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By A. S. Nowick, E. S. Machlin

ONE of the main criteria used to rate the heat-resisting properties of alloys is stress rupture.1 During a stress-rupture test a tensile specimen is held under a constant load at a constant temperature until it fractures. The chief measurement made during this test is the time required for rupture at the specific test stress and temperature. It was found empirically from a series of stress-rupture tests at a constant temperature that when the logarithm of the time for rupture is plotted against the logarithm of stress a straight line is obtained within experimental error.2~3 This method of showing stress-rupture data has been adopted by many investigators and the KACA.4 By interpolation and extrapolation from these plots, values of the stresses required to rupture the specimens (the rupture strengths) in 10, 100, and 1000 hr are obtained for specific temperatures. Alloys are then rated for a particular application on the basis of their rupture strengths at the rupture life that most nearly represents the application. Inasmuch as stress rupture is an important criterion in rating heat-resisting alloys, it would be advantageous to know the quantitative dependence of the time for rupture on stress, temperature, com- position, and structure. In order to obtain this information, an investigation was made at the KACA Cleveland laboratory during the spring of 1945. The theory of rate processes was used because it has been found to apply to certain processes such as chemical reactions, viscous flow, and creep that occur at a definite rate for given conditions. It was thought that stress rupture was such a process. An equation was derived that gives, for a given com- position and structure, the dependence of the time for rupture on stress and temperature. The investigation is part of a general program to provide information that will lead ultimately to the development of better alloys in order that the efficiency and power output of gas turbines used in aircraft propulsion can be increased. THEORY The theory of rate processes will first be discussed as a general theory. It will then be shown that if stress rupture of heat-resisting alloys can be treated as a rate process, certain equations must be satisfied. Later sections will then show that these equations are satisfied. General Theory of Rate Processes The theory of rate processes5 eveloped by Eyring and others has been applied to chemical reactions as well as to other processes such as viscosity of liquids and diffusion. In every case in which rate- process theory can be applied, there is a small subdivision, so that the macroscopic process is the net effect of all the small processes. This smallest subdivision is called the "unit process.'' For example, in a chemical reaction the unit process is

Jan 1, 1947

By J. E. Hilliard

It is proposed that shape anisotropy in the internal structure of materials be defined by distribution functions which specify what fraction of the total line length or boundary area lies in a given direction. Methods are descriibed for determinirg these distribution functions from measurements on sections through an opaque material. New derivations, that have certain advanifages over those given previously, are Provided for well-known expressions used in estinzating the total density of lineal or areal features. INCREASING attention is being given to the quantitative description of imicrostructures in metals and other materials. This interest stems from the recognition that the structure often provides a convenient half-way point between the properties on the one hand and the processing variables on the other. Such cross correlations become increasingly desirable as materials become more complex and the demands on them more stringent. One of the principal aims in structure analysis is therefore to find parameters that are readily measurable and specific enough to be correlated with other properties of the material. Certain properties, such as magnetic and mechani cal behavior, are strongly influenced by structural anisotropies; in order to relate such properties to the structure it is obviously necessary to have means of specifying and measuring the type and degree of anisotropy. For the determination of preferred orientations in crystal structure, X-ray diffraction methods are available and are widely used, but scant attention has been given to the estimation of anisotropy in the shape of grains and particles. It is the latter problem that will be considered in this paper. It is evident that shape anisotropy can be describe in terms of preferred orientations of lineal and area elements of the structure. It will be shown that these preferred orientations can, in turn, be specified by distribution functions that define what fraction of the total line length or boundary area lies in a given direction. Methods will be given for determining the distribution functions from measurements on sections through the structure. Even when the orientation distributions are of no interest per se, they still have an important bearing on the measurement of the total line length or boundary area by means of an intercept analysis. The treatment in terms of orientation distribution functions leads to new derivations, that have certain advantages of those given previously, for the well-known expressions used in estimating the total density of lineal or areal features. The treatment is divided into two main sections. The first deals with the orientation distribution of a two-dimensional array of lineal features such as occurs in the projected image of dislocations in electron transmission microscopy. The other section treats the estimation of the distribution of lineal and areal features dispersed in three dimensions.

Jan 1, 1962

By M. R. Geer, H. F. Yancey

THE performance of coal-washing equipment, that is, the effectiveness with which coal and impurity are separated, is a subject of undisputed interest to all concerned with the preparation of coal. Through the years much has been written in both American and European literature on the performance of coal-washing equipment and its interpretation, but until recently no effort has been made to consolidate this wealth of information into a single, comprehensive treatment of the subject. A splendid effort in this direction was made at the First International Conference on Coal Preparation held in Paris in June 1950 in which representatives from virtually every coal-producing country participated. Although the scope of the conference covered the entire field of coal preparation, many of the sixty-odd papers and a great deal of the discussion dealt with the subject of evaluating washery performance. Prominence was given this subject by the Centre d'Etudes et Re-cherches, des Charbonnages de France, which sponsored the conference. This research organization, generally referred to as Cerchar, was formed in 1948 following the nationalization of the French coal industry. Since that date it has conducted an intensive study of coal preparation. Perhaps because of a fresh viewpoint, Cerchar realized immediately that complete information on the performance of French washeries and a thorough understanding of the mechanism of gravity separation were the fundamental prerequisites in a program to improve preparation practice. For this reason Cerchar concentrated on obtaining performance data and on a comprehensive study of methods of evaluating such information. Some idea of the magnitude of this work will be appreciated from the fact that 175 performance tests were made in 44 plants. The work performed by Cerchar emphasized a condition that is recognized by many of those concerned with coal preparation, namely that the lack of uniformity in presenting data on washery performance, the diversity of methods used in evaluating such information, and the frequent confusion of the terms related to performance have been prime factors militating against the progress from art to science. Thus, Cerchar feels that standardization of the methods employed for evaluating washery performance, not only in France but in the entire world, is essential to progress, and the prime objective of the Paris conference was to seek international standardization of the evaluation methods advocated by Cerchar. At the conclusion of the conference the question of standardization was referred to the International Standards Organization. A careful study of the dozen papers on the subject of evaluating washery performance presented at the conference reveals that none of the methods is new; most of them date back over a decade. Nevertheless, the intensive scrutiny of these methods brought about by the conference unquestionably has resulted in a valuable exchange of ideas and a clarification of thought that could scarcely be achieved in any other way. The object of the present report is to make available to the American coal industry the ideas developed at the conference which seem most important from an American viewpoint and to provide a critical analysis of some of the evaluation methods advocated by Cerchar. The various methods of evaluating washery performance are illustrated partly with data that have been published in American literature, and some new data have been obtained as the result of experimental work undertaken since the conference to provide information on certain controversial points. An English translation of the proceedings of the conference, including the discussion as well as the papers, will be available,' and previous to the conference Coal Age2 published a very brief description of some of the principal evaluation methods used by Cerchar. Americans will appreciate as well as do the French the desirability of standardizing both the termi-

Jan 1, 1952

By AIME AIME

IT is unlikely that any oil field has ever threatened the future course of the oil industry as does Kettleman today. It seems that nature has striven to outdo herself in combining in this field every possible factor conducive to a tremendous production of the petroleum product in greatest demand-gasoline. This field already has 13,700 acres of proved land and an oil zone of known thickness of 1400 ft. It has wells yielding several thousand barrels of oil of virtually motor fuel grade, together with millions of cubic feet of gas at almost unheard of pressures. The field would have been the. answer to an oil man's prayer in times of under-supply, but now it is the oil man's nightmare, for drilled in -the manner of most other fields and without regard to available markets for oil and gas, the greatest physical and economic losses in the his¬tory of the oil industry will result.

Jan 1, 1930

By L. E. Snow, L. F. Pett

AT the Utah Copper Pit of Kennecott Copper Corp. a versatile mobile drill unit has been developed and tested. Through increased drilling speed and additional available drilling time, an improvement of 233 pct in drill performance has been realized. Operators using drill power can quickly and easily convert the unit from a vertical to a toe hole drill. Drilling is done with the machine in line with the unit or at right angles to it. Table I covers the 1950 drill record at the mine, showing the types of machines used and the footage obtained. [ ] Development of the new units was prompted by a desire for solution of the following problems: 1-The ever-expanding operations within the Utah Pit, requiring some 65 miles of transmission pipe lines radiating from a central compressed air plant, have now taxed this compressor plant beyond capacity. While 100 lb per sq in. pressure is maintained at compressors, transmission losses from innumerable small leaks result in low terminal pressure at the drills. Fig. 1 illustrates that while terminal pressure varies according to size of air hose and fittings used, the average drill is operating on air pressures within the 60 to 70-lb range. The compressor plant is operated primarily for air rock drills. All drilling is done on day shift, but it is necessary to run two of the three 3720 cu ft capacity compressors during night shift in order to prevent drastic loss of pressure through leaks. On day shift all three compressor units are operated at capacity, so that there is no reserve safeguard available for extensive repairs to any compressor. The calculated volume of compressed air required for operation of 25 drills is but 33 pet of three day-shift compressors. While compressed air is being used to a minor extent for purposes other than drilling, it is felt that satisfactory substitute facilities could be provided in the event that air lines were no longer available. 2-Drill performance has increased beyond the capacity of present 3 ½ -in. drifter machines. 3-The installation, maintenance, and moving of air lines in routine mining is a growing problem. The 2-in. level lines are placed outside electrification towers and must be moved to new location upon completion of each shovel cut. In addition to these moves it is often necessary to dismantle level lines so that excessive shovel spillage, or material covering track following a blast, can be pushed in the clear with bulldozers. Where level room is limited, it is often necessary to remove air lines in giving bulldozers room to prepare grades for wagon drills. In spite of precautions taken, many level lines become buried, twisted, and constricted, with excessive air loss resulting. Excessive back break in blasting often leaves several sections of air line suspended in mid-air. Occasionally air lines come in contact with defective electric transmission towers, so that holes are burned through pipe. 4-Rail-handling of drilling equipment such as wagon drills from one location to another requires considerable locomotive crane crew time. Any new unit developed should travel under its own power. 5-Present practice requires accessory material including hose, water pressure tanks, water barrels, drill steel, and bits to be transported by means of push cars when drill locations are changed on any level. 6-In order to supply numerous drill locations with material, many stock piles of new drill rods, drill bits, and other essentials must be left at strategic points, usually in the vicinity of powder magazines. This practice makes for poor housekeeping and contributes to the loss of supplies. Planning the Unit It was felt that a mobile drill unit which would rectify the foregoing problems should meet certain demands: 1-It must furnish compressed air to operate a 4-in. rock drill at a pressure of 90 to 100 lb.

Jan 1, 1952

By Sherwin Kelly

THE need for geophysicists to adopt a uniform mode of expressing the electrical resistivity of geological formations has been stressed by Dr. A. S. Eve.1 The present paper is to emphasize the point he raised, to bring the weight of disinterested authority to bear on the matter, and to urge the adoption henceforth, save in exceptional cases, of a standard expression for resistivity; all in the hope that the needed reform will thus actually be brought about. The general definition of the resistivity of a material is the resistance in ohms between two opposite faces of a unit cube of that, material. No account need be taken here of the cases in which the unit volume is not a cube, and the units of length and cross-section are different, encountered principally when dealing with metallic conductors such as wires. The idea of the resistance of a unit volume of earth or rock has found expres-sion in geophysical literature in a number of forms and with a variety of units. Fortunately, the metric system has been adhered to in most cases, so ordinarily the meter or the centimeter, usually the latter, has been the measure chosen. The resistivity is then the resistance of a cube of the given rock, or soil, one centimeter on, an edge. This is far from always being the same thing, however, as the resistance of a cubic centimeter. A long thin wire could contain a cubic centimeter and have a high resistance, whereas the same volume formed into a flat plate would have an entirely different, and quite low, resistance between faces. Con-sequently, it is not proper to express resistivity in ohms per cubic centi-meter, inch, etc., as has been done occasionally by .some writers. In an effort to emphasize the idea of cubic volume, some geophysicists, the writer among them, have used the phrase, ohms per centimeter cubed. This is a graphic way of picturing the measure, but is not in favor among highly qualified authorities. In this connection, an appeal was made to the U. S. Bureau of Standards for advice, and the Director, George K. Burgess, kindly replied in detail as to the practice adopted by his Bureau: ." . .' such expressions as ohms per centimeter cubed' or any similar expressions are objectionable, because they certainly carry the implica-tion that the resistivity is found by dividing ohms resistance by the volume in cubic centimeters." Actually, of course, resistivity is found

Jan 1, 1932

By Gilbert H. Cady

Extensive sampling of coal in Illinois during the past 10 or 12 yegrs by the State Geological Survey, in cooperation with various organizations, such as the U. S. Bureau of Mines, the University of Illinois, and the Illinois Cooperative Mining Investigations, has made possible the delineation of two areas of low-sulfur coal in the southern part of Illinois. The $fur content is less than 1.25 per cent., so that, if otherwise suitable, these coals can be employed for metallurgical uses and for the manufacture of water-gas and retort gas. One of these areas is small and lies in Jackson County, near Murphysboro, the other is much larger and includes a large part of the famous Franklin County field. A small area of No. 2, or Murphysboro, coal has been worked for many years near the town of Murphysboro, Jackson County, Ill. In two mines, at least, the coal has a sulfur content of less than 1.25 per cent. It is doubtful, however, whether this field will ever be a source of large tonnage as the total area underlain by low-sulfur coal in workable thickness is probably less than 15 sq. mi. (24.14 sq. km.), and a large part of it has already been worked out.. The location of the area of low-sulfur coal in the Franklin County field is shown in the accompanying map. The small area underlain by the Murphysboro low-sulfur coal is shown near the town of that name in the central part of Jackson County. The larger area lies in the west side of Franklin County, extending also about 6 mi. (9.65 km.) south into Williamson County, about 4 mi. (6.43 km.) west into northern Jackson and western Perry County, and northward an undetermined distance into Jefferson County. All but the northern limit of the area is fairly well defined by sampling in numerous mines. The inner cross-lined area is underlain by coal having less than 1 per cent. sulfur, the outer boundary surrounding the area underlain by coal having less than 1.25 per cent. sulfur. The coal mined in the district is No. 6 or Herrin coal, commonly known as the Carterville or Franklin County coal. The bed has a thickness varying from about 8 ft. (2.4 m.) on the border of the low-sulfur area up to more than 10 ft. (3 m.) in the central portion, locally having a thick-

Jan 1, 1920

By Vsevolod Krivobok

IT is generally recognized that "low temperatures" have a definite effect on the properties of metals and alloys. Furthermore, it is also generally understood that the effect is decidedly adverse. The possibility that the same low-temperature treatment might be employed for the purpose of improving certain properties of the .alloys has received less attention until recently, and the experimental and theoretical knowledge consequently is meager. The effect of low temperatures may be studied in two ways: by studying such properties as tensile strength, hardness, impact resistance, etc., at low temperature, and by studying the properties of alloys at room temperature after these alloys have been subjected to a low-temperature treatment. Even in the latter case, certain properties will differ materially from the same properties obtained on identical material but without cold treatment. In other words, subjecting alloys to cold treatment results in an irreversible change in mechanical properties. Changes of this character are usually indications of the appearance of a new phase or phases, and would be likely to occur in alloys which, either by virtue of their composition or by heat treatment, are retained at room temperature in a metastable condition. Consequently, studies of the effect of low temperatures logically should be conducted from the physicochemical point of view, since the results of such studies not only would furnish metallurgists with interesting theoretical data but would clearly indicate the classes of alloys that would hold promise of improvement, and, possibly, of new applications. As the present investigation deals with chromium and chromium-nickel alloys of iron of the stainless variety, it has been thought desirable to present the data concerning low-temperature properties of these alloys, available from the most recent and most comprehensive work of H: S. Russell.' A summary, of these data is given in Table 1. The data are confined to a limited number of alloys of the type dealt with in the present

Jan 1, 1931

By John A. Oberteuffer, Ionel Wechsler

High gradient magnetic separation, first introduced in 1968 as a means for the removal of very fine magnetic contaminants from clay, is no longer a new technology. Applications to a number of solid-solid and solid-fluid separation problems are now being exploited. Recent pilot tests and full-scale industrial installations of high gradient magnetic separators and filters have established their commercial viability and have demonstrated their superiority both in efficiency and cost effectiveness to conventional prior-art methods for water treatment and mineral processing. In high gradient magnetic separators, the magnetic trapping force for fine, even weakly magnetic particles is greatly increased over those available in previous magnetic separators. These very strong trapping forces are created on the edges of fine filamentary ferro- magnetic materials in the presence of a strong background magnetic field. In the basic cyclic high gradient magnetic separator, particles are trapped in the filamentary matrix until it is loaded, at which point the magnetic field is turned off, and the filter is back- flushed. Applications of cyclic high gradient magnetic filtration for water treatment include filtration of waste and process waters in steel mills. Treatment of hot rolling mill scale pit effluent and cold rolling mill emulsion has been successfully tested, and 2-meter diameter SALA-HGMF® magnetic filters have been installed at Japanese steel companies for the treatment of recirculating scrubber waters in a de-gas- sing system. A second major application in water treatment is for the polishing of recirculating waters in power and steam generating systems. High gradient magnetic filters can operate under conditions of

Jan 1, 1980

By Allen Rogers

THERE are few natural monopolies comparable with the nitrate industry. Perhaps the only other one is, curiously enough, also an essential fertilizer material, viz., potash, of which the Germans have heretofore held practically a-monopoly due to the existence in their territory of the most important known deposits of potash salts. And although nitrates in minute amounts are found in many desert regions, the only deposits callable of being worked commercially exist in Chile. Combined nitrogen in the oxidized form is an essential for plant life. Nature provides it mainly through the agency of nitrogen-fixing bacteria. But where lands are cropped artificially this supply is too small; and gradually the nitrogen supply becomes exhausted. In order to continue farming, it is necessary to furnish a supply of nitrogenous plant food, and this is clone by putting on various substances containing combined nitrogen. These consist of various animal wastes, ammonium sulphate, the ammonia of which is obtained in the destructive distillation of coal, and Chile saltpeter. The latter is immediately available as a plant food, the nitrogen being in the required form. The other substances must oxidize before they are available. Besides its use as a fertilizer, Chile saltpeter is the source from which the bulk of the nitric acid of commerce is derived. The use of nitric acid in the manufacture of almost, all modern explosives is, of course, well known.

Jan 2, 1918

By J. W. Stewart

ONE of the postwar problems posed for mineral engineering educators is the desire of some mature student veterans to finish their college education under the G. I. Bill of Rights as quickly as possible, a desire that is quite understandable. Not only have they lost several years of education, which they wish to make up as quickly as possible, but many are married and have families and want to become productive as soon as possible in order to support their families properly. The obvious solution to this problem, if it really is serious, would appear to be a continuation of the wartime Accelerated Program, as it was carried on in most colleges and universities. As a matter of fact some schools are known to have continued their wartime programs in one or another form. To ascertain just what our mineral engineering schools generally are doing to meet this postwar problem, last April a questionnaire was sent to administrative officers at colleges and universities

Jan 1, 1946

By Sherwin F. Kelly

The need for geophysicists to adopt a uniform mode of expressing the electrical resistivity of geological formations has been stressed by Dr. A. S. Eve.1 The present paper is to emphasize the point he raised, to bring the weight of disinterested authority to bear on the matter, and to urge the adoption henceforth, save in exceptional cases, of a standard expression for resistivity; all in the hope that the needed reform will thus actually be brought about. The general definition of the resistivity of a material is the resistance in ohms between two opposite faces of a unit cube of that material. No account need be taken here of the cases in which the unit volume is not a cube, and the units of length and cross-section are different, encountered principally when dealing with metallic conductors such as wires. The idea of the resistance of a unit volume of earth or rock has found expression in geophysical literature in a number of forms and with a variety of units. Fortunately, the metric system has been adhered to in most cases, so ordinarily the meter or the centimeter, usually the latter, has been the measure chosen. The resistivity is then the resistance of a cube of the given rock, or soil, one centimeter on an edge. This is far from always being the same thing, however, as the resistance of a cubic centimeter. A long thin wire could contain a cubic centimeter and have a high resistance, whereas the same volume formed into a flat plate would have an entirely different, and quite low, resistance between faces. Consequently, it is not proper to express resistivity in ohms per cubic centimeter, inch, etc., as has been done occasionally by some writers. In an effort to emphasize the idea of cubic volume, some geophysicists, the writer among them, have used the phrase, ohms per centimeter cubed. This is a graphic way of picturing the measure, but is not in favor among highly qualified authorities. In this connection, an appeal was made to the U. S. Bureau of Standards for advice, and the Director, George K. Burgess, kindly replied in detail as to the practice adopted by his Bureau: 'I.., such expressions as 'ohms per centimeter cubed' or any similar expressions are objectionable, because they certainly carry the implication that the resistivity is found by dividing ohms resistance by the volume in cubic centimeters." Actually, of course, resistivity is found

Jan 1, 1932

By O. P. Hood

.NONE of the methods now in use for the transportation of materials underground is entirely free from more or less serious objection. The great flexibility, ease, of control and economy of operation of electric tramming are accompanied by the serious menace of a trolley-wire distributing system. As the gasoline locomotive has even greater flexibility of application and requires no similar dangerous distributing system, it might be considered a safety device which would make possible the elimination of the dangerous trolley system were it not possessed of other objectionable qualities peculiar to itself. It is found that the exhaust gases from the engine may be injurious to the health of those breathing the air in which the locomotive has been operating. While electric shock may kill the individual who makes contact with uninsulated parts, the gasoline engine may be detrimental to the health of all those who have to work within the atmosphere corrupted by exhaust gases. The degree of pollution meas-ures the magnitude of the menace. This may be negligible at times, but with careless operation it becomes serious. The exhaust gases from an engine are composed of, nitrogen, a little free oxygen, hydrocarbons, hydrogen, carbon monoxide, and carbon dioxide, the last two being considered dangerous. The presence of carbon dioxide as a product of combustion of the gasoline was recognized as an objection from the beginning of the use of these machines, but attention was called to the fact that the amount produced was relatively small as compared to that from other sources of this gas, and it was not likely to be made in dangerous quantities. The effect of carbon dioxide, except in relatively large percentages, is confined to the effect it may have in reducing the oxygen content of the air that is breathed.

Jan 10, 1914

By G. Wranglen

On account of the possibility of isolating carbides in steel it is generally assumed that the electrode potential of iron carbide is more noble than that of ferrite.1,2,3,4,5 Differences from 0.032 V1 to 0.4 V4 have been recorded. However, it is important to realize that the more noble behavior of cementite in relation to ferrite is not an issue of thermodynamics but of reaction kinetics. Theoretically, cementite is less noble than ferrite, which is a direct consequence of its thermo-dynamic instability. With the value ?F°298 = +4700 cal per mol for the free energy of formation of cementite6 it is easily calculated that the electrode

Jan 1, 1950

By Ken-ichi Hirano, B. L. Averbach, Morris Cohen, N. Ujiiye

The influence of plastic deformation in compression on the self-diffisivity of a iron has been measured in the temperature range of 742º to 885°C. The diffusivity is enhanced in proportion to the strain rate, but this dependence decreases with increasing temperature. The magnitude of the strain is relatively unimportant in this connection. Strain rates from 0 to -2 x 10-3 sec-1 were investigated, with a corresponding increase in diffusivity up to 3 x 103 times. The results are analyzed in terms of vacancy diffusion and the excess vacancies introduced during dejornzntion. It is concluded that grain boundaries are the main vacancy sinks in polycrystalline iron and that the vacancy lifetime is therefore dependent on the grain size. A typical vacancy lifetime at 800°C with a nzean grain-boundary intercept of 0.3 cm is of the order of 1 sec. LATTICE imperfections are considered to be the dominant mechanism of diffusion in close-packed crystals. Vacant lattice sites are usually the most important defect, but the enhancement of diffusion along grain boundaries and other short-circuiting paths has been well documented. Inasmuch as plastic straining produces a variety of defects, it would be expected that the application of stresses sufficient to cause plastic flow during a diffusion run might result in an increase in the self-diffusivity. Enhanced self-diffusion in a iron under compressive creep has been observed by Buffington and Cohen' and subsequent coworkers.2 Lee and Maddin3,4 have also found an enhancement in the self-diffusivity of silver single crystals undergoing torsional deformation. On the other hand, Darby, Tomizuka, and Balluffi5 have not observed any significant diffusion increase in single crystals of silver deformed either in tension or in compression, although the results in this case may have been affected by the occurrence of recrystallization. With poly crystalline silver, however, Forestieri and Girifalco6 have found en- hanced diffusion during compressive creep. A small decrease in the self-diffusivity of zinc single crystals under compressive loading has been reported,7 but the applied stresses in these experiments were too low to cause appreciable plastic deformation. For the cases in which enhanced diffusion has been found, a number of common effects have been noted. Usually, the ratio of the diffusivity during straining, Ds, to the diffusivity in the unstrained condition, D,, varies linearly with the strain rate, and does not seem to be a function of the plastic strain, at least up to ? = 0.2. Values of Ds/Du of the order of 100 have been reported'-4 but the enhancement decreases with increasing diffusion temperature. The activation energy for diffusion decreases markedly with increasing strain rate and approaches a level of roughly one-half the unstrained value. Most of the current explanations of these observations assume that excess vacancies are generated by the deformation, but rather large concentrations of excess vacancies and/or long lifetimes are required by these theories.',',',' Since the original work on iron, there has been an important improvement in the compressive-loading technique.2 The early data were also analyzed without taking into account the motion of the coordinate system in the specimens undergoing plastic deformation. This problem has now been solved by a number of investigators (see Refs. 11, 12, and the appendix of the present paper). Consequently, the strain-diffusion runs on iron for the Ds measurements were repeated and extended over wider ranges of temperature and strain rate. In addition, the original diffusivity data9 on the unstrained iron have been corrected for the divergence of the beam in the counting system and new data points have been added, resulting in somewhat different values for the self-diffusi-vities in a iron.10 The new values for Du are used in this paper. A comparison of Ds and Du confirms the large enhancement in the self-diffusivity of iron during compressive creep, as previously reported.',2

Jan 1, 1963

By R. Maddin, W. R. Hibbard

A series of X ray experiments conducted by G. I. Taylor' in 1927 and later substantiated in 1939 by J. A. Collins2 both on axially strained aluminum single crystals, revealed evidence that during single slip crystallite rotation occurs in such a manner that " all parts of the material rotated about the transverse direction in the plane of slip."l The actual method of preparing the specimens for X ray examination is not discussed in detail by Taylor except to say that "this specimen was cut parallel to the plane of slip, as calculated from measurements of marks in the surface of the specimen. It was ground and etched till the effect of the new cuts had disappeared. This was verified by applying the same treatment to an un-distorted specimen. The X ray reflectionsl in this case were perfect ones."' Collins, on the other hand, cut his crystals in a mechanical shaper. These surfaces were polished on No. 1, No. 1/0, No. 2/0 and No. 3/0 papers and on a broadcloth lap using No. 600 alundum as a polishing medium. "Finally, the surface was deeply etched in Tucker's reagent. An unde-formed crystal was prepared in the manner described and X rayed to determine whether or not the machining and polishing operations had produced any strain or distortion in the crystal. The Laue spots all seem to be sharp, free from tails and streaks indicating no detectable strains had been introduced in the crystals." Taylor's X ray technique involved the use of "homogeneous X rays from an iron anti-cathode"; whereas Collins used Ka radiation of copper at 31kv and 20 milliamperes. Glancing angle X ray photograms were taken (1) with the axis of rotation of the spectrometer table in the plane of slip and at right angles to the slip direction, and (2) with the axis of the spectrometer table lying along the slip direction. However, eight minute exposures were used in each case and the angle setting of the spectrometer table was increased by one degree for each exposure. With the discovery of the action of three slip systems3 in the plastic deformation of single crystalline alpha brass where, formerly, only one had

Jan 1, 1950

By Charles O. Thompson

In 1867 the city of Worcester walled in the Mill Brook for its main sewer. This stream, one of the important affluents of the Blackstone River, flows through the city in a southwestenly course from Salisbury Fond, and along its valley a considerable part of the heavy manufactories of the city are placed. At two points, a mile apart, a sufficient fall occurs to be turned to account for motive power, and at many points it was the right and practice of the riparian proprietors, prior to 1867, to use the water for steam and other manufacturing purposes. But the

Jan 1, 1881

HeRbert A. MeGRaw, San Luis de la Paz, Guanajuato, Mex. (communication to the Secretary*) :—Although Mr. Bordeaux prefaces his paper with the statement-that it is a general outline of practice in the Republic, many of his statements seem to be made from the view-point of a particular case, which does not always agree with general practice. For the purpose of calling attention to some of these variations, I respectfully offer the following comments: The operation of crushing and grinding is performed by so many different methods and systems that it is useless to select any one as the standard. However, primary crushing in rock-breakers followed by stamps is thus far so general that it might be so classified. Whether or not it is the best way, is open to question. Regrinding may be performed by any of the various types of Chilean mills, Huntington mills, or similar machines, or the material may be taken directly from the stamps and delivered to the tube-mills. Mr. Bordeaux's statement that " the slimes can be treated only by decantation; the new Butters slime-filter, as used in Nevada, does not seem to be successful with silver-ores," is surely an error. All over Mexico many of the purely silver-ores are being successfully handled by the Butters or similar filters, such as the Moore and the Burt filters, and a letter to the manufacturers of these filters will undoubtedly bring a list of the silver-ores now being successfully treated in this way. The statement that crushing silver-ores in solution is impossible is equally erroneous. Most modern mills crush the ore in solution, in some cases containing as much as 0.12 per cent, of KCN. I cannot for the moment recall any modern mill in Mexico which does not follow this practice. There may be some reason for it in particular instances, but, generally speaking, the practice is to crush in solution. Care in installation avoids any mechanical loss of cyanide, and the chemical loss is so small as to be negligible.

Jan 1, 1910

By G. W. Josephson

Since the earliest years of recorded history the durability and protective qualities of asphalt and tar have been known and utilized. The mummies of early Egyptian kings were coated with asphaltic materials, and asphalt mastics were common in Babylon. However, according to various authorities, it was not until 1780 that the first forerunner of present-day composition roofing was discovered,l and the large-scale expansion of the industry has taken place since 1900. Historical Background Development was stimulated by the growing popularity of manufactured gas. The by-product tars from these operations accumulated in large waste piles that had no commercial value and were a source of annoyance and expense to the gas companies. These tars were offered at very attractive terms to anyone who would take them away, and the infant "composition" roofing industry benefited accordingly. At first the process consisted simply of dipping sheets of burlap or other fabric in a tank of molten tar or asphalt. The long strip of roofing was rolled up for convenient handling, and the early experimenters soon found that it was necessary to dust the surface of their new "roll roofing" with some kind of material that would prevent the tarred surfaces from sticking together. Any finely divided, low- priced local material like sand or fine gravel served this purpose and from its application the roofing-granule industry grew. As time went on other characteristics of a properly applied mineral surfacing were recognized. As with wooden shingles, tar and asphalt can be ignited by flying embers from near-by fires. It was found that by increasing the largest particle size to the maximum that could be successfully embedded, and by properly controlling the amount of smaller fractions retained in the grade so as to cover the asphalt completely a high degree of resistance to fire was attained. Needless to say, in this early period asphaltic roofing needed such selling points to gain acceptance in a field dominated by wood, slate, and tile. When asphalt is protected from the sun's rays it is extremely durable, but when exposed to sunlight its surface is comparatively rapidly decomposed. Completely covering asphalt roofing with mineral surfacing protects the asphalt and adds materially to the life of the roof—conservatively, 500 per cent. Slate Graftules In the production of split slate shingles a large quantity of waste slate is accumulated, as 60 to go per cent of the rock quarried is discarded. This waste was a continuing burden on the industry. Some was marketed as ground slate flour for filler in paint and linoleum, and there is a record that as early as 1906 two carloads of coarse screenings from slate flour were marketed as granules for surfacing roofing. This new field appeared to the slate Pro-

Jan 1, 1948

By G. W. Josephson

Since the earliest years of recorded history the durability and protective qualities of asphalt and tar have been known and utilized. The mummies of early Egyptian kings were coated with asphaltic materials, and asphalt mastics were common in Babylon. However, according to various authorities, it was not until 1780 that the first forerunner of present-day composition roofing was discovered,l and the large-scale expansion of the industry has taken place since 1900. Historical Background Development was stimulated by the growing popularity of manufactured gas. The by-product tars from these operations accumulated in large waste piles that had no commercial value and were a source of annoyance and expense to the gas companies. These tars were offered at very attractive terms to anyone who would take them away, and the infant "composition" roofing industry benefited accordingly. At first the process consisted simply of dipping sheets of burlap or other fabric in a tank of molten tar or asphalt. The long strip of roofing was rolled up for convenient handling, and the early experimenters soon found that it was necessary to dust the surface of their new "roll roofing" with some kind of material that would prevent the tarred surfaces from sticking together. Any finely divided, low- priced local material like sand or fine gravel served this purpose and from its application the roofing-granule industry grew. As time went on other characteristics of a properly applied mineral surfacing were recognized. As with wooden shingles, tar and asphalt can be ignited by flying embers from near-by fires. It was found that by increasing the largest particle size to the maximum that could be successfully embedded, and by properly controlling the amount of smaller fractions retained in the grade so as to cover the asphalt completely a high degree of resistance to fire was attained. Needless to say, in this early period asphaltic roofing needed such selling points to gain acceptance in a field dominated by wood, slate, and tile. When asphalt is protected from the sun's rays it is extremely durable, but when exposed to sunlight its surface is comparatively rapidly decomposed. Completely covering asphalt roofing with mineral surfacing protects the asphalt and adds materially to the life of the roof—conservatively, 500 per cent. Slate Graftules In the production of split slate shingles a large quantity of waste slate is accumulated, as 60 to go per cent of the rock quarried is discarded. This waste was a continuing burden on the industry. Some was marketed as ground slate flour for filler in paint and linoleum, and there is a record that as early as 1906 two carloads of coarse screenings from slate flour were marketed as granules for surfacing roofing. This new field appeared to the slate Pro-

Jan 1, 1948