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By M. E. True, B. L. Stone

To cope with the problems encountered when drilling at greater depths and to reduce the amount of physical effort required on the part of drilling crews in making round trips, a new type of semiautomatic power-operated drilling machinery has been developed which permits round trips to be made without the drill pipe being touched by hand. This equipment consists of hy-draulically operated tongs which perform the stabbing, spinning, and tong-ing operations, and two power-operated racking units mounted in the derrick for carrying the pipe to and from the center of the hole and positioning it on the mat and in the rack. With this equipment all of the operations of the various units are controlled remotely by manipulation of hydraulic valve levers and electric switches. INTRODUCTION As horsepower rises to meet the demand for deeper drilling, it is necessary to increase the weight of surface drilling equipment. Also, the duration of repetitive operations in making round trips to change bits is greatly increased with depth. Harder formations encountered at greater depths reduce bit life rapidly, resulting in more frequent round trips and in some instances more time is consumed in changing bits than in drilling. Since the introduction of the first rotary employed to drill for oil in 18951, there has been relatively little change in the general procedure for making up, breaking out, stabbing, and racking drill pipe in making round trips to change bits. The conventional method of making round trips with the drill pipe requires that drilling crews lend strenuous physical assistance to manually operated tools. Although many new devices have been developed to improve efficiency, increase speed of making round trips, improve safety, and reduce the amount of physical effort required in handling drill pipe, it is considered a vital necessity to substitute automatic or semiautomatic power-operated machinery for many of our more or less manual operations if extremely deep drilling is to be carried out successfully on a production basis in the same manner as our shallower drilling of today. Field tests have been made of remotely controlled power-operated tongs, spinner, stabber, and racking equipment. The tongs, which include a built-in pipe spinner, are mounted on a column, are capable of gripping and supporting the weight of a 90-foot stand of drill pipe, and are provided with means for moving the pipe vertically as well as to and from the center of the hole. The racking equipment consists of two units, one at the level of the conventional monkey board and the other at the first girth on the ladder side of the derrick. Most of the physical effort of making round trips with drill pipe has been eliminated in that all of the operations of tonging, spinning, stabbing, and racking of pipe on the floor are controlled by an operator in a seated position by manipulation of hydraulic and electric valve levers and buttons. The driller is relieved of operating the cathead, leaving only the hoisting and slips to be controlled. Complete round trips are made without the drill pipe being touched by the drilling crews. Although the speed of pulling or running a single stand with the power-operated equipment is approximately the same as that with conventional equipment, it is possible to maintain this rate for long periods, whereas fatigue slows crews working conventionally during round trips, especially under adverse weather. After completing round trips with this equipment, drilling crews are not exhausted, consequently, are able to perform effectively their duties while drilling, which is essential for maximum over-all efficiency. Safety is substantially improved as the derrickman performs his duties from a platform enclosed by rails and the tong lines and spinning chain are eliminated from the derrick floor. The hazards encountered in racking drill pipe on the floor and in stabbing are also eliminated. Figure 1 shows a drawing of a derrick equipped with the power-operated drill'pipe handling equipment.

Jan 1, 1949

By M. E. True, B. L. Stone

To cope with the problems encountered when drilling at greater depths and to reduce the amount of physical effort required on the part of drilling crews in making round trips, a new type of semiautomatic power-operated drilling machinery has been developed which permits round trips to be made without the drill pipe being touched by hand. This equipment consists of hy-draulically operated tongs which perform the stabbing, spinning, and tong-ing operations, and two power-operated racking units mounted in the derrick for carrying the pipe to and from the center of the hole and positioning it on the mat and in the rack. With this equipment all of the operations of the various units are controlled remotely by manipulation of hydraulic valve levers and electric switches. INTRODUCTION As horsepower rises to meet the demand for deeper drilling, it is necessary to increase the weight of surface drilling equipment. Also, the duration of repetitive operations in making round trips to change bits is greatly increased with depth. Harder formations encountered at greater depths reduce bit life rapidly, resulting in more frequent round trips and in some instances more time is consumed in changing bits than in drilling. Since the introduction of the first rotary employed to drill for oil in 18951, there has been relatively little change in the general procedure for making up, breaking out, stabbing, and racking drill pipe in making round trips to change bits. The conventional method of making round trips with the drill pipe requires that drilling crews lend strenuous physical assistance to manually operated tools. Although many new devices have been developed to improve efficiency, increase speed of making round trips, improve safety, and reduce the amount of physical effort required in handling drill pipe, it is considered a vital necessity to substitute automatic or semiautomatic power-operated machinery for many of our more or less manual operations if extremely deep drilling is to be carried out successfully on a production basis in the same manner as our shallower drilling of today. Field tests have been made of remotely controlled power-operated tongs, spinner, stabber, and racking equipment. The tongs, which include a built-in pipe spinner, are mounted on a column, are capable of gripping and supporting the weight of a 90-foot stand of drill pipe, and are provided with means for moving the pipe vertically as well as to and from the center of the hole. The racking equipment consists of two units, one at the level of the conventional monkey board and the other at the first girth on the ladder side of the derrick. Most of the physical effort of making round trips with drill pipe has been eliminated in that all of the operations of tonging, spinning, stabbing, and racking of pipe on the floor are controlled by an operator in a seated position by manipulation of hydraulic and electric valve levers and buttons. The driller is relieved of operating the cathead, leaving only the hoisting and slips to be controlled. Complete round trips are made without the drill pipe being touched by the drilling crews. Although the speed of pulling or running a single stand with the power-operated equipment is approximately the same as that with conventional equipment, it is possible to maintain this rate for long periods, whereas fatigue slows crews working conventionally during round trips, especially under adverse weather. After completing round trips with this equipment, drilling crews are not exhausted, consequently, are able to perform effectively their duties while drilling, which is essential for maximum over-all efficiency. Safety is substantially improved as the derrickman performs his duties from a platform enclosed by rails and the tong lines and spinning chain are eliminated from the derrick floor. The hazards encountered in racking drill pipe on the floor and in stabbing are also eliminated. Figure 1 shows a drawing of a derrick equipped with the power-operated drill'pipe handling equipment.

Jan 1, 1949

By Arthur Gibson

Synopsis.-A new feature in coal mining, where the coal is to be conveyed from a high to a lower elevation and the topography of the country is such as to preclude surface haulage. The distance from the mine to the tipple inn this instance is about 3,000 ft. and the difference in elevation between the terminals 321 ft., of which 225 ft. occurs in the first 1,300 ft. from the loading terminal. A mine car was designed especially for this plant consisting of two tramway buckets on one pair of trucks, the buckets being lifted from the truck, attached to the train line automatically, and conveyed to the tipple. THROUGHOUT eastern Utah, in the Book Cliff range and the Wasatch plateau, the coal-bearing measures are admirably exposed, in the bold and for the most part bare escarpments. The geology is simple, the rocks being almost flat, or at the most dipping not more than 10 per cent. The coal beds occur in a formation, or group of strata, consisting of sandstone and shale, 600 to 800 ft. thick, which has been correlated with the Mesaverde formation of the Cretaceous. Above this occurs about 2,000 ft. of alternate layers of buff-colored sandstone and shale. Below the coal lie the Colorado shales, which are estimated to be about 1,500 ft. thick, below which are the red rocks of the Jura-Trias. As a rule the coal beds all clip in a northerly direction and under the high mountain. The canyons opening out into what is known as Castle valley all cut the coal beds, and the beds rising in the direction of the valley are found frequently high up on the escarpment, often as much as 1,000 ft. above the valley. The surface features of the region have an economic bearing on the availability of the coal. The valleys and gulches in the Colorado shale extend out from the coal areas across the edge of the plain, so that it is impracticable to build transportation lines parallel with the boundaries of the field within several miles of the coal land. It will be necessary, therefore, to build branch lines up to the coal lands from points on the Denver & Rio Grande Railroad traversing Castle valley.

Jan 10, 1914

By J. G. Hadley

IN THE early stages of the depression the Utah Copper Co. realized that an unemployment problem would he created which demanded an intelligent and sympathetic solution. The company recognized that as many men as possible must be kept at work on a basis which would ultimately permit of the most efficient reabsorption of displaced labor. The company therefore determined to distribute available work among the greatest number of men and to that end adopted a system of rotating employees on a part-time basis. An employer requires a certain number of days' or shifts' work during the month. Obviously one employee working thirty days or shifts a month is equal to two employees each working fifteen. In principle, therefore, where two employees equally fitted to do certain work are available the work could be divided between them on an equitable basis and twice as many persons would benefit. A rotation plan on this basis was adopted by the Utah Copper, Co. on Jan. 30, 1930. Some variations of the orig¬inal plan have been made from time to time, the reasons for which will be discussed.

Jan 1, 1932

By R. Adair, W. R. Hudspeth, W. T. McDaniel

A NEW method for concentrating the flake mica either from present washing plant tailings or from new feed has been developed. In this paper, flake mica refers to that which occurs in weathered granites, alaskites, pegmatites, and schists in a form too fine to be considered sheet mica. It ranges in size from 1 in. or more down to 200-mesh or finer and occurs with kaolin, quartz, and partially kaolinized feldspar. Scrap mica, a term often used indiscriminately to describe everything other than sheet mica, will be used to denote the waste product from sheet mica mines and fabricating plants. Both flake and scrap mica are used in the mica grinding plants to produce wet-ground or dry-ground mica, although some flake mica recovered from clay mining operations is fine enough to be marketed without grinding.

Jan 3, 1951

By F. L. Grammer

THE analyses given in Table I. were made several years ado at my request at a plant using Lake ores. The, are of two furnaces, one making basic, the other Bessemer pig-they gave 6 casts each in 24 hr., also two flushes of cinder between each cast. They- are offered simply for the sake of reference as, so far as I know, it is unusual to find so frequent fall analyses made and none are on record. The variations iii manganese-content in the first and second flushes on the basic furnace are interesting, if no more than a freak-the first flash being invariably higher in manganese. The iron-content of the two slugs from an. average of 12 flushes shows: Basic. Bessemer. Per Cent. Per Cent. Total iron 2.55 1.70 Combined iron 0.72 0.52 Free iron 2.13 7.15

Jan 3, 1913

By Archer Wheeler

Introduction. THERE are two general methods in use for the production of metallic copper from matte which are worthy of consideration : (1) the Welsh blister process, and (2) the converter process.1 As practically all of the copper produced to-day is made in converters, we will give a brief outline of that process before proceeding with the special subject of this paper. Matte may be roughly defined as a mixture of the sulphides of copper, iron, nickel, silver, etc. In the converter process this is blown up to metallic copper in a modified type of Bessemer converter. The conversion of matte consists mainly in, (1) the removal of sulphur in the form of SO2, and (2) the slagging of the iron. With this brief statement we come to the two subdivisions of the process of converting mattes: Converting with acid linings. Converting with basic linings.

Jan 12, 1913

By Katherine Mather

This paper is an attempt to put together petrographic, physical, and chemical data about the large and varied group of rocks generally called limestones. Results of the properties of these rocks on their performance as concrete aggregates are discussed. CRUSHED stone classified as limestone comprises about 70 pct of the crushed concrete aggregate and roadstone produced in this country, and the product has amounted in the recent past to about 97 million tons per year, valued at more than $123,-000,000.' Therefore an evaluation of the properties of rocks classified in these statistics as limestones and an ability to predict their behavior as aggregate in portland cement concrete are matters of considerable economic consequence to producers and consumers of aggregate. This paper is an attempt to put together petrographic, physical, and chemical data about the large and varied group of rocks generally called limestones. It also points out certain results of the properties of these rocks on their performance as concrete aggregates. The problems encountered in efforts to explain the behavior of limestones, dolomites, and related rocks as concrete aggregate lie on the frontiers between the ignorance of the geologists and the ignorance of the engineers. The mineral composition and textures of the rocks have not been adequately explored and described, and the effects of mineral composition and texture on the performance of aggregates have been worked out in only a few cases. There are instances of unsatisfactory performance and some generalizations of those experiences. There are many more examples of satisfactory performance than of unsatisfactory, but there is practically no published information as to why a particular aggregate was satisfactory in a specific use. There are all too few investigations of undeteriorated concrete; more is known about the pathology of concrete than about its normal structure and aspect. As part of the investigation of aggregates, the classification of rocks is not an end in itself, but is a step toward recognition of properties expected to influence the behavior of aggregates in their intended use. Rock of any type may perform well or poorly as concrete aggregate, depending on the physical condition of the rock, its physical and chemical properties as compared to those of the matrix in which it is placed, and the circumstances under which the concrete is exposed. Some classification and descrip- tion of the limestones is necessary to distinguish subgroups whose members will probably behave in similar ways and to evaluate the group as a whole. The group name, limestone, includes and tends to conceal the identity of rocks that have a very great range in chemical and mineralogical composition, structure and texture, conditions of deposition, subsequent history, and suitability for use as concrete aggregate. All the rocks classified as limestones include one or both of the most abundant rock-form-ing carbonate minerals, calcite and dolomite, as major constituents. Carbonate rocks is a more descriptive and more accurate group name than limestone, which has generally been used to include dol-omitic or magnesian limestones and dolomites as well as calcitic limestones. Classification and Description of the Carbonate Rocks The question of names to be applied to the carbonate rocks may appear academic, but it is of practical importance as long as there are specifications for aggregate that result in acceptance or rejection of rocks by name and as long as failure to make distinctions among the carbonate rocks leads to misunderstandings of their properties and of what may be expected of them in performance. Materials included in production statistics as limestone and tested for concrete aggregate as limestone range in fact from calcareous shale and calcareous or dolomitic sandstone and argillaceous limestone and dolomite to calcitic limestone and pure dolomite and to rocks close to calcitic and dolomitic marble. To take a simple example: consider two manufactured coarse aggregates, both dense and unweathered, one composed principally of crystalline calcite and the other of crystalline dolomite, but both known as limestone. If each is used as coarse aggregate in a standardized concrete mixture with the same fine aggregate used in both cases, made into concrete specimens, and tested in accelerated freezing-and-thaw-ing, the test results will probably be quite different, because of the differences in internal bond and thermal properties between the two aggregates. As long as both aggregates are called limestone, the test results cannot be explained, or used except in a very limited way; if the aggregates are distinguished as limestone and dolomite and the consequent differences in texture and thermal properties are recognized, the results are reasonable. Classification of the carbonate rocks used as aggregate should be based on structure and on composi-

Jan 1, 1954

By W. G. Pfann

THE problem of forming points on wires that were from 0.002 in. to 0.010 in. in diam arose in the recent appearance of silicon and germanium point contact rectifiers as elements in microwave radar.1 In these devices a pointed tungsten wire makes a delicate contact with the surface of a semiconductor. Because the quality of such rectifiers is largely determined by the nature of this contact, considerable attention has been given to the formation of the metal point. Reproducibility of contour and freedom from burrs and even microscopic irregularities are considered essential. The operations involved must be simple and rapid enough for mass production. Previously tungsten wires had been provided with conical points by a grinding method which involved rotating a wire about its axis and causing it to bear at an oblique angle against a spinning abrasive disc. This was later complemented with an electrolytic polishing treatment which removed irregularities from the ground point and also rounded it off at the tip-a desirable feature. Finally, these operations were supplanted by the electrolytic pointing method described here. MECHANISM OF POINT FORMATION The wires to be pointed are partially immersed- in an electrolyte in a .vertical position whereupon they are provided with smooth rounded points entirely by electrochemical action. The process is independent of the depths to which the wires penetrate the electrolyte because the points are formed at the surface level. It may be used to point a single wire or many of them simultaneously and is applicable to wires of different diameters within a limited range. Solution of the immersed portion of a tungsten wire is accomplished by making it the positive electrode in an electrolytic cell, as shown in Fig I. While the wire is maintained at constant voltage the current through the cell falls continuously, principally because of the decrease in wetted area which results from solution of the tungsten. This increase in resistance occurs in a reproducible manner and is used as a control in the process. As the immersed portion of the wire dissolves, it remains cylindrical in shape except for the short section which is wetted by the meniscus. Here the rate of solution is lower and decreases as the top of the meniscus is approached. The result is the formation of a tapered section inside the meniscus. As solution continues, the cylindrical section either dissolves entirely or drops off just before complete solution, leaving only the taper which is now sharply pointed. Further action causes this point to become rounded and then quite blunt, until finally the end of the wire is almost plane. Fig 2 shows the stages in this development. Contour PF is most representative of those used in point contact rectifiers. Thus a variety of point

Jan 1, 1947

MONDAY, FEB. 17 9.00 A.M. to 9.00 P.M. Registration at Institute Headquarters. 9.00 A.M. Meeting of Committee on Development of the Activities of the Institute, Room 905, 9th Floor. 10.00 A.M. Simultaneous Sessions of Institute of Metals Division, Room 2, 5th floor. Industrial Organization, Room 1, 5th Floor. 12.30 P.M. Luncheon at Headquarters, 5th Floor. 2.00 P.M. to 4.25 P.M. Simultaneous Sessions of Institute of Metals Division, Room 2, 5th Floor. Industrial Organization, Room 1, 5th Floor. Petroleum and Gas, Room 905, .9th Floor. 2.30 P.M. Sightseeing trip by automobile for the ladies. Among the points visited will be: The American Museum of Natural History. The Episcopal Cathedral of St. John the Devine. The Spanish Museum. The American Geographical Society. The American Numismatic Society. The visits will be followed by Tea. 4.30 P.M. Memorial Service to Dr. Rossiter W. Raymond, Auditorium. 8.30 P.M. Smoker, 5th.floor.

Jan 2, 1919

By Norman Yarborough

Much has been written about the energy fuels including their standing with respect to reserves, their delivered Btu costs, their potential in the electrical generating market and their capabilities to meet a burgeoning demand. Yet, when all factors are placed in their proper perspective, the spiraling electrical energy market alone should guarantee each fuel a better than average market for the foreseeable future. In fact, a study made by the U.S. Federal Power Commission on the spare capacity utilities have on hand indicated that 39 of the 181 major utility systems had less than 10% reserves on hand at the end of 1969. Fuel supplies are critically low in some areas, especially in the Southeast, South Central and Midwest areas of the U.S. In other systems equipment shortages resulting from faulty equipment or delays in getting new equipment deliveries causes power failures during peak loads. In addition, lack of labor curtails the erection of some new facilities and prevents many other facilities from operating at capacity.

Jan 1, 1970

By W. A. Vine

When a hole is made in a stressed solid, such as rock pierced by mine openings, equilibrium of the solid is destroyed. To restablish that equilibrium the stress condition in the rock surrounding the opening becomes rearranged. This rearrangement may or may not develop local stresses in the vicinity of the opening which exceed the elastic strength of the rock. Since stability of the opening depends, therefore, on the strength of the naturally occurring rock surrounding the opening, this rock is an engineering material of construction, and all rock affected by the associated opening or system of openings may be considered a structure. The term invert is chosen to describe the formation of the structure built from the inside, as it were, and a consequence of mining rather than an entity built for a purpose. By definition, an invert structure is formed when openings are made underground and is com- posed of that material on the solid side of a rock-air interface wherein the stress condition is affected by the associated opening or system of openings. The shape of an invert structure is never clearly defined; the skin of the structure may be mapped, and even described, but the boundary of the structure within the solid rock mass must be arbitrarily set.

Nov 1, 1955

By Edward Martinez

The literature on the beneficiation of serpentine asbestos ore states that the specific gravity of the rock containing fiber and the fiber itself is the same so that specific gravity cannot be used as a basis for separation. An investigation of particles of asbestos ore ranging in size from 4 mesh to 5 in. revealed that the fiber-bearing particles generally had a lower specific gravity compared to essentially barren particles. The difference in specific gravity was sufficient to make an effective gravity separation of ore particles and reject a low grade tailings product. The results of laboratory tests are described that lead to the running of pilot plant tests with 20-ton ore samples using a heavy media separator. These tests indicated that a large amount of low grade material could be rejected from the raw ore at a coarse size. Although the process used is a wet separation, it can be added to a conventional dry asbestos mill. A gravity preconcentration would allow the mining of lower grade ore, increase the life of the mine, increase the value of the feed to the fiber recovery section, and decrease maintenance costs by removal of low grade tailings early in the flowsheet.

Jan 1, 1975

By Sabert Oglesby, Albert L. Thomas

Until recently, probably the best means of sampling airborne dusts has been the impinger method. Dust-laden air is drawn into a sampling tube, and the particulate matters separated from the air and collected in the liquid in the impinger. A sample of the suspension is prepared on a slide and counted through a projection microscope. This method is simple and reliable, but it does suffer drawbacks. Since the collected particles must be counted visually, results of the dust count are taken. This seriously impedes studying the effectiveness of dust inhibitors, such as water sprays, or making adjustments in equipment. Greatest disadvantage of all, however, is the tedious task of counting particles in the sample. With the growing desirability of taking more samples, the effort involved in making these counts is a real factor in the cost of dust control. Finally, it is generally recognized that impinger dust counts can be related to health hazard only for specific kinds of dust and under similar conditions. This is because the rather complex mechanism of dust damage depends so much on size distribution of the dust. Counts determined by impinger samples cover a limited size range that does not necessarily correlate with retention by the lungs and upper respiratory tract.

Jan 3, 1959

By C. E. Webber

THE economical recovery of the valuable constituents from the effluent of gas-con-densate wells has developed into a problem of balancing the cost of recovery against the cost of compressing the residual gas back into the formation. A possible method of extracting the gasoline and distillate from the natural gas is by oil absorption at high pressures. In order to design and evaluate an absorption plant, fundamental data on the composition of the coexisting hydro-carbon vapor and liquid phases at various temperatures and pressures are essential. A review of the literature indicated that the necessary data for the design of such plants are lacking. The nearest approach to desired published data is that of Katz and Hackmuth,5 who experimentally deter-mined the composition of the coexisting vapor and liquid phases in a natural gas-crude oil system at pressures up to 3000 lb. per sq. in. and at temperatures from 40° to 200°F. This paper presents the results of the experimental determination of the equilib-rium distribution of the hydrocarbons methane through hexane between natural gas and a typical absorber oil. The ranges of temperature and pressure chosen were from 33° to 180°F. and from 100 to 5000 lb. per sq. inch.

Jan 1, 1940

By W. W. Harvey, F. O. Dudas

Toward hot hydrochloric acid, the usual order of reactivities of the common copper sulfide and associated minerals is reversed, and the rates of H2S formation vary as [ ]. The iron component of chalcopyrite and bornite reports to the solution as ferrous chloride, while pyrite remains essentially unreacted. If a pressure of H2S is maintained in the reactor, copper solubilization is suppressed, and the primary copper sulfides are converted to finely divided secondary sulfides (principally covellite). The HCl leach reside then consists mainly of covellite, pyrite and acid-insoluble gangue. Copper can be selectively leached from this upgraded concentrate to yield a clean, strong copper sulfate solution for direct electrowinning. Preliminary analysis indicates competitive economics with respect to established hydrometallurgical processes. Other concentrate treatments based on an initial HC1 leach are proposed and relative advantages compared. The common denominator of the major process routes considered is the requirement to regenerate HC1 from an FeC12 solution. Five distinct concentrate compositions were employed in the experimental study, which included some attention to the fates of selected minor constituents of the copper concentrate, especially gold, silver, molybdenum, arsenic and selenium. Significant mineralogical features of reactants and products are described.

Jan 1, 1978

By Hans Lundberg

IN ORDER to comprehend the help and information that may be expected from electrical prospecting, it is necessary to have at least a general knowledge of the methods and principles involved in preparing and interpreting results obtained in the field. Electrical prospecting is rather complicated, both in theory and practice, and in order to make a brief description clear to the practical mining man it has been necessary to idealize and generalize the problems, at the risk of having such simplification criticized by the theoretical man. This simplification must not be misinterpreted as showing a lack of theoretical knowledge. FIG. 1.-FLOW OF CURRENT IN AND AROUND A CONDUCTING BODY. For its operation, electrical prospecting mainly, depends on the fact that most metallic ores conduct an electric current much more readily than barren rocks. If an electric current flows through a block of ground within which a body of chalcopyrite is enclosed in country rock of. schist, the current will find less resistance to its passage through the chalcopyrite than through the schist, even though the passage through the latter be much shorter. This is because the longer path through the chalcopyrite offers less resistance, owing to the superior electrical conductivity of the chalcopyrite (Fig. 1).

Jan 1, 1928

By Richard A. Busch, Roy L. Soderberg

Large, high, open stopes resulting from vertical crater retreat (VCR) and similar methods are usually filled with sand tailings to support the stope walls and make it possible to mine the pillars. The hydrostatic head resulting from these high stope fills demands extremely heavy bulkheads in the crosscuts to withstand the pres- sure. Occasionally, these bulkheads fail because there are no drains or the installed drains are inadequate. Costly flooding of the mine and loss of life result from these failures. With proper design of blanket drains and filters, the fill can be made failure-proof, requiring only a minimum bulkhead, designed specifically for zero water retention. The effectiveness of the blanket drains can be increased by laying perforated pipes on the bottom of the crosscut within the blanket drain. These drains can have a safety factor of 10 with minimal expense. When the water is properly drained, the hydrostatic pressure on the bulkhead is reduced to zero, leaving only the lateral pressure of the sand. This lateral pressure is partially dissipated by arching and shear against the crosscut walls and consolidation of the tailings as the water is drained. The bulkhead should be placed at least one cross-cut diameter back from the collar of the drawpoint.

Jan 1, 1983

By Hans Lundberg

IN ORDER to comprehend the help and information that may be expected from electrical prospecting, it is necessary to have at least a general knowledge of the methods and principles involved in preparing and interpreting results obtained in the field. Electrical prospecting is rather complicated, both in theory and practice, and in order to make a brief description clear to the practical mining man it has been necessary to idealize and generalize the problems, at the risk of having such simplification criticized by the theoretical man. This simplification must not be misinterpreted as showing a lack of theoretical knowledge. FIG. 1.-FLOW OF CURRENT IN AND AROUND A CONDUCTING BODY. For its operation, electrical prospecting mainly depends on the fact that most metallic ores conduct an electric current much more readily than barren rocks. If an electric current flows through a block of ground within which a body of chalcopyrite is enclosed in country rock of schist, the current will find less resistance to its passage through the chalcopyrite than through the schist, even though the passage through the latter be much shorter. This is because the longer path through the chalcopyrite offers less resistance, owing to the superior electrical conductivity of the chalcopyrite (Fig. 1).

Jan 1, 1928

By M. F. McCarty, R. S. Olson

New organic flocculants of high-molecular weight are replacing lime, glue, and starch in liquid-solid separation. Of these synthetic materials, poly-acrylamides are outstanding. Polyacrylamides form a class of compounds varying widely in composition and activity. Separan 2610, one of the first of these flocculants' released to the mining industry in 1954, is described' as a high-molecular weight polymer of acrylamide with or without a copolymer material and with some replacement of amide by carboxylic groups. MECHANISM OF FLOCCULATION In practice, flocculation makes solids settle faster and filter better. But two opposing factors control it. The random motion that causes particles to collide favors Van der Waals' forces, which hold the particles together. The effect of zeta potential opposes this contact, and particles are mutually repelled. Flocculation can be achieved by reducing the magnitude of the zeta potential; this is the mechanism of flocculation by lime addition. The way in which polyacrylamides accomplish flocculation is not fully understood, but the action is undoubtedly comp1ex and probably varies considerably depending on the system. To begin with, the active groups of these compounds have an extremely high affinity for solid surfaces, probably by hydrogen bonding." Initially some active groups of the molecule attach themselves to the solids with a large portion of the molecule extending into the solution. Two particles can become tied together by long flocculant molecules in the following ways—by bonding between the active groups of two flocculant molecules on different particles, or by an extended molecule from one particle attaching itself directly to the surface of the other particles." These flocculant bridges prevent the particles from moving apart through random motion, but when such motion moves them together other active groups on the flocculant bridge bond to the solids, holding them in the closer position. This process is repeated until the particles are close together. Although bridging is probably a major flocculation mechanism, it is not the only phenomenon involved. Relatively neutral acrylamide flocculants reduce the magnitude of the zeta potential by increasing the viscosity of solution in the immediate vicinity of the solid surface which contains the mobile counter ions of the double layer. In other words, it moves the shear surface which bounds the zeta potential out into the solution containing counter ions which tend to neutralize the zeta potential. This effect is probably more pronounced during the initial adsorption period, before the flocculant molecules are pulled close to the solid. In some cases the slight charge of the polyacry-lamide molecule tends to neutralize a zeta potential. However, this is not a primary flocculation mechanism, as evidenced by the fact that the polyacrylamides will flocculate solids with either positive or negative zeta potential. Adsorption of polyacrylamide flocculants by a solid is substantially an irreversible reaction. Since the flocculant molecule is attached to the particle surface by many active groups of high bonding strength, desorption would require the simultaneous breaking of many bonds—an unlikely occurrence. UNIQUE PROPERTIES The irreversible adsorption of certain polyacrylamides, the flocculant's high affinity for solid surfaces and its rapid adsorption make it effective, but these unique properties require special techniques to achieve maximum flocculation. If flocculants of this type are added to a pulp as a relatively concentrated solution, the solids in the

Jan 1, 1960