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By H. Shaw

GRAVITATIONAL measurements made by means of the Eötvös torsion balance over any area enable a representation to be obtained of the total gravitational effects over the surface of that area arising from the combination of all sources of gravitational disturbance. The investigation of gravitational anomalies occurring in the upper layers of the earth's crust, in this way, has been attended with considerable success, and, especially in areas in which no undesirable disturbing factors were present, it has been possible to locate geological structures and mineral deposits with remarkable accuracy and also to delineate their confines and to indicate their depth below the surface with a certain amount of precision. Before this can be done successfully, however, it is necessary to determine the gravitational effect arising from all other extraneous .anomalies in order that these may be satisfactorily eliminated. Disturbing features giving rise to these gravitational anomalies may be divided into two classes, according to whether they are situated at or below the surface. The former are determined readily by a detailed leveling of the ground surface, and may be satisfactorily eliminated provided the specific gravity of the terrain material is known, but the latter are generally unknown, and can only be ascertained with difficulty. When, therefore, the observations obtained by means of the Eötvös torsion balance have been corrected for all surface irregularities, known as terrain and topographical effects, there remain residual gravitational values which are due entirely to subterranean conditions. The task of interpreting these results consists in disentangling the various subsurface anomalies, and subsequently in computing and recombining the effects of these various masses in order to verify the interpretation. When the gravitational anomalies are due to large and comparatively simple structures it is a matter of little difficulty to arrive at a satisfactory interpretation of the subterranean conditions, but in more complex areas, where the geological conditions are more complicated and several irregular features exist, the process of disentangling the various constituents of the complex mass arrangement is more difficult and requires the expenditure of considerable time and labor.

Jan 1, 1929

By Jr. E. H. Dix.

In selecting the subject, "Acceleration of the Rate of Corrosion by High Constant Stresses,'' for the 1940 Institute of Metals Division Lecture, I have been influenced by its highly theoretical and speculative nature as well as by the great practical importance of the correct interpretation and appraisal of the engineering significance of the phenomenon. I lay no claim to originality in talking on this topic, since it has been the subject of discussion for over a quarter of a century. However, as our technical thinking advances, old phenomena take on new and more significant aspects. In our studies at the Aluminum Research Laboratories, we have encountered many perplexing and seemingly contradictory results and have been fascinated by the problem of dovetailing all of the many pieces of information to make a complete picture. I hope that in the brief period of this lecture I may share with you some of the enjoyment we have had in attempting to meet this challenge to metallurgical science. The emphasis generally has been placed on the spontaneous failure by cracking of a metal under the combined action of high stress and corrosion, hence the present-day use of the terms "stress corrosion" or "stress corrosion cracking." The older term "season cracking," applied more specifically to copper-base alloys, includes, by inference, the element of time. For the purpose of the discussion today I will use "stress corrosion" to cover broadly the effect of stress in accelerating the rate of corrosion of metals. To stay within the limits of allotted time the disrussiorl will cover the effect of high static stresses rather than repeated or dynamic stresses, which would take us into the related field of corrosion-fatigue. The subject is particularly appropriate for an Institute of Metals Division Lecture because much the same phenomenon has been observed in almost all metal systems. Thus, in addition to the season cracking of brass may also be mentioned the "caustic embrittlement" of steel boiler

Jan 1, 1940

By O. George Specht, Carl A. Zapffe

In recent print, some remarkably contradictory statements have appeared regarding the importance to be attached to sponge Iron,1-6 a metallurgical commodity whose history goes back at least to the time of Diodorus Siculus in the fourth century B.C. This disagreement, however, expresses the lack of a satisfactory method for producing sponge iron rather than defection in the commodity. The blast furnace is admitted to have certain inherent disadvantages, such as a general unsuitability for magnetite and the heating and blowing of vast quantities of undesirable nitrogen, so that a workable sponge-iron process remains attractive. In this respect, low-temperature gaseous reduction shows especial promise; but confusion persists regarding the factors involved. The present paper, therefore, has three principal divisions: (I) an exhaustive examination of all previous work on low-temperature gaseous reduction, (2) experi- mentation on the reduction of a magnetite with hydrogen, and (3) development of certain thermodynamic relationships in reduction, with a summarized depiction of the factors in the general process. PREVIOUS INVESTIGATIONS Gaseous media used in the reduction processes under discussion can be classified in three types: (I) H2, (2) CO, and (3) other gases. In the second, the CO is often admixed with H2. The third principally comprises hydrogeniferous gases, such as natural gas and producer gas, and in addition includes chlorine. Because hydrogen therefore features in all three, a study of hydrogen reduction based on investigations using pure hydrogen alone may be incomplete. The present paper reviews the three groups of investigations in the listed order, paying particular attention to hydrogen reduction. For the benefit of future workers, an exhaustive bibliography has been prepared and similarly classified. Group I: Reduction with Hydrogen Equilibria Although the present problem is specifically one of kinetics, a first consideration is the equilibrium of the system, since the reactions to be studied comprise that equilibrium, and their direction and end points are defined by it. The historic development of these researches is interesting and informative.

Jan 1, 1947

By J. Kent Smith

The object of this investigation was to ascertain the effect of varying percentages of beryllium upon pure copper and the properties of the resultant alloys in their softest condition, the effect of heat hardening on them, and the extents to which these properties could be augmented by different combinations of heat hardening and cold rolling. The data compiled in this paper represent partial results of continuing work done by the writer during the years 1930 and 1931, which was a continuation of the unpublished ground work incepted in the laboratory of the Beryllium Corporation of America by H. B. Pulsifer in the year 1926. A short bibliography on beryllium alloys is appended to this paper. It has, of course, long been known that copper subjected to cold work is hardened and strengthened to a considerable extent; furthermore it had been qualitatively noted in previous experiments that copper-beryllium alloys seemed to take on hardness and strength as the result of cold work at a greater rate even than does plain copper. It was decided therefore to endeavor quantitatively to determine such rate of increase, as also the relative increases by combinations of cold working and heat hardening. The results are summarized in Tables 3, 4 and 5. A preliminary series of experiments had indicated that by an exposure to the heat of 575" F. for 2 1/2 hr. age-hardening of a 2.50 per cent beryllium-copper alloy took place. Slab ingots of nine different beryllium-copper alloys were prepared under identical conditions by means of the addition of a previously prepared 12.5 per cent beryllium-copper alloy to well melted and deoxidized pure copper. The ingots were then reduced by hot rolling to 12 gage (about 0.080 in.). These strips were heated to 1450" F. and quenched in cold water, and thus brought to their softest condition. (See Table 1.) Strips were next "precipitation-hardened" by reheating to a definite temperature. Similar strips to those itemized in Table 1 (which had been quenched from 1450" F.) were reheated for varying periods of time at 575" F. The hardness figures show that a metastable condition, of which the range of stability is dependent entirely upon time at the given temperature, begins to be noted in copper samples containing as little as 0.85 per cent beryllium. It is extremely noticeable in samples containing

Jan 1, 1932

By Alexander R. Troiano, Eugene P. Klier

SINCE the very early work on quenched structures, where the products of the martensite transformation had been recognized, this transformation has provoked much interest and study. Theoretically it was desirable to account for the extreme changes in physical properties resulting from the formation of martensite, as that information might lead to results of practical importance. Desirable information, therefore, was on the kinetics of transformation from austenite to martensite as well as on the physical constitution of the martensite. It has been known for years that certain steels quenched to room temperature will contain persistent austenite as well as martensite. Other important and now well- established features of the martensite reaction are the progress of the reaction on cooling only and the independence of Ar" with cooling velocities exceeding the critical velocity. These facts have been experimentally determined by various methods and investigators. Notable among the early investigators were Tammann and Scheill and Wever and Engel.2 Unfortunately, all investigators did not fully interpret their results, which, coupled with several investigations that yielded conficting results, caused a state of confusion that was not clarified until quite recently. X-ray investigations of martensite in steels3-6 indicate it to be a supersaturated solid solution of carbon in alpha iron. This supersaturation is evident from the appearance of a body-centered tetragonal structure with the addition of sufficient carbon. The dimensions of this tetragonal structure are alinear function of the carbon content within the limits of accuracy of the determinations. Slight tempering of tetragonal martensite leads to the destruction of the tetragonal structure, which is converted to a body-centered cubic structure. This phenomenon has precipitated a controversy concerning the nature and mechanism of the tempering of martensite. The facts in the case have been outlined by Epstein7 and more recently by Antia, Fletcher, and Cohen.8 The significance of Ar" on theoretical grounds is not clear, however, although considerable study has been devoted to its determination. The precise position of Ar" as a function of carbon content was first stated by Greninger and Troianos for steels covering a range of approximately 0.7 to 1.8 per cent carbon. The effect of alloying elements on Ar" has recently been the subject matter of investigation by various methods.

Jan 1, 1945

By I. Cornet

With the greatly expanding use of magnesium during the war, it appeared necessary to the War Metallurgy Committee that the notch sensitivity of magnesium alloy extrusions be further investigated and the influence of various factors upon notch sensitivity be noted. Accordingly, the National Defense Research Committee of the Office of Scientific Research and Development placed a research contract with the University of California, supervised by the War Metallurgy Committee. The work discussed herein was done under "Restricted" Project NRC-21, reported in Dec. 1943~; it has been released for publica-tion by the O.S.R.D. Scope of the Investigation The notch sensitivity of various magnesium alloy extrusions was determined under axial tension, and also under several conditions of nonaxial tension. Hardness, grain size and other metallographic features were observed; stress-strain data were obtained, and the chemical compositions of the alloys were determined, in order to correlate these quantities with thc notch sensitivity. Notch sensitivity under axial tensile load was determined for a few specimens which had been cold worked to various degrees by tensile prestraining. Magnesium alloy extrusions studied included Dowmetal 0, X, J, and A(. For comparison, extrusions of aluminum alloy 24s-T, cast bars of aluminum alloy 122-T2, and cast bars of magnesium alloy C were also tested. The specified chemical composition of these alloys is given in Table I. All bars tested were within specification limits of composition. Investigation of thc tensile notch sensitivity of various magnesium alloy extrusions, under conditions of axial and eccentric load, showed little or no correlation with stress-strain or other conventional data. Since the many uncontrolled variables present might mask significant relationships, one alloy was selected for intensive study. Magnesium 0 alloy extrusions were subjected to experimental heat treatments, and the ,Changing hardness, tensile strength, microstructure, and notch sensitivity observed. Experimental Techniques and Procedures Tensile Testing Bars used for axial loading were machined with % in.- and with 34-in. minimum diam1 and included specimens with 60" V notches (Fig I and 2). Each V-notched specimen was roughed out carefully and then finished with a honed tool. These Y-notched bars were sampled frequently, sectioned, polished, and examined at 500 X magnification to control

Jan 1, 1949

By E. L. Corp, J. C. Johnson, W. G. Pariseau, M. Poad, M. E. Fowler

This paper describes a comprehensive geomechanics case study of a full¬scale test stope at the Carr Fork Mine. The mine is owned by Anaconda Miner¬als Company and is located near Tooele, Utah. Large diameter blast holes were used in a new method known as blast hole post-fill (BHPF). The new design proved highly successful in contrast with earlier experience with vertical crater retreat (VCR) stopes. The main geomechanics objective was the estab¬lishment of a design procedure for optimizing stope and pillar dimensions with respect to productivity and recovery. An integrated three-part approach consisting of mine measurements, laboratory testing and finite element calcu¬lations was taken. Independent correlations of 0.88 and 0.89 between calculated and measured displacements and between estimated and observed yield :ones substantiate the finite element design approach using UTAH-II. Subse¬quent stope and pillar design analyses indicate that doubling of the original stope width at 50% extraction is quite possible without sacrifice of safety or stability.

Jan 1, 1984

By John S. Johnson, Thomas Fraser

SIZING is the process of separating mixed particles into groups of particles all of the same size, or into groups in which all particles range between certain definite maximum and minimum sizes. In coal preparation, sizing is generally accomplished by passing the coal over screens. Separation by differential settling in air or water currents has been adapted to the special field of separating very fine sizes, and these processes are in commercial use to a relatively small extent in the coal industry. Separation with screens is a very old industrial practice. Agricola described the use of screens for ore treatment in the middle ages. In the literature of the British coal industry references were made to the screening of coal as early as 1589, but the practice of extensive sizing for the market did not become general until the last half of the nineteenth century. In America, the practice of sizing developed first in the Pennsylvania anthracite region, beginning with the use of rakes in the mine working places to recover coarse coal. This mining procedure left the fines in the mine. Preparation outside the mine started with the installation of stationary cast-iron plates with 4 to 6-in. square holes. The run-of-mine coal was dumped upon the platforms, the large pieces of rock were picked out by hand, and the large lumps of coal were broken with hammers. The term "breaker," which still applies to the anthracite-preparation plant, originated with this practice, but the term is no longer descriptive of the entire function of the plant. In 1884, the first power-operated anthracite coal breaker was erected by Gideon Bart at his colliery at Wolf Creek near Minersville, Pa. This plant utilized a system of rolls for breaking the coal and revolving screens for sizing. The plant was driven by a steam engine. It could handle coal at the rate of 200 tons a day. By 1860, revolving screens were in wide use in the Pennsylvania anthracite field. Shaking screens were introduced in the Pennsylvania anthracite region in the 90's and they rapidly displaced the lower-capacity revolving screens.

Jan 1, 1950

By H. Le Chatelier

SILICA brick are indispensable in the manufacture of steel because they alone are able to withstand the high temperature of regenerative furnaces. All attempts to replace silica brick by other refractory materials for this purpose have failed, but the reason for this failure has remained obscure; we shall give an explanation later in this paper. Before the war, silica brick employed in France came principally from abroad, for which reason, since the beginning of hostilities, certain French steel works have been seriously handicapped. Our attention was first directed to the question by M. Bred, Engineer of the Teil Works. With him, we began certain investigations, at first using our laboratory and the furnaces of neighboring steel works. The larger part of our experiments, however, have been made in the laboratory of the Faculty of Sciences at the Sorbonne. For the heating of our samples, we are deeply obliged to MM. Charpy, Yeatmann and Guérineau. In undertaking these studies, our first aim has been to render assistance to French industry, by indicating, as precisely as possible, the necessary conditions for the manufacture of high-grade brick; but at the same time we have intended to give an example of the manner in which scientific methods may be put to practical application in the solution of industrial problems. Although our work has been confined to samples of only a few grams, we are nevertheless convinced that our information can be directly utilized by brick-works of which the output is measured in thousands of tons

Jan 9, 1918

By Henry Fay

THE erosion of guns is a complex problem which can be solved only by a detailed study of all the factors involved. In the present paper it is proposed to submit the results of observations and experiments which have extended over several years. Certain facts have been established and preliminary reports have been published.' Conclusions have been reached since then which, it is believed, are worth presenting for the purpose of promoting discussion, and with the hope that ultimately the whole truth will be known. The particular phase of the problem which will be presented here is the hardening of the inner surface of the gun tube. It has been known for a long time that after firing a large caliber gun for some time, the surface of the metal becomes hard and brittle, cracks, and wears away.2 The character of this phenomenon may be learned by an examination of some results which are typical, obtained from a detailed study of a 12-in. gun. The gun was trepanned and rings representing various sections of the gun were cut out for examination. The first ring represented the metal at the muzzle end, and the other rings were removed at approximately 120, 240, 325 and 337 in., respectively, toward the breech end. The appearance of the surface of the metal in the different sections is shown in Fig. 1. The greatest amount of wear and maximum amount of hard surface layer was found in section marked E, which is nearest the powder chamber and at the beginning of the rifling; the maximum amount of cracking in D; the maximum amount of copper deposition in C. Section B showed heat cracks on both lands and grooves, and section A showed heat cracks on the driving edge of the lands only. There was much flow of metal in both sections E and D, and there was progressively less effect noticeable toward the muzzle end. The polished cross-section of these same pieces is shown in Fig. 2. The

Jan 12, 1916

By J. C. Jaeger

The study of brittle fracture of rocks has been a much neglected subject until quite recently and now is in a state of transition and rapid development. Historically, three methods of testing were used by engineers: uniaxial tension, bending, and, by far the most common, uniaxial compression of cubes. This latter was probably adequate for engineering requirements, but from the last century onwards there has been a demand from geologists for a study of the properties of materials under conditions comparable with those at depth in the earth's crust. King1 remarked that "in engineering practice a cube of the material is put into a testing machine and the stress required to crush the cube is measured. This gives the limiting stress difference for the material so long as the boundary conditions are similar to those existing during the test . . . this may by no means be the case when the boundary conditions are very different from those existing in the test, for instance, in the case of rupture in the neighbourhood of a cavity. . . ." Despite this very clear statement of principle, many writers until recently (e.g. Jeffreys2 used the uniaxial compressive strength as a measure of the 'strength' of rock. In the last century (Becker 3, it was both conjectured and, for some rocks, known qualitatively, that plastic deformation could occur under confining pres- sure; the demand from geologists has been for the study of flow rather than fracture of rocks.. From the time of von Karman (1911) and Böker5 (1915) onwards, apparatus has been built which could provide confining pressures sufficient to make some rocks plastic. Many experiments tended to be made on rocks such as marble, which readily become plastic, and the general tendency was to make relatively few experiments in the brittle range. This is particularly true of many experiments on combined stresses. As a result of this, there is not sufficient data to provide adequate information

Jan 1, 1967

By Wm. Reuben Webster

BRASS is an alloy of copper and zinc. The brasses (using this term to denote all useful proportions of the two constituents) are the most valuable and widely employed of all [ ] nonferrous alloys, because of their high resistance to ordinary corrosive agencies and the very wide range of properties that may be imparted to them by variations in the proportions of the constituents and by variations in mechanical treatment and heat-treatment. Fig. I shows the normal physical properties, as determined by standard tensile tests, of the series when in the annealed condition. Fig. 2 shows the effect of varying amounts of cold-working on an almost pure brass containing 70 per cent copper and 30 per cent zinc. Fig. 3 shows the effect of annealing at various temperatures on the same alloy. This effect is somewhat modi- [ ] fied by the degree of cold-working to which a brass has been subjected, as shown by Fig. 4. A fourth test, which is empirical, has been found useful because of its simplicity the hot hammer test. Samples 1/2 in. in diameter and 3/4 in. long are placed in a suitable furnace. These are withdrawn one at a time at successively higher temperatures and are subjected to the blow of a drop hammer weighing 50 lb. with a drop of 4 ft. The percentages of reduction in length of the cylinders are plotted against temperatures and give a comparative measure of plasticity at different temperatures. The results of this test on several

Jan 1, 1942

By A. T. Goldbeck

THE use of stone as a building material in relatively large blocks is recorded in ancient historical records but only within the past 200 years has broken stone in small sizes begun to have extensive use, principally in highway construction. Tresaguet, in 1764, describing his method for highway construction in France, required the top surface to be built of stone about the size of a walnut, broken by the use of a hammer. It is said that the Romans, in the top layer of their rather massive roads, used large stones bonded together with lime mortar and bedded in small stones mixed with mortar. Much of the early macadam as built by McAdam around 1815 in England was made with hand-sledged broken stone. In 1858, the use of crushed or broken stone received a great impetus from the invention in that year by Eli Whitney Blake of what is said to be the world's first stone crusher. As a consequence of that invention, stone could be crushed to small sizes with considerable ease and, as a natural result, the use of crushed stone in macadam roads and as railroad ballast increased at a great rate. Also, as portland cement came into use, machine-produced crushed stone furnished readily available aggregate. Rapidly, other uses developed, such as for fluxstone in the production of pig iron and for other metallurgical operations and chemical utilizations. These utilizations made for the rapid growth of the crushed-stone industry and this growth is still proceeding with the growth of population and the development of new uses, notably the employment of limestone for the improvement of soils for agricultural purposes. The industries of which the production of crushed stone is a part have a tonnage second only to that of mineral fuel in the mineral industries of this country.

Jan 1, 1949

By R. Steven Maxwell, Ulrich Petersen

Most minerals have experienced a slow hut perceptible decline in their annual primary production growth over the past hundred years. This decline is due to a combination of factors: (1) increased recycling; (2) exhaustion of the more accessible or higher grade ores; (3) partial substitution; (4) the more efficient use of materials; (5) progressive saturation of markets as living standards rise. Therefore, future demand for new mineral resources will probably be lower than anticipated. As the world population stabilizes, this slowdown in production growth will become even more pronounced.

Jan 1, 1979

By J. R. Low, M. Gensamer

During the course of an investigation into the drawability of automobile-body sheet steel, it became apparent that certain advantages would be possessed by a deep-drawing steel with a very low yield strength, but almost normal tensile strength, provided a reduction in yield strength could be accomplished without sacrifice of ductility and fine grain size. It would also be desirable to have this steel free from strain-aging; that is, free from the tendency for the yield point to return after it had been eliminated by straining. It was known that, wet hydrogen treatment acted to eliminate aging, but as carried out by other investigators, at relatively high temperatures, this treatment resulted in grain coarsening. It has been established by some of the experiments reported in this paper that all of these objectives can be accomplished by treatment in wet hydrogen at a low temperature, in the neighborhood of 72o°C. The time of treatment is relatively short (about 3 hr, to completion with 20-gauge sheet) if the water content of the hydrogen atmosphere is made fairly high, say aimost 30 per cent by volume. At this temperature. the grain size remains fine in the time required. After this treatment sheet reduced the usual amount by cold-rolling has a grain size of about A.S.T.M. No. 7. The yield point is completely eliminated, and the yield strength is reduced to a very low value, in the neighborhood of 15,000 lb. per sq. in. The stress-strain curve departs gradually from the straight-line elastic part after the fashion of nonferrous deep-drawing alloys. This elimination of the yield point is accompanied by a verv low indentation hardness; for example, 32 Rockwell B or even lower. There is no aging as measured by increase in the yield strength upon aging at room temperature or for 3 hr. at 200°C., after stretching about 10 per cent in tension. Tensile strength is only slightly less than the box-annealed sheet, seldom dropping much below 40,-ooo lb. per sq. in. Elongation is practically unchanged, or increased slightly. The term yield point, as here used, refers to the phenomenon of heterogeneous deformation occurring at a substantiallv constant load, observed principally in annealed low-carbon steels. If such a steel is loaded in tension, the load increases steadily with elastic strain, suddenly falls, fluctuates slightly about some constant value for a time and then begins to rise again as deformation proceeds. The maximum initial load before the sudden drop is generally called the "upper yield point"; the value of the load where deformation proceeds at a

Jan 1, 1944

By J. K. Stanley, R. F. Meel

The recrystallization of cold-worked metals is studied ordinarily by determining the temperatures required for complete recrystallization to occur within a given arbitrary time period, usually within 15 min. to 2 hr. The results obtained are conventionally assembled in a three-dimensional diagram relating this temperature to the amount of cold-work (percentage deformation) and the resultant grain size, though sometimes other modes of representation are emp1oyed.l Such three-dimensional diagrams are not complete, for the number of variables exceeds the number represented. The process of recrystallization is characterized by a time-rate, a fact that is not portrayed upon ordinary recrystallization diagrams. It is known that recrystallization consists in the formation of new nuclei and the growth of these nuclei, a process that continues until the matrix is completely consumed and the original set of grains entirely replaced by the new. This knowledge is old.2 Truly heterogeneous reactions invariably proceed by nucleation and growth; the decomposition of eutectoid solid solutions provides an example about which much is known,3 and freezing, originally studied by Tammann, provides the classic example. Although recrystal- lization is not a heterogeneous reaction within the orthodox meaning of the term, the mechanism of the process is the same. As in eutectoid inversion and freezing, it should be possible to study the rate of isothermal recrystallization as a function of time, and it should also be possible to analyze the isothermal reaction curve into the component rates of nucleation and growth that determine them.* Other methods, not employing the rates of nucleation and growth, have been used to represent the rates of such reactions, but these in general have been artificial and have not led to progress. 4,5 The theory of recrystallization is not in advanced state; if recrystallization data were obtained in terms of the rate of isothermal recrystallization, and in terms of the rate of nucleation and the rate of growth of recrystallized grains, and in particular if the temperature coefficients of these rates were measured accurately, an adequate theory should be more readily developed.27 Such an effort requires proper experimental technique, but especially requires suitable methods of mathematical analysis to convert mcasurements made upon a surface of polish into values for the rate of nucleation and the rate of growth and to combine these into a rate of isothermal recrystallization. These methods are now available for the case of three-dimensional recrystallization (recrystallization of

Jan 1, 1942

By R. Hoffmann

THE Waelz process produces oxides of volatilizable metals from ores, metalliferous products and residues. The process was originally used for recovering zinc and lead, where tailings and residues containing those metals had accumulated at mines or smelters, but it is applicable for obtaining tin, arsenic or other volatilizable metals. It is useful when other methods of obtaining the metals from the ores or residues are too difficult or expensive or show too low a recovery. FIG. 1.-DAILY CAPACITY OF WAELZ PLANTS RUNNING OR BEING ERECTED. The Waelz process was developed in 1923 for the treatment of large calamine dumps in Upper-Silesia, which showed zinc contents of 8 to 10 per cent. and lead contents up to 3 per cent. The rapid development of the process, from the first trials up to the plants now working or in course of erection, is shown in Fig. 1. -The first industrial Waelz plant was started in 1925. Within two years the capacity of the working plants reached 700 tons material per day of 24 hr. During the year 1928 the daily capacity of the plants now at work or in course of erection will rise

Jan 1, 1928

By George Enos

As the coating formed affects the corrosion rate, duplicate samples of eight non-ferrous alloys were placed in flowing mine water. The alloys tested were as-cast or as-rolled and machined or polished. The paper describes the tests and gives the corrosion losses and the appearance of the samples at the end of the test. AN IMPORTANT factor affecting the rate and nature of corrosion of metals and alloys is the film, or coating, formed on the surface; and this may accelerate or retard corrosive action once started. The formation of films and coatings is intimately associated with the chemical composition and physical constitution of both the metal and the corroding medium. A film or coating may be either the corrosion product resulting from oxidation; that is, an oxide or salt, or a deposition of suspended matter from the corroding media upon the surface of the metal, or a mixture of both. The coating may adhere tightly or loosely to the surface of the corroded metal. In short, a film or coating is the reaction product of the corroding medium and the metal, which adheres to the surface of the metal and with which may be intermingled material from the attacking media not concerned in the chemical reactions. As the, terms film and coating are used by different writers for very different things, distinction is made between the two, by the present writers, on the basis of thickness. Thus, a film is defined as a corrosion product or deposition, on the surface of a corroded metal, that is of such thickness that it cannot be measured by the metallurgical microscope. A coating, on the other hand, is of such thickness that it can be measured. If the resolving power of the 2 mm. (equivalent focal length) apochromatic oil immersion objective (N.A. 1.4) is taken as the limit of the microscope, the limiting resolution is two lines that are 0.0002-0.0004 mm. apart. It is thus possible to measure coatings that are greater than 0.0002-0.0004 mm. thick. This thickness is equivalent to 200,000-

Jan 7, 1924

By R. F. Mehl, B. Lustman

THE formation of intermediate phase layers in cementation processes has been subjected to extensive qualitative investigation though to relatively little quantitative study; this work has recently been fully summarized by F. N. Rhines.1 It is necessary here only to enumerate the general conclusions drawn concerning the kinetic laws governing the growth of intermediate layers and to state what is known concerning the structural changes accompanying the generation of phase layers. I. When the intermediate phase is protective in type-i.e., when its density is less than that of the base metal, so that a continuous coating is formed and maintained the isothermal growth of the phase follows a simple parabolic equation: X2 = kt [I] where X is the thickness of the alloy layer, k the reaction rate constant, and t the time. The applicability of this equation to diffusion processes is tested by plotting the square of the thickness versus time, or by plotting the thickness versus the square root of time; the resultant achievement of a straight line in such. a plot has been con¬sidered sufficient proof of the validity of this equation. Exceptions have been found where liquid phases are involved in the reaction, where the diffusion layer is cracked,2 and where thin semimetallic oxide and sulphide coatings are formed on metals.3 In the first two cases the thickness increases linearly with time, and in the latter it is a logarithmic function of time. 2. The rate of thickening varies with temperature according to the Arrhenius equation k = Ae-Q/RT [2] where k is the parabolic rate constant of Eq. I, or some other rate-descriptive function, A is the action constant, e the base of natural logarithms, Q the heat of activation, R the gas constant, and T absolute temperature. This equation has been found to be generally valid except when transformations occur during reaction in either the base metal or in the reaction layer; in such instances Eq. 2 is still applicable with different values for the constants A and Q above and below the transformation temperature. 3. All phases that are stable at the temperature at which diffusion occurs will appear in the interdiffusion of two components. In some cases certain of the phases may be too thin to be observed and identified easily. Nonequilibrium phases have never been noted in thick reaction layers; i.e., layers of a thickness that may be discerned microscopically. The relative, thickness of each phase in a diffusion layer is proportional to the concentration gradient and to the rate of diffusion in that phase .4 The reaction layers tend to have a

Jan 1, 1942

By Ellis Clark

The mining town of Pribram is situated in Central Bohemia, on the western slope of the Heiliger Berg. 30 miles southwest from Prague. Birkenberg, the village ill which most of the shafts and ore-dressing establishments are situated, is built on a mountain of the same name. It is about a mile from Pribram, is 1700 feet above the sea, and is surrounded by graywacke rocks of Silurian origin, which arc intersectd by greenstone dikes, and in the southerly, southeasterly, arid southwesterly direction are bounded by granite. The graywacke formations consist on one side of graywacke sandstone and quartzite, and on the other of graywacke slate. These last are separated from the first in the immediate vicinity of the mines by a graywacke seam converted into clay. For many years this so-called clay seam (lettenkluft) was considered as a boundary of the ore deposits in both zones of graywacke. The graywacke formation L divided according to its harduess, structure, texture, and color, into fine, coarse, compact, slaty, whitish-gray, reddish-gray, and black graywacke. The miner divides the formation into four divisions. The first or lowest division, which is in contact with the granite, consists of a fine-grained dirty gray slate; the -second is a very fine to a very coarse schist, white to reddish-gray in color, and rich in quartz, but containing little mica; the third consists of a slate with a confused cleavage, which has a dirty gray, dark gray, and very often black color and is often graphitic in its composition; the fourth consists of a fine to coarse-grained graywacke schist, of a grayish-white or reddish-gray color, and rich in quartz. The cleavage in all four divisions strikes from northeast to southwest, and the dip is sometimes northwesterly, sometimes southerly, and often vertical. All four zones are cut through by a great number of diorite arid greenstone dikes and chimneys. The thickness of these dikes, which are of

Jan 1, 1881