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By Russell G. Wayland

SINCE the installation at Kropfmuehl, Bavaria, of a modern flotation concentrator in 1938, the flake and fine graphite from the Passau area can now be delivered in about any normal specified carbon content of any size range up to a flake averaging about 0.7 mm. The graphite finds a wide German and export market for crucible manufacture, pencil leads, dry cells and other uses.

Jan 2, 1951

By Howard A. Smith

OF late considerable experimental and theoretical interest has been shown in the rates of transformation from a single phase, usually a supercooled solid solution, into one or more phases. Such reactions may involve both diffusion and transformation of the major constituent, as in iron alloys, or it may simply involve diffusion, as in superstructure formation and in age-hardening systems. Most of the work has been confined to ferrous alloys1-9† although two investigations have been made on copper alloys 10-11. That such work may be of considerable practical importance has been demonstrated by Bain12, by the workers at the Kaiser Wilhelm Institut für Eisenforschung13, 14, and by the everyday use of precipitation and age-hardening principles15. Experiments in this country have generally followed Davenport and Bain's technique of rapid supercooling followed by isothermal treatment. In Germany16, 17 the work has been extended to the study of the influence of accurately controlled and measured rates of cooling. The work on steel indicates that there are two subcritical temperature ranges where reaction starts sooner after quenching and proceeds at a more rapid rate than at other temperatures. At subcritical temperatures above Ar" where reaction is dependent upon atomic migration there is a period of time of which the length depends upon the alloy content and the temperature, before which no reaction has been detected. Davenport and Bain1 find that different sorts of atoms in solid solution in gamma iron affect the length of this "prereaction" period differently, manganese

Jan 1, 1935

By Albert Sir Kitson

THE manganese ore deposits of the Gold Coast, British West Africa, occur in very ancient rocks, of both sedimentary and metamorphic types. In. certain respects they strongly resemble those of India and Brazil, as contrasted with those of Tertiary age in Georgia. Viewed from the present condition of the maganiferous rocks, the oldest deposits are in the sediments. Later than these are the progressively metamorphosed representatives of these sediments; youngest are the products of decay and degradation with the concentration of manganese oxide of both areas. The oldest occurrences are in argillaceous and siliceous phyllites and slates, which show only a moderate amount of metamorphism. They belong to a series which also includes mudstones, sandstones, grits, conglomerates and subordinate limestones, with tuffs and lava-flows largely of basic types. To this series I have given the name Birrim. Its age is unknown, for no definite fossils have been discovered in it. As the characteristics of these non-fossiliferous strata at many places are the same as those of strata in many parts of the world that are suitable for the preservation of fossils and that contain them, it is assumed that the Gold Coast deposits are pre-Cambrian. These rocks of the Birrim series have normally a northeast-southwest strike and are folded, but not to any very great degree except in certain belts., From the Eastern Province of the Gold Coast they may be traversed across their strike for more than 600 miles to the extreme northwestern corner of the Northern Territories. Thence. they probably extend much further into French Territory.

Jan 5, 1927

By L. J. Gurevich

IN the course of the examination, at the Bureau of Standards, of fusible tin boiler plugs for the Steamboat Inspection Service, it became evident that an investigation should be undertaken to determine the precautions necessary in the manufacture of acceptable plugs. The results of the tests of these plugs show that their manufacture has improved, though at present not all of the plugs tested are satisfactory. Table 1 gives the result of tests of some 1500 plugs from about 100 makers. Records of the tests show that several of the makers were able to produce satisfactory plugs with every pouring. The Steamboat Inspection Service has the following specifications for fusible plugs: "Fusible plugs for use in boilers of steam vessels under the Jurisdiction of the Steamboat Inspection Service shall be made of bronze casing with the bore tapering continuously and openly from end to end, and filled from end to end with tin not less than 99.7 per cent. pure and to contain not more than 0.1 per cent. of lead and not more than 0.1 per cent. of zinc. The small end of the bore may be countersunk not more than 1/32 in. in depth and width, but no recess, thread, or cavity other than this countersink shall be allowed."

Jan 8, 1919

By C. H. Brehaut, W. N. Taylor, R. S. Douglas, H. A. Shannon

The name for this new method of mining is derived from a composition of Horizontal, Radial, Diamond, and the drilling is from raises. This method, worked out at Copper Mountain, B.C., is believed to be distinct in many features from other known methods. Geology The ore deposits of copper Mountain are related to the copper Mountain stock, which is an ideal example of the magmatic in in that it grades from a basic gabbro at the border to an almost pure orthoclase-pegmatite core. The "contact" ore bodies lie along the contact of the gabbro and an older complex of volcanies and sediment termed the "Wolfe Creek" formation. These older rocks, collectively referred to as greenstone, had been fractured prior to the intrusion of the stock and were highly metamorphosed during the intrusion. The "outlying" ore bodies are somewhat different in character, though a similar structural pattern prevails. It is believed that a deep-seated magma of which the Copper Mountain stock is a part has given off solutions that caused a partial graniti-zation of some of the volcanies. Mining problems are caused further by the presence of a series of soft barren dikes intersecting a great many of the ore bodies, which are about 30 ft. wide, strike north-south, and dip at a high angle to the east; and are further increased by the presence of four major faults, with a great many minor faults running at acute angles from them. Fault zones average 8 ft. in width, and consist of gouge and breccia. They strike northeast and dip steeply to the northwest. The faults cut through the ore zones and the dikes, and continue on into the gabbro. The general mine structure with two types of Ore bodies, bounded by weak walls and intersected by several series of soft barren dikes and major faults, indicated that a method of mining should be devised that would remove the ore at low cost with the least disturbance of the waste walls and dikes. , Theoretical Estimate of Stoping with the Diamond Drill After consideration of various methods, the most suitable one appeared to be horizontal drilling to break the ore in a manner similar to shrinkage stoping Drilling vertical holes or rings from a bench and breaking to an open slot was eliminated because the weak walls of ore, dike or waste would not permit this type of opening. It was then decided to drill either horizontal radial holes from a raise or parallel holes from a slot cut across the ore body. After discussion, the latter method was believed unsuitable, for the following reasons:

Jan 1, 1946

By W. C. Hittinger, J. McGlassan, J. W. Peterson

THIS paper describes the result of an investigation of the production of thin alloyed layers on a thicker substrate of pure germanium as one step in the manufacture of transistors.' The technique of alloying materials with semiconductors is a means of introducing small amounts of impurity elements in the alloyed regions of the crystal lattice of the semiconductor, the presence of which make possible the junction type transistor.2 Impurity elements are added which will produce regions having differing electrical resistivities and means of carrying current. Impurities are of two types: those which produce an excess of electrons (negative or n-type), and those which produce a deficiency of electrons (positive or p-type) in comparison to the pure semiconductor. The boundary between two such regions is designated a p-n junction. Elements in Group V of the periodic table, having five valence electrons, give rise to an excess of electrons when present substitutionally in the semiconductor lattice (usually germanium or silicon from Group IV). Similarly, elements in Group III create a deficiency of electrons. Germanium and silicon which are substantially free of impurities of either p or n-type are designated intrinsic (i-type) semiconductors. The usual junction ----trarnsistor has

Jan 1, 1958

By R. M. Keeney

Jan 1, 1915

Jan 1, 1961

By Simon D. Strauss

COPPER In terms of mining activity, copper is the leading nonferrous metal. It is true that in recent years the volume of aluminum consumption in the non-Communist world has exceeded the volume of copper consumption, but virtually the entire primary aluminum supply is derived from bauxite. On the average, only four tons of bauxite need be mined to produce a ton of aluminum. By contrast, the highest-grade, large-scale copper mines now in operation (those in the Congo) must mine at least 20 tons of ore to produce a ton of copper. In the United States an average of 150 tons of ore must be mined to produce a ton of copper. This does not take into account the huge amounts of waste overburden that must be stripped from the open-pit mines to account for their steadily rising share of the world's copper output. Copper epitomizes the economic problems of the mining industry in many ways. Its price is highly volatile, considering its great economic importance. It has been a tool of mankind longer than any other of the base metals-the dawn of history has been classified as "The Bronze Age." World Copper Production Although copper is mined in many countries, in recent years 70% of the non-Communist world production has come from six countries. Two of these are industrialized countries and are large consumers-United States and Canada. The other four are developing countries with very small domestic requirements-Chile, Zambia, Zaire, and Peru. Heavily dependent on copper exports to sustain their domestic economies, these countries find themselves oscillating between prosperity and depression with the changing levels of copper prices. In an effort to control their own destiny, in 1968 they formed an organization of copper exporting countries (CIPEC) which was designed to study copper markets and possibly to intervene actively in these markets. (When this chapter was being prepared, no actual steps along such lines had been taken.) Many of the leading industrialized nations are wholly dependent on imports for their primary copper supplies. These include West Germany, the United Kingdom, France, Italy, and many others. Japan, now the non-Communist world's second largest copper consumer, produces only 10 to 15% of its requirements from domestic mines. Although the bulk of the copper output is smelted in the country where it is mined, there is a limited international trade in copper concentrates. Canada, the Philippines, Australia, and Papua-New Guinea are significant exporters of copper concentrates; Japan, Germany, the United States, and Sweden are importers. However, this trade accounted for only about 10% of the non-Communist world production of copper during the decade of the 1960s.

Jan 1, 1976

By R. T. Gallagher, C. G. Brennecke

This paper is the result of a research program entered into cooperatively by the General Reinsurance Corporation and Lehigh University in January 1944. The research program was instituted to find a more positive method to determine the presence of hazardous roof conditions in mining operations. The co-authors, together with Mr. R. D. Currie, Engineer for the General Reinsurance Corporation, started working on the project in January 1944, first undertaking a library search; second, a preliminary study based on some existing equipment; third, the design of new and more suitable equipment; and finally, the field testing of equipment and methods. PURPOSE Any study of the accident statistics of mining operations will disclose the rather startling fact that approximately 50 to 60 per cent of all fatal underground accidents in the anthracite and bituminous mines are caused by falls of roof and coal, the metal and nonmetal mines showing only a slightly smaller percentage. Advancements in safety engineering have produced definite results in the decrease of accidents due to blasting, haulage, electricity, and explosions but no such decrease is shown in those caused by falls

Jan 1, 1946

By F. A. Schaufelberger

METAL can be recovered from a leach solution either indirectly by precipitation as a compound that is later reduced or directly by electrolysis, cementation, or chemical reduction, for example, with hydrogen. The widely used electrowinning processes suffer from the inefficiency of converting fuel to low voltage dc and from low current efficiency when complete recovery is attempted. With the batch hydrogen reduction methods outlined here, a unit of fuel converted to hydrogen in modern gas reform plants will make two to three times as much metal as can be obtained with electrolysis. With continuous hydrogen reduction, four to six times as much metal is obtained. Precipitation by reducing a metal salt solution with H, has been known for almost 100 years.' Commercial use of the process, however, awaited the research and development program initiated by Chemical Construction Corp. Within the last few years this program has brought about construction of commercial plants, listed on page 545. Ideal hydrogen reduction will precipitate a pure metal from a solution obtained by commercial leaching methods at a rapid rate without excessive temperatures and pressures. The metal precipitate will be of desired size and density, less than a percent left in the vessel being deposited on the wetted parts. The present discussion will outline Chemical Construction Corp.'s early development program and will discuss the chemistry and mechanics of reducing copper, nickel, cobalt, and cadmium from solution by H2. Work on selective reduction of nickel from cobalt has been described earlier.' The article is not concerned with precipitation of copper by disproportionation of cuprous solutions where yield is limited3 to 50 pet.* It does not discuss use of gaseous reducing agents other than hydrogen, such as SO2,4 which may lead to contamination with sulfur, or C0,5 which is considerably more expensive than hydrogen and produces a gaseous reaction product, CO2.† The article does not include use of other nongaseous reducing agents,7 which are far more expensive than CO. Also, notes on the history, engineering design, and performance of commercial plants have been given elsewhere.' It will be shown that a pure metal can be precipitated by reduction with hydrogen from solutions obtained by commercial leaching methods when the solution composition is controlled and proper acidity, proper metal ion concentration through controlled complex formation and hydrolysis, and adequate agitation for suspension of metal and for transfer of reducing gas are maintained. Reasonable temperatures and pressures are used which are less excessive than those used by previous workers, although they are maintained at above equilibrium values because of process kinetics.' It has also been found necessary to induce nuclea-tion and to control growth and agglomeration in order to get a powder product of suitable physical properties. Review of the Literature Muller, Schlecht, and Schubardt of I. G. Farben10 claimed a successive reduction of silver, copper, nickel, cobalt, and zinc from ammoniacal solution by applying progressively higher temperatures and hydrogen pressures. Metals produced by this technique were not pure, since no attempt was made to adjust the solution composition between the different reductions. It is doubtful that the zinc product contained any metallic zinc. The major contribution to the literature" was made by the Ipatiews,12 who prepared platinum, iridium, copper, nickel, cobalt, lead, tin, arsenic, antimony, and bismuth at often extreme conditions, up to the critical temperature of water (373ºC), at 1500 to 7500 psi, for as long as several days. Even cadmium and zinc were claimed to have been observed in trace quantities precipitated together with basic salts. In the early experiments solutions were not stirred. Extensive formation of oxides and basic salts occurred, probably long before sufficient hydrogen could be supplied in the unstirred liquid to decrease the metal concentration in solution by reduction. The importance of hydrogen pressure was

Jan 1, 1957

By H. S. Kalish, F. J. Dunkerley

Introduction and Previous Work THE determination of the low temperature tensile properties of tin and tin-lead alloys was initiated as part of an extensive research program on the phasial equilibria of tin binary systems below 13.2°C and the property changes associated therewith. A survey of the literature revealed that, although some room temperature tensile data were available for tin and a few tin-lead alloys, there existed no survey report of the low tcmPerature tensile properties of these alloys. Accordingly, the tensile data for tin and a series of pure tin alloys containing from 0.01 to 50 pet lead were measured at eleven temperatures horn — 196 to +20°C and are presented here in survey form. In addition to the importance of these tensile data as a preliminary to certain fundamental research, this information promises also to be of commercial importance because of the extensive use now being made of tin-lead solders in refrigeration and gas liquefaction equipment. Occasional failures of the solders in low temperature service have been attributed by some metallurgists to low temperature embrittlement, while others hold that failure results from the transformation of the tin-rich phase of the solder from the solid white (beta) to the powdered gray (alpha) form. From the data previously available in the literature, neither of these explanations can be completely corroborated. cohen and van Lieshout have estab-lished the beta to alpha tin transformation at 13,2°C and have shown that strain accelerates the transformation. Further, they showed that although I pct lead retarded the transformation, it was not eliminated. It will be pertinent, then, to note whether the beta to alpha transformation of the tin.rich phase will occur in a short-time tensile 'test. polanyi and schmid2 studied the tensile properties of tin single crystals at — 185°~ and report that tin is britlle at this tem-perature. In 1946, Kostenets3 reported that pure tin was brittle at —Ig6 and — 253°~, while lead remained ductile at both these temperatures. He also studied the tensile properties of tin-lead alloys containing from 10 to 75 pet lead at —253, —196 and + I~OC. The ultimate tensile strength increased more than two times in going from room temperature to — I96°C and about three times that value on further cooling to — 253 C- All the alloys were brittle at — 196'C except those containing more than 75 pct lead. Even at — 253'C, the 75 pct lead alloy retained 36 pet elongation in a 30 mm-ga. length. Creep is also an important phenomenon

Jan 1, 1949

By H. E. Mussey

When the American Institute of Mining Engineers visited the Birmingham district in May, 1888, the four Ensley furnaces (Fig. 1) then completed were referred to as monumental.' Their dimensions are givcn in Table 1. Mr. Gordon stated, with considerable satisfaction, that on the preceding day one furnace had produced 165 tons. The blast was

Jan 1, 1925

By Donald E. Grimes

In conjunction with Inland Steel&apos;s development of lead-bearing steels possessing improved machin-ability because of tellurium and/or selenium additions, it was decided to determine liquidus and solidus temperatures in the Pb-PbTe-PbSe sub-ternary system. With the exception of alloys in the PbTe-PbSe system, it is believed that no previous study of this subternary has been performed. Thermal analysis was employed in a general survey of the subternary. In addition to PbTe, PbSe, and pure lead, ten ternary compositions were selected at intervals of ten at. pct. Sixty-gram alloys were prepared by sealing an appropriate mixture of the elements in quartz crucibles with a central thermocouple-well under a vacuum of less than 10 p. All three elements were 99.999+ pct pure with only trace impurities detected by spectroscopic examination. After the alloys had been heated at least 20°C above the liquidus in a Kanthal furnace, cooling and heating curves were obtained. Two or more cooling curves were employed both for the determination of each alloy liquidus and for the solidus of those al- loys containing greater than 50 at. pct Pb. Cooling rates were 0.5° to 3.5°C per min during the 5 min immediately prior to the start or end of solidification. For those ternary alloys containing 50 at. pct Pb, the solidus was determined from heating curves. Temperatures were measured with a Pt/Pt-10 pct Rh thermocouple which was calibrated in the same apparatus against the freezing points of zinc (A. D. MacKay—99.999 pct), antimony (A. D. MacKay-99.999 pct), and copper (ASARCO—99.999+ pct) both before and after the experimentation. The only interruptions in the continuous strip-chart recording of the temperature occurred for brief periods at significant points of interest when direct readings were made with a Rubicon Type B potentiometer sensitive to * 1 µv. The average liquidus and solidus temperatures obtained in this investigation are listed in Table I together with probable errors based on the accuracy of the thermocouple calibration and the reproduci-bility of the data. No chemical analyses of the alloys were performed because the synthetic or as-charged compositions were felt to be reliable. The melting points obtained for PbTe (924.7° ± 0.7°C) and PbSe (1084.0° ± 0.6°C) compare favorably with recent findings of other investigators.&apos;-&apos; As indicated in Table I, both the liquidus and solidus temperatures increase as selenium replaces tellurium for a constant atomic percent lead. As a result, the ternary liquidus and solidus temperatures for a given percent lead lie between the corresponding binary temperatures published in the literature. It should be noted that those ternary alloys containing 50 at. pct Pb exhibit a relatively narrow liquid-plus-solid region (<80°C) when compared with alloys containing greater than 50 at. pct Pb. Alloys with 60, 70, or 80 at. pct Pb not only have a much wider liquid-plus-solid region (>500°C) but also exhibit considerably lower and approximately constant solidus temperatures which thus form a virtually isothermal solidus "plane" slightly below the melting point of pure lead (327.3°C). For these alloys

Jan 1, 1965

By Frank Wartman

RECENTLY Horace Freeman1 obtained a patent on a successful method of conducting a roasting procedure described as to general features by Carl Schnabel2 almost forty years ago. Essentially, the Freeman process of roasting consists in introducing the finely powdered sulfide mineral, suspended in air or any other suitable gaseous medium, into the upper portion of a heated chamber. The stream of suspended particles is directed vertically downward. A counter-current stream of gas introduced at the bottom of the chamber flows upward. The mineral particles are oxidized as they fall through the heated atmosphere of the chamber. All air required for the oxidation may be admitted either at the top or the bottom of the chamber, or may be divided between the top and bottom inlets in any desired proportion. Heat may be recovered by passing the gases leaving the furnace through a waste-heat boiler or other form of interchanger. In speaking of the results obtained in roasting pyrite, Freeman says:3 Steam yield from the boiler exceeds 1 pound of steam per pound of pyrite con-sumed, which pays the cost of operation of the burner. The oxide produced is in the form of fused particles or hollow shells of magnetite, containing about 65 per cent of iron. It contains the gangue material ordinarily produced in flotation concentrate, of course, but it is being found that most of this can be eliminated by magnetic separa-tion, and that the sulfur content, as consistently produced, is below 0.2 percent. This material is especially interesting as a high-grade iron ore, free from phosphorus and low in sulfur. It may be sintered or briquetted. It is even more interesting as a raw material for sponge-iron production, to be directly smelted in electric furnaces without the usual cooling of the iron powder and magnetic separation between the reducing kiln and the electric furnace.

Jan 1, 1933

By C. K. Stoddard, R. G. Knickerbocker, E. T. Leidigh, R. R. Lloyd, K. L. Mattingly

During July 1941, a study was initiated at the Boulder City Experiment Station of the Bureau of Mines on proposed methods for the production of magnesium metal. The major emphasis was placed upon development of a process that required minimum reliance upon the sale or utilization of by-products to meet economic competition from processes already in operation. It was felt that only through the development of such a process could the nation&apos;s vast resources of dolomite and low-grade magnesite that are contiguous to large blocks of firm power be properly utilized. During the course of exploratory tests on electrolytic and electrothermic processes, it was noted that fused magnesium chloride would dissolve appreciable quantities of magnesium oxide in the presence of small amounts of boric oxide. The use of such a solution in an electrolytic cell employing a graphite anode and a steel cathode caused the deposition of magnesium at the cathode and the evolution of carbon oxides at the anode with minimal amounts of chlorine The original results were sufficiently encouraging to justify further investigation on an enlarged scale, since the process seemed to present advantages over other proposed processes.1,2 for the direct use of magnesium oxide in a fused chloride electrolyte. When work oil a larger scale was initiated it was found that the addition of boric oxide to the electrolyte resulted in dispersion of metal and constantly decreasing current efficiency. However, by this time solubility studies had shown that magnesium oxide was sufficiently soluble in magnesium chloride melts containing no boric oxide to effect the same anode reactions, and development work was continued. Over two years of development work have been carried out, and considerable work remains to be done. It is desired to emphasize the fact that many of the difficulties met require a long period of continuous operation before they become serious enough to affect operation of the cell. ACKNOWLEDGMENTS This paper is one of many reporting on various aspects of the Bureau of Mines&apos; program initiated in August 1939 by passage of the Strategic Minerals Act the scope of which was greatly expanded by subsequent legislation. Some of these papers are published as war minerals reports. others as bulletins, technical papers, reports of investigations

Jan 1, 1949

By Paul Foote

The temperature of a material may be ascertained by measurement of the intensity of the radiant energy it emits. This measurement may refer to the radiation of all wave lengths emitted by the material, or, if the material is glowing, the measurement may refer to the visible light emitted, or to the radiation in n very restricted portion of the visible spectrum. In general, the intensity of radiation depends not alone upon the temperature of the source, but, also upon its nature. Thus, glowing carbon appears to the eye about three times as bright as glowing platinum, at the same temperature. This is technically expressed by saying that the emissive power or emissivity of carbon is about three times that of platinum. A material having the highest theoretically possible emissivity is known as a "black body;" it is customary to assign a numerical value of 1 to the emissivity of a black body. A black body is experimentally realized by uniformly heating a hollow enclosure and observing the radiation coming from a small opening in the wall. The intensity of radiation emitted from this opening depends only on the temperature of the walls, and not on the material of which they are constructed. If E is the emissivity of any non-transparent material and R is its reflection coefficient, it can be shown that E + R, = 1. If a material having an emissivity of, say, 0.40, and hence a reflection coefficient of 0.60, is placed inside a black body it becomes indistinguishable from its Surroundings, because the total intensity of radiation leaving the material is the same as that emitted by the black body. While the material actually emits only 40 per cent of the intensity of a black body at the same temperature, 60 per cent. of the radiation falling upon it from the walls of the enclosure is reflected. However, if the material is removed from the black body and placed in the open air, the reflected intensity is no longer present and the object appears but 40 per cent. as bright as a black body at the same temperature.

Jan 8, 1919

By the courtesy of Sir Robert Hadfield, we have received the fol¬lowing communication relating to the development and encouragement of science and research in Germany at present. These statements have been translated by Sir Robert from various German sources, and are presented here as an indication of what Germany is doing not only to further her military power, but also to prepare for the period of trade rehabilitation to which she is looking forward after the close of, the war. KAISER WILHELM TRUST FOR PROMOTION OF WAR SCIENCE The Kaiser has approved the foundation of a Trust with the name given above. The aim of the Trust is to further the development of scientific and technical aids to warfare, by uniting the scientific and the military forces of the country for work together. The scientific Work is to be carried on by the following technical committees (or commissions) (1) Committee for the chemical raw materials, for the production of munitions-manufacturing materials. (2) Committee for chemical war materials (powder, explosives, gas, and the like). (3) Committee for physics, including ballistics, telephony, telegraphy, determination of targets and distances, measurements, and the like. (4) Committee for engineering and communication. (5) Committee for aeronautics. (6) Committee for obtaining and preparation of metals.

Jan 8, 1918

By Robert Pring

IN addition to the humanitarian aspects of a dust-control program, certain economic benefits are becoming more fully recognized and now furnish a greater incentive to the mill operator to eliminate the dust from his plant. It is well known that a favorable working environment promotes increased efficiency and improves the morale of em-ployees, with a consequent decrease in labor turnover rates. One progressive mining company estimates its direct and indirect labor turnover costs at from $40 to $50 per man; for skilled labor, such as machine operators, the cost may approach $100 per man. While these figures may not be typical of every plant, they do indicate a potential savings in operating costs. Dust signifies waste; its elimination de-creases maintenance costs of mechanical and electrical equipment; its recovery is often justified from the standpoint of values contained in the collected material, although in large-scale milling operations handling low-grade ore this may not be an important factor. Perhaps the most significant trend in industrial sanitation is that dust-control equipment and procedures are becoming recognized as integral parts of the mill flow-sheet. Exhaust ventilating systems are now afforded equal care in design and mainte-nance to that given other machinery more closely related to the process,

Jan 1, 1940

By W. E. Pugh

The object of the following is to discuss a few of the problems encountered in the practical field application of reflection seismology. Very little has been published on this phase of the work and it is to be hoped that discussions will be presented by many seismologists who have met with these problems in the field. No attempt will be made to discuss the general principles of reflection prospecting, nor to outline the general field procedure. These phases have been presented more or less in detail in previous publications1 while economy of space and time prevents their being repeated or amended here. If, in the following pages, some criticism is offered of those who have already given their time and efforts to present valuable papers on reflection shooting, we trust that it will be accepted in the constructive light under which it is offered. We do not wish to give the impression that the following paragraphs represent ultimate achievement in field procedure; they are presented more to illustrate methods we have found satisfactory thus far. We believe that the following three subjects are inexorably linked with the continued future successes and more widespread use of the reflection method which, at the present time, is the most

Jan 1, 1934