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YEAR OF ELECTION 1922. FEDERICO GIOLITTI Torino, Italy. 1917. HERBERT HOOVER Washington, D. C. 1941. DANIEL COWAN JACKLING San Francisco, Calif. 1939. HENRY KRUMB New York, N. Y. 1942. Essington Lewis Melbourne Vic., Australia 1921. C. McDERMID London, England. 1942. PAUL DYER MERICA New York, N. Y. 1913. EZEQUIEL ORDONEZ Mexico City, Mexico. 1938. A.M. PORTEVIN Paris France 1937. JOHN V.W. REYNDERS, New York, N. Y. 1937. GEORGE S. RICE Washington, D. C. 1911. ROBERT H. RICHARDS Cambridge, Mass. 1934. T.A. RICKARD Victoria, B.C., Canada

Jan 1, 1943

RESEMBLING in some respects the enterprise at R Chuquicamata is that of the New Cornelia Copper Co. at Ajo, Arizona. Controlled from its inception by the Calumet & Arizona Mining Co., New Cornelia became a unit of the Phelps Dodge Corporation when the latter absorbed the Calumet & Arizona company in 1931. Both Ajo and Chuquicamata are situated in low mountains in extremely arid desert country. Both ore deposits consisted-the past tense is used advisedly because the oxidized ore has nearly all been mined at Ajo-of a horizon of leachable oxidized ores overlying sulphide or concentrating ore. The principal technical problem in each case was the development of a method for treating the oxidized ore. In both instances the capping of waste rock was comparatively thin and power-shovel mining in open cuts was the obvious method of exploitation. Nature had smiled on neither place in the matter of climate. Though Ajo does not have the persistent winds for which Chuquicamata is notorious, the comforts of living are largely artificial. And it is only fair to emphasize that at each place the mining companies have achieved remarkable success in providing these comforts. Of course, in point of size New Cornelia must be content with the inferior role. From May, 1917, when production was started, to the middle of June, 1930, the company leached 16,368,000 tons of oxidized ore, thereby virtually exhausting the ores of this class. Up to the same date, about 15,000,000 tons of sulphide ore had been mined, and a rough estimate gives 170,000,000 tons remaining in reserve. The total tonnage does not loom very large in comparison with Chuquicamata's billion tons; but it is exceeded by similar figures for only four of the Porphyry group.

Jan 1, 1933

By E. G. De Coriolis

The development of huge production facilities and of new or improved processes for manufacturing magnesium from its raw sources has been an outstanding achievement of this war. Furthermore, at least one new method has reached a stage of pilot production that offers promise. Its potentialities seem to indicate that a reduction in cost and simplification or elimination of problems incident to the use of at least one of the present processes are quite within the realm of possibility. Although magnesium of very high purity (99.9 per cent and higher) is obtained, and the rate of recovery reasonable (60 to 70 per cent). the ferrosilicon reduction process is open to a serious objection, which at the time its use was proposed was thought to be sufficient to raise some doubts as to its success, at least on a high production basis. The temperature range at which the reaction is carried out—namely, 2100" to 2150°F.—is very close to the failure temperature of the material of which the retort is made. It is so close that for a time it was assumed it might make commercial use of the process an impossibility. However, at the time under discussion, the demand for magnesium was so great that it was felt by those who had to go ahead and produce this essential metal that the emergency warranted their taking a chance on this process. Subsequent developments have fully justified the soundness of their decision. Fortunately for the war effort, when the plants were put into operation it was discovered that although the retorts did collapse in rather short periods of time, as predicted, they could be blown back into operable shape by application of high-pressure air. This practical method of operation so relieved the situation that the problem disappeared. Nevertheless, if the process had not been successful, or the production of magnesium by the electrolytic process had not been able to keep pace with demands, our war program would have been seriously impaired. Fireless Cooker'' Process For this reason a program was set up and assigned for the development of a new method that had been suggested to the War Production Board in 1941. It is believed justifiable in terming the method "new" for several reasons: (I) while utilizing the same (ferrosilicon) process as the Pidgeon, hence involving similar reactions, the type of retort or furnace is essentially different, (2) the method of operation, reaction temperatures, etc., differ materially, and, most important of all, (3) the problems to be overcome in making the process successful were not and could not have been anticipated by anything previously known about the Pidgcon process. As will be shown later, the briquetting process, the condenser, the furnace lining

Jan 1, 1949

By William F. List, Marvin A. Schuster

Monolithic electrooptical mosaics of 2500 photo-transistor elements with internal row and surface column interconnections have been fabricated by epitaxial-planar diffsion techniques. Unique access to any elemed of the mosaic is provided through one of the fifty X and one of the fifty Y external leads. The sensor mosaic can be used for imaging applications and has a 1:1 aspect ratio, a resolution of 100 lines per in., a dynamic range in excess of lo3, a sensitivity of 0.5 per pw, element response within a 2:l range over 75 pct of the mosaic, and a minimum detectable signal of the order of 10-' w. Design considerations which ilnpose particclar fabrication yequirements are disctussed along with some of the problems peculiar to the epitaxial and planar-dijfision techniqes by which this device is fabricated. The solid-state silicon monolith has an imaging area of 0.5 by 0.5 in. and an element center -to- center spacing of 0.010 in. J monolithic solid-state electrooptical device has been developed as the photon-sensing mosaic for use in an image-converter system.' This system is the solid-state equivalent of the vidicon and can image radiation in the visible and near-infrared regions of the spectrum. The electrooptical image converter has the desirable size, weight, reliability, and low-power characteristics inherent in solid-state devices. It is read out by direct-wire means rather than by beam-scan techniques. The packaged unit is shown in Fig. 1. A selection of material for the sensor was based on considerations of both reliable fabrication techniques and material spectral response. Silicon was selected both for its response from the lower end of :he visible to the long-wavelength cut-off above 11,000A and for its well-developed epitaxial planar-diffused technology. The electrical image is composed of M x N discrete information bits with each bit emanating from one of the individual phototransistor sensors. The interconnected mosaic concept was introduced to provide a structure which is both manageable in its number of leads and compatible with conventional viewing systems which accept XY data. Interconnections along the Y direction are provided by internally diffused strips, while interconnections along the X direction are formed by vacuum-deposited metal surface bars. Unique access to any individual element of the M x N mosaic is available through one of the M and one of the N external leads. PHOTOTRANSISTOR DESIGN A phototransistor structure2 was selected for the discrete photon detectors of which the mosaic is com- posed. Basically, the mode of phototransistor operation is such that incident quanta are absorbed in the base area of the element where they generate electron-hole pairs. If the electrons are liberated within a diffusion length of the depletion region around the collector junction, they will diffuse to this depletion region and be swept across the junction where they account for a small component of the photocurrent. Similarly, the holes which are created within a diffusion length of the emitter junction will diffuse to this region where they forward bias the emitter and so induce injection of minority carriers into the base. This accounts for the substantial transistor photocurrent. This mechanism of operation implies several design and fabrication goals for the individual sensor elements: high electrooptical conversion efficiency, sufficient carrier lifetime in the base regions, and a maximum volume in which photons can be absorbed within a diffusion length from the depletion layer about the junction. Moderately high transistor gain is desirable to permit readout at low light levels; however, very high gain has a deleterious effect on mosaic dynamic range. The mosaic must also be characterized by good uniformity of element response as well as by good isolation between elements. The above set of conditions imply that junction depths must be optimized with respect to photon ab-

Jan 1, 1967

PRESIDENT ARTHUR DWIGHT District 0 NEW YORK, N Y PAST PRESIDENTS EDWIN LUDLOW District 0 MINNEAPOLIS, MINN HERBERT HOOVER, District 4 WASHINGTON, D C FIRST VICE-PRESIDENT JVC REYNOLDS NEW YORK, N Y

Jan 1, 1923

Doctor David Yang has presented an important new flotation development in the area of fine particle flotation technology; at the same time Dr. Yang presents an explanation for the effectiveness of this improved new fine flotation system in terms of an optimum dispersion state. The same statement is made for the case of carrier flotation (ultraflotation), in the removal of anatase from kaolinite by addition of calcite (selective flocculation of the anatase - calcite system and dispersion of kaolinite). Dr. Yang's data and statements raise some important questions, and I will adress myself to the more fundamental aspects of this new flotation system. The addition of sodium silicate, well known as a good depressant-dispersant agent for siliceous gangue minerals, is proved to be greatly enhanced by the incorporation of polyvalent metal salts into sodium silicate prior to flotation, producing in this manner a condition, as described by Dr. Yang, of optimum dispersion, which in the case of fine-grained oxidized taconite can be described as selective flocculation (coagulation) of hematite and almost complete dispersion of siliceous gangue components. Dr. Yang recognizes that the main mechanism, while not completely understood at this time, seems to operate by modifying the surface characteristics of the gangue slime particles so as to prevent collector from bonding there to, and making the particles strongly hydrophilic so they will become fully dispersed and consequently will not float during froth flotation. At the same time it appears that the conditioning reagent also modified the surface characteristics of the floated minerals (hematite and spodumene in this case) so that they will aggregate and tend to more readily adsorb the collector, resulting in an improved flotation kinetics and selectivity.

Jan 1, 1979

By Charles Fulton

This paper describes experiments carried on at the Case School of Applied Science, together with their results. Their success led to the design of the larger furnace herein described, but which has not been built. A PREVIOUS article' by the authors contained a general description of the new roasting furnace herein described but it did not go into detail as to the metallurgical behavior or the results obtained. Believing that such information would be of great value, they have elaborated on the subject and have given many unpublished details. The furnace described applies the principle of roasting finely divided zinc-sulfide ores, now produced in large quantity by the flotation process, in gaseous suspension; that is, the ore particles are carried, in suspension, in a current of air and gaseous products of the roast. The relatively great fineness of flotation concentrate presents difficulties and problems of roasting in furnaces of the ordinary type; the fine ore is forwarded through the furnace in the form of a shallow bed and its very fineness leads to dense impervious bedding which prevents oxygen from reaching the interior of the bed, thus unduly lengthening the time of roasting and preventing the elimination of the last of the sulfur. The fineness of the concentrate, normally, should lead to a rapid and complete roast, for the speed of roasting is a function of the surface exposed to oxygen, which surface is greatest, per unit of weight, in very fine material. The difficulty in bed roasting is to get the oxygen to the particle. If the fine ore, during the roasting, could be freely suspended in oxidizing gases, full advantage could be taken of the great surface conferred by its fineness. This fundamental idea, of course, is not new, for the Stedtefelt furnace, familiar to the older metallurgists, is an example of it; but the manner in which this is accomplished may be new.

Jan 10, 1924

By D. D. Pollock

The resistivity, temperature coefficient of resistance, and absolute thermoelectric properties of some binary terminal solid solutions of silver were determined. Equations are given which permit the calculation of these properties. CONSIDERABLE work has been done on the constitution and electrical conductivity of binary alloys of silver.1-l2 Some of these alloy studies are apparently complicated by doubtful chemical analyses. In some cases the limits of solid solubility are questionable. Those references which present electrical properties of binary silver alloys usually give just one particular set of characteristics such as conductivity (or resistivity). As a means of checking and extending this earlier work, an investigation was undertaken to describe and calculate the resistivity, temperature coefficient of resistance, and thermoelectric power of binary terminal solid solutions of silver. PREPARATION OF ALLOYS All of the alloys were made with silver containing less than 0.014 pet (by weight) of impurities. These materials were carefully weighed out into 225-g heats and melted in a high-frequency induction furnace. The indium, tin, and antimony systems were melted in Al2O3 crucibles, under a boric anhydride cover, and poured into split graphite finger molds. The aluminum, germanium, arsenic, lead, and bismuth alloys were melted in machined graphite crucibles, and they were also covered with boric anhydride and poured into split graphite finger molds. The alloys containing magnesium and manganese

Jan 1, 1964

By A. G. Metcalfe

THE failure to detect any change in the thermal properties of cobalt at the Curie point would appear to indicate that the apparatus may have a limited sensitivity. The Curie temperature has been determined by direct methods to be 1121+3°CP and 1131°C.3 The specific heat has been determined many times'.' and weighted values are given in Table I. The allotropic transformations in iron and titanium, used by the authors to test the experiment method, involved a volume change of the order of 3 pct on going from the close-packed to the body-centered-cubic lattice. These energy changes are likely to be much larger than those involved in a diffusionless transformation from a hexagonal to a cubic-close-packed lattice. However, it has been pointed out that thermal observations are unreliable in the detection of phase changes when these are near a Curie point.' James 0. McCaldin and Pol Duwez (authors' reply)—The sensitivity of the present technique is limited to first-order transformations, so that gradual changes in specific heat, e.g., in the vicinity of Curie points, are not detected. Furthermore, the existence of first-order transformations with latent heats much smaller than those occurring in the known allotropic transformations of iron and titanium is, we agree, still pending.

Jan 1, 1956

By R. L. Vaughn, A. G. Moon

In 1972 a major renovation of the flotation and regrinding circuits was completed at Kennecott Copper Corporation's Chino Mines Division concentrator at Hurley, New Mexico. At that time a new lime distribution and control system was placed in operation. Lime is used to depress pyrite, and flotation at a high pH or alkalinity is required for optimum recovery of principal copper minerals, chalcopyrite and chalcocite with good rejection of the pyrite. Regrinding is also required to liberate chalcocite, much of which occurs as intimately associated chalcocite-pyrite middling grains. Accurate control of the lime addition is necessary to obtain both optimum metallurgy and minimum lime usage. At low pH levels, flotation cell control is difficult due to excess froth, but excessively high pH levels can go unnoticed because froth characteristics do not change from those experienced at the desired pH. With manual control of the lime addition, the desired pH can be exceeded for periods of up to two hours. Test Work Plant test work on a lime control system using conventional pH probes gave disappointing results with high electrode maintenance and poor control characteristics. For example, the rougher flotation cells are operated at a pH between 11.4 and 11.6 and the probes required cleaning at least once a day, and occasionally every shift. These high maintenance requirements were considered unreasonable for a plant-wide system using six or more control loops.

Jan 1, 1979

By R. T. Rometti, C. A. Bossard

INTRODUCTION Whenever a new mining property is developed or a new concentrator is built, considerable time, money, and planning are invested for the exploration, engineering, and construction of the required facilities. Yet, when these facilities are ready for startup, all too often insufficient time, money, and planning are invested in this critical phase of the project. Failure to plan for this phase results in untimely personnel mobilization, insufficient operator training, and inadequately prepared budget estimates, which combine to create excessive costs, lack of communication, unclear responsibility divisions, unnecessary delays, and poor production levels. Insufficient or excessive leadership, due to unclear assignment of responsibility, results in irrevocable problems within the startup team. A carefully planned and budgeted startup phase can avoid many of these problems. SCHEDULING A key element in properly planning the startup phase lies within the area of scheduling. Once the schedule has been established, planning can be greatly simplified through the expansion of each specified item. The overall project schedule should specify the date when the startup and initial operating management team will be brought onto the project. This team should be mobilized at least two years prior to the anticipated startup date, to allow sufficient time to begin to plan, assemble the startup groups for the various areas of the plant, initiate a workable communications system, and implement the development of the training program. This team is responsible for the preparation of a startup schedule, which would detail the dates for all key items associated with this phase of the project. These key items would include training program development, personnel hiring dates, prestartup plant checkout, etc.

Jan 1, 1982

By D. R. Bomberger, M. Deul

An automatic microscope has been developed to measure the size and populations of macerals and minerals in fine coal particles. Differentiations are made on the basis of reflectance. This study is concerned with the size distribution of pyrite inclusions. Most fine coal cleaning processes do not remove pyrite as completely as a straight density separation. Consideration of the pyrite size distribution is suggested as a more accurate method of predicting sulfur reduction by a cleaning process. Analyses of float-sink results and Deister Table operation in terms of pyrite particle sizes are made. Other potential applications of automatic microscopy are also discussed. In the study of coal cleaning by pseudo-gravity methods (tables, cyclones, hydrotators, etc.), it is customary to express the deficiency of the process relative to float-sink measurements in some form of "percent efficiency". These have been calculated in many different ways in order to provide a means of extrapolation of test data to untested coal feeds. This works quite well with coarse coal (here defined as larger than one-eighth in.). Large, heavy pieces of refuse are rejected rather thoroughly by many cleaning processes, and the efficiencies relative to float-sink results approach 100%. In coarse coals, the difference in the sizes of fine pyrite is masked by the averaging effect of the large coal envelopes. The existence and fate of fine pyrite is often hidden in the larger numbers representing coarse (and easily removed) pyrite. There are cases where it is desirable to subject fine coal (here defined as smaller than one-eighth in.) to cleaning processes. This is true of naturally occurring fie coal streams and in cases where comminution followed by cleaning is necessary to provide the quality desired. It is in this area that the use of process efficiency relative to float sink fails. Percent efficiencies decline to very low figures, and equivalent separation densities become a matter for conjecture. The net result is that an attempt to estimate product quality from float-sink data and a process efficiency figure often results in large errors. This work represents a new approach to the problem by observing the fate of pyrite particles, grouped by sizes, in a cleaning process. Examples are given which relate pyrite size measurements to float-sink washability and to a Deister Table operation. EXPERIMENTAL WORK The automatic microscope used here has been previously described.' Briefly, it is an instrument which measures the diam of particles (as defined by a range of reflectance) exposed on a polished specimen. The instrument scans a sample briquet, measures diam of exposed pyrite inclusions and records the data by size intervals. Preparation of the briquet is critical, due to the automatic nature of the process. The principal requirement is for an optically flat surface, so that focus will be maintained as the motorized stage moves the specimen under the lens. The various substances present must be polished to the same level in spite of the wide difference in hardness between coal substance and minerals. The polishing method must not pluck out small grains, which might be rather loosely held by surrounding coal. The procedure below was successful in producing all of these results. The coal sample (8 mesh or finer) was riffled (a micro vibrating riffle is essential) to obtain 15 g. One volume of Lucite powder (thermosetting plastic mounting medium) was mixed with three volumes of coal and mixed thoroughly. A briquet was formed using a cylindrical die (1 1/4 in. diam) at 3000 lb per in.* pressure and 150°C. Preparation of the optical surface was accomplished on automatic polishing equipment, according to the following schedule: 1) Grinding: 3 stages, using successively fine Carborundum grits of 180, 320 and 600 mesh. 2) Rough polishing: 2 stages, using 3µ alumina on cast iron, followed by 1µ alumina on lead. 3) Fine polishing: 2 stages, using 0.5µ alumina on napless broadcloth over bronze, followed by 0.1µ alumina on silk filament cloth over bronze. Raw data were corrected for the fact that the chords

Jan 1, 1964

CONTENTS PAGE GEISMER, H. S.-Coal Washing Practice in Alabama. Discussed by William Kelly, H. S. Geismer, H. D. Pallister, L. E. Bryant, Milton H. Fies, Elmer F. Harris, James A. Barr, George G. Crawford, E. C. Wright, George S. Rice, R. V. Norris 1 MILLER, F. W.-Byproduct Coking in Alabama. Discussed by Theodore Swann 4 FIES, MILTON H.-Alabama Coal Mining Practice. Discussed by Milton 11. Fies, R. V. Norris, R. D. Hall, L. E. Bryant, George S. Rice, H. S. Geismer 5 MUSSEY, H. E.-Blast-furnace Practice in Alabama. Discussed by C. A. Meissner, Franklin H. Crockard, H. E. Mussey, W. H. Oldham 14 Coal Washing Practice in Alabama Discussion of paper of H. S. GEISMER, presented at the Birmingham Meeting, October 1924, and issued, as Paper No. 1363-C, with MINING AND METALLURGY, September, 1924. WILLIAM KELLY, Iron Mountain, Mich.-Is the dry-cleaning method used? H. S. GEISMER.-Neither the dry-cleaning process nor the Chance sand-liquid method has been tested in Alabama; but all other methods used for cleaning bituminous coal have been largely brought to perfection in this state. H. D. PALLISTER, Tuscaloosa, Ala.-Have you the results from the recent work on the tables with reference to fine coal? H. S. GEISMER.-None of the iron-producing companies has adopted the tables, though three commercial operators have installed tables within the last six months. I tried to learn the results, but they were not willing to release the data just now. At the mines producing domestic coal, fines present a difficult problem; until within the past six months all the fine coal was wasted. The operators are trying to recover some of it on the table. L. E. BRYANT, Rockwood, Tenn.-Is there any connection between the sulfur content of the sludge and the effect of the sludge on vegetation?

Jan 7, 1925

By D. Coutsouradis, L. Habraken, P. Nicolaides

The TTT curves of 0.1 pct C, 13 pct Cr steels containing up to 12 pct Co have been determined in order to establish whether the effect of cobalt is similar to that observed m plain carbon steels. It is shown that cobalt increases the incubation time and decreases the transformation rate, though not in an uniform way. The bainitic transfornation is displaced to lower temperature and overlaps partially the martensitic zone. ThE effect of cobalt on the transformation of a plain carbon austenite has been studied by many investi-gators.'-3 It was shown that cobalt displaces the TTT curves to shorter times and diminishes the harden-ability. The interpretations given for this effect of cobalt are conflicting. According to E. Houdremont,4 cobalt increases the transformation rate of austenite because it increases the diffusion of carbon as shown in the experiments of E. Houdremont and H.Schrader,' R.Smoluchowski,5 and M. Blanter.6 On the other hand, M. Hawites and R. Mehl3 deny on the basis of their own experiments any effect of cobalt on the diffusion of carbon and they assume that an explanation should be found in an eventual effect of cobalt on the mechanism of nucleation and growth of pearlite. W. C. Hagel, G. M. Pound, and R. F. Mehl7 have shown by calorimetric measurements that cobalt increases the free energy of the austenite-pearlite transformation in an eutectoid steel and this result explains qualitatively the observed effect of cobalt on the rate of nucleation and growth of pearlite. The purpose of this research was to see by determination of TTT curves, if this same effect exists in 13 pct Cr steels. EXPERIMENTAL PROCEDURES The preparation of the alloys was carried out in an

Jan 1, 1960

By A. Adiassevich

PETROLEUM has been found in Russia in various localities from north to south, as may be seen from the list given below: (a) In the basin of the Petchora river, Northern Russia. (b) In the basin of the Volga river, in the governments of Samara and Saratoff. (c) In the government of Astrakhan and in the Uralsk territory, close to the northern and eastern coast of the Caspian sea. (d) At Grozny in Northeastern Caucasus. (e) In the Daghestan territory, Eastern Caucasus, on the Caspian sea. (f) On the Apsheron peninsula (Baku and other districts) close to the Caspian sea shore. (g) On the island of Tcheleken in the Caspian sea, also on the island of Sviatoi. (h) In the Transcaspian territory on the Neftianaia Gora (Oil hill) and on the surrounding hills. (i) In the Ferghana valley in Russian Central Asia. (j) On the Kertch and Taman peninsulas on the Black sea. (k) In Siberia it has been discovered in the Transbaikal territory and on the island of Sakhalin. In the above-mentioned districts petroleum has been found to exist under different geological conditions and to vary in its chemical and physical properties. At the present time petroleum is produced in Russia at Baku, Grozny, on the island of Tcheleken, in the Ferghana district, and in the Uralsk territory. The yearly production in 1912 throughout the Russian Empire amounted to 69,400,000 barrels, of which the Baku fields were responsible for 52,000,000 barrels. This shows that the Baku fields on the Apsheron peninsula are the chief oil-producing centers in Russia, being at the same time the oldest of all our oil fields.. In this paper I shall discuss the Baku fields only, leaving all the others until a later date.

Jan 5, 1914

The beginning of Colorado's mining industry is linked on one side with that of the Appalachian districts and on the other side with that of California, because the first discoveries were made by pioneers when on their way from Georgia to California. In the summer of 1849 a party of seven Georgians were taking a herd of thoroughbred horses across the continent to the Pacific coast. They reached Camp Lyon, on the Arkansas river, in October, and, meeting James Dempsey, a Government guide, they were persuaded by him that it was too late to cross the mountains that season. His advice was accepted, and, moving northward, they established a winter camp at the junction of Cherry creek with the Platte, close to the site of the city of Denver. Upon a sand-bar, lining the south side of the river, they built two cabins. During the closing months of 1849 they prospected the alluvial banks of Cherry creek, but they made no attempt to penetrate into the mountain canyons, near them, westward, for fear of the Indians.* They found gold in several places along Cherry creek, and particularly at a spot 16 miles up the stream from their camp. From the feathers of the wild geese that they shot they obtained quills in which they placed their gold-dust. This party of Georgians consisted of Dr. L. J. Russell and his brother, Green Russell, also A. T. Lloyd, G. W. Kiker, and P. H. Clark. Early in 1850 they crossed the main range of the Rocky Mountains by the Bridger pass and went on to California. They mined near Downieville, and were successful. Occasionally mention was made by them of the gold

Jan 1, 1932

E. A. Peretti (University of Notre Dame, Notre Dame, Ind.)—Mr. Deitz and Professor Halpern are to be congratulated on a fine piece of work which adds to our knowledge of precious metal—cyanide-solution reactions. I should like to offer the following comments: The authors state, "the rate plots were always linear, indicating a zero order reaction rate." This appears to conflict with the data of Fig. 6 which clearly show the rate to vary with the NaCN concentration. It seems to me that the rate curves are linear because of the experimental setup. The volume of solution is so large that over a three-hour period the change in NaCN concentration is very small. A rough calculation for the experiments of Table I where the initial NaCN strength was 0.0096 mol per liter show a change of NaCN concentration of about 0.0009 mol per liter at the end of three hours. In short, over the period of time that the experiment was in progress, the NaCN strength was practically constant; hence the rate of dissolution remained practically constant. Eq. 10, as written, specifies that 1 mol of H202 and 2 mol of hydroxyl ion are formed when 2 mol of silver react. Is this true? The effect of H,O2 on the rate was made in solutions having an oxygen pressure of 4.8 atm. Were any tests made in solutions containing hydrogen peroxide, but no oxygen? G. M. Willis (University of Melbourne, Melbourne, Australia)—The authors have shown that, under their experimental conditions of high O2 concentrations, the rate of solution of silver in aqueous cyanide solutions is controlled by diffusion of O2 or CN- to the metal surface. With diffusion control, it is generally not possible to obtain further information about the mechanism of a process.

Jan 1, 1955

By D. Harrington

ONE of the main functions of the United States Bureau of Mines is to obtain and disseminate information that will promote safety in and around mines, and the health and safety of employees engaged in mining. Serious health and safety conditions arising out' of contamination of air in metal mines by dust, fumes from explosives and fires, and absorption of oxygen by timber and other causes, led the Bureau of Mines to cooperate with the United States Public Health Service in the study of dust occurrence and ventilation in metal mines in various parts of the country. Dr. A. J. Lanza, of the U. S. Public Health Service, and Edwin Higgins, mining engineer of the U. S. Bureau of Mines, in 1915, made a detailed study in the mines around Joplin, Mo., their reports1 are now available. In 1916, 1917, and 1918, a similar study was made in the Butte, Mont., region by Doctor Lanza and D. Harrington, mining engineer of the Bureau of Mines; the reports of this investigation will be available soon. In 1919, the study was continued in some of the Arizona mines by D. Harrington, of the Bureau of Mines, and G. E. McElroy and Dr. R. A. Koronski, of the U. S. Public Health Service, the underground work being completed in June, 1920; these reports are now being prepared for publication. In the spring of 1920, the scope of the work was extended, with D. Harrington in charge as supervising mining engineer, and short studies made in the mines of the Coeur d' Alenes in Idaho and around Oatman, Ariz. It is hoped soon to extend the work into mines of California, Nevada, Colorado, Michigan, and Minnesota, and ultimately to other states should the mining companies be willing to cooperate.

Jan 2, 1921

By David Kramer, Cecil G. Rhodes

Critical transport currents were measured as a function of perpendicular external magnetic field in Ti-22 at. pct Nb wire samples. These samples were heat-treated to yield w Phase precipitates at denslties ranging from 10 to 10 17cm-3. The Precipitates are ellipsoids of revolution with major axes of 50 to 1300A. Flux-Pinning by w precipitates is responsible for the high critical transport currents that were ob- ThE ability of a type II superconductor to sustain a zero-resistance transport current (Jc) in an external magnetic field (H) is due to the presence of micro-structural features which can impede the motion of magnetic flux penetrating the superconductor under the influence of a Lorentz force. Such features are referred to as pinning sites. The pinning strength is tained. A sample cooled from 800°C and annealed 1 hr at 450°C carried a critical tramport current of 10 amp per sq cm at 30 kG. Variations in the current-carrying ability of this alloy are due to changes in its pinning strength which is a function of precipitate density and composition and of the composition of the matrix. the reaction of the bulk superconductor to the Lorentz force and depends on the efficiency of the individual pinning sites and on their volume density. The super -current density increases with pinning strength, other things being equal. The above concepts are discussed in detail in a comprehensive review by Livingston and Schadler.' In Ti-Nb alloys, as in other binary titanium alloys, the metastable hexagonal w phase usually forms below the p/a + p phase boundary near the titanium side of the phase diagram. Stiegler et a1.' have summarized much of what is known about w phase in titanium and zirconium binary alloys. The present work deals with

Jan 1, 1968

By John J. Reed

This paper was prepared as a supplement to the general review by Dr. N. G. W. Cook. His analysis of the problem in terms of the strain energy involved in making the excavation is excellent. It will contribute much towards a clearer understanding of rock behavior and control. Several of the practical applications described herein can be directly related to Dr. Cook's theories and conclusions, and are based on the very same principles. CONTROLLED BLASTING IN ROCK EXCAVATION Generally speaking, the natural rock is a relatively strong and competent structural material, if we conserve its inherent good properties and perhaps reinforce its weak spots. The difficulty often lies in blasting out the tunnel or chamber without damaging the walls and roof we wish to have remain afterwards. Much progress has been made in the last five years in better understanding the controlled excavation of rock. The specialized techniques known as smooth wall blasting and presplit blasting have now developed from the status of curiosities of rock excavation to the point where these techniques are specified in contracts drawn up for such rock excavation projects as tunnels, underground pourer houses, etc. These techniques have been well described and discussed in previous publications; there is no need to reiterate here. It might be well to point out that recent research has demonstrated the effect that inherent rock stress may have on presplitting in certain directions. Material can be presplit most readily parallel to the direction of maximum compressive stress, and this may not always be in the direction desired. Inherent rock stress measurements by stress relief over coring, etc., may have important value in deciding how to best presplit proposed excavations. In addition, recent work at the Colorado School of Mines has demonstrated the feasibility of con-

Jan 1, 1967