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By R. Woods

INTRODUCTION Gaudin (1), considered that "the mechanism of mineral collection is the central problem of flotation theory". From their work on adsorption phenomena in flotation for more than fifty years (2), Gaudin and his co-workers have made major contributions to the elucidation of this mechanism, a fact acknowledged by their contemporaries in the field (e.g. (3)). Their investigations in a number of areas, e. g. demonstrating that submonolayer quantities of adsorbed collector species can induce flotation, or identifying the influence of substances which can activate or depress (1), have helped to provide the basis for and the development of a theory to account for the interaction between mineral and collector. It was established in the late fifties (4) that the presence of oxygen is a prerequisite for the flotation of metal sulfides with thiol collectors. This fact rendered inadequate the concept of simple ion adsorption being responsible for rendering these minerals hydrophobic. The requirement for oxygen has been explained (1) in terms of this species being a component in chemical reactions between the sulfide surface and the collector. Gaudin has been instrumental in identifying the products of chemical reactions at sulfide minerals (1, 5), a line of work which has been continued particularly by Finkelstein and co-workers in South Africa (6). In presenting a detailed mechanism of the mineral-collector- oxygen interaction, it has often been considered that the mineral surface [must] first be oxidized to a metal oxy-sulfur species which

Jan 1, 1976

By Leendert de Witte

A review is given of the principles on which recently proposed methods of electric log interpretation in shaly sands are based and of the evidence brought up in support of the theoretical derivations. It is. pointed out that the qualitative techniques suggested to date have a tendency to be too pessimistic in the prediction of the presence of commercial hydrocarbon accumulations. In the quantitative treatment, a new concept is introduced, namely that of strongly reduced activity of the double layer counter ions which are present near the negatively charged rock surfaces. This lemmu when applied to the calculation of the equilibrium concentratiotls of interstitial waters yields a set of very simple relations. The resulting expressions for electrochemical potentials across rock samples appear in satisfactory agreement with laboratory experiments. The formulae obtained for the electrical conductivity of shaly formatioris are of the same form as those arrived at empirirally by previous workers. Combination of the expres.riorls for potentia1s and conductivities gives a direct proof of the Tixier relation which states that for shaly water sands the product of apparent formation water resistivity and apparent formation factor equals the resistivity of the sand 100 per cent .saturated with formalion water and which was verified by the work of Wyllie and Perkins and their co-workers. The relations for the resistivities and spontaneous porer11inI.s have been extended to the case of hydrocarbon hearing shaly formations, thus laying a formal basis for the quantitative interpretation of electric logs in shaly oil sands. INTRODUCTION The presence of disseminated clays in porous rocks saturated with electrolytic solutions has a strong influence on the transference of ions taking place under electrical or chemical potential gradients. Both the electrochemical emf's in evidence on the SP curves of electric logs and the electrical conductivity measured on resistivity logs arc directly dependent on the ionic transference in the interstitial waters of the formations traversed by boreholes. A large number of researches have been carried out on the nature and magnitude of the effects of clays on ionic transference. The most recent of these have been described in papers by McCardell and Winsauer,1 2 Wyllie and Southwick,3 poupon, Loy, and Tixier,4 and by Perkins et al.5 Most of these authors consider the effects of the clays as due to the fixed negative charges on the clay lattice. These charges cause the formation of diffuse surface layers with a high concentration of positive ions. The internal solution of the shaly reservoir rock has therefore a different ionic composition and concentration than the electrolyte with which it is in equilibrium (connate water produced from the formation or mud filtrate by which the formation is invaded). To calculate the equilibrium concentration of the internal solution, use is made of the Donnan6 relation, which states that the mean ionic activities of the internal solution and of the external electrolyte must be equal. From this and the

Jan 1, 1956

By M. S. Smani, P. Blazy, J. M. Cases

Investigations on the beneficiation of sedimentary Moroccan phosphate ores are reported in four separate parts. The first discusses electrochemical phenomena at the solid-aqueous solution interface for minerals of the apatite group. In the second part, the electrochemical properties of the calcareous gangue associated with the phosphate ore are investigated. The flotation of calcite and phosphate oölites, using both anionic and cationic collectors, is discussed in the third part. It is shown that selective recovery could be obtained for precise concentrations of collectors and pH ranges. Results of work aimed at optimizing depression of phosphate oölites during inverse flotation of the carbonate gangue with sodium oleate are reported in Part 4.

Jan 1, 1976

By Edmund Kirby

THE results to come from the application of cheap oxygen to industry in general will be so great that it is not possible to enumerate them beforehand and still less to estimate them. We naturally think first of the fuel to be saved; yet this is only a minor item. The main results will be changes in methods of manufacture or of operation. The speed of operation will be greatly increased, with consequent savings in labor and fixed charges, and also, in most cases, in the cost of fuel. High temperature will be brought within the reach of every manufacturer, whereas it is now available only to those operating expensive electric furnaces located within reach of large water power. New speeds and new temperatures mean improvements and processes not thought of at present. Incidentally the changes in methods will probably change the location of important world industries, the tendency being to concentrate at the fuel centers. The whole subject is so new that most of the data which an engineer requires for definite estimates do not exist. All that is possible now is to obtain a general view of the subject with rough and fragmentary estimates for some of the industries with which we are specially concerned. Most of the figures presented deal with fuel saving merely because there are available no data from which to estimate the effect on speed of operation. When working out the practical problems involved in substituting oxygen for air, in most cases the change will be made step by step; by trying out air enriched with increasing percentages of oxygen. Such partial applications of oxygen will be temporary expedients during the transition and there will be no stopping place short of the complete substitution of air by oxygen. This final stage is therefore the one discussed in this paper.1

Jan 11, 1924

By J. F. Wolff

During the past 4 or 5 years, much has been added to the detailed geologic knowledge of the Mesabi Range. This has not been in the direction of discovery of any new fundamental facts, but of detailed study, subdivision and correlation of different parts of the whole formation and of individual orebodies. Prior to this time, mining engineers in the district were so engaged with the commercial interests of exploring and developing orebodies that close geologic study and subdivision were done in a few instances only. The demand for refinement of work in .this direction has led 'the engineers of the Oliver Iron Mining Co. to do extensive structural subdivision and correlation in all exploration work during the past 4 years. Such work has become a commercial necessity rather than a scientific refinement, and at the present time is being extended to all parts of the Range. In the summer of 1914, the author of this paper wrote a series of articles on the orebodies and special features of the Mesabi Rangc, which was published in the Engineering and Mining Journal, issues of July 17 to Aug. 7,1915. Since that time studies of subdivision of the iron-formation have been extended considerably. The principal feature of this paper is the presentation of the subdivisions of the iron-formation. To this is added a discussion of the relations of the orebodies to the gentle folding and fracturing of the formation, and special features of the Range. The outline will be as follows : I. General geology. 11. Subdivision of Biwabik iron-formation. 111. Relation of orebodies to folding and fracturing of the iron-formation. IV. Special features. Acknowledgnlent is due to W. J. Olcott, President, and John Uno Sebenius, General Mining Engineer, of the Oliver Iron Mining Co., for permission to use the information presented in this paper.

Jan 1, 1917

By James M. Stapleton

It has long been recognized by blastfurnace men that correct top distribution of materials is very important in efficient and economical furnace operation. Thousands of experiments on top design, filling, sizing, and other operations have been carried out to improving furnace performance by securing uniform distribution. Many of these experiments have worked out satisfactorily and have been passed along to the industry. Many of them have been discarded and forgotten. It has been the custom to judge the results of such experimentation by the results shown in improved or lowered furnace efficiency. While the effect on furnace practice will have to continue to be the final criterion of experimental changes, it has always been a desire of blast-furnace men to ascertain the reason for failure or success. Efficiency in the blast furnace approaching the maximum can be measured in several ways: (1) by actual operating results as revealed in the coke rate and tonnage figures, and (2), in the degree to which the top gas approaches the limiting ratio of CO/CO2 for the reduction of iron oxide by CO gas. This ratio is shown in the equilibrium curve in Fig. I for the system Fe-O-C and CO2-CO-C. The closer the top gases approach this limiting ratio (set at 1.08 by Martin1 because of the effect of limestone calcination) the more efficiently we may expect a furnace to operate. The fact that low CO/CO2 ratios parallel eficient operating performance caused us to investigate the cause of good or poor distribution and the effect of filling and other changes on furnace operation. Heretofore it has been possible to take a sample of furnace gas (usually from the dust catcher) and from it determine how closely the reducing gases were to the ideal or limiting value as set by the equilibrium diagram. However, to find just where in the top area the distribution was distorted and the top-gas CO/CO2 ratios were distant from equilibrium values has been a difficult and expensive investigational procedure. In an effort to overcome this difficulty, apparatus was designed to take gas samples and temperatures across the top radius of the furnace. It was hoped that with the aid of this apparatus traverse sampling of the ascending gases could be simplified, and the cost of sampling substantially lowered. Routine experimenting could then be maintained and results checked with furnace operation. It must be emphasized that a traverse sampling is necessary for a true picture, as single samples at any one point are unreliable. This statement can be verified by an examination of Tables 3 to 6, showing results obtained at our furnaces in a large number of tests. Apparatus The design of the equipment for taking the samples was governed by the need for providing a simple, routine test that could be performed fairly quickly without adversely affecting normal furnace operation.

Jan 1, 1943

By James M. Stapleton

It has long been recognized by blastfurnace men that correct top distribution of materials is very important in efficient and economical furnace operation. Thousands of experiments on top design, filling, sizing, and other operations have been carried out to improving furnace performance by securing uniform distribution. Many of these experiments have worked out satisfactorily and have been passed along to the industry. Many of them have been discarded and forgotten. It has been the custom to judge the results of such experimentation by the results shown in improved or lowered furnace efficiency. While the effect on furnace practice will have to continue to be the final criterion of experimental changes, it has always been a desire of blast-furnace men to ascertain the reason for failure or success. Efficiency in the blast furnace approaching the maximum can be measured in several ways: (1) by actual operating results as revealed in the coke rate and tonnage figures, and (2), in the degree to which the top gas approaches the limiting ratio of CO/CO2 for the reduction of iron oxide by CO gas. This ratio is shown in the equilibrium curve in Fig. I for the system Fe-O-C and CO2-CO-C. The closer the top gases approach this limiting ratio (set at 1.08 by Martin1 because of the effect of limestone calcination) the more efficiently we may expect a furnace to operate. The fact that low CO/CO2 ratios parallel eficient operating performance caused us to investigate the cause of good or poor distribution and the effect of filling and other changes on furnace operation. Heretofore it has been possible to take a sample of furnace gas (usually from the dust catcher) and from it determine how closely the reducing gases were to the ideal or limiting value as set by the equilibrium diagram. However, to find just where in the top area the distribution was distorted and the top-gas CO/CO2 ratios were distant from equilibrium values has been a difficult and expensive investigational procedure. In an effort to overcome this difficulty, apparatus was designed to take gas samples and temperatures across the top radius of the furnace. It was hoped that with the aid of this apparatus traverse sampling of the ascending gases could be simplified, and the cost of sampling substantially lowered. Routine experimenting could then be maintained and results checked with furnace operation. It must be emphasized that a traverse sampling is necessary for a true picture, as single samples at any one point are unreliable. This statement can be verified by an examination of Tables 3 to 6, showing results obtained at our furnaces in a large number of tests. Apparatus The design of the equipment for taking the samples was governed by the need for providing a simple, routine test that could be performed fairly quickly without adversely affecting normal furnace operation.

Jan 1, 1943

By George W. Bain

Methods of mining building stone of any sort are planned to produce as few fractures as possible, and present a strong contrast to methods of mining metallic ores, which must be crushed eventually and have fractures produced in as great profusion as possible. Shocks transmitted to a stone invariably make it more porous and more permeable and reduce its effective life, therefore methods of mining building stone involve as This building illustrates the fine detail of workmanship, unprotected sharp corners and thin edges, and tall narrow columns characteristic of marble structures. These features require exceedingly coherent stone, and preservation of these features for decades or centuries demands many special quarrying precautions to keep absorption to 0.14 per cent or less, a detail not essential to stone for coarser architectural types. few shocks as possible. This is singularly true for marble because marble structures are intended to have long life, greater delicacy of line, more gracefulness and fineness of sculpture than those made from any other structural material (Fig. 1). So that delicate lines may remain in almost perfect preservation for decades, or even centuries, it is important

Jan 1, 1938

By George W. Bain

Methods of mining building stone of any sort are planned to produce as few fractures as possible, and present a strong contrast to methods of mining metallic ores, which must be crushed eventually and have fractures produced in as great profusion as possible. Shocks transmitted to a stone invariably make it more porous and more permeable and reduce its effective life, therefore methods of mining building stone involve as This building illustrates the fine detail of workmanship, unprotected sharp corners and thin edges, and tall narrow columns characteristic of marble structures. These features require exceedingly coherent stone, and preservation of these features for decades or centuries demands many special quarrying precautions to keep absorption to 0.14 per cent or less, a detail not essential to stone for coarser architectural types. few shocks as possible. This is singularly true for marble because marble structures are intended to have long life, greater delicacy of line, more gracefulness and fineness of sculpture than those made from any other structural material (Fig. 1). So that delicate lines may remain in almost perfect preservation for decades, or even centuries, it is important

Jan 1, 1938

By R. H. Pemberton

The principle of airborne electromagnetic prospecting is well-known. The basic geophysical texts in most cases discuss the main elements involved in electromagnetic prospecting. However, there is certainly little information available to the public concerning the present types of airborne electromagnetic systems being flown today by both contracting companies and some of the mining companies which have their own instruments. This is unfortunate since it is difficult for those people not conducting such operations to understand thoroughly the large variation in the electromagnetic instruments available.

Jan 1, 1961

By O&apos, P. E. T. Connor

Production of petroleum in Trinidad during 1938 reached the record figure of 17,737,061 bbl., an increase of approximately two and a quarter million barrels over 1937. The principal development during the year was along the Guapo fault, which extends from Point Ligoure to Coora across the southwest portion of the island. This fault has been proved to be a major factor governing oil accumulation in the area. At the southeast end of the fault the Coora field has been actively developed during the year and already ranks as one of the major productive fields of the island. Approximately seven miles to the northwest, another richly productive area has been developed on the north side of the fault at Los Bajos, while several widely spaced wells along the fault in the intervening area suggest that the whole seven miles betwen Los Bajos and Coora will prove productive. The Penal field was placed on regular production during the early part of the year on completion of a pipe line to the Point Fortin refinery. This is a shallow pumping field with a daily output of 2000 to 1500 bbl. of heavy oil. Down-flank extension of the oil-producing structures of Forest Reserve, Kern and Point Fortin have considerably extended the proven acreages on these structures and exploitation of the deeper Cruse sands on these structures has also materially increased the known reserves. Wildcat drilling has been active in several areas. Four wells have been completed in the Mayaro district; four at Moruga; six at Cedros; six in the Morne Diable area; one at Erin and one at Point Ligoure. Few data are available from these areas, but it is understood that some cncouraging results have been obtained. In the northern basin, north of the Central Range, two locations were spudded in at the end of the year after extensive seismograph surveys. Both these locations are scheduled for depths in excess of 10,000 ft. This northern basin is entirely untested by the drill and the present drilling program is being keenly followed by all operators in Trinidad.

Jan 1, 1939

By P. E. T. Connor, O&apos

Production of petroleum in Trinidad during 1938 reached the record figure of 17,737,061 bbl., an increase of approximately two and a quarter million barrels over 1937. The principal development during the year was along the Guapo fault, which extends from Point Ligoure to Coora across the southwest portion of the island. This fault has been proved to be a major factor governing oil accumulation in the area. At the southeast end of the fault the Coora field has been actively developed during the year and already ranks as one of the major productive fields of the island. Approximately seven miles to the northwest, another richly productive area has been developed on the north side of the fault at Los Bajos, while several widely spaced wells along the fault in the intervening area suggest that the whole seven miles betwen Los Bajos and Coora will prove productive. The Penal field was placed on regular production during the early part of the year on completion of a pipe line to the Point Fortin refinery. This is a shallow pumping field with a daily output of 2000 to 1500 bbl. of heavy oil. Down-flank extension of the oil-producing structures of Forest Reserve, Kern and Point Fortin have considerably extended the proven acreages on these structures and exploitation of the deeper Cruse sands on these structures has also materially increased the known reserves. Wildcat drilling has been active in several areas. Four wells have been completed in the Mayaro district; four at Moruga; six at Cedros; six in the Morne Diable area; one at Erin and one at Point Ligoure. Few data are available from these areas, but it is understood that some cncouraging results have been obtained. In the northern basin, north of the Central Range, two locations were spudded in at the end of the year after extensive seismograph surveys. Both these locations are scheduled for depths in excess of 10,000 ft. This northern basin is entirely untested by the drill and the present drilling program is being keenly followed by all operators in Trinidad.

Jan 1, 1939

By C. M. Sellars, F. Maak

Electvomotie -force measurements hazle been made on ten Au-Ni alloys at temperatures 7754 825O, 900O, and 935°C using galvanic cells with solid electrolyte. Partial and ivtegral thermodynamic functions are derived from the determined activities. which show la9,ge positive deviations jvom Raoult's law. The enthalpies of mixing- are in close accord with calorinletric data and are of comparable accuracy. The results are used to determine the miscibility gap and the spinoidal curL1e, and are qlalitaticely interpreted in terms of the large size difference and electvonic interactions between gold and nickel. Tabulated nalues of the actielities and partial and inteqal free energies, entropies , and enthalpies of mixing are given in the appendix. The Au-Ni binary alloys are of particular interest thermodynamically as despite the large size difference between gold and nickel atoms they have a simple phase diagram.' This shows complete solid solubility above a miscibility gap with a maximum at about 71 at. pct Ni and 810°C. Activity measurements (over a range of temperature) have been made previously on this system using an electrolytic-cell method with a liquid chloride eletrolyte. The accuracy of this data has, however, been queried3'4 as it leads to values for the enthalpy of mixing which are too high when compared with calorimetric measurements.46 Also, the entropy of mixing is too high when compared with the values derived from specific-heat measrements. It was therefore considered worthwhile redetermining the activity data using a galvanic cell with a solid electrolyte (0.85 ZrO, 0.15 CaO). This method is based on a technique introduced by Kiukkola and aner'' and has been used to determine the thermodynamic data for Cu-Ni alloys.' THE ELECTROLYTIC CELL The cell used to determine the activity of nickel in Au-Ni alloys was: The cell reaction, which is discussed for a similar cell by Rapp and Maak, gives a direct measurement of the activity of nickel in the alloys as where aNi(alloy) is the activity of nickel in the alloy, 3 is Faraday's constant, E is the measured electromotive force, R is the gas constant, and T is absolute temperature. For the valid application of this type of cell the arrangement must be ther modynamic ally stable, which means that: 1) The free energies of formation of the oxides fulfill the relation 2) The vapor pressures or dissociation pressures of each component must be so small that during the time of the experiment the amount of any material transported by the gas is negligible. 3) Side reactions which change the alloy composition must be negligible. These reactions are possible both with the surrounding gas atmosphere and with neighboring solid material. The first two conditions are fulfilled by the above cell.' The third condition is approached by care in the experimental technique. The factors which control the attainment of equilibrium in this type of cell have been considered by Rapp and aak, who conclude that metallic diffusion in the alloy is the rate-control ling step. A lower temperature limit for the practical application of this cell is therefore set by the condition that equilibrium must be attained in reasonable times. EXPERIMENTAL MATERIALS AND TECHNIQUE The starting materials were mint gold (99.99 pct Au) and Mond nickel (99.9 pct Ni). Alloys, nominally 5 at. pct Ni and then each 10 at. pct across the system, were produced by vacuum-levitation melting compacts of mixed drillings of the pure metals. The nickel used for the reference tablets in the cells was melted in a similar manner. The alloy ingots, cast in boron nitride molds, were cold-forged and

Jan 1, 1967

By A. E. J. Gallagher, W. D. Charles

The chapter is a review of published and unpublished data concerning energy usage and material wear in commercial crushing and grinding operations. Examples are given from practice and factors influencing power and wear are discussed.

Jan 1, 1982

By R. E. Head

SOME mixtures of sulphide and oxide ores from the Tintic district in Utah are of a sufficiently good grade to be shipped to the smelter without beneficiation. In mining this type of ore, however, a material tonnage of ore of a similar composition but of lower grade is obtained. It is a ques-tion of economics whether such ore should be shipped with a certainty of a small return or concentrated if that would yield a sufficiently increased return to amortize plant construction and upkeep and yield a higher rate of profit than at present. It may be assumed that the tonnage of this borderline ore is constantly increasing and that eventually it will, attain such proportions as to justify plans for milling on a relatively large scale. Under existing conditions, the producer of mixed sulphide and oxide ores is not greatly concerned about the physical characteristics of his ore or of its mineralogical complexities, since his contract with the smelter calls for payment on the basis of chemical analysis. When concentration is contemplated an entirely different picture is presented. Percentages of valuable metal content must then be con-sidered in terms of minerals, for it is in the form of minerals that recoveries are made and losses sustained. In describing the performance of a given flotation mill and reagent combination, it may be stated as a generality that a specific percentage recovery of valuable elements is made. Tech-nically, however, the concentrator is really constructed and the reagents are selected to recover the valuable minerals. These considerations must be given prominence in discussing border-line ores from the Tintic district because of their physical characteristics and mineralogical composition. Because of these peculiarities they may be justly termed complex, since their lead, silver, and copper contents are each represented by two or more minerals of different chemical composi-tion and presenting widely divergent physical properties. This paper sets forth the results of a microscopic study of a type of borderline ore from the Tintic district that is now being treated by direct smelting. A

Jan 1, 1938

By O. C. Ralston, William C. Hunter

DUring experimental study on the separation of a zinc concentrate from the heavy sulfide ores of Jerome, Ariz., a great deal of attention has been given to proper activation of the sphalerite content of the ore. The sphalerite at Jerome contains enough iron to class it as a marmatite, as picked specimens have only about 60 per cent. zinc, whereas pure zinc sulfide contains 67 per cent. zinc. This marmatite in large pieces is black in color, but in dry powdered state is brown. A flotation froth made from it has a silvery black luster in comparison with a brassy luster caused by chalcopyrite which occurs in the same ores. The sample used in most of the experiments described below consisted of about 3000 Ib. of diamond-drill core from the zinc-bearing orebodies of the United Verde mine, and had the following analysis: Per Cent. Per Cent. Oz. peR Ton Cu............... 0.695 Al2O3............ 0.83 Ag................. 1.30 Zn............... 6.17 S................ 43.35 Au................ 0.02 Fe...............36.23 CaO............. 0.46 SiO2............. 9.27 Mineralogically, this analysis is calculated to the following, which is in agreement with the microscopic examination: Per Cent. Per Cent. Chalcopyrite................... 2.0 Schist........................... 3.2 Marmatite..................... 10.32 Quartz........................... 8.2 Pyrite........................ 73.0 Calcite.......................... 0.9 All samples were ground in a laboratory ball mill in order to leave about 3 per cent. on a 200-mesh sieve, fine grinding being essential to liberate the minerals in the ore. Most of the Jerome ores are so intimately crystallized that reasonably complete unlocking by grinding does not take place until 800 mesh is approached. Therefore, the 200-mesh grind adopted contains a considerable amount of locked mineral grains, but not so much as to render impossible the preparation of commercial grades of concentrate.

Jan 1, 1930

By C. B. Clark, W. H. Bruckner

Since the end of World War II interest has been increasing in the use of shaped charges in the mining industry and in other industries using explosives for blasting purposes. Shaped charges employ the principle known as the "Munroe effect," which was discovered by Charles E. Mun-roe more than 50 years ago (in 1888). Details of their design have been explained elsewhere.1,2,3 Fig I shows the essential features of design of two types of shaped charges (with conical and hemispherical cavities) and a schematic sketch of their action upon detonation. The following discussion deals with the behavior of the metal in the cavity liners when they are subjected to intense Pressures exerted when the explosive charge is detonated. Among the conclusions reached in research On shaped explosive charges, the following have been established concerning cavity liners:1'2 I. The optimum wall thickness of a conical cavity liner is dependent upon the apex angle of the 'One as well as On the base diameter of the charge. Acute apex angles require thinner walls for optimum perfmnance and more obtuse angles require thicker walls for the same base diameter' 2. Cones were more effective in forming a penetrating jet when the walls were tapered; that is, the thickness of the wall of the cone increased from the apex down. 3. The physical and mechanical properties of metals have a marked effect upon their performance as cavity-liner material. Boiling point, ductility, malleability, tensile strength, and hardness are among the properties that influence the effectiveness of a metal used as a cavity liner. Lead, for example, makes a wide, flat crater in steel plates. Aluminum makes a deeper crater than lead, and an aluminum alloy having a high tensile strength makes a deeper hole, but slightly smaller in diameter. Cast iron makes a deep, narrow hole. These findings, together with the following analysis under Metallographic Survey of slug, offer solutions to many of the problems involved in solving the mechanism of the formation of Munroe jets. It has been fairly well established that cavity liners collapse in a manner similar to that indicated in Fig 2, Conical liners are known to collapse upon themselves while hemispherical liners are believed to turn inside out in the process of jet formation. The first has been definitely proved by recovery of collapsed portions of cones, while liners from partly detonated charges show that hemispheres may turn inside out. Fig 3 shows a sketch of a recovered slug from a 6-in. shaped charge using a 45° cone made of cast iron. (This size of charge drilled holes up to 3 ft in depth in solid granodiorite.)

Jan 1, 1949

By C. B. Clark, W. H. Bruckner

Since the end of World War II interest has been increasing in the use of shaped charges in the mining industry and in other industries using explosives for blasting purposes. Shaped charges employ the principle known as the "Munroe effect," which was discovered by Charles E. Mun-roe more than 50 years ago (in 1888). Details of their design have been explained elsewhere.1,2,3 Fig I shows the essential features of design of two types of shaped charges (with conical and hemispherical cavities) and a schematic sketch of their action upon detonation. The following discussion deals with the behavior of the metal in the cavity liners when they are subjected to intense Pressures exerted when the explosive charge is detonated. Among the conclusions reached in research On shaped explosive charges, the following have been established concerning cavity liners:1'2 I. The optimum wall thickness of a conical cavity liner is dependent upon the apex angle of the 'One as well as On the base diameter of the charge. Acute apex angles require thinner walls for optimum perfmnance and more obtuse angles require thicker walls for the same base diameter' 2. Cones were more effective in forming a penetrating jet when the walls were tapered; that is, the thickness of the wall of the cone increased from the apex down. 3. The physical and mechanical properties of metals have a marked effect upon their performance as cavity-liner material. Boiling point, ductility, malleability, tensile strength, and hardness are among the properties that influence the effectiveness of a metal used as a cavity liner. Lead, for example, makes a wide, flat crater in steel plates. Aluminum makes a deeper crater than lead, and an aluminum alloy having a high tensile strength makes a deeper hole, but slightly smaller in diameter. Cast iron makes a deep, narrow hole. These findings, together with the following analysis under Metallographic Survey of slug, offer solutions to many of the problems involved in solving the mechanism of the formation of Munroe jets. It has been fairly well established that cavity liners collapse in a manner similar to that indicated in Fig 2, Conical liners are known to collapse upon themselves while hemispherical liners are believed to turn inside out in the process of jet formation. The first has been definitely proved by recovery of collapsed portions of cones, while liners from partly detonated charges show that hemispheres may turn inside out. Fig 3 shows a sketch of a recovered slug from a 6-in. shaped charge using a 45° cone made of cast iron. (This size of charge drilled holes up to 3 ft in depth in solid granodiorite.)

Jan 1, 1949

A-Metal Mining B-Minerals Beneficiation F-Coal H-Industrial Minerals

Jan 11, 1950

By D. B. Kibler

Pill Florida hard-rock field extends from Suwanee and Columbia Counties in northwest Florida to south of Croom, Florida, in Hernando County this area is approximately 100 miles long and varies from 2 to 30 miles 1n width Florida hard-rock phosphate was discovered at Hale Springs, about one mile northwest of the town of Dunnellon Marion County, in the year 1888, by Albertus Voight who lived within a few hundred yards of the spring Soon after this discovery there was a great influx of land speculators and wildcat operators into the vicinity of Dunnellon A few years later phosphate was found in Alachua, Levy, Citrus and Hernando Counties, and a great number of small crude plants were built from Newberry, Alachua County, all the way to Croom, Hernando County Phosphate was found in many places as "outcrops " Looking for outcrops was the first method used by the early prospectors in searching for deposits Several years passed before any systematic method of prospecting was used EARLY MINING The early method of mining hard-rock phosphate was with picks and shovels, wheelbarrows, mules and wagons The pick-and-shovel method was used altogether until about 1900, when some of the larger operators began to use railroad-type steam shovels of from 1/2 to 1-yd capacity Picks and shovels, with negro labor loading the phosphate ore (called "matrix") into wooden side-dump skip-cars, was continued until about 1907 From the discovery of hard-rock phosphate until approximately 1905, overburden was removed with mules and scrapers At some places, the overburden was loaded into side-du nip skip-cars by negro laborers and the cars were then pulled up an incline with a steam hoisting engine The maximum depth of overburden that could be economically removed by hand labor mules and scrapers was approximately 15 feet About 1905 one of the companies erected a producer-gas powerhouse near Dunnellon and generated its own electricity and about the same time the larger companies began using hydraulic methods for the removal of overburden From the year 1888 through the year 1939, approximately 75 companies were operating at one time or another in the hard-rock territory, on approximately 500 locations The hard-rock deposits are more irregular and have higher mining costs than the pebble-rock deposits, therefore they have not been competitive in the domestic market, but because of the higher grade of the hard rock it is in demand for the export trade Discovery of phosphate outside of the United States has made it increasingly difficult in recent years for the hard-rock companies to survive, so today only three companies are operating These

Jan 1, 1941