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By Samuel Taylor

IT is customary for the president of an engineering society, in his annual address, to describe either some engineering problem with which he has beer connected or to review the work of the society during his administration. My first thought, this being the sesquicentennial year of our nation, was to review the advance in coal mining for the past fifty years, during which period I have been more or less intimately con-nected with the bituminous coal industry, and have personally witnessed most of the great changes which have occurred in methods and machinery used in the production of coal, but preparation of the requisite address would take more time than could be spared to prepare it, and its presentation would consume so much time that it .would not be suitable. The new arrangement providing for giving the presi-dent's address at the business meeting makes it more .appropriate to review the work of the Institute during the past year, together with some suggestions which appeal to me as being of advantage to the future wel-fare of the Institute, which I will try to do briefly. The work of the business office has been reviewed in the Secretary's report and it will not be necessary for me to dwell on it. Suffice it to say, it seems to be going along very well. Additional work could be done which would be to the advantage of the Institute, if we had the money with which to defray the necessary ex-pense incident to it, but I will refer to this again later. I would be derelict if I did not refer to the splendid work of the Secretary and the Assistant Secretary. Keeping in touch with all the sections, which number now about 26, and affiliated student societies which number 40, besides special committees, and represent-ing the Institute on various boards, provides work enough to occupy the Secretary's time almost exclu-sively. In addition to this the Secretary and the As-sistant Secretary have the work of editing and publishing the TRANSACTIONS of the Institute; the issuing of the magazine, MINING AND METALLURGY, in the splendid manner in which it goes out to the mem-bership is no light task and I think they should receive the commendation of the membership for this work.

Jan 3, 1927

TO THE BOARD OF DIRECTORS AND THE MEMBERS OF THE AMERICAN INSTITUTE OF MINING AND METALLURGICAL ENGINEERS GENTLEMEN: Herewith are submitted the report of the Treasurer for the year 1936 and the reports for the same year of the following committees: Admis¬sions, Membership, Papers and Publications, Library, Student Relations, and MINING AND METALLURGY. To these reports you are referred for details of the year's activities. Finances.-Income for the year was $173,091 including an appropria¬tion of $2500 from the Rocky Mountain Fund earmarked to defray expense for official visits to western Sections and student societies. This compares with $141,754 in 1935 and exceeds by more than $50,000 the income of 1933 wherein the low point during the depression was reached. The major items of increase were: $6,700 from current dues; $10,600 in initiation fees and dues of newly enrolled members; $10,800 from the monthly magazine MINING AND METALLURGY. Sundry small declines were offset by minor increases. Expenditures for the year totaled $176,007 compared with $148,361 in 1935. Major increases were $5,700 for MINING AND METALLURGY; $4,000 for TRANSACTIONS and TECHNICAL PUBLICATIONS; $1,500 for meetings; $1,300 for Local Section appropriations; $6,500 for Technical Division expense; $5,000 for Increase of Membership expense; and $2,500 for visits to Local Sections and educational institutions. Comment on several of these items will appear under subsequent heads. Net deficit for the year was $2,915, this sum being made up from the accumulated surplus. It is interesting to observe that the net excess of income over outgo for the five-year period 1932-1936, inclusive, is $760. Membership and Dues.-During the year there was a net gain in membership, including Members, Associates, Junior Members and Junior Foreign Affiliates of 755 (from 7116 to 7871). In addition there was a gain of 616 in Student Associates (from 1004 to 1620). Taking account of small losses totaling 5 in the other grades, the net increase was 1366 bringing the total to 9607, the highest figure reached in the history of the Institute except at the end of 1921 when the total was 9850. In part the gain is accounted for by the smaller number lost by suspension

Jan 1, 1937

By Henry Rogatz

During the year 1937, there were 663 oil wells drilled in the Texas Panhandle, making a daily initial production of 322,332 bb1.—that is, 191 more oil wells drilled than in the previous year, with an increase in the total daily initial production of 66,283 bbl. The total daily potential of the field as determined by the Texas Railroad Commission in its Schedule of Dec. 17, 1937, was 1,039,982 bbl., or an increase of 205,094 bbl. over the previous year. On Dec. 17, 1937, the daily allowable of 68,578 bbl. was assigned to the entire field. The total amount

Jan 1, 1938

The income of the Institute is derived mainly from dues, advertising in MINING AND METALLURGY and sale of publications. These sources are fortunately supplemented by the interest from invested funds now amounting to over $500,000, a considerable portion constituting endowments for especial purposes. Aside from the medal funds the principal endowments are the James Douglas Fund for support of the Library, the Rocky Mountain Fund and the Seeley W. Mudd Memorial Fund. The income from the two last named is available for the support of research and a variety of other purposes. It is allocated by the Board of Directors upon recommendation of standing committees in each case. An active effort is being made to increase the endowments of the Institute, it being felt that unusual opportunities exist for research and public and professional service through the organization.

Jan 1, 1939

Jan 1, 1929

By F. H. Spedding

CONSIDERABLE confusion exists in the literature concerning the phase transformations exhibited by the lighter rare earth metals; namely, lanthanum,1-8 cerium,1,3,5,8,9-15 praseodymium,8 and neodymium.1,8,16,10 To obtain further information

Jan 1, 1958

By Leland Van Wert

IN 1888, Howard,1 working at the Watertown Arsenal on the tensile properties of ferrous materials at various temperatures, noted the curious fact that the stress-strain diagrams of low-carbon steels tested within a certain temperature range (200° to 350° C.) departed more or less from the normal regularity of such diagrams as secured by testing at either above or below these temperatures. This same jagged appearance of similar diagrams for steels has been observed by at least one other investigator, and de Forest2 has reported similar irregularities in the tensile testing of some nonferrous alloys. Recently again, this anomaly in diagram contour has been shown in a most striking fashion, apparently because of its accentuation by the method of testing employed, by Dr. Albert Sauveur.3 He described (for nonaustenitic steels) two quite distinct types of torsional stress-time diagrams: (1) those with a regular and smooth outline, derived normally by testing at temperatures above 300° C., or below 200° C. (as, for example, Figs. 4a or e); and (2) those presenting a decided "stepped" appearance, which are invariably produced when twisting is done within the 200° to 300° C. range (examples, Figs. 5a and b). The torsion test brings out so much more sharply (and convincingly) the irregularities occurring at 200° and 300° C. than does the tensile test that they can no longer be considered as resulting from simply idiosyncratic or accidental and inconsequential causes. Clearly, from the temperatures involved, the "stepped" type of diagram, or more accurately, the peculiar manner of response to torsional stress which manifests itself in the diagram, is an aspect of the "blue-heat" phenomenon. One's curiosity if, nothing else, prompts an inquiry as to the nature and significance of these "steps." What do they mean? What causes them? To these questions there are no completely satisfactory answers. The following experimental observations are offered as suggestions towards the solution of the problem.

Jan 1, 1931

By J. O. McCaldin, P. Duwez

ALLOTROPIC transformations between 1000° and 1900°C have recently been reported for several metallic elements. Since the proposed transformations are based on limited evidence, it was decided to examine the elements in question as well as some refractory metals by thermal analysis with a photoelectric technique similar to that described by Hug-gins, Roll, and Udin.1 In this method, a lead sulphide cell was used to detect thermal radiation from an electric-resistance heated strip specimen. A thermocouple spot welded to the specimen was used to calibrate the temperature of the system under steady temperature conditions, and recording was accomplished with a cathode ray oscilloscope. In the method used by the present authors, the temperature calibration was omitted and the cathode ray oscilloscope was replaced by a recording galvanometer. This technique, in which electric current passing through the specimen heats it, will be referred to henceforth as Method 1. Another arrangement was required for those cases where the specimen could not be formed into a wire or strip suitable for resistance heating. In such cases the specimen was a sintered compact heated by thermal radiation from a hot tungsten strip, Fig. 1. The specimen was insulated from the heating strip with a thin layer of thoria powder or suspended on 0.004 in. tungsten wires. The take-up spring had just sufficient tension to prevent buckling of the heating strip due to thermal expansion. This technique will be called Method 2. Both methods were tested with specimens of iron and titanium and the well known allotropic transformations, a toy and ? to 8 in iron and a to in titanium, were very clearly detected. Fig. 2 shows one of the records obtained for titanium. For this particular experiment, the iodide titanium specimen was a square rod 0.080 in. on an edge and 3 in. long.

Jan 1, 1955

Jan 1, 1931

MONTANA SECTION J. L. BRUCE, Chairman W. C. SIDERFIN, Vice-Chairman WALTER E. GABY, Secretary-Treasurer, 834 W. Granite St., Butte, Mont. N. B. BRALY W. T. BURNS A special meeting of the Directors of the Montana Section was held on July 24, 1916, with W. C. Siderfin, Vice-Chairman, presiding. The meeting was called for the purpose of electing a Secretary-Treasurer to fill the, vacancy created by the resignation of M. H. Gidel. Upon proper motions, the resignation of M. H. Gidel was, accepted, and Walter E. Gaby was elected to fill the office for the balance of the fiscal year. No further business was transacted, and upon motion the meeting adjourned WALTER E. GABY, Secretary.

Jan 9, 1916

Aamot, Olav Crone, Chem. Engr., Norsk Elektrokemisk, Kongensgt. 18, Oslo, Norway. '29 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. '28 Abel, Walter D., Cons. Engr 364 S. Cloverdale Ave., Los Angeles, Calif. '32 Abele, Louis T R.F.D. 1, Adamsville, Ohio. '31 Abell, Leo M., Ore Dressing Investigator, School of Mines Adelaide, S. Australia. '31 Abenius, Hakan V., Mine Supt., Bolidens Gruvaktiebolag Boliden, Sweden. '37 Aborn, Robert H., Asst. Met., Research Lab., U. S. Steel Corp., Lincoln Highway, Kearny, N. J. '19 Abraham, W. E. V., East India United Service Club, 16 St. James' Sq., London, S.W. 1,, England. '28

Jan 1, 1937

John M. Cairns, in an interesting letter dated June. 19, 1918, tells us of his experiences in Italy. He says, "It may interest you to know I came out to Italy after being on the Afghan frontier of Indian Baluchistan, in August last year, and for some time was posted at Turin as Railway Transport officer. At that time Turin was in the toils of the riots which were the forerunners and preliminaries which led up to the great Italian retreat (Capretto). Since then I have been all over Italy from (deleted by the censor) in Transportation intelligence, and now have just been transferred to the Directorate of Requisitions and Hirings, which now permits great opportunities of going nearly all over Italy (deleted by the censor). My address is L. of C. Branch, D. R. & H., A. P. 0. L/1, I. E. F.

Jan 9, 1918

By H. l. Burghoff, J. S. Porter

THIS paper presents the results of an investigation of the effect of cold-working and annealing treatments upon the occurrence of preferred orientation in annealed brass wire. The subject has received less consideration than has the same phenomenon in annealed brass sheet or strip, and perhaps very properly so in view of the obvious and undesired results obtained in the forming or drawing of strip having preferred orientation, which results are in contrast with the lack of any spectacular visual evidence in wire. The factors of cold-working and annealing that control preferredness in strip are naturally expected to function similarly in wire. Indeed, one might expect the condition to be commoner in annealed wire, because the severity of the cold-working between anneals in commercial practice is usually much greater for wire than for strip. For example, a wire that is to be finished in the annealed condition on a diameter of 0.040 in. is commonly subjected to a final reduction of 96 per cent between the last two anneals, the large reduction being accomplished in the successive drafts of a multiple-die machine. Wire for rivets, for instance, on 0.125-in. diameter, although given a slight reduction of about 10 per cent after the final anneal, may have been given a prior reduction of 75 to 80 per cent. Barrett1 states the fiber axis of annealed 70-30 brass wire to be [111] with some indication of [100] as a secondary fiber axis. Croft and Sachs2 have reported briefly on some differences in brass wire with random and with preferred orientations. They showed statistical plots of the twin-band angles with respect to the wire axis or direction of drawing as observed on an axial plane. They also pointed out that the resistance of the wire to corrosion-cracking when externally stressed and exposed to a mercurous nitrate solution decreased as the degree of the preferred orientation increased. MATERIAL AND PROCEDURE All the wire for the investigation was processed from one. portion as cut for extrusion from a cast billet of the following analysis: 70.13 per cent copper; 0.01 lead; 0.01 iron; 0.02 nickel; 29.83 zinc (by difference). The billet section, 8 in. in diameter, was extruded hot to 3/4 -in. diameter, after which it was processed by alternate cold-drawing and annealing treatments as indicated in Fig. I. The earliest anneals in process were at about 1100°F. and the next to the last reductions by drawing were 58 per cent. The diameter of the finally annealed wire was 0.132 in. Semifinal anneals were at 800°F., 950°F. and 1100°F. and reductions of 47.5, 74, 83.5 and 89.5 per cent were employed in drawing to 0.132 in. The final anneals were at 875°F., 1050°F. and 1250°F. and were

Jan 1, 1944

By Harold B. Janzen, M. A. Nobles

Campbell and Martin1 described a new exploratory logging tool which was developed as the result of a new concept of the phenomenon that takes place when a porous formation containing mobile hydrocarbons and irreducible interstitial water is invaded by mud filtrate. They postulate that invasion will create a bank of interstitial water between the flushed zone and the undisturbed formation. This postulate was confirmed by Wyllie.' Thus, if R,, is greater than R, and mobile hydrocarbons are present, the resistivity profile with increasing radii from the borehole is high:low:high, as shown in Fig. 1. If mobile hydrocarbons are absent, the bank of interstitial water is indistinguishable from the undisturbed formation and the resistivity profile, when R is greater than R,, is high:low, as shown in Fig. 2. The zone containing the bank of interstitial water and residual oil was named the "low zone". Campbell and Martin conducted extensive electrolytic wedge and resistivity analog model studies to select a logging system that would reflect the presence or absence of the low zone. The system they selected was that of a family of lateral curves. The model studies indicated that the presence of a low zone could be detected in approximately 60 to 70 per cent of the producing sand reservoirs with a family of lateral curves provided that the sonde effectively occupies 90 per cent of the diameter of the hole. These studies were conducted with D, = 5d. The presence or absence of the low zone is best determined by a plot of the apparent resistivity vs spacing as shown in Figs. 3 and 4. A dip or inflection in the profile that repeats at successive depth intervals is considered diagnostic. To reduce the shunting effect of the hole and mud, a sonde of insulating material that is surrounded by a series of flexible rubber bumpers was designed. The bumper efficiency is considered to be the ratio of the bumper diameter to the hole diameter. Field tests conducted by Campbell and Martin on 10 wells with a tool that provided for station readings indicated that dips or inflections could be detected in 19 out of 25 known producing zones. INSTRUMENT DEVELOPMENT Halliburton developed a logging system to simultaneously and continuously record eight lateral curves. The instrumentation is described in the literature.' The original logs made

By D. R. George

Preliminary research has identified several organic and aqueous solutions that are effective absorbents for SO, from simulated smelter gas containing 0.3 to 2% SO2. These SO2 loaded solutions are also compatible to the reaction of H2S and SO2 to precipitate a readily filtered elemental sulfur. The economic removal of SO2 and production of elemental sulfur from stack gases discharged by base- metal smelters is a challenging goal. The magnitude of this task is illustrated by the estimate that about 3.5 million tons of SO2 are discharged to the atmosphere by smelters annually in the U.S. The SO2 concentration of the gases ranges from about 0.5 to more than 3%. As the sulfur content of SO2 is 50% a potential production of 1,750,000 tons of sulfur per year is indicated.

Jan 1, 1970

By W. F. Hower, W. Brown

Large-scale sand consolidation tests were conducted in an effort to determine the reasons for the successes and failures of this method of sand control. Several different consolidating materials were used in treating both clean and bentonitic sands that were packed in a chamber having a capacity of 3.3 cu ft. The results were essentially the same for all of the different consolidating materials, The data show that low-viscosity consolidating materials pumped at a relatively slow rate gave the best results. Where the formation has produced sand, the treating fluids can compress the formation, thus permitting the channeling of fluids to another horizon. Pressure-packing these zones before attempting to consolidate is recommended. Sands containing more than 4 per cent of water-swelling clays are not good candidates for consolidation. It is indicated that loose sand, particularly when it is bentonitic, can be fractured during the placement of the treating fluids. INTRODUCTION Sand production in oil and gas wells has plagued the industry for many years, and numerous cures for this problem have been suggested. Most methods have been successful to a certain degree, but the great variety of well conditions that exist in the different areas has magni- fied the problem and limited the successful use of the various systems. Four review papers1-4 present a wealth of information concerning the degrees of success that have been obtained by the different sand-control methods. The bridging of sand grains by the use of gravel packs and screens has been quite successful. However, these methods do not leave the casing clear for all types of multiple completions, and the cure does not last for the production life of the well in some instance:;. The control of loose sands by sand consolidation with resins has never been as successful as desired. It has always been hoped that such a treatment would eliminate all sand problems for the life of the well, but. initial applications, starting in the middle 1940's, were only moderately successful. Lott, et a1,3 reported a success ratio of approximately 50 per cent and made the following conclusions. The highest percentage of successes were obtained where: a. Consolidation of a zone was made at the time of initial completion or prior to the production of sand. b. The interval treated was less than 12 ft in length. c. Between 30 and 50 gill plastic/ft of producing interval was displaced through the perforations. REASONS FOR SAND CONSOLIDATION FAILURES Our own experiences in the field of sand consolidation point toward the following conditions as the major reasons for the failure of sand consolidation attempts. 1. Mud-plugged perforations and mud invasion of the formation. 2. Sand in the casing covering all or part of the perforations. This sand could be either formation sand or one of the coarser sands used as propping agents in hydraulic fracturing. 3. Holes in the casing. 4. Channels behind the casing. 5. Attempting to treat too long a perforated section. 6. Too high a percentage of water-swelling clays in the formation. 7. Formations that have produced sand. Recent attempts were made to treat perforated sections ranging from 10 to 30 ft, in wells that have produced sand, by using a straddle packer that was raised and lowered through the perforations as the consolidating material was being pumped. In most instances, the pressure required to pump fluid into the formation varied considerably as the tool was raised and lowered. This suggested the possibility that significant differences in permeability were present or that only part of the formation had produced sand. There were times when a sudden break in pressure indicated that a fracture was being formed. Research conducted several years ago concerning the problem of the control of water in air and gas drilling indicated that shale sections could be fractured quite easily. In addition, it was determined that it was easier to pump fluids into shale bodies by fracturing the shale itself, or the interface between the shale and sand, than to pump into a fluid-saturated formation. Formations that produce sand are usually adjacent to shale bodies and frequently have shale streaks of various thicknesses inter-bedded in the sand. Therefore, where shale is exposed to fluid pressure it

By Alfred James

John Stewart MacARthUr, born in 1856, was the son of Robert MacArthur of Glasgow, and came of Scots stock distinguished for character and religious conviction. His election as elder of the Free Kirk gave him greater pride than the receipt of the gold medal of the Institution of Mining and Metallurgy. The former honor was for character— it marked him as a son worthy to follow in his father's footsteps; the latter was awarded for his life work of eminent service to the gold industry. Cheery optimism, resolution, tenacity of purpose, and industry ever characterized his actions. Apprenticed to the Tharsis Sulphur & Copper Co., his work on the chemical staff brought him to the notice of the Cassel Gold Extracting CO.,. at that time struggling with an unworkable electrolytic process..He was engaged by that company, in 1886, as technical manager and before long brought out the perchloride process, which was speedily followed (in 1887) by the epoch-making cyanide process. This process revolutionized gold mining and directly led the way to the elevation of the mining engineer to the most broadly trained product of the engineering profession. A noteworthy feature of the cyanide process was its completeness when introduced. Over thirty years have elapsed and the use of the process has been worldwide, but no suggested improvement has stood the test of time. The extension of the process to the beneficiation of silver ores—containing far more metal per ton and thus requiring the employment of stronger solutions—has brought us the Merrill and Crowe improvements in precipitation and the Nipissing desulfurization process for certain silver-hearing minerals. Roasting apparatus, fine crushing, filtration, and settling equipment have all aided the extension of the process in and from its original field. As Hennen Jennings put it,, the cyanide process today is essentially that of 1890. This self-containedness of the cyanide process arose from no mere chance; it was directly due to MacArthur. It was he who personally investigated every known method of precipitation and then every form of zinc from sheet, punchings, filings, millings, rods and shaving down to fume; it was he who investigated the effect of protective alkalies, of so-called accelerators, and of the addition of lead salts; he was determined to leave nothing to chance.

Jan 1, 1921

Jan 1, 1943

By J. P. Martin, A. H. Geisler, J. H. Crede, E. Both

The investigation of a 50 pct Co alloy was undertaken to determine whether there was any direct correlation between the structure and properties of Co-Fe alloys which were given various magnetic heat treatments. The magnetic anisotropy and texture of the 0.002-in. cold-reduced 98 pct material tend to decrease and change in nature with increasing temperature of the recrystallization anneal. Annealing samples in a magnetic field had little effect on either the magnetic properties or texture. However, cooling them in a magnetic field greatly improved their magnetic properties. THE beneficial influence of a magnetic field applied during the heat treatment of certain soft magnetic materials has been known for a long time. Early work showed that the presence of a magnetic field of a few oersteds during the heat treatment of Fe-Ni alloys will cause a large increase in maximum permeability. A pronounced increase in the residual induction which is produced by the magnetic anneal causes the hysteresis loop to approach the shape of a rectangle. Such results are beneficial since the desired properties are high permeability, high induction at maximum permeability, high residual induction, and low coercive force. More recently Libsch and coworkers1 studied the effect of magnetic annealing on the hysteresis properties of a series of Co-Fe alloys prepared from powders. They observed good response for the 35 and 50 pct Co alloys but little response for the 42 pct Co alloy. They pointed out that this was somewhat surprising since the 42 pct alloy has a high linear magnetostriction and zero crystal anisotropy and similar conditions in Fe-Ni alloys give excellent response to magnetic annealing. They found optimum properties to be at the 50 pct composition with residual induction, Br = 19,000 gauss and coercive force, Hc = 0.68 oersteds after the magnetic anneal. Before the magnetic anneal these values were B, = 12,600 gauss and Hc = 1.15 oersteds. The optimum treatment consisted of cooling from above the y-a transformation temperature to 900°C in a field of 20 oersteds, holding 11/2 hr at 900°C, then cooling at a rate of 20° to 25°C per min in the field to below 230°C. Cooling rate mainly affected coercive force with the value decreasing from 1.09 to 0.88 oersteds as the rate was increased from 3° to 48°C per min. Cooling from 1020" to 900°C in a field followed by further cooling to 230°C without the field gave properties decidedly inferior to those for samples annealed with the field applied throughout the cooling. They concluded that to get the best properties the samples must be cooled in a field to a threshold temperature above which the alloy is plastic enough to be affected by magnetostriction. In this respect the holding temperature must be high enough so that the alloy exhibits good plasticity to permit the optimum orienting of magnetic domains by relaxation of magnetostriction. In contrast, the holding time was of less significance for there was little improvement when the time exceeded 1/2 hr. The improvement in properties effected by magnetic annealing has usually been attributed to the establishment of a domain texture caused by the "freezing in" of magnetic strains. On the other hand, Smoluchowski and Turner2,3 apparently found that a magnetic field applied during recrystallization could alter the crystal texture. If this effect is real, improved properties would also be expected when

Jan 1, 1954

By A. T. Beckwith

The Lehigh Navigation Coal Company Inc. operates steep-pitch, relatively deep mines in the Panther Creek Valley, at the eastern end of the southern anthracite coal field. Commercially minable coal beds are the Mammoth,† Primrose, Orchard, and Buck Mountain;‡ their respective thicknesses average 50, 15, 10 and 12 ft. Sand slates immediately overlie and underlie these beds, though in some locations sandstone or conglomerate beds occur. Underground operations extend to a depth of 1200 ft. below the surface, and comprise a bulk of virgin work on the lower levels, and a small amount of remining on the upper levels. With increase in depth, ventilation has become a more important factor. Development In early days slopes or drifts were driven in the outcropping coal on the hillsides. Subsequent development was by water-level tunnels, with portals above high water in Panther Creek. These tunnels have been maintained because they intercept and drain much water that enters the mined-out portion of the bed and otherwise would follow down to the deep workings+ Below these tunnels, the coal was customarily developed by slopes. Muleways, which are zigzag chutes easy to travel, were also driven to connect lower openings with the water levels. When it became necessary to go still deeper, the slopes were abandoned, and vertical multicompartment shafts were sunk from the surface. Levels have been at vertical intervals of from 175 to 250 ft. Recent practice has been toward the latter spacing, splitting the total lift, however, by starting to mine from chutes extending halfway up to the level above. Chutes customarily are spaced at 50, 60 or 70-ft. centers along the gangways. At some mines, additional shafts have been sunk from the surface to the level containing the main pumping station, and these carry the discharge lines from the pumps. As the mines are ventilated by the exhausting system, both the hoisting and so-called water shafts serve as intakes. The main fan is always on the surface, and is connected with the return airways from the various levels by an air hole or a vertical shaft. For economy, when the present deepest levels were developed, and return-air shafts or air holes were not extended to the new level, but connections were made from the new level to that above by two or more holes. It is doubtful that this method will be continued, as complications in the system, increased resistance to flow, and other difficulties undoubtedly will counterbalance any economies this provision may afford. During the early years of mining, when operations were at no great depth, all development headings were driven in the coal bed. As mining progressed downward, increased ground pressures slowed develop

Jan 1, 1942