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By Edward Wisser

THE Pachuca silver district, situated about 100 kilometers northeast of Mexico City (Fig. 1), covers roughly the southeastern half of the Sierra de Pachuca. The latter is a mountain range with northwest trend, and forms a part of the northeastern rim of the topographic basin known FIG. 1.-LOCATION OF PACHUCA DISTRICT AND OTHER MINING CAMPS. as the Valley of Mexico. The length of the Sierra proper is about 50 km., its greatest width about 9 km., and it rises to a maximum of 600 meters above the general level of the basin floor. The Pachuca district consists of two contiguous subdistricts, the Pachuca area and the Real del Monte area. The center of the Real del

Jan 1, 1936

By Thomas Egleston

The copper-bearing rocks of Lake Superior are composed of a series of metamorphic rocks, comprised under the names of amygdaloid and conglomerate, in which the copper and silver found with them are pseudomorphs. These rocks, generally, have Well-defined walls which cause them to separate easily. Generally, the country rock is sterile, but it occasionally rises into the copper-bearing rock, and then carries copper. Usually, the amygdaloids carry copper, and the greenstones or melaphyres which encase them do not. There is a very generally received opinion that the copper in these beds occurs in shoots. This does not appear to be proved, though the opinion seems to have some foundation from the experience of the Calumet & Heela Mine, where a body of poor rock has been left, which, on the mine map, shows a general direction. The theory may be true of that individual mine, but too little work has been done in the other mines to draw any decided conclusion. The copper is very unequally disseminated in the rock, if any given piece be taken as an example, but, if the whole copper-bearing series be considered, its distribution is uniform. It may prove that there are certain directions in which the copper has been deposited more abundantly than in others, and these may be found to correspond with certain geological causes, but up to the present time the knowledge gained is not sufficient to warrant any general conclusion. These rocks are supplemented by a series of true fissure veins, of which there are several systems, making the amount of native copper very large. Unfortunately, except in the fissure veins, known as " mass-mines," the copper is so scattered through the rock, and is in such a fine state of division, that, although it is not always difficult to mine, it is always difficult to dress it sufficiently to make it pay. The metal is so unifornily distributed throngh these copper-bearing rocks that detached pieces, called " float," are found in digging on almost any land in the country. These pieces vary from very small fragments, weighing not more than a few ounces, up to many pounds. In one instance, in making an excavation for a cellar of a

Jan 1, 1879

By F. F. Aplan, D. W. Fuerstenau

This chapter presents modern concepts of the flotation of nonmetallic minerals. In particular, it is concerned with such minerals as metal oxides, silicates, sulfates, carbonates, and halides. It is not the purpose to duplicate the two excellent, recent treatises by Gaudin l and by Sutherland and ark,^ but rather to expand their correlations of data, particularly in view of recent, ex- citing new experiments which are shedding new light on the principles of non- metallic flotation. Outstanding success has been achieved over the past 50 years in separating one sulfide from another or from the gangue constituents using a minimal amount of reagents. In contrast to this, selective flotation in nonmetallic systems is often difficult in that one class of compounds alone, the carboxylic acids, may float nearly the entire array of nonmetallic minerals under the appropriate conditions. Moreover, while lime, cyanide, sodium sulfide, and copper sulfate constitute the principal modifiers used to obtain selectivity among the various sulfides, the nonmetallic mineral flotation engineer is con- fronted with a vast array of modifying reagents. In sulfide and native-metal flotation, a strong chemical adsorptive bond is generally formed between the mineral and sulfhydral collector. In fact, re- cent radio-tracer studies show that below monolayer coverage as much as 98% of added mercaptan is adsorbed on the surface of gold.? Contrasted to this, Bloecher's data indicate that for the quartz-amine system only about 60% of the collector is adsorbed.4 This greater residual concentration in the solution results from weaker forces of adsorption in the quartz-amine system. In the flotation of nonmetallic oxide minerals, collector adsorption results from rather weak physical forces, primarily electrostatic attraction and van der Waals attraction between hydrocarbon chains. In the flotation of salt-type minerals, carboxylic acids are adsorbed both by physical and chemical forces. It is a study of the effect of the electrical forces superimposed on the chemical adsorptive forces that contributes most toward understanding nonmetallic mineral flotation. The need for quantification of general rules for the flotation of nonmetallic minerals is so great that Taggart 5 with unmasked sarcasm suggested that after trying anionic and cationic collectors:

Jan 1, 1962

By Albert G. Zima

ACCORDING to recently published statistics, it is predicted that as much oil must be produced during the next 16 years as has been produced during the past 75, in order to satisfy the high rate of consumption of petroleum products. During 1934, over 17,000 oil wells were completed in the United States, and it is expected that over 20,000 additional wells will be drilled during the current year. Were it not for the remarkable progress made during recent years in the improvement of drilling technique and in the development of equipment used in the production phase of the oil industry, it is doubtful whether sufficient oil could be produced to meet present requirements. A few years ago, wells seldom were deeper than 3500 to 4000 ft., owing to the limitations of the drilling methods and equipment employed.. Today, 'however, through the application of scientific drilling methods and the adaptation of modern equipment and improved materials, many wells range from 6000 to 8000 ft. in depth, and a few recent completions exceed 10,000 feet. DRILL TOOLS Modern rotary drilling tools are the product of ingenious design and careful selection and adaptation of materials used in their construction. They must withstand terrific abrasion and, because of their compactness, must be designed to resist exceedingly high unit stresses. In bits, core drills and reamers, the bodies are made of either forged or cast alloy steels, heat-treated to develop a combination of high strength and toughness. To provide sufficient strength to the threaded portions and to protect the threads from distortion or damage, the box or pin sections of the tools are hardened to approximately 310 to 330 Brinell hardness

Jan 1, 1935

By Nathan C. Rockwood

LIME is a very general term applied to products of limestone, in popular treatises often incorrectly, including ground or pulverized limestone used in agriculture. When used without qualifying adjective, the term usually means burned or calcined limestone, or quicklime, or calcia. The corresponding calcined product of magnesite is magnesia. If the calcined rock is relatively pure calcium carbonate, the resulting lime is a "high-calcium" lime; if the rock is dolomite, or a combination of calcium and magnesium carbonates, the lime is a "dolomitic" or a "high- magnesium" lime. There are various grades in between, depending on the percentage of magnesium carbonate and other ingredients in the raw rock. For some industrial purposes only high-calcium limes are suitable; in other processing-as, for example, neutralizing acid wastes -the relative percentages of magnesium and calcium carbonates in the raw material are not important. Limestone is burned (roasted or calcined) in furnaces known as lime kilns by direct exposure to the hot gases and flames. When heated to incandescence, the carbon dioxide content of the rock is expelled, leaving calcium and magnesium oxides, according to the formula usually written: [ ] This thermal reaction is reversible, which requires that the lime be withdrawn from the "calcining zone" of the kiln about as fast as made. Pure calcium carbonate would lose 44 pct of its weight in the calcining process; dolomite, 48 pct. Generally, the lime will retain the approximate size and shape of the piece of rock from which it is made but some few limestones tend to break down into granules or dust. Hence lime (quicklime) comes from the kilns in lumps or granules and normally is packed in water- tight containers in these forms, or is pulverized after calcination.

Jan 1, 1949

By Gerald Edmunds

Although the phenomenon of season cracking is still imperfectly understood, there seems to be ample evidence that season cracks are propagated by the combined action of corrosion and a stress of either internal (residual) origin or external origin. The factors that influence season cracking may therefore be grouped according to corrosive media, nature of stress, and character of the material. Thus the important mass of evidence pointing to ammonia as the most frequently active corroding agent causing season - - cracking of brass has naturally led to the development of laboratory tests of a moderately accelerated character based upon ammonia together with auxiliary agents such as air, water vapor, and carbon dioxide as the corroding agent. Similarly, the knowledge that stress must be present has led to the use of externally applied and therefore accurately measurable stresses in laboratory testing. A companion paper(^)^ to the present one discusses the development of these test methods in our laboratories. The present paper discusses data bearing on factors concerning the nature of stress such as its magnitude and direction of application. It also deals extensively with the character of the brass, particularly in regard to the copper-zinc ratio and the structure as developed by mechanical work-

Jan 1, 1945

By Hans Lundberg

In order to comprehend the help and information that may be expected from electrical prospecting, it is necessary to have at least a general knowledge of the methods and principles involved in preparing and interpreting results obtained in the field. Electrical prospecting is rather complicated, both in theory and practice, and in order to make a brief description clear to the practical mining man it has been necessary to idealize and generalize the problems, at the risk of having such simplification criticized by the theoretical man. This simplification must not be misinterpreted as showing a lack of theoretical knowledge. For its operation, electrical prospecting mainly depends on the fact that most metallic ores conduct an electric current much more readily than barren rocks. If an electric current flows through a block of ground within which a body of chalcopyrite is enclosed in country rock of schist, the current will find less resistance to its passage through the chalcopyrite than through the schist, even though the passage through the latter be much shorter. This is because the longer path through the chalcopyrite offers less resistance, owing to the superior electrical conductivity of the chalcopyrite (Fig. 1). The good conductor, chalcopyrite, in the poor conductor, schist, thus attracts the current and deflects the normal flow far outside the conduct-

Jan 1, 1929

By Carl Allen

INTRODUCTION IN any discussion of mining one is repeatedly confronted with the difficulty of dealing with so many variable conditions. It is not an exact science and in the choice of a method each varying factor has a certain weight, which, in many cases, experience alone can determine. In mathematical terms, it is a function of many variables. A discussion of mining also loses much of its value unless, costs are considered, because the expectation of profit is the only excuse for carrying on mining at all. As conditions vary they cause fluctuations in cost and there are few operations to which a definite cost can be assigned. The character of the ore may make it difficult to drill, yet because of the ease with which it breaks the total cost of drilling and blasting may be low. In preparing this article the attempt has been, not to cover the whole field of mining, but to describe the different methods of stoping and mining which have distinct principles. In addition to this an effort has been made to show the advantage of dissecting the methods into their detailed operations and applying to these a mathematical study as an aid to the judgment in determining which is the best method to adopt, or in attempting to reduce the cost of a method already in use. Methods of mining include stoping, caving, and various methods of working large deposits which, in addition to the method of actually breaking the ore, require elaborate and definite plans of, development of the orebody. The ordinary methods of stoping are too familiar to all for any elaborate discussion, but it has seemed advisable to review the subject and give the principal advantages' and disadvantages of the different methods.

Jan 8, 1914

By W. H. Hoffman

During the autumn of 1891, several heavy blasts (each throwing down some 3000 tons of ore) were made on what is known as the Theall side of these mines. Immediately after one of these blasts, the writer found that at least one-third of the ore was largely impregnated with pyrites, and besides this, fully 15 per cent. of the entire blast was composed of irregular lumps of magnetic pyrites. This was a revelation wholly unexpected, as previous examinations by many experts had failed to disclose any such quantity of sulphury ore. Over the center of the Theall tunnel there suddenly appeared a perfect keystone, as it were, of pyrites, 3 feet wide at the arch of the tunnel, 13 feet ride at the top, and 20 feet high. This keystone pinched out in February, 1892; but in that month large blocks of pyrites were more plentiful on or near the western wall, and these deposits extended the entire height of the workings, some 43 feet. The second blast in November, in the face and over, and on each side of the tunnel, was far more surprising. The whole cross-section it exposed was thickly interspersed with layers of magnetic pyrites, ranging in thickness from 10 to 24 inches, and quite irregular in form, while all of the ore carried much more than the usual amount of sulphur in the non-magnetic pyrite. One hundred and fifty-five tons from a portion of this breast (western side), showed the following composition upon sampling and analysis: Per cent. Metallic iron,...45.080 Phosphorus,..........304 Sulphur,...........23.510 And the balance of the blast showed: Per cent. Metallic iron,.....• 33.210 Phosphorus,...........349 Sulphur,.......... 6.680 vol. xxI.-33

Jan 1, 1893

By Harold Cook

THE purpose of this paper is to state briefly the inspection requirements of the Bureau of Ordnance, the specifications governing the inspection, and the physical and chemical properties of the steel used in the construction of ordnance for our Navy. It would be of interest to evoke discussion on points in these specifications which do not tend to insure the production of the very best material for the purpose intended. In other words, what requirements of our specifications are useless and also in what manner are our specifications deficient? It might be well at the, start to answer the first criticism of this paper which will probably be made, and that is that the title does not agree with the subject matter. Considering metallographic work as covering only the macroscopic and microscopic examination of metals, this paper will have gone beyond the subject; but it is believed that a broader definition of metallography is that it is the study of the relation of the internal structure of metals and alloys to their composition and to their physical and- other properties. The internal structure of steel is dependent on its physical and its chemical properties. These physical properties are dependent on the chemical composition and the mechanical and thermal treatment of the steel. So it seems that this subtitle would not be entirely necessary and that the title "Metallography of Steel for Ordnance Purposes" would cover a study, not only of what we can learn of macroscopic and microscopic examination, but broadly of the whole subject of the specifications, the fulfillment of the requirements of which produce the structural conditions revealed by macroscopic and microscopic examination. .

Jan 2, 1916

By R. B. Hoy, Stanley J. LeFond, K. Reckling

World production of natural diamonds prob¬ably exceeds 50,000,000 carats a year. The Republic of Zaire is the leading producer, with an output which is primarily industrial rather than gem grade. The USSR ranks second, and the Republic of South Africa third. Diamonds are also mined in South-West Africa, Angola, Ghana, Sierra Leone, and other African coun¬tries. In the western hemisphere, Brazil and Venezuela are the principal producers (Fig. 1). A very small output of diamonds is mined today in India, which was the first source of commercial production. In the U.S., efforts at commercial diamond mining have been con¬fined to a small area near Murfreesboro, Ark. The first diamond was found in a kimberlite pipe there in 1906. Small-scale trial mining has not, however, proved economical. Since diamonds were first discovered over 2000 years ago, only about 130 tons have been mined. In order to obtain 1 g (5 carats) of diamonds, it is necessary to remove and process approximately 25 tons of rock. Recovering this small percentage involves a combination of highly developed techniques in mining, quarrying, and earth-moving, and extremely sophisticated recovery processes. End Uses Diamonds are used for two unrelated end uses; gem diamonds are jewels of great beauty while industrial diamonds are essential ma¬terials of modern industry. Although imitation stones are substituted for the gem diamond, none of these matches its properties sufficiently well to offer real competition. Synthetic indus¬trial diamonds are now of a quality that per¬mits wide substitution in the fine-grained sizes. Gem Diamonds A diamond is a natural prism. It has the ability to bounce light rays (reflection), to bend them (refraction), and to break them into all colors of the rainbow (dispersion). This ability to "modify" light gives the diamond three characteristics for providing beauty. First is brilliance, the reflection of light back to the eye. Second is fire, dispersion of light into the colors of the spectrum. Third is scintillation, the "twinkling" that occurs when the diamond is moved (Bauer, 1969). The skill of the diamond cutter is required to unlock the brilliant, fiery beauty of a gem dia¬mond (Fisher, 1966). Diamond-cutting skills have gradually developed over the centuries. The first cutters, in India, learned how to grind one rough diamond against another to remove their "skins" and to give them various shapes. This revealed some fire and beauty, but little compared to that of the diamonds that are cut today. About 1475, a Flemish cutter named Van Gerquem discovered that diamond dust on an iron wheel would polish facets on a diamond to provide more brilliance and fire. Cutters continued to experiment with facets, and shortly before 1700 a Venetian cutter named Peruzzi developed the 58-facet brilliant cut. With the development of the science of optics, cutters have learned more about the behavior of light within the diamond. Early in the 20th century, they learned how to angle Peruzzi's

Jan 1, 1975

By Gregory M. Dexter

Recent litigation in Pennsylvania between three coal-mining companies and a private water company resulted in the payment by the coal companies of the equivalent of about $500,000 to buy a new water supply to replace that which had been damaged by acid drainage from strip mining. An investigation of the relevant facts indicates that the water could have been treated by spending about $40,000 on equipment and $15,000 yearly for chemicals, labor, and power until the contarnination could be reduced about 80 pct. The water company's supply, furthermore, had deteriorated largely by reason of dry weather before stripping was begun by the coal companies. Payment to the water company should not have exceeded $300,000 and could have been as low as $100,000. Strip mining of coal is common in Pennsylvania. The most important objection to it in Pennsylvania is generally acid pollution of runoff water. An outline of the methods, therefore, that could be used to reduce such pollution, to compare acid-contaminated waters. and to treat such waters to make them satisfactory for public and industrial use is worth-while. The watershed of the West Penn Water Co. covers about 4.5 square miles, 20 miles west of Pittsburgh, and has two 90,000,000 gal reservoirs supplying about 1,300,000 gal daily for public and industrial use of which 450,000 gal daily are for two railroads. The pollution arises from weathered derivatives of typical'" Coal Measures"' rocks, the principal source being pyrite (and marcasite) in Pittsburgh and Rooster coals. Springs and seeps on hillsides issue from sandstone and limestone formations intersecting shale or clay land surfaces, or from perched water tables. The two reservoirs create an artificial permanent water table. Soap-hardness tests on three seepage samples taken in a dry summer ranged from 150 to 500 ppm. Water sampled came from aquifers above Pittsburgh and Rooster coals, obviating the possibility of contact with pyrite-containing coal. Since acid contamination of mine waters is the result of chemical reactions of oxygen and water with pyrite, it will be reduced by the exclusion of either air or water. The Sunnyhill Coal Co. has applied this principle in its "contouring" method of strip mining by burying contaminated coal-waste material under a compact, smoothed-up surface of top-soil, gravel, clay, and sand at a cost

Jan 1, 1950

By C. H. Fulton

Page Introduction........................... 280 Distillation Products from Reduction of Zinc Ore........... 281 Preliminary Investigations..................... 290 Equilibrium of Reaction Zn + CO2 + ZnO + CO in Temperature Range of Condensation........................ 293 Requisites for Successful Condensation................ 299 Discussion............................ 300 Introduction The study of the condensation of zinc from its vapor was undertaken to shed light on certain problems encountered in large-scale electric zine-furnace work. recently conducted. It is a matter of common knowledge that one of the disadvantages of the arc type, electric zinc furnace, is the production of a large amount of blue powder and proportionately little liquid spelter, for, as stated by Stansfield,l "A notable defect in the electric smelting of zinc ores is the difficulty experienced in obtaining the distilled zinc in the liquid state; ...... when zinc ores are smelted electrically, very little liquid metal is commonly obtained, nearly all of the zinc being in the state of powder." This difficulty was not encountered in the electric furnace used12 the main difficulty being the destruction of the fire-brick lining of the large condenser, in certain parts, and the formation of .some oxide and dross coatings on the condensing surfaces. The reason for these difficulties could readily be explained by the infiltration of air whenever the condenser was changed from one retort base to the other, the zinc absorbed in the fire-brick forming oxide and causing rupture by its expending volume. Two facts, however, tended to disprove this theory for the rupture of the fire-brick lining: first, the large distilling retort, lined with fire-brick, which was shifted from charge to charge on alternate bases at temperatures between 1200 and 1300 C., fully exposed to the air, showed no signs of disintegration whatever; second, marked disintegration in the condenser occurred .only in places that were at tempera-

Jan 1, 1919

By J. J. Kanter

There has been much research and commercial development in recent years in the use of chromium and nickel in steels of various types, including those intended for high-temperature service. By "high-temperature steels" are meant those specifically designed for service at elevated temperatures in steam plants, oil refineries and other industries where high-temperature operations are conducted. This paper is devoted to some preliminary data on the effect of silicon on certain of the most popular chromium-molybdenum steels now being used in quantity by the refining industry and includes a short statement on the influence of copper in steels intended for high-temperature service. Uses of Silicon Next to oxygen, silicon is the most widely distributed and abundant of the earth's substances. Although classed as a nonmetal, it is highly important in the metallurgy of all steels, having been used for years as an efficient and economical degasifier and deoxidizer. Silicon is added to various steels in the form of ferrosilicon, generally at the end of the heat so as to avoid oxidation losses. With acid steels it is added in the furnace (also in the ladle) and generally with basic steels is added in the ladle, so as to avoid reaction with the basic lining through high-temperature acidic reaction with silica, which may be formed by oxidation of the silicon alloy. Several grades of ferrosilicon are available, containing, respectively, 15, 50, 75 and 90 per cent Si. By far the largest tonnage produced is the 50 per cent grade although the 75 and 90 per cent ferro-silicons are used as ladle and furnace additions in the manufacture of steels of high silicon content. The introduction of silicon into steel as an alloying element is well known in connection with high-yield-strength constructional steel for bridges, ships, car construction, etc., and it is also well known as an alloy-

Jan 1, 1938

By J. J. Kanter

There has been much research and commercial development in recent years in the use of chromium and nickel in steels of various types, including those intended for high-temperature service. By "high-temperature steels" are meant those specifically designed for service at elevated temperatures in steam plants, oil refineries and other industries where high-temperature operations are conducted. This paper is devoted to some preliminary data on the effect of silicon on certain of the most popular chromium-molybdenum steels now being used in quantity by the refining industry and includes a short statement on the influence of copper in steels intended for high-temperature service. Uses of Silicon Next to oxygen, silicon is the most widely distributed and abundant of the earth's substances. Although classed as a nonmetal, it is highly important in the metallurgy of all steels, having been used for years as an efficient and economical degasifier and deoxidizer. Silicon is added to various steels in the form of ferrosilicon, generally at the end of the heat so as to avoid oxidation losses. With acid steels it is added in the furnace (also in the ladle) and generally with basic steels is added in the ladle, so as to avoid reaction with the basic lining through high-temperature acidic reaction with silica, which may be formed by oxidation of the silicon alloy. Several grades of ferrosilicon are available, containing, respectively, 15, 50, 75 and 90 per cent Si. By far the largest tonnage produced is the 50 per cent grade although the 75 and 90 per cent ferro-silicons are used as ladle and furnace additions in the manufacture of steels of high silicon content. The introduction of silicon into steel as an alloying element is well known in connection with high-yield-strength constructional steel for bridges, ships, car construction, etc., and it is also well known as an alloy-

Jan 1, 1938

By Max Mason

IN 1923 a Western mining company was experimenting with the device of an inventor designed to locate buried ores by radio. Because the progress was slow and the results were confusing, the company began to doubt the usefulness of the method and invited me to review the whole question of the application of physics to ore detection. I was fortunate in securing the cooperation of several physicists who had worked with me during the war on the problem of submarine detection. This group has been increased and has been studying the problem of physical exploration for ores since that time. It was evident that the problem is a big one, with many angles of approach. Its general features may be set down, in rough outline, as follows: The soils, rocks and ores hidden beneath the surface differ, one from another in many respects. These differences may be made to furnish a clew for the physicists working from the surface. To bring these differences into action the physicist creates some kind of an effect, which penetrates into the ground and is distorted and, reflected when it meets boundaries between different sorts of underground structure. In other words, he sends a message down, and the rocks and ore send back signals in, reply. In picturing this process, we should not regard the ground as dense and impenetrable. The kind of messages used pass through the earth about as readily as a sound wave travels the air. If, then, the fundamental procedure is to shout down questions in the hope that an orebody will hear and answer back to us, it is clear that a large part of the expert's study must relate to the kind of questions best suited to the temperament and intelligence of orebodies. It will be easier for the ore to, reply to some of our questions than to others, and it is for us to find the right questions. In certain cases, we are-spared the necessity of using a messenger, because nature has already provided one. For example, we already have a terrestrial magnetic field which auto-matically and continually conveys messages from underneath. We also have available the earth's gravitational field which furnishes us

Jan 1, 1927

By Edgar M. Dunn

Part I. Determination oF Gases in Smelter Flues. General considerations. Regular methods for carbon monoxide, oxygen, nitrogen, moisture. Sulphur oxides-—Methods of Lunge and Hempel tried, and either modified or discarded, with reasons therefor. Gravimetric method developed at Anaconda. Description of apparatus used. Brief notes on Richter and Hawley methods for the direct cietermination of sulphur trioxide. Carbon dioxide, with complete notes on same. Arsenic trioxide. Table of percentages of flue gas constituents found at a Western smelter. Some final notations as to the value of flue gas analysis, in connection with an intelligent log of furnace operations. Part II. Notes on the Determination oF Dust Losses at the Washoe Reduction Works, Anaconda, Mont. Discussion of problem, with description of flue system. Various places and methods for determinations of velocity. Instruments used. Procedure in making determinations for velocity. Soundings of cross-section for depths of dust. Calculation of velocities and areas. Daily volume of gas, and plant operations during tests. Place for dust determinations. Apparatus and methods of 'sampling. Results obtained, with table of daily amount of dust losses. Analysis of dusts for values, from various sampling stations. Complete analysis of composite sample of stack emanation. Last analysis totaled to show form in which present. Discussion of recovery as a commercial proposition. References on Pitot tube and calculations.

Jan 1, 1914

By H. H. Campbell

In the extending employment of open-hearth steel for structural purposes, it is a matter of prime importance that the test-piece shall represent with practical accuracy the characteristics of every portion of the heat from which it comes. In ordinary practice this homogeneity is assumed; but inasmuch as leading exponents of the revolving-hearth system have claimed that a reasonable uniformity could be obtained by their method alone, it may be pertinent to offer a few facts on the subject. The following heats made by the Pennsylvania Steel Company, for bridge-work, were tested by casting two four-inch ingots, one being taken during the first third and the other during the last third of the cast. Test-pieces obtained from these small ingots usually give results inferior to those obtained from larger sizes; but for purposes of cornparison they are equally conclusive. Many of the tests were made for experimental purposes within a few hours of the time of rolling, and before sufficient time had elapsed for the usual molecular redistribution necessary for the best results. All the tests were made on 3/4-inch rounds just as they left the rolls and without annealing; the results, therefore, are subject to the errors caused by variations in the diameter, and in the temperature at which the bar was finished. The tests from any one heat, however, were always nude as nearly as possible under the same conditions; and inasmuch as these data include the results of every heat so tested, and inasmuch as the errors could not by any chance always support any single theory, we may be certain that the unanimons testimony of the experiments indicates a valid conclusion.

Jan 1, 1886

By W. A. Anderson, F. N. Rhines, W. A. Johnson

THE rate of the high-temperature oxidation of pure copper has been measured repeatedly by numerous investigators. It appears to be generally agreed: (I) that at constant temperature, after the initial stages of oxidation have been passed and the scale has attained a substantial depth, the film thickness increases in proportion to the square root of the time of oxidation; and (2) that for any given period of oxidation the logarithm of the square of the film thickness is proportional to the reciprocal of the absolute temperature of oxidation.' These relationships are explained upon the basis that the rate of diffusion of copper to the external surface of the film is the controlling factor in establishing the rate of growth. Extensive studies have been devoted also to the mechanism and rates of the early stages of oxidation. There is thus available a reasonably well established theory of the oxidation of pure copper upon which to construct an explanation of the more complex oxidation of copper alloys. Few general principles have as yet emerged from the chaos of observations that have been reported in the field of the oxidation of alloys.2 It is evident, however, that the copper alloys may be divided into two main groups, whose oxidation characteristics are distinguish able. The first group, composed of the alloys with the noble metals, forms substantially pure copper oxide scales; the alloying element is concentrated within the residual metal, and sometimes particles of almost pure noble metal are found in the scales completely surrounded by copper oxide. In the second group, composed of the alloys of copper with the baser metals, the alloying element appears as an oxide in the scale, often in greater concentration than in the alloy itself and sometimes to the exclusion of copper oxide. The oxide scales of the latter class have been found to be made up of one, two, and sometimes more distinguishable layers of which the innermost is often metallic in character, composed of particles of the oxide of the alloying element embedded in essentially pure copper and known as the subscale or zone of internal oxidation. The need for a thorough quantitative study of these modes of oxidation is evident. Since it is apparent that several mechanisms must be cooperating to produce the complex oxide scales found on copper alloys, the analysis of the process into its several simple operations should prove instructive. Fortunately, it is possible experimentally to produce internal oxidation in the absence of an external scale; this permits the isolation and intensive study of one of the steps in the oxidation process. In the present research the rates of internal oxidation of an extensive series of dilute solid solution alloys of copper have been measured and a theory has been developed to predict the observed

Jan 1, 1941

By Samuel M. Cassidy, John A. Garcia

In some districts of the bituminous coal field the problem of constructing bulkheads to seal off water under pressure is becoming increasingly important. Recently this matter has been brought very much to the front by the loss of a large Illinois mine due to failure of a bulkhead that separated it from several old, flooded mines. As this great misfortune has provoked much inquiry about proper bulkhead design, it is felt that a description of the successful and extensive water-sealing practice at three mines that have different natural conditions will be of considerable interest to those connected with properties having a present or future water problem and to engineers that may have to design safe bulkheads of economical construction. These three mines are the Saxton and Dresser, near Terre Haute, Ind., and the Hegeler, near Danville, Ill. All three have water conditions that make it necessary to regularly seal off all worked-out sections of the mine, and there are considerably over a hundred bulkheads in each. AS far as the writers know, these three mines are the only ones in the bituminous coal fields of the United States with anything like so large a number of water seals and experience, although a number of other mines are known to have a few bulkheads. More detail will be included herein on the Saxton mine than on the others, as the writers are more familiar with it. General Mining System All three of the mines use the same general panel room-and-pillar system, which consists of rooms turned both ways off room entries and a solid block of coal left on all sides of the completed panel except on the cross-entry side, where a heavier pillar is pierced by two entries for haulage and air. On completion of the panel the two entries arc sealed and the panel is then isolated from the rest of the mine. Owing to water conditions, no pillars are pulled; recovery inside the panel barrier pillars is approximately 65 per cent.

Jan 1, 1938