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By Christopher H. Bierbaum

The first significant fact observed in the study of bearing metals is that not a single pure homogeneous metal has given satisfactory service; all bearing metals are alloys made up of two or more phases; that is, they consist of hard and of relatively soft microscopic particles intimately mixed. The function of the hard particles, or bearing crystals, is to support the load and resist the wear when actual metallic contact exists between the bearing surfaces. The functions of the softer particles are to allow the harder particles to adjust themselves to the surface requireinents of the journal and to wear down slightly below the surface of the harder, forming slight depressions on the apparently smooth wearing surface of the bearing, in which some of the lubricant is held when the bearing surfaces are brought into contact with each other. It is this characteristic of certain alloys to form these slight depressions, and thus provide the means for retaining a lubricant, that characterizes them as true bearing metals; in fact, a bearing metal has been defined as "an alloy that is capable of retaining a lubricant upon a bearing surface."' The extent to which the lubricant can be so held determines the most valuable characteristic of an alloy as a bearing metal. An alloy which, perhaps, most characteristically represents a bearing metal is the composition of copper and tin that contains sufficient tin to produce the tin-copper eutectoid, or delta crystal. The depressions worn upon the surfaces of the softer crystals of the teeth of a motor-truck worm wheel, made of an ll-per cent. tin bronze, in many cases were from 5 to 6 microns in depth; all other conditions remaining constant, this depth of wear increases with an increase of working pressure. This copper-tin bronze contains intercrystalline shrinkage cavities, which also

Jan 1, 1923

By T. A. Rickard

Our Transactions contain two notable papers descriptive of the stamp-milling practice of the Black Hills and of Grass Valley, namely, the elaborate and complete treatise of Prof. H. 0. Hofman, on " Gold-Milling in the Black Hills,"" and the paper describing the North Star mill, by E. R. Abadie, its superintendent. Having visited and examined the stampmills of both localities, I venture to offer here such comment as more recent information or a different point of view has suggested.†

Jan 1, 1896

By John M. Dealy, Robert D. Pehlke

Values for interaction parameters in nonferrous systems, as calculated from published data, are tabulated and discussed. The influence of temperature on the parameter is derived and compared with the results of the literature study. Wagner's relationship between the interaction parameter and the self interaction coefficients is compared with the tabulated data. A problem which has been of considerable interest in the field of metallurgy is the prediction of the effect of one alloying element present in dilute concentration on the thermodynamic properties of another dilute alloying element. Ultimately, the prediction may be accomplished entirely from statistical mechanical considerations. At the present, however, the problem remains unsolved since liquid solution models which are simple enough for analytical treatment are inadequate for such purposes. Thus, we desire some means of organizing the information on dilute systems which will serve as a guide for further study on interactions in dilute alloys, and also provide a basis for the utilization of thermodynamic data in the engineering design of alloys.

Jan 1, 1963

By C. P. Proctor, J. T. Crawford, John Griffen

TROUGH washers were among the earliest methods used for concentrating ores; they are referred to by Agricola about the middle of the sixteenth century as already being used while the hand- operated jigging sieve had only recently come into use. For cleaning coal the trough washer apparently was first used in France and Belgium about 184.1. The early trough washers were intermittent and the refuse at least was shoveled out by hand. The invention of a continuous jig washer, by a Frenchman, Berard, in 1848, acted as a stimulus to coal washings in jigs and retarded progress in trough washing in the nineteenth century. Chapman and Mott 1 describe a number of trough washers developed in England and on the Continent from 1850 to 1900, such as the Bell and Ramsay, Ramsay, Bell and Green, Wunderlich, Scaife, McLellan, Lodge, Elliott, Blackett, and Murton. The later of these removed the refuse mechanically, either intermittently or continuously, but in ways that interfered with stratification. THE RHEOLAVEUR A Belgian engineer, Antoine France, is responsible for the development of means to remove refuse materials continuously from a trough washer, while preserving stratification and preventing the loss of coal with the refuse. The methods and equipment devised, which have become known throughout the world as rheolaveur, were initiated at the St. Nicholas mine near Liége, Belgium, about 1912. This installation consisted of two units to wash 20 to 8-mill. (3/16 to 5/16-in.) and 8-mm. to 0 (5/16-in. to 0), each having only two superimposed inclined troughs. The first few "Rheo" boxes on the top trough removed refuse directly and the remaining Rheo boxes discharged impure refuse to the lower trough for rewashing. On the lower trough the first few boxes removed refuse and the following boxes removed a middling product used for boiler fuel or other purposes. The overflow of both troughs was joined to form the washed coal product.

Jan 1, 1950

By K. H. Ribe

Water often enters an oil reservoir during completion or workover operations on a well and forms a partial "water block" to oil production. A mathematical study of radial two-phase flow, neglecting capillary effects, has been employed to study the formation of such a water block and subsequent re-moval by production from the well. The effects of reduced oil permeability about the well on the well productivity were studied. The fluid saturation distributions about the well during formation and removal of the water block have also been computed. Several relative permeability relations and viscosity ratios were employed. If water has invaded the formation, its influence through relative permeability effects alone can cause the following. 1. Oil productivity will be depressed for extended periods after production is resumed and will build up only gradually as the water is removed. 2. Oil injected for treatment of water blocking will delay rather than promote restoration of full well productivity by enlarging the region invaded by water. Thus, unless the specific action of chemicals contained in the oil is needed, oil injection appears undesirable. INTRODUCTION During oilwell workover operations, water may enter the oil-bearing formation from the wellbore. When production is resumed, oil must flow through the region invaded by this water. The presence of this region can cause both well productivity and oil production rate to be low and oil to be produced with high water-oil ratio for some time after production is initiated. This situation is sometimes described as a water block. The introduction of water into the formation may result in other actions which also lead to reduction in well productivity and which are also usually included in the connotation of the broad term, water block. Often considered, for example, are the possibilities of clay swelling by contact with fresh water and the formation of emulsions with the formation oil. If it is suspected that such specific actions have taken place, remedial treatments are undertaken which usually involve the injection of chemicals in oil. Since the introduction of water, even in the absence of specific interactions with the formation or oil, will cause a temporary water block (which might be misinterpreted as evidence of a more severe situation), it is of importance to evaluate the magnitude and duration of this blocking which results purely from the reduction in relative permeability to oil in the vicinity of the wellbore. It is also of interest to evaluate the effect of oil injection on the productivity of a well blocked by water in this manner. Inasmuch as this unfavorable condition may persist for some time, it may lead to premature condemnation of a workover or premature abandonment of a potentially productive pay zone. A quantitative evaluation of the influence of water entry on the oil productivity through changes in relative permeability was made by solving a radial form of the Buckley-Leverett equation. The distribution of water saturation around the wellbore during the entry of water was calculated and was followed by a similar calculation of the saturation distribution during the period of resuming production. At any stage in the removal of the invading water, knowledge of the distribution of its saturation permitted calculating the attendant loss in oil productivity. The influence of the shape of the relative permeability relationships was also evaluated by carrying out the calculations for two hypothetical cases. Further, the effect of the oil-water viscosity ratio was examined by repeating the calculations, for several ratios of unity and greater, with the same relative permeabilities. Fi-nally, results are presented to show how the length of time a well must be swabbed to resume production depends on the length of time it has been subjected to invasion by water. STATEMENT OF THEORY Differential Equations Water is assumed to enter a producing formation which is initially at the connate-water saturation and contains no gas. The water and oil are treated as in-

As 1970 develops and industrial minerals stand at a crucial point in their progress, research and development programs appear to be the key needed to open up new uses for each mineral's future growth. Radically new processes are needed for making a host of new synthetic products from mineral raw materials which will more nearly meet the demanding specifications required for high performance in space, nuclear and defense applications. Consumer applications for high temperature environments will be needed and are important for continuing the nations economic mineral position. In addition, an acute materials problem limits the effectiveness of some of the newer concepts for controlling ail pollution. What is needed then, according to a report printed by the National Academy of Sciences, is the carefully planned development of a limited number of major centers at universities to provide for both basic research and training of personnel; the nurturing of interdisciplinary mechanisms for research and problem solving within these centers; the achieving of a better balance between physics and chemistry within research, emphasizing the chemical aspects of the material sciences; and the enhancement of a broader professional identity by unifying the various disciplines involved into a possible federation of existing societies which have an interest in the problems. [EE] presents its 1969 annual industrial minerals review, where individual authors evaluate the status of each industrial mineral and recount the major developments which occurred during the year.

Jan 1, 1970

By William E. Newman

When Hugh Lee Pattinson discovered, in 1829, that the crystals formed during the slow cooling of molten lead were poorer, and the remaining liquid richer in silver, than the original lead, an important step was made in the metallurgy of this metal. Being the first process applicable to the desilverization of low-grade lead bullion, it soon found its way into all European countries having such a product to treat, thereby effecting the saving of many ounces of silver annually which previously had been thrown away. The old hand process was expensive, as viewed from the standpoint of more modern methods; the labor was great and the tonnage was small, but on the other hand the results were fairly satisfactory. This process flourished for some time after the introduction of the cheaper Parkes process in 1852 and it is still in use in a few European smelteries. Only one notable improvement was made on the original process, that of Luce and Rozan at Marseilles, France. It consisted in the application of steam for stirring and the tapping of one-third of the liquid lead, through perforated plates covering the tap holes flush with the bottom of the kettle, thus leaving two-thirds in the form of crystals in the original kettle. This modification considerably lowered the operating costs as it permitted of much larger kettles, an increased tonnage and eliminated much of the slow, hard labor of the hand process. The Luce and Rozan process has persisted in its original form to the present day. Stephen Tredinnick, English born, spent most of his years around the Luce and Rozan plants at Marseilles and elsewhere in Europe, coming later to Eureka, Nev., in 1878, to operate the Luce and Rozan plant at that point. Mr. Tredinnick was a competent Luce and Rozan operator and being devoted to the process he firmly believed that with modifications the costs could be so lowered as eventually to supplant the Parkes process. Out of many schemes he decided that this could be accomplished by placing the Luce and Rozan kettles upon hydraulic rams so that each

Jan 1, 1918

By N. F. Foster

The use of piezoelectric semiconducting materials for the fahrication of ultrasonic transducers has raised the upper fundamental frequency limit for transducers from about 200 mc to above 10 kmc, Several types of semiconductor transducer configurations have been proposed and examined experimentally. Depletion-layer transducers have been made and operated at frequencies below 1 kmc hut they appear to he better suited for operation at considerably higher frequencies around 10 knzc. Diffusion-layer transducers have been made and operated in the range 50 to 1000 mc and have exhihited considerably improved conversion losses and bandwidths compared with other transducers available in the frequency range. A variety of novel structures are possible using these new types of transducers, some of which could lead to substantial advances both in research and in the fabrication of ultrasonic delay lines and memory elements. THE field of ultrasonics today spans some five decades of the frequency spectrum from the audible to the kmc range and finds applications ranging from fundamental research into the atomic structure of matter to the degreasing of machine parts. To cover this wide range it has been necessary to develop a great many types of ultrasonic trandsucers utilizing a variety of materials and physical phenomena. The first ultrasonic transducers were made during World War I for a submarine-detection system. They consisted of plates of single-crystal quartz bonded between metal plates and were one of the first applications of the phenomenon of piezoelectricity discovered nearly 30 years previously. Despite the many advances which have been made in transducer technology, piezoelectric transducers using single-crystal quartz are still used almost exclusively for application above about 30 mc. Transducers at these frequencies are normally made in the form of thin quartz plates which are then bonded onto the medium in which the ultrasonic wave is to be propagated. The crystallographic orientation and geometry of these plates determines the type of wave generated and the way in which the efficiency of the electromechanical conversion varies with frequency. Analysis of the design parameters shows1 that the frequency of maximum efficiency (the fundamental or resonant frequency) is that frequency at which the transducer is approximately half the wavelength of the ultrasonic wave in the material. As the frequency increases, the ultrasonic wavelength, and therefore the optimum transducer thickness, decreases and in practice the fabrication of quartz transducers with fundamental freauencies above 100 mc becomes extremely difficult due to the extreme thinness required. For frequencies above 100 mc quartz transducers can be used in overtone-mode operation, and for very high frequencies (500 to 24,000 me) a technique using a quartz rod inserted in a high-Q microwave cavity4 is available. These techniques, however, exhibit comparatively low fractional bandwidths and rather poor conversion efficiencies. The present trend in ultrasonics is towards high frequencies and greater bandwidth to allow the use of shorter pulses which can give increased discrimination in radar-system delay lines and greater storage capacity in computer applications. The increasing demand for more efficient transducers with greater bandwidth

Jan 1, 1964

By Frank H. Riddle, Wilfrid R. Foster

GENERAL treatment of the various minerals of importance in refractories appears in the chapter entitled "Refractories" elsewhere in this volume. The present chapter is restricted to a discussion of minerals of the sillimanite group and brings up to date the excellent information contributed by Prof. Paul F. Kerr to the first edition (1937). Since the appearance of that edition, the status of the group has changed some- what. Kyanite remains the preferred source material for mullite refractories but total consumption of kyanite has increased considerably.85 The exigencies of World War II forced an increased dependence on domestic sources and led to an intensification of the search for higher-grade deposits of kyanite and allied minerals. The first discovery of massive kyanite similar to that of India has been reported from Georgia.37 British East Africa has joined India as a substantial supplier of our imported kyanite, but that from India continues to hold preference.85 During World War II, prices of both domestic and foreign grades reached peaks unparalleled since the earliest years of the use of kyanite and as yet have shown no tendency to return to prewar levels. Topaz, by virtue of the deposit outlined in South Carolina, merits inclusion in the group.20,36,95 Large andalusite deposits, which threaten to rival our one large domestic occurrence, have been found in Russia.69,88 Sillimanite has not yet attained an important position among these useful minerals because of the lack of accessible deposits of high-quality material in adequate supply.37,50,58 Tests by the Bureau of Mines have indicated the possibilities of economically beneficiating low-grade sillimanite and kyanite.105.106,140 Government, university, and industrial

Jan 1, 1949

By G. Sachs, E. J. Ripling, J. J. Lynch

It is general practice to evaluate the strength properties of a particular metal from its stress-strain (s1 — el) curve obtained by means of a conventional tension test. Such a stress-strain curve, Fig I, illustrates two important properties of a metal, its ability to strain harden, and its ability to withstand a certain limiting stress, the "fracture stress," (s), and a certain limiting strain, the "ductility" (es), before it fails by separation. These two fracturing characteristics are the coordinates of the point of fracture in Fig I. In the case of a metal which necks in a tension test, both the fracture stress and the ductility (measured in a tension test) are dependent upon (I) the shape of the neck and (2) average values of the stresses and strains over the cross-section at the moment of fracture. However, for the pur. pose of this investigation, these average quantities, rather than the actual values, may be considered for reasons of simplicity. It appears that the conclusiom also hold true if the analysis were carried out for actual values of fracture stress and ductility at the locos of failure. In this paper, the effects of straining (at room temperature) by various methods on the above metal characteristics, which were determined by subsequent tension tests will be discussed. According to Our present knowledge, any such prestrainitlg results in a stress-strain curve (in subsequent testing by tension), Fig 2, the general shape, or flow characteristics, of which can be derived from the original stress-strain curve of the unstrained metal minus a certain portion exhausted by the initial straining. This phenomenon is called strain hardening, and may be measured by the magnitude of the cut-off, or the "effective strain,'' from which the new curve must start in order to coincide in its plastic branch with the original stress-strain curve.

Jan 1, 1949

By K. J. Brondyke, P. D. Hess

Lack of correlation between densities of aluminum alloy samples solidified under reduced pressure (vacuum gas test) and hydrogen content of the metal is explained on the basis of inclusions serving as nuclei for hydrogen bubble formation. As a result of these findings, the vacuum gas test is suggested as a practical tool to indicate metal cleanliness and the potential effects of hydrogen. Visual obseroation of the sample during solidification under vacuum provides more useful information than that obtained either from density meas -urements or sectioning of the solidified sample. A rapid, practical method of detecting and measuring gas in molten-aluminum alloys has been sought for many years. The development of the vacuum gas test appeared to solve this problem. However, the vacuum gas test is subject to certain limitations, and the results must be interpreted mindful of these limitations, as described herein. Since the only gas which is appreciably soluble in aluminum is hydrogen, the terms gas and hydrogen will be used interchangeably in this paper. In the early days of the aluminum industry, when techniques were not as refined as they are today, it was customary to pour small "pancakes" of alumi- num on a metal plate. These were allowed to solidify under atmospheric pressure. Excessive gas in the metal was evidenced by the appearance of small bubbles on the surface of the "pancake".' It is obvious that such a method would only show very high gas levels far above any which could be tolerated by today's standards of quality required for most applications. Various attempts were made to develop methods which would be more sensitive. Among these were measurements of density of aluminum alloys solidified under controlled conditions, radiography of cast slabs, and examination of fractures. The method which showed the greatest promise and appeared most practical was the solidification of a sample of the molten aluminum alloy under vacuum. The samples so solidified are evaluated either by observation for bubble emission during solidification, by sectioning the solidified sample and examining for porosity, or by determining the density of the solidified sample. This test is known internationally as the Straube-Pfeiffer test or the reduced-pressure solidification test, but in America it is commonly referred to as the vacuum gas test2-' and will be so designated in this paper. The determination of density appeared an attractive and convenient means of providing a numerical rating for the samples. Attempts were made in some instances to correlate densities to hydrogen contents. Unfortunately, the visible loss of gas during solidification of samples with high gas contents precluded a correlation of vacuum gas test densities with the observed gas evolution. This led to Alcoa's use of two different pressures; 50 mm of

Jan 1, 1964

By H. Hanemann

THE application of other than mechanical methods to the study of the mechanical-physical properties of metals has become in the last few years a topic of investigation of ever-increasing interest, both from the theoretical standpoint and from that of the engineer and constructor. Besides the investigations which have been made of 'the magnetic properties of ferromagnetic metals, in their relation to the mechanical properties of these metals, which will be discussed more in detail below, there have been made studies of other phenomena in the same relation, and methods for the mechanical testing of metals have even been suggested, for example, the microscopic method of Tammann,1 and the thereto-electric, method of Turner2 for determining elastic limits. The application of all such methods, which are based upon the dependence of some physical, crystallographic, or possibly chemical property, upon the mechanical state of the metal, must be preceded by close and careful correlation of these various "test" properties with the known mechanical state of the different metals or materials. It is with this view that the present work, as well as that of many previous investigators of, what .may be termed in the interests of brevity, the mechanical-magnetic properties of ferromagnetic materials of construction, has been done.

Jan 12, 1915

Discussion of the paper of James R. Finlay, presented at the New York meeting, February, 1912, and printed in Bulletin No. 75, March, 1913, pp. 487 to .503. CHAIRMAN JOHN BIRKINBINE :-Having been invited to preside at this session, the Chairman feels that the part he takes in discussions should be limited, although the subject presented is one of much interest to him and there are diverse viewpoints concerning methods of valuing expectancies from what may be considered " ore in sight," a term itself subject to various definitions. Estimates of quantities upon which valuations are made may differ without subjecting the estimators to criticism of unfairness if made by a prospective purchaser or by a seller, or if they are used as the basis for taxation. The hopes of the seller may influence a liberal allowance for estimated reserves, while the expectancies of a willing purchaser are less optimistic, and the tax assessor is expected to limit his consideration to the producing capacity of a mine, with possibly modest allowance for reserves. The knowledge that a property contains or yields mineral or the expectancy that it may be a producer of value adds to the estimate placed upon it by any of the above classes, and a just determination of this value is often a complex problem.

Jan 5, 1913

By Charles H. Jacoby, Stanley J. LeFond

Salt, or halite, has had a long and most varied history. While we know the Chinese were producing salt as early as 3000 B.C., the first written reference to salt appears in the book of Job recorded about 2250 B.C., which reads: "Can nothing which is unsavory be eaten without salt?" We do not know when man first used or realized that he needed salt. Perhaps one of our early Eolithic ancestors noted a piece of salt shining along the shore of a salt lake or a bay. He may have been attracted by its shining luster and tasted it. He found that it had a tart, zesty, distinctive flavor and perhaps chewing a large piece, became ill. However, by experimentation he soon learned that taken in the proper proportions salt was a very pleasant additive to his food. He may have noticed, too, that it increased his feeling of well-being. Thus, when the curtain of recorded history rises, we find man using salt for his health's sake, seasoning his food with it, feeding it to his animals, and using it in many superstitious and religious ceremonies. These uses, however, are a far cry from the uses for salt today. The first attempts of white man to make salt in continental United States were reported in the year 1614, while the first commercial production was in 1790. Practically all of this salt was for human consumption, preserving food, and curing hides. Prior to the coming of the "white man" Indians are known to have made salt from such salt springs as those that existed at Avery Island, La., Charleston, W.Va., Saltville, Va., and Onondaga, N.Y. In 1862 the first rock salt was mined in the U.S. from the Avery Island salt dome. Almost immediately thereafter, rock salt was mined at Saltville, Va., and then at Retsof, N.Y., in 1885. Of the more than 40 million tons produced annually in the United States, about 68% or 27 million tons are consumed by the chemical industry in the production of chlorine, caustic soda, hydrochloric acid, sodium metal, and some 30 other basic chemicals. These basic chemicals, in turn, are used in the preparation of approximately 14,000 chemicals which range from soap and detergents, to such chlorinated hydrocarbons as DDT, BHC, carbon tetrachloride, etc.

Jan 1, 1975

By C. A. Hansen

ROASTING FERRUGINOUS ZINC-SULFIDE ORES IN 1912, Mr. J. B. Ideating was developing an electrolytic-zinc process for application to the ores of the Bully Hill mines of the General Electric Co. These ores consist of blende and pyrite so finely crystallized and so intimately mixed that no mechanical separation of the individual minerals had been found possible. The ore was reduced to about 60 mesh and roasted in a hand-rabbled reverberatory furnace preparatory to leaching with sulfuric acid. The extractions obtained were quite irregular, varying from a minimum of about 70 per cent. to a maximum of about 90 per cent. This irregularity led to the construction of a small electrically heated roasting furnace, and to the study of roasting under definitely controllable conditions. From time to time, these studies have been extended to other ores. Several commercial-plant operators profess to have gained useful information from the results of these studies and it is hoped that their usefulness may be extended by this publication. EXPERIMENTAL ELECTRIC ROASTING FURNACE The furnace used for experimental work is shown in Fig. 1. One fire-clay sagger, or pot, was set within another and the space between the two filled with Silox heat insulation. The hearth is a cast-iron plate with an imbedded ribbon of nichrome wire; this wire heater is connected to a potential regulator, which permits a very close voltage control. A mechanically driven arm is fitted with rabble blades so arranged that a uniformly thick ore bed may be maintained indefinitely. This arm is usually driven at about one revolution per minute but its speed of rotation can be varied as desired. Compressed air is led into the furnace through a meter, and it was found necessary to preheat the air in order to secure the definitely isothermal conditions sought.

Jan 8, 1919

By R. H. Doremus

From measurements of carbide precipitation rates in a iron it was concluded that the carbides nucleated on dislocations in both strained and unstrained samples, except for the latter at lower temperatures and higher carbon concentrations, where there were more muclei than could form on the dislocations. The equation of Cottrell and Bilby for the segregation of atoms to dislocations was found to be inapplicable to this system. No satisfactory theory for the growth process is available. A study of the rate at which a second phase separates from solid solution can frequently reveal much about the mechanism of separation. There are still many features of the precipitation of carbon from a iron that are not understood, although this system has been examined extensively. To provide more insight into the mechanism of carbide precipitation in a iron, rates of this process were measured at different temperatures, carbon concentrations, and densities of dislocations in the iron. The concentra- tion of carbon in solution was followed from the height of the internal-friction peak; this height is directly proportional to the amount of carbon in solution and is not affected by the growing carbide particles. In this paper these rates are compared with those found by earlier investigators, and the mechanism of precipitation is discussed in light of these results as well as two earlier studies1, 2 and the electron microscopic work reported in the preceding paper. EXPERIMENTAL The amount of carbon in solution was followed by

Jan 1, 1961

By David R. Mitchell, R. B. Hewes

MANY processes for cleaning coal that are in use depend primarily on physical properties of coal and refuse other than specific gravity and surface conditions relating to froth flotation. These properties are shape, coefficient of sliding friction, resilience, friability, magnetic susceptibility, and electrical conductivity. In many of these processes specific gravity does have some effect and many separators are designed to utilize more than one of the physical properties cited. Although the processes described herein do not have a widespread application, yet for specific coals and specific conditions, they are economically important. A problem confronting many coal-mining districts is the marketing of the slacks or screenings and dust passing the final sizing screens. Processes in commercial use installed primarily to increase the form value, and hence the market value, of these slacks and dusts include briquetting, packaging, and low-temperature carborization. MECHANICAL PICKERS Machines utilizing shape, fictional resistance, and differences in resilience of coal and impurities are usually called mechanical pickers. They require a closely sized feed, therefore their use is confined to the pea, nut, and egg sizes. Various types of these devices are described by Berrisford, 1, 2 Taggart, 3 and Peele. 4 Shape In general, coal differs in shape from its accompanying dirt throughout the range of commercial sizes. Coal, breaking into roughly, cubical particles, contains a greater number of axes that are approximately the same length than does the dirt. The latter, consisting of pieces of slate and shale and lenses of pyrite, is flatter in nature. Further, flat coal often has a dirty, slaty appearance, even though of high quality. Mechanical pickers known as flat pickers, or "flatters," are widely used in the Pennsylvania anthracite region to remove flat coal from the final clean coal. This practice greatly improves the appearance of the final market product.

Jan 1, 1943

By R. W. Raymond

[NoTE.—-This paper was presented at the Pittsburgh meeting in a partially completed form, and I fully expected to obtain, before the period of its publication, both the data and the leisure required for its completion. The hygiene of collieries was to have been separately considered, and the sanitary conditions of various metallurgical industries connected with mining were to receive an extended discussion, while at the same time the points treated in the paper as prosented at Pittsburgh were to have more ample illustration from American and European sources. Delay in obtaining expected information, and the continuous pressure of professional work, have prevented hitherto the execution of this plan ; and I can now publish only a portion of what I had designed to contribute to the subject. In the meantime this portion, but slightly changed, has been included as a chapter on the Hygiene of Metal Mines in a work entitled Hygiene and Public Health,, edited by Dr. A. H. Buck, of New York. An excellent chapter on the Hygiene of Coal Mines, contributed to the same work by Mr. Henry C. Sheafer, of Pottsville, affords me an opportunity to supply one of the deficiencies above alluded to. Mr. Shearer's chapter contains much material in the way of explanations not required by professional readers; And be moreover devotes a considerable space to the explosive gases, falls of roof, and other causes of accidents to life or limb—a branch of the subject not belonging strictly to bygiene. I therefore make extracts only from his treatise.—R. W. R ] It is convenient to divide mines, with reference to this subject, into two classes, collieries and metal-mines. Subterranean quarries, rock-salt mines, etc., present no conditions requiring them to be separated from the latter class.

Jan 1, 1880

By Carl R. Davis, J. L. Willey, S. E. T. Ewing

The first tube-mill on the Rand was put into operation in May. 1904, at the Glen Deep Mine. From that time onwards, tube-mills were added to various plants, although little was known regarding the capacity of a given tube-mill when working on banket ore. Within a few years, however, the so-called standard size (length of shell, 22 ft. 0 in.; diameter, 5 ft. 6 in.) was generally used until the last year or two. Practically the only exceptions were about 30 tube-mills having a length of 16 ft. and a diameter of 6 ft., and a few open-end mills of the roller-supported type. Most of the information obtained during the last 15 years has been obtained with mills of the standard dimensions. The adoption of the tube-mill as an accessory to the stamp mill was rapid; and where 3 tube-mills were working on the Rand at the end of 1904, 244 were in use seven years later.' By 1910, good practice provided 1 tube-mill for 20 stamps of 2000-lb. falling weight. The horsepower of the motors driving the tube-mills had increased from 80 to 100 and then to 125 at this date. Broadly speaking, current practice at that date aimed at a ha1 product of which 60 per cent. was suitable for sand treatment and 40 per cent. for slime. The sand grading was +60 mesh, 6 per cent.; +90 mesh, 25 per cent.; — 90 mesh, 69 per cent.; and the slime grading +200 mesh, 2 per cent.; —200 mesh, 98 per cent. It was recognized comparatively early that the tonnage of — 90-mesh product produced by a tube-mill per 24 hr. was a convenient measure of

Jan 1, 1925

By Glenn Allen

SAN FRANCISCO Mines of Mexico, Ltd. owns and operates an extensive group of claims in the San Francisco del Oro-Santa Barbara district, about 15 miles southwest of Parral, Chihuahua. The property comprises the mines, aerial tramways, flotation mill, power plant, shops, offices, assay and testing laboratories, modern hospital, water and sanitary system, quarters for miners, mechanics and operators, a well housed colony for Mexican staff employees and residences for foreigners. Each colony has a club house and mess and tennis courts. The employees have constructed a nine-hole golf course. In other words, the property is self-contained and completely integrated for production of lead and zinc concentrates from complex sulfide ores.

Jan 1, 1930