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By T. E. Gray

This report describes the preparation characteristics of the more significant coal beds in Allegheny County, Pa. It is one of a series planned to determine coals suitable for producing metallurgical coke, either as mined or after beneficiation. More than 7 million tons of coal was produced in Allegheny County in 1957. Of this, more than 5 million tons was cleaned mechanically in nine cleaning plants. The Bureau of Mines estimated that, as of January 1, 1953, more than 384 million tons of recoverable coal remained in the county in beds 28 inches or thicker.

Jan 1, 1959

The coal-bearing areas of Kansas cover approximately 18,800 square miles (23 percent of the state's total area). Coal in Kansas ranges from lignite to high volatile bituminous, located principally in the south-eastern part of the state. Kansas reserves are estimated to be 987,500,000 tons, approximately 0.2 percent of U.S. reserves. Coal beds generally occur in thin seams up to five feet thick. The overburden-to-coal stripping ratios in Kansas are among the highest in the nation, typically 20 to 1, with some ratios up to 35 to 1. The first commercial coal mining operation in Kansas opened in 1865 at Fort Scott in Bourbon County. As in other states, coal production in Kansas increased during the industrial revolution, and then fell as industry converted to alternative fuels. Production peaked in 1916 and 1917, with annual production of 7,250,000 tons. Coal production today is by surface mining methods. The Kansas regulatory program was approved April 14, 1982; the Abandoned Mine Land Program was approved February 1, 1982; and the emergency program authority was approved January 10,1989.

Jan 1, 1992

By E. W. Newman

During 1943 and 1944, there was an urgent need for certain grades of optical calcite (Iceland spar) for instruments for ' military uses. To find a supply of this material, prospecting was carried out in Montana, California and Colorado. Although some production was obtained by the work in California, the best results were from prospecting the large calcite veins of south central Montana. The bulk of the optical calcite mind during World War II has come from that area. The Bureau of Mines took an active part in the search for optical calcite in Montana. It examined most of the known calcite veins in the 70-mile distance between Wilsall, on the Shields River: and Absarokee, on the Still water River, and conducted exploration on several of the deposits. The Geological Survey also took an active part by mapping many of the veins. Actual mining of the calcite was performed at first by Calcite Operators, Inc., and later by the Metals Reserve Co., through an agent. A sorting plant was established at Clyde Park, where custom material could be sold. These activities stimulated mining by private operators. To be suitable for military uses, the calcite mined had to meet rigid specificstions as to both size and quality. Individual crystals had to be clear and transparent and if in the form of rhombs had to measure at least 7/8 in. on each edge. Some color and a few inclusions in the calcite were allowable, but material with incipient or developed cleavages, or showing twinning other than parallel to the base, was unacceptable. History of Deposits The existence of large veins of calcite in south central Montana has long been known, and for many years the farmers of this region have used the common vein calcite for producing grit for chicken feed. According to reports, the fist optical calcite produced from Montana came from the Cartwright deposit near Grey-cliff,' but until recently the mining of optical calcite in Montana has been limited to spasmodic searching for small crystals suitable for making nicol prisms for saccharimeters and microscopes, or for mineral specimens. The possible need of substantial amounts of optical calcite for military uses began to appear late in 1942 and early in 1943, therefore the Polaroid company began searching for a source of supply in Montana and California. Work on the Wade property near Clyde Park was started on a small scale in the fall of 1942, by .4. H. Hansen, of Clyde Park. During the winter and spring of 1943, a modest quantity of optical calcite was mined and shipped to the Polaroid Corporation, Cambridge, Mass. Most of this was produced from the "Hansen vug," which was found close to the surface. Early in the summer of 1943, mining on the Wade property was undertaken by Calcite Operators, Inc., a company organized for mining optical calcite from the

Jan 1, 1948

By William Glenn

That basic slag will rapidly destroy ordinary (i.e., siliceous) fire-bricks is known to every smelter; and the smelter of copper-ores in particular knows that any kind of slag occurring in his practice is destructive. From this fact arises the chief distress of those who attempt to smelt copper-ores in any manner of furnace constructed of bricks or stone, or other similar material. We have passed the fire-brick stage of our experience; and now, having entered upon the period of the water-jacketed cupola, we will employ no furnace other than that having steel walls, kept cool by water. But,, unfortunately, the bottom of a water-jacketed cupola, kept cool by another water-jacket, fails of its purpose, being thereby made so cold as to chill both slag and regulus to a degree not bearable. The situation is more or less ameliorated when the upper surface of the water-jacketed bottom is covered with fire-bricks, since, so long as they last, they prevent the molten material from contact with the cold bottom. My own observation leads me to suppose that most smelters construct cupola-bottoms of iron slabs, which are covered, to a greater or less depth, with fire-bricks. There are cupola-bottoms which

Jan 1, 1902

By Ole Bernt Lile

The well-known method of C. Schlumberger, Mise a la masse, has become a popular method again in ore exploration in Norway after many years of dominance by EM methods. The principle of the method is to place a current electrode within a conducting ore body and remove the other electrode to a great distance. (Figure 1). Often it is convenient to place a return electrode on each side of the area explored. The method is best suited for ores that have a conductivity contrast, relative to the host rock, of several orders of magnitude. The potential drop within the ore itself may then be neglected and the ore contact against the rock may be regarded as an equipotential surface. One may say that the ore body is electrically charged. Therefore, in Norway the method is now most often called the Charged Potential Method (abbreviated CP). The most usual way to present data obtained by CP, is to draw equipotential lines based on potential values measured in profiles on the surface. Such a potential map gives an immediate picture of the outcrop of the ore and also indicates disturbing conductors in the neighborhood. It may also be useful to look at the potential profile and its horizontal gradient along the strike axis of the potential map. These profiles may give information about the strike length of the conductor. Figure 2 shows the theoretical profiles of potential and gradient along the axis of the potential picture on the surface over a charged line plunging 15 degrees. It may be seen that the maximum of the gradient curve clearly indicates the lower end of the conductor. Figure 3 shows the corresponding pro- files over a charged line plunging 45 degrees. In this case, it is not possible to see an indication on the curve of the lower end. Only curve fitting could help interpretation in this case.

Jan 1, 1975

By H. Landsberg

The curriculum presented here is an outgrowth of discussions by the Committee on Geophysics Courses of the A.I.M.E. in previous years. It had to be a compromise between the desires voiced by employers of geophysicists, professional geophysicists and the possibilities at an average college. There one has to face the questions of the available teaching staff, the inertia of administrators and teachers set in their ways, and the red tape involved in modernizing antiquated curricula. It is, of course, not ideal to have colleges and universities lag Io years behind the times. Rather, instead of being prodded by industry, they should be ahead of industrial needs. There should also be a certain amount of leeway for the student in any college curriculum. All these points had to be considered in drawing up a curriculum, which, instead of being narrowly termed "geology" or "geophysics" was rather called "earth science." It gives the student a chance to specialize in one of the various branches represented by teachers on the faculty of The Pennsylvania State College, giving as options Geology (with subdivisions of Mineralogy and Paleontology), Geophysics, Geography, and Meteorology. Table iA represents the option of geophysics in the curriculum that envisages that a student may want to make his career in any of the fields encompassed by the American Geophysical Union or in geoexploration. This is, of course, only the start of an education that in most cases will have to be followed by graduate work for complete professional training. The outlined curriculum is definitely of an engineering type and is identical for all of the four options mentioned for the first two years. Specialization will start in the junior year but even thereafter the branches are kept as closely allied as feasible in order to permit a student to change from one tO the other (e.g., because of a different aspect in the mployment situation) with a minimum of additional work. Table IB shows the geophysics option according to subject matter, indicating the considerable amount of work in the fundamentals of mathematics, physics and chemistry with a liberal number of geology courses, and some engineering. The courses in the field of geophysics are limited—just two lecture courses as a general introduction and one field course, to permit the student a visualization of the correlation between mathematically analyzed physical data and the geological realities. Thesis work is considered essential to teach the student, while he is still in college, some things S. F. Kelly has mentioned as desirable: (I) following of instructions for somewhat independent work; (2) organizing of material, and (3) producing a readable report. This, together with the personal contact with the advising faculty member, will help in forming a student's personality. The seminar course attempts to get the student into the habit of reading current literature, so that he can keep abreast of the times.

Jan 1, 1946

In March 1990, Heritage Mining conducted a 2000 line km high resolution aeromagnetic survey of all its prospects in the Coromandel Peninsula. One of the areas covered was the Onemana Peninsula, situated about 5 km north of Whangamata. Details of location and geology are given by Robson and Stevens (this volume).   The detailed helicopter-borne magnetic and radiometric survey over the Onemana area consisted of 163 line kmÆs of flying, and was carried out in order to assist in the definition of hydrothermal alteration and pre- or post- mineralisation structures. The line spacing chosen was 100 m, flown east-west, with a mean sensor terrain clearance of 80 m. Tie lines were flown north-south every kilometre for levelling purposes. The sensor was a Geoinstruments G-813 proton precession magnetometer in a towed bird, with data recorded using a Geoinstruments G-2000 acquisition system.   The Onemana alteration system is at the northern end of a major north-north east trending structural corridor defined by regional aeromagnetic surveys performed by AMOCO in 1980 (Rabone, 1991). T his structure hosts a number of other extinct hydrothermal systems including Karangahake and Golden Cross. In the Onemana contour plot the predominant north-northeast structures form the boundaries of a large area of subdued magnetism in the southern part of the surveyed area that is caused by intense hydrothermal alteration. This area is about 3.5 km long by 1 km or more wide and contains outcropping sinters and hydrothermal eruption breccias, as described in Robson and Stevens. A number of other structures transect this alteration zone, with strike directions ranging from northwest to north. A northwest feature notably truncates the zone to the south, while the northern end seems to be simi1arly bounded; however as data coverage ends at the coast, this feature is less conclusive.    Two distinctive types of strongly magnetic rock were discernible the contoured data. The strong negative magnetic anomalies the north and west are caused by fresh negatively magnetised rhyolites. This was confirmed by ground follow-up work that showed the rocks to be fresh biotite rhyolites with high magnetic susceptibilities.

Jan 1, 1991

By I. Southern, S. Kelebek

"Smelting furnace bricks contain significant quantity of base metals trapped in refractory material. A series of flotation tests were carried out on samples of old bricks from Sudbury area to examine upgrading behaviour for recycling purposes. Depending on the grind size used nickel recoveries varied from 60 to 90.6% with corresponding grades of 20% and 14.7%Ni. There is a trade-off between nickel and copper. The nickel has responded well to fine grinding, however, the copper recovery suffered from it. Mineralogical characteristics and flotation behaviour of the brick material are discussed in reference to those from the primary ore. INTRODUCTIONMineral processing is well recognized as a mature technology not only for the mining industry, but also for the environmental industry for the purpose of remediation and recycling. Materials available for recycling are usually the products of many years ago. There are multiple stake holders in this area. In general, when the processing results in a product that can be reused or sold, the company carrying out the remediation makes a profit, while the regulators and the public are pleased due to a cleaner environment. From these points of view, there have been many papers published over the years on various mineral processing techniques applied to separation of many different materials including from mining and metallurgical industries (Wilson et al., 1994; Tsunekawa et al., 2005; Saikia et al., 2012).Flotation may be viewed as the backbone of the mining and metallurgical industry since its invention for separation of solids from one another almost a century ago. It is capable of recovering a variety of finely divided different solids following their liberation from each other. Its versatility and highly competitive nature in terms of cost per tonne of material processed, accounts for its occasional uses in the environment engineering area. In the mining industry, flotation is the standard method used for the sulphide ores. It can be applied as a bulk flotation and/or differential flotation. Bulk flotation, which refers to co-flotation of several components from their source, is most suitable for environmental cleanup objectives. Desulphurisation of various plant tailings is a typical example of this (Benzazzoua et al., 2000)."

Jan 1, 2012

By Thomas H. Dubaniewicz

The National Institute for Occupational Safety and Health, Pittsburgh Research Laboratory, conducted a study of past mine explosions to identify the ignition locations and ignition sources responsible for the most severe explosion events resulting in death. Since the Scotia disaster of 1976, many fatalities from underground coal mine explosions have been linked to nonpermissible electrical equipment ignition sources located in intake air courses. With few exceptions, explosion protected equipment is generally not required in intake air courses of gassy underground coal mines in the US. Cigarette lighters were another prevalent ignition source for fatal explosions ignited in intake air courses. Several mine rescue/ recovery teams have encountered electrical ignition hazards. The study provides evidence that intake air courses of gassy underground coal mines fit the description of certain Hazardous (classified) locations described in the US National Electrical Code®. Class I Division 2 or Zone 2 explosion protection tech¬niques may be used to design intake air equipment so that it does not present an ignition source under normal operation, before mine power is shut down in emergency situations. Nonpermissible circuits in intake air courses that are likely to remain energized during emergencies, e.g. battery powered equipment, should be protected by more stringent Class I Division 1, Zone 1, or Zone 0 techniques, to protect rescue/recovery personnel.

Jan 1, 2009

By Mike Rogers

Platinum production in Southern Africa amounted to 80% of world production in 2005with a small increase from 5 117 000 ounces to 5 275 000 ounces. For the seventh consecutive year the platinum market is on course to record a moderate deficit in supply. This is reflected in the price increase from a trading range US$860 to US$880 in June 2005 to an excess of US$1 200 in September 2006. Southern Africa, with its extensive platinum reserves, will continue to be the dominant platinum producer and has a number of new mines in an advanced stage of planning. The slogan ?Platinum Surges Ahead? was selected to describe the exciting and vibrantnature of all aspects of platinum mining, beneficiation and marketing. This conference will cover these aspects from exploration and orebody delineation, through mine design, development and operation to mine closure; mineral beneficiation, marketing and compliance with the Mining Charter will also be subjects for discussion and debate. It is also anticipated that the issue of overall increases in productivity, through the introduction of technology, will demonstrate Southern Africa?s status as a premier mining district. It is my pleasure to welcome delegates from abroad and locally, on behalf of the SAIMM, to the Second International Platinum Conference ?Platinum Surges Ahead?. I trust that you will find the proceedings informative and value adding and will participate in the discussions and debate in order to obtain maximum benefit from the conference. I am sure that the post-conference tours will be interesting and of great benefit to participants. Finally, a big word of thanks to the members of the Organising Committee, the management and staff of the SAIMM, and to our willing sponsors, without all of whom this conference would not have been possible.

Jan 1, 2006

By M. Leroux, J. A. Finch

"Sizing below 38 µm (400 mesh) is an increasing requirement in mill testing laboratories. The Cyclosizer is gaining wide acceptance in this role. A recent alternative is to use electro-formed sieves (micro-sieves), which are available with openings down to 5 µm. The advantage of micro-sieving is a cut size which is independent of mineral density, easier retention of the fi nest fraction and reduced purchase cost. A simple method of microsieving using an ultrasonic bath, which performs readily to 10 µm, is described.A systematic study of Cyclosizing and micro-sieving is reported for three samples; silica, copper oxide and a lead concentrate. Micro-sieving gave comparable results. Comparison with a standard sizing method, the Sedigraph 5000D, revealed misplaced material in each fraction by both methods. The range for micro-sieving was from 20% to 60% depending on the sieve and material; for the Cyclosizer it was a consistent 40-50% for all cones and all materials. The Cyclosizer can be sensitive to feed mass and particle size for dense materials. It is recommended that for minerals of specific gravity greater than 5, no more than 35 g of -38 µm be used.The disadvantage of micro-sieving is that it requires continuous operator attention and sieving time depends on sample mass. To fractionate 35 g-as used on the Cyclosizer and considered at reasonable mass for mill testing purposes-through 25-, 15- and 10-µm sieves requires about 80 minutes.IntroductionParticle size has a pronounced influence on mineral separation processes. Consequently, the measurement of particle size plays an important part in mill testing. By far the most common method is by screening. This, however, is usually limited to 38 µm (400 mesh) or occasionally 25 µm (500 mesh). Increasingly, mineral products are becoming finer than this limit and consequently finer sizing methods are required."

Jan 1, 1982

By M. Misra

The dielectric properties and flotability of different ranks of Argonne Premium Coal samples are presented. The flotability of different ranks of coal are correlated with the dielectric properties and intrinsic moisture (or bound water) content. Measured dielectric properties of as-received coals and other constituents are incorporated into a mixture equation to calculate the dielectric properties of bound water present in the different ranks of coal. The nature of bound water present in low-rank hydrophilic coals is significantly different from that present in high-rank hydrophobic coals. The water molecules present in low-rank lignite have an oriented dipole-dipole interaction and are tightly bound to the surface. For high-rank coals, the water molecules are not bound to the surface and have a randomly distributed clathrate ice-like structure. Controlled thermal treatment can modify the structural nature of bound water present in low-rank hydrophilic coals and increase their flotability.

Jan 1, 1990

By E. Luttgen

The substance referred to in the title is the artificially prepared basic carbonate of magnesia, a compound of the carbonate with the hydroxide. It is the "block-magnesia " of commerce, the magnesia alba of the pharmacist. Its composition, though somewhat indefinite, may usually be expressed by the formula : 4MgCO3,Mg(OH)2, 5H2O; it is found to vary slightly with the details of the method of preparation. This substance has been employed recently with much reported success, as a non-conductor of heat. It is moulded to form coverings suitable for steam-pipes and their fittings and sectional jackets for boilers and cylinders; it is furnished also in forms suitable for lining refrigerators, walls and roofs of buildings, fire-proof safes, etc. It was with a view of ascertaining the efficiency of this material as a non-conductor, or, rather, its relative efficiency among the various non-conducting materials in use, that the writer made the experiments about to be described. A block of magnesium carbonate or magnesia alba exhibits some interesting physical qualities. It is a smooth, white, close-grained solid, in outward appearance resembling a block of Paris plaster. It possesses the lightness of cork, the porosity of sponge, and withal a degree of firmness and strength that, in view of its levity, is quite remarkable. To examine more closely the properties of this substance, a number of 1-inch cubes were sawed from the commercial block-carbonate, also some bricks, that is, blocks measuring accurately 2 x 4 x 8 inches, the dimensions of an ordinary brick. The cubes weighed from 2.2 to 2.7 grammes, the bricks weighed 140 to 175 grammes (5 to 6 ounces). The bricks were carefully measured and weighed, and placed in vessels containing distilled water, in which they became gradually submerged, owing to the displacement by water of the air inclosed in the structure of the magnesium carbonate. After twenty-four hours the blocks were removed from the water, dried superficially by contact with filter-paper and weighed. From the increase in weight, the volume of the water absorbed, and consequently that of the air displaced by it, were obtained. For example: a block which when dry weighed 155

Jan 1, 1887

By Abdalla MH

The deformation resulting from the presence of a tunnel may signifcantly affected, nearby structures and need to be considered during design of both tunnel and structure. The aim of this paper is to study the effect of different factors which may affect the interaction between the tunnel and the str- ucture. These include; the depth of both tunnel and foundation level of the structure ( z and t ), distance between C.L. of tunnel and loads, breadth of the loaded area, Diameter of tunnel and lining of the tunnel. The problem is studied as a two dimensional plane strain model by the boundary element technique. The results of this study indicated that the presence of a cavity/tunnel increases, in general, the vertical displacement on the ground surface and at the foundation level as well as the horizontal and vertical stresses in the cavity/tunnel level. The effect of eccentricity is increasing as e/D decreasing. For pile foundation there is a quite different- influence of the presence of cavity/tunnel in both cases of friction pile and end bearing pile type of foundation.

Jan 1, 1987

By Eric Cather

A mineral investigation of prospects in the Sawtooth Mountains B Wilderness Study Area (WSA) by the U. S. Bureau of Mines in 1983 revealed none had mineral production, resources, or development potential. The area is underlain by tonalite and smaller amounts of schist, One developed prospect and one prospect pit are in the WSA. They are in schist similar to host rock which has yielded gold in nearby mining districts, Sand and gravel deposits in the WSA are large but too far from markets to be considered resources. No energy (oil, gas, coal, or geothemal) resources were identified in the USA.

Jan 1, 1984

By Drummond Earley III

The U.S. Bureau of Mines is currently conducting laboratory experiments to study the reactions occurring during in situ leaching of oxide copper ores hosted by biotite-poor granite and biotite-rich granite porphyry. Detailed pre-leach and post-leach petrographic examinations of the rock samples are combined with the leach solution chemistry resulting from core leaching experiments to enable an evaluation of the various reactions which are responsible for the observed fluid chemistry. The information resulting from these laboratory studies is being utilized to support the design of the Bureau's ongoing field research project at the Santa Cruz deposit near Casa Grande, AZ. Atacamite and chrysocolla are the primary copper minerals present in this deposit, and both are readily soluble in the dilute 5% sulfuric acid solutions used in these experiments. In addition to the dissolution of copper minerals, biotite dissolution also occurs during the experiments, contributing K, Mg, Fe, and Al to the leach solution. The biotite dissolution appears to be non-stoichiometric, as it is progressively altered to vermiculite and finally, amorphous silica. While K, Mg, and Fe concentrations in solution steadily increase with time, Al quickly reaches a maximum, and then remains relatively constant for the remainder of the experiment. This suggests that Al saturation is achieved, and this Is supported by the presence of precipitated Al sulfate and aluminosillcate clay mineralization in the post-leach rock samples.

Jan 1, 1990

By W. K. Connor, O&apos

The Bureau of Mines is investigating the Co and Mn resource of the West-Central Arkansas District, including field investigations, mineralogical characterization, beneficiation, and hydrometallurgical tests. The deposits occur within the Ouachita Mountains and are con-trolled structurally, occurring along the axes of anticlines making up the mountain ridges. Brecciated novaculite is cemented with a mixture of Mn oxides, primarily cryptomelane and psilome-lane. Cobalt is concentrated within a particular Mn oxide phase, lithiophorite. Chemical analyses on head samples reported up to 25 pct Mn and 0.17 pct Co. Magnetic separation yielded products with up to 41 pct Mn and 0.22 pct Co at recoveries of 95 pct Mn and 93 pct Co.

Jan 1, 1991

By J. R. Giegerich

THE problem of dust control in metal mines has, of late years, received considerable attention. In 1932, a detailed study of dust conditions at the Sullivan mine was undertaken and, while there are no actual data available regarding conditions prior to that date, there has unquestionably been a great improvement as a result of the investigation and of the preventive methods adopted. In attacking the problem, three main factors were considered: first, and most important, how to prevent dust from being formed; second, how to depress or collect it if formed; and third-if unable to accomplish these-what precautionary measures must be adopted to prevent inhalation of this dust. Seven distinct methods of dust control are now practised at the Sullivan. Six of these are employed underground; they are tabulated below in the order of their relative importance. The seventh method is used in the crushing plants on the surface. (1) Improved ventilation (2) General use of water sprays and atomizers (3) Curtailment of secondary blasting during shift hours ( 4) 100 percent wet drilling-primary and secondary (5) Wearing of protective equipment (6) Change from carbide to electric lamps (7) Installation of dust collectors

Jan 1, 1936

By Christopher Mark

"Many problems in rock mechanics are limited by our imperfect knowledge of the material properties and failure mechanics of rock masses. Mining problems are somewhat unique, however, in that plenty of real world experience is generally available and can be turned into valuable experimental data. Every pillar that is developed, or stope that is mined, represents a full-scale test of a rock mechanics design. By harvesting these data, and then using the appropriate statistical techniques to interpret them, mining engineers have developed powerful design techniques that are widely used around the world. Successful empirical methods are readily accepted because they are simple, transparent, practical, and firmly tethered to reality.The author has been intimately associated with empirical design for his entire career. But where his past papers have described the application of individual techniques to specific problems, the focus of this paper is the process used to develop a successful empirical method. A six-stage process is described:1. Identification of the problem, and of the end users of the final product2. Development of a conceptual rock mechanics model, and identification of the key parameters in that model3. Identification of measures for each of the key parameters, and the development of new measures (such as rating scales) where necessary4. Data sources and data collection5. Statistical analysis6. Packaging of the final productEach of these stages has its own potential rewards and pitfalls, which will be illustrated by incidents from the author’s own experience. The ultimate goal of this paper is to provide a new and deeper appreciation for empirical techniques, as well as some guidelines and opportunities for future developers."

Jan 1, 2015

By Edgar Schweitzer

The original Dorrance breaker of the Lehigh Valley Coal Co. was erected in 1883. The coal beds were clean and dry, consequently a dry preparation system was used, consisting of revolving cylindrical screens for sizing and hand-picking, to remove the few impurities from the run of mine coal. The picking or cleaning room contained long parallel rows of chutes with seats mounted on them, for the use of the breaker boy, who bent over the chute and picked out the refuse material from the coal as it gravitated down the chute. The introduction of dry mechanical pickers, of, the sliding frictional type, in the early nineties lessened the number of boys, but hand-cleaning on the coal and refuse discharge ends of the mechanical picker was necessary. The Pardee spiral pickers, which were brought out about 1900, were better than the gravity pickers and gradually replaced them. In 1912 the breaker was entirely remodeled, although the original frame was retained. The revolving screens were replaced by shaking screens, and Pardee spirals were installed on all sizes of coal from egg to pea coal, inclusive. Hand-picking still was necessary on the coal and refuse ends of the spirals, although the changes did result in a reduction of the former breaker force. As mining advanced, and the thick clean bed became exhausted, it was necessary to mine veins containing a high percentage of impurities, which complicated the preparation problem. The most serious difficulty was the increase in the quantity of damp or wet run of mine, which could not be fully cleaned on the spirals. When this quantity exceeded approximately 5 per cent. of the feed, it was necessary to send the excess of the wet coal to the company's Prospect colliery for wet washing. This plan worked well for a time, but as the amount approached 15 per cent., with the prospect of a further increase, the company considered the building of a wet-washing plant. The Dorrance breaker was the only dry-cleaning plant operated by the company. At the seventeen other collieries, wet washing was employed, and jigs, both plunger and pan, were used. All the practical methods used in the anthracite fields were investigated, and it was finally decided to adopt the Rheolaveur system. The decision was due largely to the experience gained from the the operation of a Rheo-

Jan 1, 1931