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By W. B. Mather

A RKANSAS is not only a geologist's paradise, but Ait is also particularly fortunate in possessing a wide variety of mineral resources. The future mineral production and mineral industry of Arkansas, like the other states in Mid-America, will probably depend to a large degree on efforts to increase the exploitation of the non-metalliferous deposits of the state. The term nonmetalliferous, as used in this paper, embraces all types of mineral deposits, except fuels, water, and those deposits from which, after bene-ficiation, metals are ultimately derived. For example, bauxite is the ore of aluminum, but a considerable portion of the bauxite mined eventually is employed in the production of nonmetallic alumina, an important oxide in the abrasive and ceramic industries. The bulk of the production, however, becomes metallic aluminum and therefore this type of mineral resource is considered metalliferous and is omitted from this paper. Arkansas' nonmetalliferous deposits are of many different types, too numerous to discuss in detail in a single paper; therefore, only their salient features are presented. Many types of deposits such as limestone, glass sand, novaculite, shale, and sandstone are exposed over wide areas, providing inexhaustible reserves. Other types of deposits, such as barite and tripoli, contain large reserves which certainly are not unlimited. Still other types of deposits, such as celestite, kaolin, and vermiculite, appear to occur in small isolated deposits containing relatively small reserves. Of course, all of Arkansas' nonmetalliferous deposits probably have not as yet been recognized, nor have all of the known deposits been prospected, tested, and evaluated. Various types of deposits are too low grade or too limited in extent to be profit- ably produced by today's standards. In the case of other deposits, the known uses are few in number, thus acting as a retarder to their development. Due to anticipated technologic advancements, the future demands of industry are not expected always to be the same as they are today, and therefore idle deposits or those of current limited production may readily become the important revenue producers of the future. The types of nonmetalliferous deposits discussed here include: clays, shales, and slates; silica deposits including glass sand, novaculite, tripoli, sandstone, chert, and quartz crystals; limestone and dolomite; barite; gypsum; celestite; nepheline syenite; green-sand; phosphate; vermiculite; fuller's earth; ben-tonite; diamonds; sand, and gravel. The location of the various types of deposits are presented on the accompanying map (fig. 1). Symbols indicate the general area of occurrence. Many deposits, such as limestone, shale, novaculite, and so on, are represented by formations which could only be properly shown on a geological map. In these instances only active deposits or those of exceptional merit are indicated by symbols on the map. A general northeast-southwest line divides the interior highland from the Gulf Coastal and Mississippi Alluvial Plains of south and east Arkansas. The data presented in this paper are only a surnmary of a portion of a more comprehensive survey and study of the natural resources of the entire state.' The study was sponsored and underwritten by the Arkansas Power and Light Co., Little Rock, as a public service to the state and its residents. Permission to present some of the data and conclusions resulting from the survey is gratefully acknowledged. Table I, prepared by the Arkansas Geological Survey from state severance tax records, presents the annual production secured from Arkansas nonmetalliferous mineral deposits. Clays, Shales, and Slates Clays: It is realized that each method of classifying clays is prone to criticism. In this paper, Arkansas' clays of potential value are arbitrarily

Jan 1, 1951

By Harrison Schmitt

IN the practice of ore finding the geologist is continually confronted with the question of oreshoot extension, so that the general problem seems worthy of systematic investigation. This problem appears when the reserves are estimated and when the advisability of deepening the shaft comes up. Moreover, there is need for lower development cost to keep pace with cost reductions in other departments, or even to offset a rising cost of ore finding or ore following. This can be gained by close geologic control of the development; and much of the geology involved is that bearing on the downward, upward, and horizontal extensions of shoots. Furthermore, the purchase of a mine or prospect often depends directly on the question of shoot extension; because it is seldom that the ore is fully developed and the purchase price is almost invariably based largely on "possible" and geologically prospective ore. Most current methods for estimating '(possible" and the more nebulous classes of ore are crude and indecisive. In the following pages the extension of oreshoots is the major theme, although the more basic subject, the general art of ore finding, is given some space. (A) Direct Methods of Extension Prediction (I) Extrapolation and Interpolation of Shoots by Use of Conventional Geologic and Assay Plans, Projections and Cross-sections There is little need for stressing the desirability of detailed geologic plans, assay plans, projections, and cross-sections as a basis for the study and extension prediction of shoots. Underground and surface mapping, in most cases, ought to be done in exhaustive detail. All features of obvious bearing should be mapped and it is good practice to record all possible details, some of which may become significant when studied in the ensemble. It should be emphasized that the mapping should be done with an impartial mind, with interpretation reduced to the minimum. The symbols of the map can be made to distinguish observed facts from interpretation.

Jan 1, 1929

By William H. Hamilton

Tunnel-driving capabilities in terms of feet per hour have advanced several hundred percent in the last century. Indications are that this capacity will double each decade for the next three decades. These future improvements will be made possible by a greatly increased need for underground excavation and the awareness of industry of its own latent capabilities. The factors of most interest to any potential user of a tunneling machine are those making possible an increase in production. The first and most obvious factor, and probably the one that has created the excitement and interest of most people, is the increase in boring rate through faster rock fracture and improved support systems. Boring rate can be increased by more horsepower in the form of increased thrust, torque, and cutterhead speed, and by better cutters and cutting methods, better material-handling systems, and better ground-control systems. All of these items are extremely important and are the basis of much discussion and effort by everyone concerned with the excavation of tunnels by machine. The second factor, just as obvious and equally important as an increase in boring rates, is "increase in production through better utilization of the tunneling machine and related equipment," which means a reduction in downtime through greater reliability of equipment. Mechanical rock attack is presently capable of cutting hard rock at 5 fph and soft rock at more than 20 fph. In current practice, however, this advance rate is maintained for less than 50% of the shift time. I predict that tunnel-driving contractors and their supporting manufacturers of tunnel-boring equipment will provide machinery that will maintain these advance rates for more than 90% of the shift time. This increase in effective production will be due to the increase in reliability of the tunneling machine and tunneling system components. Such a percentage increase in utilization of the tunneling equipment is just

Jan 1, 1970

THE CHALRYAN.--I think that we have set the stage for the balance of the sym- posium. Most of the emphasis has been placed on the immediate value of every- thing we can do and everything we can learn for the furtherance of the war effort. I believe that ought to be first, but I also believe that this is the time for us to con- sider very seriously not only what these improved methods and techniques do to form a closer approach to ideal segregation but what effect these great quantities of scrap metals and alloys that are going to be produced this year and next, are going to have-what their impact will be-on post- war industry in general and in particular ,, on the primary metals fields. In some cases we have been hearing in the last month or two of the law of diminishing returns coming to the fore. We find alloy simplification growing and certain alloys being produced in great quantities, which will perhaps drop out of the picture some- what as the war ends but never to the lower ( stage they had before. We have I think a pretty good cross- section of the producers, the refiners, the reclaimers and ingot makers, the ultimate users here, and there ought to be some good and helpful discussion. The papers are open for discussion. Mr. Beattie, do you want to make any 1 comment? H. J. BEATTIE.*-To start the discussion I might ask Mr. Deitz what they do with manganese bronze turnings? We segregate the manganese bronze turnings from the other bronze turnings. The value of it seems to be much out of line with the price of ingot, that is, as compared to some of the other alloys like 88-10-2 or 85-5-5-5. I assume it is because they can only use a

Jan 1, 1943

By S. A. Hoenig

In an earlier publication, the application of exoelectron technology to the monitoring of dry grinding in a ball mill was reported. Recently, the author has investigated the ball mill problem in more detail with the system shown in [Fig.1]. Here, some of the current generated in the ore-ball-water mixture was picked up by the metal chains and served as a measure of the rate of grinding. While the mechanism of current generation has not been completely clarified, a parallel study of electrical effects associated with rock drilling indicated that the major driving force is the zeta potential*, while oxidation of the freshly fractured material provides the remainder of the current. Both of these effects are sensitive to the exposed surface area, and it might be expected that the observed currents would provide a measure of the grinding rate. This "surface area" effect allows the measurement system to be used in any type of rock or ore grinding. Some studies with sulfide copper ore indicate higher currents than those observed with silica sand, but the overall pattern of current versus grinding rate is essentially the same. Experimental Studies The experimental system was set up as shown in [Fig. 1]. The initial studies were done with silica sand because of its availability and for comparison with the data of reference 1. The sand was sized to an average of 425 /MI (40 mesh); a typical charge consisted of 2.5 kg (5.5 lb) of sand, 0.85 L (0.22 gal) of tap water and 2.5 kg (5.5 lb) of iron grinding balls 25.5 mm (1 in.) in diameter. For a typical "run," the mill was loaded with a fresh charge of ore and operated for periods ranging from 10-60 min. During this time, the current was measured with a Keithley 417 picoammeter and a chart recorder. At the end of the grinding period, the charge was removed and sieved to recover the 425, 300, and 212 µm (40, 50, and 70 mesh) fractions which were then drained and weighed. A fresh charge was used for each test and every attempt was made to keep the draining and weighing processes uniform.

Jan 1, 1985

By E. M. Norris

In the summer of 1917 it was decided to fireproof the main Tramway hoisting shaft of the Anaconda Copper Mining Co. at Butte, Mont. The shaft has three hoisting compartments and one pump compartment; it is timbered with 12 by 12-in. (30.5 by 30.5-cm.) fir timber, and is 2475 ft. (754 m.) deep. Subsidence and displacement of the surrounding country rock had produced exceedingly heavy ground, and had carried the shaft out of line, in several places, by as much as 2 ft. (0.6 m.) displacement. Constant repairing and realigning of the timbers had been necessary in order to maintain clearance for the cages. The most feasible method of fireproofing, therefore, seemed to be to cover the timbers with a coat of concrete applied with the cement gun. The cement gun, which is operated by compressed air at ordinary mine pressures, feeds a mixture of sand and cement through a hose to a nozzle having a water connection. The mortar in fluid form is thus sprayed upon the prepared surface in thin layers, which can be built up to any desired thickness. The cement gun can be set up at any convenient point; satisfactory results have been obtained with the nozzle a distance of 500 ft. (152 m.) from the gun. The shaft was thoroughly overhauled and the timbers put in the best possible state of repair. Between the 1000 and the 1400 levels, much loose ground lay against the shaft timbers on the north side; this was breast-boarded back and a 30-in. (76-cm.) reinforced-concrete retaining wall was erected, leaving a space of 12 in. (30.5 cm.) outside the shaft timbers to allow for future movements of the ground. For convenience in handling men and materials, it was arranged to concrete the auxiliary hoisting-cage compartment and the pump compartment first, using the cages of the main hoist to serve the cementing crews. The auxiliary cage was then available while the remainder of the shaft was being concreted. A tight partition of 2-in. (5.08-cm.) plank was erected between the auxiliary and the adjoining hoisting compartments, for better protection of men riding on the cages. The application of concrete made this

Jan 1, 1920

By R. V. Whetsel, V. R. Garfias

Production of crude petroleum in Mexico during 1936 totaled approximately 40,309,000 bbl., showing a negligible increase over the previous year. While only four producing wells were completed in the Poza Rica area in 1936, its production increased from 9,468,000 bbl. in 1935 to 13,417,000, making it the ranking producing field in Mexico. This gain in output, however, was offset by abnormal losses due to artificial curtailment mainly the result of strikes and other disturbances in the heavy-oil district of the Northern fields, which declined 2,500,000 bbl., and in the South fields (Golden Lane), where output decreased 1,500,-000 bbl., while production in the Isthmus of Tehuantepec fields remained practically stationary. Production of natural gasoline for 1936 is estimated at 800,000 bbl., or 200,000 bbl. greater than in 1935. Crude run to stills in local refineries increased about 1,000,000 bbl., totaling 31,000,000 bbl. for 1936. Exports of crude and refined products were approximately 24,400,000 bbl., or over 2,000,000 bbl. greater than in 1935, the increase representing withdrawals from storage in Mexico. Exclusive of ships' bunkers, domestic consumption increased about 1,000,000 bbl. during the year, reaching an estimated total of 15,200,000 bbl. The Mexican domestic demand for gasoline is estimated at 2,540,000 bbl. for the year, an increase of 310,000 bbl. over 1935. In all, 70 wells were completed in Mexico during 1936, as compared to 74 in 1935 and 148 in 1934. In proven areas 59 completions resulted in 31 producers and 28 failures. Unusual results were obtained during the year over a scattered area in northeastern Mexico near the United States border, where out of eight completions six were fair-sized gas wells. A wildcat dry hole was completed in Chocoy in an attempt to extend the Northern fields to the northeast, and another in Quebrache, to the southeast of the heavy-oil district. A deep test (10,168 ft.) through the Cretaceous lime into the Jurassic was completed as a dry hole in Metlal-toyuca, 9 miles southwest of the Old Alamo field on the Golden Lane.

Jan 1, 1937

By Y. S. Bonillas

IRA B. JORALEMON, Warren, Ariz.-This paper has covered the situation so well that I have few suggestions to offer. Two points, however, are shown more clearly in the lower mines of the Calumet Arizona Mining Co. than in Copper Queen workings, and may be worth mentioning. The first is the usual association of high-grade primary sulphide orebodies with much larger masses of pyrite and silica, averaging less than 1 per cent. copper. The richer areas occur sometimes around the borders of the lean pyrite bodies, and sometimes entirely within them. While as yet we have not been able to find any certain reason for the location of high-grade sulphides in low-grade masses, it seems likely that the age of fracturing is one controlling feature. The first stage of mineralization, with pyrite and silica, had the effect of sealing up the rock. The later solutions, richer in copper, could pene-

Jan 12, 1916

By John E. Gale

Seven, 15 cm diameter, cores of gneissic granite, four containing induced fractures and three containing natural fractures all oriented normal to the core axis, were tested in an uniaxial compression mode over a range of 0 to 30 MPa. At given normal stress increments, over two or three loading and unloading cycles, the flowrates and changes in fracture aperture were measured. The induced fractures gave lower initial (at low stresses) and lower final flowrates (at maximum stress) than the natural fractures. Both types of fracture exhibited permanent fracture deformation between loading cycles as well as highly nonlinear, with distinct hystersis, loading and unloading flowrate-stress curves. A significant finding of this stud is the breakdown of the cubic law for fracture flow in induced fractures subjected to normal stresses greater than 20 MPa, with the breakdown occuring at much lower stresses in natural fractures.

Jan 1, 1982

By C. E. Shoenfelt

There were 110 important discoveries of either oil or gas in Co1orado in 1935. There was, however, further development of the Price structure in southern Colorado and developments since the first of the year indicate. that an important oil field may be in the making. The discovery of oil in Price structure was made by the Oil City Petroleum Co. late ill Novem-ber, 1934, in its No. 2 Garnett in the northeast corner of lot 3 in the SW.¼ of sec. 25-33N.-2E. This well developed a good showing of oil in Dakota sand at 970 ft. The hole filled up 15 ft. with 40° gravity oil overnight and after standing for several days the oil level was 400 ft. higher. As a result of the discovery of oil by the No. 2 Garnett, three wells were drilled by the William E. Hughes Estate. Two of these wells had good showings of oil and may make good producers but it is doubtful whether they will produce the estimated capacity of 500 bbl. each with which they have been credited. Although the Hughes Estate wells have been completed for some time, they have not been given thorough production tests because of the isolated position of the field and lack of proper facilities. The. first well drilled by the Hughes Estate was located on the west side of the Navajo River on the downthrow side of a fault. It encoun-tered water ill the Dakota sand at 1285 ft, and was abandoned in green shales of the Morrison at 1405 ft. Well cuttings from the Dakota sand showed some evidence of once containing oil, so a 1ocation was selected for No. 2 Fee on the east side of the river and on the upthrow side of the fault. Oil was discovered in Dakota sands ill 1935 by Continental Oil Co. in its No. 3 Hoye, NW.NW.NE. of sec. 34-9N.-78W., on the South McCallum anticline in North Park, Jackson County, Colo., but on account of heavy flows of carbon dioxide gas under high pressure it has been impossible for the company to get an accurate gage of the oil production. The freezing action of expanding carbon dioxide makes the producing of the oil difficult and costly.

Jan 1, 1936

By C. E. Shoenfelt

There were 110 important discoveries of either oil or gas in Co1orado in 1935. There was, however, further development of the Price structure in southern Colorado and developments since the first of the year indicate. that an important oil field may be in the making. The discovery of oil in Price structure was made by the Oil City Petroleum Co. late ill Novem-ber, 1934, in its No. 2 Garnett in the northeast corner of lot 3 in the SW.¼ of sec. 25-33N.-2E. This well developed a good showing of oil in Dakota sand at 970 ft. The hole filled up 15 ft. with 40° gravity oil overnight and after standing for several days the oil level was 400 ft. higher. As a result of the discovery of oil by the No. 2 Garnett, three wells were drilled by the William E. Hughes Estate. Two of these wells had good showings of oil and may make good producers but it is doubtful whether they will produce the estimated capacity of 500 bbl. each with which they have been credited. Although the Hughes Estate wells have been completed for some time, they have not been given thorough production tests because of the isolated position of the field and lack of proper facilities. The. first well drilled by the Hughes Estate was located on the west side of the Navajo River on the downthrow side of a fault. It encoun-tered water ill the Dakota sand at 1285 ft, and was abandoned in green shales of the Morrison at 1405 ft. Well cuttings from the Dakota sand showed some evidence of once containing oil, so a 1ocation was selected for No. 2 Fee on the east side of the river and on the upthrow side of the fault. Oil was discovered in Dakota sands ill 1935 by Continental Oil Co. in its No. 3 Hoye, NW.NW.NE. of sec. 34-9N.-78W., on the South McCallum anticline in North Park, Jackson County, Colo., but on account of heavy flows of carbon dioxide gas under high pressure it has been impossible for the company to get an accurate gage of the oil production. The freezing action of expanding carbon dioxide makes the producing of the oil difficult and costly.

Jan 1, 1936

By Lawrence Addicks

ONE of the properties of copper, which has done much to give it its present prominent place among the useful metals, is its electrical conductivity, a property which has now become the chief criterion of 'the value of the commerical product. In pursuance of that distinctively American principle that, 1' the best is none too good," metal of the highest conductivity is usually called for even where such extreme purity is of no advantage, for instance, in the making of brass and other alloys. The average brass-founder feels nervous unless his copper is so very pure that it shows a conductivity of 99 or 100 per cent., while the character of the zinc used is usually overlooked in his anxiety. Electrolytic refining has made it possible to produce copper of a' very high degree of purity, the metallic impurities averaging but a few thousandths of 1 per cent.; oxygen, usually present in the form of cuprous oxide, bringing the total up to about a tenth of 1 per cent. The published data bearing upon the relationship between chemical purity and electrical conductivity is, however, very scant,' nearly all the work that has been done having dealt with alloys carrying considerable quantities of the foreign elements. In this paper I have brought together the results of experiments extending over a period of several years that have been carried out with the idea of determining the amount of various elements which would lower the conductivity 3 or 4 per cent.-a series of impure coppers rather than alloys. There are many precautions necessary to keep the conditions

Mar 1, 1905

THE Directors of the Institute at the May meeting voted to take a referendum of our members on the subject of licensing engineers. At the June meeting, this action was rescinded, it being felt that the proportion of the members of this Society who would respond to such a referendum at the present time would not be large enough to give the data for which the referendum was intended. It was deemed advisable in its place to publish in this issue of Mining and Metallurgy arguments in favor of and against licensing. Two arguments by proponents of the movement follow. Many articles against licensing have appeared in these columns, in the last two years, covering most of the arguments on the negative side so that the sole contribution herewith is a summary of a referendum taken by the Mining and Metallurgical Society in 1920-21.-EDITOR.

Jan 7, 1923

B. R. Coil (Electrical Installations at the Miami Mine are Cheaper with Flexible Cable, P. 356) was born in Higginsville, Mo., and attended McKinley High School and Missouri School of Mines. He received a B.S. in mining engineering. Mr. Coil has worked for the Braden Copper Co., Rancagua, Chile as junior engineer and foreman. He was employed by Miami Copper Co. as a jigger boss, shift boss, development engineer and mine foreman. He worked as mine superintendent and general superintendent of the Castle Dome Copper Company, Inc. Mr. Coil may be reached at Box 100, Miami, Ariz. He is an AIME Member. Mr. C. R. Ross was co-author with Mr. Coil in the preparation of this paper. His paper covers the present installation of electrical equipment in block caving stopes along with background data. In this paper he has given one solution to wiring problems in heavy stopes.

Jan 1, 1952

By Roy Hardy

THE Getchell mine is a comparatively recent discovery in the old Potosi mining district, Humboldt County, Nevada, a district organized in the seventies and eighties, in which some prospecting was done in several metamorphic zones along a monzonite-sedimentary contact. The district had no production in the early days and no further work was done until the same metamorphic zones were prospected for tungsten (scheelite) in 1917 and 1918, when a few small lots were shipped. It again lay dormant until 1934, when prospectors investigated a large siliceous escarpment at one end of the old district where outcroppings were a prominent feature of the topography. Undoubtedly, during the early prospecting of the district, the outcroppings had been investigated for mineral, probably by panning, with negligible results because the gold later found is invisible in the concentrate and is refractory. A fire assay revealed the presence of sufficient gold to warrant develop-ment work. The outcroppings were easily prospected by short tunnels having their portals in the siliceous material on the hanging-wall side, with a maximum distance to crosscut to the footwall of 135 ft., or a distance at right angle to dip of 60 to 90 ft. Development work, reaching a depth of over 600 ft. on the dip of the vein, was done by means of various crosscut tunnels, winzes and laterals. A churn-drill hole was also sunk, which intersected the vein at a depth of 1100 ft. on the dip. Sufficient development work of this character was completed by 1937 to justify the erection of a reduc-tion plant to roast the sulphide ore and cyanide the calcine, and to treat the oxidized ore by straight cyanidation, to make a doré bullion for shipment to the mint. The erection of the plant was started that year and finished early in 1938, with a combined capacity of about 800 tons per day. It has operated continuously since erection and recently was enlarged to handle 1000 tons per day. The vein dips with the slope of the mountain, and by stripping the hanging wall the ore may be mined by power shovel for several hun-dred feet below the outcrop. Thereafter underground methods will be necessary.

Jan 1, 1940

By R. J. Lutton

Basic features occurring on tensile fracture surfaces in rock are hackle marks, steps, and rib marks. Rib marks define the leading edge of the fracture and indicate that it was free of irregularities. In turn, fractures characterized by these features are believed to have propagated elastically and to be truly brittle. On the other hand, most fractures in rock exhibit hackle marks and steps in a plumose arrangement, indicating a ductile fracture process. Accordingly, the edge of the fracture apparently advances by extending en echelon fingers, each of which is in turn a small plumose fracture. Plastic-like deformation takes place in this zone prior to complete rupture. Some of the propagation is directed sideways and some shearing also occurs in this direction. Such lateral movement contributes little to forward propagation and may make this process particularly sensitive to load rate and duration and help account for greater fracture strengths of materials under dynamic loads.

Jan 1, 1971

By John Dasher, M. C. Chang

The Crucible mine in Pennsylvania, operating on Pittsburgh seam coal, is rated at 5000 tpd. The washing plant, built in 1943, is rated at about 400 tph, using hydroseparator boxes to wash the coarse coal (4 x 5/16 in.) and hydrotator units for the fine coal (5/16 x 0). It is generally acknowledged that gravity concentration equipment cannot be used efficiently to beneficiate coal finer than about 65 mesh. Before the present flotation circuit was installed, Crucible recovered its fine coal slurry, predominantly -24 mesh material, by passing it through a battery of five 14-in. and one hundred and ten 3-in. Hey1 & Patterson cyclones in parallel with a 75-ft Dorr thickener. About two thirds went to the cyclones and one third to the thickener. Underflows from cyclones and thickener were filtered, respectively, in one 12-disk Eimco and two 4-disk Oliver filters fitted with stainless steel cloth. The resulting cakes were added to the coarse metallurgical coal. The filtrates, overflow from the 3-in. cyclones, and thickener overflow were recycled to the coarse coal plant.

Jan 3, 1959

By H. R. Drullard

TO obtain the best results from hammer drills, close attention must be paid to two factors in drill maintenance, which are of equal importance; one is lubrication, the other is the shank. With the exception of stoping drills, most modern rock drills require both oil and grease. The oil ports are in the lubricator, on or behind the hammer cylinder; the grease port for the lubrication of the chuck sleeve and rotating mechanism is on the chuck end. Ordinary machine oil is not adapted to rock drills; a heavier more gelatinous oil such as castor machine oil or liquid grease should be used. The lubricators should be filled once for every 12 or 14 ft. (3.5 to 4 m.) of hole drilled. Grease guns should be used to fill the port in the chuck end once a shift; a medium (No. 3) grease is well adapted to this purpose. Hard grease must not be put into the lubricators, as it will not flow through that part. Contrary to the popular belief, oiling a machine once or twice a shift does not provide sufficient lubrication; the drills should be oiled once for every 12 or 14 ft. of hole drilled. The rotating handle of a stoping drill is an oil reservoir and is provided with a port for oiling. The rotating handle is packed with wick-ing, or similar material, which causes the oil to feed slowly from the handle to the other parts of the machine. Stoping drills require oil at least twice a shift; lighter oils than castor, such as Arctic Ammonia, may be used. Drills used in shaft sinking can be oiled satisfactorily by placing a good-sized, drop, sight lubricator on the station above the sinking operations and connecting it with the air-line supplying the sinking drills. If this lubricator is properly filled and adjusted, a uniform oiling of the sinking machines will be effected without the necessity of oiling the drills individually. The grease end should be filled at the station or surface before each drilling period. The shift boss should see that the machines are greased and also that the lubricators at the station function properly. The life of the air-drill hose is somewhat shortened by this method, as oil attacks the inner tube; but as some oil is always present in the compressed air, this is not a serious objection to the method.

Jan 1, 1922

By V. C. P. Morfopoulos, N. Arbiter

Theoretical and experimental studies of the interactions of mineral particles with electrical fields of cylindrical symmetry have been made. Theoretically, an expression relating field gradient and intensity to the force experienced by a dielectric particle was derived in a manner paralleling the magnetic analog. Pauthenier's and Cohen's expressions were considered in the evaluation of coulombic forces. Comparison of dielectric and coulombic interactions of minerals exhibiting a wide difference in dielectric susceptibility revealed the potential significance of dielectric forces in a field of appropriate characteristics. Experimentally, apparatus was designed for the study of forces experienced by a single stationary particle in an electrostatic field. This permitted the separate and precise measurement of dielectric interactions in the field. The experimental results were in good agreement with the theory and with relevant published data. Dielectric forces were found of comparable magnitude with coulombic in the presence of an adequate field gradient. Prolonged exposure of minerals to an inhomogeneous field was found to enhance the dielectric response. Dielectric inter- actions properly employed may thus be important in electrostatic concentration techniques. Conventional electrostatic separation techniques employ forces between charged particles and field electrodes to establish the trajectories which effect separation. Uncharged mineral aggregates, although unaffected by homogeneous electrical fields, should respond to fields exhibiting appropriate orientation and electrical gradients. The purpose of this paper is to establish the theoretical and experimental base for the comparison of the forces due to dielectric-field interactions with those of electrostatic origin. Apparatus and techniques developed for the determination of dielectric interactions are described and data on the dielectric forces experienced by stationary particles in cylindrical fields are reported. Finally, a quantitative comparison of dielectric and electrostatic forces is given. THEORY Dielectric Forces: When dielectric particles, minerals for example, are placed in an inhomogeneous field they experience interactions that give rise to substantial dielectric forces.' The latter were shown proportional to the intensity of the field, the potential gradient, the size of the particles and the dielectric permittivity difference between the particles and the medium. The properties of the inhomogeneous field, E, and the magnitude of the gradient, dE/dl, depend on the geometry of the system in question.

Jan 1, 1965

By Takao Kobayashi

Micro-crack formation zones developed near a crack tip in rocks and ceramics play a significant role in fracture behavior of these materials. In order to study micro- crack formation near a crack tip and its effects on crack behavior, a mica-epoxy composite material was developed. Multi-layer mica flakes were embedded in an epoxy matrix. Under high stress in the vicinity of a crack tip the mica delaminated, simulating the micro-cracking along grain boundaries or crystal planes in rocks and ceramics. A compact tension specimen was fabricated from mica-epoxy composite material. During the test the load and crack opening displacement were measured following the ASTM E561 (R-curve determination) procedure. Through the compliance calibration method the effective crack length and the KR were computed. The experiment clearly demonstrates the formation of micro-cracks and their effects on the overall behavior of the specimen. The paper discusses the significance of micro-crack formation on fracture toughness characterizations, and the advantages of the use of mica-epoxy composite for detailed studies of interaction between the micro-crack formation zone and the specimen geometry and size.

Jan 1, 1982