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By Philip H. Nelson, Richard Lingle

Vibrating wire stressmeters (VWS's) and borehole deformation gages (BDG) were deployed in two in-situ heater experiments at Stripa, Sweden to determine the thermally induced stress changes in the rock mass. The heater experiments ran for 18 months, including a six- month cool-down period after the heaters were turned off. Gages were installed in both horizontal and vertical boreholes and were subjected to temperatures ranging from 10°C to 120°C, depending upon the distance of a gage from the central heater. Most gages operated in a moist environment because groundwater flowed into many of the instrument boreholes during the experiments Of the 36 VWS's installed, six failed. Failures were attributed to corrosion of the vibrating wire due to moisture entering the gage body. Of the 30 BDG's installed at the beginning of the experiments, 22 failed, also as the result of water entering the gage body. Modification and reinstallation of the gages eliminated the problem of water infiltration, but much data from early stages of the experiments was lost due to gage failures. Calibration of the VWS in blocks of Stripa granite showed a lack of repeatability. Variability in calibration results are attributed to seating effects, to variations in the elastic modulus of the rock, and to changes in temperature. These three effects combined to produce an error judged to be approximately ±33% of the stress changes measured at Stripa. In contrast, the major source of error in determining stress with the BDG appears to be the uncertainty in rock modulus and thermal expansion coefficient. Sample calculations based on data acquired near the end of the experiments (during cool-down)

Jan 1, 1982

By Thomas Egleston

DURING the year 1873, my attention was called to the frequent accidents, resulting from the breaking of rails, on the different railroads in this' country, and I was requested to investigate the subject. The plan of investigation I proposed was to ascertain, in as many cases as possible, the exact hist* of broken rails, both in this country and in Europe; to collect information in Europe relating to the tests which rails used there were required to undergo, and to experiment upon the pieces of rails broken on the road, with a view to ascertain whether their fracture was due to their chemical constitution, bad manufacture, to a reduction in strength owing to temperature, or to physical changes in the constitution of the rail. The investigation was commenced by the collection of statistics, and for this purpose I spent several months in Europe, collecting information on the subject of broken rails, as well as the life of iron and steel rails generally, and inquiring into the systems of purchasing and of testing them employed by the railroads there, intending, on my return, to make a series of analyses of rails broken, both in this country and in Europe; to ascertain, if possible, how far great cold had an influence on the fracture; to examine whether the rail broken, either on the road or afterwards, underwent, at or about the fracture, any physical change, and to make a series of experiments on the strength of rails manufactured in the United States or sold in the American market. Unfortunately, the panic of 1873 came on, just before my return from Europe, and prevented the carrying out of the larger part of the plan proposed; as, however, I had collected in the meantime, a large number of statistics of different kinds from all parts of Europe, and had made a number of interesting experiments and investigations, I have thought it would be worth while to communicate some

By P. Duwez, C. B. Jordan

A. J. SHALER*—I should like to congratulate the authors for having carried out such a precise set of experiments. It has been found useful, in sintering experimental compacts in vacuo, to make certain that the residual gas is not one which reacts with the metal. Since traces of oxygen can be kept away only with great difficulty, the technique is often adopted of using a "getter " of powder in the vicinity of the compacts, and, in addition, of permitting a small hydrogen leak to flow into the vacuum chamber. Did the authors use similar devices? This paper brings up a question concerning the definition of the word ' sintering.' The authors restrict its use to the adhesion between particles. Kuczynski, in a paper presented at this meeting, applies the word to the growth of areas of contact between particles. I have used it to mean both these phenomena and also the dimensional changes which continue to take place after the first two have run their course. May I suggest that we should come to an agreement on the use of these words ? Fig 1 and 2 show an interesting feature: extrapolation of the curves to zero time does not give a densification parameter of zero. The higher the temperature, the higher is the intercept on that axis. These observations agree with the concept of a practically instantaneous densification taking place while the compact is being brought to heat. Such a change may be brought about by plastic deformation and primary creep. The stress pattern causing this first rapid flow is, to my mind, due to the force of attraction between the surfaces of opposite particles in the regions immediately flanking their common areas of contact. The stress is not temperature-sensitive, but at room temperature plastic deformation only proceeds until the metal in the area of contact can support it elastically. As the metal is heated, the elastic limit falls, and further plastic flow occurs. At the higher temperatures, this is followed by primary creep, and finally by the steady-state rate-reaction which the authors are seeking. If they were to recalculate their densification-parameter values, using, not the initial density of the cold compact, but the density after the compacts have been brought to temperature, the systematic deviations from linearity in Fig 3 and 4 might be eliminated. Such initial densities might be obtained by extrapolating the curves of Fig 1 and 2 to zero time. I am naturally pleased to see that such a very well done series of experiments leads to a heat of activation (for the densification process in hydrogen) that is much higher than that for self-diffusion, in confirmation of the less elaborate results reported by Wulff and myself (Ind. and Eng. Chem., (1948) 40, 838). J. T. KEMP*—I would like to comment on Dr. Shaler's remarks. There are apparently different interpretations of the word "sintering." It seems to me that an accurate definition of our word is essential in all metallurgy. May I point out, in this connection, that in practical metallurgy the word "sintering" has been applied to a bonding process in the preparation of ores and flue dust for fur-nacing. It would be unfortunate if in the area of powdered metallurgy we should establish a definition that is essentially different in meaning. F. N. RHINES*—I think that I can answer the question by saying that I see no essential difference between the use of the term "sintering" in extractive metallurgy and in powder metallurgy; physically the same things are going on. I admit sintering is used for different end purposes in the two cases. When we resort to the sintering of lead ore mixture we are doing so to obtain a chemically reactive, loose texture of some rigidity. This is only a difference in use. After all, in powder metallurgy we sometimes deliberately produce a very porous material which has just a little strength, just as in the case of sinter cake. P. DUWEZ (authors' reply)—We agree that it would be helpful to have well-established definitions of such terms as "sintering." Since the question has now been raised, the time might be appropriate for its consideration by some suitable committee of one or more of the metallurgical societies. In answer to Dr. Shaler's first question, no getter nor hydrogen leak was used in our vacuum experiments, except insofar as the guard disks (used to reduce friction between specimens and trays) may have acted as getters. Dr. Shaler's statement that extrapolation of the curves of Fig 1 and 2 does not lead to zero densification at zero time apparently overlooks the logarithmic

Jan 1, 1950

By NEWTON B. KNOX

IN Bolivia, mining is still the principal economic activity, as it was before and during the Spanish Colonial period. Tin, tungsten, antimony, copper, lead, zinc, gold, silver, sulphur, and a little bismuth are produced. The Andes mountains are divided into two main ranges in Bolivia; the Western range marks the border with Chile and the Eastern range forms the backbone of the country; in the North it drops rather abruptly eastward, to the plains of the Beni, whereas in the South it splits and is separated from the Chaco flatlands by a series of folded mountain ranges. In general the mineral deposits are found within the Eastern range or in the hills that rise from the high plateau between the ranges - really parts of the Eastern range partly submerged by recent sediments. The mineral belt is thus over 500 miles long and about 100 miles wide and includes most of the principal centers of population and the most important means of communication. The region is mountainous and the roads are bad; furthermore labor is a serious problem, for the land is poor and the agricultural population is never far from hunger. The floating supply of miners is limited and soon exhausted in any emergency like the present.

Jan 1, 1945

By J. A. Herbst, D. W. Fuerstenau

This paper examines the zero order production phenomenon in the context of the size discretized batch grinding model. A restrictive interrelationship between the selection and breakage parameters of the model, which is mathematically sufficient to ensure zero order behavior, is delineated. Based on this interrelationship, a scheme is developed for predicting the values of the selection and breakage parameters for all size fractions from a minimum of experimental data. To test this scheme, dolomite was ground in a laboratory batch ball mill. Successful simulation of the comminution behavior of this system was achieved using the batch grinding model with the parameter values obtained from the proposed scheme. Historically, a preponderance of comminution research has centered on attempts to relate breakage energy to the performance of comminution machines. Concomitantly, grinding data were interpreted almost exclusively in terms of inherently empirical energy-size reduction relationships1-3 or "laws of comminution"4- 6 which were based on highly oversimplified descriptions of the fracture process. In some instances, these relationships provide a crude basis for the correlation of experimental data, but, invariably, this approach is inadequate for meaningful process simulation. The control and optimum design of comminution circuits require a mathematical model capable of depicting the size reduction behavior of every size fraction for grinding conditions of technological importance. Energy-size relationships do not provide this detailed information. For example, an energy-size analysis for batch ball-milled dolomite has recently been completed in the authors' laboratories.7 This analysis provided a satisfactory correlation between the hypothetical size modulus, which characterizes only the finer portion of the size distribution, and the input energy. However, this relation did not constitute an adequate description of the complete system. In general, one of two distinct viewpoints toward simulation has been adopted in recent comminution research. The first approach focuses on the fracture of single mineral specimens, with the essential aim of representing the over-all process in terms of the breakage characteristics of individual particles and the characteristics of the stress field which the particles experience within the particular size reduction device. As illustrated by Harris's review,' the actual incorporation of single-specimen fracture information into a description of the behavior of a multiparticle comminution system has seldom been attempted. The only model to accomplish this incorporation was the one developed by Schönert.8 The Schonert model treats single-passage grinding machines in terms of a distribution of effective loads acting on a particle, a distribution of required particle breakage energies, and the breakage product distribution. However, the use of single-particle fracture behavior to derive models of the size reduction process is at present limited to machines in which the particle residence time is approximately equal to the time required to apply stress. As a result, Schönert's analysis cannot be used to advantage to simulate the complex environment which prevails within a tumbling mill. For multiple-passage systems a second approach to the description of comminution processes has been more fruitful. This approach entails the formulation of a mathematical model which is phenomenological in nature in that it lumps together the entire spectrum of stress-application events which prevail in a system under a given set of operating conditions. The appropriately defined average of these individual events is then considered to characterize the over-all breakage properties of the device. Thus, to analyze the performance of a tumbling mill, the manner in which the particles of a particular size (or size fraction) are stressed need not be distinguished. Instead, a single parameter is assumed to represent the resistance of that size to fracture, given the average grinding environment which exists in the mill. The isolation of such a parameter and a related set of quantities, which constitute the breakage product size distribution for the average event in this size fraction, allows the formulation of physically meaningful descriptive equations capable of yielding precise and detailed information for simulation.

Jan 1, 1969

By L. J. Murphy

The production of crude oil in the United States is exceeding consumption by one-quarter million barrels per day and, with the possibilities of West Texas, this condition of overproduction, unless controlled, is likely to continue for some time. The resulting low price of oil has caused the operator to observe closely his lease operating costs. The installation of more efficient and reliable machinery has followed and it can well be said that the art of producing oil is on the threshold of a new era. In this advancement electricity has played a leading part. This paper covers only the problem of electricity as applied to lease operation and does not consider other phases of the industry, such as drilling and pipe-line pumping, in which electric power has been utilized economically. In considering electrification of pumping wells, the first question the operator asks is whether or not his costs will be reduced and the second question is whether or not the production will be increased. The third question, although in effect it is closely allied to the first, is the cost of power. The last question can be answered only after a thorough analysis of operating conditions and a study of the power rates prevailing in the particular field under consideration. Within the past few years, the power companies have realized the desirability of a steady 24-hr, pumping load, have made their rates for oil-field service particularly attractive, and in general have shown splendid cooperation in assisting the oil companies in the satisfactory application of electric power to their leases. When everything is taken into consideration, the first cost is practically the same for electric drive as for gas engines when pumping on the beam with individual motors. This cost, at prevailing prices, should aver-age approximately $2200 to $2400 per installation when using 15 to 35-hp., two-speed pumping equipment, including motor and control, countershaft, motor house, belt, installation charges, and a prorated portion of the cost of transmission lines and transformers for serving a number of wells. Since there is practically no difference in the cost of the two installations, it is evident that electricity, to justify its consideration, must have a lower operating cost or produce more oil.

Jan 1, 1928

By C. V. Millikan

New developments in air-gas lift practices in the Mid-Continent area since our Pall meeting in Fort Worth have done much to increase the efficiency of installations, and thus bring within economic limit of air-gas lift many wells which could not have been flowed profitably before. After the gas-lift had so thoroughly demonstrated its value in the Seminole field, its use spread to other areas and many installations were made of which the economy could be questioned. In the Seminole area, when production began to decline it was necessary either to increase the efficiency of the air or gas-lift or to put the wells on the pump, and pumping was not a process of lifting oil to which any operator looked forward with confidence. These conditions have resulted in the development of many practices which increase the efficiency and permit wells to be flowed with air or gas which earlier could not have been flowed economically, and wells which have been flowing to continue to a lower rate of production. The practices which have come into more common usage in the Mid-Continent area recently are mostly revivals of and improvements on practices which have been known in air-lift work for several years. Many arc peculiar to the individual well on which they are used. Intermittent Flowing Some interesting results are being obtained in Seminole and other districts by intermittent injection of gas. Gas is introduced during per-iods iods of 3 to 5 min. at a rate considerably over that necessary to acquire the production at a steady rate of injection, and is then cut off for a period of 3 to 15 min. Two to five wells are run from the same group of conlpressors. The total volume of gas required is sometimes reduced as much as one-third of that required when it is introduced at a constant rate, without changing the amount of oil production. The maximum pressure required is usually higher, but the average equal to or lower than that required for constant rate of flow. The effect on the wells is usually an irregular rate of flowing which may cause inconvenience where recycling is practiced. It would seem that this increase in efficiency is due to less slippage when the gas is introduced intermittently than when it is intro-

Jan 1, 1928

By R. I. Jaffee, J. W. Roberts, D. N. Williams

DISPERSION hardening as an alloying process has aroused increasing interest in the past few years. This alloying procedure, in which an insoluble phase is dispersed randomly through a metal or alloy, is believed to be especially suited for the attainment of creep strength at elevated temperatures since the dispersed phase is metallurgically stable. Another advantage is that the physical properties of the matrix phase, such as electrical conductivity, remain relatively unaffected by alloying. These two characteristics resulted in interest in the applicability of dispersion hardening to copper and copper alloys. A study of copper alloys prepared by powder metallurgy methods has shown some strengthening from oxide dispersions.' However, powder metallurgy processing would not be economical for large scale production of dispersion hardened copper-base alloys. Therefore, the research described in this article was initiated to examine methods of forming dispersion alloys which would not require powder metallurgy processing. If powder metallurgy processing is to be avoided, a method must be found by which the dispersion material can be introduced into and dispersed through the melt before casting. When the dispersed phase is an oxide or similar nonmetallic, it is extremely difficult to form a satisfactory liquid: solid dispersion since successful mixing requires that the melt wet the dispersed phase. It is almost impossible to force a nonwetted particle beneath the melt surface. This difficulty can be avoided, however, if the oxide particles are produced in molten copper by reaction within the melt. The problem would then reduce to maintaining randomness until solidification. Four procedures were considered for producing an oxide particle within molten copper by reaction. In all cases, the intent was to react oxygen (0) with a reactive metal (X) to form an oxide (XO) within the copper melt. These reactions were as follows: 1) (Cu-X), + (O)g (Cu)1 + (XO)S [1] 2) (Cu-X)1 + (Cu2O)s (Cu)x + (XO)S [2] 3) (Cu-OK)1 + (Cu-X)1 (Cu)1+(XO)9 [3] 4) (Cu-OK)1 +(X)s (Cu)1 +(XO)s [4] The reactions were carried out in an 8-lb melt of 99.98 pct Cu maintained in the vicinity of 2200oF by induction heating. Where possible the amount of the reactants was controlled to give 1 to 5 vol pct oxide. Mechanical stirring during the reaction period was used to minimize agglomeration of the reaction product. The presence of a reaction product was determined metallographically by study of an ingot cast from the melt at the end of the reaction period. Reaction [I] was studied by dissolving aluminum in the melt followed by forcing oxygen through the melt. The melts became quite sluggish during the reaction period suggesting that A12O3 was formed. However, the reaction product rose out of the melt rapidly, possibly due to the flushing action of the oxygen stream, and little dispersed phase was formed. Reaction [2] was examined by dissolving aluminum, silicon, or nickel i; the melt and then adding Cu20 (melting point 2250F). This procedure was unsuccessful. Although Cu2O was easily stirred into cop-

Jan 1, 1961

By Carlos D. da Gama, Charles R. Nelson

Griffith’s theory of brittle fracture, as modified by McClintock and Walsh to fit rock behavior in cases of failure by compression, has been successfully applied in various fields of rock mechanics. Extension of the Griffith's criterion to rock blasting problems may also be more representative of rock behavior than the simple consideration of a criterion of failure based on the dynamic tensile strength of the material. If consideration is given to pre-existing cracks within rock structure, occurring not only because of the discontinuous properties of rocks, but also as a result of drilling operations that normally precede blasting, those cracks can be propagated under the action of the dynamic stresses (radial and tangential) induced by the passage of the wave emitted by the explosion. Conditions for initiation and propagation of pre-existing cracks are deduced in terms of rock properties and explosives performance. Influence of the different variables governing the phenomenon is discussed after considering an actual example. Results seem to be well correlated with experimental evidence of radial cracking observed in blasting with high explosives acting within hard rock.

Jan 1, 1971

Discussion of the paper of HENRY M. HONE and ARTHUR G. LEVY, presented at the New York meeting, February, 1915, and printed in Bulletin No. 99, March, 1915, pp. 587 to 600. J. E. STEAD, Middlesbrough, England (communication to the Secretary*).-As I have not personally studied the question of quenched and distorted manganese steels I cannot give any information of my own on the subject. The question as to whether certain indications in strained manganese steel are "slip bands" or "twins" might be settled, I think, by heat tinting-a method I have applied with success to certain meteorites and other alpha irons in which there were undoubted twins. After polishing and very slightly etching with picric acid in alcohol, and then "heat tinting," the colors assumed by the twinned strata and the adjoining metal are different. The reason of this, as I have proved repeatedly, is that different faces of the iron crystals are differently attacked by oxidizing and other reagents, and consequently some of the faces take temper oxidation tints more rapidly than others. This simple method enables one to determine with certainty whether the "twins" are actually, twins and differently oriented from the bed in which they are found. After correspondence with Dr. Howe, I think we both agree that Neumann lines should not be called "lines" but "bands" or "strata," preferably the latter term, as I have found that they are more or less continuous throughout the crystals, and it would be just as improper to call the edges of cementite plate by the term "lines" as to call stratified twins by the same term.

Jan 5, 1915

By R. E. Rettger

The area referred to in this paper is the southern part of the Permian Basin lying in southwest Texas and southeast New Mexico (Fig. I). Those fields lying along the northern rim of the basin; namely, the Panhandle fields, are not included. The fields within this area are

Jan 1, 1930

By Robert C. Freas, William H. Lane, David J. Krohn

Maysville, Kentucky, is the location of Dravo Lime company's new 9 070 mt(10,000 tons) per day limestone mine and 2 727 mt (3000 tons) per day calcination plant. This complex has been designed as a unit, and capitalizes on recent technological advances. Geologically the Dravo facility is.located on the eastern flank of the Cincinnati Arch, with the high calcium limestone being found at a depth of approximately 274 m (900 ft). A systems approach has been employed in designing and equipping the mine. This allows for maximum production while maintaining flexibility and versatility. All hydraulic drilling, large LHD equipment, and an extendable mine conveyor system are utilized in a five-part mining cycle. A modular concept modifies the room and pillar system to optimize ventilation. The limestone is calcined in three 5.18 x 61.87 m (17 x 203 ft) KVS rotary kilns with a design capacity of 909 mt (1000 tons) per day of lime per kiln. The kilns are coal fired and equipped with preheaters. Lime storage is provided by three 57 m (186 ft) high concrete silos with a combined capacity of 40 909 mt.

Jan 1, 1976

By Luther W. Bahney

Jan 1, 1912

By M. N. Nabighian, J. R. Odekirk, D. M. Hausen

Preliminary investigations based on the concept of cross-power indicate that quantitative volume percentages of minerals, including quartz, orthoclase, plagioclase, fluorite, and chalcopyrite can be obtained by X-ray diffraction analysis. Pulverized samples are scanned from 4° to 65°, 2e, using a Norelco diffractometer, with the output recorded on a punched tape at 40 intervals per degree, 29. Errors from crystal orientation are minimized by (1) gridded surface packing, (2) sample spinning, and (3) quantitative measurement of all major diffraction peaks. Computer programming enables rapid quantitative evaluation of X-ray diffraction data. Results to date indicate that most minerals analyses can be performed within an accuracy of ±2%. Metallurgical applications include analysis of various flotation concentrates and tailings.

Jan 1, 1973

By Paul D. Merica

Jan 1, 1937

By H. P. Greenwald

Those interested in the early developments and experiments, both in the United States and abroad, that led to modern rock dusting, will find an excellent summary in a paper by George S. Rice,13 published in 1914. The period from 1914 to 1924 was one of intensive experiment on coal-dust explosions in the United States; abroad, war activities and rehabilitation stopped this work over a large part of that decade. American findings were published by the Bureau of Mines, particularly in Bulletins 167 and 268. It is convenient to consider that in the United States rock dusting to prevent coal-dust explosions in mines was initiated in 1924 with the publication of tentative specifications.17 This was followed in 1925 by an investigation of methods and costs12 and approval by the American Engineering Standards Committee of a Recommended American Prac-tice.18 Approximately 13 years have elapsed since this approval, and inasmuch as changes in rock-dusting practice in the United States have been evolutionary, it is necessary to consider this entire period as "recent" in some phases of the work. There have been no official changes in the Recommended American Practice since its approval. This paper reviews as briefly as possible knowledge acquired since the issue of the earlier papers mentioned, through experience in mines and experiments conducted by different organizations engaged in the promotion of mine safety. Size of Rock Dust The Recommended American Practice states that the dust shall be 100 per cent minus 20-mesh and 50 or more per cent minus 200-mesh. Results of large-scale tests on the relative effectiveness of rock dust of different sizes were published by the Bureau of Mines15 in 1933 and are reproduced here as Fig. 1. The limiting curve of this figure shows that

Jan 1, 1940

By H. P. Greenwald

Those interested in the early developments and experiments, both in the United States and abroad, that led to modern rock dusting, will find an excellent summary in a paper by George S. Rice,13 published in 1914. The period from 1914 to 1924 was one of intensive experiment on coal-dust explosions in the United States; abroad, war activities and rehabilitation stopped this work over a large part of that decade. American findings were published by the Bureau of Mines, particularly in Bulletins 167 and 268. It is convenient to consider that in the United States rock dusting to prevent coal-dust explosions in mines was initiated in 1924 with the publication of tentative specifications.17 This was followed in 1925 by an investigation of methods and costs12 and approval by the American Engineering Standards Committee of a Recommended American Prac-tice.18 Approximately 13 years have elapsed since this approval, and inasmuch as changes in rock-dusting practice in the United States have been evolutionary, it is necessary to consider this entire period as "recent" in some phases of the work. There have been no official changes in the Recommended American Practice since its approval. This paper reviews as briefly as possible knowledge acquired since the issue of the earlier papers mentioned, through experience in mines and experiments conducted by different organizations engaged in the promotion of mine safety. Size of Rock Dust The Recommended American Practice states that the dust shall be 100 per cent minus 20-mesh and 50 or more per cent minus 200-mesh. Results of large-scale tests on the relative effectiveness of rock dust of different sizes were published by the Bureau of Mines15 in 1933 and are reproduced here as Fig. 1. The limiting curve of this figure shows that

Jan 1, 1940

By Edward C. J. Urban

ESSENTIAL requirements for ensuring safe working atmospheres in underground metal mines are planned systems of ventilation and provision for effective distribution of sufficient volumes of air by auxiliary equipment. Investigators1 in the past have suggested that quantities of air supply ranging from 300 to 800 cu. ft. of air per minute per man underground are necessary, to establish adequate general ventilation. These fundamentals are just as important as the use of water in dust suppression, control of blasting, the use of personal protective equipment, frequent inspection of working areas and education of employees in good dust-prevention practice. During the past two years the necessity for direct control of the underground working environment has become particularly urgent. The increase in production rate, with two-shift and three-shift operation replacing the single shift, has complicated the problem of dealing with excessive concentrations of blasting fumes and gases, carbon dioxide and monoxide, heat and oxygen deficiency. Although previous industrial hygiene programs had given consideration to these factors, they were generally regarded by mine operators as secondary to the control of dust hazards. Today, blasting smoke in a mining area means delayed production because the miner cannot return to his work place after a short interval. Smoke on the haulage level means a safety hazard and exposure of the underground employees to excessive concentrations of atmospheric contaminants. Exposure to the moderately excessive concentrations of carbon dioxide and monoxide found in metal mines has caused physiological disturbances and a decreased capacity for work; deficiency of oxygen, in some cases to as low as 3 per cent, has resulted in fatalities. During the past 10 years the Saranac Laboratory2 has been associated with the iron mines in the Upper Peninsula of Michigan and Wisconsin in developing and maintaining an industrial hygiene and silicosis-prevention program. At present, about 35 underground iron-ore mines are operated full time in this area. With two exceptions, all of them are ventilated by main fan installations installed either on surface or underground. ,The types of mining used in these mines may be classified either as sublevel cave, radial top slice or sublevel stope, and the procedures commonly employed in the ventilation of these three types are described in Figs. 1 and 2. A number of different methods of mine ventilation had been in use in this area when the study was started. Natural ventilation had proved unsatisfactory. The wide variation between low air volumes during the summer months and higher volumes during winter led to unpredictable conditions that were difficult to control. In the majority of the mines two separate shafts or openings to surface are utilized in

Jan 1, 1943

By D. Harper

The National Pocahontas Mine in Wyoming County, WV, has been developed in the Pocahontas No. 3 coal. During 14 months of ventilation surveys, the locations of large rockfalls, many in areas infrequently visited by mine personnel, were mapped. Several dozen rockfalls were later studied in detail. Kettlebottoms, rider seams, root-penetrated roof strata, slicken sides, and shales that spall are common in areas with a high density of rockfalls. Large-scale crossbedding and micaceous and carbonaceous films in sandstones are less common. Density of rockfalls in any area is related to the time elapsed since mining, thickness of overburden, and orientation of entries and panels. Some linear features overlie areas where rockfalls are densest. Most rockfalls occur during summer.

Jan 1, 1983

By Klaus Schwerdtfeger, Hans-Jürgen Engell

Activities of silicon in Ni-Si melts have beelz determined in the temperature range 1480° to 1610°C from electromotive-force measurements involving the cells The data obtained are used to derive the activities of nickel and the integal free energies of mixing. Entropies of mixing are calculated from the free energies of mixing as obtained in the present study and the heats of mixing as available in the literature. ACTIVITIES in Fe-Si and Co-Si melts have been determined recently by the authors&apos; using galvanic cells consisting of alloy, an oxygen electrode, and an oxide melt as electrolyte. The present paper deals with activities in Ni-Si melts as measured with the same technique. A schematic diagram of the cell is shown in Fig. 1. The alloy and the electrolyte consisting of CaO and SiO2 are contained together in a silica-glass crucible. During the experiment the silica glass crystallizes to cristobalite on the surface of the crucible. Nickel contents of the electrolyte are very small (<0.1 pct as checked with chemical analysis), because of the noble character of nickel in comparison with silicon. A tapered silica tube is connected to the crucible through which a platinum or molybdenum wire is inserted, as shown in Fig. 1. A platinum tube reaches the surface of the CaO-SiO2 electrolyte from above. The platinum tube is provided with four holes on its side, through which oxygen of 1 atm pressure is blown over the electrolyte. The cell reaction is given by the equation Si(metal) + O2(gas) = SiO2(electrolyte) [3] and the galvanic electromotive force of the cell is given by the formula

Jan 1, 1965