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By Luis N. Henriquez

One form of encouragement for the small copper mining sector in Chile has been the construction and management of custom mill facilities to process the ore. The paper describes an economic analysis framework for the evaluation of government custom milling opportunities. Feasible mill locations and capacities within a region are selected and the infrastructure and milling costs associated with each combination of location and capacity are assessed. For each combination, the economics of developing and operating known copper deposits in the region is evaluated, and an optimum cut-off grade and mine capacity is selected for the deposits which justify development. Since the total ore supply from mines in the region may exceed a particular custom mill capacity, mine development is scheduled to optimize the economics of the mill facility. Finally, the best custom mill location and capacity is selected on the basis of overall costs and benefits. A copper mining region in northern Chile is used to illustrate the application of the model. A mobile mill approach is examined and compared with the fixed location mill alternatives. Results are analyzed as a function of copper price.

Jan 1, 1977

By E. L. Vickers

Over the years, the pure theorist in economic analysis has accumulated a formidable array of facts in bringing his subject matter under control. Business managers and mining engineers are aware of the theorist's weapons, but the question of applying them to the mastery of practical problems seems hardly feasible, especially in view of the almost innumerable variables plaguing the everyday scene in the mining enterprise. One such sophisticated tool of long-standing in the theorist's arsenal is marginal analysis. Equally long-standing for the operating company and valuation engineer is the problem of defining the cut-off grade the point below which a mineral re- source ceases to be economically amenable to extraction. In other words, what part of a mineralized body of rock is ore and what is waste?

Jan 6, 1961

By Fredrick Laist, J. P. Cooper

In the spring of 1931 an experiment was made at Anaconda with a small reverberatory furnace, with which was combined a roasting shaft. The arrangement is shown in the accompanying drawing (Fig. 1) and requires but little explanation. The general idea was to roast flotation concentrates, mixed with the proper fluxing materials, by dropping them down a heated shaft, from which the calcines would enter the smelting zone of the reverberatory furnace through an opening in the roof. The hearth of the reverberatory was 3 ft. wide by 21 ft. long. The roasting shaft was 3 ft. square inside and had an effective height of about 20 ft. The reverberatory furnace was arranged so that it could be charged either directly through the roof with regular hot calcines, in the usual manner, or by means of the shaft, at the top of which were a feeding arrangement by which cold flotation concentrates, suitably fluxed, could be fed continuously and a pipe through which cold air was blown in. Means were provided for distributing the feed over the cross-section of the roasting shaft. At first a mechanical arrangement was used but later it was found that a simple cone served the purpose equally well and gave less operating trouble. On account of the small size of the equipment, it was realized that absolute capacity and fuel consumption figures would mean but little. It was not to be expected that ratios comparable to those obtained in large furnaces could be gotten, and the only way in which any idea could be obtained as to the possibilities of the combination furnace was to run it in parallel with the reverberatory furnace charged in the usual manner and operating without the shaft. The results of such parallel runs are given in Table 1. The amount of oil burned in the reverberatory was purposely maintained at substantially the same rate during both runs in order that the benefits resulting from the shaft might be gaged. It was expected that the shaft would considerably increase the capacity of the reverberatory and that a better fuel ratio would be obtained on account of the high temperature at which the calcines would enter the

Jan 1, 1934

LINN BRADLEY, H.' D. EGBERT and W. W. STRONG (communication to the Secretary*).--In the discussion of the paper, a request was made for a further explanation of the curves given on Chart I. In preparing the curves given on this chart, a typical blast-furnace top gas having the following composition by weight was assumed: Per Cent. C02 21.00 CO 24.00 Hz 0.25 CH4 0:25 N2 54.50 For any given top-gas temperature, Curves A, B, C, D, and E indicate in British thermal units the sensible heat lost in cooling the top gas to 60° F. by wet-cleaning methods. Top-gas temperatures are plotted as abscissae, sensible heats above 60° F. in British thermal units are plotted as ordinates, and separate curves are drawn for top gases carrying various amounts of moisture. For any given stove exit-gas temperature, curves A1,-B1, C1, D1, and E1, indicate in British thermal units the sensible heat carried out of the stoves by the moisture which is left in the top gas when it is dry-cleaned and enters the stoves hot. This moisture is removed when the gases are wet-cleaned and the sensible heat which it carries out of the stoves is therefore saved. As before, separate curves are drawn for top gases carrying various amounts of moisture. The curves in Fig. 1, therefore, indicate graphically how much more sensible heat is conserved by cleaning the top gases by the dry-hot method than is conserved by cleaning the top. gases by a cold-wet method and thus removing the greater part of the moisture carried by them. They also show of how little moment it is from a heat conservation standpoint whether or not the moisture carried by the top gases is removed before they enter the stoves. That wet cleaning secures the removal of this moisture and is thus to be recommended from a heat conservation standpoint is an argument often advanced by advocates of wet cleaning. The curves of Fig. 1 show how fallacious such an argument is.

Jan 6, 1917

By Chester N. Truax

Still another shadow was cast over coal's largest market-the electric utilities-when President Johnson signed into law the Federal Clean Air Act of 1967. Air pollution-sulfur reduction-was thus brought into sharper focus as one of the central problems of the coal industry. Industry executives testified in both Houses of Congress to enable the lawmakers to develop a workable and economic law. The new legislation calls for the Secretary of Health, Education and Welfare to establish air control regions. After the regions are outlined the Department will publish air quality criteria on pollutants. Anticipating this legislation, the coal and utility industries have for the last several years been involved in extensive research programs to develop solutions to the air pollution problem. Even though the coal industry has been under strong attack for its part in adding contaminants to the atmosphere, it is by no means the major contributor.

Jan 2, 1968

By F. M. Leonard

Churn-drill hole sludge samples have proved their reliability at Cananea

Jan 5, 1951

By G. W. Jones

THIS paper describes experiments in which eight test samples of gelatin dynamite were fired in three different types of apparatus and the quantity and composition of the gaseous products of detonation determined. The special dynamites were so prepared that the oxygen balance of the samples varied from -35.0 to +6.0 g. per 100 g. of explosive, including the wrapper. By means of this graded series of explosives, the relation between oxygen balance and gaseous products of detonation could be studied explicitly. The effect of varying oxygen balance on explosive strength has been discussed in another paper.1 The apparatus employed in the work described in the present paper included (1) the Bichel gage, a steel bomb of 15-1. volume; (2) the Crawshaw-Jones confined detonation apparatus, a steel cannon from which the explosive is fired into a pipe of 90-1. volume; and (3) the Hercules tank, an apparatus in which the explosive is confined in a quartz block which is placed in a steel tank of about 4500-1. volume. A full description of the apparatus is given later. VARIABLES AFFECTING COMPOSITION OF DETONATION PRODUCTS The character of the detonation products of commercial explosives is governed in part by the same factors that affect the combustion products from explosive mixtures of air with gases or vapors. In either case, combustible materials-namely, carbon, hydrogen, and sometimes sulfur-are present and combined variously. In an exploding gas mixture the combustibles are oxidized by oxygen in the admixed air, whereas with explosives the necessary oxygen is provided by oxygen-carrying materials in the explosive ingredients.

Jan 1, 1928

By D. W. Duncan, A. Bruynesteyn

An ore containing chalcopyrite was microbiologically leached in 6 ft columns at particle sizes ranging from -2 +1 ½ inches, to -3/8 + 3/16 inches. The rate of leaching increased exponentially as the particle size decreased. The controlling factor was the active leaching volume made up of the particle surface area and the depth of penetration of the bacteria and leach liquor into the particle. This volume became an increasingly larger part of the total volume as the particle size decreased. The sample under test leached poorly at larger particle sizes and it was calculated that under commercial conditions, it would produce at best a pregnant solution containing 100 mg/l (0.2 lb/ ton) of copper per 100 ft of dump height.

Jan 1, 1974

By Louis D. Huntoon

SHORTLY after publication of the article in the July, 1924, issue Of MINING AND METALLURGY, entitled "Canada as a Gold Producer," requests were received to determine the ownership of production. Advices have also been received that considerable discussion has taken place on the same questions both in Canada and Great Britain. The author is indebted to R. H. Coates, Dominion Statistician, and George C. Bateman, Secretary, Ontario Mining Association, for the following figures and takes this opportunity of expressing his appreciation. There have been no statistics compiled as to ownership of production. Statistics were compiled as of Dec. 31, 1921 relative to the distribution of stocks, bonds and "other securi¬ties" in industrials, agriculture excepted, throughout the Dominion, and "distribution of ownership of securities issued by mining companies incorporated and operating in Ontario" for the same year. Stock registration does not necessarily represent actual ownership' as large blocks may be endorsed and not transferred; neither does registration actually represent production. When the charts are studied individually and collectively one cannot help but be impressed with the fact .that in the mineral industry of Ontario and the Dominion at large, Canadian registration predominates, the United States registration is about half that of Canada, and Great Britain is about half that of the United States. When the nickel-copper industry is excepted the British registration falls to a very low percentage. Since Dec. 31, 1921, British capital has commenced to flow into mining enterprises in Ontario and it has been already rewarded by the discovery of valuable ore deposits.

Jan 1, 1925

By Philip Drinker

IN THE mining and metallurgical industries, numerous problems arise requiring determinations of solid and of liquid particles suspended in air. Frequently, these problems are of local interest and involve purely economic or operating difficulties; on the other hand, toxic effects from the inhalation or the ingestion of substances suspended in air may be a matter of concern. For checking up process improvements or for determining ventilation efficiencies in problems of this general nature, various methods have been proposed. Although simpler methods are often satisfactory, precipitation combines several desirable features that other methods lack. This paper is, therefore, devoted to a discussion of portable alternating-current precipitators applicable to the quantitative determination and microscopy of dusts, fumes, and smokes in air. Small particles suspended in gases, such as air, are referred to in the literature as aerosols or suspensoids. Of these terms, suspensoids appears to be preferable as being more nearly in keeping with words in everyday use. In problems involving air pollution by small, particles-by suspensoids-it is convenient to distinguish three broad classes based on the size, the degree of dispersion, and the method by which the particles become suspended in the air. Dusts.-Particles or aggregates of particles, 150 to 1 micron in diameter, that are thrown into the air by mechanical agencies are termed dusts. Examples are silica, talc, cement, organic dusts such as hard rubber, starch, and cocoa; flocculated fume and smoke products. Fumes.-Particles, 0.2 to 1 micron in diameter, formed from chemical or physicochemical reactions are known as fumes. Examples are ammonium chloride, lead and mercury, zinc and magnesium oxides, fogs, and acid mists.

Jan 3, 1925

By F. A. Kjellin

The problem of smelting steel by electricity attracted years ago the attention of inventors, and as early as 1879 C. W. Siemens constructed his first furnace for the smelting of metals, especially steel. His furnace was of the arc type in which the voltaic arc was formed between a carbon electrode and the metallic content of a crucible, the length of the arc being regulated by an electromagnetic device. This electric furnace, as well as others of similar construction, has the inconvenience that the source of the heat—the voltaic arc—possesses a temperature of 3,700' C., which is much

Jan 1, 1904

By Louis Jordan

THIS paper presents in an abbreviated form the chief points of interest in an investigation of the tarnish-resistant qualities of silver alloys, an investigation which has been carried out as a joint research by the Bureau of Mines and the Bureau of Standards and will later be reported in detail in an official publication from these bureaus. In 1923 a Commission of Gold and Silver Inquiry was created by a Resolution of the U. S. Senate to study the causes of the depressed condi¬tion of the gold and silver industry. In cooperation with this commission the Bureau of Mines made a preliminary survey to determine in what ways, if any, it might be possible to increase the uses of silver. One of the possibilities indicated by this survey was the development of silver alloys which should be non-tarnishing, or at least less-tarnishing, than the usual sterling silver (copper-silver). The preparation of a rather wide variety of silver alloys and the determination of their behavior under accelerated tarnish tests in the laboratory was therefore undertaken by the bureaus, of Mines and Standards as a joint investigation. PREVIOUS WORK ON TARNISH RESISTING SILVERS At about the time this work was undertaken interest in tarnish-resisting silvers was rather keen due to announcements from England that there had been developed a new silver alloy, "Silanca," which was resistant to tarnish. It was even frequently described in the popular press as "non-tarnishing." A few samples and several analyses of "Silanca" which were available indicated that it was an alloy of sterling fineness, that is, it contained about 93 per cent. of silver, with approximately 4.5 per cent. of antimony and either cadmium or zinc, or both, to make the remaining 2.5 per cent.

Jan 1, 1927

By Raymond Mancha

TO determine the optimum inside dimension of an airshaft, it is necessary to strike the proper balance between the cost of power for air friction and turbulence losses within the airshaft, on the one hand, and the cost of sinking the airshaft, on the other. An airshaft larger than necessary is extravagant because the increased amortization rate exceeds the reduction in power cost. Conversely, an airshaft smaller than is needed wastes more power than can be justified by the corresponding reduction in amortization rate. The airshaft power is a function of the air volume Q cu. ft. per min. and the air- pressure drop p in. water gauge across the airshaft The airshaft pressure drop is calculated by the formula: [ ] wherein R is the air-friction coefficient for the portion of the airshaft 1 ft. deep, 0 ft. in perimeter and A sq. ft. in area, when passing an air volume of Q cu. ft. per minute. The airpower w kw. dissipated within the airshaft is computed by the formula: [ ] With a combined over-all unit efficiency of the fan and drive of E per cent, the air- shaft power requirements become [ ] There are 8760 hours per year, so with energy at I cent per kilowatt-hour the annual cost per kilowatt for continuous operation is $87.60; therefore, with energy at C$ per kw-hr. the annual airshaft power cost MI dollars per year becomes: [ ] which, expressed by the component parts, becomes : [] The amortization rate a dollars per year per dollar invested includes both depreciation and interest on the investment. These in turn involve the expected useful life of the airshaft and available monetary interest rate. For the purpose of this discussion the cost of airshaft sinking is assumed to comprise a fixed move-in charge Y dollars, which covers the cost of transporting, erecting and removing the shaft-sinking equipment and is independent of the air- shaft size. Also, it is assumed that the cost of shaft lining, if any, is fixed at $X per cu. yd. of lining material and that excava-

Jan 1, 1946

By D. D. Dunkin

SANDSTONE has been prepared for glassmaking purposes, and marketed from the White River Valley in-Arkansas at Guion, Izard County, since about 1910-soon after the completion of the White River Branch of the Missouri Pacific R. R. Co. Until 1921, operations were somewhat spasmodic and ended in many failures. In that year a plant was built by the Silica Products Co., Inc., and since that time the operation has been continuous and steady. The land is held under leases, covering about 30 sq. mi. of the best sandstone adjacent to the railroad. Most of the product is shipped to glassmakers. GEOLOGY The St. Peter sandstone is rather widely distributed in north central Arkansas and- is exposed most prominently in outcrops along the slopes of the White River Valley and its tributaries that form the division between the Boston Mountains to the south and the Salem Plateau of the Ozarks to the north. It is of Ordovician age and is generally underlain by Cotter dolomite and capped by Plattin limestone, except in the vicinity of Bellefonte and Everton. At those places, it is a massive cross-bedded, laminated, saccharoidal sandstone; underlying it is the Everton limestone and overlying it, the Joachim magnesium limestone. The sandstone at Everton contains numerous phosphatic pebbles and inclusions of sandy limestone. The irregularity of cross-section, the evidence of sorting action and the phosphatic pebbles appear to be indications of secondary deposition.

Jan 1, 1928

By D. H. Newland

New York has a small but not insignificant place in the oil and natural gas industries of the United States. It has had a continuous record as an oil producer since 1872, with an aggregate yield of about 104,000,000 bbl. The reported output for 1935 was 4,237,000 bbl., a gain of more than 10 per cent for the year and a total that has been exceeded only in the early period of flush production half a century ago. The industry has been steadily building up since 1920 with the successful practice of the water drive, which has given a new lease of life to pools that had been practically drained of oil recoverable by pumping. An additional output of 2000 bbl. or more per acre is being procured by this method. Altogether the fields in New York State cover about 55,000 acres. Their limits are well defined and it is unlikely that they will be extended in the future, although there is some prospect of finding additional supplies by deeper drilling. The oil from New York is all classed as Pennsylvania grade, for which the recent price has been about $2.50 a barrel. It is refined at Olean, Wellsville and Bolivar, in the oil district, and partly in Pennsylvania refineries. Exploration for natural gas, outside of the established districts, was considerable during the year. Altogether 59 wells were drilled, distributed over 13 counties, of which 33 were listed as producers and 26 were dry. At the close of the year, 13 wells were in process of drilling. The 33 producing wells had a combined estimated flow of 278 million cubic feet per day. The best results were obtained from exploration in Allegany County, where out of eight wells drilled to the Oriskany sandstone five were successful and showed a combined open-flow capacity of 107 million cubic feet. The Oriskany sandstone was encountered at a depth of 4500 to 4900 ft. In Steuben County, next east of Allegany County, two out of seven wells to the Oriskany proved productive, and one of these, in the town of Greenwood, on the Watkins structure, was probably the largest that has so far been opened in the state, with a reported yield of 35 million a day. In the central part of New York interest was awakened by the activity shown in exploring for gas in the Trenton limestone, in Camden, Florence and Rome townships, Oneida

Jan 1, 1936

By D. H. Newland

New York has a small but not insignificant place in the oil and natural gas industries of the United States. It has had a continuous record as an oil producer since 1872, with an aggregate yield of about 104,000,000 bbl. The reported output for 1935 was 4,237,000 bbl., a gain of more than 10 per cent for the year and a total that has been exceeded only in the early period of flush production half a century ago. The industry has been steadily building up since 1920 with the successful practice of the water drive, which has given a new lease of life to pools that had been practically drained of oil recoverable by pumping. An additional output of 2000 bbl. or more per acre is being procured by this method. Altogether the fields in New York State cover about 55,000 acres. Their limits are well defined and it is unlikely that they will be extended in the future, although there is some prospect of finding additional supplies by deeper drilling. The oil from New York is all classed as Pennsylvania grade, for which the recent price has been about $2.50 a barrel. It is refined at Olean, Wellsville and Bolivar, in the oil district, and partly in Pennsylvania refineries. Exploration for natural gas, outside of the established districts, was considerable during the year. Altogether 59 wells were drilled, distributed over 13 counties, of which 33 were listed as producers and 26 were dry. At the close of the year, 13 wells were in process of drilling. The 33 producing wells had a combined estimated flow of 278 million cubic feet per day. The best results were obtained from exploration in Allegany County, where out of eight wells drilled to the Oriskany sandstone five were successful and showed a combined open-flow capacity of 107 million cubic feet. The Oriskany sandstone was encountered at a depth of 4500 to 4900 ft. In Steuben County, next east of Allegany County, two out of seven wells to the Oriskany proved productive, and one of these, in the town of Greenwood, on the Watkins structure, was probably the largest that has so far been opened in the state, with a reported yield of 35 million a day. In the central part of New York interest was awakened by the activity shown in exploring for gas in the Trenton limestone, in Camden, Florence and Rome townships, Oneida

Jan 1, 1936

By George Burgess

1. Introduction.-THE methods of production of sound steel ingots have been described in several papers read recently before this Institute. It was thought by Director Stratton, of the U. S. Bureau of Standards, and ourselves to be of sufficient interest and importance, as a further contribution to this subject, to compare the properties of rails rolled in one mill according to American practice, from several types of ingot of substantially the same chemical composition but cast by several processes; and to compare in considerable detail the properties of an ingot manufactured by the Hadfield special-feeding process and one of the usual type for rolling into rails. We are greatly indebted to F. W. Wood, President of the Maryland Steel Co., who made this investigation possible by kindly placing his rail mill at our disposal; and he and his associates at Sparrows Point did everything possible to make the experiment a success, including the execution of several of the tests and analyses. 2. Classification and Manufacture of Ingots.-Of the ingots used in this investigation, eight were made in Sheffield and furnished by Sir Robert Hadfield, and one was made and furnished by an American steel company,' as a comparison ingot, and was supposed to represent the usual type of ingot from which rails are made.

Jan 2, 1915

By Robert Peele

TWO outstanding members of the Institute will be honored at the Annual Meeting this month: Robert Peele, who will accept his election to the small group of Honorary Members; and Clinton Hoadley Crane, president of the St. Joseph Lead Co. and William Lawrence Saunders Medalist for 1936. Eminence in the profession character, interest in Institute activities, and general recognition as a gentleman and a friend by so many people, have contributed to the election of Professor Peele. The Saunders Medal is for "achievement in mining." In awarding it to Mr. Crane the citation reads "For distinguished achievement in the successful development and operation of low-grade lead mines."

Jan 1, 1936

By W. J. Reagan

All of the material described in the following paper is within the following specifications: carbon, 0.50 to 0.85 per cent; phosphorus and sulfur, 0.04 per cent max.; manganese, 0.60 to 0.85 per cent; silicon, 0.20 to 0.30 per cent. Steels with much lower carbon contents can be handled in exactly the same manner. One of the first things necessary to basic open-hearth slag control is uniformity of charge, particularly as to the silicon content and the percentage of lime charged. Our past work has shown that the silicon content of the charge is more important than the carbon content in determining the carbon at which a heat will melt. We have found that by keeping the silicon content of the charge about 0.60 to 0.65 per cent, and with a lime charge of about 7 per cent (limestone equivalent), our heats melt sufficiently high in carbon to allow a moderate feed of ore and the slag will be of low iron oxide content. In making a heat of 0.75 carbon steel we endeavor to have the heat melt at about 1.20 per cent carbon. The iron oxide content of the finishing slag depends upon the final phosphorus desired; for a given ratio of lime-silica in the slag, the lower the phosphorus desired in the final steel, the higher the iron oxide content of the finishing slag must be. By reducing the lime charge to a minimum, the heats melt faster, and by keeping the silicon content at the desired figure the heats melt with a high SiO2 slag, which has been shown in previous work to give a low iron oxide slag. In most of our work, using a 180,000-lb. charge and with basic pig containing about 1.20 per cent silicon, we use a lime charge of 8500 lb. of limestone and 2000 lb. of burnt lime. The pig charge is about 48 per cent of cold pig, and the charge contains a large percentage of works scrap. This causes a heat to melt with about 1.20 to 1.30 per cent carbon, for a heat that will finish about 0.75 per cent carbon. This gives a heat that will need a feed of about 2000 lb. of ore, and also a slag with an FeO content of about 4 to 5 per cent at melting. The additional FeO obtained from the ore addition will bring the FeO in the slag at tapping to about 6 to 7 per cent. It is necessary to carry quite a fluid slag to prevent pickup of FeO, as a too heavy slag causes FeO to build up in it, giving a finishing slag with a greater FeO than is desired. By adjusting the lime charge of a basic open-hearth heat, a very sensitive adjustment of the slag may be obtained. The figures in Table 1

Jan 1, 1935

By W. J. Reagan

All of the material described in the following paper is within the following specifications: carbon, 0.50 to 0.85 per cent; phosphorus and sulfur, 0.04 per cent max.; manganese, 0.60 to 0.85 per cent; silicon, 0.20 to 0.30 per cent. Steels with much lower carbon contents can be handled in exactly the same manner. One of the first things necessary to basic open-hearth slag control is uniformity of charge, particularly as to the silicon content and the percentage of lime charged. Our past work has shown that the silicon content of the charge is more important than the carbon content in determining the carbon at which a heat will melt. We have found that by keeping the silicon content of the charge about 0.60 to 0.65 per cent, and with a lime charge of about 7 per cent (limestone equivalent), our heats melt sufficiently high in carbon to allow a moderate feed of ore and the slag will be of low iron oxide content. In making a heat of 0.75 carbon steel we endeavor to have the heat melt at about 1.20 per cent carbon. The iron oxide content of the finishing slag depends upon the final phosphorus desired; for a given ratio of lime-silica in the slag, the lower the phosphorus desired in the final steel, the higher the iron oxide content of the finishing slag must be. By reducing the lime charge to a minimum, the heats melt faster, and by keeping the silicon content at the desired figure the heats melt with a high SiO2 slag, which has been shown in previous work to give a low iron oxide slag. In most of our work, using a 180,000-lb. charge and with basic pig containing about 1.20 per cent silicon, we use a lime charge of 8500 lb. of limestone and 2000 lb. of burnt lime. The pig charge is about 48 per cent of cold pig, and the charge contains a large percentage of works scrap. This causes a heat to melt with about 1.20 to 1.30 per cent carbon, for a heat that will finish about 0.75 per cent carbon. This gives a heat that will need a feed of about 2000 lb. of ore, and also a slag with an FeO content of about 4 to 5 per cent at melting. The additional FeO obtained from the ore addition will bring the FeO in the slag at tapping to about 6 to 7 per cent. It is necessary to carry quite a fluid slag to prevent pickup of FeO, as a too heavy slag causes FeO to build up in it, giving a finishing slag with a greater FeO than is desired. By adjusting the lime charge of a basic open-hearth heat, a very sensitive adjustment of the slag may be obtained. The figures in Table 1

Jan 1, 1935