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By C. Wert, D. Keefer

The results of this study indicate that sudden increases in aging temperature lead to reversion phenmena in carbon in the a, iron system. These phenomena are thought to be associated with the dissolution of carbide precipitates. Reversion is studied with respect to three variables: 1) Specimen grain size, 2) the initial amount of carbon in solution, and 3) difference between initial and final aging temperature. It is found that of these variables the initial carbon concentration has the greatest effect on reversion. THE solid solution of carbon in n iron has been the subject of numerous investigations throughout the past few years. Despite the great amount of effort which has been put forth toward understanding this system, however, there persist a number of interesting aspects of the system which are open to further research' Studies Of the precipitate which forms as a result of aging a supersaturated solution of carbon in a, iron appear to be particularly interesting. The present work is an attempt to determine certain

Jan 1, 1960

By Orrin Peterson

THE decision of the Supreme Court of the United States not to review the findings of the lower courts closes an interesting chapter in the mining litigation that has arisen as a result of the extralateral feature of the mining law. The time seems opportune to record some of the important geological features, and also some of the legal features, of the controversy, in the hope that these will be permanently accessible to members of the mining profession. After many rumors of litigation, the Utah Consolidated Mining Co. sued its neighbor for the ore that had been, it was alleged, wrongfully extracted from its so-called Yampa limestone lode. This ore lay beneath Utah-Apex surface and was claimed by virtue of the extralateral rights conferred on the Utah Consolidated Co. through the ownership of certain specific mining claims, one of the principal claims being the Yampa. Previous to bringing suit, the Utah Consolidated Co. had strengthened its position by purchasing the Old Yampa mine and by making an agreement with the Utah Metal & Tunnel Co., which gave it clearer title to the outcrop of the Highland Boy limestone. Access to the workings of the Utah-Apex Co. was secured and reciprocal privileges gave Utah-Apex representatives the right to enter the properties of the Utah Consolidated Co. This resulted in the Utah-Apex immediately bringing countersuit for ore alleged to have been wrongfully extracted from under its surface in the Leadville country, see Fig. 4. Six cases came up for consideration: five related to the original suit and the countersuit, and one related to the Dana extralateral claims of the Utah-Apex Co.

Jan 6, 1924

By M. D. Flavel

The paper describes the physical aspects of the compression and impact crusher types along with the information needed to apply, install and operate them to best achieve designed performance levels. It reviews key performance parameters such as energy size relationships for crushing processes and how automation devices can optimize machine productivity. Weaknesses of existing application engineering methods are discussed. The use of pilot plant information and appropriate laboratory testing procedures are reviewed from the point of view of the application design engineer so that the best type of machine can be selected for a proposed installation.

Jan 1, 1982

By J. P. Matoney, E. J. Sandy, D. A. Dahlstorm

INTRODUCTION Before an understandable discussion concerning coal dewatering processes can be initiated, it is necessary to define some terms of usage. The many different meanings and interpretations of terms preclude development of standard definitions so the terms defined in this chapter should be regarded primarily as working terms intended to facilitate communication.

Jan 1, 1979

By E. Gregory, A. Coucoulas

Carbm dioxide, which exists metastably as a constantly subliming molecular solid in a normal room-temperature environment, has been shown to exhibit many microstructural features which are similar to those observed in metals and ceramics at temperatures approaching their melting points. An examinution has been made of some of the factors affecting a brittleness condition known as "smzdiness" which occurs in solid carbon dioxide. It has been shown to be highly dependent on manufacturing and storage conditions and is thought to be a marked intergranu-lay brittleness which results from a combination of excessive grain growth and a concentration of gas-filled pores at the grain boundaries. In the course of an investigation carried out to explain certain physical and mechanical properties of solid carbon dioxide, observations were made of the microstructure and fragmentation of samples after fabrication and storage under varying conditions. Many similarities between the structures of solid carbon dioxide observed under ambient conditions and those existing in metal and ceramic systems at temperatures approaching their melting points have been observed. There are, however, important differences between solid carbon dioxide and the common metallic and ionic solids which result primarily from the differences in the nature of the bonding forces. Despite these differences, the relative ease with which certain microscopic observations can be carried out, may make solid carbon dioxide a useful material model for the physical metallurgist and the ceramist. It could also prove a valuable material for educational purposes where it is required to illustrate grain phenomena which normally can only be seen with the aid of a high-temperature microscope, and after prolonged chemical or thermal etching.

Jan 1, 1963

By Heinrich Ries

Jan 1, 1907

Jan 1, 1907

By J. W. Lewis

This review covers that portion of the area between the Llano mountains and the Red River which lies between Fort Worth and Abilene. The counties and fields included are listed in Tables 1 and 2. During 1929 there was a marked lull in both prospecting and development in this part of Texas. Archer, Coleman, Cooke, Wilbarger and Young were the counties most active. The total gross production of the year was 52,611,000 bbl., 3 per cent. more than for 1928. The production of the Coleman, Cooke-

Jan 1, 1930

At the eastern end of the Mesabi Range, 70 miles due north of Duluth, is the vast plant of Erie Mining Co. Operated by Pickands Mather G Co. for the mine's four owners-Bethlehem Steel, Youngstown Sheet and Tube, Inter- lake Iron, and Steel Co. of Canada-Erie Mining Co, has earned just fame as a pioneer and a leader in the mining, beneficiation, and agglomeration of the lean iron ores of the Lake Superior district. Here is the story of Erie and the integrated operations that have made it such an outstanding member of America's iron ore industry.

Jan 5, 1963

By Jr. W. L . Phillips

The deformation and fracture characteristics of lithium-fluoride single crystals stressed in compression at room temperature have been studied. In as-cleaved specimens the stress-strain curves were variable; two types of {110} fractures were observed in the vicinity of kink bands. The stress-strain curves of annealed crystals were reproducible; {100} cracks formed which propagated along the (100) and (110) planes. The deformation and fracture characteristics were affected by quenching and X-ray irradiation. STUDY of the mechanical behavior of nonmetallic materials has received considerable impetus in recent years because of the need to overcome the problem of brittleness before the refractory properties of nonmetallics can be fully exploited. Ionic crystals provide a convenient and simplified starting point from which to study the deformation and fracture processes in nonmetallic materials. Early investigations of the mechanical behavior of non-metals were restricted largely to determinations of the crystallographic indices of the cleavage and fracture planes and the glide and twinning elements. Until recently, only occasional systematic studies of the deformation characteristics of non-metals have been made; and investigations of the forces necessary to initiate plastic deformation and the factors which affect the flow characteristics have been restricted largely to studies of sodium chloride'-7 , magnesium oxides-l3 and lithium fluoride. 14-22 Fracture studies on alkali halide and metal oxide single crystals have been limited despite the fact that these materials have a number of advantages for fracture studies. Because they are transparent, the cracks which form can be viewed in three dimensions instead of in two dimensions as in metals. Also, they exhibit stress birefringence under polarized illumination, which enables the internal stress pattern and, therefore, the distribution of dislocations to be examined in the vicinity of the fracture. Early workers1-4 have shown that ionic crystals with a cubic structure fracture in tension along the (100) plane normal to the applied stress. These fractures were brittle at room temperature and propagated very rapidly across the cross section of the crystal. More recently, Stokes, Johnston, and Lil0 have studied crack formation in compressed magnesium-oxide single crystals. They found that the cracks, which were observed after about 3 pct strain, formed in the region of a kink band and lay on conjugate (110) slip planes instead of the usual(100) cleavage plane. Two different types of cracks were noted: stroh23 and secondary. The Stroh cracks did not exist merely on the surface but extended through the specimen in the form of tiny slits. A secondary

Jan 1, 1962

By Richard P. Rothwell

The ores treated by the Canada Consolidated Gold Mining Company at Deloro, Ontario, have been described in a paper read before the Institute in 1881. They are gold-bearing arsenical sulphurets of iron (mispickel), carrying the theoretical proportions of 42 per cent. of arsenic, 20 per cent. of sulphur, and the remainder iron. The gangue is quartz, calc spar, and some talcose, slaty rock, evidently resulting from the decomposition of the wall-rock, which on each side of the veins is syenitic granite. The treatment of the ore consists of: 1. Crushing. 2. Concentrating.

Jan 1, 1883

By D. V. Doane, G. A. Timmons, W. G. Scholz

Molybdenum of high purity can be produced by direct dissociatiott of commercial molyhdenm disulfide in vacuo at 1600° to 1700°C (2910° to 3090°F). The Product is lower in oxygen than commercially available molybdenzdm powder. Analyses of ingots arc-cast from commercial molybdenum powder, hydrogen-re-cluced from animonium molybdate, and from thermally dissociated molybdenum disulfide indicate that the levels of chemical impurities in these ingots are similar. Equipment now in operation will produce 100-lb hatches of powder product. The paper describes development of processing equipment, control of processing varzahles, handling of the product, and evaluatiotl of the melal produced. MOLYBDENITE (molybdenum disulfide) can be decomposed by heat in the absence of oxygen to produce elemental molybdenum and sulfur, which is evolved as a gas. The temperatures required for the dissociation are above 1370°C (2500°F); the sulfur must be continuously withdrawn to permit the reaction to proceed to completion. This is accomplished by continuous evacuation of the thermal dissociation chamber and condensation of the gaseous sulfur in another part of the system. Cognizance of the fact that the dissociation takes place in two steps is important in controlling the process. Basically, the molybdenite dissociation process has two potential advantages as a method of produc- ing pure molybdenum: 1) The materials entering into the process contain little or no oxygen. Since the process is carried out in vacuum at high temperature, the quantities of interstitial oxygen, nitrogen, and hydrogen in the product should be very low. 2) The process is more direct than the commercia1 method of producing high-purity molybdenum. In the conventional process, molybdenite is roasted to molybdic oxide, the oxide is purified first by sublimation, then by conversion to ammonium molybdate, and finally, the molybdate is reduced in a hydrogen atmosphere (usually in two steps) to the metal lic molybdenum powder. This paper presents a description of the stages in scaling-up of the dissociation equipment and an account of attempts to evaluate the molybdenum produced by thermal dissociation, rather than a report of a fundamental study of the dissociation reaction. Since little has been written on the subject, it is appropriate, before detailing the development of the process, to review briefly the research that has been conducted over quite a period of years. LITERATURE SURVEY The first accounts of the possibility of thermal dissociation of the mineral molybdenite were re-

Jan 1, 1962

By D. A. Elgillani, M. C. Fuerstenau, M. C. Kuhn

The species responsible for flotation when xanthate is added as collector for pyrite is dixanthogen. Measured oxidation potentials of these systems show that xanthate should be oxidized to dixanthogen, and the presence of dixanthogen on the pyrite surface is confirmed by infrared absorption. Zeta potential measurements are presented and related to collector adsorption. In spite of the normal presence of pyrite in most sulfide ore deposits, only a modest amount of study has been devoted to the xanthate-pyrite flotation system in the absence of activators and depressant~.'-~ As a result, little is known about the mechanism of xanthate adsorption on pyrite. From the few studies that have been made, however, a number of significant observations have been forthcoming. For example, the dependence of flotation response on the state of oxidation of the surface was noted in two studies — one conducted by Plante and Sutherland4 and a later one by plaksin.~ In another study, Gaudin and wilkinson3 found that ferric xanthate was not present on a pyrite surface. In a later investigation, however, Gaudin' and his colleagues did extract a small amount of ferric xanthate into benzene when pyrite was ground in an evacuated mill with water, benzene, and xanthate. This quantity was apparently

Jan 1, 1969

By E. B. Swanson

Crude oil production in Iraq during 1932 was maintained at slightly higher levels than in 1931, but the output continued to be restricted to the requirements of local consumers. The Iraq Petroleum Co., representing British, American and French interests, which has been operating within its concession east of the Tigris River since 1926, began drilling operations on Apr. 5, 1927, and completed its first well at Baba Gurgur on Oct. 14, 1927, to which area the company has since confined its drilling activities. Relatively small quantities of oil have been produced annually, but the products have been utilized in company operations and have not been offered on the Iraq market. The Khanaqin Oil Co., which has its field of operation at Naft Khana in the so-called Transferred Territories, has been supplying the Iraq market with petroleum products from Iraq wells since March 12, 1927. The output of the Khanaqin Oil Co. refinery, at Alwand, during the past three fiscal years ending March 31, has been as follows: (In Barrels of 42 Gallons Each) 1930 1931 11931 Gasoline................................. 102,940 104,571 118,012 Kerosene................................ 104,010 108,112 111,624 Fuel oil...........................1 286,9001 332,142 354,244 503,850 544,825 583,880 The Iraq Petroleum Co. has a small topping plant, with a capacity of about 150 bbl. a day, used in the manufacture of petroleum products for the company's own needs. During the 1932 fiscal year, the production was 3918 bbl. of gasoline and 2235 bbl. of kerosene, as compared with 8157 bbl. of gasoline and 6308 bbl. of kerosene during the preceding fiscal year.

Jan 1, 1933

By John L. Ham, Robert M. Parke

The melting point of molybdenum is 2625° + 50°C. Heretofore the metal has been considered too refractory to be melted in commercial quantities; hence, it has been formed into rod, wire, and sheet by the methods of powder metallurgy, wherein the temperatures do not exceed 90 per cent of the melting temperature. The manipulation of liquid metals at temperatures of about 2000°C. and above presents some difficult problems in heat transfer, in purification, and in container materials. For metals melting at such high temperatures, it is generally regarded as expedient to circumvent the more common melting and casting process by resorting to powder metallurgy. This circumvention is not accomplished without some penalties, the more notable of which are the relatively high cost of the powder metallurgy method and particularly the size limitations of its product. In an effort to overcome the inherent disadvantages of the powder metallurgy method, especially in respect to the limit of size, a project was begun in 1943 at the Climax Molybdenum Co. laboratory to develop a method of melting and casting molybdenum capable of producing larger bodies of molybdenum than were then obtainable. Later, from Feb. I, 1944, to Aug. 31, 1945, the project was under the supervision of the National Research Committee, Division One. In peacetime, too, there are needs for molybdenurn, which make consideration of another process desirable; for example, large parts for heat engines generally, the omnipresent demand for metal of higher quality and lower cost, and the development of molybdenum-base alloys. This paper describes methods for melting and casting molybdenum, with details of the special process needed to make molybdenum castings ductile, and reports some of the properties of what may be regarded as a new, or at least modified, form of the metal. First Process for Melting and Casting Molybdenum The maintenance of a temperature greater than 2625°C. in a 'pace large enough to melt several pounds of molybdenum may involve the loss of heat at a Very considerable rate. For melting molybdenum, therefore, the source of heat must be of high potential and of fairly high power. Evidently, also, the source of heat must not impair the purity of the product. The electric arc operating in vacuum appeared to meet these requirements and was accordingly the first choice as a source of energy. A number of arc devices for melting molybdenum were examined, and several were tried. In the first experiment, a 20-kw., 60-cycle-per-second alternating-current arc was operated between two horizontal and opposed electrodes of molybdenum- In this arrangement the falling droplets of molybdenum solidified below the arc in an irregular mass. This experiment did not produce a useful casting, but the data obtained indicated that

Jan 1, 1947

By John L. Ham, Robert M. Parke

The melting point of molybdenum is 2625° + 50°C. Heretofore the metal has been considered too refractory to be melted in commercial quantities; hence, it has been formed into rod, wire, and sheet by the methods of powder metallurgy, wherein the temperatures do not exceed 90 per cent of the melting temperature. The manipulation of liquid metals at temperatures of about 2000°C. and above presents some difficult problems in heat transfer, in purification, and in container materials. For metals melting at such high temperatures, it is generally regarded as expedient to circumvent the more common melting and casting process by resorting to powder metallurgy. This circumvention is not accomplished without some penalties, the more notable of which are the relatively high cost of the powder metallurgy method and particularly the size limitations of its product. In an effort to overcome the inherent disadvantages of the powder metallurgy method, especially in respect to the limit of size, a project was begun in 1943 at the Climax Molybdenum Co. laboratory to develop a method of melting and casting molybdenum capable of producing larger bodies of molybdenum than were then obtainable. Later, from Feb. I, 1944, to Aug. 31, 1945, the project was under the supervision of the National Research Committee, Division One. In peacetime, too, there are needs for molybdenurn, which make consideration of another process desirable; for example, large parts for heat engines generally, the omnipresent demand for metal of higher quality and lower cost, and the development of molybdenum-base alloys. This paper describes methods for melting and casting molybdenum, with details of the special process needed to make molybdenum castings ductile, and reports some of the properties of what may be regarded as a new, or at least modified, form of the metal. First Process for Melting and Casting Molybdenum The maintenance of a temperature greater than 2625°C. in a 'pace large enough to melt several pounds of molybdenum may involve the loss of heat at a Very considerable rate. For melting molybdenum, therefore, the source of heat must be of high potential and of fairly high power. Evidently, also, the source of heat must not impair the purity of the product. The electric arc operating in vacuum appeared to meet these requirements and was accordingly the first choice as a source of energy. A number of arc devices for melting molybdenum were examined, and several were tried. In the first experiment, a 20-kw., 60-cycle-per-second alternating-current arc was operated between two horizontal and opposed electrodes of molybdenum- In this arrangement the falling droplets of molybdenum solidified below the arc in an irregular mass. This experiment did not produce a useful casting, but the data obtained indicated that

Jan 1, 1947

By A. J. Conelius, D. P. Sobocinski

This paper presents a correlation for predicting the behavior of a water cone as it builds from the static water-oil contact to breakthrough conditions. The correlation is partly empirical and involves dimensionless groups of reservoir and fluid properties and of production and well characteristics. The groups were deduced from the scaling criteria for the immiscible displacement of oil by water. The correlation is based on a limited amount of experimenfal data from a laboratory sand-packed model and on results from a computer program for a two-dimensional, incompressible system. Because the correlating groups are dimensionless, they can be used to estimate the performance of water coning cases not specifically considered in the correlation. However, despite its dimensionless nature, the correlation is not completely general and will not provide meaningful estimates of cone behavior in many situations. INTRODUCTION AND BACKGROUND The production of water from oil wells is a common occurrence which increases the cost of producing operations and may reduce the efficiency of the depletion mechanism and the recovery of reserves. We will deal with one cause of this water production, namely, coning. The coning of water into a producing well is caused by pressure gradients established around the wellbore by the production of fluids from the well. These pressure gradients can raise the water-oil contact near the well where gradients are most severe. Gravity forces that arise from fluid density differences counterbalance the flowing pressure gradients and tend to keep the water out of the oil zone. Therefore, at any given time, there is a balance between gravitational and viscous forces at points on and away from the completion interval. When the dynamic forces at the wellbore exceed gravitational forces, a cone of water will ultimately break into the well to produce water along with the oil. We can expand on this basic visualization of coning by introducing the concepts of stable cone, unstable cone and critical production rate. For instance, if a well is produced at a constant rate and the pressure gradients in the drainage system have become constant, a steady-state condition is reached. If, at this condition, the dynamic forces at the well are less than the gravity forces, then the water or gas cone that has formed will not extend to the well. Moreover, the cone will neither advance nor recede, thus establishing what is known as a stable cone. Conversely, if the pressure in the system is in an unsteady-state condition, then an unstable cone will continue to advance until steady-state conditions prevail. If the flowing pressure drop at the well is suffcient to overcome the gravity forces, the unstable cone will grow and ultimately break into the well. It is important to note that in a realistic sense, stable cones may only be "pseudostable" because the drainage system and pressure distribution generally change. For example, with reservoir depletion, the water-oil contact may advance toward the completion interval, thereby increasing chances for coning. As another example, reduced productivity due to well damage requires a corresponding increase in the flowing pressure drop LO maintain a given production rate. This increase in pressure drop may force an otherwise stable cone into a well. The critical production rate, well known in the literature, is the rate above which the flowing pressure gradient at the well causes water (or gas) to cone into the well. It is, therefore, the maximum rate of oil production without concurrent production of the displacing phase by coning. At the critical rate, a built-up cone is stable but is at a position of incipient breakthrough. Numerous papers have been published on critical rates. Some of the better known of these include the work of (1) Muskat and Wyckoff,' who first dealt with the coning problem; (2) Chaney, et al,' who developed expressions similar to those of Muskat but who presented results in a conven ient-to-use graphical form (the "Sun" method); and (3) Meyer and Garder,b hose analysis is based on radial-flow formulas. One assumption in critical production rate analyses is that the cone has built-up to just before its breakthrough into the well. But, these analyses reveal nothing directly about the time it takes for the cone to build up to this incipient breakthrough position. Thus, water-free oil can be produced from a well for prolonged periods at rates above the critical rate before the well reaches the condition to which the critical rate applies. The published literature contains little on the rate of growth of a cone. Experimentally, Meyer and Searcy studied the rate of rise of a cone in a Hele-Shaw model.' Additional related work on water breakthrough and produced water-oil ratios in water driven reservoirs was reported by Muskat," Hutchinson and Kemp," Henley, et al,' and Stevens, et a1.B Theoretically, the basic coning equations for a water-oil system can be developed by applying the conservation of mass to each of the phases, relating flow velocities with pressure by Darcy's law, and relating pressures across water-oil interfaces by capillary pressure. With the usual boundaries at the well and reservoir limits, the solution of the resulting equations for the time behavior of a water-oil interface constitutes a free-surface, boundary-value problem. The shape of the boundary depends on the internal potential distribution, while this

Jan 1, 1966

By DeVerle P. Harris

Risk for most mineral investments is greater than that of average business ventures, because the physical and economic characteristics of the mineral deposit are never known with certainty. Inasmuch as the merits of a potential mineral investment cannot be fully appraised without consideration of the impact to the investor of the possible unfavorable events associated with the adoption of the project, methods of risk analysis are important in project evaluation and investment selection. The conceptual framework for risk analysis and the means by which some of the recommended practices might be implemented are examined. In addition to the normal business risk due to market forces, the physical and economic characteristics of the mineral deposit are never known with certainty, for only partial or indirect information is available, such as data from drill cores or surface and underground workings. Consequently, risk for most mineral investments is greater than that of average business ventures. Inasmuch as the merits of a potential mineral investment cannot be fully appraised without consideration of the impact to the investor of the possible unfavorable events associated with adoption of the project, methods of risk analysis are important in project evaluation and investment selection. This paper examines the conceptual framework for risk analysis and means by which might be implemented some of the recommended procedures. Utility Theory A discourse on risk and its impact upon investment selection quite often leads the reader into the concept of utility theory, for utility theory is a device constructed by economists to measure the satisfaction an individuai receives from a good; in the case of investment analysis, that good is the outcome of an investment. It briefly is reviewed here to describe the reaction of the individual to risk and as a stepping stone to other techniques more suited to risk analysis at the level of the firm. Utility theory proposes that an investor possess a utility map (curve), such as indicated in Fig. 1, which indicates the value in utiles of potential monetary rewards to an individual with some specific endowment of resources. Points on this map are obtained from the following relationship:

Jan 1, 1971

By J. D. Livingston, H. E. Cline

Cu-Pb alloys in the vicinity of the monotectic composition have been directionally solidified under a high temperature gradient at rates up to 2 X l0-' cm per sec. Over a wide range of compositions, high growth rates yield a composite structure consisting of continuous rods of lead in a copper matrix. This range of compositions increases with increasing growth rate, in agreement with arguments based on the relative velocities of composite growth and the growth of copper dendrites or lead drops. The breakdown of the composite structure at slow growth rates is explained in terms of the relative interphase surface energies. The observed interrod spacings of the composite structure are large compared with the predictions of the Jackson-Hunt equations of eutectic growth. ThE directional solidification of many eutectic alloys produces fine composite structures of parallel lamellae or rods. There has been considerable interest not only in the fundamentals of this two-phase solidification process,'-3 but also in the interesting physical properties produced by such regular and aniso-tropic microstructures. Composite structures can be grown only over a limited range of composition, beyond which coarse primary dendrites of one phase appear. In organic eutec-tics, this composition range of composite structures has been shown to increase with increasing growth rate.7"10 These results were explained in terms of the relative velocities of composite (coupled) growth and dendritic growth. Although similar arguments should apply to metallic eutectics,11-13 suitable experimental results are lacking. In contrast to the work on eutectics, the directional solidification of monotectic alloys has received little attention. (The monotectic reaction is similar to the eutectic reaction, except that one of the resulting phases is a liquid, which subsequently solidifies in a separate reaction at a lower temperature.) Directional solidification of some monotectic alloys'4715 yields regular rodlike microstructures, whereas in other cases macroscopic separation of solid and liquid phases occurs.16 chadwick17 rationalized these results in terms of the probable relative magnitudes of the various interphase surface energies. A recent study of chill-cast Cu-Pb alloys18 revealed a fine rodlike microstructure in alloys near the monotectic composition. It was decided to investigate the directional solidification of such alloys, and to determine the range of composition and growth conditions yielding composite structures. The Cu-Pb system is convenient for such a study, both because it is simple metallurgically, with no compound formation and negligible solid solubilities, and because its basic properties are well-documented. Recent literature on the Cu-Pb system includes studies of bulk thermo-dynamic properties,'g surface energies,20"21 densi-ties,25 and diffusion constants.a6 A similar study of the directional solidification of Cu-Pb alloys was recently undertaken, independently, by Kamio and Oya." EXPERIMENTAL Alloys were prepared by melting 99.999 pct Cu and 99.999 pct Pb in a graphite crucible, stirring well, and pouring into a cold graphite mold. Rods 0.175 in. in diam were machined from the ingots. Alloy compositions studied ranged from 25 to 55 wt pct Pb. Samples were placed in graphite crucibles 5 in. long with 4 in. OD and 0.035-in. walls. They were melted under flowing argon in a vertical, two-zone. platinum -wound furnace. A voltage stabilizer was used to minimize fluctuations in input power. The narrow specimen diameter minimized convection. Directional solidification was achieved by driving the crucible downward into a +-in. hole in a water-cooled copper toroid. The toroid was located immediately below the narrow end zone of the furnace. The end zone was separately powered to maintain high local temperature. Therefore a high temperature gradient (approximately 300 deg per cm) was maintained in the specimen throughout the run. The crucible motion was screw-driven. and a wide range of drive speeds were available. The limited rate of heat removal caused a thermal lag in the specimens at high drive rates. However. temperature-time curves from thermocouples imbedded in a representative sample indicated that the average growth rate still approximately equaled the drive rate. Although the specimens were initially homogeneous, melting and re solidification redistributed the lead. producing composition variations of several percent along the specimen length. (During melting. lead melted first and ran down the sample surface. Rapid freezing tended to reproduce the resulting composition gr~dient, but slow freezing did not because a slow-moving interface tended to reject lead. as discussed later.) To determine local composition. ;-g samples were cut from regions exhibiting various microstructures and were chemically analyzed for lead content. Micrographs were taken on as-polished or lightly etched surfaces. Three-dimensional structure of the lead network was viewed with a scanning electron microscope after removal of some of the copper matrix with nitric acid. RESULTS Several different microstructures are observed, depending on composition and drive rate. Because melting and resolidification produced composition gradients, results are best presented in t&ms of final local composition, rather than initial or average composition. The ranges of local compositions and drive

Jan 1, 1970

By C. W. Lawr

The ores mined by the Santa Gertrudis Co. at Pachuca, Mexico, arc mainly silver-bearing; they also yield some gold and carry a little copper. Strong cyanide solutions are used to dissolve the silver and gold, and the mechanical loss of cyanide at the tailings filter has been considerable. Prior to the year 1923, the pulp, after agitation, was given a 35 to 37-min. wash with barren solution in a Butters-type leaf filter; the discharged slime cake was repulped and pumped into eight Merrill self-sluicing slime presses in which the slime was given a further wash with barren solution for 25 to 35 min., followed by a 10-min. water wash. At that time the barren solution titrated around 0.350 per cent. free KCN and 0.500 per cent. total KCN. (Aero brand cyanide is used.) It can readily be seen that a 10-min. water wash would leave considerable cyanide in the filter cake, which of course was a total loss. This averaged 0.522 kg. (1.15 Ib.) KCN per ton of solution. As the daily discharge to the dam was 1600 tons' of slime of a 2:1 ratio of liquid to solid, the value of this mechanical loss of cyanide was an important item and it's recovery held alluring possibilities. Principle of Cyanide-recovery Process As it had acquired the patent rights to theLayng (H. R.) and Halvor-sen (A. L.) processes, also those of Mills (L. D.) and Crowe (T. B.) after considerable experimental work in its own laboratory and at Tonopah, Nev., The Merrill Company of San Francisco early in 1923 notified the Mexican Corporation and compania de Santa Gertrudis of its process for the recovery of cyanide from weak wash solutions, or for the transference of cyanide from a foul mill solution to a clean alkaline solution. This method is known as the Mills-Crowe process, the principle of which is as follows: The solution from which the cyanidc is to be removed is made acid by bringing it into contact with sulfur dioxide (SO2). The acidified solution is the; transferred to a closed tank in which air and solution are brought into intimate contact. The air leaving the tank charged with HCN is then passed to another tank in which it is mixed with an alkaline solution,

Jan 1, 1930