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By Carl Zapffe

THE manganese ore reserves of Lake Superior, because of their location and nature, have recently achieved a marked degree of importance as compared with the world's manganese reserves. To appreciate fully the significance and the adequacy of this reserve, one should understand how such ores are used, where obtainable, the quantity used, possible avenues for increasing use or application, and the chemical and physical characteristics of the available ores. Only with that data at hand, is it possible to arrive at a convincing answer to the question whether the reserves of manganiferous iron ores are adequate to satisfy the annual demand of the presently known iron ores for the full life of the latter. That they should last is vital; and to ascertain whether they will last was the purpose of the present investigation, which marks the first attempt to study these Lakes Superior reserves. The Lake Superior region possesses and supplies the full assortment of iron ores needed for the conversion of ore into pig iron and steel ingots and castings. These ores are named bessemer; low-phosphorus and high-phosphorus non-bessemer, manganiferous and siliceous; and to include the term aluminiferous, would be in keeping with the most recent no men clature adopted by some dealers. About 35 or 40 years ago, perhaps less, most of the Lake Superior ore which is being used today was the material then considered either useless or too poor for immediate use; perhaps it was considered no more than a future reserve. An examination of the analyses of ores and the guarantees in the sales of those older times, convinces one that the opinions of those days must have been governed by only small differences in analyses. Some grades of ores used today in substantial amounts were used most sparingly only one or two decades ago. The relative quantities of the different ores used is ever changing; and, bit by bit, the metallurgy and the opinions are every changing and the prejudices against certain ores and practices decrease. This is unquestionably more pronounced for the manganiferous ores than for any other kind. If, when using the present data for manganiferous ores, we will only be

Jan 5, 1927

OPEN-HEARTH refractories are not merely an accessory to the furnace. They themselves ore the furnace, to all intents and purposes. The steel work of the main structure is merely a frame which helps to support the refractories; and the regenerators, a necessary part of the furnace system, consist almost entirely of refractories with very little supporting structure. Not only do refractories constitute the essential part of the furnace, but they also carry the liquid steel all the way to the point where it begins to solidify. On leaving the furnace the liquid passes through a refractory runner into a refractory-lined ladle, then through a refractory nozzle closed by a refractory stopper on the end of a refractory- protected rod. The liquid is sometimes sent through an additional refractory-lined tun-dish, a supplementary ladle, or a refractory runner for bottom pouring, until it finally enters the iron mold in which it solidifies. Even in the mold, refractory materials are sometimes used to provide a non-conducting "hot top." These materials, from ladle to hot top inclusive, are often referred to as the "pouring-pit refractories." CAUSES OF FAILURE Compared with the equipment used in most industrial processes the open-hearth furnace has a relatively short life. The most important quality of an open-hearth refractory, therefore, is its rate of failure. The discussion here of the individual refractory materials will therefore keep uppermost the question "Why, how, and where does it fail?" The principal causes of failure of open-hearth refractories are, in their order of importance: 1. Reaction with iron oxides. 2. Reaction with slag. 3. Flow and failure under load. 4. Melting. 5. Spallimg. 6. Mechanical breakage. Reaction with Iron Oxides and Slag. This is by far the most important cause of failure. Liquid iron oxide comes very near to being the

Jan 1, 1944

By R. C. McFarlane, T. D. Mueller, J. E. Walstrom

In evaluating uncertainty, experiments are usually performed repeatedly and then conclusions are drawn from the distribution of results. With the advent of high-speed electronic computers, it is possible to perform experiments using mathematical models constructed to simulate complex experiments or operations. Statistical methods are then applied to the results of the simulated experiments. This procedure forms the busis of this paper. Demonstrated is the need for properly accounting for uncertainty in petroleum engineering problems. How uncertainty affects solutions is evaluated in three example illustrations. The method used to evaluate uncertainty in petroleum engineering studies is the Monte Carlo simulation procedure.'-" INTRODUCTION The solution to most technical problems may be derived from interrelationships among several quantities called variables or parameters. There may be only a few variables or several hundred. Interrelationships among parameters may be explicit or implicit, well established or only approximate. Some variables that fully or partially depend on the magnitude of others are called dependent variables. Input variables for most practical problems are not precisely known; there is usually an uncertainty in their value. The degree of uncertainty may vary from one variable to another. Variables that are known accurately are called determinates.' For instance, the gravity of crude obtained from a particular pool may be known precisely, and therefore is a determinate. The degree of precision with which a quantity can be determined increases as data describing the pool are accumulated during the development of the field and the producing life of the pool. The uncertainty of a parameter may result from difficulty in directly and accurately measuring the quantity. This is particularly true of the physical reservoir parameters which, at best, can only be sampled at various points, and which are subject to errors caused by presence of the borehole and borehole fluid or by changes that occur during the transfer of rock and its fluids to laboratory temperature and pressure conditions. Uncertainty may also result in attempting to predict future parameter values. This type of uncertainty is particularly evident in investment analyses involving future costs, prices, sales volumes and product demand. Uncertainty in the solution to investment problems is often called risk, and its study is called risk analysis.' Uncertainty also enters into biological and sociological analyses in which indeterminate factors are often important due to limited control of the experimental material. It is customary, in evaluating uncertainty, to perform repeated experiments and to draw conclusions from the distribution of the results of these experiments. With the advent of the high-speed electronic computer, it is possible to construct mathematical models which simulate complex experiments or operations and to perform the experiments repeatedly, utilizing the models. Statistical methods are then applied to the results of the simulated experiments This method forms the basis of the investigation reported here. PROBABILITY DISTRIBUTIONS FOR VARIABLES The uncertainty in the value of a variable may be indicated by a probabilistic description accomplished by expressing the quantity by a probability distribution. Many recognized probability distributions can be used to describe physical quantities. Recent studies used various types of distributions to describe core analysis data.',' However, for the examples in this paper, the uniform and triangular distributions are believed to reasonably approximate the data used (Fig. 1). The uniform distribution confines the variable between an upper and a lower limit. The variable may lie anywhere between the two limits. This distribution is used when no one range of values for a variable is more probable than any other, but information or intuitive reasoning indicates the variable will lie somewhere between the chosen limits. The triangular distribution is used for a variable when more data are available to indicate a central tendency of distribution. This allows postulating a "most likely" value to the distribution and upper and lower limits. In this case, as for the uniform distribution, the variable is not expected to assume a value less than the lower limit or greater than the upper limit. However, with improved quality of data it can be postulated that the variable will tend to assume a value close to the most likely value, and that there will be a decreasing probability for values away from the most likely value. The area under either of these probability distributions is equal to unity since it is assumed that there is a 100 percent probability that the variable will lie somewhere under the curve. An ordinate erected at any particular value of the variable divides the area under the curve into two parts: the area to the left of the ordinate represents the probability that the value of the variable will be equal to or less than the value of the variable at the position of the ordinate, and vice versa. The probability is zero that the variable will have any specific deterministic value. If two ordinates are drawn for any two values of the variable, the probability that the variables will have a value lying between these ordinates is equal to the area under the curve lying between the ordinates.

By C. W. Mueller, P. H. Robinson

A technique was developed for depositing single -crystal films of silicon on single-crystal sapphire substrates via the pyrolytic decomposition of SiH4/H2 mixtures. Electron diffraction and X-ray Laue reflection examinations of these films revealed single-crystal patterns. These films were characterized by measuring conductivity type, thickness, resistivity, and Hall mobility. Chemical etching, dislocation staining, and electron-microscopy examination have indicated the presence of low-angle grain boundaries and microtwinning in the silicon films. The role of the sapphire substrate with respect to its quality, orientation, surface finish, and thermal and chemical treatment was investigated. Hall mobility as a function of sapphire orientation was measured. A mobility equal to 88 pct of bulk silicon mobility was attained. Insulated-gate field-effect transistors which have a transconductance of 4000 pmho at 6 ma were fabricated using these films. THE technology of the fabrication of microelectronic circuits with active and passive components directly on a single wafer of semiconductor material has attained a high degree of perfection during the last few years. One inherent difficulty with the single-wafer approach has been undesirable coupling between components arising from the common base material. Several techniques have been developed for minimizing this coupling and obtaining good electrical isolation between components; however, these result in extra capacitance being added to the circuit. The extraneous capacitance of the connecting leads, resistors, and capacitors degrade circuit performance and limit the high-frequency operation of these circuits. Recently there has been considerable interestl-3 in the deposition of silicon films upon insulating substrates. The use of silicon as the semiconductor allows the subsequent utilization of the large amount of technology which has been developed for silicon for the fabrication of good active components. A sapphire substrate supplies an excellent insulating material which at the same time gives a thermal-conductivity improvement of an order of magnitude over glass-type substrates. This paper will describe the results obtained for the deposition of single-crystal silicon layers upon single-crystal sapphire substrates as well as the characterization of these films. I) APPARATUS The 'system used for the growth of silicon films on sapphire substrates by means of the pyrolysis of SiH4/H2 mixtures is shown in Fig. 1. The all-quartz reaction chamber is water-cooled and includes a quartz optical-flat window for use in conjunction with a 5 kw, 2.5 Mc per sec constant-temperature controlled rf generator. The temperature sensor for the rf generator is a thermopile which is focused through the quartz optical flat onto the susceptor surface. With this system the rf generator will hold the temperature of the susceptor to about +0.3°C at 1200°C. The susceptor is supported on a quartz sled inclined to the gas flow to increase the uniformity of the deposition. The water jacket surrounding the reaction chamber is used to keep the quartz wall temperature low enough to limit the decomposition of the silane to the rf-heated susceptor which contains the sapphire substrates. This eliminates the reaction of silicon with the hot quartz to form SiO which deposits out on the apparatus walls, thus obscuring vision, and interferes with the optical measurements of the temperature as well as with the growth process itself. Provision is also made for "n"- and 'p"-type doping by using mixtures of either phosphine or diborane in hydrogen which are added to the silane during the growth process. The hydrogen used is the purest commercially available tank hydrogen further purified by use of a palladium diffuser. The susceptors which were used include 1) spectro-scopically pure graphite, 2) high-purity molybdenum, 3) high-resistivity silicon using a low-resistivity insert to facilitate coupling to the rf generator, 4) silicon carbide-coated graphite. The latter two susceptor materials produced silicon films on sapphire substrates with more reproducible resistivities. Prior to silicon deposition all connecting lines as well as the reaction chamber are thoroughly flushed with argon and then hydrogen. After the hydrogen flow is set, the growth temperature is adjusted to 11009 to 1150°C, and when thermal equilibrium is reached the silane flow is started. The flow rate of the hydrogen must be fast enough so that turbulent flow occurs in the size of reaction tube used, otherwise a streaked nonuniform silicon deposit occurs. After the deposition

Jan 1, 1967

By Courtenay DeKalb

Revision of the United States mining law is needed chiefly because of the following reasons: 1. The conceptions as to the characteristics of orebodies that were held at the time the statute of 1872 was enacted have since proved to be in many respects erroneous. 2. The operation of the existing law has been found to work unnecessary hardship upon many claimants to mineral land. 3. The existing statute fails in large degree to encourage development of mineral resources. 4. The existing law often produces conflict between placer and lode-claim rights, working unnecessary injustice to placer claimants. 5. The methods of establishing the rights of locators on United States mineral land are defective, and are not uniform throughout the States within which such lands exist. Law of the Apex The objections to the so-called "law of the apex" are so well known as to require no detailed statement. It is sufficient to point out that the apex rule was based upon the notion that ore deposits consisted of well-formed veins included between definite walls, like the slice of ham in a sandwich. The fact is that veins conforming to that simple type are rare. Irregularity is the rule, and the chief metal production of the United States comes from mass? which bear no resemblance to the tabular form of vein. Manifestly the law of the apex fails completely in such cases. Moreover, the tendency is constantly toward the exploitation of ores of lower grade than could formerly be worked, and such deposits exist mainly in the form of large irregular impregnated zones and masses, so that the future development of our mineral resources would be continuously embarrassed by shadowy claims to extra-lateral rights by the locators of so-called apexes.

Jan 1, 1915

By C. M. Young

THIS is an attempt to bring together some of the knowledge of the .coal-forming conditions obtaining during the Pennsylvanian period in the Western Interior Coal Province, to sketch briefly the present extent and character of the coals produced, and to show the beginning of cor-relation of beds over wide areas. Coals of later age than the Pennsyl-vanian are not included and, for reasons that will appear later, little attempt is made to cover the districts of eastern Oklahoma and western Arkansas, and northern Texas is omitted entirely. GEOLOGICAL CONDITIONS The conditions that made possible the formation of large coal beds in the United States were most favorable in the Pennsylvanian period, formerly known as the Upper Carboniferous. The geological conditions can be determined from the records, but not the reasons for them. Preceding the Pennsylvanian was the Mississippian, formerly known as the lower Carboniferous and still later as the sub-Carboniferous. Dur-ing this time, large bodies of limestone were deposited and at the close f the Mississippian they were warped upward and for along period were eroded. Then there began a period of subsidence, more or less inter-rupted at times, during which the Pennsylvanian strata were deposited (see table on page 2). " These consist of sandstones, limestones and shales, with occasional coal beds: At the beginning of the Pennsylvanian there was subsidence, which allowed the sea to extend over the eroded Mississippian surface to the north and east, extending over eastern and central Texas, a large part of Oklahoma, with a projection into Arkansas, over Kansas and part of Nebraska, all the northern and western part of Missouri, a large part of Iowa except a strip in the north, most of Illinois, practically all of Ken-tucky, northern Tennessee, most of Indiana, all of the eastern part of Ohio, practically all of West Virginia, western Maryland, the west end of Virginia, and a large part of Pennsylvania. The Ozarks were already

Jan 1, 1935

By J. C. METCALF

MORE than 80 per cent. of the iron produced in the United States and over 30 per cent. of the world's annual production is obtained in the Lake Superior district. Though iron ore was discovered on the Marquette range in 1844, the poor transportation facilities retarded the development of this region for many years. The structure of the Lake Superior basin is essentially an east-west synclinorium with steep dips on the south side of the lake and considerably flatter ones on the north and west. The Upper Huronian series, which -is the iron-bearing one of the formation, on the south side of the lake dips north from 55' to 80°, and on the north side dips south from 8" to 200. The series has been subjected to local folding and faulting, which have influenced the development of the mining systems used.

Jan 1, 1921

By H. H. Alexander

PRIOR to 1915, numerous attempts were made to treat tin concentrates in the United States, but for various reasons they were unsuccessful. Tin ore is said to have been found in nearly every state, but none of the deposits have proved to be of commercial importance. The only domestic production is in Alaska, but only a few hundred tons annually have been produced; hence any considerable production of tin in the United States must be from foreign ores. The most promising occurrence of tin was found in the Black Hills, S. Dak.; in the early development stage, it was called the Cornwall of America. Associated with the tin is tungsten. The story is told that an exceedingly fine specimen of the Black Hills ore was sent to England to encourage stock promotion; the desired effect was produced until a skeptic chipped off a small piece, which the analysis showed to be wolframite. FIRST ATTEMPTS AT SMELTING One of the first promising attempts at tin smelting in the United States was made by R. T. White at Bayonne, N. J., in 1903. Mr. White, after spending some time in England studying the methods of tin smelting, organized a company called the International Tin Co., and erected a plant to treat tin concentrates from the Straits of Malacca. About the time the plant was completed, the English Government placed an export duty of 40, per cent. ad valorem on tin .concentrates exported to other than British smelters, which duty made it impossible to operate this plant so the enterprise was abandoned. As this export duty is still effective, the only source of tin-ore supply for 'the United States is the Bolivian concentrates.

Jan 3, 1924

By M. H. Gaskell, D. C. Lindley

Small, steeply inclined reservoirs without natural water drives often are found associated with salt domes or other highly faulted structures. Frequently, only one well may be economically justified in these reservoirs, from which oil is produced by an expanding gas-cap drive or by a dissolved-gas drive. Although a large fraction of the oil upstructure from the well may be recovered during primary depletion, only a small fraction of the downdip oil can be produced because of gravity effects. This downdip oil has been defined as cellar oil991 in contradistinction to "attic oil" which is the oil above the structurally highest well in reservoirs where a natural water drive is present. In this study, two methods of producing cellar oil by water flooding a one-well reservoir were investigated by means of a laboratory model. This model was scaled to represent a prototype reservoir having an area of 30 acres, a permeability of 500 md, and a thickness and dip of 30 ft and 30°, respectively. One method considered, the simultaneous injection of water and production of oil from a single well, would require that the lower portion of the productive interval of a well be completed for water injection and the upper portion for oil production. The other method considered, intermittent injection, would involve alternate injection of water into and production of oil from a single well. Injection of water into the formation would repressure the reservoir, causing gas to go back into solution. Since some of the injected water would flow updip from the well, water injection usually would be followed by a waiting period during which the water could drain from above the wellbore. Production of oil by gravity drainage and gas-cap drive could be initiated when water drainage became sufficiently complete. The amount of water produced along with the oil would naturally depend on how soon after water injection ceased that production was started. This process could be repeated in cycles until oil could no longer be produced economically. Of these two methods, the intermittent injection technique would be simpler to put into operation since it does not require a dual completion. Also, it is probably more generally applicable than the simultaneous injection-production method. It is to be expected that in some reservoirs the rock and fluid properties would be such that practical oil-production rates could not be achieved by the simultaneous technique. However, in reservoirs where the simultaneous method will result in practical rates of oil production, it does have the advantage of permitting immediate, continuous oil production; whereas in the intermittent method, oil production is interrupted by periods of water injection and drainage. It was the objective of this study to determine whether these two methods of cellar oil production are practical for the representative prototype investigated and to evaluate their relative merits. DESIGN OF LABORATORY MODEL SCALING REQUIREMENTS The prototype reservoir and fluids were selected to have the dimensions and physical properties shown in Table 1. The laboratory model was then designed in accordance with well known scaling criteria, as discussed by Croes, et al,2 except for one modification. According to Croes, et al, one requirement of scaling a laboratory model to a reservoir prototype is that both the relative permeabilities and dimensionless capillary pressure be the same functions of water saturation for the model and the prototype. Since unconsolidated sand packs are used in the laboratory model to represent the consolidated porous media of the prototype, it is virtually impossible to satisfy this requirement. Much of the difficulty stems from the fact that unconsolidated sands usually exhibit lower residual oil and connate-water saturations than do reservoir rocks. To satisfy the scaling requirement as nearly as possible, Perkins and Collins' have suggested that the relative permeabilities be re-defined as

By John T. Eash

DURING the course of the war the supply of tin in this country has steadily decreased and a continued effort has been made since the beginning of the emergency to use alloys that are either tin free or contain appreciably lower quantities of it. Even with the use of emergency materials, the tin supply has become particularly acute, and it is estimated that after recovery of the far eastern mines probably one to two years will be required before our normal annual supply is attained. One of the major tin-consuming fields is the bronze industry. Recommendations were made several years ago by the War Production Board toward the use of bronzes of lower tin content and manganese bronze and yellow brass for the customarily used tin-bronze alloys. The substitution of 88-5-5-2 copper-nickel-tin-zinc for composition G received considerable attention before the war, and consequently this alloy and modifications of it have been adopted for some current structural and pressure castings requiring high mechanical properties. Another of the commonly used bronzes is the 10 per cent tin, 10 per cent lead copper alloy for heavy-duty bearings. It has been known for some time that about 2.5 per cent nickel could be substituted for an equal amount of tin with retention of equivalent casting and tensile properties; however, it was desirable that a still greater conservation of tin be made. Consequently the present paper deals with the development of an alloy of low tin content that could be used for bearings. SELECTION OF COMPOSITION While the final criterion of the suitability of an alloy for a bearing must 0f course be determined by practical applications where all the ramifications of service conditions are encountered, certain short cuts in the initial selection of compositions are necessary to avoid an extensive and time-consuming investigation. The present program has been to match certain metallurgical properties of the 80-10-10 bronze that have been shown by previous investigations to be related to good bearing qualities. Such properties as microstructure, hardness, compressive yield strength, ductility, and castability have been considered, and certain simple wear tests have been made. Of the readily assessed characteristics desired in a good bearing alloy, one can be certain that a uniform distribution of lead is required in a leaded bronze. It has generally been found that segregation of lead is one of the chief difficulties with this type of material. Tin has a powerful effect on lead distribution, and with 10 per cent present produces a random distribution of chunky particles, such as are shown in Fig. I. In addition, the tin bronze contains the hard alpha + delta eutectoid constituent distributed through-

Jan 1, 1945

By H. D. Hibbard

At the beginning of a Henry M. Howe lecture it seems fitting to refer to Howe's great contributions to steel metallurgy, and particularly to the literature thereof. Most of my predecessors in this role have been able, from their association with him, to give direct testimony as to his great services; but although connected with him for years in a business way, I am less familiar with what might be called his academic side, except as it is embodied in his utterances, written and oral. Howe was adept in his genial way in extracting information in any line which, at the time, was of interest to him. In a technical lecture one expects as a rule new knowledge-—something about recent advances relating to the subject. On this occasion, however, I will ask you to go back with me to the primary department of steel lore, as the title of my lecture shows, to review the more fundamental features in that field for the purpose of seeking some gaps which we can fill and so give the subject renewed interest. In thus going back one must inevitably repeat many familiar facts, but that seems to be necessary in order to reach a clear understanding of the unrecorded matters. The full interpretation of a steel analysis is at present unattainable, though much progress toward that end has been made. The ultimate analysis, giving the percentages of the five commonly determined elements, does indeed usually give a fair idea of what the steel is, and is ordinarily enough, with knowledge of its history and physical condition, to enable it to be assigned to some purpose or use for which it is reasonably suitable. Rut discrepancies arise. Every maker and every User of steel knows, from at least occasional examples in his own experience, that the ultimate analysis is insufficient by itself to enable one to tell positively, from its interpretation, either the mechanical properties of the steel or its adaptability to the purpose for which it was made. Further, if, while having the specified composition, it is abnormal or unsatisfactory, why it is so. Good, bad and indifferent steels may have substantially the same ultimate analysis.

Jan 1, 1928

By R. W. Guard, M. E. Fine

By treating the dislocation like a surface and ap-plying the usual thermodynamic treatment to the adsorption process a Gibbs adsorption equation for dislocations was derived. For extended dislocations in binary solutions the adsorbed concentration on the fault, X2a, may be computed from (jo/da2b) where a2b is the activity of the solute in the bulk material and s is the stacking-fault energy. Using the data of Howie and Swann for s the adsorption concentration goes through a maximum at 2 at. pct Al in Ag-Al, 10 at. pct Zn in Cu-Zn, and 8 at. pct A1 in Cu-Al. The pinning stress calculated from this concentration difference goes Ihrough a maximum at the same concentration us the peak in X2 a. The computed pinning stress thus does not vary with composition in the manner predicted by Suzuki, as was also pointed out by Hendrickson. The results are compared with the stress increment which can be attributed to Suzuki locking in Cu-Zn and Cu-Al stress-strain curves. They both agree in magnitude and in the location of the maximum. The predicted and observed maximum values for the Cu-Zn system (where activity data are available) are 700 g per sq mm (predicted) and 1000 g per sq mm (measured, laking into account the orientation factor of 2.2 to convert poly-crystalline to single-crystal data). CERTAIN simple internal surfaces may be regarded as dislocation grids. This fact suggested that it might be profitable to consider certain phenomena related to segregation of solute atoms at dislocations from the point of view of the thermodynamics of surfaces and surface adsorption. A general treatment of this type is given and then the results are applied to Suzuki segregation and pinning. Confirmation of the results is obtained from comparison of stress-strain behavior for copper and copper-base alloys. Two kinds of dislocations need be treated: perfect and extended dislocations. In either case the line tension of a dislocation, ?. the work which must be done to increase the length of dislocation by a unit length, is analogous to the surface tension. For an undissociated dislocation ? is the self-energy of a unit length of dislocation; for an extended dislocation where is the self-energy per unit length of a pair of partials far enough apart so that there is no interaction energy, is the interaction energy per unit length, is the stacking fault energy per unit area, and w is the equilibrium separation of the paired partials. In the absence of an applied stress the force pushing the dislocation partials apart in a close-packed structure is Gb2/12p where G is the shear modulus, b is the Burgers' vector of the complete dislocation, and is the separation of the partials. At the equilibrium separation, w this force equals s. Thus

Jan 1, 1965

By Ernest A. Hersam

Accurate ore-sizing with screens is drawing attention to certain details that now, more than ever before, require attention. There are many tests that must be preceded by careful sizing. The assayer often could profit by a more careful selection of screens. In milling, more attention is given the slimes produced. Cement-manufacturers are pulverizing and screening finer than they formerly did, and others are reducing materials to fine sizes at high cost, with screens used to govern the fineness of the pulverized product. Fine screens are expensive, easily injured by misuse, are carried in stock sparingly by most dealers, and are handled often by those who know little about them except their designated number. More attention, on the whole, needs be given the actual size of the mesh-openings, and less emphasis placed upon any custom or conventionality in numbering. An effort to classify wire screens, in this respect, leads at once into computations, where one is confronted with details of sizes and standards, of different wires, different gauges, and different customs. There is always uncertainty about the exact working-size of a screen until one gives the matter special attention, and devotes more time to it than its simplicity seems to demand. To know only the number is not sufficient for all uses. Often, in sets, superfluous sizes are used; and sizes are omitted that are of critical importance. In wire screens, the use of different standard sizes of wire makes important differences in dimensions that must be taken into account. The dealer usually grades screens by the number of openings per linear dimensions, regardless of the size of the openings or of the wire. Certain 100-mesh screens in use are found, by measurement, to be actually coarser than others of 90-mesh, a result which is due, of course, to the use of larger

Jan 1, 1907

By George A. Laird

THIs old and once famous district played, through its enormous production of silver and gold, an important part in the history of the State of San Luis Potosi. According to a pamphlet prepared under the direction of the Governor of the State, Sr. Don Blas Escontria, and presented to the visiting members of the Institute during the Mexican meeting of 1901, this district is situated 20 km. east of the city of San Luis Potosi, in a range of mountains of moderate height, extending 135 km. N. and S., and 16 km. E. and W.; and the mineralized area hitherto developed is about 600,000 sq. m. The history of the district, as given by the record dated 1778, and formerly kept in the Sail Francisco convent, says that it was discovered in 1575 by Sr. Don Pedro Irarte, and adds that the city of San Luis Rey de Francisco de1 Potosi received its name (in allusion to the famous Potosi mines in Bolivia) by reason of the remarkable productiveness of its gold- and silver-mines in the first period of their exploration, during which they paid to the Crown, as quintos (the fifth part of the product), $97,000,000, as appears from the accounts of the royal treasury. The amount of the quintos paid during the " bonanza period " of 80 years was $72,000,000. The larger sum first mentioned probably represents a longer series of years. But either will suffice to indicate the great wealth of the mines. In 1663, the decadence of the industry began with the caving-in of several mines, concerning which the record of 1778, already cited, says, in substance, that on Good Friday one of the owners in the enterprise, in view of the unfavorable prospect of a lawsuit in which he was engaged, set fire to the timbers supporting the underground galleries and workings of the Sail

Jan 1, 1905

By R. E. Anderson, R. S. Busk

The mechanical properties of many nonferrous alloys can be modified by heat-treatment. This is almost always effected by controlling the amount of alloy in solid solution and the amount and distribution of second-phase material. The latter often is accomplished through precipitation or age-hardening treatments. The procedure is to solution-heat-treat the metal to provide a supersaturated solid solution and then cause precipitation of the dissolved material at some temperature below the solvus for the alloy. The generally used magnesium sand-casting alloys arc based on the ternary alloy system Mg-Al-Zn. Solid diffusion reactions in the system are slow enough so that a substantially completely supersaturated solulion is maintained even though the metal is relatively slowly cooled from heat-treating temperatures. Consequently, it is general practice to air-cool magnesium-alloy castings from the heat-treatment temperature prior to aging at an elevated temperature. Since it is necessary with many other alloys to cool quite rapidly before aging if optimum benefit from the aging is to be obtained, this study was undertaken to determine the effects of quenching on magnesium alloys. The] alloys used are shown in Table I, being selected as typical of the presently used magnesium alloys. Cooling Rates Since quenching is a means of rapidly extracting heat, there are two factors of interest in its study: (I) the rates of cooling that can be obtained and (2) the effect of various rates on the as-cooled as well as subsequently aged metal. The cooling rates were measured by drilling a hole 1/16- in diameter longitudi~lally in the center of a cylinder % in. in diameter and 3 in. long. The drilling was stopped to place the end of the hole at the center of the long axis of the cylinder. An iron-constantan thermocouple was inserted in this hole and wedged in place. The temperature drop during rapid quenching was recorded by a special1y built General Electric potentiometer recorder capab1e of measuring ' 500°F. temperature drop in 1/10 sec. For the slower cooling rates in air or oil, the temperature drop was measured by a Leeds and Northrup potentiometer recorder with the chart speed increased to One inch per minute' The cylinder was heated to the desired temperature, quenched as desired, and the temperature-time curve recorded. The cooling rates in still air, in oil at 350°F., in water at 180°F. and in a cold, high-pressure water spray were determined in this manner. The results of this study are presented in Fig. I. There is a great difference between water quenching and either air or oil quenching. There is little difference between the hot water quench and the cold water spray. Cooling rates were also

Jan 1, 1945

By Richard Hamburger

Calculating machines permit the use of the more rapid cotangent and semigraphic solutions of plane triangulation. The results of these methods are as accurate as those of other methods. Simple adjustment of the net, and ease of calculation encourage more complete field work. Errors in field work or in computation are easily localized.

Jan 2, 1950

By Jack A. Caldwell

Jan 1, 1985

Jan 6, 1953

By W. A. Jr. Slippy, E. P. Dahlberg, R. B. Reed-Hill

A large room-temperature mechanical-hysteresis effect under cyclic tensile loading was observed in zivconium specimens prestrained at 77°K so as to form large numbers of (1121) twins. The observed hysteresis loss was a maximum when the prestrain was just under 1 pct It also depended strongly on the maximum applied cyclic stress, but only moderately on loading rate and temperature (-72°to 100°C). The phenotnena have also been studied in terms of the elastic aftereffect where the data has been found to cotlforln closely to the functional relationship between strain and time, c = -RT/a In tank ft. t to)/Zr, for strains cts large as about 10-4 This eyication can be derived directly from the strain-rate equation There may be important commercial implications to the present discovery since it appears that within rather wide limits it may be possible to obtain any desired magnitude of damping capacity in zirconium melal. The damping propevties may also be given directional characteristics. It is shown that the observed anelaslic phenomena can he explained on the assumiplion that they are the resuilt of stress-induced twin-boundary movements in which the average twin increases its thickness by only a few percent. In polycrystalline zirconium, a grain is least favorably oriented for slip when its basal plane, containing the (1130) slip directions, lies nearly perpendicular to the principle normal stress. Mechanical twinning is favored by this orientation and under simple tensile deformation at room temperature the primary twinning mode is {1012).' The (1012) twinning shear is small (0.17) so that, during deformation, twin growth does not greatly enhance ductility. At 77°K, on the other hand, the predominant twinning mode shifts to {1121), and many thin (1121) twins can form at small strains.' Twins thus nucleated can grow readily during subsequent room-temperature deformation and permit easy deformation in unfavorably oriented grains. In addition, the (1131) twinning shear is large: 0.63. These facts have lead to a process' for greatly improving the room-temperature ductility of zirconium when it contains a sizable fraction of grains with basal planes nearly normal to the stress axis. Optimum results are obtained by slightly less than 1 pct prestrain. The effect is large so that a 50 pct elongation increase is readily attained. A large room-temperature mechanical-hysteresis effect has also been observed in zirconium specimens prestrained at 77°K. The present paper is concerned with some aspects of this effect which the experimental observations strongly indicate is primarily the result of strain-induced {1121) twin-boundary movements. This clearly suggests that mechanical twins formed by plastic deformation can cause anelastic effects similar to those previously observed2 for annealing twins and twins associated with phase transformations. EXPERIMENTAL PROCEDURES All specimens were prepared from arc-melted sponge zirconium plate stock as previously described,3 which has a preferred orientation with basal planes aligned parallel to and uniformly distributed around the rolling direction. Both lonti-tudinal and transverse tensile specimens, with axes parallel and transverse, respectively, to the plate rolling direction, were cut from this plate. In a longitudinal specimen most grains are favorably oriented for slip, while in a transverse specimen a large fraction are unfavorably oriented. Prestraining at 77°K was performed in two ways. In one, annealed zirconium plate stock was cooled in liquid nitrogen and then rolled in the transverse plate direction to strains varying from 0.5 to 12 pct. Cylindrical 1/8-in.-diameter by 1-1/4-in.-gage-length tensile specimens were machined from this material. In the other, previously machined tensile specimens were prestrained in tension at 77°K between 0.2 and 3.8 pct. Type FA 25-12 SR4 strain gages were cemented to all specimen gage sections. All tests were performed on an Instron testing machine of 10,000-lb capacity. EXPERIMENTAL RESULTS Fig. 1 shows a typical two-cycle room-temperature stress-strain diagram for a specimen prestrained 0.65 pct by rolling at 77°K. The maximum stress in both cycles was 14,500 psi. Note that in the first cycle the loading and unloading curves are unsymmetrical so that a residual strain, er, remains after unloading. In the second cycle the stress-strain curves form a nearly symmetrical hystere-

Jan 1, 1965

By William Y. Holland, Roger M. Cook

In view of the increasingly widespread deterioration of concrete structures as the result of the interaction of the alkalies sodium and potassium released by hydration of portland cement and susceptible rocks and minerals in aggregates, it is believed that a paper summarizing the geographic distribution of these aggregates will be of interest to producers and users of concrete, concrete products, and concrete-making materials. THIS paper reviews the problem of alkali-aggre-gate reaction in concrete and describes the geologic and geographic occurrence and distribution of alkali-reactive sand and gravel in western United States. It includes no discussion of crushed stone or synthetic aggregates. Most deposits of sand and gravel are accumulations of particles of rocks and minerals from a variety of sources, and it is not unusual for at least one or two varieties of the rocks to contain some form of reactive material. Examination by petro-graphic methods of many sands and gravels, as well as manufactured aggregates, has shown that a comparatively high proportion of the deposits does contain, in greater or lesser degree, rocks and minerals known to be deleteriously reactive with the alkalies of cement. Fortunately the amount of reactive materials is commonly less than that necessary to cause deleterious effects in concrete. As investigation of unsound concrete structures progresses, it becomes evident that the alkali-aggre-gate reaction is even more widespread than supposed, Figs. 1 and 2. Even though some parts of the country appear at present to be immune, further investigations will probably show that the effects of alkali-aggregate reaction can be seen in many structures in these areas, although only on a small scale in most of them. Many concrete structures will, of course, have lived their useful life before disintegration from this cause is serious, and in others the alkali-aggregate reaction may never become significant even though the microscopic evidence of reaction is present. The alkali-aggregate reaction first was reported to be a cause of deterioration of concrete in 1940 when Stanton1 described expansion of concrete pavements in California. Similar expansion and deterioration of concrete was recognized during succeeding years in concrete structures located in many parts of the country, but particularly in the western states. A number of concrete laboratories2 became interested in the problem. It was soon determined that only certain combinations of aggregate and cement caused the alkali-aggregate reaction to take place, and moreover that the reaction progresses only in the presence of water. Further research proved that cements containing more than 0.60 pct total alkalies (pct Na,O + 0.658 x pct K2O), when used with aggregates containing appreciable amounts of reactive ingredients, caused the reaction to take place, usually with subsequent deterioration of the concrete. During the last few years this limitation has been adhered to in both government and private construction as the maximum allowable alkali content of cement to be used with aggregates of known alkali reactivity. Because of this limitation, it appears that deleterious reaction either has been reduced or eliminated in many recently built structures in which it probably would otherwise have occurred. Recent tests have shown that the degree of expansion obtained with any particular cement-aggre-gate combination depends not only on the alkali content of the cement but also upon the relation of this alkali content to the amount and degree of reactivity of reactive constituents in the aggregate.' In laboratory mortar bars, opal and cements with alkali content of as low as 0.2 pct (as equivalent of Na2O) have produced deleterious expansion as the result of alkali-aggregate reaction. These experiments demonstrate that aggregates containing even 0.1 pct of opal are deleteriously reactive. It was soon determined that alkali-silica gels were formed by the interaction of the alkalies of the cement and the reactive aggregate, Figs. 3 and 4. Osmotic or swelling pressures produced by the continued hydration of these gels cause expansion of the concrete with resulting cracking, warping, and dislocation. Evidence of the alkali-aggregate reaction can be seen by a petrographic study of the deteriorated concrete. Among the first structures studied by this method was Parker Dam on the Colorado River, California-Arizona. In the concrete from this dam pebbles of rhyolite, andesite, siliceous limestone, and chalcedonic chert were found to be reactive.

Jan 1, 1954