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Jan 1, 1953

By Robert S. Dalzell, Ernest A. Curth

Following the introduction of shields to the U.S. longwall mining scene and the steady increase in the number of shield faces during recent years, the occurrence of longwall -ground-control -associated accidents has shown a welcome downward trend. But even though the accident experience is favorable, problems exist. New mining systems, however efficient, have run afoul of roof control. Shield faces have suffered extended stoppages because of roof cavities. Therefore, the Bureau of Mines has reviewed foreign remedial techniques to evaluate their potential for domestic application. Such technology includes cribbing, strain absorbent modules (SAM'S), inflatables, wire meshing, chemical rock stabilization, synthetic foams, and monolithic fills.

Jan 1, 1984

By Morris Cohen

STAFF: Editor, Gerhard Derge Acting Editor, Paul G. Shewmon Carnegie Institute of Technology Schenley Park Pittsburgh 13, Pa. Editorial Assistant, M. A. Redmerski Production Editor, Otto T. Johnson THE METALLURGICAL SOCIETY: Karl L. Fetters, President; J.S. Smart, Jr., Past-President; R. C. Cole, Vice President; R. L. Hennebach, Treasurer; R. W. Shearman, Secretary. PUBLICATIONS COMMITTEE OF THE METALLURGICAL SOCIETY: W. O. Phil-brook, Chairman; H. L. Bishop, R. C. Cole, J. N. Hobstetter, W. A. Krivsky, E. R. Morgan, F. C. Langenberg, R. E. Lund, Paul Queneau, L. L. Seigle, R. L. Smith, and T. V. Wainwright. Review and selection of manuscripts is under the supervision of the following Publicotions Committes: Extractive Metallurgy Division: R. E. Lund, Chairman; M. E. Wadsworth, Vice Chairman; D. H. Baker, Jr., G. M. Bell, R. E. Grace, W. A. Krivsky, R. A. Lewis, Charles O'Neill, A. W. Schlechten, R. E. Shinkoskey, and W. W. Stephens. Iran and Steel Division: T. V. Wainright, Choirman; H. L. Bishop, R. E. Boni, T. E. Dancy, D. W. Murphy, Johannes M. Uys, J. B. Wogstoff, and R. G. Ward. Institute of Metals Division: J. N. Hobstetter, Chairman; P. A. Beck, J. J. Becker, G. F. Bolling, J. 0. Brittain, J. B. Clark, R. S. Davis, A. E. Dwight, R. W. Fountain, L. R. Girifolco, J. C. Gurland, H. S. Kalish, E. L. Harmon, J. J. Heger, A. A. Hendrickson, L. Himmel, J. P. Hirth, H. H. Johnson, Jr., R. R. Nosh, T. N. Rhodin, R. H. Richman, H. C. Rogers, W. Rostoker, C. Sherby, C. W. Spencer, L. Slifkin, J. K. Stanley, R. Steinitz, H. C. Stumpf, and R. Swalin. Published bimonthly by the Americon Institute of Mining, Metallurgicol, and Petroleum Engineers, Inc., 345 East 47th Street, New York 17, N. Y. Telephone PLaza 2-6800. Subscription $30 peryear for non-AIME members in United States and North, South, and Centrol America; $32, foreign; $30per$7.50 for AlME members. Single copies, $6.00, single copies foreign, $6.50. The AlME is not responsible for any stotement made or opinion expressed in its publications ... Copyright 1962 by the American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. . . . Registered cable address, AlME New York . . . Indexed in Engineering Index, Industrial Arts Index, and Chemical Abstracts . . . Second class postage paid at New York, N. Y., and Ann Arbor, Mich. Volume 224, Number 4.

Jan 1, 1962

By James W. Malcolmson

This paper treats of the history and development of the Sierra Mojada mines in the north of Mexico, the character and extent of the ore-deposits, and the methods of mining the ore. The growth of the smelting industry in Mexico in recent years is, to a large degree, due directly to the output of the lead-bearing ores from the Sierra Mojada mines, and at the present time (1901) new smelters are being built, looking to this district for their supply of lead-ores. These mines are located in the southern part of the State of Coahuila, in the Republic of Mexico, in latitude 27 24' N. and longitude 103O 43' W. of Greenwich. The last account of the Sierra Mojada published in our transactions was contributed by Mr. Richard E. Chism, in October, 1886.* Since that time some 3,000,000 tons of ore have been extracted from the mines, and much additional information has been developed regarding the mineral deposits. Since 1886, the Mexican Northern railroad, 78 miles in length, has been built from Escalon, connecting the camp with the Mexican Central railway, a trunk-line from El Paso, Texas, to Mexico City. The distances by rail from Sierra Mojada to the principal smelting-centers are as follows : To Torreon, Coahuila, Mex., 179 miles; to Monterey, Nuevo Leon, Mex., 422 miles; to El Paso, Tex., U. S., 494 miles; to Aguas Calientes, A. C., Mex., 522 miles; to San Luis Potosi, 8. L. P., Mex., 644 miles; to Pueblo, Colorado, U. S., 1158 miles; to Argentine, Kans., U. S.,

Jan 1, 1902

By O. Cuscoleca

The Austrian plants at Donawitz and Linz were the first to blow steel with high purity oxygen. The paper shows how the process was developed and gives a survey of the results achieved to date. Compared with open hearth steel of equal quality, the obvious advantages of oxygen steel are the low investment and conversion costs. The nitrogen content of oxygen steel is not higher than that of good open hearth steel. Rimmed and killed steel products made by the oxygen process are superior to rimmed and killed steel products made by the best open hearth process. TWO new steel plants using the principle of making steel with high purity oxygen went into operation in Austria, one at Linz (Vereinigte oster-reichische Stahlwerke) in November 1952 and the other at Donawitz (dsterreichisch-Alpine Montan-gesellschaft) in May 1953. An estimated 330,000 metric tons were produced by the two plants in 1953, the first year of operation. In 1954 production by Austrian plants- using the high purity oxygen approach will be raised to 450,000 metric tons. This will be in addition to facilities in Huckingen (Man-nesmann A. G., Düsseldorf, Germany), those planned and under construction at Hamilton, Ontario, Canada (Dominion Foundries and Steel, Ltd.), and elsewhere. It is expected that by 1955 a total capacity of one million tons of high purity oxygen steel will be available. At the close of the last century, because of increasing availability of scrap, open hearth steel production forged ahead at an ever increasing pace. This caused world steel production to rise faster than pig iron production and finally to overtake it. In 1911 65 million tons of steel were produced against 64 million tons of pig iron. World steel production was 209 million tons in 1951, while pig iron output was only 147 million tons. The 1951 breakdown for steel shows 118 million tons made from pig iron, while the balance, 91 million tons or 44 pct of the total tonnage of steel produced, was made from scrap. This increase in crude steel production on a basis of high scrap consumption led to the world market scrap shortage and soaring scrap prices. In the United States and other nations, production of converter steel has fallen far behind that of open hearth steel. The surplus of processing scrap, un-absorbable by converting mills and thus a welcome source for open hearth and electric melting shops in the past, together with regular scrap purchases, no longer can meet requirements of both open hearth and electric steel production in Europe. In addition, recent modification of the basic bessemer process, blowing with oxygenated blast, substantially raised the scrap capacity of these plants. Any further expansion of world steel production will necessitate utilization of self-containing processes in regard to scrap because of the shortage.

Jan 1, 1955

By F. Hass, N. W. Lord

This paper gives the results of experiments conducted in the metallurgical laboratory of the Ohio State University with the objects of determining: First, the calorific powers of a number of coals in general use in Ohio; and second, how far ordinary analytical methods could be used as a basis for computing these values. Incidentally a test of the performance of the calorimeter was involved. The chemical work has been carried on in the department for some time, so that the whole investigation has extended over three or four years. The Mahler calorimeter was purchased from L. Golaz in Paris, and is practically identical with the one described and figured by Mahler in his monograph "Contribution a l'Etude des Combustibles," from the Bulletin de la Société d' Encouragement pour l'lndustrie Nationale. A figure and description is also given by William Kent in The Mineral Industry for 1892, page 97. There were furnished with the instrument three thermometers covering a range of from 7°.5 C. to 31° C. Thermometer "A" (17°.5 to 31°) was carefully calibrated by reading the ends of a thread of mercury in sixteen positions covering the whole scale, supplementing this by readings of longer threads and deducing the errors of scale by the method published by Prof. Holman in the Technology Quarterly of September, 1887. The maximum error of a single reading was found to be 0°.0042 C. Thermometer "B" (13° to 25°) was compared directly with " A " over the scale common to both, and a variation was found of 0°.0145 C. for 7°.5 (or 0°.002 for l°) of the scale. Thermometer " C" ('7°.5 to 19°.0) was omitted from the cornparison, as it was rarely used, being only required where measurements were made at low temperatures. From the

Jan 1, 1898

By H. S. Munroe

As elaborate discussion under this heading formed a chapter in one of the reports made by Professor Raymond as Commissioner of Mining Statistics." In a subsequent report? was printed a paper., by Mr. William Main, Jr., of Columbia, South Carolina, containing a theoretical investigation into the effect of the velocity of impact on the effective ditty of stamps. A visit to the Lake Superior copper region last summer suggested an inquiry into the relative efficiency and economy of the enormous steam stamps of the copper-mills, as compared with the results obtained with the cam and tappet stamps commonly used in the West. The atmospheric stomp used at the Phoenix Mill promised to add interest to the inquiry, as giving an example of unusually high speed, this stamp making 160 drops per minute. In introducing his subject Dr. Raymond makes the following remarks, which are quite apropos of the present investigation: "In considering the economical application of stamping machinery, we meet, at the beginning, with serious difficulties in obtaining accurate data for comparison. The weight and fall of stamps vary as the shoes and dies wear out; and this may lead to a change of speed also. Moreover, defects in engines, boilers, or machinery for the transmission of power, may occasion serious losses, which cannot fairly be charged to the arrangements of the stamps proper. Again, the capacity of stamp-mills is directly dependent, in some degree, upon the nature and extent of discharge, fineness of screens, and other peculiarities of the battery. Finally the hardness and tenacity of the rock crushed varies so much that comparisons between different localities cannot be implicitly trusted. The safest experiments are those made in the same mill, by changing first one arid then another condition of working; but this is seldom possible for such

Jan 1, 1881

By P. H. Brace

THE study of the relations between gases and metals is one of perennial interest to all who are connected with the production of high-grade metallurgical products. The data reported here are the outcome of work of which the object is to determine the effects of dissolved gases upon the properties of metals and to gain a more detailed knowledge of the reactions between gases and molten metals, particularly iron, under definitely controlled conditions. We have attempted to reduce our margin of error by dealing with relatively large quantities of metal, from 4 to 13 lb. (2 to 6 kg.), and keeping the ratio of refractories to metal as small as practicable. The ingots produced are large enough to provide adequate material for making determinations of magnetic and other physical properties. In choosing the bell-jar type of furnace we were influenced by the results of considerable experimentation along the same general line which indicated that, for the scale or which we were to work, it was important to have the furnace structure independent of the vacuum enclosure. The use of a bell-jar surrounding the entire furnace accomplishes this and also gives great freedom of observation during operation and ready accessibility for the replacements which are necessary after each run. Our choice of analytical method was made in the light of the results secured by H. M. Ryder, who used a method similar in principle for the analysis of very small quantities of gas extracted from strips of metal heated electrically in high vacuum. We have presented some selected preliminary experimental data as being illustrative of the quantity and nature of the gases which occur in iron of different origins, but do not urge any hypothesis at this time.

Jan 1, 1928

By E. Heaton Hemingway

DURING the past year, the Watertown Arsenal has been interested in the occluded gas and oxide content of certain ordnance steels in order to determine, if possible, whether some of the peculiar failures in their physical properties might not be traced to these causes. For the purpose of best accomplishing a study of this nature, it was decided to heat the various samples of steel in a vacuum for definite periods of time at high temperatures and carefully examine the quantity and composition of the gases evolved. By the use of a fused quartz tube fitted with a water-cooled, ground-glass stopper, it was possible to maintain a vacuum at a temperature of 1000° C. for 10 hr. without perceptible leakage being evidenced as measured by a McLeod gage. The silica tube was connected with an evacuating system so constructed that the volatilized gases could be removed from time to time and a low vacuum of 0.002 to 0.0010 mm. of mercury continuously maintained. At no time during the period of heating or in the removal of the gases did the evacuated system come in contact with rubber stoppers or any rubber connections, making contamination from such a source impossible. In other words, the only volatile products that could be obtained must necessarily have come from the steel itself or from the glass and fused quartz system or from the mercury used as a sealing agent. In the earlier experiments, the steel treated was in the form of turnings, but this practice was discarded because the weights of the turnings before and after being heated were widely inconsistent, even when taken from the same piece of steel. This discrepancy developed largely through variation in the amount of metal volatilized with the gases; this metal could always be seen in the form of a ring where it condensed in the cooler portion of the tube either in the amorphous or crystalline condition. Because of the frequency in occurrence and the variation in the manner of deposition, this material was roughly analyzed and found to consist for the most part of iron. At the same time two samples of steel that had been

Jan 8, 1920

By William L. Fink, Dana W. Smith

Many investigators have attempted to determine the true nature of the internal changes taking place during aging. Merica, Waltenberg and Scottlt were the first to propose a theory of age-hardening. They attributed the age-hardening of duralumin to the precipitation of minute particles of the compound CuA12. Later Zay Jeffries and R. S. Archer2 augmented the above theory by suggesting that the small CuAl2 particles acted as "keys" causing "slip interference." Many other investigators3 have devoted much time to the mechanism of age-hardening, some corroborating the "precipitation" and "slip interference" theory, others coming to different conclusions because of effects that to them seemed unexplainable by the early theories; e.g., the increase of electrical resistance upon aging, the fact that no change in lattice parameter could be detected during the early stages of aging even at elevated temperatures, and the fact that the density did not change as would be predicted. In 1932, Merica revised4 his earlier precipitation theory to take care of these presumably anomalous effects. This revised theory, the "knot" theory, assumes that substantial age-hardening occurs before actual precipitation of solute as discrete particles. The assumed mechanism is one of diffusion of solute atoms into groups forming distorted regions which act as "hard" spots and cause slip interference. These "knots" are assumed to have approximately the same lattice arrangement as the solvent. The anomalous behavior of lattice parameter, density, and electrical conductivity, require a modification of the simple precipitation-hardening theory, only if it is assumed that the precipitation of minute particles during aging has the same effects on these properties as the formation of large particles under equilibrium conditions. Data obtained by the authors in the study of the aluminum-magnesium system5 indicated that

Jan 1, 1936

By John Wulff, Richard P. Seelig

The importance of the pressing operation in the forming of articles by powder metallurgy depends to a great extent on the type of product to be made. While in some few cases the pressing is merely a means of compacting loose powder particles into a solid mass preliminary to a sintering treatment, in most applications it constitutes a molding operation with the purpose of shaping the raw material in powder form into a certain predetermined, accurately defined part not altered in shape by subsequent sintering. In still other cases, no pressing at all but sintering in molds gives useful articles. A limited number of products are made by the simultaneous application of pressure and heat. The factors that control the product of the pressing operation are raw material, lubricant, type, size and shape of die and compact, magnitude and time of application of pressure, as well as temperature of pressing. All such factors need to be controlled; yet, depending on the function of the pressing operation, greater emphasis may be placed on processing factors other than the pressing operation. In any complete discussion of pressing, subsequent sintering cannot be disregarded. For the sake of brevity, the present paper has been limited to the mechanics of pressing and only occasionally refers to sintering. For the same reason, hot-pressing has been omitted as beyond the scope of this paper In any survey of the literature on the pressing of metal powders, the 1938 paper of Balshinl on the theory of the process of pressing deserves mention. The first attempts at an interpretation of pressing phenomena were made by Balshin' and RakovskL2 The experimental results of both are of great interest. Since the experimental results are not described, the work was repeated, using our own interpretation of the possible techniques, and is reported in the following pages. The basic theory of Balshin,' based on a hydro-dynamic analogy, however, leads to hut another way of plotting density and pres- , sure against height of a pressed compact. Since it does not give any new insight into the phenomena, nor account for the influence of side-wall friction, a discussion of the theory has been omitted from this paper. Density Gradients in Compacts The process of pressing metal powders in a die (disregarding for this consideration the powder filling and ejection operations) may be divided into three phases: (I) packing, (2) elastic and plastic deformation, (3) cold-working with or without fragmentation. It must be emphasized that these three steps do not follow each other in sequence; on the contrary, in practice

Jan 1, 1946

By John Wulff, Richard P. Seelig

The importance of the pressing operation in the forming of articles by powder metallurgy depends to a great extent on the type of product to be made. While in some few cases the pressing is merely a means of compacting loose powder particles into a solid mass preliminary to a sintering treatment, in most applications it constitutes a molding operation with the purpose of shaping the raw material in powder form into a certain predetermined, accurately defined part not altered in shape by subsequent sintering. In still other cases, no pressing at all but sintering in molds gives useful articles. A limited number of products are made by the simultaneous application of pressure and heat. The factors that control the product of the pressing operation are raw material, lubricant, type, size and shape of die and compact, magnitude and time of application of pressure, as well as temperature of pressing. All such factors need to be controlled; yet, depending on the function of the pressing operation, greater emphasis may be placed on processing factors other than the pressing operation. In any complete discussion of pressing, subsequent sintering cannot be disregarded. For the sake of brevity, the present paper has been limited to the mechanics of pressing and only occasionally refers to sintering. For the same reason, hot-pressing has been omitted as beyond the scope of this paper In any survey of the literature on the pressing of metal powders, the 1938 paper of Balshinl on the theory of the process of pressing deserves mention. The first attempts at an interpretation of pressing phenomena were made by Balshin' and RakovskL2 The experimental results of both are of great interest. Since the experimental results are not described, the work was repeated, using our own interpretation of the possible techniques, and is reported in the following pages. The basic theory of Balshin,' based on a hydro-dynamic analogy, however, leads to hut another way of plotting density and pres- , sure against height of a pressed compact. Since it does not give any new insight into the phenomena, nor account for the influence of side-wall friction, a discussion of the theory has been omitted from this paper. Density Gradients in Compacts The process of pressing metal powders in a die (disregarding for this consideration the powder filling and ejection operations) may be divided into three phases: (I) packing, (2) elastic and plastic deformation, (3) cold-working with or without fragmentation. It must be emphasized that these three steps do not follow each other in sequence; on the contrary, in practice

Jan 1, 1946

By S. R. Zimmerley, John Gross

A survey of the status of ore dressing in 19231 placed particular stress on the need of research in the crushing and grinding of ore, especially on the need for a method of measuring the surface of the products obtained in crushing and grinding and for fundamental data on the law of crushing, in order that intelligent conclusions may be drawn from actual crushing or grinding experiments. There has been no satisfactory means of determining the surface of crushed products. The results have been judged entirely by the amount of the various sizes produced, based on sieve sizing for particles above 74 microns in size and on microscopic measurement or elutriation for particles below 74 microns, a method which could give only a general idea of what had been accomplished. The fact that the long controversy between the followers of Kick and of Rittinger has resulted in no accepted conclusion is evidence of the need for fundamental data on the crushing law. Some Methods of Measuring Surface of Particles A dissolution method was used by Wolff to measure surfaces of glass powder. A mixture of sodium carbonate and sodium hydroxide was the solvent and the amount of glass dissolved in two hours from the powder was compared with that dissolved from a glass plate.2 Lately Herbert F. Kriege has used the dissolution method in determining surface of calcite and limestone.3 Dr. Geoffrey Martin and his coworkers in England have also used a dissolution method to determine surface on quartz. They compared the amount of quartz dissolved from the sample in one hour by a hydrofluoric acid solution with the amount dissolved from a measured quartz

Jan 1, 1930

By M. King Hubert

The growth of human knowledge is an evolutionary process. Historically our separate sciences came into existence as people became interested in various apparently unrelated domains of phenomena, and in this manner we acquired the sciences of physics, chemistry, astronomy, biology and geology. As various of these sciences became established, cognizance of them came to be taken by the universities and in this manner there arose the traditional departments of physics, astronomy, chemistry, biology and geology of our American universities. As there was no particular rationality in the boundaries separating the various sciences, in the university departments the jurisdiction of each has assumed quite arbitrary limits. In the domain of earth phenomena the first science to grow up was that of geology, which arose originally from the activities of the collectors of rocks, minerals and fossils. Thus geology evolved as a descriptive science dealing with directly observable terrestrial phenomena for which elementary rational explanations were offered. The traditional treatment of phenomena by the science of geology has rarely been with more than an elementary regard for the fact that these phenomena were also phenomena of physics and chemistry. Since the latter part of the nineteenth century, a new approach to terrestrial phenomena has been emerging and becoming of so great a significance that it can no longer be ignored. This approach has been made by people trained primarily in the sciences of physics and chemistry, who have investigated terrestrial phenomena as constituting phenomena of their respective sciences. In this manner we have acquired the so-called "borderland sciences" of geophysics, the physics of the earth, and of geochemistry, the chemistry of the earth. Neither of these fields is new, having arisen chiefly at the hands of European investigators during the latter part of the nineteenth century. The European universities have long since given official recognition at least to geophysics, by the establishment of departments or institutes of geophysics, which are on a par with the university departments of the other sciences.

Jan 1, 1940

By H. S. Munroe

AN elaborate discussion under this heading formed a chapter in one of the reports made by Professor Raymond as Commissioner of Mining Statistics.* In a subsequent report- was printed a paper, by Mr. William Main, Jr., of Columbia, South Carolina, containing a theoretical investigation into the effect of the velocity of impact on the effective ditty of stamps. A visit to the Lake Superior copper region last summer suggested an inquiry into the relative efficiency and economy of the enormous steam stamps of the copper-mills, as compared with the results obtained with the cant and tappet stamps commonly used in the West. The atmospheric stamp used at the Phoenix Mill promised to add interest to the inquiry, as giving an example of unusually high speed, this stamp making 160 drops per minute. In introducing his subject Dr. Raymond makes the following remarks, which are quite apropos of the present investigation : "In considering the economical application of stamping machinery, we meet, at- the beginning, with serious difficulties in obtaining accurate data for comparison. The weight and fall of stamps vary as the shoes and dies wear out; and this may lead to a change of speed also. Moreover, defects in engines, boilers, or machinery for the transmission of power, may occasion serious losses, which cannot fairly be charged to the arrangements of the stamps proper. Again, the capacity of stamp-mills is directly dependent, in some degree, upon the nature and extent of discharge, fineness of screens, and other peculiarities of the battery. Finally the hardness and tenacity of the rock crushed varies so much that comparisons between different localities cannot be implicitly trusted. The safest experiments are those made in the same mill, by changing first one and then another condition of working; but this is seldom possible for such * Mineral Resources West of the Rocky Mountains, 1871, p. 380. †- Mineral Resources West of the Rocky Mountains,, 1873, p. 345.

Jan 1, 1881

By M. King Hubert

The growth of human knowledge is an evolutionary process. Historically our separate sciences came into existence as people became interested in various apparently unrelated domains of phenomena, and in this manner we acquired the sciences of physics, chemistry, astronomy, biology and geology. As various of these sciences became established, cognizance of them came to be taken by the universities and in this manner there arose the traditional departments of physics, astronomy, chemistry, biology and geology of our American universities. As there was no particular rationality in the boundaries separating the various sciences, in the university departments the jurisdiction of each has assumed quite arbitrary limits. In the domain of earth phenomena the first science to grow up was that of geology, which arose originally from the activities of the collectors of rocks, minerals and fossils. Thus geology evolved as a descriptive science dealing with directly observable terrestrial phenomena for which elementary rational explanations were offered. The traditional treatment of phenomena by the science of geology has rarely been with more than an elementary regard for the fact that these phenomena were also phenomena of physics and chemistry. Since the latter part of the nineteenth century, a new approach to terrestrial phenomena has been emerging and becoming of so great a significance that it can no longer be ignored. This approach has been made by people trained primarily in the sciences of physics and chemistry, who have investigated terrestrial phenomena as constituting phenomena of their respective sciences. In this manner we have acquired the so-called "borderland sciences" of geophysics, the physics of the earth, and of geochemistry, the chemistry of the earth. Neither of these fields is new, having arisen chiefly at the hands of European investigators during the latter part of the nineteenth century. The European universities have long since given official recognition at least to geophysics, by the establishment of departments or institutes of geophysics, which are on a par with the university departments of the other sciences.

Jan 1, 1940

By Henry Mulryan

Diatoms are microscopic aquatic plants of the order Bacillariaceae. They are unicellular plants with skelctons made up of amorphous opaline silica. The skeletons show highly ornate, complicated geometrical designs. Diatoms live in water virtually everywhere. They are found in clean sea water, brackish water, and fresh-water lakes and ponds. When conditions are right, diatoms propagate by subdivision in huge numbers. Alkalinity, temperature, and the presence of high concentrations of silica in the water largely control diatom life. When the diatoms die the skeletons drop to the bottom of their habitat to form oozes of varying thicknesses. Diatomites Diatomite, or diatomaceous earth, is composed essentially of the siliceous remains of the diatoms, although other organic skeletons are also present, especially in sea-water deposits where radiolaria, sponges and silico-flagellates are common. Impurities are generally carbonaceous material, fine-grained silt, volcanic ash and dust, and occasional coarse grains of sand. Diatomites are marine, brackish, or fresh-water, depending upon types of diatoms and their method of deposition. Diatoms More than 8000 species of diatoms have been named and classified. Some are definitely classified as to their habitat; some are so well recognized as to their living conditions that they can be stated to be diagnostic types, and when encountered in a deposit determine the origin of the deposit. Some of the commoner types of diatoms found in the freshwater diatomites on the Pacific Coast are: Cymbella lanceolata Agardh Fragilaria virescens Ralfs Encyonema prostratum Ralfs Diatoma vulgare Dory Surirella biseriata Brebison Eunotia major Ehrenberg Amphipleura pellucida Kützing Stictodiscus niagarac Ehrenberg Gomphonema geminatum Lynberg Melosira granulata Ehrenberg Epithemia turgida Kützing

Jan 1, 1942

By Henry Mulryan

Diatoms are microscopic aquatic plants of the order Bacillariaceae. They are unicellular plants with skelctons made up of amorphous opaline silica. The skeletons show highly ornate, complicated geometrical designs. Diatoms live in water virtually everywhere. They are found in clean sea water, brackish water, and fresh-water lakes and ponds. When conditions are right, diatoms propagate by subdivision in huge numbers. Alkalinity, temperature, and the presence of high concentrations of silica in the water largely control diatom life. When the diatoms die the skeletons drop to the bottom of their habitat to form oozes of varying thicknesses. Diatomites Diatomite, or diatomaceous earth, is composed essentially of the siliceous remains of the diatoms, although other organic skeletons are also present, especially in sea-water deposits where radiolaria, sponges and silico-flagellates are common. Impurities are generally carbonaceous material, fine-grained silt, volcanic ash and dust, and occasional coarse grains of sand. Diatomites are marine, brackish, or fresh-water, depending upon types of diatoms and their method of deposition. Diatoms More than 8000 species of diatoms have been named and classified. Some are definitely classified as to their habitat; some are so well recognized as to their living conditions that they can be stated to be diagnostic types, and when encountered in a deposit determine the origin of the deposit. Some of the commoner types of diatoms found in the freshwater diatomites on the Pacific Coast are: Cymbella lanceolata Agardh Fragilaria virescens Ralfs Encyonema prostratum Ralfs Diatoma vulgare Dory Surirella biseriata Brebison Eunotia major Ehrenberg Amphipleura pellucida Kützing Stictodiscus niagarac Ehrenberg Gomphonema geminatum Lynberg Melosira granulata Ehrenberg Epithemia turgida Kützing

Jan 1, 1942

By R. W. Schenker

INTRODUCTION Environmental and occupational safety and health requirements often have a major impact on the design of comminution circuits, leading to increased capital and operating costs and reduced income. A project's capital cost can be increased by environmental permitting delays and the addition of dust collection equipment. Income can be reduced by lost production during unscheduled plant shutdowns for dust collection equipment maintenance. Dust collection equipment must be carefully selected and sized to minimize impact on the project. The equipment performance must comply with environmental regulations and allow working areas to comply with occupational safety and health regulations. Unnecessary overdesign could jeopardize the project's desirability from an economic standpoint. The equipment must be sufficiently reliable to avoid interference with production schedules. This chapter provides practical information on the selection and sizing of comminution circuit dust collection equipment that is consistent with the requirements stated above. It presents information on the reasons and general principles of dust collection; various types of dust collection equipment; and design criteria for ventilation hoods, duct systems, fabric filter dust collectors, and fans. An example discussing the selection and sizing of dust collection equipment for a simple comminution circuit is also presented. REASONS FOR DUST COLLECTION Dust collection equipment should be installed in comminution circuits for a variety of reasons, some of which are discussed below. These include compliance with government regulations, minimization of housekeeping requirements, product recovery, and improvement in public and employee relations. Compliance with Government Regulations Dust emissions from comminution circuits must comply with both air pollution control and occupational safety and health regulations. The regulations that may influence the selection of comminution circuits are discussed in more detail in Chapter 2. Air pollution control regulations limit the emission of dust, as well as visible emissions to the atmosphere and the concentration of dust in the ambient air. These regulations minimize the degradation of air quality and impact to other environmental considerations such as the health of the general public,

Jan 1, 1982

By George K. Foster, Charles D. Borror

THE Jeffrey mine of the Canadian Johns-Manville Co., Limited, is in the town of Asbestos, situated approximately 100 miles northeast of Montreal and about the same distance southwest of Quebec, in Richmond County, Quebec. Mining operations were started in 1881 on outcrops on a hill, as a side-hill cut, followed by a second and third cut. This development was the forerunner of the present large open-pit operations, the mine now ranking as the largest openpit asbestos mine in the world. Operations were first carried on by hand, then by horsepower and later by stem cableways. By 1924 the derrick spans, 2000 ft. or more long, became unwieldy. To overcome this, and also to eliminate hand labor as much as possible, steam shovels and railroad haulage were introduced. The steam shovels were replaced in 1928 by larger electric shovels of the full-revolving type. THE ORE BODY The ore body is a serpentinized peridotite rock mass. The chrysotile fibers form a network of veins throughout, varying from microscopic width to two or more inches measured across the veins (Fig. I). These veins may be continuous for a few or many feet; they may increase or decrease in width within a few feet. The veins in which the fibers occur perpendicular to the veins are known as cross fiber. Those in which the fibers lay parallel to the veins are known as slip fiber. The cross fibers are of better quality, and more in demand. The majority of the fiber [ ]

Jan 1, 1946