw compared to a like amount of sandstone. Increased amounts of sandstone were accompanied by a greater surface subsidence relative to the mining height. The total thickness of overburden did not appear to influence the subsidence magnitude above super-critical panels. The greater the thickness extracted, the smaller percentage of that thickness shows up at the surface as subsidence. The greater the percent of the seam extracted, the greater the subsidence reaching the surface. The maximum subsidence above room-and-pillar panels de¬pends on the pillar height and minimum width as well as the other factors listed.

Jan 1, 1984

By M. Tanaka, S. Kita, Y. Jinnouchi, Y. Sawada

This paper generalizes the results of the recent theoretical and experimental investigations on the air-pulsated jigs in Japan. The pulsating mechanism is analyzed as a special vibratory system, and the jigging mechanism as a mass system subjected to the law of hindered settling. The results of investigations on the following items are reviewed: dynamics of the pulsating mechanism; pulsation in a practical TACUB jig development of a new type of air valve; uniform pulsation in a large Baum jig; motion and mobility of bed particles; separating speed in hindered conditions; and standard deviation in practical jigs.

Jan 1, 1985