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By P. S. Bagga, P. T. Luckie

Liberation (the process of destroying the interlock between unwanted materials, such as mineral matter and pyrite, and coal) is one of the most important precursors to the benefication of raw coal in order to produce high grade marketable coals at economical recovery levels. Liberation is achieved usually by comminuting the raw coal. However, because of the significant interaction between the production of fine particles to achieve liberation and the cost of separating fine particles, the coal industry needs a method projecting the change in washability with size reduction. Such a projection can be combined with size reduction and separation simulators in order to examine completely beneficiation circuitry to produce coals of stringent specification. This paper presents the development of an appropriate liberation model for coal and its solution by Monte Carlo simulation to predict the expected washability of the raw coal as a function of comminution. It includes model validation with a known binary mixture as well as with a known teritary mixture.

Jan 1, 1983

By Elmer W. Pehrson

NINETEEN FORTY-SIX was an eventful year for the mineral industries. Perhaps the most significant development was the socialization of industry in Great Britain, initiated in 1945 but carried to fruition in the coal industry in 1946. On Jan. 1, 1947, management of the coal industry will be vested in a National Coal Board, responsible to the Ministry of Fuel and Power. A sum of £164,660,000 has been provided to compensate private owners for assets transferred to the Board. The British coal industry has been a problem for many years. Production has declined to a point where serious shortages of fuel for domestic needs have developed. Exports have dwindled to a small fraction of the previous trade. Costs have increased greatly, and quality has deteriorated. The industry's physical plant has not kept pace with the rapidly mounting wage scales in recent years. Some claim that the best and most accessible coal reserves of Britain are heavily depleted. The industry has been harassed by difficult labor problems, including bad morale among the workers and a shrinking labor force.

Jan 1, 1947

After a three-year period characterized by inflation, recession, depressed metal prices, lack of demand, enormous world inventories, and rapidly escalating costs, the Canadian mining industry is showing welcome signs of recovery. A rise in world metal prices and particularly strong demand for gold, uranium, and coal have stimulated the industry in early 1979. In this atmosphere of growing optimism, over 3000 mineral industry executives, economists, geologists, and mining and metallurgical engineers convened in Montreal, April 26-29, for Canada's largest mining convention, the Annual General Meeting of the Canadian Institute of Mining and Metallurgy.

Jan 6, 1979

By A. T. Shurick

THE NRA Administrator's casual reference to the coal code as the next "pineapple" to be fixed was a conservative estimate of his job. This thorny and adamantine morsel now looms as a critical test of NRA. A failure in coal supplies would have the gravest potentialities in the Administration's program at this time. And the loss of prestige from a breakdown of the enforcement machinery in this initial large-scale test of strength would accentuate the incipient indications of insurrection in other directions. General Johnson has had a difficult task. It involves problems festering for a quarter of a century. A succes¬sion of Presidents have been glad to tide over their respective regimens with inconclusive expedients; they have been baffled by the complexities of the technical angles and hopelessly irreconcilable concepts of powerful conflicting interests with large issues at stake.

Jan 1, 1933

Jan 1, 1967

Jan 1, 1967

TO THE BOARD OF DIRECTORS OF AMERICAN INSTITUTE OF MINING AND METALLURGICAL ENGINEERS Gentlemen:-I have the honor to present the following, report for the calendar year 1920. The activities which seem to call for special comment are: THE NEW FORM OF MAGAZINE MINING AND METALLURGY appeared every month during the calendar year and has been developed until it contains some ten departments. It has brought forth more commendatory letters than have been received at headquarters on any other subject throughout the year. Less than a dozen letters unfavorable to the change have been received, and the indications are that the magazine has met a want deeply felt, especially by members distant from headquarters. The technical papers printed by the Institute are published in abstract in the magazine and opportunity is given to members who desire them to receive full copies of any or all papers published. The Bound Volumes, as usual, contain all the papers in full and discussions thereof. FINANCES The greatly increased cost of paper and printing has put a tremendous burden on the Institute's finances, since the dues of $12 per year are only 20 per cent. greater than the members paid when the Institute was founded forty-nine years ago. This has resulted in a temporary deficit, similar to that encountered by many of our sister engineering societies. The fact that our Institute has lower dues and gives more in the way of publications to its members than any other of the national engineering societies has rendered the situation more difficult for us. MEETINGS The Annual Meeting in New York, the Field Meeting in the Lake Superior District, the meeting of the Petroleum and Gas members at St. Louis, and of the Institute of Metals Division in Columbus, Ohio, have all been described in full in the magazine.

Jan 1, 1925

TO THE BOARD OF DIRECTORS OF THE AMERICAN INSTITUTE OF MINING AND METALLURGICAL ENGINEERS Gentlemen: - I herewith present a report of some. of the more important activities of the Institute for the year of 1922. The outstanding feature of the year is the optimism felt by our members despite the continued depression in the mining industry. January 1, 1921, found many of our members out of employment or drifting into other industries to tide them over the depression, but almost universally the feeling has been that this was but a temporary condition and that sooner or later the necessary production of raw materials would enable these members to return to their former activities and renew their participation in Institute affairs. As the year passed conditions improved and, before it ended, many had found employment in their previous occupations. Bearing in mind that this depression has been very real, we have reason to be well satisfied with the work that the Institute has been able to do. The loss of members through inability to pay, dues has been large, and income has been correspondingly reduced, but it proved to be materially in excess of that anticipated early in the year, so that a substantial and unanticipated balance was carried forward toward the activities of 1923. PUBLICATIONS Following the example of other technical societies, and to conserve our resources, no Year Book was published in 1922. The lack of an up-to-date membership list for the use of our members was regrettable, but the saving of $5000 proved to be worth while. During the year, Volumes LXV, LXVI, and LXVII were printed and sent to members. These volumes were composed largely of the papers of 1920 and 1921, publication of which had been delayed partly through lack of funds and partly for the purpose of segregating into volumes those papers dealing with the same general subject. The segregation of papers had been suggested by a number of members who had advised that they were not primarily interested in all subjects

Jan 1, 1925

By B. F. Zwick

The entire production of oil in Ecuador so far has come from the Santa Elens Peninsula, Province of Guayas. Both the shallow fields of the northern and the deeper fields of the southern part of the peninsula have been in constant exploitation, though the former are of doubtful economic value. In Table I herewith, which commences with the total amounts produced by the various companies up to 1940, annual company totals are given for the succeeding years. The figures for 1944 have been partly estimated. Table 2 gives figures on casinghead gasoline. Shell Company of Ecuador (formerly known as Anglo-Saxon) has continued active exploration in the Oriente region east of the Andes, and during 1944 the Company's first wildcat well was spudded in. International Ecuadorean Petroleum Co. (formerly International Petroleum Co., Limited) has pursued an active exploration campaign since the latter part of 1939, and a drilling string was placed in operation about a year later. A second string of tools was added during 1943 and a third a few months ago. Ten wildcats, all dry, have been completed in this period, two wells are drilling at the present time and other locations are on the program. Seven of the wells thus far drilled are in the area between Guayaquil and the Santa Elena Peninsula, one up the Daule River beyond Balzar, one on Puna Island in the Guayas Estuary and one in the northern province of Esmeraldas. Both the present drilling wells are in the Guayaquil-Santa Elena zone. The situation in regard to concessions has changed during the past four years because I.E.P.C. has made its selections from the extensive Daule-Guayas Study Concession, as a result of which large tracts were returned to the Government; because of the expropriation of the holdings of the "Ecuapetrol," a German concern whose acreage has passed into other hands; the Peruvian-Ecuadorean boundary settlement, which has reduced Shell's holdings somewhat; and the transfer of most of the holdings of the Cia. Minero-Petrolera del Pacifico to I.E.P,C. The greater part

Jan 1, 1945

By R. Laird Auchmuty

A NUMBER of factors, of varying importance, should be considered in assessing mineral land-here specifically coal land -for tax purposes. (1) Is the coal developed or un- developed'! (2) If undeveloped, is it surrounded by active development in adjoining properties? (3) Accessibility of railroad facilities to the property. Sometimes the railroad itself is of importance. (4) Cost of development of the seam under consideration, whether it can be developed by a drift from the outcrop or whether it will require deep and costly shafts or slopes. (5) Is it definitely known that the coal seam being assessed is of minable thickness and quality on the property? (6) Thickness of recoverable coal from the seam. (7) Quality of the coal. (8) Is the seam being assessed likely to be more costly to mine than other seams in the same district? (9) Is there an active market demand for coal from the seam being assessed? (10) Is the coal held only as protection to surface structures and in such location that it can never be mined? (11) Is the coal in a solid piece or is it in pillars that have been standing for some years as a result of incomplete mining in an old operation? (12) Expected percentage of recovery from the seam being assessed as determined by present mining practice in similar properties. (13) Value of the seam as indicated by sales of similar mineral rights in the immediate district. (14) Current royalty rates of leases for coal in the seam under consideration.

Jan 1, 1939

By George Holderer

THE Enos Coal Mining Co. owns an area underlaid by coal, of approximately 5000 acres. This property is situated 9 miles from Oakland City, in the southern part of Indiana. The mine has been in operation 5 years, during which time some 350 acres have been stripped, and stripping is now proceeding at the rate of about 100 acres per year. TOPOGRAPHY These coal lands consist of gently-rolling agricultural fields which in times past were farmed for wheat. There is no timber and but very little brush to contend with. The overburden varies from 10 to 60 ft. in depth. A thin bed of slate overlies the coal, followed by limestone, which varies from 3 to 15 ft.; this, in turn, is followed by sandstone, slate, shale and clay. There is a very wide variation in the thickness of all of these beds. The coal has an average thickness of 5 ft., and is a good grade of high-volatile bituminous. MINING OPERATIONS Briefly, the sequence of operations is: drilling holes with churn drills; blasting with L. 0. X.; stripping overburden to uncover coal and, finally taking up the coal, which is sent to a tipple for cleaning and sizing. In order to show what is being accomplished by the use of L. 0. X., results will be shown from May to November, 1926, inclusive, and compared to the same period in 1925. No work was done in No. 1 pit during May, 1925, hence all figures are unduly low for this month. Drilling There are in use 8 No. 44 Loomis clipper drills, caterpillar traction with gasoline engines; recently these were equipped with extra heavy stems, measuring 26 ft. overall and 4 ½ in. dia., to increase the speed of drilling. In addition, 4 No. 1 ½ G non-traction drills have been acquired, and are used to save the time of the larger drills when recleaning is necessary.

Jan 1, 1927

By E. R. Darby

When bronze is melted in open-flame furnaces a considerable amount of slag is formed during the melting operation. This slag may be incidental to the melting practice or it may be formed intentionally by slag-forming constituents added to the furnace charge to provide a covering for the melted metal When this slag is removed from the furnace, it contains, in addition to the free metal carried with it by the skimming operation, a considerable amount of metal as oxide either combined or mechanically mixed with it. By the usual crushing and washing methods this metallic oxide generally goes to the tailings pile, so diluted by other foundry waste that its recovery is economically impossible. If this furnace slag is not inixed with other foundry waste, practically all of the metal oxide as well as the free metal may be recovered by some form of smelting operation. The first side of the problem to be considered is the amount of slag produced. It may not be true that the majority of foundries have no record of the amount of slag made, but it is certainly true that a very great many either have no record or pay little attention to it. Usually the collection of furnace slag for one normal week's run will be sufficient to determine the advisability of its being handled in a different manner from the crushing and concentrating generally employed. If a large representative sample of the accumulation is crushed and concentrated and the recovery compared with the results of a careful assay, it will be found that a large percentage of the total metal content was lost in the washing process. The percentage of loss will be greater than the metallic oxide content, as some free metal in extremely fine particles always is carried away in grains of slag. From such a comparison, it may be determined whether or not the slag should be melted, sold or treated as before. An example of an actual test of this kind is given below. In a foundry melting 50,000 to 80,000 Ib. of bronze per day, a week's accumulation of furnace slag and ladle skimmings amounted to 16,500 1b.—over three times as much as the foundry superintendent estimated before the accumulation was made. Two tons of this material was taken as representative of the lot. This was ground through a thoroughly cleaned ball-mill and concentrated over a Wilfley table. The

Aamot, Olav Crone, Chem. Engr., Elektrokemisk Raadhusgt..23, Oslo. Norway. '29 Abadilla, Quirico A., Dir., Bureau of Mines Manila, P. I. '3S Abbott, Clarence E., V.P., Charge of Raw Materials, Tennessee Coal, Iron & R.R. Co., 1242 Brown-Marx Bldg., Birmingham, Ala. '04 Abel, Raymond L.. Prof., Dept. of Pet. Refin., Univ. of Pittsburgh Pittsburgh, Pa. '2S Abel, Walter D., Div. of Corporations Los Angeles, Calif. '32 Abele, Louis T., U. S. Corps of Engrs 7211 Glen Oak Ave., Baltimore. Md. '31 Abel], Leo M., Research Met., Mount Morgan Ltd Mount Morgan, Queens.. Australia. '31 Abenius, Hakan V c/o Falu Gruva, Falun, Sweden. '37 Abernathy, G. E., Geol., Kansas State Geol. Survey Pittsburg, Kan. 3S Aborn. Robert H., Asst. Met., Research Lab., U. S. Steel Corp., Lincoln Highway, Kearny, N. J. '19 Abrams, Charles Jackson 1624 17th St., Denver, Colo. '3 t. Abstein. Henry T., Engr. & Mgr., Profile-Tamarack Mines CoYellow Pine, Idaho. '27 Acker, E. O'C., Met L28 East Washington Lane, Germantown, Philadelphia, Pa. '86 Ackerman, D. E., Met., Assoc. Prof. of Met., Purdue Univ Lafayette, Ind. '35 Ackerman, E. Dumont, Sub-Surface Geol., Temblador Camp, Standard Oil Co. of Venezuela, Caripito, Venezuela. '3S Ackerman, George F.,. Div. Foreman. The Fresnillo Co Fresnillo, Zac., Mexico. '36 Adami, A. F., V.P. & Prof. of Min. Engrg., Montana School of Mines Butte, Mont. '19 Adami, Charles J., Min. Engr 99 S. Downing St., Denver. Colo. '12 Adams, Army, Cons. Engr 714 W. Main St., Grass Valley, Calif. .'37 Adams, Clyde B.. Geol.. Socony-Vacuum Oil Co., Inc 26 Broadway, New York, N. Y. '39 Adams, Ernest C., 6th Engrs Fort MacIntosh, Laredo, Tex. '35 Adams, F. J., Gen'l Agent, Gulf Production & Pipe Line Cos Fort Worth, 'lox. '29 Adams, F. S., Supt., Power Dept., Anaconda Copper Min. CoAnaconda, Mont. '37 ADAMS. FRANK DAWSON, Hon. Mbr., 1913; Logan Prof. of Geology and Dean, Faculty of Applied Science. McGill Univ., Montreal, Que., Canada. '13 Adams, Gale L., Supervisor, Process & Dev. Lab., General Pet. Corp. of California, Higgins Bldg., Los Angeles, Calif. '18

Jan 1, 1939

By W. E. Stiles

A method is presented for predicting the performance of water flooding operations in depleted, or nearly depleted, petroleum reservoirs. The method makes use of permeability variations and the vertical distribution of productive capacity. From these two parameters can be calculated the produced water cut versus the oil recovery. Derivations of the mathematical analogy is shown and sample calculations and curves of prediction are presented. Comparison is made of the predicted and actual performance of a typical 5-spot in an Illinois water flood. INTRODUCTION The use of water as a flooding medium in both depleted and "flush" oil reservoirs is gaining greater recognition and acceptance. Many of the shallower fields, depleted by primary production, have been and are being subjected to water injection in order to obtain some part of the large volume of oil remaining after primary production. Some of the earlier water flood installation proved highly discouraging and the value of water flooding was often questioned. Many of these earlier floods were haphazardly selected and developed as little was known of the physical characteristics and contents of the producing formations. The prior evaluation of the flood performance was impossible. During the past decade the development of the required reservoir engineering tools-—core analysis, reservoir fluid analysis, electric logs, fluid flow formulae, etc.—has allowed the engineer to construct and apply the methods which are presently being used to evaluate the economic and mechanical susceptibility of a reservoir to flooding. This discussion will present a method for taking into account the effect of permeability variations in predicting the performance of water floods in depleted reservoirs. PERMEABILITY AND CAPACITY DISTRIBUTION It is generally agreed by most investigators that in a single phase system fluid will flow in a porous and permeable medium in proportion to the permeability of the medium. Producing formations are usually highly irregular in permeability, both vertically and horizontally. However, zones of higher or lower permeability are often found to exhibit lateral continuity. Thus, while structurally comparable stringers in adjacent wells may differ several fold in permeability values, they usually bear resemblance as being part of a general continuous higher or lower permeability section. It is generally agreed that where such stratification of permeability exists, injected water sweeps first the zones of higher permeability, and it is in these zones that "break-through" first occurs in the producing well. It is a basic assurnption of the presently described method that penetration of a water front follows the individual permeability variations as if such variations were continuous from input to producing well. This is admittedly not rigorously true, but can be justified as making possible a simplifying mathematical approach to an otherwise extremely complicated three dimensional flow problem. As a basis for study of the lateral flow of fluids in formations of irregular permeability, the irregularities may be conveniently represented by a permeability distribution curve and a capacity distribution curve. In obtaining these curves, the permeability values, regardless of their structural position in the formation, are rearranged in order of decreasing permeability. If these permeability values so arranged are plotted against the cumulative thickness, a permeability distribu- tion curve is obtained. This curve may then be likened to a "smoothed" permeability profile of the formation. In making comparison between different distribution curves it is convenient to state the permeabilities in terms of the ratio of the actual permeability values to the average permeability of the formation. These ratios termed "dimensionless permeabilities", are used in this paper rather than the permeabilities in terms of millidarcys. The capacity distribution curve is a lot of the cumulative capacity (starting with the highest permeabilities) versus the cumulative thickness. The capacity and thickness are given as fractions of the total capacity and thickness. Mathematically, the capacity distribution is the intergration of the permeability distribution curve. In practice it is convenient to first obtain the capacity distribution curve and derive from it a smoothed dimen-sionaless permeability curve. The method of obtaining the capacity distribution curve is illustrated in the successive column of Table 1, in which capacity and thickness are derived as fractions of their respective totals. If only a small number of permeability values are available, it is generally desirable to smooth the resultant curve. This has been done to give the capacity distribution curve shown in Figure 1. The differentiation of the capacity distribution curve to obtain the permeability distribution curve is shown in Table 2. Here, the capacity values are read from the smoothed curve at intervals of cumulative thickness, and the increments of capacity are divided by the increments of thickness to obtain the dimensionless permeability, K. Due to this stepwise procedure of calculation these premeability values must be plotted at the midpoints of the successive increments of thickness. The curve so obtained from these data is shown in Figure 1. The total area under the K' curve is equal to unity.

Jan 1, 1949

By W. E. Stiles

A method is presented for predicting the performance of water flooding operations in depleted, or nearly depleted, petroleum reservoirs. The method makes use of permeability variations and the vertical distribution of productive capacity. From these two parameters can be calculated the produced water cut versus the oil recovery. Derivations of the mathematical analogy is shown and sample calculations and curves of prediction are presented. Comparison is made of the predicted and actual performance of a typical 5-spot in an Illinois water flood. INTRODUCTION The use of water as a flooding medium in both depleted and "flush" oil reservoirs is gaining greater recognition and acceptance. Many of the shallower fields, depleted by primary production, have been and are being subjected to water injection in order to obtain some part of the large volume of oil remaining after primary production. Some of the earlier water flood installation proved highly discouraging and the value of water flooding was often questioned. Many of these earlier floods were haphazardly selected and developed as little was known of the physical characteristics and contents of the producing formations. The prior evaluation of the flood performance was impossible. During the past decade the development of the required reservoir engineering tools-—core analysis, reservoir fluid analysis, electric logs, fluid flow formulae, etc.—has allowed the engineer to construct and apply the methods which are presently being used to evaluate the economic and mechanical susceptibility of a reservoir to flooding. This discussion will present a method for taking into account the effect of permeability variations in predicting the performance of water floods in depleted reservoirs. PERMEABILITY AND CAPACITY DISTRIBUTION It is generally agreed by most investigators that in a single phase system fluid will flow in a porous and permeable medium in proportion to the permeability of the medium. Producing formations are usually highly irregular in permeability, both vertically and horizontally. However, zones of higher or lower permeability are often found to exhibit lateral continuity. Thus, while structurally comparable stringers in adjacent wells may differ several fold in permeability values, they usually bear resemblance as being part of a general continuous higher or lower permeability section. It is generally agreed that where such stratification of permeability exists, injected water sweeps first the zones of higher permeability, and it is in these zones that "break-through" first occurs in the producing well. It is a basic assurnption of the presently described method that penetration of a water front follows the individual permeability variations as if such variations were continuous from input to producing well. This is admittedly not rigorously true, but can be justified as making possible a simplifying mathematical approach to an otherwise extremely complicated three dimensional flow problem. As a basis for study of the lateral flow of fluids in formations of irregular permeability, the irregularities may be conveniently represented by a permeability distribution curve and a capacity distribution curve. In obtaining these curves, the permeability values, regardless of their structural position in the formation, are rearranged in order of decreasing permeability. If these permeability values so arranged are plotted against the cumulative thickness, a permeability distribu- tion curve is obtained. This curve may then be likened to a "smoothed" permeability profile of the formation. In making comparison between different distribution curves it is convenient to state the permeabilities in terms of the ratio of the actual permeability values to the average permeability of the formation. These ratios termed "dimensionless permeabilities", are used in this paper rather than the permeabilities in terms of millidarcys. The capacity distribution curve is a lot of the cumulative capacity (starting with the highest permeabilities) versus the cumulative thickness. The capacity and thickness are given as fractions of the total capacity and thickness. Mathematically, the capacity distribution is the intergration of the permeability distribution curve. In practice it is convenient to first obtain the capacity distribution curve and derive from it a smoothed dimen-sionaless permeability curve. The method of obtaining the capacity distribution curve is illustrated in the successive column of Table 1, in which capacity and thickness are derived as fractions of their respective totals. If only a small number of permeability values are available, it is generally desirable to smooth the resultant curve. This has been done to give the capacity distribution curve shown in Figure 1. The differentiation of the capacity distribution curve to obtain the permeability distribution curve is shown in Table 2. Here, the capacity values are read from the smoothed curve at intervals of cumulative thickness, and the increments of capacity are divided by the increments of thickness to obtain the dimensionless permeability, K. Due to this stepwise procedure of calculation these premeability values must be plotted at the midpoints of the successive increments of thickness. The curve so obtained from these data is shown in Figure 1. The total area under the K' curve is equal to unity.

Jan 1, 1949

By R. Salter, C. K. Chase

Although Asarco's Silver Bell Unit, 40 miles west of Tucson, Ariz., is known primarily for copper production, molybdenite is also produced as a byproduct in the 8000 tpd flotation mill. The Silver Bell ore comes from two pits approximately two miles apart. Copper mineralization is essentially chalcocite resulting from two to three-fold secondary enrichment in a highly altered zone. A typical porphyry copper deposit, Silver Bell ore is of medium hardness. The ore consists of about one part molybdenum to 65 parts of copper. In the copper concentrate which is the starting point for separate molybdenum recovery, the ratio is also one part molybdenum to 65 of copper. Molybdenum mineralization is primary. Enrichment is not evident but it is notable that the molybdenite is more common in the more siliceous, harder rocks. The actual molybdenite occurs as diversely oriented flakes of fairly constant grain size, mostly in fractures associated with quartz veins. Most of the mineral appears unoxidized; secondary coatings on the molybdenite flakes are fortunately rare. In May 1962 a modified, improved version of the molybdenite circuit was put into operation.

Jan 7, 1964

By Oswald J. Heinrich

THE origin of spontaneous combustion in collieries is, of course, chiefly due to bad system in laying out the pits, unclean workings, insufficient ventilation, and neglect in damming off works after they are exhausted of the main coal. This is particularly indispensable in the Richmond field, because it is difficult and dangerous here, on account of the inferior roof, to remove the last vestiges of coal ; and we are compelled also to retain all the slates and bands, as far as possible, in the pit, to help fill up, although such material is liable to fire. This, however, can be prevented to a great extent, as mentioned below. I am satisfied that the only system of working this thick coal is by cross-cutting (Querbau, ouvrage & travers) or working in benches, as practiced in France (Creusot, Rive de Gier, St. Etienne), in Silesia (Kiinigsgrube), which I have used as far as it is practicable in an old pit, almost torn to pieces by former workings. Modifications may, of course, be needed, even in the same pit, on account of irregularities in the seam. I am also satisfied for economical reasons (on account of the heavy cost for timbering) that pits here ought to be worked upwards, even if it requires a longer period of time to win the coal, and a greater outlay of capital to commence with. The various saddle-shaped " troubles " making natural minor basins in the main basin aid in the execution of this plan. A pit worked once ought to be worked out clean, given up, and dammed off forever. If sections of proper height are assumed, according to the required amount of production for a certain period of time, they ought to be worked out and filled in as much as possible, dammed off, and ultimately allowed to fill up with water, in order to protect the upper works in future from fire in the gob below. This I consider indispensable, because we may not be able profitably to fill in all the ground. To do so we have to use the waste of the mine, although it is liable to fire in time. In using this stuff, it ought to be surrounded by walls of rock not liable to take fire, laid firmly in clay, the gob being in the middle, and firmly covered and packed with clay on top. In

By J. E. Tobey

NATIONAL DEFENSE should not create a dilemma in coal utilization such as obtained during the World War. Even under the heavy pressure of a total preparedness program there should be a smooth flow of the right coals from mines to plants. The more than 100,000 industrial plants of the nation must he served with coal of such characteristics and qualities for their individual requirements that no loss of production due to coal failure shall occur. This problem challenges the ingenuity and cooperativeness of producers. transportation executives, consumers and engineers.

Jan 1, 1941

By Charles R. Keyes

I. INTRODUCTORY. IN the dry regions of the globe many silver-deposits display certain remarkable features which at the same time are so totally unlike anything met with among ore-bodies elsewhere, that they have long presented exceptional difficulties not only to a satisfactory explanation of their origin, but to economical milling. A most striking peculiarity of these ores is the haloid character of many of their bonanzas. To this fact more than to any other may be ascribed most of the unusual uncertainties of mining-operations in desert countries-the marvelous local richness of the ores under certain conditions and the often abrupt transition, to utter poverty; the inadequacy of ordinary prospecting customs and the constant devising of new exploratory methods; the unaccountable losses in smelting and the continual change in treatment-practice. For these anomalies certain climatic conditions seem to be chiefly responsible.

Jul 1, 1911

By M. E. Lombardi

IN comparison with the mining industry the petroleum industry is new and inexperienced, and until now it might have been called the fortunate industry. Its great good fortune consisted in two things; a bountiful supply hidden by nature in the rocks of the earth, and a steady and large increase, during the past twenty-five years, in the demand for petroleum products. It is a remarkable fact that consumption of gasoline in the United States has shown an increase every year since automobiles first became important, and even in 1930 there was a four per cent increase, in spite of the universal depression; the estimated increase if the times had been normal, was ten per cent. This industry has, therefore, not passed

Jan 1, 1931