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By J. C. Bartlett

The following discussion was suggested by an experiment of Mr. Krom, the Manufacturer of air-jigs, to illustrate the superiority of air over water as a medium of concentration. The paper is written in the interest of no system of concentration, but simply to test the experiment, and, perchance, to add something to the general fund of information on the subject. To speak of testing an experiment by a theoretical discussion, may seem a misuse of terms, but the theories concerning falling bodies and the resistance of fluids are pretty well crystallized into laws, which may properly be used to show where experiments which seem to refute them were improperly performed, and that instead of refuting they only corroborate. It is well known that a sphere of galena & inch in diameter, and a sphere of quartz 1/2 inch in diameter, are equal falling in water ; that is, these two spheres, being placed together in a column of water at rest or in motion, will practically remain together, filling or rising together, or remaining in suspension. Mr. Krom, to show that these

Jan 1, 1879

PRIOR to the World War most of the barite used in the United States for manufacturing lithopone and barium chemicals was imported. Germany, by virtue of an abundance of high-grade ore and low labor costs, was in a position to dominate the world market. With the cessa-tion of imports and with the war demand for barium chemicals, the barium chemical industry and the mining of barite became well; estab-lished in the United States. This industry has continued to expand because of the increasing use of lithopone. In 1914 the sales of domestic crude barite was 52,919 tons and in 1934 it was 209,850 tons. Barite deposits of economic importance occur in at least 20 states, but the principal producers in 1934 were Missouri, Georgia, Tennessee, South Carolina, Virginia, California and Arizona. The main mining centers are located near the crude barite markets of the three principal marketing districts-the Pacific Coast, the Midwestern area, and the Eastern area. The Pacific Coast is supplied entirely by California, Nevada, and Arizona. The Midwestern area uses most of the Missouri crude and a small amount from the southern states. The eastern market is the chief competitive area. Practically all of the imported crude is marketed there; also the bulk of the southern crude and ground barite. In addition, this area absorbs a small part of the Missouri crude and 80 per cent of the ground barite. Besides the advantage of low delivered costs and purity of product, the imported barite has commanded a price differential because it is soft rather than hard, like many of the domestic ores. The inherent physical properties of the southern ores remain, but the purity can be controlled to a great extent by beneficiation. Simple washing or gravity concentra-tion has sufficed in the past, but in many cases a more efficient process now becomes imperative to remove impurities not amenable to these methods. Certain deposits now being opened are of lower, grade and require more precise milling conditions. In some ores, the kind of impurities has changed as the mining advanced.

Jan 1, 1936

By H. H. Kellogg

An invitation to address you on the occasion of the one-hundredth anniversary of AIME represents an honor, a challenge and an opportunity: an honor that you judge me worthy; a challenge that I present to you a picture of extractive metallurgy in the years ahead that contains some ideas of value; and finally, an opportunity for me to express some deeply felt beliefs about our profession and our industry. My topic concerns the technology of metal production in the future - the processes, new and old, that will be used to extract metals. The nature of these processes will be shaped by many forces - some technical, some economic, some political or social. A forecast of future technology must recognize the role of each of these forces, and I have endeavored to do this in the analysis that follows. In brief, my outline consists of an analysis of the forces (perhaps better called "problems") that will influence the future of our industry, followed by consideration of likely lines of technological development to meet them. Let me dwell for a moment on the nature of this industry and the profession that serves it. I have been engaged in the profession of extractive metallurgy - teaching, researching and consulting - for 30 years. I have always found the subject stimulating and rife with challenges of a scientific, engineering, economic and socio-political nature. It is a big subject - it encompasses most of the elements of periodic table; we measure the U. S. production of six metals in millions of tons per year; new plant costs range to $100 million and more. The supply of metals from our extractive plants plays an essential role in our modern industrial economy. We could do without DDT, or phosphate detergents or 300-page Sunday newspapers; we cannot do without a huge and increasing supply of metals. The Basic Goal of Extractive Metallurgy Understanding of some basic forces that shape this industry can be gained by consideration of the question: What determines the utility of metals to man? We think immediately of the inherent properties of metals - strength, ductility, electrical conductivity and so forth - but these tell only part of the story. Metal price and the available supply play equally

Jan 1, 1971

By Charles Camsell

MORE than one-third of all Canada is embraced in the federal domain known as the Northwest Territories. Its most northern point, Cape Columbia, on Ellesmere Island, is only 500 mi. from the Pole. It includes parts of the main physiographic divisions of the North American continent. In the West there is a strip of 30.000 sq. mi. lying in the Cordilleran region, where peaks in the Mackenzie Mountains rise as high as 8500 ft. East of this strip and extending roughly to a line through Great Bear and Great Slave lakes to the Arctic coast is a section of the interior plains. This section, known as the Mackenzie Lowlands, contains the great artery, the most striking feature of the Northwest Territories-the Mackenzie and Slave river waterway impressive in its width, almost two miles in places, and in it's navigability for 1357 miles without obstruction to the sea. Adjoining the Mackenzie Lowlands on the East is the greater portion of the mainland of the Territories, which, as well as a large share of the island area, is in the Canadian Shield.

Jan 1, 1937

By Nelson Severinghaus

THE Rock Chapel plant of Consolidated Quarries Corporation (Fig, 1) is three miles northeast of Lithonia, DeKalb County, Georgia, It was opened about eight years ago for crushed stone aggregate. This paper reviews a number of experiments that have been tried in drilling and blasting, and gives the practice in use today. It also presents several theories on the action of explosives in this type of blasting. FIG, 1.-PLANT OF CONSOLIDATED QUARRIES CORPORATION, WITH QUARRY AT UPPER LEFT. The rock worked is a bare dome of granite gneiss about 3000 ft. in diameter, rising 150 ft. above the surrounding ground (Fig. 2). It is uniform in composition and quality, without seams, and extends down-ward to unknown depth below the quarry floor. A water well drilled 600 ft. remained in the same rock. The principal difficulty encountered in blasting is an easy split, which tends to break down the rock in large blocks.

Jan 1, 1938

By Edgar R. Kendall

A KNOWLEDGE of the fundamental principles of locating, sampling, testing and evaluating materials is essential in prospecting for mineral aggregates. In this discussion, mineral aggregates will be considered sand, gravel, crushed stone and slag that are used as materials of construction. The quantity of mineral aggregates produced in the United States during the year 1935 for such purposes was roughly 165,000,000 tons, about 60 per cent of which was sand and gravel, 37 per cent crushed stone and 3 per cent crushed slag. The total value of this material was approximately $100,000,000. It is apparent therefore that the prospecting for suitable mineral aggregates is of considerable economic importance. In prospecting for mineral aggregates, the methods employed are the same whether the organization is large or small. In the large organization there may be available geologists for locating sources of supply, a land acquisition department to arrange for the necessary options or permits, engineers to do the sampling, a laboratory for testing, and a board of consulting materials engineers to make the final selection. Even small organizations must follow the same general procedure, though the responsibility for the selection of aggregates may rest with one man, who may or may not be an engineer, but who must depend entirely upon his own judgment. LOCATING THE SUPPLY The initial step in prospecting for mineral aggregates is the locating of suitable, adequate and economic sources of supply for the project in mind. Commercial plants in the vicinity should be investigated and a survey made of the existing structures that have been built of aggregates from these sources. If the structures are rather old and show no signs of deterioration, it is fairly good evidence that the aggregate is satisfactory. If materials of the proper quality can be obtained from commercial sources in sufficient quantity, and delivered to the job economically, it

Jan 1, 1939

By D. O. Ehrenburg, R. J. Watson

During the earlier period of electrical prospecting, the search for orebodies was by far the most important application of this method of geophysical prospecting. In the past few years, however, increasing attention has been paid to the possibilities of this method in the investigation of subsurface structures. Not only have fault zones been located, but attempts have been made to determine the depth to certain strata and thus contouring on some bed which proves to be a good "electrical marker." Many workers have published the results of field tests showing how their particular interpretations have agreed with the actual field conditions, but very few have stated their method of interpretation. Weaver, Hummel and Stefanesco and Schlumbergerl have given a more theoretical discussion of the resistivity methods. Hummel and Stefan-esco and Schlumberger have published mathematical solutions for the flow of electricity in a medium involving four layers. In this paper the authors present a solution for the flow of electricity in a medium of any number of horizontal strata. By means of this solution, curves showing the relationship between the apparent resistivity and the electrode spacing can be computed for ideal cases. Point-source in an Infinite Homogeneous Medium In resistivity measurements the current is conveyed to the earth by means of two electrodes, which can be mathematically treated as point-sources of equal and opposite strength. A point-source of strength I is defined as a point at which electricity is being generated at the constant rate of I coulombs per second, or I

Jan 1, 1932

By Frederick Laist

0. C. RALSTON, Salt Lake City, Utah.-I have merely glanced over this paper, consequently, I am hardly in a position to discuss it intelligently. There is one thing, however, that is of interest, that is, the claim that the oil mixture which they have chosen is the best adapted to the work at hand. I would like to ask Mr. Mathewson if they still feel that that is the case-if that really does give the best grade of concentration and the best extraction for the same money, compared to any particular oil mixture which they could get. E. P. MATHEWSON, Anaconda, Mont.-We are still using that mixture, and we consider it the most economical mixture used. DAVID COLE, El Paso, Texas.-I would like to ask Mr. Ralston if there are some other mixtures that would be better? E. P. MATHEWSON.-We are open to suggestions. 0. C. RALSTON.-My own paper on oils* calls attention to the fact that certain hardwood oils, especially the tars, are now being burned or wasted. A great deal of hardwood tar is available as low as 4 or 5 c. per gallon, that being its value as fuel under the boilers. As a matter of fact, a great deal of testing has been done with only the commercial products that are as a usual ride sold on the market. Very little hardwood tar is sold on the market. In asking a great many people who have tested flotation oils, I have not heard hardwood tar mentioned very often. I think I would add to that that the hardwood tars can probably be bought in quantity comparable with the sludge acid at Anaconda, and. should contain a greater proportion of the frothing constituent, and at a price fairly commensurate with what they pay for the sludge acid. E. P. MATHEWSON.-I would like to make a correction in one statement I made that there has been no change made in the mixture. This change has been made: We found that the amount of wood creosote in treating the sand from tables was extremely small, and we tried some experiments on a large scale, dropping it out and using simply the sludge acid and sulphuric acid. We found that this gave practically as good results as wood creosote. We use wood creosote in treating the slimes. We find it necessary in that operation. DAVID COLE.-I would like to ask, what is sludge acid?

Jan 10, 1916

By Charles A. Ashburner

VERY little is known of the economical value of the coal-betas of. the State of Texas. The first authentic statement in regard to their occurrence is that contained in the reports of the United States Explorations for the Pacific Railroad, near the 32d parallel of latitude, published in 1853-55. Professor William P. Blake reports, "that a number of seams of bituminous coal, varying, in thickness from two to four feet, have been opened along the Brazos River, in Young County, about one hundred and fifty miles west of Fort North." Dr: Shumard also states, "that the characteristic fossil forms of the Carboniferous Era have been found with this coal, and considers the ago of the formation established. Fossils obtained from the carboniferous limestone remove all doubt of the age of these deposits."† In the spring of 1879, I was called upon by. some Eastern capitalists to make an examination of the Brazos coal-field, in order to obtain the thickness, extent, and value of the coal which could be mined and be- made merchantable for steam, heating, and metallurgical purposes. The demand for coal in this section of the country is great, and a fuel. which in our Eastern markets might be considered of inferior quality, would here find a ready sale. It must be remembered that the market value of a coal does not depend upon its absolute purity, but upon its actual value in heat units which it is capable of producing. A poor coal which can be cheaply mined near the: consumer, is infinitely more remunerative to a mining company than a superior coal whose cost to the consumer is greatly increased by high mining charges and railroad freights. The value of the Texan coals does not depend upon their purity but upon their low first cost and nearness to a market. A glance at a geological map of the United States, will show that the Brazos coal-field is the extreme southwestern extension of what may be called the Missourian, Fourth or Western, bituminous coal * I am permitted by the gentlemen for whom the examination was made to publish the general statements contained in this paper. † Macfarlane's Coal Regions of America. More recently brief mention has been made of the coal-field in the pamphlets of the State geological survey. These reports are, however, too general, too indefinite, and too impracticable to permit of any conclusions as to the value of the coal as an economical, merchantable fuel.

Jan 1, 1881

By Hiro Minagawa

Japan's contact with the mining industry of British Columbia began as far back as 1952 with the first shipment of iron ore from the Texada mine. Five years later, the Big Three steel mills of Japan-that is, Nihon Kokan Kaisha, together with Yawata and Fuji Steel Mills-dispatched a coal survey mission to inspect coal mines in British Columbia. This resulted in 100,000 tons of coking coal being initially imported by Japan from western Canada in 1959. Also in 1959, Yawata, Fuji, NKK, Kawasaki and Sumitomo sent an iron ore survey group to Alaska and Canada. During the preceding year, Nippon Mining Company and Sumitomo Metal Mining Company initiated a project whereby they would assist in the development of Cowichan Copper on Vancouver Island. As a net result of this activity Japanese mining groups, who had heretofore concentrated on Southeast Asia and South America, finally turned their eyes toward Canada. It was in the fall of 1960 that the government of Japan, in order to keep pace with Japan's rapid economic development, announced a long-range economic plan whereby her gross national income would be doubled by 1970. This had the effect of further propelling Japan's desire to develop sources of raw material supplies abroad. With the development of Craigmont Mines and the signing of a long-term contract to export copper concentrates to Japan, and with the Sumitomo group's extending financial assistance to develop Bethlehem Copper, Canada itself began to realize that Japan was indeed a very important market for British Columbia. A number of surveys to develop mines in British Columbia was begun with an eye on Japan as the major market, and the activity has continued to this day.

Jan 12, 1963

IN CIRCLES where mining men are wont to fraternize, a statement often heard is: "Yes, I spent six (or two, or ten, or thirty) years down at 'Chuqui.' " This means Chuquicamata, the site in Chile of what in all probability is the world's largest deposit of copper ore. One hears similar remarks regarding Braden and Andes, and, in fact, regarding a score of other big mines in South America, Africa, and elsewhere, but Chuqui seems to lead the others as the locale of engineers who have done a stint in foreign countries. One reason probably is that it is the Anaconda Company's premier foreign operation. Because of its unusual size and the diversity of its operations a great many men are needed. It is a sort of training school for young engineers; but, also, Anaconda has sent down a great many mature members of its big organization for special assignments like metallurgical research or plant construction. Chuquicamata is about 150 miles northeast of Antofagasta, at an elevation of 9,500 ft. It is in an almost rainless desert country where the wind (it is alleged by some) blows most of the time. However, the copper mining entrepreneurs have done their best to make up for what nature has neglected to do in creating a pleasant environment for the people who operate the mines. These include about 160 "foreigners" of whom 86 are from the United States, most of them accompanied by their families. There are 165 Chileans on the staff. Comforts, conveniences, and many luxuries are provided to offset in some measure the disagreeable features of the climate. Nevertheless, as I have implied, engineers at Chuqui generally jump at the chance to become "alumni" when opportunity offers. At the same time, they appear to take pride in their alma mater.

Jan 1, 1957

By V. C. Smith

Reliable and detailed statistical data available for Kentucky, Ohio and West Virginia are the most meager and unsatisfactory of any of the producing states. Detailed histories and statistics are available for only a few pools. The antiquity of these pools, loose nomenclature, particularly where several names are applied to the same pool or various parts of the pool or a new namsed when the pool was rediscovered, made the collection of accurat historical and statistical data almost impossible. So many of the data reported are unreliable that a breakdown by pools or even by counties, until more accurate information is available, would lead to gross errors. Rather than perpetuate inaccuracies, we have endeavored to go to original sources wherever possible, sift these and provide data that may serve as an incentive and basis for future work. The necessity for accurate information is thoroughly recognized by the operators, particularly because of the effect of recent government regulations and request? for data in connection with the preparation of the various codes a pending legislation. Producers, both major operating companies and individuals, . freely given their time and assistance in the compilation of these data. Valuable information was obtained from tax records, rate cases, statistics published by the oil and gas publications and the Bureau of Mines. So many individuals cooperated in the preparation of these data that individual credit cannot be given. Undoubtedly many errors will be found. Some of the data are open to controversy, and many have been omitted in the hope that new information of a more reliable character may become available. Other omissions are due to an inability to contact the proper individuals, many of whom are no longer connected with this industry. Pennsylvania grade crude sold in 1933 for the lowest price since 1895. Gas production could not find sufficient new markets to fill the void left by industrial stagnation. In the gas industry, where the market price is fixed by contract, uncertainty persisted because of impending legislative action affecting both taxes and utility rates. As a result of these factors and a lack of new money, drilling was restricted to a new low. The lifting of proration toward the end of the year in the Pennsylvania

Jan 1, 1934

By J. D. Verhoeven

In the past 15 years a considerable amount of experimental and theoretical work has been done concerning the onset of convection in liquids as a result of interm1 density gradients. This work, which has been doue in many different fields, is reviewed here and extended slightly to give a rrlore quantitative understanding to the probletrz of conzection in liquid metal dlffusion experinletzts. In liquid metal systems the capillary reservoir technique is currently used, almost exclusively, to measure diffusion coefficients. In this technique it is necessary that the liquid be stagnant in order to avoid mixing by means of convection currents. Convective mixing may result from: 1) convection produced as a result of the initial immersion of the capillary; 2) convection produced in the region of the capillary mouth as the result of the stirring frequency used to avoid solute buildup in the reservoir near the capillary mouth; 3) convection produced during solidification as a result of the volume change; and 4) convection produced as a result of local density differences within the liquid in the capillary. The first three types of convection have been discussed elsewhere1-a and are only mentioned for completeness here. This work is concerned only with the fourth type of convection. Local density differences will arise within the liquid as a result of either a temperature gradient or a concentration gradient. It is usually, but not always, recognized by those employing the capillary reservoir technique that the top of the capillary should be kept slightly hotter than the bottom and that the light element should be made to migrate downward in order to avoid convection. In the past 15 years a considerable amount of work, both theoretical and experimental, has been done in a number of different fields which bear on this problem. This work is reviewed here and extended slightly in an effort to give a more quantitative understanding of the convective motion produced in vertical capillaries by local density differences. The Stokes-Navier equations for an incompressible fluid of constant viscosity in a gravitational field may be written as: %L + (v?)v = - ?£ + Wv - g£ [1] where F is the velocity, t the time, P the pressure, p the density, v the kinematic viscosity, g the gravitational acceleration, and k a unit vector in the vertical direction. A successful diffusion experiment requires the liquid to be motionless, and under this condition Eq. [I] becomes: where a is the thermal expansion coefficient [a =-(l/po)(dp/d)], a' is a solute expansion coefficient [a' = -(l/po)(dp/d)], and the solute is taken as that component which makes a' a positive number. Combining with Eq. [3] the following restriction is obtained: Since there is no fixed relation between VT and VC in a binary diffusion experiment, Eq. [5] shows that the condition of fluid motionlessness requires both the temperature gradient and the concentration gradient to be vertically directed. Given this condition of a density gradient in the vertical direction only, it is obvious that, as this vertical density gradient increases from negative to positive values, the motionless liquid will eventually become unstable and convective movement will begin. The classical treatment of this type of instability problem was given by aleih' in 1916 for the case of a thin fluid film of infinite horizontal extent; and a very comprehensive text has recently been written on the subject by handrasekhar.' It is found that convective motion does not begin until a dimensionless number involving the density gradient exceeds a certain critical value. This dimensionless number is generally referred to as the Rayleigh number, R, and it is equal to the product of the Prandtl and Grashof numbers. For the sake of clarity a distinction will be made between two types of free convection produced by internal density gradients. In the first case a density gradient is present in the vertical direction only, and, since the convection begins only after a critical gradient is attained, this case will be called threshold convection. In the second case a horizontal density gradient is present and in this case a finite convection velocity is produced by a finite density gradient so that it will be termed thresholdless convection. Some experimentalists have performed diffusion experiments using capillaries which were placed in a horizontal or inclined position in order to avoid convection. These positions do put the small capillary dimension in the vertical direction and, consequently, they would be less prone to threshold convection than the vertical position. However, if the diffusion process produced a density variation, as it usually does, it would not be theoretically possible to avoid thresh-

Jan 1, 1969

By A. W. Hale

In a work published in 1838, De Morgan, the author of the article on " Probabilities," in the Encyclopedia Metropolltimn, says: " The method of least squares is not yet introduced intb the affairs of common life,.....that many things which are denlonstrable only by the higher branches of mathematics are looked upon as useless." And he mentions an instance in which "a method was suggested for estimating the relative importance of boroughs, by considering their population and ~wntributions to the revenue con)-

Jan 1, 1881

By N. B. Pilling

THE development of a proper treatment for shells in connection with war contracts has brought to our attention the fact that the temperature of the liquid bath in which steel is quenched has a decided influence on the speed of cooling in the case of some liquids and very little in the case of others. Widely different physical results have been obtained by the use of water spray, water immersion, and oil immersion and further experiment has shown that the quenching effect of water used as a spray or an immersion varies greatly with the temperature of the water. The present experiments were undertaken with the idea of obtaining information of a quantitative nature regarding the quenching properties of a number of liquids used commercially in hardening steel. The general features of such cooling media are common knowledge and in the literature may be found records of numerous attempts to evaluate the cooling power of a liquid when used as a quenching bath. Much, if not most, of the data given on this subject is in the form of a simple statement of the time required for a certain heated mass to cool between two arbitrary temperatures when immersed in the liquid, quite regardless of the path of the temperature change. Our own purpose has been somewhat different. We have attempted to isolate that property of these. liquids having to do with their ability to absorb heat rapidly, as distinct from the behavior of a considerable mass when exposed to different thermal environments. More specifically, from the data obtained through autographically recorded cooling curves of a small standard mass quenched under various conditions, we have tried to analyze the mechanism of heat absorption by the several liquids, measure the changes in its rate as a function of the temperature of the surface of transference, and ascertain the influence of the temperature of -the liquid itself upon both.

Jan 9, 1919

By R. D. Hagni

The following is a case study illustrating the use of thin sections and polished sections of crude ore to predict metallurgical response. By examining polished sections of the metallurgical products, the textural and mineralogical reasons for unsatisfactory separation can be explained. An area of oxidized Negaunee Iron-Formation located south of Negaunee, Michigan, in the Marquette Iron Range, has been considered for roast reduction-magnetic separation. Preliminary metallurgical studies and subsequent pilot plant testing produced varied results. These results prompted this microscopic study which began with an examination of 126 thin sections and 82 polished sections prepared from 126

Jan 1, 1967

By John D. Kalasky

Continuous mining has revolutionized the coal industry but intensified the problems of earlier mechanization. From the installation of the first miner, it was recognized that face ventilation would be one of these problems. To establish an efficient work cycle for the equipment being used, conventional mechanized mining provides four or more development faces. Continuous mining, relying on a single machine, requires only one face, although more than one can be driven alternately by the same machine. In gaseous areas mined by the older methods, the intermittent rate of exposure allows time for the face to bleed off or be cleared, and the width obtained with conventional units makes it possible to hang a brattice line almost to the face. Continuous mining increases the ventilation hazards; there is no margin of time, and very limited space.

Jan 9, 1959

By Orville R. Lyons

CENTRIFUGAL force has been utilized for the dewatering of fine coal for over 50 years by means of machines commonly called centrifugal dryers. In any centrifuge the coal and water are subjected to a spinning action which usually inctedtocreases in intensity as the coal progresses through the machine. This spinning action, or the centrifugal force that it induces, tears water away from coal particles and produces a dewatered coal. The effectiveness of the dewatering action for any particular machine is governed by the size-consist of the coal and the centrifugal force imparted to the water on the coal. Four makes of centrifuge are currently being used to dewater fine bituminous coal in the United States. These include the vertical, basket-screen C.M.I. (Centrifugal and Mechanical Industries) Carpenter, Reineveld, and the horizontal solid-bowl Bird. The C.M.I. and Reineveld centrifuges are similar in construction and are variations of the Elmore centrifuge, varying principally in the slope of the basket, operating speed, size of perforations in the basket, and diameter of the basket. The same operating description suffices for both. These centrifuges are made up of two rotating elements, an outside conical screen frame and an inside solid cone which carries spiral pusher blades. The screen frame is supported by a hollow shaft, and the solid cone by a spindle shaft passing through the hollow shaft. Both the screen frame and the solid cone rotate at high speeds; the solid cone, with its scraping flights, rotating somewhat more slowly than the screen. The wet coal enters the machine at the top, falls on the cone, and is thrown against the screen by centrifugal force. The coal slides down the screen until it meets the upper end of the flights, where it is moved slowly along the flights until discharged at the bottom. The elfluent passes through the sieve basket or screen and discharges into a launder. The Carpenter centrifuge consists of a conical rotating element with a vertical axis, built up of three rows of perforated stainless-steel plates or stainless-steel wedge-wire or round-wire sections cut and rolled to conform to the surface of the cone. Wet material is delivered to a conical hopper inside the centrifuge casing and is distributed in a thin, even layer over the inner surface of the cone by a disk mounted on the rotor shaft. Impacting of the coal against the screen and the centrifugal force exerted as the material moves downwards creates a dewatering effect. The moisture is forced through the coal bed and then through the perforated plates of the basket, collecting in a circular trough built into the centrifuge. The effluent is conducted from the trough through the centrifuge casing by outlet pipes. The dewatered coal is discharged over the inside bottom edge of the rotor. The Bird centrifuge consists of a tank or truncated conical shell, which is revolved at the desired speed by means of a drive sheave. A screw conveyor rotates inside the cone or bowl at a slightly lower speed in the same direction of rotation. The feed entrance, in the center of the large end of the truncated cone, is high enough to allow formation of a pool of slurry. Adjustable effluent-discharge ports are located in the large end of the bowl so the level of the liquid can be regulated. The solids are moved forward by the screw conveyor as fast as deposited and carried above the level of the pool for an interval before leaving the bowl. In the past these four makes of centrifuge could be compared only by indirect means. The author published a rough comparison method in 1949' but

Jan 1, 1952

By T. G. Chapman

THE writer has carried on experimental work for several years with respect to the simultaneous dissolution of gold by cyanide and the adsorption of the dissolved gold on activated charcoal in ore pulps, followed by the recovery of the charcoal by flotation. The results of this experimental work have been sufficiently encouraging to suggest a new process based on the principle of simultaneous dissolution and adsorption of gold, applicable to certain ores and tailings that cannot be treated to advantage by countercurrent decantation or filtration. Applications for patents have been filed and The Dorr Company, Inc. has the exclusive right to license the use of the process. The purpose of this paper is to describe such a process, state its possible advantages and immediate field, and give some results obtained on a laboratory scale. EARLY EXPERIMENTAL WORK In the early stages of the experimental work attempts were made to precipitate soluble gold from cyanide solutions with zinc and aluminum in ore pulps followed by flotation of the precipitated gold, but since the results were not promising enough to continue with these precipitants attention was directed to carbon. The first experiments with carbon comprised the addition of cyanide and alkali to the ore pulp, the addition of carbon at or near the end of the dissolving period, and the recovery of the carbon by flotation. With this method of procedure the assumption was made that carbon functioned as a precipitant of gold from cyanide solutions and as such should be added as are other precipitants, including zinc and aluminum; namely, at the end of the dissolution period. The assumption was then made that carbon functioned as an adsorbent, and that if such assumption proved to be correct, it could be added with success to the ore pulp at the time of adding the cyanide. The first experiment along this line was successful in that the feasibility of the dissolution of gold by cyanide and the simultaneous extraction of the dissolved gold by carbon in ore pulps was demonstrated, at least with respect to such treatment on a laboratory scale.

Jan 1, 1939

By I. N. Zavarine

The observations presented in this paper were recorded during a study of the spheroidizing process. Spheroidization of cementite in steel is either brought about to develop a set of desirable mechanical properties or is an incidental result of mechanical and heat-treating manipulations. Physical properties of steel are materially influenced by the state of the cementite. Conversion of cementite from the lamellar to the spheroidal state is usually accompanied by a decrease of hardness and of strength and by an increase in ductility. The spheroidized structure is usually considered as an ultimate step in the process of the softening of steel. The unorthodox hardening of a 3.5 per cent Ni steel (SAE No. 2330) after a heat-treatment that previously proved entirely suitable for a complete spheroidization of cementite in carbon steels led to the observations that constitute the subject of the present paper. Experimental Procedure The steels used for the experiments described were bought on the market. All were in the form of 3/4-in. round bars. Their chemical compositions are given in Table 1. The spheroidization of cementite in steels can be obtained in several ways. The method used in the present work is, perhaps, the least known. It consists of cyclic heating and cooling of steel, the temperature being

Jan 1, 1939