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By R. W. Raymond

On the 27th day of March last, the day on which the Florida sessions of the last meeting of the Institute began in Ocala, occurred the death of one of its most distinguished honorary members, Bergrath Franz Posepny, of Vienna, formerly professor of the science of ore-deposits in the mining school at Przibram, Bohemia. Prof. Posepny had greatly increased his fame among American mining engineers, besides laying the Institute under special obligations of gratitude, by the elaborate, brilliant and suggestive treatise on " The Genesis of OreDeposits," which he contributed to the International meeting, held at Chicago, in 1893. This essay, constituting the first complete publication of the substance of his course of lectures at Przibram, enriched and perfected by the matured results of his investigation and reflection down to the date of its cornpletion, was a free gift of almost unprecedentecl value to the society which had distinguished him by honorary membership. In estimating the generosity of the author, it must be borne in mind that the copyright of such a work, the fruit of years of study and of practice as an instructor, is of no little value to a European professor, and constitutes one of the legitimate rewards of his (otherwise not highly-paid) labor. Moreover, Prof. Posepny performed under peculiar difficulties

Jan 1, 1896

United Engineering Trustees, Inc. WILLIAM H. BASSETT H. G. MOULTON R. M. ROOSEVELT The Engineering Foundation GEORGE D. BARRON E. DEGOLYER R. M. ROOSEVELT Engineering Societies Library Board ROBERT PEELE H. K MASTERS A. B. PARSONS, Ex-officio F. F. SHARPLESS R. H. SWEETEST

Jan 1, 1934

By William E. Ford, Edward Salisbury Dana

Twin crystals are those in which one or more parts regularly arranged are in reverse position with reference to the other part or parts. They often appear externally to consist of two or more crystals symmetrically united, and sometimes have the form of a cross or star. They also exhibit the composition in the reversed arrangement of part of the feces, in the striae of the surface, and in re-entering angles; in certain cases the compound structure can only be surely detected by an examination in polarized light. The above figures (Figs. 384-386) are examples of typical kinds of twin crystals, and many others are given on the pages following.

Jan 1, 1922

By W. F. Holbrook, C. E. Wood, E. P. Barrett

The high-frequency laboratory induction furnace with a rotating liquid crucible enables research workers to conduct certain investigations heretofore very difficult or impossible to realize because vessels are not obtainable that are capable of resisting the physical conditions or the chemical actions to which they are subjected. Applications for patents covering commercial uses of centrifugal liquid crucibles were filed in the United States in 1919,' in France in 1925, in the United States and Germany in 1926,2 and in France in 1927.3 In 1928, Schuette and Maier,4 of the Bureau of Mines, reported the construction of a whirling table beneath a high-frequency induction furnace. Shape and Size of Centrifugal Liquid Crucibles When a vessel containing a liquid is rotated, the inner surface of the liquid takes the shape of a paraboloid under the simultaneous action of centrifugal force and gravity. The internal dimensions of the paraboloid rotating liquid crucible are governed by the diameter of the container and its speed of rotation. Melted Wood's metal was poured into cylinders 2 1/2 in. in diameter, which were rotated at 180, 300, and 468 r.p.m. When the metal was solid, a slurry of plaster of Paris was added, and rotation continued until the plaster had set. Fig. 1, a photograph of sections of the cylinders, shows the effect of speed of rotation of the containers upon the shape of the inner surface of the rotating liquid crucibles. Types of Furnaces Three types of high-frequency induction laboratory furnaces using liquid-metal crucibles were designed and constructed by the Blast

Jan 1, 1939

By W. F. Holbrook, C. E. Wood, E. P. Barrett

The high-frequency laboratory induction furnace with a rotating liquid crucible enables research workers to conduct certain investigations heretofore very difficult or impossible to realize because vessels are not obtainable that are capable of resisting the physical conditions or the chemical actions to which they are subjected. Applications for patents covering commercial uses of centrifugal liquid crucibles were filed in the United States in 1919,' in France in 1925, in the United States and Germany in 1926,2 and in France in 1927.3 In 1928, Schuette and Maier,4 of the Bureau of Mines, reported the construction of a whirling table beneath a high-frequency induction furnace. Shape and Size of Centrifugal Liquid Crucibles When a vessel containing a liquid is rotated, the inner surface of the liquid takes the shape of a paraboloid under the simultaneous action of centrifugal force and gravity. The internal dimensions of the paraboloid rotating liquid crucible are governed by the diameter of the container and its speed of rotation. Melted Wood's metal was poured into cylinders 2 1/2 in. in diameter, which were rotated at 180, 300, and 468 r.p.m. When the metal was solid, a slurry of plaster of Paris was added, and rotation continued until the plaster had set. Fig. 1, a photograph of sections of the cylinders, shows the effect of speed of rotation of the containers upon the shape of the inner surface of the rotating liquid crucibles. Types of Furnaces Three types of high-frequency induction laboratory furnaces using liquid-metal crucibles were designed and constructed by the Blast

Jan 1, 1939

By Charles M. Rolker

THIS remarkable and well-known district lies about 320 miles south of Salt Lake City, in Washington County, near the Arizona border of the territory. It is now reached by the Utah Southern Railroad and its extension, and the last 100 miles are run by stages. These vehicles are called "jerkies" in the West, which name conveys a good idea of the comfort they afford, and the relief experienced when you alight. Arriving at Silver Reef, the main camp of the district, one sees at once that he stands where once a surging sea had its domain, marked now by heavy sandstone deposits of a red and white color. The town itself, a neat, clean, and orderly mining town, is encircled on the north by traohyte and granite mountains, skirting to the west. They are cut through in places by deep gorges, left us as the only trace of the force of former currents, which drained the adjoining territory to the north; and which when swelled and infuriated by tempests and cloud-bursts, took in their grasp the huge blocks of

Jan 1, 1881

By Charles M. Rolker

THIS remarkable and well-known district lies about 320 miles south of Salt Lake City, in Washington County, near the Arizona border of the territory. It is now reached by the Utah Southern Railroad and its extension, and the last 100 miles are run by stages. These vehicles are called "jerkies" in the West, which name conveys a good idea of the comfort they afford, and the relief experienced when you alight. Arriving at Silver Reef, the main amp of the district, one sees at once that he stands where once a surging sen had its domain, marked now by heavy sandstone deposits of a red and white color. The town itself, a neat, clean, and orderly mining town, is encircled on the north by trachyte and granite mountains, skirting to the west. They are cut through in places by deep gorges, left US as the only brace of the force of former currents, which drained the adjoining territory to the north; and which when swelled and infuriated by tempests and cloud-bursts, took in their grasp the huge blocks of

Jan 1, 1881

C. W. GOODALE, Butte, ,Mont.-While there are many points in Mr. Read's, paper which I am not prepared to discuss thoroughly, I am inclined to believe that difficulties are involved in the establishment of all employment bureau, which shall have exclusive control over the employment and discharge of workmen. I suppose you .have heard a great deal: about the so-called "rustling card? at the works of the Anaconda company. That is a very innocent sort of card, although the I. W. W. organization has made a great deal of noise about it. An applicant for a job is handed a blank on which he tells his nationality, his age, whether married or single, and the place of his last employment. The company then writes to the place where he says he was last employed to find out whether he is telling the truth; we do not ask the previous employer whether the man is blacklisted or has anything; against his record; but simply, "Was this man formerly in your employ?" A great hullabaloo has been made, about this practice by some of the men in Montana who are afraid, of their own records; but out of 53,000 applications for employment received by the Anaconda company since the employment bureau was formed, only 647 were rejected, which does

Jan 1, 1918

By Ralph W. Bailey, William B. Price

During the past three or four years, the fabricators of silicon-bronze alloys have endeavored to induce users of phosphor bronze to use instead the silicon-bronze alloys, claiming that the silicon bronzes are superior to the phosphor bronzes for switches and springs, or where high fatigue resistance is desired. This paper gives the results of tests comparing several phosphor bronzes with a 3 per cent silicon bronze and a copper-nickel-tin alloy (Adnic), all processed by the Scovill Manufacturing Co. So far as the authors are aware, sheet-metal fatigue tests have not been made on any of the alloys included in this report, except on one phosphor bronze, material C, Table 1, which was tested by Townsend and Greenall1. Endurance Limit The majority of fatigue tests are designed to determine the endurance limit of a material. The number of repetitions of stress that will serve to establish an endurance limit varies with different materials. For ferrous materials, H. F. Moore2 has shown that stresses that do not cause failure up to 10,000,000 stress cycles will not cause failure up to 100,000,000 (and sometimes to 1,000,000,000) cycles. Thus an endurance limit for ferrous materials can be determined with a minimum of 10,000,000 stress cycles. For nonferrous materials, no such generalization holds. R. R. Moore3 has shown that for manganese bronze and elektron metal, 13,000,000 and 28,000,000 cycles, respectively, will serve to determine an endurance limit, while certain duralumin specimens gave no indications of having reached an endurance limit up to 400,000,000 stress cycles. J. B. Johnson6 showed that an endurance limit for duralumin was not found by tests running up to 500,000,000 cycles. H. F. Moore2

Jan 1, 1937

By Colin G. Wilson

This paper considers the heavy liquid laboratory tests used to determine the amenability of a potential ore to the heavy media process. The results of the laboratory testing are correlated to actual plant performance and establish design parameters for the heavy media process. These parameters are used in the development of the metallurgical flow sheet and in the sizing of equipment in the metallurgical plant design.

Jan 1, 1978

By Norman Brown, J. V. Rinnovatore

It was found that a shear stress applied during the recovery had no effect on the amount of recovery if the stress was less than the instantaneous yield point irrespective of the direction of the stress. Large ajplied stresses during recovery had a marked effect, which depended on the direction of stressing. Single strain reversals at -72°C not only produced the Bausch-inger effect but also increased the flow stress. The increase inflow stress was attributed to vacancies, which have appreciable mobility at -72 °C. THEORIES I-' of recovery suggest that the internal stress field of the dislocations plays an essential role. Most investigations of recovery use time and temperature as the independent variables; however, here stress has been introduced as a variable in two ways: 1) by varying the internal stress field according to the amount of strain prior to recovery and 2) by applying an external stress during recovery. Tannen- baum and Kauzrnann studied the effect of applying a stress during recovery by measuring the change in creep rate after recovery; they found that stresses as high as 95 pct of the creep stress had no effect on recovery. Earlier, Wood and scrutton6 showed that an applied stress during creep increased the rate of poly-gonization. The experiment by Wood involved poly-crystalline aluminum whereas Tannenbaum and Kauzmann used a single crystal of zinc. In this investigation, zinc single crystals were used and deformed in a manner to prevent polygonization. Thus, the main difference between this investigation and that of Tannenbaum and Kauzmann is the use of the stress-strain curve instead of creep rate as the index of recovery. In addition, the applied stress during recovery varied

Jan 1, 1961

Would you briefly describe how you chose the minerals industry and reflect upon some of your earliest experiences? I wish that I could say that I had a well-formulated career plan early in life and that mining engineering was always foremost in it, but I cannot, In fact, I was quite indecisive before I finally chose my life's vocation. But in another respect, I am glad my career unfolded in the manner it did because it gave me a better insight into advising others on career opportunities. Probably the greatest problem confronting our youth, and the one I find preys upon their minds the most, is their inability to select a career path early in life. This indecision frequently has a deep psychological effect upon them and they become down on themselves. Therefore, it fortifies them somewhat to learn that others who have become successful in their careers had difficulties choosing a career path early in life. However, while assuring young people that an early choice is not absolutely essential for success, I caution them to work toward as early a decision as possible.

Jan 3, 1979

Prof. G. W. MAYNARD, New York City (communication to the Secretary): Prof. Christy, in his admirable paper on "The Growth of American Mining Schools," has overlooked the work done by the Rensselaer Polytechnic Institute in its department of mining and metallurgy. This oversight is naturally due to the fact that the department was, for lack of money, discontinued in 1871. It was organized by the writer in 1867, starting with ten students, who had already completed the first two years of the civil engineering course in the Institute. The course covered two years, specifically devoted to mining, metallurgy and assaying, which, in connection with the two years' drill in the civil engineering department made a four years' course. During the four years of the existence of the department, thirty-five students took the course, of whom twentyfive graduated; and of this number eight have been members of the Institute of Mining Engineers, and the majority of them have occupied high positions in the profession. The equipment of the department was, at that time, second only to that of the Columbia School of Mines. As Prof. Christy has cited other institutions which are not distinctively mining schools, but in which the ruining course was subordinate to other courses, it seems to me that the work in this line carried out by the oldest engineering school in the country may very properly be referred to. In addition to the regular mining course, a special course in assaying was given; and many young men were here prepared for positions in the mines and metallurgical works of the west. PROF. George F. Swain, Boston, Mass.: I have listened with great interest to Prof. Christy's valuable paper, but there is one conclusion at which he arrives that appears to me entirely unjustifiable, and to which I desire to take exception. Prof. Christy finds that of the total wage-earners in the United States in 1880,10.41 per cent. were employed in " trade and transport;" 20.24 per cent. in " manufactures and mechanics," and 1.83

Jan 1, 1894

By W. P. Sykes

RECENT investigations of the molybdenum-carbon alloys have been reported by Becker and Ebert1,? Westgren and Phragmén2, T. Takei3, and H. Tutiya4. Takei3 studied the Mo-C system by employing metal-lographic and X-ray methods, and the other publications described the determination of the crystal structure of the molybdenum carbides. In exploring this system by a technique previously applied to the tungsten-carbon series5, the results of Takei were confirmed with two definite exceptions; i.e., first the composition of the eutectic, and second the nature of the carbon-rich intermediate phase. Consequently, a more thorough examination of the molybdenum-carbon constitution was initiated in an effort to correlate the data supplied by the microstructures, diffraction patterns and chemical analyses.

Jan 1, 1935

By Rex T. Ellington

The fluidized bed is an effective method for investigating retorting phenomena and possibly a commercial means of retorting oil shale. Both were examined by Sinclair Oil (now part of Atlantic Richfield Co.) in the period 1965-1698. The results of the work show that the presence of an oxidizing environment during retorting results in loss of oil yield which indicates that vapor phase oil burns in preference to combustion of coke on spent shale. Consideration of hardware indicates that there are several possibilities for commercial embodiment. As a companion to shaft-type retorts the fluidized bed could have good potential. Realistic assessment of costs suggests that further development may have to wait commercialization of another process.

Jan 1, 1974

By R. T. Hukki

John F. Myers (Consulting Engineer, Greenwich, Corm.)—Since the art of comminution has lain practically dormant for many years, it is very interesting that R. T. Hukki approaches the subject with a new concept. One is reminded of the research carried on by A. W. Fahrenwald of Moscow, Idaho, a few years ago. Fahrenwald mounted a steel bowl on a vertical shaft. The balls and ore placed in the bowl were rotated at fast speeds, thus simulating the supercritical speeds used by Hukki. The rolling action of the balls against the smooth shell liner has pretty much the same effect. The action is horizontal in one case and vertical in the other. Both researchers report good grinding activity. It is also constructive that such able investigators give to the students of comminution their interpretation of their laboratory results in terms of large-scale operation. History shows that it takes a lot of time for such radically new ideas to be absorbed by the industry. Typical of this is the present-day activity of cyclone classification in primary grinding circuits. The idea of cyclone classification has been kicking around for 30 or 40 years. Certainly we all suspect that the ponderous grinding mills of today, and their accessory apparatus, large buildings, etc., will ultimately give way to small fast units, just as this has occurred in other industries over the past 50 years. At the moment there is no evidence that ball and liner wear is prohibitively high. In fact, at the time Fahrenwald was demonstrating his high-speed horizontal machine at the meeting of the American Mining Congress, several years ago, he assured this writer that the balls retained their shape much longer than they do in conventional tumbling mills. Rods and balls that slide (as some operators in uranium plants are experiencing) get flat. Apparently the balls have a rolling action. Mr. Hukki's references to the processing capacity of the Tennessee Copper Co. mills is adequate. Those studying this subject will be greatly interested in the paper presented by Richard Smith of the Cleveland-Cliffs Iron Co. at the annual meeting of the Canadian Institute of Mining and Metallurgy in Vancouver April 24, 1958. This paper will be published during the latter part of 1958 in the Canadian Institute of Mining and Metallurgy Bulletin. Hukki's pioneering spirit is to be commended. R. T. Hukki (author's reply)—It has been heartening to read the objective discussion by J. F. Myers. The sincerity of his opinions is further strengthened by the fact that the article he has discussed contradicts in a major way the parallel achievements of his life work. Myers is right in his opinion that in general it takes a long time before new ideas are accepted by the industry. On the other hand, revolutions usually take place at supercritical speeds. There are many indications at present that both the unit operation of grinding and the related subject of size control are now just about ripe for a revolution. In grinding, brute force must ultimately give way to science. Rapid progress can be anticipated in the following fields: 1) Autogenous fine grinding at supercritical speeds will be the first advance and the one that will gain recognition most easily on industrial scale. At this moment, little Finland appears to be leading the world. Crocker recently made a statement that in nine cases out of ten, your own ore can be used as grinding medium more effectively and far more economically than steel balls. This is true. The present author would like to introduce a supplementary idea: In eight cases out of the nine cited above, it can be done at the highest overall efficiency in the supercritical speed range. Fine grinding must be based on attrition, not impact. The path of attrition may be vertical, horizontal, even inclined. 2) In coarse grinding, the conventional use of rods is sound practice. However, even the rods can be replaced by autogenous chunks large enough to offer the same impact momentum as the rods. To obtain the momentum, the chunks must be provided with a free fall through a sufficient height in horizontal mills operated at supercritical speeds. Coarse grinding must be based on impact. Detailed analysis of the subject may be found in a paper entitled "All-autogenous Grinding at Supercritical Speeds" in Mine and Quarry Engineering, July 1958. 3) All conventional methods of classification, including wet and dry cyclones, are inefficient in sharpness of separation. Continuous return of huge tonnages of finished material to the grinding unit with the circulating load is senseless practice. In the near future the present methods will be either replaced or supplemented by precision sizing. These three fields are also the ones to which J. F. Myers has so admirably contributed in the past. Fine Grinding at Supercritical Speeds. By R. T. Hukki (Mining EnGineERInG, May 1958). Eq. 9, page 588, should be as follows: T , c, (a — 6') n D Ltph On page 584 of the article the captions for Figs. 4 and 5 have been placed under the wrong illustrations and should be interchanged.

Jan 1, 1959

By J. R. Lucas, H. E. Rutherford

The primary objective of this research was to evaluate the feasibility of ultrasonic testing for the purpose of analyzing the structure and properties of rock material. A secondary objective of this study was to determine experimentally the elastic wnstants of various rock specimens with the use of ultrasonic equipment. Elastic constants can definitely be determined quickly and accurately by ultrasonic investigation. With proper equipment there are indications that ultrasonic waves could be utilized in the detection of flaws, such as fractures and planes of weakness, measurement of thickness, and the study of structure of rock material. Ultrasonic principles have been applied in many industries for the purpose of determining the structural characteristics of various materials. The principal applications of interest here are detecting flaws, measuring thicknesses, and determining elastic constants. The main advantage of ultrasonic analysis is that it is nondestructive. It also has extreme sensitivity, high penetrability, good accuracy, rapid response, and the necessity to have access to only one side of the specimen. These various applications and advantages lead one to think that ultrasonic principles might be applied to rock material in situ for purposes of analyzing its structural characteristics. Therefore, the primary objective of this research was to evaluate the feasibility of ultrasonic testing for the purpose of analyzing the structure and properties of rock material. A secondary objective of this research was to determine experimentally the elastic constants of various rock specimens with the use of ultrasonic equipment. The term ultrasonics is given to that branch of acoustics dealing with periodic sounds whose fre- quencies are above the audible range or above approximately 15,.000 to 20,000 cps. The first practical production of this high frequency sound was made possible after World War I due to developments of electronically controlled sound wave sources. At the present, the maximum practically attainable ultrasonic frequency is approximately 1000 megacycles per sec. Sound waves of sufficiently high frequency can be made to travel in a beam with little spreading. Therefore, such a beam can explore a material and detect nonhomogeneities in it by reflection. This is the principle of the ultrasonic reflectoscope invented by F. A. Firestone' in 1942. An ultrasonic beam, on pulse-penetratink a solid material medium, produces an echo when it strikes a flaw which has different acoustical properties than the surrounding medium. This echo can be detected by the same transducer which sends out the original pulse. This principle is the basis of the important industrial techniques of nondestructive ultrasonic testing of metals and other solid material. Later developments in the field of ultrasonic testing of solid material have been mostly improvements in equipment and instrumentation. To date, most of the industrial applications of ultrasonic analysis of solid bodies have been in the aircraft, electrical, and nuclear energy fields on the nondestructive testing of metal. The one solid material similar somewhat to rock material, upon which some work has been done to apply ultrasonic testing techniques to study structural integrity, is concrete. Jones and Gatfield3 briefly summarize this work on concrete. Their basic conclusion was that the strength of concrete was a function of the change of the longitudinal sound wave velocity in the concrete. Only recently has any extensive study been made to apply ultrasonic testing techniques to rock material. Lutsch studied rock material by an ultrasonic pulse method to determine the extent and degree of fracture of rock faces. Lutsch states that the number of observed reflections is a measure of the degree of fracture and that only ultrasonic waves are able to detect fractured zones subjected to high pressure. Suzuki, Sasaki, and Siohara5 studied the characteristics of the sonic wave in rock for propagation over a wide range of wave lengths. They indicated that, in rock, the propagation constant and attenuation of the

Jan 1, 1962

Recognizing the fact that the problems of the committee named by the Board to prepare the "official ticket for officers and Directors of the Institute are various and difficult; and desiring to assist this committee by setting forth some of the principles that should guide the committee and some of the qualifications that should be required of candidates, the following instructions are formulated and the Secretary is directed to publish them in MINING AND METALLURGY concurrently with the publication of the names of each newly appointed Nominating Committee and to send a copy to each member of the Committee.

Jan 1, 1937

By R. W. Regehr, R. A. Burmeister

Epitaxial growth of GaAs 1-xPx on germanium substrates was achieved using an open tube vapor transport system. The compositional range of 0.3 < x < 0.4 was examined. The best results were obtained with (311) orientation of the germanium substrate. The physical and chemical properties of the resulting layers were investigated using several techniques. Spectrographic analyses of the layers indicate substantial incorporation of germanium into the GaAs t-X Px layer. Evidence is presented which indicates that this incorporation occurs via a vapor phase transport process rather than by solid phase dijfu-sion. Electrical measurements suggest that the germanium thus incorporated behaves predominantly as a deep donor in the compositional range of 0.33 < x * 0.40 and has a deleterious effect upon the luminescent properties of GaAs1-x Px. The increasing technological importance of GaAs1-xPx for use in light-emitting devices has led to an evaluation of several aspects of existing growth processes. The method most commonly used to prepare GaAs1-xPx for electroluminescent device applications is vapor phase epitaxial growth on GaAs substrates.&apos;-4 In a typical electroluminescent diode structure the active region of the diode is entirely within the epitaxial layer and thus the electrical properties of the substrate are relatively unimportant since it is effectively a simple series resistance (assuming hetero-junction effects to be negligible). The use of germanium rather than GaAs as the substrate material is of interest for several reasons. First, GaAs of reasonable structural quality has been epitaxially grown on germanium4-2 and it is reasonable to expect that GaAs1-xPx could subsequently be deposited on the GaAs layer. Second, germanium substrates are readily available with both lower dislocation densities and larger areas than GaAs. Finally, single crystals of germanium are more economical than GaAs single crystals. The principal objective of the present investigation was to test the feasibility of growing GaAs1-xPx epi-taxially on germanium substrates, and to evaluate the properties of such layers with regard to electroluminescent device requirements. The approach used was to a) demonstrate epitaxial growth of GaAs1-xPx on germanium, and b) characterize the relevant structural, electrical, and optical properties of the GaAs1-xPx layers. The possibility of germanium incorporation into the grown layers was of special interest since there was some indication of this in previous studies of GaAs growth on germanium.5&apos;11,12 Although a study of the electrical properties of germanium in GaAs1-xPx was not an intent of this investigation, several features of the electrical properties of the layers grown in the present study which appear to be due to germanium are described. EXPERIMENTAL PROCEDURE The open-tube vapor transport system used for the epitaxial growth of GaAs1-xPx is illustrated in Fig. 1. This system utilizes the GaC1-GaC13 transport reaction and is similar in most respects to the larger system described elsewhere.&apos; The germanium substrates were n-type, with a resistivity of 40 ohm-cm (Eagle-Picher Co.). These were cut to the orientations of {100), {111), and (3111, and were mechanically polished and chemically etched in CP-4 (5 min at 0°C) prior to growth. In some cases, a GaAs substrate was employed in addition to the germanium. The orientation of the latter was {loo}, and they were also mechanically polished and chemically etched prior to growth. The initial composition of the deposited layer was pure GaAs. After approximately 10 microns of GaAs was deposited on the germanium substrate, the phosphorus content of the layer was gradually increased over a distance of approximately 15 microns to the desired concentration and maintained at this value throughout the remainder of the growth. Typical operating parameters used during growth are given in Table I. Selenium was used as a n-type dopant in several runs to facilitate comparison of the electrical properties of the layers grown on germanium with those of layers grown on GaAs substrates, which are usually doped with selenium. The concentration of H2Se in the gas phase was adjusted to a value which would normally yield a carrier density of 1 to 5 x 101 7 at room temperature in layers grown on GaAs substrates. The terminal surfaces of the epitaxial layers were examined by optical microscopy for structural characteristics. Laue back-reflection photographs (Cu radi-ation) were also made on the terminal surface to verify the epitaxial nature of the deposit. After these steps

Jan 1, 1970

By A. N. Winchell

Petrographic studies of over 1400 rock and mineral samples, and studies of their field relations, show that there is a complete gradation between sandstone and limestone; the lime-silicate rocks were produced by recrystallization of limestone; mineralization and silicification occurred after silication and at considerably lower temperature; carbonation occurred at still lower temperatures. IN CONNECTION with law suits between mining companies at Bingham, Utah, a few years ago, the writer made petrographic studies of more than 1400 rock and mineral samples in thin sections, and also careful studies of their field relations. In petrographic studies, even when an area is studied intensively, attention is commonly centered very largely on the unusual features of special interest, so that the relative abundance of rock types (or minerals or textures) can only be determined by a study of map areas outlined largely by field methods, and cannot be based directly on microscopic work. It is very uncommon, and usually impossible, to take samples at regular short intervals along and across formations. It is precisely because such methods were used at Bingham that the work presents a rare opportunity for determining, on a microscopic basis, the relative abundance of rock types and the continuity of gradations between rock types. At the same time, a study was made of the alteration of sediments under the influence of igneous intrusions, with results that are believed to be of interest and importance.

Jan 3, 1924