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By Martin H. Rogoff

This publication combines a critical review of the literature on the microbiology of coal with an introduction to those areas of microbiology related to studies of coal as a biological material. The attack on coal by microorganisms as yet remains doubtful. Only the low-rank coals contain an indigenous microbial flora, and even these organisms are not peculiar to coal, but are common soil and water forms. No experimental data have as yet been presented, either in the literature or in the present work, which unequivocally demonstrate the oxidation of coal by microorganisms. Reasons for the resistance of coal to such attack, including insolubility, physicochemical structure, steric hindrance of enzyme action, and the presence of antibiotic materials in coal are discussed. Microorganisms do attack large aromatic molecules and the mode of oxidation of aromatic ring systems by bacteria is presented. Well-defined pathways are known for the oxidation of polycyclic compounds with one to three rings, and these paths with their key intermediates are described and related to the possible oxidation of coal.

Jan 1, 1962

By Jue Kou, Fazhao Sun, Jiang Liu, Cuili Gui, Baoqiang Yu, Chunbao Sun

A novel special magnetic separator was developed based on the special properties of precious metal-bearing alloy in highgrade nickel matte. The recovery of Au, Pt, and Pd was 77.79%, 84.79%, and 81.79% respectively at optimum operation conditions of magnetic separator feed of 2.5t/h, pulp density of 45%, and flush water of 1.5t/h, and the recovery significantly improved comparing with normal magnetic separator. Magnetic field simulation of the special magnetic separator indicates that magnetic intensity of 0.6 T can be generated on the surface of magnetic drum, which can strengthen the recovery of heavy alloy that contains precious metals. The alternate strong and weak magnetic field can also make magnetic particles rolling on the surface of drum, which will reduce the generation of magnetic agglomeration to a large extent and decrease the content of impurities in magnetic concentrate.

Jun 16, 2022

By William G. Doepken

GENERAL DESCRIPTION The Henderson mine utilizes a highly mechanized, continuous panel-caving system to extract ore from a deep, massive, molybdenum deposit. The mine site, lo¬cated 80.5 km (50 miles) west of Denver, is situated at 3170 m (10,400 ft) above sea level in a steep valley on the eastern side of the Continental Divide. The mill site, located on the western side of the divide, is linked to the mine via a 15.5-km (9.6-mile) railroad tunnel. Mine production is scheduled to reach 27 215 t/ d (30,000 stpd) from the uppermost production level. This pro¬duction rate will have been reached within the four years following an intensive ten-year preproduction development program. A second production level, due to come on stream in later years, will expand production capabilities to 31 751 t/d (35,000 stpd). The mine, which employs approximately 2000, has blocked-out ore reserves of 220 Mt (242 million st) at an average grade of 0.42% MoS2. Geology The Henderson deposit is composed of two partially overlapping ore bodies that lie 1080 m (3600 ft) beneath the peak of Red Mountain. The ore bodies are entirely within a Tertiary rhyolite porphyry intrusive complex that has intruded Precambrian granite. The de¬posit is elliptical in plan with overall dimensions of 670 x 910 m (2200 x 3000 ft). In section it is arcuate with an average thickness of 185 m (600 ft). The top of the deposit is at an elevation of 2610 m (8700 ft) while the lower limits range from 2340 m (7800 ft) on the west to below 2100 m (7000 ft) on the east. The mineralization is relatively continuous in the ore bodies and consists of molybdenite and quartz in random to subrandom, intersecting, closely spaced veinlets. Cavability RQD (rock quality designation) * values measured from Henderson drill core and compared with the RQD values from the Climax and Urad block-cave mines in¬dicated that the Henderson ore would cave but with difficulty and that a high percentage of the cave ma¬terial would be blocky. Initial caving experience shows the Henderson ore caves easier and with greater frag¬mentation than was indicated by the RQD values. Pos¬sible reasons for this are: 1) The greater lithostatic load at the Henderson has a greater effect on caving and fragmentation than anticipated. 2) The relief of confining pressure due to caving action and brittleness of the rock is enhancing breakage. Mine Layout The Henderson mine layout was designed from its inception for a large-scale, rubber-tired, continuous panel-caving mining system. The ore body is vertically divided into three major mine levels (Fig. 1). The top¬most level (8100 level), which is 2469 m (8100 ft) above sea level, is the current mine production level. The intermediate or 7700 level, which is in the initial

Jan 1, 1982

By Jessica M. Wempen, William G. Pariseau, Michael K. McCarter

"Quantitative analysis of mine-wide subsidence at the kilometer scale and details of stress distribution about an advancing longwall face are estimated using an adaptation of the finite element method. The method is well suited to the tasks at hand. For greater realism, variability of strata properties is taken into account as are the effects of joints and cleats on elastic moduli and strengths. Evolution of pillar stress and entry closure remote from the face is readily quantified in a series of analyses that simulate face advance. Computed results compare favorably with the evolution of closure measurements about an instrumented pillar in a two-entry headgate. The appropriateness of the finite element method is confirmed. This method is based on first principles that avoid empirical schemes of uncertain applicability and numerical models “calibrated” by fitting computer output to mine measurements.INTRODUCTIONMine-induced seismicity is intimately related to strata mechanics associated with longwall coal mining and room and pillar mining, as well. Strata deformed beyond an elastic limit often tend to fail rapidly by brittle fracture and, thus, to emit acoustic signals in the form of elastic waves. Understanding the induced seismicity in coal mining offers the potential for early warning of hazardous conditions. Many years of experience with seismic phenomena associated with hardrock mining suggest considerable complexity should be expected. However, recent coal mine studies (Pariseau, 2014; Pariseau, 2015; Pariseau and McCarter, 2015; Pariseau and McCarter, 2016) have shown high correlations of seismicity with element failures in finite element simulations. The main lesson learned from these studies is one elaborated by Iannacchione et al (2005); deviation from normal activity is an early warning of ground control difficulty. For example, an abrupt increase in seismic event rate, or equivalently, an increase in element failure in finite element simulation of panel advance, is a cautionary indication for ground control. Present and past study results demonstrate the effectiveness of finite element simulations for mine design and early detection of potential ground control issues."

Jan 1, 2018

By Will Mitchell

The classical definition of a beneficiation engineer as one who treats an ore in order to separate and discard worthless fractions by essentially physical means is obsolete. Technology in the profession has advanced so rapidly during the last two or three years that educators have not been able to coin definitions to keep up with the pace. In the past some people have hesitated to include leaching or even agglomeration as minerals beneficiation, because of the major chemical changes involved. This view has fallen by the wayside, especially because a majority in the profession have become actively involved in extraction and pyro processes that go far beyond the original definition of mineral dressing. To say that there is a great revival of interest in leaching is putting it mildly, for the uranium business, like the gold business, now depends almost entirely on leaching. This revival of leaching, long overdue in mineral engineering, has been stimulated this year, especially as a result of the relaxation of security restrictions surrounding the recovery of uranium from its ores. It has brought new unit operations to minerals beneficiation, namely ion exchange and solvent extraction. These operations have appeared as resin-in-pulp, solvent-in-pulp, and liquid-liquid systems. In many cases these leaching and separation procedures, now reaching the production stage, have been engineered by minerals beneficiators. The trend toward leaching has also had impact on the technology of beneficiating other nonferrous minerals, especially copper, manganese, columbium, tantalum, nickel, cobalt, titanium, and the rare earths.

Feb 1, 1956

By I. Havenaar

EXPERIMENTAL DATA In an article by C. K. Ferguson and J. A. Klotz,1 experiments on the filtration of drilling muds under borehole conditions are discussed. Experimental data on mud filtration through the wall and the bottom of the hole are presented. From the data on bottom-hole filtration it was concluded that the filtrate does not flow freely into the formation, but that the pores of the formation are plugged by the mud. A quantitative interpretation of the data can be civen, by using a formula for bottom-hole filtration, dehved below. This formula is based on the following assumptions, 1. Each time a blade of a drag bit, or a cone of a roller bit, moves along the bottom of the hole, the mud cake is completely removed. 3. A new mud cake is immediately formed on the freshly produced surface, and losses of "whole" mud into the formation are negligible (this is equivalent to an immediate plugging of the pores). 3. The filtration of the mud on the bottom of the hole follows the classic law: V = A +1—(Eq. I), where t is the time required to yield a volume of filtrate V, A is the surface area of filter cake, and C is a constant. The application of this equation means that any eroding effect of the mud stream on the mud cake is neglected. The formula for the calculation of the volume of filtrate, Q,, flowing in one second through the hole bottom (diam. d cm), when using a bit with n cones or blades rotating at a rate of rn revolutions per second, is derived as follows: The mud cake is formed on the bottom of the hole in the time t =1; the filtrate volume V which passes n through the bottom In this time 1s given by Eq. 1: After1/nmsec the mud cake is removed. In one m second this process takes place nm times. Therefore the volume of filtrate, obtained in one second is given by This equation has now been applied to the experiments of Ferguson and Klotz. The constants C were derived by means of Eq. 1 from the API filter losses of the muds used by the authors (t = 1,800 sec; A = 45.16cm2). A three-cone bit was used (n = 3) at 90 rpm (m = 1.5). The calculated figures are compared with the experimental data in the table below. The calculated values of Q, are usually lower than the experimental values. This may be due to the following causes. 1. The value of C used in the calculation is based on the API filter test (filtration pressure of 100 psi), whereas the experimental data were obtained with a filtration pressure of 200 psi. Although the effect of the pressure on C is not large, C decreases somewhat with increasing pressure, and this leads to a higher filtration rate. 2. Mud losses and the eroding action of the mud stream on the cake are not entirely negligible. 3. The values of Q, derived by Ferguson and Klotz from their experiments are too high, because of their assumption that all pore liquid within the formation drilled is picked up by the drilling mud. It is found, however, that the calculated values of Qf, except in the case of oil base muds, are of the right order of magnitude. ACKNOWLEDGMENT The author wishes to thank the management of the Koninklijke/Shell-Laboratorium, Amsterdam, for permission to publish this note.

Jan 1, 1957

By Crapp C. E

The Collinsville Coal Measures consist mainly of arenaceous sediments but indude eleven named coal seams. The Formation outcrops around the northern end of tbe Bowen Basin where it attains a thickness of 700 ft. in the Collinsville-Scottville area and overlies Lower Bowen Volcanies with angular unconformity. Most of the members in the Formation thicken basinwards. The regional dip is about 8 degrees. The Formation thins southwards and does not occur south of the Bowen River on the eastern flank. On the western flank it is represented by 60 ft. of barren sandstone at the limit of our mapping, 12 miles south of the Bowen River. Two seams are mined, the Bowen and the Blake; coal from the former produces high grade metallurgical coke, and the latter seam is mined for steaming coal. Where mined, the seams are about 20 ft. thick. The coals are of medium volatile bituminous rank and the lower coals are of higher rank than those above them.Reverse faults striking across the Coal Measures have been delineated and the existence of areas of intrusive rocks has been established. Intrusions rose up fault planes and, as felspar porphyry sills, selectively intruded coal seams, decimating reserves of coalavailable for mining. One sill, in the Blake Seam, attains a known thickness of 115 ft. Because the distribution and thickness of the sills is rarely predictable, density of drilling has been greater than in most coalfields.INTRODUCTIONThe assemblage of sediments occupying the northern portion of the Bowen Basin (Fig. 1) may be divided into four formations of Permian age:The Upper Coal Measures (U. Bowen)The Middle Bowen Marine Beds (M. Bowen)The Collinsville Coal Measures (M. Bowen)The Lower Bowen Volcanics (L. Bowen).Of these, the Upper Coal Measures and the Collinsville Coal Measures are known to contain coal seams of workable thickness.

Jan 1, 1960

The importance of factoring mining dilution into the estimation of ore reserves in an open pit mine is discussed. An example that relates the issue of mining dilution to the size of the smallest volumes that can be mined selectively is given. The relationship between the size of the selective mining units (SMUs) and the variance of their average grade is presented. The concept of variance reduction and its use in factoring mining dilution into geostatistical ore reserve estimation is described. An approach to estimate a variance reduction factor by way of conditional simulation is introduced.

Jan 1, 1998

By B Leyland

The media in Australia is currently rife with articles and pronouncements on global warming as the most significant crisis of our time, which may æthreaten the future of civilisation as we know itÆ. This has been recently reinforced by release of Al GoreÆs film æAn Inconvenient TruthÆ, and one would be led to believe that the science of global warming is settled. And yet there is a strong body of literature disputing this apparent consensus which suggests that care should be exercised in introducing radical policies to solve a crisis which may not be real. Such policies would have a major impact on those in professions such as engineering (project approvals and design to minimise greenhouse gas emissions), accounting (carbon tax issues) and the law (corporate disputes on greenhouse gas issues are already in train in the USA). This paper addresses the hysteria apparent in the climate change debate by presenting factual evidence relating to climate change and the current phase of mild global warming. Some of the more extreme statements on future impacts are repudiated with published data, and alternatives to the purported role of fossil fuels in temperature change are offered. The potential impact of political decisions on professional activity is discussed, as are the implications of a possible future reversal of the scientific consensus, as has occurred in the past. The paper concludes with a call for the professions to exercise their Learned Society role to ensure that a rational and public debate is held on the broad issue of climate change.

Jan 1, 2007

By Gray N. B, Floyd J. M

To gain further understanding of the operating efficiency of the BHP Slab and Plate Products Division (SPPD) RH vacuum degasser, physical and mathematical model studies of the process have been undertaken. The purpose was to investigate how the various process parameters affect the liquid circulation rate, to visualise the flow patterns, and to identify and eliminate the cause of localised wear in the downleg. In the physical model mixing times were measured using an acid tracer technique. The results were applied to predicting trends in times required to obtain homogenous melt composition under varying conditions. A 2-dimensional mathematical model describing the liquid metal flow has been developed using the PHOENICS fluid-flow package. The physical model results were simulated and incorporated into the mathematical treatment and an improved design for vessel geometry is proposed. The effect of rounding the downleg entrance or installing a baffle between the legs is discussed.

Jan 1, 1987

The use of operational research in mining is illustrated by simple examples of the techniques of simulation, linear programming, theory of sampling, and experimental design.Statistical simulation of the delays in answering telephones was used to compare the efficiency of alarm systems in collieries, and to determine stock control policy for a bin in mucking, filling, and tramming operations. Linear programming was used to help minimize transportation costs between collieries and washeries. The theory of sampling was applied to separate and balance the components of error introduced at the' various stages in the collection and reduction of routine samples of coal, and to the assessment of errors of estimates of grade in orebodies from drill samples. 'l'he principles of experimentaldesign were used to compare wear of different conveyor beltings and costs of battery and diesel locomotives in underground transport.INTRODUCTIONIn operational research some of the procedural techniques and professional attitudes of mind found among scientists and, in particular, mathematicians and statisticians, are applied to operational problems in industry ranging from policy making in the broadest sense to the humblest sampling procedures. These apply in mining equally with other industries.Anyone who reviews a procedure critically and in a systematic way may legitimately claim to be doing operational research. On the other hand, what is found in books on operational research is usually a collection of mathematical and statistical techniques which, though forming only a corner of operational research activity, illustrate the novel approaches to problems which characterize the discipline and which would probably not occur to the un...

Jan 1, 1962

With the signing of the armistice on Nov. 11, the direction of the main concentration of effort of the United States was changed. In order to win the war, all industrial efforts had to be organized and centralized. With the war won and peace in sight, this centralization of effort stopped and the full play of individual initiative was allowed to resume its sway in the community. During this period of reversal of direction of effort, there was a natural loss of momentum and the United States, as well as the rest of the world, is in for a period of readjustment. The immense progress that was made in one direction under the stress of the necessities of war, which focused the energies of a nation in one direction, is an outstanding example of what can be accomplished if a community with many varying interests can be united on one objective which it desires to attain. The realization that the fusing of many interests into one stream of effort is difficult should not prevent us from taking the long view ahead that is necessary in order to be able to measure the progress made. If we don't have a mountain peak to guide us, we are very likely to run in circles in the plain without reaching the goal to which we strive. The most efficient development of natural resources is an ideal that, from a material point of view, appeals to the engineer. This ideal includes giving of opportunities to everyone to take a share in the development of these resources.. It also contemplates rewarding foresight

Jan 4, 1919

The International Symposium-cum-Workshop on Management andControl of High Gas Emissions and Outbursts in Underground CoalMines was held in Wollongong in March 1995. Coverage of high gasemissions was virtually confined to instantaneous outburst implications, essentially seam gas pre-drainage. Globally, instantaneous outbursts have been known for 150 years, andthe first Australian outburst occurred in 1895 and Australian occurrences and mines affected have increased since. Few significant coal producing countries are unaffected. The coals affected range in rank from lignites to anthracites. Geological disturbances are the most likely environments for occurrences. The most likely mining geometry is of virgin headings, with some occurrences on longwalls and in other situations. Widespread research into many aspects of the problem has yet to produce a generally accepted explanation. Explosive inducement is a well-known control. Apparently high advance rates increase face gassiness and create higher stress abutments, increasing proneness. The most popular preventive measure, pre-drainage of virgin coal ahead of faces has produced highly successful very long hole drilling performances but without the precision necessary for accurate geometric hole patterns, despite quite sophisticated drilling equipment and hole surveying instruments. For the future, more precise degasification is sought, even from the surface, together with rapid face coal gassiness assessments to confirm lowering below threshold values, as well as other proneness lowering measures, perhaps related to new heading and longwall geometries and to new equipment to provide them. But above all, safe management plans are required for each operation, to safeguard the miners and their working environments, and thus to protect underground coal mining from this mounting threatening problem.

Jan 1, 1997

By J. P. Ducarme

Numerous fatal/nonfatal accidents involving underground workers struck by powered machinery occur yearly, with continuous miners and roof bolters involved in the majority of these accidents. In an attempt to reduce these accidents, researchers at the the National Institute for Occupational Safety and Health (NIOSH) Pittsburgh Research Laboratory conducted studies of operator interactions with the motions of continuous mining machines and roof bolter boom arms. These operators generally perform their tasks in close proximity to the equipment in confined workspaces, often employing awkward postures. Since experiments with human subjects using the actual equipment were not feasible due to safety concerns, researchers opted to conduct controlled experiments in laboratory settings. Utilizing motion capture technologies and computer simulations, the studies collected data on equipment and operator movement in a range of seam heights and working postures. This article details the results of these studies to examine operating speeds based on usage and seam height.

Jan 3, 2010

By Anthony D. Songer, James E. Diekmann, Jarrett E. Carlson

Computer Aided Design (CAD) systems are currently recognized as a necessary tool for the management of projects. Currently, CAD is used for TBM and conveyor setups, concrete lift design and overall constructability reviews. Typically, such CAD models exist only in 2 dimensions. The advent of more powerful computers, enhanced CAD programs and after market animation packages provides tremendous potential to the Tunneling industry. In particular, effective application of these technologies enhances cost, time and quality in field operations.

Jan 1, 1997

By H. S. Venkatesh, G. Gopinath, R. Balachander, G. C. Naveen

Punatsangchu Hydroelectric Project Authority is constructing 1020 MW underground hydroelectric project in Bhutan. The project envisages construction of concrete dam, Desilting Chamber, Head Race Tunnel, Power House Complex and Tail Race Tunnel. Tunneling is one of the major activity in any underground projects as they are driven for multiple activities. By and large the tunnels are a major part of connecting networks from surface to caverns/underground working sites. Many tunnels in hydropower project are part of water conducting systems and one such important tunnel is the Tail Race Tunnel in this project and had to be excavated in thinly foliated rockmass conditions by D&B method.

Feb 1, 2020

By K. L. Ludeke, A. D. Day

For many reasons, it appears that deep rooted, perennial shrubs offer potential for improved stabilization and provide maintenance free vegetative cover to harsh sites where perennial grasses have not been successful. The major objective was to select various shrub species of arid plants for initial soil stabilization of disturbed mining areas. The very fact that a drought-adapted shrub has a massive root system that can use moisture from a greater volume of mineral waste soil materials suggests that arid environment disturbed soils may be vegetatively stabilized using desirable forage shrubs. A secondary effort is underway to assemble information and plant materials of promising species from many arid regions of the world for reclamation of mined lands. Surprisingly, many of the better plants for arid sites are quite high in protein content. With proper management, breeding, and selection, they may prove to be very desirable livestock feed when mined lands are used in range land areas. Advancements in arid land solid waste stabilization hold favorable promise for many industries that mine and mill in arid regions for effective reclamation of disturbed areas. Particularly exciting is the possibility of establishment of high density maintenance free vegetative cover of climax vegetation that reclaims the disturbed area back to its original land use. Due to high shrub productivity, stabilization potential, nutritional quality, and reclamation success, greater use should be made of shrubs in disturbed land reclamation associated with mining and milling operations in harsh aril environments.

Jan 1, 1986

By Georges Cote, Ehsan Alavi, Eren Kusdogan

The City of Toronto's Coxwell Bypass Tunnel is currently being constructed by North Tunnel Constructors (NTC) ULC, a joint venture of Jay Dee Canada, C&M McNally Tunnel Constructors and Michels Canada. This project includes construction of approximately 10.5 km of 6.3 meter finished diameter rock tunnel, five 20 meter diameter storage shafts and eleven tunnel connection drop shafts, along with associated deaeration and adit tunnels. 120 m of Starter tunnel and 70 m of Tail tunnel were excavated with roadheaders to help with the launch of the TBM and as part of the contract base scope work. JayDee Canada in Collaboration with Everest Equipment Co. developed an innovative approach to design and build a stand-alone Ring Machine Erector nicknamed Enterprise to erect precast segmental lining in Starter and Tail tunnels in lieu of Cast-In- Place concrete. This paper describes the design and provides feedback on the innovative procedure used to install the rings.

Jun 23, 2024

By David M. Parkes, Mike Fisher

In 1947, coal production in Western Canada was 10 Mt (11 million st) which predominantly came from 120 underground mines. By 1968 production was down to 1 Mt (1.1 million st). Production in 1981 was back up to 29 Mt (32 million st), but only 1.5 Mt (1.7 million st) of the total was from underground mines. In fact, because of competition from open-pit mines, only two underground mines were operating in 1981-the McIntyre and B.C. Coal mines. While several other underground mines are being planned, this article will deal with only the two in production. Geology The geology in Western Canada is frequently complicated; hence only more regular deposits are mined. Coal is generally thick, often steeply pitched and usually soft or well cleated. The 5000-km (3,100-mile) coal belt that runs from the Yukon to Mexico is well developed in Western Canada. It is divided into two distinct regions-the Rocky Mountain Lower Cretaceous coals and the mostly uniform level Upper Cretaceous coals of the plains area to the east. Isolated pockets of coal occur at Vancouver Island and Hat Creek. Hat Creek's massive 300-m (984-ft) thick geologically recent lignite deposit is 250 km (155 miles) inland. Geography The infrastructure of Western Canada is shown in Fig. 1 along with the locations of the two mines. Both rely on exports of premium low volatile metallurgical coal mostly to the Pacific Rim. The rail distance from both mines to port is 1100 km (684 miles)-accounting for a significant portion of the sales cost of the coal. Mining Methods Two main mining methods are used-room and pillar and hydraulic. Longwall has been attempted and is being considered again. In the past, a simple hand method used gravity to help mine most of the coal on steep pitches. Levels were driven in the seam, rising slightly to assist in draining. On the advance, mining would start at the upper level, usually from adits driven in the side of the mountain. Rooms or angles were driven up 100 m (328 ft) at a suitable angle for the coal to flow down. On retreating out of the level, the pillars would be taken, starting from the highest point, using batteries to stop coal or rock flushing down the room. Batteries consisted of three to six stout wooden posts set at an angle to resist material flow. Coal loading was directly from chutes at the bottom of raises into 1- to 2-t mine cars hauled by diesel or battery locomotives. Often output was restricted by the supply of empty cars. Mechanization began in the 1960s but was difficult in these conditions. Mines such as Canmore and Coleman continued operation into the 1970s but closed because steep seams, high methane emissions, and faulting made mining difficult. McIntyre Mines The McIntyre mines are located 360 km (224 miles) west of Edmonton, Alberta, in the foothills of the

Jan 4, 1983

By Albert J. Phillips

As EARLY AS 1824, Haidinger1 described crystals of native copper that were, according to Dana,2 "probably twinned parallel to the octahedral plane and normal to this axis." In 1837, Rose3 very clearly demonstrated that native copper crystals were commonly twinned on the octahedral plane. Lasaulx,4 in 1882, described polysynthetic octahedral twins and stated that enclosed twinning lamellae were observed. Even on crystals formed artificially by electrolysis, twinning was observed as early as 1886, by Brown.5 Many other descriptions of twinning in native copper and in gold and silver are to be found in the literature, and in every case with which we are acquainted the twinning is conformable to the spinel law; i. e., the octahedral plane is both twinning and composition plane. Metallurgists have long been familiar with the straight-sided bars or bands that commonly occur within the irregularly outlined grains of metallic crystalline aggregates. They are certainly found in nearly all metals of the face-centered cubic type after cold working and annealing. If a specimen showing these bands is rotated, keeping the angle of incidence of the illuminating beam constant, they usually exchange color contrast periodically with their respective matrix crystals. Also slip lines, when produced in these specimens, nearly always show a change in direction upon passing through the bands, giving rise to the "stairway" effect often illustrated in metallurgical textbooks. Apparently the only quantitative observations on bands of this sort were made by Osmond and Cartaud6 on austenitic steel. They selected,

Jan 1, 1928