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By F. Pagliacci

Retaining walls for the construction of underground urban infrastructures have to be executed considering the impact of a deep foundation job-site within an urban network. Traditional excavation systems, based on the use of grabs and bentonite mud, involve serious problems such as: the opening of trenches adjacent to existing buildings; the cleaning of the working area; the site installation for the production and storage of the bentonite mud; the transport and disposal of soil contaminated with bentonite mud. Alternative solutions have therefore been developed in order to overcome these problems. For temporary works soil consolidation methods, combined with the use of sheet piles, have been implemented, by a combination of traditional mixing methods and jet grouting systems to speed up the operations, consequently reducing the construction time. For permanent works two new techniques named respectively CSP (Cased Secant Piles) and CDW (Continuous Diaphragm Walls) have been studied, applied and tested.

Jan 1, 2000

By U. Paakkinen, P. Eerola

In connection with theoretical studies of the dynamics and control of the flotation process, flotation cells and circuits at the Pyha- computer control of selective Cu - Zn - Fe sulfide flotation in the latter half of 1969. In this paper, the practical conclusions of these studies, conducted through simulation techniques, are summarized. The application of these results for control purposes implies a knowledge of the dependence of the flotation rate coefficients and the grade of concentrate on several factors, including aeration rate, froth depth, and reagent consumption. The relationships found in laboratory and plant scale tests are described. Off-line optimization studies, based on the relation- ships, are also described. The proposed steps in executing the computer control schedule are presented. In the first stage, a stabilizing control will be carried out using feed-back loops. A feed-forward control system which utilizes simple process models will also be tested. After these elementary stages, a proposed mathematical model of the circuit will be checked out and implemented with computer- run, plant-scale process tests. Off-line simulation will be continued in advance development of the control system. As a final step in the program optimal control of the process will be carried out through this model.

Jan 1, 1969

By Wilbur I. Duvall

INTRODUCTION This chapter outlines some general principles and procedures that a rock mechanics engineer can use to arrive at a logical design for the size, shape, and spacings of underground openings in various types of com¬petent rock formations. Rock formations can be clas¬sified into six major categories which are useful for design purposes, provided the necessary input data are available regarding the geology of the site, the physical properties of the rock, the in-situ stress field in the rock, and the general geometry of the underground openings. The US Bureau of Mines (USBM) developed a rock classification system based upon these concepts and found it to be useful for design purposes (Obert, et al., 1960; Obert and Duvall, 1967). This classification sys¬tem is given in Table 1; however, an extra column has been added to the original classification to indicate the appropriate design techniques for each rock class. In this classification system, two main classes of rock are considered: competent rock and incompetent rock. Competent Rock Competent rock is any rock which, because of its mechanical and geological characteristics, is capable of sustaining underground openings without the aid of any structural support except that provided by unmined rock in the form of pillars and side walls, etc. Roof bolts and small random props which support only local loose rock are not considered structural supports. Competent rock is further subdivided into three ad¬ditional categories-massive, laminated, and jointed¬ which are defined as follows: Massive Rock: Massive rock is a rock formation where the spacing between mechanical defects such as joints, partings, or faults is equal to or greater than the critical dimensions of openings, or where the strength of the bond across these mechanical defects is com¬parable to the rock strength. Laminated Rock: Laminated rock is a rock forma¬tion divided by approximately parallel planes of weak¬ness into lamina whose thicknesses are small compared to critical dimensions of openings and where the bond between the lamina is weak compared to the rock strength. Elastic Rock-This is rock whose physical proper¬ties will permit the use of elastic theory to predict strains and displacements from applied stresses. Inelastic Rock-This is rock whose physical proper¬ties are such that strains and displacements are a strong function of time as well as applied stress. Incompetent Rock Incompetent rock is any rock which, because of its mechanical and geologic characteristics, is not capable of sustaining underground openings without the aid of additional structural support in the form of linings, steel sets, or systems of props. This classification system for rock depends not only on the mechanical and geologic characteristics of the rock but on the size of openings and their depth be¬low the surface. For example, many competent rocks at shallow depths for small stress fields could become inelastic rock at greater depths and larger stress fields, or competent massive rock for small openings could be¬come laminated or jointed rock for larger openings. Thus, to classify rock for design purposes requires a knowledge of the geologic properties of the rock mass, the physical properties of the rock, the general size of the openings to be mined, and the average range of the in-situ stress field to be encountered. To design underground openings and structures in rock, it is necessary to use criteria of failure for rock under various stress conditions, and to use safety factors to allow for differences between laboratory and in-situ strength properties of rock and to account for errors in¬troduced by the various assumptions made in the design process. Criteria of failure based on maximum stresses have been found to give reliable results in practice. Thus, it is assumed that rock will fail in tension when the tensile stress exceeds the tensile strength of the rock as determined by a standard modulus of rupture test on samples of rock core. If the tensile stresses in rock are small, then it is assumed that the rock will fail at a value of compressive stress equal to the compressive strength of the rock as determined by standard uniaxial compres¬sive strength tests on samples of rock core. These fail¬ure criteria, when used with appropriate safety factors, can be expressed as:

Jan 1, 1982

By Robert W. Ageton

The Bureau of Mines is currently conducting a comprehensive study to evaluate all aspects of recovering gold from large, low-grade deposits in the Golden Sunlight area, Whitehall mining district, Jefferson County, Mont. Prior to World War II this area produced significant quantities of gold. The study includes geologic mapping, diamond drilling, assaying, computer analysis of assay data, metallurgical research and ore testing, mine and mill planning, and an economic evaluation of all factors bearing on the establishment of a producing gold mine. Preliminary evaluation of the deposit indicates about 31 million tons of submarginal gold resources. American Exploration and Mining Co. (AMEX) has assisted the Bureau in this project by providing drill site preparation, control assays, and geological aid for the Bureau's exploration work and by furnishing comprehensive assay information of the property and copies of base and geologic maps. This report presents the geology and mining history of the area, together with a summary of Bureau work in progress.

Jan 1, 1969

By W. B. Frank

Events of the mid-1970s have materially affected US coal production and transportation by railroad. Coal, as a replacement or substitute for petroleum fuels, has been hauled in significantly increased tonnages. Concurrent with the new demand, the railroad regulatory environment has undergone major changes, especially in deregulation activity. Those two events have produced considerable litigation regarding coal rates. This paper discusses the factors involved with railroad rates and topics such as revenue adequacy, Ramsey Pricing, stand-alone cost, and differential pricing. In addition, an update on the western railroad merger situation and the implications for coal transportation are presented. The paper concludes with an evaluation of the current regulatory climate and future prospects.

Jan 1, 1985

By von Wielligh. L., D. G. Hattingh, M. N. James, W. Thomas

"SynopsisThe process of joining materials by friction is based on generating the heat necessary to create a solid-state mechanical bond between two faying surfaces to be joined. In simple terms, the components to be joined are subjected to frictional heating between rubbing surfaces, causing an increase in interface temperature and leading to localized softening of interface material, creating what is described as a ’third body’ plasticized layer. This plasticized zone reduces the energy input rate from frictional heating and hence prevents macroscopic melting. The plasticized layer can no longer transmit sufficient stress as it effectively behaves as a lubricant (Boldyrev and Voinov, 1980; Godet, 1984; Singer, 1998; Suery, Blandin, and Dendievel, 1994). The potential for this solid-state frictional joining process to create high-performance joints between, for example, dissimilar materials with limited detrimental metallurgical impact, and reduced defect population and residual stress level, has had a very significant impact on fabrication and repair in industrial sectors such as transport. This paper presents a brief overview of the advances made within the family of friction processing technologies that could potentially be exploited in the nuclear industry as alternative joining and repair techniques to fusion welding.Modern friction processing technologies can be placed into two main categories: those that make use of a consumable tool to achieve the intended repair or joint (friction stud and friction hydro-pillar processing) and those making use of a non-consumable tool (friction stir welding). The most mature friction joining technology is friction rotary welding, where a joint is formed between original parent materials only. A new addition in this category is linear friction welding, which opens the potential for joining complex near-net-shape geometries by friction heating. The continuous innovation in friction processing over the last 25 years has led to the development of a number of unique processes and applications, highlighting the adaptability of friction processes for specialized applications for high-value engineering components.IntroductionAssessing the potential for using alternative joining and repair techniques for specific applications in a given industrial sector is informed by an appreciation of the current size and potential growth in that sector. Power generation by nuclear fission has been out of favour over the past few years, due to several high-profile nuclear incidents, e.g. the Fukushima Daiichi nuclear disaster, as well as concerns over disposal of nuclear waste and spent fuel rods. However, due to rapid increases in the demand for electricity, coupled with many fossil-fuel fired plants reaching end-of-life, there is renewed interest in installing additional nuclear capacity."

Jan 1, 2015

The use of solid state detector and radioisotope x-ray source for x-ray fluorescence analysis is illustrated by analysis for iron, copper, zinc, tin, and lead in about 700 samples taken from Australian mineral process streams. Limits of detection based on counting statistics (3 standard deviations) range from 0·001 to 0·004 per cent by weight element. The analysis accuracy was usualIy between 2 to 10 per cent (rms) of the mean element concentration and was determined by comparison with assays supplied by mineral companies. In most cases the main cause of error appears to be due to this assay and not the x-ray fluorescence technique.Some potential fields of application of solid state detector and radioisotope x-ray source for analyses in the mineral industry are indicated.

Jan 1, 1974

By A. T. Sapulek, C. S. Özveren, D. W. Dixon

The prediction of underground methane emission from longwall coal faces has been extensively researched for a number of years and numerous prediction methods have been devised. Many coal mines employ sophisticated environmental monitoring equipment which generates large amounts of data including, methane concentration, air velocity and barometric pressure. Presently this information is mainly used only to indicate alarm and danger levels of the monitored data for management purposes, however, the potential uses of this data are enormous[1]. This information could be used to good effect within a production/methane emission strategy as detailed in a previous paper[2]. The paper presents a practical application of artificial neural networks to underground methane prediction. Data on methane concentration and coal production has been obtained from an underground coal mine. The data is used in a neural network architecture and forecasts of methane concentration have been obtained. The forecasts are examined and there is a discussion of the potential use of the predictions from neural networks in the field of mining production control.

Jan 1, 1995

By Dennis N. Poffenroth

One concern of the Mine Safety and Health Administration is the structural integrity of steel wire ropes used on mine personnel hoists and elevators. Failure of such ropes has resulted in loss of life and property. Although thorough and regular visual examinations are performed, hoist ropes may still fail from undetected internal wear, corrosion, and broken wires. To complement visual examinations, nondestructive rope inspection techniques have been developed to determine deterioration and removal criteria. The techniques use electromagnetic and permanent-magnet test instruments designed by a Canadian firm. This paper describes the operating principles, field and laboratory testing of these nondestructive testing instruments, and discusses the feasibility of using this type of testing as a supplement to visual examination and destructive tests.

Jan 1, 1983

By Surendra K. Mishra

With increasing regulatory pressure from the environmental authorities, waste management has become a focal point of industrial operation. To offset the waste management costs, industry has made conscious effort to recover usable resources from the waste streams. This paper reviews the technical developments and current practices in processing of waste materials. Methods for recovering metallic, non-metallic and organic species from solid wastes and effluents generated by operating plants are discussed.

Jan 1, 1997

This paper examines the feasibility of combining network modeling and computational fluid dynamics for modeling of underground mine ventilation systems. Both simulation methods have specific advantages and disadvantages for analysis of mine systems. Network modeling is widely utilized by many operations and allows for assessment of current systems and simulation for planning purposes. Alternatively, CFD has been utilized only marginally by operations and is typically a research tool, requiring considerable computational power, complex models, and careful analysis and calibration of results. Network modeling allows for a holistic approach to the ventilation system, giving quantity, velocity and pressure in every branch, but CFD modeling can resolve the flow regime in 2-D or 3-D, which is idea when examination of an area on a more detailed basis is useful, such as dust and gas control. Integration of the two can allow for more flexible systems analysis. The feasibility of integration, along with application to limited underground mine data are examined.

Feb 23, 2014

By James A. Barr

THE writer's first experience with flotation was during World War I, in the beneficiation of Alabama graphite schist ores. One plant used a cone with a peripheral overflow; dried ore was distributed by a rotating disk onto the surface of the water. No reagents were added. The flake-graphite film floated along with some fine silica. Dewatering screens separated the flake. Naturally unit capacities were low but results were satisfactory. Minerals Separation mechanical flotation machines were used in another graphite mill. Pine oil was added directly to the head cells, with very good results. All the graphite concentrates from both types of flotation were carefully refined after drying by passing through burr mills, followed by very close sizing on sifters. In March 1927, the writer ran a very successful flotation test on minus 28-mesh, deslimed, Tennessee brown phosphate "sand,"[t] using a mechanical laboratory machine built in the shops of the Anaconda Copper Mining Co., through the courtesy of Ernest Klepetko. The machine was soon converted to a subaeration type, with improved results. This phosphate research program was greatly enlarged and led to the formation of the Phosphate Recovery Corporation. The development of nonmetallic flotation followed rapidly. The first flotation machine for beneficiation of phosphate was installed in January 1928, in a pilot mill, by International Minerals and Chemical Corporation, at Mulberry, Florida. These machines were Minerals Separation, 24-in., subaeration types, with weir control of pulp between cells. The sand bleeders were very small-about 1 ¼ -in. diameter. As the feed contained 15 to 25 per cent plus 28-mesh material, the cells choked up frequently. This was corrected by cutting a 2 by 6-in. bleeder opening above the impellers, at grid level, which short-circuited the coarse fractions directly into the feed of the next cell. The matter of size classification and grinding was a considerable problem, which does not come within the scope of this article. Because of the troubles noted above, cascade-type roughers were installed in the second flotation plant, built about 1930. Experimental cells had been tried in 1928. General plant layout is shown in Fig. I and details of the cascade construction in Fig. 2. The cascade installation in plant No. 2 gave good results and eliminated troubles due to choke-ups and coarse feed. The capacities and metallurgical results equaled those of the modified 24-in. Minerals Separation flotation machines in plant No. I The objections to the cascade installation are the floor space and mill height required. In 1939 an improved Minerals Separation machine was tested in parallel with the cascades. Extensive tests indicated

Jan 1, 1945

By Narendra N. Khatri, Michael Deutscher, Jozef F. Zurawski

Five sewer connections were required to divert Combined Sewer Overflow (CSO)from existing outfalls to an old underutilized large diameter brick sewer (the Easterly Interceptor). The connections were part of an on-going CSO control program by the Northeast Ohio Regional Sewer District (NEORSD) in the City of Cleveland, Ohio. Each connection was made by pipejacking and hand-mining a fiberglass-reinforced polymer (FRP) pipe through soft glaciolacustrine clays and silts. Jet grouting was utilized to stabilize the soils and fill the voids surrounding the interceptor prior to making the underground connection. Reinforced concrete liners were constructed inside the aging brick sewer to provide structural stability during ground improvements and connection work. The project also involved micro tunneling two approximately400 foot lengths of FRP pipe through soft ground using a slurry pressure balanced machine.

Jan 1, 2005

By Jennifer Riefenberg

Research efforts by the U.S. Bureau of Mines include running a series of displacement-discontinuity, boundary-element models to simulate the gateroad design at an underground coal mine in northwestern Colorado. The initial mine design is a yield-abutment chain pillar arrangement in a three-entry, longwall gateroad system. Pressure effects from mining the first and second panel were recorded using borehole pressure cells (BPCs). These field data were then compared directly to the model output. Observed yielding in the field was approximated by reducing material property values and/or removing pillar elements in the model. Model results using this calibration technique mirrored the field measurements consistently. Using the calibrated model parameters, a suite of models was run simulating an experimental entry design: exchanging the yield and abutment pillar locations. These model results reflect a 20¬to 33-percent reduction in core stresses in the yield pillar during mining of the second panel. Improved pillar and entry conditions are suggested by these predictive results. The design modifications were then implemented at the mine along a 150-m (500-ft) test section. Field observations and measurements from the experimental design test site compared favorably with trends of the model predictions.

Jan 1, 1993

By R. A. Feemster, C. M. Rader

Because of the necessity for taking regularly occurring open-flow tests in prorated high-pressure oil fields, much gas is turned to atmosphere by way of vertical vent lines leading away from the oil and gas separator. In the past, measurement of such gas has been accomplished by several methods, usually by use of the open-flow Pitot tube. The use of the closed-flow Pitot tube has been avoided apparently chiefly because the ordinary vent-line hook-up makes it necessary to apply the instrument closer to a bend, valve, or obstruction in the pipe than is recommended by rules of good practice. The many advantages that would result from the application of the closed-flow Pitot tube prompted investigation of the actual effect upon quantity rate of flow measurements computed from data obtained with the tube in a normal working position, which is closer to the tee at the base of the vent riser than is usually considered as giving highly accurate results. An effort Was first made to compare the results thus obtained to those under ideal conditions and at high velocities To make this comparison, knowledge of the characteristics of gas flowing at very high velocities is essential. Research for such information indicated that little or no work had been done that would give data necessary for such a comparison, therefore the problem was changed to a test designed to determine the relationship between quantity rates of flow as measured by an orifice meter and a Pitot tube placed at the center of a pipe eight diameters from a tee or ell at the base of a vent riser, through which gas is flowing under low pressures at very high velocities. To determine this relationship, a series of tests was run on a number of 8-in. iron-pipe vent riser., in which the Pitot tube data were taken at the position as stated above. Gas from a wet-gas gathering system was passed through an orifice meter setting and thence to atmosphere by way of the vents. Data were taken simultaneously from the orifice meter and Pitot tube from which computations for comparisons were made. The actual method of comparison is discussed later in this paper. Since Pitot-tube information is usually given in general terms, and not readily usable, it will be the purpose of this paper to discuss the applica-

Jan 1, 1934

By D. H. Gieskieng

THE advent of curved jaw crusher wearing plates made an approach other than segmental layout analysis desirable for prediction of capacities. For some time it had been known that the drawing board capacities of crushers using these plates had to be considerably modified by complicated experience factors to achieve agreement with results. Because these apparent capacities could be readily increased severalfold by minor crushing chamber shape changes, it was necessary that the utmost precaution be taken in predicting capacities of jaw plates modified for nonchoking, special wear characteristics, or any other reason. To this end the laboratory and field tests outlined by the author in a previous paper1 were made on Blake-type jaw crushers. The results of these tests were summarized in a simple first degree equation applicable to crushers using either straight or curved jaw plates. This equation first outlines the maximum capacity potential of a given crusher, then reduces this figure in accordance with installation circumstances by means of a realization factor. It was found subsequently that this equation, with the addition of an eccentric throw factor, is applicable to standard types of single-toggle or overhead eccentric jaw crushers as far as maximum capacity potential is concerned. However, these crushers have realization factor curves somewhat different from those outlined for the Blake type. While this paper is concerned principally with standard type single-toggle crusher capacities, the evaluation of data obtained with these machines is simplified by comparative reduction to the 10 x 7 in. Blake-type equivalents upon which the summary of the preceding paper was made. Convertibility of data from one type of crusher to the other also tends towards confirmation of both. The agreement of these data is sufficient to be considered complimentary. Consequently the feed factors, f, previously reported for Blake crushers are slightly adjusted to an average with the single-toggle crusher results. Blake-type equation: C = f.d.w.y.t.n.a.r [I] Single-toggle type equation: C = f.d.w.y.t.n.a.e.r [21 where C is the capacity in short tons per hour through the crusher, f is a feed factor, dependent upon the presence of fines in the feed, and the surface character of the jaw plates used. Values of f : Smooth Plates Corrugated Plates With normal fines 0.0000414 0.0000319 Fines scalped out 0.0000368 0.0000252 Large pieces only . 0.0000312 0.0000215 d is the apparent density of the broken product in pounds per cubic foot. (If the true specific gravity of the feed is known, 40 pct voids may be assumed and d becomes 37.4 times sp gr). w is the width of crushing chamber in inches. y is the openside setting of the crusher, in inches. In the case of corrugated jaw plates it is measured from the tip of one corrugation to the bottom of the valley opposite. t is the length of jaw stroke in inches at the bottom of the crushing chamber. It is the difference between open and close-side settings. n is rpm, or crushing cycles per minute, a is the nip-angle factor. It is unity for 26" and 3 pct greater for each less nip-angle degree. A nip-angle of 20" has an a value of 1.18, and an angle of 30" has an a value of 0.88, see Fig. 1. r is the realization factor. It is unity for perfectly uniform choke feeding and usually less for actual operating conditions according to the method of feeding used and the probabilities of hang-ups involving the size of feed and crusher opening. Approximate values are given by the curves in Fig. 2. These values are further reduced by intermittent feeding, e is the throw or diameter of gyration of the single-toggle crusher eccentric in inches. As evident in Fig. 1A, variation of feed size will generally have little effect on nip-angle if both jaw plates have flat areas. Jaw plates having continuous curvature, as in Fig. 1B will have different nip-angles, depending upon the size of feed. For test work as described in this paper this effect was accounted. For general compilation of capacities for average feeds it is suggested that the nip-angle be taken at the various settings computed, at an arbitrary level, such as is indicated in Fig. 1C. Data Evaluation To bring the Blake and single-toggle type crusher capacity test results to common terms for evaluation, all data are converted to terms of 10 x 7 in. Blake-type performance at conditions of 100 lb per cu ft, 10 in. chamber width, 250 rpm, 0.65 in. stroke, 3-in. openside setting, and 18° nip-angle. (The nip-angle of the 10x7 in. Blake is 18° at 3-in. setting.) The single-toggle crusher performances are also divided by the eccentric throw to bring this effect to unity. As outlined,' laboratory and field tests made on Blake-type crushers ranging from 10 x 7 in. to 60 x 48 in. were summarized along the foregoing conditions of speed, stroke, etc. This resulted in groups of data which correspond to feeds with fines, feeds

Jan 1, 1952

By Donald R. Irving

ALTHOUGH the quantity of material handled at metal and nonmetal mines in the United States in 1962 was 2.7 billion tons, the same as in 1961, a larger proportion was waste. At metal mines, crude ore production declined 1 million tons and waste output rose more than 18 million tons; at nonmetal mines crude ore production declined 6 million tons and waste output rose 36 million tons. Copper and iron ore producers increased their share of crude ore and material handled from about three-fourths to four-fifths of the national metals total, and sand and gravel and stone producers in-creased their share of the nonmetals total, also from three-fourths to four-fifths. Six States-Arizona, California, Florida, Michigan, Minnesota, and Utah-each handled more than 100 million tons of ore and waste, and together they accounted for 43 percent of the U.S. total. When the large-volume construction materials (sand and gravel and stone) were excluded from the totals, four States-Arizona, Florida, Minnesota, and Utah-supplied over half of the material handled.

Jan 1, 1963

By R. M. Geisenheyner

We are in the midst of a transportation revolution. From the Wright Brothers to the SST. From the Toonerville Trolly to the 120-mile-an-hour Northeast Corridor train. From Christopher Columbus to Neil Armstrong. There is another side to this revolution and it is going on every day at our mines and factories. We call it bulk distribution. Perhaps ordinary sounding, but every bit as exciting as those other transportation innovations. Basically, we have gone from bag to bulk, and in the process reached that Last Frontier in manufacturing cost savings. By revitalization of our distribution system, we have made it possible for our mines and factories to realize fully the vast economies of spage-age manufacturing techniques and accomplishments. The pacesetters in this distribution revolution have been you gentlemen, the producers and shippers of dry mineral products. In this area bulk distribution grew up. And here most of the current innovations are being introduced. Management of your industry was early to realize the economic advantages of bulk distribution. Distribution costs of your products comprises a sizeable, portion of the selling price and management is sensitive of any developments which may even slightly reduce the cost of transportation, marketing or the exploration of new frontiers.

Jan 1, 1969

By V. Králová

The TESCAN Integrated Mineral Analyzer (TIMA), an automated mineralogy system, enables fast and quantitative mineral analyses of rocks, ores, concentrates, tailings, leach residues or smelter products. It combines BSE and EDX analysis for identification and measurement of mineral concentrations, particle size distribution, and liberation/locking parameters. In addition, it can provide bright particle searches for PGM, gold-silver ores, and/or REE. With the newly developed Automated Loading System (AutoLoader), the TIMA has become the world?s first automated mineral analyzer which permits robust, continuous and unattended sample loading. With the AutoLoader (robotics) system, the TIMA has emerged as a powerful plant support instrument. It increases the sample throughput, minimizes manual labor and enables 24/7 operations. As such, it can be used in daily, continuous mineralogy for mine geology/ore control, concentrators, leach operations, and smelter support. It will also increase the capabilities of technical service centers for mining companies, commercial laboratories, large drilling programs or pilot test campaigns. In combination with a highly automated sample preparation lab (sizing, potting and polishing), TIMA technology can establish high-throughput and fast-turnaround automated mineralogy lab modules for mine-site production support.

Feb 23, 2014

By C. F. Willis

The time is no longer when a man can act as an independent unit; the appreciation of the interdependence of one man upon another has emphasized the importance of the social unit. Epidemics have made us recognize that even a man's health is not distinctly his own to control as he pleases. The physical examination of workmen previous to employment started with an effort to prevent the spread of tuberculosis, for tuberculosis may be detected in its early stages and cured. But it was soon found that many other diseases were detected and the saving of lives made possible. The physical examination does not mean the elimination of the unfit—on that basis it would utterly fail—but rather the measuring of a man's physical fitness and placing the man where he can do the best for himself, his fellow worker, and the company. Industry as a whole cannot expect to live up to the standard of physical examination set for the army, nor should it expect to do so, for in all branches of industry there are types of work that do not require the same amount of endurance as does army work, and the lacing of men with physical limitations in the work for which they are capable permits a higher average of physical fitness for the work requiring physical excellence. Objects of Physical Examination The objects of physical examination are: The early detection of illness, particularly at a time when a full restoration of health is possible; the protection of employees from infection caused by working in contact with contagious diseases; the discovery of a man's physical limitations, in so far as his possibility for rendering good service is concerned; assistance to the safety movement by eliminating association in hazardous occupations with men whose physical condition renders them likely to accident to themselves and others; and the lessening of time lost by sickness. Statistics issued by the United States Department of Labor show that 22.54 per cent. of idleness is caused by sickness, with an average number of 7.71 weeks idle; whereas only 1.66 per cent. is caused by acci-

Jan 1, 1920