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By Frank Firmstone

IN 1871, two furnaces at the Glendon Iron Works, which had been blown out on account of the "coal strike," were altered from the open-top plan with side flues for collecting the gas, to closed tops with cup and cone. In one furnace the suppression of the side flues permitted a considerable alteration in the profile, but in the other (No. 5) no change in this respect was made; the side flues were simply bricked up and new ones cut through the sides close to the top. This furnace was in blast over four years, and we can, therefore, form a pretty good idea of the effect of the alterations on the furnace process. The principal dimensions are; Height 72'; greatest diameter, 18'; diameter at tuyeres, 8'; diameter of top, 10'; diameter at stock line (point at which the top of the materials is kept), 11'; cubic contents, 11,900 cubic feet. The table below shows the average results for periods of twenty-six weeks each. 1st, of the open-topped furnace; 2d, of the furnace with the first charger used, which was an ordinary cup and cone (diameter of cone 5' 2") 3d, with the charger used ever since, a "double" cone 7' 5" diameter outside, having a central opening 3' in diameter. The diagram (Plate II) shows the daily variations, in the grade of the irons for the same periods.* * In calculating the average grade of each day's iron, each twelve hours was taken by itself whenever more than two kinds of iron were made in the 24 hours, and the diagram drawn accordingly. By counting, it will be found that there were more such days with the single cone than with the "double" cone, and more with this than with the open top. † Anthracite.

Jan 1, 1876

By J. J. Dowd

1. The Pittsburgh bed is the most important bed in Marshall County, and virtually the entire production of coal in the county comes from this bed. 2. Known measured and indicated reserves in all beds, based on a minimum thickness of 14 inches and 1,800 tons per acre-foot of coal in place, were estimated at 3,158 million short tons as of January I, 1954. Of this total, 3,071 million short tons is in beds 28 inches and more thick. Areas in each bed except the Pittsburgh were omitted from the estimate because available data relative to the bed characteristics are too meager to make an estimate that conforms with the definitions of measured and indicated coal adopted for this study. Should future drilling or development prove reserves in these areas, such reserves should be added to the total estimated reserves.

Jan 1, 1956

By AIME AIME

T HE Mining Methods Committee held its initial meeting* on Tuesday afternoon, with F. W. Bradley in the chair and W. Y. Westervelt as vice- chairman. The first paper to be presented was "A Plea for a U. S. Court of Patent Appeals," for which Kenneth W. Greenawalt ably pleaded. The paper (which was published in full in last month's issue) is so carefully prepared that no synopsis can do it justice. It discusses the opposed views of some patent lawyers and other lawyers and members of the judiciary as, for example, Chief Justice Taft who is quoted as saying in 1921: "I think it is a great deal better to take a first class lawyer and a first-class judge and make him a good patent expert than it is to take a patent expert and try to make him a first-class lawyer and a good judge." Mr. Greenawalt argued the need for specialized scientific and engineering interest and understanding to enable a lawyer or judge to prepare or interpret patent specifications and decide the originality necessary for a valid invention. He proposed the special U. S. Court of Patent Appeals to also counteract the costly confusion and injustice now ruling where a patent may be declared valid in the courts of certain States and invalid by the courts of other States.

Jan 1, 1930

By M. Li, J. D. Miller

Recently water insoluble alcoholic solutions of alkyl hydroxamic acid collectors have been shown to be particularly effective in the flotation of coarse feed material sampled from phosphate operations in Florida, North Carolina and Utah (Miller et al., 2000). The experimental results indicate that high separation efficiencies can be achieved in single stage flotation with these new collectors. In some cases the concentrate grade reached 34% P2O5 with 93% recovery from single stage bench scale flotation experiments. Critical aspects of the composition and structure of these new collectors are discussed with respect to their effectiveness in phosphate flotation. The wetting characteristics at fluorapatite, francolite, dolomite and quartz surfaces are being investigated with the new collector. Finally, other surface chemistry considerations in the development of these new collectors for phosphate flotation are discussed.

Jan 1, 2002

By Charles W. Briggs

The steel foundries of Germany were investigated for the purpose of ascertaining (1) the type and classification of steel structures produced as castings, (2) processing methods, (3) the mechanical properties of carbon and alloy cast steels, (4) the type and character of defective castings, (5) the appearance of castings, (6) research in steel castings, and (7) plant lay-out and equipment.

Jan 1, 1946

By Roger L. Beals, George A. Tweedy

I. INTRODUCTION. THE results of the cyanide-operations, given in detail in the following paper, show the progress that is being made at the Minas del Tajo. The old pan-amalgamation process, in operation up to and including 1905, while paying a profit on high-grade ores, was no longer able to treat profitably the ores in sight at that time, hence an alteration in the process was imperative. The success of this alteration is eloquently expressed by the following data Pan- Amalgamation. Cyanidation. 1905. 1907. 1903. Tons treated, . . 51,387 53,983 69,300 Value per ton (U. S. currency),. $10.75 $8.39 $8.28 Extraction, per cent., 65.00 88.50 S7.45 Extraction, per ton. .- $7.00 $7.4.; $7.24 Total cost, per ton treated, 6.50 4.311 4.01 Profit, per ton treated, . . 0.50 3.07 3.23.;

Feb 1, 1910

By Lon Santis, Gregory M. Rumbaugh, Christopher Mark

This paper examines the relevant theory, experience, and past practices relating to development mining near gas or oil wells. It addresses setback distance for both coal and stone room-and-pillar mining. This study also involved a review of accident reports involving well interceptions and downhole well surveys. It provides technical considerations for decisions regarding safe setback distances for development mining throughout the United States. The study’s scope is limited to mining near active or inactive (i.e., non-producing, abandoned or inadequately plugged) wells with known surface locations.

Jun 25, 2024

By Robert Drummond

Away back in the eighties of the last century, when Sir Charles, then Doctor, Tupper, was not only a prominent but a dominant figure in the political life of Nova Scotia, his opponents brought the railing accusation against him that he was the foremost of egotists because of his frequent use of the personal pronoun. I heard Tupper speak and had no sympathy with the railers, because I could not well see how the pronoun could be dispensed with without laying himself open to a charge of affectation. I shall make reference in what follows to incidents in which I have taken part, and shall be at no pains to dispense with the pronoun, even though thereby I lay my-self open to the charge of being a pupil of the deceased states-man. EVENTS LEADING UP TO THE ORGANIZATION OF THE PROVINCIAL WORKMEN'S ASSOCIATION The Springhill Mining Company began development work at Springhill in the early seventies of last century. So vigorously was the work prosecuted that in 18 7 4 two slopes, the east and the west, were in active operation, with a considerable. output, the east slope on occasional days producing 800 tons. The President of the Company, the late Senator McFarlane, was a Nova Scotian, the other directors were mainly merchants from St. John, N.B. From the first the enterprise was an .astonishing success, due in the greatest part to its geographical position, and in large part to the untiring vigilance of the directors, a majority of whom visited the collieries at short intervals, thereby keeping the manager, much of the time, on tenter hooks.

Jan 1, 1924

By M. A. Schimmelpfennig, A. D. S. Gillies

M.J. McPherson Having worked on the thermodynamics of air/liquid-water mixtures passing through the surface fans of deep mines, I find this paper of great interest and congratulate the authors on producing it. There are two matters, however, deserving discussion. First, the authors have described the classical theory of fog formation with fogging occurring at "supersaturation." In fact, the process of fog formation begins well below 100% humidity. The more strongly hygroscopic nuclei in the atmosphere will attract water molecules and begin to grow at a relative humidity perhaps as low as 70%. The process is a dynamic one with both condensation and evaporation taking place throughout the mixture on microscopic liquid surfaces. As saturation is approached, the rate of condensation accelerates rapidly producing the familiar reduction in visibility. Hygroscopic nuclei are present in all natural atmospheres and under the appropriate conditions of pressure and temperature, will produce clean fogs. However, if the air is polluted by particulates from combustion or other processes then the resultant coagulation with growing liquid particles may produce dense (and sometimes photochemical) smogs. It is this process that is likely to occur in underground mines when moist air is cooled below dew point. Second, the authors have summarized very well the individual measures that might alleviate the problem. In particular, I agree that neither heating nor refrigerating the air, by themselves, provides a satisfactory solution. However, there is a combination of these that provides a neat and effective control of fog formation. This involves a small, self-contained refrigeration unit within a duct but without the usual external heat rejection facility. The air is cooled below dew point and, hence, dehumidified on passing over the cold evaporator coils. The heat from the condenser is rejected back into the air downstream from the water eliminator, as shown in Fig. 1. The duct configuration can be designed to create good mixing at the outlet. I have used a climatic simulation program to illustrate the effect, assuming a 500-m (1,640 ft) long airway of cross section 60 m2 (645 sq ft), an airflow of 9 m3/s (318 cu ft per sec), inlet conditions of 19/19.25°C (66/67°F) wet bulb/dry bulb temperatures, a virgin rock temperature of 17°C (63°F) and typical rock thermal properties for a hard-rock mine. I have also assumed that 10% of the rock surface is wet. Figure 2 shows the variation in temperatures along the airway if no measures are taken. The relative humidity remains close to 100% and condensation will occur throughout the length of the airway. Before any such installation is designed, the exercise must, of course, be repeated for each location with accurate data. However, this example demonstrates the potential of the system. The idea is not new - the principle is sometimes used in air-conditioning plants for buildings. Figure 3 shows the effect of removing 30 kw of heat by evaporator coils sited 40 m (131 ft) along the airway and rejecting that heat (plus another 10 kw of compressor and fan power) into the air at 60 m (197 ft). Condensate water is produced, at a rate of 0.45 L/min (0.12 gpm). The result of this sequential cooling/dehumidification/heating process is to separate the wet and dry bulb temperatures along the length of the airway. The relative humidity increases from 80% at the duct outlet to 92% at 500 m (1,640 ft). The airway is maintained free from fog.

Jan 11, 1983

By D. A. Koss, R. O. Gordon

Changes in the ultrasonic attenuation in steel specimens have been observed during tensile tests. Samples of AISI 1020, 1045, and 1095 steel quenched and tempered to a spheroidized condition have been used. Both attenuation and microstrain measurements fail to reveal preyield dislocation motion in the as-tempered specimens. Upon reapplication of the load to samples in the strain-aged condition there is a large preyield attenuation increase but no observable micvostrain up to 90 pct of the flow stress. These and other observed changes can be related to changes in the free disloca-tion density and the average dislocation segment length. The results show that the increase inflow stress in the strain-aged condition is caused by increased fric-tional stresses rather than by dislocation pinning. Strain aging is found to proceed through three distinct stages. The second of these follows the t2,3 law and is characterized by an activation energy of 20 kcal per mole. RECENT years have seen substantial progress in the understanding of the sharp yield-point phenomenon in metals; the influence of solute atom pinning of dislocations, of dislocation multiplication, and of the stress dependence of dislocation velocity on the stress-strain curve has been investigated. Evaluation of the relative importance of these factors in the various metals and alloys is not complete, however, because observation of the stress-strain curve alone is not sufficient to determine the yield mechanism. In the experimental study of the sharp yield point it would be desirable to be able to directly observe the dislocations in a bulk specimen. Ideally, the observations should be made during deformation because of the rapidity of recovery processes in lightly strained metals. While direct observation of dislocations under these conditions is not possible, certain physical properties sensitive to the dislocation structure can be observed while a test specimen is undergoing deformation. Of these properties, one of the most useful is the ultrasonic attenuation. The total observed attenuation, a, is due to a number of causes: acoustic diffraction, scattering by inhomogeneities in the structure, heat flow, magnetostriction, and dislocation damping. Satisfactory measurements of the absolute a are difficult to make because all of these factors cannot be evaluated in any given specimen, but changes in a due to changes in the dislocation contribution alone can be reliably observed by appropriate technique. Because dislocation damping is sensitive to small concentrations of long, free dislocation segments, observation of acoustic attenuation due to dislocations is particularly useful in the study of the early stages of plastic deformation. In the experiments to be described, acoustic-attenuation measurements have been made on steel samples as these were pulled through their yield in tension. While many details of dislocation-damping phenomena in the bee metals remain obscure, the main characteristics of this type of internal friction are established. At low strain amplitudes and at frequencies well below that of dislocation resonance (the conditions of these experiments) the dislocation contribution to a is given by1 where A is the density of freely oscillating dislocation segments, L is the average segment length, B is the damping constant for a moving dislocation, w is the frequency, O is an orientation factor, C is the dislocation line tension, and t is a numerical factor relating average segment length to the distribution of lengths. Because of its fourth-power dependence on L, a is highly sensitive to changes in dislocation free segment length such as might arise from unpinning, recovery, jog formation, or dislocation intersection. The above equation is not valid near the resonant frequency of dislocations, but the segment length in steel is believed to be much too short to cause over-damped resonance near 10 Mc; this will be discussed later. In the present experiments plastic-strain measurements with a sensitivity of 2 x 10-5 were also made during the early stages of loading in order to detect preyield strain. The general plan of the experiments is to observe

Jan 1, 1967

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Jan 1, 1938

By H. Foster Bain

I. INTRODUCTION. By H. FOSTER BAIN.+ THE recently aroused public interest in the conservation of our natural resources has peculiar importance to mining-men, since they deal with resources which are stored products. Within certain limits, the fertility of a worn-out soil may be restored, deforested areas can be replanted, one year's wasted water-supply is followed by another; but coal and ores, once taken out, cannot be mined again, and should therefore be conserved with especial care. This means, however, not that mining should be restricted, but that it should be done most economically and with the minimum of waste.

Nov 1, 1908

By D Lozada, A Salazar

Geometallurgy is a tool that, for more than a century, has been present in the implicit operations of mineral beneficiation. There’s a need to understand the characteristics of the material to be processed. This has led metallurgists to ask geologists what type of rock and mineralogy is entering the Beneficiation Plant and vice versa. The geologist needs to understand the beneficiation process in order to be able to carry out the production programming. The paradigm is whether geometallurgy can be applied to small-scale mining or if it is only aimed at large companies that invest millions of dollars to conduct studies. With this work, we provide an example of how geometallurgy can help improve the processes of a small mining company located in Ecuador (South America). We performed characterizations of geological and mineralogical and metallurgical tests in universities and the National Research Institute of Geological Metallurgical Mining. The origin of the theme is based on the fact that gold has been detected in the final tailings. The flotation concentrates meet the standards in terms of the content of economically profitable metals, but this isn’t the case with regards to the percentage of arsenic, which has hindered sales. The hypothesis is: conducting technical and scientific research will optimize the metallurgical process for the recovery of gold and concentrates. The referential framework is the mining geology of the Bella Rica District, current status of the Beneficiation Plant. In the theoretical framework there are parameters of the veins, comminution operations, gravimetric concentration, flotation, and cyanidation. The methodological framework contemplates the characterization of the gold ore, the chemical, mineralogical, textural, metallurgical analysis and the interpretation of the results. Thus, the design of a geometallurgy model of the deposit, with its main characteristics, is a conclusion that serves as a basis for the proposal of the optimization of the metallurgical process.CITATION:Lozada, D and Salazar, A, 2018. Geometallurgy applied to small-scale mining: a case study, in Proceedings 14th AusIMM Mill Operators' Conference 2018, pp 153–162 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Aug 29, 2018

By J. A. Taylor, H. F. Yancey

"INTRODUCTION Froth flotation as applied to coal is a process for separating desirable carbonaceous material from undesirable inorganic matter. In general, the feed must be finer than one eighth inch in size. The principal use of the process in the preparation of coal appears to be in the treatment of the fine sizes produced by breakage during mining and preparation.The Bureau of Vines in Information Circular 6714 has published general information on coal flotation, summarized investigative studies of the process, and described operating plants throughout the world with their tonnage, reagent consumption and operating costs.4ACKNOWLEDGMENTSThe present study of means for depressing pyrite and reducing ash ty froth flotation was conducted at the Northwest Experiment Station of the United States Bureau of Wines in cooperation with the College of vines. University of Washington, under the general direction of A. C. Fieldner, chief engineer, Experiment Stations Division, Bureau of Wines. Grateful acknowledgment is made for suggestions and criticisms received from W. H. Coghill, supervising engineer, U.S. Bureau of Mines Mississippi Valley Experiment Station, Rolla, Mo.; J. B. Morrow, and R. E. Zimmerman, of the Pittsburgh Coal Co.; and Dean Milnor Roberts and Prof. Joseph Daniels, of the College of Mines, University of Washington.FLOTATION AND DEPRESSIONA substance will tend to float if its surface attracts a gas film more strongly than it does a liquid film when both air and liquid are competing for this attraction. On the other hand, a substance will not float if its surface attracts a liquid film more strongly than it does a gas film. All theories of depression depend upon this fact. A wetted particle of floatable size most likely will be found in the tailings after the flotation process has been completed.The crux of flotation is the selective wetting of the undesirable material that tends to float. Two general methods 5, 6, 7 of depression are in use: One combines a chemical substance with the surface to form a wettable compound, and the other employs some colloidal or ionic substance which the surface selectively adsorbs, thereby forming a wettable surface."

Jan 1, 1935

By N. A. Duke, R. L. Carpenter

Abstract - The West Meliadine area is underlain by structurally interleaved panels of mafic and minor ultramafic metavolcanic rocks and metasedimentary rocks that occur along the northern margin of the Neoarchean Rankin Inlet greenstone belt. Three structural and metamorphic domains are recognized: (1) the easterly Wesmeg domain; (2) the central Barracuda-Ridge domain; and (3) the westerly Peter Lake domain. The Wesmeg domain is characterized by a series of southeast-trending, north-dipping, foliation-parallel panels of greenschist facies mafic metavolcanic and metasedimentary rocks. The Barracuda-Ridge domain is comprised of greenschist to amphibolite facies mafic metavolcanic rocks that define an east-northeast-trending structural grain. The Peter Lake domain consists of amphibolite facies mafic metavolcanic rocks and minor metasedimentary rocks intruded by a monzonite pluton. West Meliadine hosts the economically significant Wesmeg gold deposits, as well as other important gold showings across the Barracuda-Ridge and Peter Lake domains. The geological setting of the Wesmeg gold deposits resembles that of a break or fault zone. The Pyke Break is a major geophysical discontinuity (>65-km strike length) and is the first-order structural control on gold mineralization at West Meliadine. It is several kilometers wide and characterized by polyphase deformation and shear zone development accompanied by lode-gold mineralization. In general, gold concentration is related to quartz and iron-carbonate veining, iron sulfides (mainly arsenopyrite and pyrrhotite), and accompanying silicate alteration minerals that overprint favorable chemical and structural traps late in the history of deformation.

Jan 1, 2004

By Herbert Tomlinson

The United States Bureau of Mines has engaged in a study of the conditions under which coal mine accidents, resulting in the loss of life, limb, or time to the injured person, occur from falls of roof and coal. This publication is devoted to the results of a study conducted in the coal mines of the Book Cliffs and Wasatch Plateau coal fields of Utah. To show the necessity of this study, a statement of the fatalities that have occurred during the period 1928-1930, inclusive, in the bituminous mines of the United States and of Utah, is presented (Table 1), followed by a brief description of this Utah district, its coal beds and immediate roof, thickness of cover, dip of coal beds, methods of mining, supervision, roof testing and timbering for roof support, all of which are factors in any plan devised for preventing accidents from falls of roof and coal.

Jan 1, 1932

By F. N. Kissell, C. D. Litton

This study ranks the factors impacting survival during a coal mine fire. It bas already been established that reducing time delays is the most important factor in saving lives. Consequently every event during afire is measured in terms d its duration, and the effectiveness d any action taken to improve survival is measured in terms d the time it saves. By ranking actions according to time saved these authors found that a comhination d actions was most effective. This combination was: • installing lifelines. • moderately decreasing air leakage and • decreasing the fire growth rate. Changing ventilation leakage alone was much less effective, as was altering the CO (carbon monoxide), sensor alarm threshold. These results confirm an earlier fault-tree study on escape from mine fires. The fault-tree study bad shown that, with the exception d delays, single factor changes have minimal impact. Significant reductions in fire fatalities only take place with multiple factor changes.

By H. W. Gillett

UNLIKE most previous Howe lecturers, I had not the good fortune to be associated with Henry Marion Howe, nor to be directly one of his students. Yet, through his writings, he has been my teacher, as he has of all American metallurgists. Instructive as his writings are-I use the present tense because Howe thought so keenly and reasoned so surely, seeing clearly, as if by intuition, what was hazy to lesser minds, that his writings are still vital-it is not, those books and papers, nor even the minds he trained in his classes, that were his most outstanding service. It was the spirit of Howe in his: approach to the problems of metallurgy, his broad-mindedness and fair-ness, his recognition of the need for theories and hypotheses to explain metallurgical phenomena, his willingness to use them as servants, as well as his questioning attitude-his refusal to accept them as masters-that comprise his greatest service. This most thoroughly warrants the honor the Institute pays each year to his memory. These traits I so respect and honor in any man that I glory in this opportunity to do reverence to him in whom they were so notably united.

Jan 1, 1939

By J. D. Price, W. M. Bertholf

A. C. RICHARDSON*—First of all, [ think that the paper represents a lot more work, study, and correlation than has been indicated by the brief talk by Mr. Price. I like the way he started out and described the areas from which the samples were obtained, the locations of the washing plants, the available tonnages, and other background information with which to evaluate the data he submitted later on. Then I like the way in which he described the various types of washing plants, the tonnages handled and the difficulties of the washing problems; showing the amount of material that lies close to the specific gravity at which the washing separation is made. Later he gave figures from washing plant operations showing recoveries and cleaning efficiencies. He then discussed his own plant at Pueblo. It is the same old plant, I think, that I worked around a good many years ago. It is unusual to find a plant treating nearly 5000 tons of coal a day on tables. But this table plant is, I believe, more efficient than is indicated by the figures that Mr. Price gave. To determine the efficiency of a cleaning operation or to compare it with another it is necessary to consider the quantity and character of the material close to the specific gravity at which the separation is made. It is not fair, I believe, to penalize the table operation by something like 4 pct of out-of-place-material as he has done here. The variety and difficulty of the coals that he has to wash, the continuous shift and change in their composition make a very difficult cleaning problem and the table performance is excellent. I believe that the information in this paper will be of interest and value to anyone operating or planning to build a coal cleaning plant in this or other areas; particularly where the cleaning of fine coal is a problem. The data may be used for comparative purposes in determining the relative efficiencies of other cleaning plant separations. E. D. HAIGLER*—What is a Baum jig? J. D. PRICE (authors' reply)—A Baum-type jig is one in which the pulsations of the water is secured by means of a pulsating air current applied on top of the water. I imagine you are all familiar with the old plunger-type jig which is in effect a U tube in which a plunger on one side of the U, moving up and down, causes a corresponding pulsation on the far side of the jig. In the Baum jig, the pulsating air current is applied on the surface of the water on one side of the U tube of the jig and gives a corresponding pulsation on the other. It is also commonly known as a pneumatic jig. The control of the rise and fall of the water in the jig body proper is under much better control than it is in any of the other type jigs. Mr. Richardson could enlarge on that feature, for I know that he has had considerable experience with these jigs. A. C. RICHARDSON—You have asked how to control a Baum-type jig. The pulsations in a Baum jig can be modified and regulated to a marked degree by the amount of water admitted to the jig and by the adjustments of the valve which regulates the manner in which air is admitted. The number of pulsations per minute is controlled by the number of cycles of the air valve. Thirty to forty cycles per minute is a good speed for large jigs treating coarse sizes of cod. With an air valve it is possible to modify the time-velocity curve of the pulsating water to some extent which in turn determines the action in a jig bed. Within limits the following parts of the air valve cycle may be regulated: (1) the rate and period of air admission, (2) the period of air expansion, (3) the rate and period of air exhaust, and (4) the period of air compression. The rate and period of air admission determines the acceleration of the water at the beginning of the pulsion stroke and the amplitude of the stroke. The period of air expansion, after inlet port is closed, is one in which the water has reached the desired velocity, positive acceleration reduced, and the bed held in a mobile condition. The rate and period of the air exhaust can be adjusted to modify the degree of suction and so modify the manner in which the particles in the bed stratify. The compression period, alter the exhaust port closes and before the intake port opens may be used to advantage in retarding the downward velocity of water during the suction stroke. An ideal jig stroke is one in which during the up stroke the bed is lifted slowly in a mass and opens up like an accordian with the bottom layers dropping away first. With the bed open and mobile the particles adjust themselves according to their hindered settling rates. During the down stroke, while the bed is still open the particles of high specific gravity are accelerated toward the bottom layers. It is possible to approach this stroke with all types of jigs but it is less difficult to approximate it with a Baum jig.

Jan 1, 1950

By G. L. Oldright

In the first Report of Investigations of the present series?(No. 4562) the usual course of progress ill reducing the minerals of low-grade ores to their valuable metallic components had been noted as advancing along two lines to concentrate a usually diminishing percentage of these minerals to a smaller bulk of richer product, and then to smelt the smaller bulk more cheaply per pound of metal produced. Fundamental properties of lead compounds made it difficult to treat much richer lead products than are treated at present in several steps of conventional lead smelting, unless ?marked modifications were made. No limits to the richness of the feed itself' were set by the ore (Scotch) hearth; on the contrary, the richer the feed, the better the results given by the hearth. The natural field of operation of the hearth, as determined by the ores available, was seen to lie in the Central United States, with their lead concentrates containing negligible quantities of precious metals and. with few ores of such metals available for use as fluxes. It was noted) however, that even in its chosen field, the Scotch hearth, or "ore" hearths developed from them, was not always used; the usual smelting practice was followed, at times, of sintering followed by blast-furnace smelting for even rich ores.

Jan 1, 1949