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By R. L. F. Kay, T. A. Fletcher, A. J. Boyce, C. M. Rice

Paper presented at Mineralisation in the Caledonides, the Mike Gallagher memorial meeting held in Edinburgh, 27-28 June 1996. The synorogenic, mafic Ordovician intrusion comprises orthopyroxene-rich xenoliths and mafic-ultramafic cumulates with low-grade pyrrhotite, chalcopyrite and pentlandite mineralisation. Despite abundant textural, mineralogical and O isotope evidence for significant assimilation of country rocks, S isotopes indicate only a modest uptake and suggest that mineralisation is dominated by magmatic sulphur. The preferred explanantion is that the magma was close to S saturation on emplacement. Uptake of elements such as Si and O led to early crystallisation of orthopyroxene, resorption of olivine and early segregation of a sulphide liquid. Post-magmatic interaction with a high-temperature, surface-derived fluid, whose movement may have been controlled by regional shear zones, reset biotite and whole-rock O isotope values but not those of orthopyroxene. This model identifies the presence of olivine-rich rocks and evidence of extensive assimilation as guides to prospectivity

Jun 19, 1905

J. Chipman (Massachusetts Institute of Technology, Cambridge, Mass.)—The fact that the experimental work has been applied to copper rather than iron and that the paper is presented to the Iron and Steel Division, I regard as rather significant. It shows the unity of metallurgy and the fallacy of trying to cut it up by metals. This result for the solubility of sulphur in molten copper correlates with Professor Schuhmann's finding that the published data on the other side of the copper-sulphur miscibility gap are also in error. I should like to ask the author to say a little bit more about the sulphur capacity of the slag. T. Rosenqvist (author's reply)-—I hope that Dr. Chipman will find the derivation of the expression for sulphur capacity more clearly explained in the printed version of the paper than in the oral discussion at the meeting. I feel that this quantity, which actually is the ratio of two activities, can be measured more easily than the individual activities. Even if the ratio CaO/CaS is chosen as the standard state, the expression can be used for any slag, even for slags completely free of lime, and it represents a way to put the desulphurizing power of all slag constituents into one bag. Some doubt has been expressed as to whether oxygen ions really exist in calcium oxide and in molten slags. From a thermodynamic view point that question is of minor importance. The term oxygen ion activity, or any activity for that matter, is defined rigorously by the equation: activity = exp u/RT, where u is the change in free energy connected with the transfer of one mol of ions from the standard state into the slag. Whatever happens to the ion in the slag is of no concern to the thermodynamicist. Regardless of whether the ion is "free" in the slag or not, or whether it is present in a very small amount, its activity can always be expressed, and for a thermo- dynamic calculation that is all we need. However, ionic activities will only be of some real value if they are simple functions of the slag composition, or can be measured easily. Concerning the real nature of the oxygen in the slag, my feeling is that the oxygen atom has a rather multiplex nature depending on how strongly it is tied by covalent forces or polarized by the other atoms or ions present. The oxides of iron, cobalt, and nickel differ from calcium oxide and blast furnace slags as to the amount of free electrons that can give rise to electronic conductivity. In slags we know that the conductivity is mostly ionic. The fact that reversible emf's can be obtained with oxygen electrodes in certain salt melts, indicates a significant amount of oxygen ions in these melts. But extended work, e.g. polaragraphic studies and measurements of transference number; are needed to obtain quantitative information about the real structure of the slags. D. E. Babcock (Republic Steel Corp., Youngstown, Ohio)—-With reference to the ion, it might be well to remember Dr. Moses Gomberg. All of his life he had no use for the ionization theory and he contributed greatly to the field of chemistry on the assumption there was no such thing as ions. I do not think we have to worry about whether the oxygen is ionic or not. I think one thing specifically should be brought to your attention and this I think is one of the important contributions of Dr. Rosenqvist. He pointed out what we know as oxygen potentials or what is described as oxygen potentials. I have used this concept for a long period of time and I want to state that if this concept is properly applied, it vitiates much of what we have in the literature, or makes our usual ideas regarding oxidation seem primitive. That one thing is more valuable than almost all the rest of the discussion as a fundamental basis on which to build a reasonable in-

Jan 1, 1952

By Charles J. Haas

The objective of this research was to investigate the interaction phenomena of rock and types of rock bolts to develop design principals for using grouted roof bolts. The investigation was to determine the effectiveness of grouted bolts in resisting lateral displacement and axial separation along fracture planes, and also to determine if grouted bolts eliminate the axial tensile stress near the anchor and the resulting rock fracture. The first year's effort involved defining the post-tensioning response of grouted bars and determining the amount of shear resistance generated by conventional and resin-grouted bolts. A finite-element analysis showed that if the rock and resin grout behave in an elastic manner, the post tensioning of a grouted bar will affect mine roof stability only if movement occurs near the collar. An experimental shear test program revealed that both conventional bolts and resin-grouted reinforcing bars significantly increase shear resistance along fracture or bedding plane when the average normal compressive stress on that plane is low (in the order of 25 psi) and when the bolt is oriented so that the shear displacement tends to lengthen the bolt. An increase in shear resistance is also noted at the higher normal pressure of 250 psi; however, the increase is small compared to the corresponding shear resistance without a bolt. Conventional bolts oriented so that they tended to loosen with shear displacement added no significant shear resistance.

Jan 1, 1974

By John E. McCullough

The purpose of this development program is to design and develop a known volume air sampling pump for use in measuring the amount of radio-active material in the atmosphere of an underground uranium mine. The principle nuclear radiation hazard to underground uranium mines comes from the mine atmosphere. Daughter products of 222-radon, namely 214-polonium, 214-lead, 214-bismuth and 214-polonium, are inhaled by the miner, resulting in a relatively high lung cancer rate among these workers.

Jan 1, 1976

By J. Sottile, J. L. Kohler

Component failures in the electrical control circuits of mining machines account for a large percentage of the total downtime of the machine. Once a failure has occurred it is always a tedious and usually a time-consuming task to locate the failed component. Moreover, the pressure to quickly locate the cause of a delay can lead to compromises in safety. Thus an onboard diagnostic system, essential for an automated machine, would be a very useful addition to existing machines. This report details U.S. Bureau of Mines development of a generic procedure for synthesizing diagnostic systems for electrical-control-circuit failures in mining machinery. A continuous mining machine is used as the testbed to illustrate the application of the developed methodology. Substantive differences among mining machine control circuits made it impossible to achieve a generic diagnostic system, but a generic approach for the synthesis of the diagnostic system was possible. As the research progressed, it became apparent that an algorithmic approach was better than an expert- system-based implementation. A prototype system was constructed and used to evaluate the diagnostic system. Prototype implementation issues are also examined.

Jan 1, 1993

By H. Kim

"IntroductionThe Hat Creek coal field contains low-grade coal deposits which are the thickest in the world. The diamond drilling and geophysical surveys conducted by B.C. Hydro over the last six years have indicated in excess of 2 billion tonnes of sub-bituminous to lignitic coal. The coal field is in the Interior Plateau Dry Belt, about 240 km northeast of Vancouver, and contains two explored, nearsurface coal deposits amenable to surface mining (Fig. I). The No. I deposit contains approximately 740 million tonnes of coal at 17.71 MJ / kg, or 7,600 Btu/lb, at 34.82% ash and 24% moisture. The No. 2 deposit to the south contains appreciably more coal resources at somewhat lower grade, but it has not been explored so extensively because of its higher stripping ratio. Therefore most of the exploration activities to date have been directed toward the development of the No. I deposit. The No . I coal deposit has been selected as the source of fuel for a proposed thermal powerplant to be built about 5 km east of the deposit. The purpose of this paper is to summarize the data obtained from the diamond drilling and the geophysical logging in the No. I deposit between 1974 and 1979. An attempt is made to explain the depositional environment of the Hat Creek coal measures. Because the understanding of the depositional environment in.a particular basin is essentially an evaluation of all the geologic properties of the area, the available geological information in the No. I deposit has been compiled on the basis of consistent criteria. This includes data on the lithology of the coal measures, thickness and areal distribution of the elastic sediments, and on the changes in the megascopic stratigraphic profile based on geophysical correlation. The palynopetrographic relationship and detailed sedimentological aspects are not examined in this paper. Such studies should provide important information relating the causal vegetal and chemical responses of the coals to -environmental changes. Extensive deposition of surficial materials during de-glaciation left most of the area of the Upper Hat Creek Valley devoid of bedrock exposures. Structural and stratigraphic features are hidden beneath glacial deposits and/or post-Eocene volcanics. As a result, the geological interpretation of the Hat Creek coal basin has been based primarily on drilling and geophysical data. Because of this, any explanation of the depositional environment details is tentative until the deposits are stripped for development."

Jan 1, 1985

By Y. L. Su

Deterministic and stochastic simulation were combined to develop a computer model of an open pit mining system using bucket wheel excavators and related materials handling equipment. The model is closed and dynamic in the sense that information is fed back to control activities at various levels and reservoirs. The results of interaction between unit operations in one time interval determines overall system behavior for the next interval. Equipment performance curves and system profile characteristics rather than time studies are applied to determine the operation of each activity at any time period. For that part of system where performance is dictated by a random variable~ subjective probabilities are employed. Two stages of research were considered to formulate this model. Stage one involved the formulation of equipment sub-assemblies for the sequence of equipment moves along with related assignments and routines for information retrieval. The second stage of research combined all sub-assemblies into an integrated open pit mining simulator. The model is not tailored for any specific open pit operation but is readily adaptable to any system of surface mining including operations having a high degree of complexity. Questions answered by the model include: 1) system design and selection of equipment for a new mining operation; 2) analysis of existing operations for possible changes, additions or general

Jan 1, 1971

By M. S. Ellis, D. J. Nichols

In 1999, 1,100 million short tons of coal were produced in the United States, 38 percent from the Northern Rocky Mountains and Great Plains region. This coal has low ash content, and has sulfur content in compliance with Clean Air Act standards (U.S. Statutes at Large, 1990). The National Coal Resource Assessment for this region includes geologic, stratigraphic, palynologic, and geochemical studies and resource calculations for 18 major coal zones in the Powder River, Williston, Green River, Hanna, and Carbon Basins. Calculated resources are 660,000 million short tons. Results of the study are available in U.S. Geological Survey Professional Paper 1625-A (Fort Union Coal Assessment Team, 1999) and Open-File Report 99-376 (Flores and others, 1999) in CD-ROM format.

Jan 1, 2001

By B. Gillenwater

This report describes the results of investigations into four specific areas related to trolley wire power distribution systems in coal mines. These are: 1. Partially insulated (shielded) trolley wire 2. High-speed insulator fault detectors 3. Dual-wire trolley systems 4. Insulator failure indicators. Prototype devices or designs were developed in each area. In addition, a brief survey was made in an attempt to assess the Future of mine trolley systems, and data was collected and reviewed in an attempt to analyze the nature of trolley wire related accidents. Other options for decreasing the risks associated with trolley systems that arose .during the study are briefly described in appendices. These include insulating equipment and miners from return and/or energized conductors and use of a segmented trolley wire with local control of current delivering capability.

Jan 1, 1981

By Joseph Grumer

An instrumented spherical vessel has been used for many years to study laminar combustion waves. Concurrent measurements of flame speed and pressure-rise rates have led to evaluations of burning velocities, the pressure dependence of the burning velocity, and the expansion ratios of the gases passing through the combustion wave. For the most part, these studies have involved flames initially at atmospheric or subatmospheric pressure. The old spherical vessel used by the Bureau of Mines was not designed for use at elevated pressures. Moreover, being made of wrought iron, it was susceptible enough to corrosion to prohibit its use with many combustible mixtures that figure in industrial research. In mid-1956, under sponsorship of the Office of Naval Research, the Bureau undertook the development of a stainless steel spherical vessel capable of withstanding explosions of gaseous mixtures at initial pressures as high as 20 atm. and initial temperatures as high as 250° C. The design called for a double array (cross) of closely spaced small windows for observation of the flame as it traversed the vessel and a piezoelectric transducer to measure concurrently pressure-rise rates. Because no commercial contractor was willing to bid on the construction of such a vessel, it was built at the Bureau's Bruceton machine shop.7

Jan 1, 1961

By W. C. Ellis, E. S. Greiner

Metallic titanium has been prepared in small quantities since the beginning of the century. Hunter1 reported in 1910 that he obtained a malleable product of 99.9 pct purity by the reduction of the tetrachloride by sodium in a closed container. Later Van Arke12 and Fast prepared small quantities of malleable titanium by thermal decomposition of titanium iodide. Another method for producing malleable titanium from tetrachloride was reported by Kr0ll4 who used magnesium as the reducing agent. More recently Dean, Long, Wartman, and Anderson5 working at the U.S. Bureau of Mines have reported the preparation of the metal on a pilot plant scale by the reduction of titanium tetrachloride by magnesium in an atmosphere of helium. Their product, which is malleable, was used in the present investigation. Early in 1948 after the work of this paper was completed Campbell, Jaffee, Blocher, Gurland, and Gonser6 described the strength and working characteristics of pure titanium which was prepared by the iodide method on a scale producing 300 to 600 g per run, in the form of 0.3- to 0.4-in. diam rods. Their product is characterized by low hardness and large capacity for cold work which they attribute to a high degree of purity with respect to oxygen, nitrogen, and carbon. Titanium has a melting point of about 1725 C," it may be classed as a light metal since the specific gravity is 4.5 g per cc-I. The crystal structure is close-packed hexagonal from room temperature to 885°C. Above this temperature the structure is reported7 as body-centered cubic. The change in crystal structure has been associated with discontinuities in specific heat,8 electric resistanceg and theimoelec-tric force10 at temperatures near 890°C. It is reportedll that annealed titanium has a tensile strength of 78,700 psi which can be increased by cold-work to 123,000 psi. In the present investigation, the lattice constants at room temperature, the thermal expansivity between 30 and 800°C, as well as the electrical resistivity and thermoelectric force against platinum between — zoo and I000 C have been determined. Materials For the measurements, two series of specimens were prepared from titanium furnished by the U. S. Bureau of Mines. The first was made from an annealed sintered compact, 0.38 in. thick. Sections of the compact were cold-swaged with intermediate anneals in vacuum to the sizes used. Sizes over 0.25-in. diam were annealed at I000°C and smaller sizes at 800°C. Specimens originating from the sintered compact are designated in this paper as A. The second series of specimens was made from a rod of titanium, 0.19 in. in diam, which was cold-swaged with the necessary intermediate anneals to the required sizes. This series of specimens is designated B. The impurities in the specimens of titanium, determined by chemical analysis, are given in Table 1. Oxygen and nitrogen which Were not determined by analysis, are probably present although in small quantities in view of the ductility of the material.

Jan 1, 1949

By Terkel Rosenqvist

J. Chipman (Massachusetts Institute of Technology, Cambridge, Mass.)—The fact that the experimental work has been applied to copper rather than iron and that the paper is presented to the Iron and Steel Division, I regard as rather significant. It shows the unity of metallurgy and the fallacy of trying to cut it up by metals. This result for the solubility of sulphur in molten copper correlates with Professor Schuhmann's finding that the published data on the other side of the copper-sulphur miscibility gap are also in error. I should like to ask the author to say a little bit more about the sulphur capacity of the slag. T. Rosenqvist (author's reply)-—I hope that Dr. Chipman will find the derivation of the expression for sulphur capacity more clearly explained in the printed version of the paper than in the oral discussion at the meeting. I feel that this quantity, which actually is the ratio of two activities, can be measured more easily than the individual activities. Even if the ratio CaO/CaS is chosen as the standard state, the expression can be used for any slag, even for slags completely free of lime, and it represents a way to put the desulphurizing power of all slag constituents into one bag. Some doubt has been expressed as to whether oxygen ions really exist in calcium oxide and in molten slags. From a thermodynamic view point that question is of minor importance. The term oxygen ion activity, or any activity for that matter, is defined rigorously by the equation: activity = exp p/RT, where p is the change in free energy connected with the transfer of one mol of ions from the standard state into the slag. Whatever happens to the ion in the slag is of no concern to the thermodynamicist. Regardless of whether the ion is "free" in the slag or not, or whether it is present in a very small amount, its activity can always be expressed, and for a thermo- dynamic calculation that is all we need. However, ionic activities will only be of some real value if they are simple functions of the slag composition, or can be measured easily. Concerning the real nature of the oxygen in the slag, my feeling is that the oxygen atom has a rather multiplex nature depending on how strongly it is tied by covalent forces or polarized by the other atoms or ions present. The oxides of iron, cobalt, and nickel differ from calcium oxide and blast furnace slags as to the amount of free electrons that can give rise to electronic conductivity. In slags we know that the conductivity is mostly ionic. The fact that reversible emf's can be obtained with oxygen electrodes in certain salt melts, indicates a significant amount of oxygen ions in these melts. But extended work, e.g. polaragraphic studies and measurements of transference number; are needed to obtain quantitative information about the real structure of the slags. D. E. Babcock (Republic Steel Corp., Youngstown, Ohio)—-With reference to the ion, it might be well to remember Dr. Moses Gomberg. All of his life he had no use for the ionization theory and he contributed greatly to the field of chemistry on the assumption there was no such thing as ions. I do not think we have to worry about whether the oxygen is ionic or not. I think one thing specifically should be brought to your attention and this I think is one of the important contributions of Dr. Rosenqvist. He pointed out what we know as oxygen potentials or what is described as oxygen potentials. I have used this concept for a long period of time and I want to state that if this concept is properly applied, it vitiates much of what we have in the literature, or makes our usual ideas regarding oxidation seem primitive. That one thing is more valuable than almost all the rest of the discussion as a fundamental basis on which to build a reasonable in-

Jan 1, 1952

By Laurence Delisle, Aaron Finger

THE alloys formed by the addition of nickel to iron by convelltional metallurgical procedures show physical properties that differ widely from those of the individual metals. The effect of alloying on the mechanical properties is most pronounced in alloys containing between 15 and 25 per cent nickel. The tensile strength of an alloy containing, for example, 20 per cent nickel and 80 per cent iron (with 0.06 per cent carbon), in an annealed condition, is above 150,000 lb. per sq. in.? owing to a martensitic type of transformation, as compared with about 50,000 lb. per sq. in. for pure iron in the same condition. The object of this work was to determine whether the same beneficial alloying effect could be obtained in alloys of iron and nickel prepared by powder metallurgy technique. PROCEDURE Bars and pellets for tension and compression tests, respectively, were made. Two groups of specimens were prepared: (I) by cold-pressing the powders and sintering; (2) by cold-pressing the powders, sintering, repressing and resintering. Raw Materials Nickel powder supplied by Metals Disintegrating co., marked MD-151, was used. A typical analysis of this powder was as follows: sulphur, 0.040 per cent; copper, 0.18; iron, 0.23; manganese, 0.002; magnesium, 0.001 5 ; lead, 0.035; tin, 0.025 ; silicon, 0.08; chromium, 0.008. Electrolytic iron powder supplied by Plastic Metals Inc. was used. A representative chemical analysis for impurities other than gases, supplied by the vendor, gave the following results: carbon, 0.005 per cent; manganese, 0.002; silicon, 0.003; phosphorus, 0.001; sulphur, 0.004; nickel, 0.008. The fractions from these powders passing a 3 2 5-mesh sieve were reduced in hydrogen at 600°C. for one hour, to clean the surfaces of the particles. The reduced powders, slightly caked, were ground in a mortar and screened again through a 325- mesh sieve. Mixing The proper proportions of the powders were mixed overnight on rolls, in glass jars fitted with iron-wire baffles to break aggregates of particles that might form. Pressing All specimens were compacted on hydraulic presses. The pellets were compacted in a cylindrical die, ½ in. diameter. The ratio of thickness to the diameter of the pellets was maintained as nearly as possible at 0.9, as specifed for standard short compression pieces. The tensile bars were made by compacting 30 grams of powder. Their shape is shown in Fig. I. The compacting pressures for the pellets and the tensile bars were:

Jan 1, 1946

By Caroline Antunes Corrêa

Filmes híbridos estão sendo utilizados como revestimentos de substratos metálicos para proteção contra corrosão. Este trabalho tem como objetivo verificar o comportamento corrosivo de filmes híbridos com diferentes concentrações de polietilenoglicol (PEG) sobre folhas de flandres pela técnica de varredura por eletrodo vibratório (SVET). Os resultados demonstraram que o aumento da concentração de polietilenoglicol ocasionou a formação de fissuras e delaminação do filme híbrido. As análises por SVET demonstraram a possibilidade de analisar a corrosão localizada em regiões com defeitos no filme e no substrato metálico.

Aug 16, 2017

By Nathan Feldstein

The wetting of coal dust by aqueous solutions of surface active agents (surfactants) has been studied. Selected for study were thirty coals and typical surfactants selected from the typical classes of anionic, non ionic and cationics. Of these three classes the practical use of cationics in aqueous solutions has been eliminated due to the inherent negative Zeta potential charge of the representative coals studied. The wetting of the coals has been examined by column flow, contact angle, and settling rate measurements. Results indicated that both anionic and nonionic surfactants are to be considered viable for use; low critical micelle concentration values are also preferred for the surfactants. Study of native waters showed substantial variation in properties, i.e., pH, calcium ion concentration, and conductance. pH variations were also noted to affect the effectiveness of selected surfactants. Combinations of nonionic and anionic surfactants have, in certain instances, produced synergistic enhancement in the coal wetting superior to the effectiveness of each surfactant alone.

Jan 1, 1981

By José Dimas de Arruda

O conhecimento do campo de fluxo dentro do molde de lingotamento contínuo pode oferecer uma oportunidade de se melhorar a limpidez interna do produto. Modelagem física, aplicação da técnica PIV juntamente com a modelagem matemática via Ansys Fluent foram empregadas para avaliar a distribuição de velocidades na região de interface metal escória num molde de lingotamento de placas. Os resultados foram analisados com base em critérios de estabilidade da interface metal – escória disponíveis na literatura e ressaltam o papel do empuxo e tensão interfacial.

Aug 16, 2017

By Howard J. Pincus

The purpose of the study is to investigate the effects of fracture filling and associated alteration on the mechanical behavior of rocks. Results are presented for specimens from the Climax and Henderson mines in Colorado and the San Manuel mine in Arizona. The rock types studied from each location are from 1) Climax, medium-grained - granite, fine-grained granite, granite porphyry, schist, and gneiss; 2. Henderson, rhyolite porphyry; 3. San Manuel, quartz monzonite and quartz monzonite porphyry. A description of the rocks was made including: color, texture, mineral composition, composition and fabric of fracture fillings, density and porosity. Unconfined and triaxial compression tests were run on the Climax and San Manuel specimens. Sonic relocities were measured during the compression tests; Shore sceleroscope hardness was measured before the compression tests. Tentative conclusions are that some relation appears to exist between compressive strength and the following properties and features for all the specimens: dynamic Young's modulus, sonic velocity, density, rock composition, and composition and fabric of fracture fillings - veinlets. There appears to be some relation between compressive strength and Shore scleroscope hardness and porosity for quartz monzonite (San Manuel). A relation appears to exist between compressive strength and texture for schist and between com¬pressive strength and extent of failure on fracture fillings for fine-grained granite, schist, and gneiss (Climax). We plan to perform additional analyses of data collected so far and data yet to be collected in the next few months, with emphasis placed on devising a practical index of alter¬ation that can be used in the field. Limitations on interpretations arise from such factors as heterogeneity of the rocks studied, the small range of confining pressures used, and other factors presented in the text.

Jan 1, 1973

By Alberto Pesamosca

The paper presents the results obtained by the AC EAF supplied by Danieli at Kroman Çelik (Gebze-Turkey) after the planned upgrade to 150 ton. The EAF – 7,4 m diameter, based on the full platform standard design - is able to handle a maximum power of 114 MW and is equipped with the most advanced and reliable technology, including module injection system and the Hireg electrodes regulation system. Excellent results were already obtained with 120 heat size in terms of fast start-up and excellent performance figures. After the upgrade, productivity was increased up to 212 t/h, maintaining high process efficiency (365 kWh/t with 32,1 Nm3/t O2).

Jul 30, 2018

By A. D. LeClaire

This paper claims to provide a description of diffusion processes in solids which is said to be a reformulation of Fick's Laws and therefore, presumably, is supposed to be as general as those laws. In fact, it appears to provide no more than an atomic model of a rather restricted type leading even to results in conflict with experiment. The restriction lies in the assumption, carried throughout the paper, that even in a chemical gradient the jump frequency i of an atom of species i is a function only of the composition on the plane from which it jumps, i.e., ?i = ?i(cl, c2 ...). This means that atom jumps in opposite directions from a site would occur with equal probability. There would then be no tendency for atoms to migrate preferentially in one direction along the gradient, so the model is incapable of accommodating the well established phenomenon of atom drift in a chemical gradient.10-" A more general model that does not suffer this difficulty was discussed in a paper13 I wrote in 1958, and the results therein already contain as a special case those given by Dr. DeHoff. The simplest sufficiently general assumption is to suppose that ?i is a function ?i(a1 a2,...; wl, w2, ..-) of the concentration aj and ? ?j at the site from which and to which, respectively, a jump is made. Any such function can always be expressed as a function of the sum and difference of its arguments. Thus d is the jump distance and g a geometrical constant. Obviously this is zero, i.e., no drift, if ??ri/??j = 0. X is written in this form, revealing two components of the total drift, because it can be shown that only the second component, depending on ??'i/???(?j -aj), actually contributes to the net diffusion flux Ji. This component can be shown,13 by a straightforward ther-modynamic transcription, to be responsible for the so called "thermodynamic factor" in the Darken approximation for a chemical diffusion coefficient is the activity coefficient of i. Because the jump rate ?i in DeHoff's approximation has no dependence on the concentration gradient it does not seem possible to derive the Darken equation from his Eq. [6] without the further rather arbitrary assumption that ?i = const ri. It is to be noted too that the author's derivation of Eq. [12] is only valid when ?i is in fact a function only of the cj at the plane from which the atom jumps—for only then is ci?i a unique function of position and therefore of A. Author's Reply R. T. DeHoff I am indebted to Dr. LeClaire for his penetrating discussion of my paper, "A Reformulation of Fick's First Law". I concede that it does appear initially that the relationship presented in my paper could be derived from the detail atomic model of random walk and atom drift presented in Dr. LeClaire's approach. However, there are some important differences in concept and viewpoint which deserve further amplification. Dr. LeClaire's description is penetrating, detailed, and fundamental. His approach describes an extremely complex phenomenon, the displacement of atoms in a multicomponent gradient, at a sophisticated level. For precisely these reasons, his analysis has not proved to be useful for experimental studies that have practical objectives. For example, in order to obtain the information required to complete the analysis of the jump frequency distribution in a ternary system, the following series of experiments would, I believe, be required: 1) chemical (gradient) experiments, covering the composition range;

Jan 1, 1970

By W. L. Hill, W. H. Armiger, S. D. Gooch

The physical properties, chemical behavior under thermal treatment, and fertilizer value of fluorine-containing pseudowavellite (hydrous calcium aluminum phosphate) that occurs as phosphate clay admixed with quartz sand in an extensive deposit near Bartow, Fla., were determined by experiments in laboratory, pilot-plant, and greenhouse. When the mineral was heated at 500°C, 80 pct of the phosphorus become citrate soluble. The heated product, however, deteriorates markedly under moist conditions such as obtain in the soil. EXTENSIVE beds of a soft aluminiferous phosphate lie in the Bartow-Pembroke region of Florida. Although the extent of the deposit is unknown, it is thought that the equivalent of at least five million tons of material containing 25 pct P,Os exists on one large mine property alone, and soft phosphates similar in nature are known to occur elsewhere in the state. This aluminum phosphate, unlike fluorapatite, is rendered fairly soluble in neutral ammonium citrate solution merely by heating it at a temperature below 600 °C, a property made the basis of a process patent by the junior author.' The possibility of producing an available form of phosphorus from what has hitherto been a worthless natural phosphate prompted the Bureau of Plant Industry, Soils, and Agricultural Engineering to make a brief study of the Pembroke phos- phate during the war years with a view towards determining the optimal temperature for heat treatment and the reactions involved in the process. The results of this study supplemented by data and information furnished by the junior author are presented in this paper. Description of Natural Phosphate: The phosphate with admixed quartz sand and siliceous matter occurs as a low-grade (8 to 9 pct P2O5) clay-like material that can be beneficiated cheaply by making a water separation of the very fine material from the sand, floating off the fine material, settling the suspension to a thick slurry, and finally de-watering the slurry by vacuum filtration followed by drying. The product dried at 100 °C contains about 16 pct water and 25 pct P2O5, about 1/12 of which is citrate soluble. Partial analyses of representative samples of the crude ore and corresponding concentrate are given in table I. The concentrate is light yellow in color and even after being dried at 100°C sticks very noticeably to laboratory grinding and screening equipment. Under the microscope the ground material is predominantly light brown crystalline aggregates with index of refraction near 1.61. The principal phosphate mineral constituent was identified as pseudo-wavellite with admixed phosphosiderite.2 Pseudo-

Jan 1, 1951