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` LAWRENCE ADDICKS, New York, N. Y.-We have really two competitive processes for the production of electrolytic zinc. In the process used at Great Falls, the ore is roasted and the calcines leached, leaving a residue which has to be smelted; in the other method, the ore is burned, the zinc and lead fumed off, and the condensed fumes are leached. I do not think that we can yet come to any decision as to which is the better way to attack the problem. Of course if we roast first and then leach, various substances remain in the calcines which may consume sulphuric acid; whereas if we do the burning first, we obtain simply the zinc and lead oxides, with considerable sulphate, in the fume, and there is no shortage of acid. It also depends partly on the complexity of the ore. The one that Mr. Hall is treating and the ore they are treating at Great Falls are not quite alike, but I think they are sufficiently similar to make a comparison of the two methods, working in competition, on different parts of the country, very interesting. C. E. SCHWARTZ, Miami, Okla.-Mr. Hall states that the Joplin conditions are not suitable for the manufacture of electrolytic zinc. When we speak of Joplin ore in general, we consider, of course, a 60-per cent: concentrate with comparatively low iron, but if a low-grade concentrate could be made from tailings and so-called chats, then the problem would be quite different. A Joplin ore is comparatively simple to treat electrolytically, and I believe the electrolytic process would open a field for the treatment of such ores as would not be ordinarily smeltable; that is,

Jan 1, 1918

To the Members It has been, and is the endeavor of the A. I. M. E. to serve each and every member. One of the means of letting the membership know what is going on in the mining; metallurgical and chemical fields, and by far the most important, has been our monthly Bulletin. To publish this costs money, and to partly defray the costs, it was decided to accept such advertising as could be secured. The A. I. M. E. is the only one of the American National engineering societies whose dues are as low as $10 per year, and it actually spends more upon the Bulletin and Transactions than the sun total it receives for clues. Hence the need of advertising revenues. We are planning even greater improvements for your Bulletin-improvements that will help you in your work. It will mean a better publication, with more information than ever before. To successfully carry out our plans, we must have your co-operation. We are not asking you for financial, but for your moral support. With that we shall accomplish a great deal. What we ask of you, brother member, is to give evidence to those patronizing our advertising pages, that you not only read the editorial pages, but the advertising section as well, and that you have in mind the welfare of your Institute by consulting the advertising pages when in the market for equipment. Do you realize that if you mention your Bulletin when writing advertisers or purchasing supplies, that not only would your publication secure more advertising, but better satisfy present advertisers. We have reason to know that our advertisers secure business as a result of our publication, but they demand some evidence that you see their advertisement. Unfortunately, our members do not as a rule mention where they saw the advertisement, and as a consequence advertisers have no means of knowing whether their investment in the Bulletin is paying. The A. I. M. E. Bulletin can be made the best advertising medium in the mining, metallurgical and chemical fields, simply by each member doing his bit. It is very little to ask of you, and the returns to the mining industry will be enormous.

Jan 9, 1915

By Jill Dill Pasteris

Several mineralogical prospecting techniques are used in diamond exploration. Most are concerned with identifying indicator minerals such as pyrope garnet and magnesian ilmenite, which are derived from mantle xenoliths hosted by kimberlites. The first goal of such prospecting is to locate kimberlite intrusions; the second goal is to identify the diamond-bearing kimberlites. Explorationists have worked much less on the indigenous kimberlite phases. The kimberlitic opaque oxides, ilmenite and particularly spinels, promise to be useful in discriminating between intrusion episodes in identified kimberlites, and perhaps in the evaluation and prediction of diamond grades. Several petrologists have showed that spinel compositions and zoning patterns are specific to certain intrusive facies in South African and Canadian kimberlites. Careful evaluation may indicate a correlation between spinel parameters and diamond content.

Jan 1, 1984

By C. C. Hagenbuch

Machine loading of coal into mine cars is increasing rapidly. Particular reasons for its use frequently apply to certain localities, but in general, it is profitable to install mechanical coal-loading equipment: (I) when existing hand-loading contract rates prevent further cost reduction; (2) when the height of the coal bed requires that either top or bottom must be taken to place cars in rooms; (3) when labor shortage or limited house-plant capacity prevents the production of desired tonnage ; (4) when tonnage requirements are in excess of possible hand-loaded production from developed areas; (5) when working places are scattered and it is possible to concentrate production, and therefore supervision, by the installation of mechanical equipment; (6) when rapid development is essential. Having decided to install loading equipment, the problem then arises as to what type is best adapted for a particular mine or coal bed, the choice lying between mobile track equipment, pit-car loaders, scrapers, shaker conveyors, belt conveyors and drag conveyors. MajoR FactoRs Influencing Choice of Equipment In determining the type of equipment to be used, the following major factors must be studied: Grades.—Adverse grades, while permitting other types of loading equipment to work successfully, may prevent the success of a shaker conveyor installation. Thickness of Bed.—The thickness of coal governs the choice of equipment. A machine that requires 5 ft. of head room should not be selected for a 3-ft. bed where otherwise it would be unnecessary either to brush top or to lift bottom. Nature of Pavement.—Soft or scaly bottoms are unsuitable for the use of any type of digging loader, shaker conveyors or scraper loaders. nigging loaders and scraper loaders scale the bottom, mixing it with the coal and causing preparation difficulties; shaker-conveyor drives frequently work themselves loose, destroying the conveyor alignment and creating maintenance problems. Nature of Roof.—With any type of loading machine, it is policy to obtain the maximum possible tonnage per move per set-up. This must

Jan 1, 1931

By R. L. Ash, R. R. Rollins, C. J. Konya

An investigation was performed to determine conditions for optimizing the spacing of simultaneously initiated multiple explosive columns. This was done by using models of mortar, dolomite, and Plexiglas with 10-grain mild detonating fuse as the explosive charge. It was desired to simulate blastholes with multiple primers initiated by detonating fuse or when high-velocity explosives are used in low-velocity materials. It was found that optimum spacing between multiple charges was strongly influenced by charge length. At less than optimum charge length, the spacing at which complete shearing was possible between adjacent charges decreased exponentially with a subsequent loss of broken material volume. For charges fired simultaneously, larger burdens and spacings were possible as compared to those necessary for single-crater charges. For each material studied, there was a characteristic optimum charge length and a maximum attainable spacing at any given burden. Proper selection of the spacing distance between charges is fundamental to successful blasting. Its value directly affects the cost of drilling and explosives used per unit of broken material. In addition, the choice of a spacing that is Compatible with a given set of blasting conditions aids in the control of fragmentation sizing, ground vibrations, overbreak, and throw which in turn, influence other production costs. For example, normally loaded blastholes that are spaced too closely invariably promote overbreak and usually give coarse fragmentation. Unless care is taken, airblast and violent flyrock will occur and under certain conditions cutoffs and misfires may result. Too large a spacing, on the other hand, frequently leads to conditions that form bootlegs or toes. The choice of a particular spacicg to use, however, is largely a matter of individual experience and judgment, usually based on trial and error. Very little is known or can be found in the literature with regard to how the spacing between charges is related to field conditions and charge geometry. As a general rule, the firing time sequence of adjacent charges and properties of a material are thought to have the most significant influence on the spacing distance best suited for any given field condition. For example, delayed initiation of adjacent charges usually always requires a closer spacing than when charges are fired at the same time. This should be expected if one considers that the energy normally dissipated and lost in the surrounding ground from charges fired independently would be captured and utilized for breaking material between charges when they are initiated together. Spacing can be extended also when charges are aligned with structural planes of a material, such as jointing, along which shearing is relatively easy. It is customary to relate the spacing (S) between charges to their common burden (B) in the form of a spacing ratio, or SIB. The burden normally is considered as the optimum depth or distance from any single charge perpendicular to the nearest free or open face at which the desired fragmentation and maximum crater yield are obtained. For production blasting, value of the ratio is generally considered to vary from 1 to 2, depending on conditions.1-6 When adjacent charges are fired independent of one another, the value varies from 1 to about 1.4, the closer amount being employed to square corners or produce craters having the ideal 90" apex angle. The larger ratio is the geometric balance value for craters having an apex angle of 135". The basic ideal crater forms in the plane of the charge diameter for charges fired independently are shown in Fig. 1. In the event charges are fired simultaneously, geometric balance in the plane of their charge diameters suggests that a spacing ratio near 2 would be appropriate, as illustrated by Fig. 2. In practice, however, some compromise ratio value must be selected to conform with the specific ground conditions. An example would be where the jointing planes tend to produce 60° or 120° crater angles, the appropriate geometrically balanced charge arrangement being given by Fig. 3. In this condition, the spacing ratio is 1.15, not 1 or 1.4 as suggested for the 90° cratering of independently fired adjacent charges. In view of the foregoing, it would seem logical to assume that whenever charges all having the same burden are fired at the same time, spacing distances always can be greater than those permitted by charges fired independently. In practice this is not the case, however.

Jan 1, 1970

By R. R. Unterberger

Three different physical techniques have been used to see through or probe into rocks, so miners might know what is ahead or overhead. These are radar, sonar, and a unique type of sonar called nonlinear sonar. Five radar systems have been developed. The highest frequency used is 4300 MHz for detecting small fractures at close range. This gives the best resolution. For longest range (over 2000 m, or 6560 ft) we use the 30 MHz radar for finding faults ahead of mining or ranging to salt dome flanks. Two types of salt, dome and bedded, are recognized. Radar works well in dry (dome) salt, but not in bedded salt which contains small amounts of water. The dipole moment of water absorbs energy from the radar. Thus was born the 30 MHz radar system and sonar probing systems. These can probe to 100 m (328 ft) even into wet salt. All probing systems measure data in time, which are converted to distance by measuring the time of travel of radar or sonar through salt pillars of known thickness. Ranges of probing in salt are from less than 1 m (3.3 ft) to more than 2000 m (6560 ft). Uses of radar and sonar probing in mines include mapping the top of salt above a mine; mapping salt dome flanks; finding impurities in salt such as anhydrite, sandstone, or potash stringers; locating old boreholes in salt pillars; locating fractures in salt; and finding faults or water zones ahead of mining.

Jan 1, 1985

A new $18-million hydrometallurgical ore treatment facility for the recovery of molybdenum oxide was dedicated at Climax, Colo., on November 19 by Climax Molybdenum Co., division of AMAX. The Company has been producing molybdenum from molybdenite (MoS2) ores since 1918. Now oxide values, formerly lost in the sulfide flotation plant tailing are to be processed to yield about 3 million Ib per year of metal. In 1965, Climax produced about 50% of world molybdenum from sulfide ore. This ore is mined at the rate of 42,000 tpd. The annual production of concentrate is 100 million lb containing 90% to 92% MoS2, or about 50 million lb of metal. As only a relatively small portion of the total Climax production is sufficiently enriched in oxide molybdenum to process through the new plant, 5700 tpd of selected ore containing 1.5 lb of Mo per ton is now treated by the new process.

Jan 12, 1966

By S. Arthur Krom

(Wilkes-Barre meeting, June, 1911.) RECENT experiments indicate that the usual type of concentrating-table is not only poorly adapted to produce the desired results, but also is based upon an incorrect principle, namely, the use of riffles to perform the work of stratifying the various minerals. We have heard a good deal about riffles for concentrating-tables; exhaustive experiments have been made to discover the proper form of riffle, or to prove the superiority this or that form; disputes and patent-litigation have arisen over the matter of riffles, and thus many have been led to believe that the riffle is the saving-device upon which the process of concentration depends. In the present paper it is proposed to show that the riffle is greatly overrated as to the part it performs in the concentration of minerals, and that, in the near future, it may possibly be eliminated entirely from that process. The experiments in question have shown that the troublesome riffle can be considered of secondary importance at the most, and should be so classed in the construction of a concentrating-table built upon the right lines. The action of any form of riffle on a concentrating-table is such as to upset and retard the process of settling and stratifying the various minerals on the table-deck. From the deck of a riffled table no concentrates can be delivered until the deck is "bedded," that is, until a sufficient amount of metallic values have been fed to the table to spread over a large portion of the deck, forming a substratum of the heavier minerals. This substratum must be maintained by the feed within quite narrow limits, and directly proportional to the rate of discharge from the table, in order that the bed shall not be lost. On the other hand, the riffles having a very lim-

Jul 1, 1911

By J. D. Lubahn

Prior tests by Dorn, where the strain rate in a tensile test was suddenly changed, have shown a small, but definite rate-history effect to exist. If this effect is neglected in the calculation of creep behavior from tensile results, an error should occur. This paper shows that this error is smaller than experimental scattering, and may be neglected. DORN1 has found a small but definite rate-history effect in the aluminum alloy 250 at liquid-nitrogen temperature using tensile tests with an abrupt rate change. Such an effect is to be expected from pre-viously known2-6 temperature-history effects, together with general experience that effects produced by changing the strain rate a large amount are simi-

Jan 1, 1959

By S. G. Malghan, J. P. Van Dillen

Some uranium minerals are paramagnetic and hence are amenable to concentration by high gradient magnetic separation (HGMS). This paper describes effects of the HGMS parameters-pulp velocity, field strength, matrix loading, and magnetic field gradient-on the product recovery and grade. Unsatisfactory separation of uranium minerals by HGMS is related to ore-specific properties, such as lack of liberation, fine dissemination of uranium minerals, uniform distribution of magnetic minerals throughout the ore matrix, and interference of fine-sized slimes. Experimental techniques to identify and resolve some of these problems are outlined.

Jan 1, 1984

BUMPS in No. 2 Mine, Springhill, N. S., furnished the main feature for discussion at the morning meeting* on Ground Movement and Subsidence on Feb. 18. Walter Herd, the author of the paper by which the discussion was introduced, not being well, was unable to be present. The paper was presented by T. L. McCall, who laid stress on the presence of sand- stone as the cause of bumps, on the value of retreating longwall in eliminating such phenomena at the coal face and on the advantage of wide headings with packs on either side, leaving space behind them for any coal that bumps might dislodge. George S. Rice, who presided, referred to his visits to the Nova Scotia mines and said that bumps usually occurred only where the coal was thick and strong and the roof and floor both more than usually hard. If any of the three were weak, bumps were not likely to occur. In the Nova Scotia mine, to which Mr. Herd referred, there was no material for packwalls and for this reason as well as for safety he had been convinced that long- wall retreating with a small percentage of pack walling was the most feasible plan.

Jan 1, 1929

W. ROWLAND Cox,* New York, N. Y. (written discussion?).-The process described by Mr. Malcolmson undoubtedly represents a great stride toward conservation of our natural resources. Without discussing the subject from an economic standpoint, I wish further to emphasize the fundamental principles of the Smith process in order that its economic value may be fully appreciated. The process is essentially a means of producing an ideal fuel, as regards its combustion qualities, by the removal of the so-called volatile matter from the coal, in the form of byproducts, which have value for other purposes far in excess of their fuel value. In other words, coals which contain. large amounts of gas, tar, and ammonia, and are not suitable for domestic or industrial fuel, or for treatment in byproduct coke ovens or gas retorts; because they possess poor coking qualities, can he prepared for commercial use by the. Smith process with a very high degree of efficiency. Much work has been done along this line, both in this country and in Europe, in developing a means of preparing coal, as the economic advantages have long been recognized. To the best of my knowledge, the Smith process is the only one that has proved its commercial adaptability. Distillation of coal at 900° to 1000° F. (480° to 540° C.) yields a large amount of tar and oils. The residue of the distillation, however, is a very friable semi-coke, wholly unsuitable for use as a fuel, unless it can be charged directly into a byproduct gas producer. The problem which confronted the inventor was then to convert this carbon residue into a commercial product, and it is in this step that the Smith process has overcome the obstacles which prevented a number of other methods from becoming commercially practicable.

Jan 10, 1918

By A. U. Seybolt

DURING the course of an investigation of hot corrosion of nickel-base superalloys (combination oxidation-sulfidation attack at high temperature), it was considered possible that sulfur might gain entrance to the alloy in part, at least, by diffusion through the scale. Cr203 is nearly always observed as a prominent component of the oxide scale, and hence some experiments were carried out to examine the tracer diffusion of sulfur through Cr203 at 1000° C in the upper temperature range experienced by jet engine blades and vanes. Some hot-pressed Cr203 discs of quite high density were available from an earlier investigation1 on the rate of crf3 migration through Cr203. The Cr203 was 99.3 pct pure and contained -0.06 pct Fe as the largest metallic impurity. Additional data is given in Ref. 1. In this earlier work it was found that the rate of cation diffusion was independent of the atmosphere of thermal equilibration when using nitrogen, argon, or air, and also that the electrical conductivity of the hot-pressed Cr203 compacts was likewise independent of atmosphere in this range, thus indicating that the de-

Jan 1, 1969

Downtime cannot be tolerated on electric shovels whose cost may approach or exceed $400,000 each. The same may be said for larger-variety off-highway trucks which require an operational expenditure upwards of $50 per hour. One company, for instance, in order to ensure a more continuous operation, has specified centralized lubrication for all of its new equipment. In wet or dry weather, the mining of asbestos can place undue strains on machinery and other equipment. When the mineral is dry, its dusty, loose fibers work their way into crevices, and when wet, the glutinous asbestos may adhere to axles, gears and other wear components. Such conditions are multiplied during the extreme cold winters of eastern Canada. It is more difficult to lubricate and maintain equipment, and erosiveness becomes more punishing to wear parts. Resultant breakdowns rapidly drain off profits.

Jan 1, 1971

By O. A. Kiehn, C. A. Born, F. N. Bender

Development of the flotation reagent scheme at Climax Molybdenum Company's mine at Climax Colorado is reviewed. Features of the mineralogy, milling practice and background of reagent changes are outlined. Special attention is given to the hitherto unpublished details of the application of depressants for copper and lead impurities. The present rougher flotation reagent scheme utilizes a neutral hydrocarbon oil, low in unsaturates and wax, as collector with a sulfated coconut oil emulsifier and pine oil frother. Lime and sodium silicate are used as rougher conditioning and slime dispersant agents. Chalcopyrite and galena impurities are depressed in both rougher and cleaner plants by stage addition of Nokes reagent and sodium cyanide to yield a metallurgical grade molybdenite concentrate containing greater than 90% molybdenite and less than 0.5%, 0.1% and 0.05% iron, copper and lead impurities, respectively.

Jan 1, 1976

By K. F. Veit, R. L. Marovelli, T. S. Chen

There is an error at the bottom of the right-hand column of p. 11, and the top left-hand column of p. 12. The first paragraph of the section EXPERIMENTAL RESULTS should read: "Thermal shock tests were conducted on circular discs of basalt, quartzite, and taconite. Average grain sizes ranged between 0.10 and 0.25 mm. Individual discs were tested only once, either in a cooling or heating shock. Several discs of the same rock type were shocked at a temperature, and the temperature level then was increased for another test by 10° to 20°F until complete fracture occurred when a specimen was quenched. The minimum temperature difference required to initiate cracking, TmiN was observed and used, together with other property values, to compute the dimensionless stress o*max . The observed ?Tmin for cooling shock in different media is tabulated in Table I. The property values E, St, a, and K are shown in Figs. 6, 8, 10, and 11, respectively. Discs of various rocks shocked in different isothermal baths gave o*max values for a wide range of Biot numbers. These o*max values were then compared with the theoretically predicted values."

Jan 1, 1968

By AIME AIME

REGISTRATION and licensing of engineers is now being given consideration by a special committee of the Institute, authorized at the March meeting of the Board of Directors. The subject is one that has recently been or is now actively before engineering organizations in many of the States of the Union. In Washington, D. C., the Washington Society of Engineers and the local sections of ten national engineering societies, including the A.I.M.E., recently had a joint committee investigate the subject: this committee formulating a proposed law that has been presented to Washington engineers for their consideration. At the same time, the committee has summarized the reasons for and against registration of engineers in Washington, D. C. As many of these reasons are of more than local application, they are here reprinted so that all members of the A.I.M.E. may be informed on the subject. It is expected that some report of the Institute's Committee on Registration, State Councils and Professional Development will he made at some forthcoming meeting of the Board of Directors.

Jan 1, 1932

By L. E. Shiffman

This paper describes the operation of two kerosine flotation plants in Alabama for cleaning —10 mesh bituminous coal. One plant treats washer sludge, the other raw coal. Data on capacity efficiency and capital and operating costs is given. Methods for increasing cell capacity are discussed. IN cleaning coal it has long been recognized that methods which give excellent results for the coarser sizes may give poor or even no cleaning for the finer sizes. Effective cleaning of the fines, therefore, is usually a separate and distinct problem. For many years the problem of fines was considered of relatively minor importance. Now there is growing interest in methods of cleaning the fine sizes of coal because: 1. There are more fines. Increasing mechanization and the adoption of full seam mining methods have resulted in the production of a greater percentage of smaller particles than were produced by hand loading methods. 2. The fines have deteriorated in quality. The same causes that have led to increased quantity have also operated to decrease quality through greater contamination with slate, rock, and other diluents. 3. The fines have become more valuable. When coal was comparatively cheap, loss of the finer sizes was tolerated but, with the rapid increase in the cost of mining coal, it has become imperative that the maximum amount of clean coal be recovered from the mixture of coal and rock delivered to the tipple. 4. In many cases, the fines have become a stream pollution problem. Increasing governmental activity and legislation to prevent stream pollution often have made it necessary to retain the fine material which formerly was permitted to escape with the washer effluent into flowing streams. The Sloss-Sheffield Steel and Iron Co. operates four coal mines, all within a 20-mile radius of Birmingham, Ala., with a total annual production of 1,-250,000 tons of washed coal. Three of these mines are in the Mary Lee seam and one in the Jefferson seam. Although some steam and domestic coals are produced, the major portion of the coal is used to make coke for blast furnace operation. Fine coal is desirable for coking, and all the coal so used by Sloss is crushed to 1/4 in. Therefore, there is no problem of an outlet for even the finest sizes of coal. Since the coal is used for metallurgical purposes, low ash is of greater importance than would be the case if it were used for steam generation or domestic heating. Based on present blast furnace practice at Sloss, it is calculated that each percentage of ash in the coal carries a penalty of $0.22 per ton of coal. Thus there is a considerable margin for operating costs in a fine coal cleaning method that will result in materially lowering the ash content of the cleaned coal. Development of Fine Coal Cleaning Problem In 1942 Sloss reopened its Bessie mine and constructed at this location a new preparation plant to clean 11/4 in. x 0 coal from the Mary Lee seam.

Jan 1, 1951

By L. E. Shiffman

This paper describes the operation of two kerosine flotation plants in Alabama for cleaning —10 mesh bituminous coal. One plant treats washer sludge, the other raw coal. Data on capacity efficiency and capital and operating costs is given. Methods for increasing cell capacity are discussed. IN cleaning coal it has long been recognized that methods which give excellent results for the coarser sizes may give poor or even no cleaning for the finer sizes. Effective cleaning of the fines, therefore, is usually a separate and distinct problem. For many years the problem of fines was considered of relatively minor importance. Now there is growing interest in methods of cleaning the fine sizes of coal because: 1. There are more fines. Increasing mechanization and the adoption of full seam mining methods have resulted in the production of a greater percentage of smaller particles than were produced by hand loading methods. 2. The fines have deteriorated in quality. The same causes that have led to increased quantity have also operated to decrease quality through greater contamination with slate, rock, and other diluents. 3. The fines have become more valuable. When coal was comparatively cheap, loss of the finer sizes was tolerated but, with the rapid increase in the cost of mining coal, it has become imperative that the maximum amount of clean coal be recovered from the mixture of coal and rock delivered to the tipple. 4. In many cases, the fines have become a stream pollution problem. Increasing governmental activity and legislation to prevent stream pollution often have made it necessary to retain the fine material which formerly was permitted to escape with the washer effluent into flowing streams. The Sloss-Sheffield Steel and Iron Co. operates four coal mines, all within a 20-mile radius of Birmingham, Ala., with a total annual production of 1,-250,000 tons of washed coal. Three of these mines are in the Mary Lee seam and one in the Jefferson seam. Although some steam and domestic coals are produced, the major portion of the coal is used to make coke for blast furnace operation. Fine coal is desirable for coking, and all the coal so used by Sloss is crushed to 1/4 in. Therefore, there is no problem of an outlet for even the finest sizes of coal. Since the coal is used for metallurgical purposes, low ash is of greater importance than would be the case if it were used for steam generation or domestic heating. Based on present blast furnace practice at Sloss, it is calculated that each percentage of ash in the coal carries a penalty of $0.22 per ton of coal. Thus there is a considerable margin for operating costs in a fine coal cleaning method that will result in materially lowering the ash content of the cleaned coal. Development of Fine Coal Cleaning Problem In 1942 Sloss reopened its Bessie mine and constructed at this location a new preparation plant to clean 11/4 in. x 0 coal from the Mary Lee seam.

Jan 1, 1951

By S. Harries Daddow

THE INSUFFICIENCY OF PILLARS OF COAL FOR THE PURPOSES DESIGNED-THE FRUITFUL CAUSE OF DANGER, EXPENSE, AND WASTE-THE PROOF OF INSECURITY-SUBSTITUTE FOR PILLARS OF COAL-PILLARS AND PANELS COMPARED. PILLARS of coal, which are designed and left in our mines as the means of supporting the overlying strata of our coal-beds, and securing protection to the miner, are not only insufficient for these purposes, but the most objectionable means of providing the desired security to life and property. Though such pillars are left at a great sacrifice to the owners of collieries and mineral lands, loss to the resources of the commonwealth, and ultimate privation to the public, they defeat the very ends for which they are designed, and not only do not secure life and property, but are as fatal to the one as ruinous to the other. Propositions.-It is eminently desirable that the resources of the commonwealth-particularly our mineral wealth in anthracite coal, which is limited-should be carefully utilized and made available, not only to ourselves but our posterity. Yet, speaking as an anthracite miner, we are wasting our resources of coal with a recklessness which will bring ruin in the end, unless checked, not only to the iron manufacturing interests of the East, whose chief protection, in competition with the iron-masters of the interior, lies in a cheap and abundant supply of anthracite furnace fuel, but to the best interests of the State. It is, consequently, not only desirable, but necessary, that we should realize every ton of coal from each colliery, and every acre of coal area, in order that our resources may not be wasted at present, to breed want in the future, and to realize the greatest present benefit to the mine, the miner, and the public. It is not possible, however, to secure these ends, if we continue to leave, as we do at present, from one-third to one-half our resources in anthracite as pillars in our mines. But our sad bills of mortality, our abandoned collieries, and our yawning mountain-sides, present ample evidence that even this enormous waste of coal, though left for the purpose of protecting life and property, is as totally inade-

Jan 1, 1873