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L. E. WEMPLE, St. Louis, Mo. (written discussion *).-Mr. Stone refers to cadmium as one of the worst impurities in ores used for the production of zinc oxide for pigment purposes, because it is very volatile and its dark brown oxide and bright yellow sulphide both have strong coloring powers so that small fractions of 1 percent. injure the whiteness of the oxide. Numerous tests have recently been made by the American Zinc, Lead and Smelting Co. to determine what effect the percentage of cadmium, as ordinarily present in zinc ores, has upon the color of oxide made from such ores by the usual grate-furnace process. It has been found that while the cadmium is readily volatile and may be detected in the oxide product by chemical analysis, the oxide product is not discolored, but is of a clear white color. Analysis of the 12 leading brands of zinc oxide, French process, lead-free, and leaded grades now on the market for pigment purposes, show them to contain from 0.02 to 0.35 per cent. cadmium, figured as metal. If these proportions of cadmium were present as oxide or sulphide, the percentages would run from approximately 0.022 to 0.40 per cent. in the first case and 0.025 to 0.45 per cent in the latter case. All these grades of oxide are widely used for pigment purposes and are of a clear white color, except the leaded grades, the whiteness of which may be diminished by the lead sulphate. Tests made with admixtures of as low as 0.02 per cent. of cadmium oxide or sulphide to zinc oxide of the greatest hiding power (lead-free

Jan 1, 1918

By Albert Williams

A large proportion of the work performed in wet-crushing silver mills is devoted to the handling and re-handling of pulp between the battery and the pans. There seems to be no generally applicable substitute for the settling-tanks, and in the present system of constructing mills the tanks involve an amount of labor which may be regarded as disproportionate and unnecessary, in view of the automatic improvements which have been introduced in other directions. This diffculty has been met, however, by Boss's continuous process, in which the pulp flows directly from the mortars to the first of a series of constantly working overflow-pans. This method has been adopted at the Noonday mill, Bodie, California; the Harshaw, Arizona; the Sierra Grande, New Mexico ; and the Prietas, Sonora. The continuous process, while giving excellent results with special ores, and under peculiar local conditions (such as a deficiency in water supply), is not, I believe, claimed to be available for all raw-amalgamating mills, notwithstanding its well-merited popularity for certain work. Some trouble has been experienced from the tendency to concentration in the pans, though this can be avoided by skilful manipulation. It has also the disadvantage inherent in combinations of distinct operations ; it requires a very nice adjustment of the water supply to obtain full battery efficiency without running the pans too thin, though the latter defect is partially compensated for by the gradual thickening of the pulp as it proceeds through the series of pans. The objection is similar to that which holds in a parallel duplex process, that of combining roasting and smelting in a single furnace, where each operation is injuriously affected by the necessity of fitting it in with another and entirely different one.

Jan 1, 1883

By W. S. Ayres

I AM well aware that this subject is not strictly in the line of mining engineering, yet as it is a subject with which mining engineers at times have something to do, I have thought, perhaps, it might not be wholly out of place to communicate to the Institute something of the method used in determining deflection, and of its final issue. Having felt a need of some simple formula for determining the deflection of girders of uniform cross-section under any load, I have been led through the counsel of Mr. Frederick J. Slade, to whom I am indebted for many suggestions, to undertake a labor of which I shall in this paper give only some of the most important features. The results arrived at agree with those obtainable from the received formula; of Weisbach, Rankine, and others, but the expressions given by these authors, and by all others that I have at hand, are of such a form that they are not easily applied by those whose higher mathematics have become rusty from disuse, and they require, moreover, too much labor in their application to be of practical value. The general formula that I have adopted is similar to that given by Rankine, and is deflection = [mWl3 -El], in which l is the span, W the total load, E the modulus of elasticity, I the moment of inertia of the uniform cross-section of the girder, and m a factor depending for its value on the mode of distribution of the load. The problem then is to find the value of this factor m in the formula, and for some distributions of the load it leads to a number of mathematical difficulties. In this place I shall consider first the girder to be loaded symmet-

Jan 1, 1877

By A. B. Parsons

PUBLICATION of this little volume is a luxury that the Institute itself could scarcely afford. In truth, no engineer nor geologist, no assayer nor metallurgist would be likely to enhance his knowledge, improve his technique, or cut his own operating costs by reading this excellent translation of two booklets first published circa A.D. 1520. It is doubtful if the present enterprise would, in a practical or tangible way, "promote the arts and sciences connected with the economic production of the useful minerals and metals." And such, is the prescribed purpose for which the funds of the Institute should be spent. Fortunately for the Institute, the Seeley W. Mudd Memorial Fund is not so circumscribed; and the Fund Committee enjoys, greater liberty of action. The sponsorship by the Mudd Fund in 1942 of the publication of The Pirotechnia of Vannoccio Biringuccio, as translated by Dr. Smith and Mrs. Gnudi, was an innovation-indeed something of an experiment. Not only was the content of the volume significant mainly for its "cultural" and "scholarly" attributes; -but the format, an outstanding example of the fascinating art of bookmaking, bore no resemblance to the ordinary technical book. The Committee, frankly, was surprised at the enthusiastic reception accorded the volume. When a second edition was required, the Committee became convinced that the publication of material of this type, particularly if printed and bound in attractive form, was an appropriate avenue for utilizing a moderate proportion of the monies available from the Fund. The Bergbüchlein and the Probierbüchlein antedate by some years the first publication of De la Pirotechnia and of De re Metallica; but Georgius Agricola, the author of the latter work, made good use of the material in the earlier volumes. As pointed out in the Introduction, both

Jan 1, 1949

ON July 2 the Krupp plant in Essen was occupied by the French. The City of Frankfurt, on the edge of the Mayence Bridgehead was surrounded by the French. French infantry and cavalry occupied some more towns in the Ruhr. These moves were apparently in the way of reprisals. The Bank of England on July 5 raised its discount rate from three per cent. to four, per, cent., the lower rate having previously prevailed for almost exactly a year.. The advance appears to have been inspired by the reserve ratio, but especially owing to the fact that the low rate in the London market had led to the out-flow of funds from there to other markets. Philip Snowden brought up again in the British .Parliament his motion in favor of the condemnation of the capitalistic system and the substitution of socialism. The motion was put to vote and was defeated by large majority, only the members of the Labor party voting for it. The Allies and the Turks finally came to an agree-ment at Lausanne, the Turks getting about all for which they asked. It would be tiresome to record the details. The main fact is that the Turks, after having been ejected from Europe in 1918, are now going to return. Russia agreed to the settlement respecting the Straits. The Soviet Government of Russia formulated and adopted, subject to ratification, a constitution for the United States of Russia, which appears to be patterned after the constitution of the United States of America and the unwritten constitution of Great Britain. The important thing about this seems to be that it definitely reunites the constituent parts of the old Empire, the semi-independence of the Ukraine being surrendered.

Jan 7, 1923

By C. Max Bauer

THE most important development in the petroleum industry in Montana, during 1924, was the bringing in of the Hepp well on May 12, by the Midwest Refining Co. This followed three years of active prospecting and drilling in the state by this company. The well is located 35 miles west of Billings, in Stillwater County, and makes a high-grade paraffin oil from the Dakota sand at a. depth of 3825 ft. After flowing for several months at the rate of 150 bbl. per day, the well has been shut in for lack of storage, awaiting further development in the field. TABLE 1. Production Cat Creek and Kevin-Sunburst Fields Month Kevin-Sunburst Pipe- Estimated Cat Creek Pipeline Estimated line Runs Fuel Oil Used Runs Fuel Used January 3,214 0 133,400 140 February 3,250 0 134,248 490 March 11,989 595 163,129 910 April 116,897 1,155 125,918 980 May 179,726 2,310 152,179 770 June 126,131 2,697 122,270 910 July 132,173 2,170 118,034 770 August 202,001 2,695 142,313 1,120 September 187,201 2,135 110,012 350 October 162,589 1,995 121,683 350 November 130,392 2,520 139,900 350 December 107,465 1,780 124,169 0 Total 1,363,028 20,052 1,581,255 .7,140 There are two producing oilfields in the state-the Cat Creek and the Kevin-Sunburst, which produced a total of 2,971,475 bbl. in 1924. The only other field of proved value is Soap Creek, which contains a heavy black oil and is shut in for lack of marketing facilities. Gas is produced for local use at Havre, Chinook, and Baker, and a carbon-black plant is located at Baker.

Jan 3, 1925

W. H. LINNEY, Chairman, OSCAR LACHMUND, Vice-Chairman LYNDON K. ARMSTRONG, Secretary-Treasurer, P. O. Drawer 2154; Spokane, Wash. STANLY A. EASTON, S. SHEDD. Mining camps from Mexico to Alaska and from the Pacific coast to the Atlantic were represented by delegates at the 5th Annual Northwest Mining Convention which was held in Spokane, Wash., Feb. 19-24, 1917. About 300 delegates from outlying regions were present, this being fully 100 more than have been counted at any previous mining convention in Spokane. Graham B. Dennis, president of the Northwest Mining Association, made the address of welcome. In part, he said: "Heaven has made us the possessors of an area great enough for an empire, varied enough in climate and possibilities to compass the whole complex field of modern industry. In the development of this broad heritage, we are not only actors for today, but trustees for future ages. "It is to foster this spirit of unity; to create and maintain strong bonds of mutual good will and confidence, that we founded the Northwest Mining Association. Wee support it because we believe it will give us strength; because we believe we shall learn from each other; because, in industry as in every other walk of life, personal contact and establishment of ties of friendship enrich and round out the characters of men." One of the interesting lectures of the week was that on "Alaskan and Russian Gravel Mining," by Dr.' Henry Mace Payne, consulting engineer for the Russian government and Consolidated Goldfields of South Africa. Dr. Payne's illustrations showed the different appliances in use in the countries mentioned. The Resolutions Committee reported back to the Convention six of the seven resolutions that had been presented to it. These were adopted as submitted, with some minor changes.

Jan 5, 1917

EUROPE continued to be unsettled, financially, commercially and socially. October opened with Germany in a state of turmoil following the Government's cessation of passive resistance to the French and Belgians. In many places there were riots with much bloodshed. In Bavaria a military dictator-ship was set up in order to keep peace. In the meanwhile France continued in an uncom-promising position.. Great Britain, having been diplo-matically discredited, disappeared from any prominence in the international picture. Under the constraint of circumstances the policy of deflation in Great. Britain was temporarily abandoned. Perhaps no other course was open, for with declining trade and heavily reduced revenue, and no chance for cutting expenses propor-tionately, a check to deflation comes of its own accord. The effects of this should become manifest in the course of a few months and should appear in the form of an improved margin between the prices for commodities and the wage costs in producing them. About Oct. 20 an effort was made to set up the Rheinland as a separate republic. On Oct. 26 were published communications from Lord Curzon to Secre-tary Hughes and the latter's reply. In these Lord Curzon drew attention to the gravity of the situation in Europe and expressed the hope that France might listen to renewed suggestions for a general inquiry. Secretary Hughes promised American cooperation, in this, with the reservation that the question of inter-national debts should not enter into the situation. In the latter part of October there were military mutinies and disorders in Greece, which resulted in the reestablishment of martial law by order of Col. Plas-tiras, who is virtually the dictator of Greece. The incipient revolt was promptly crushed.

Jan 10, 1923

THE TRANSACTIONS of the Institute for the early years display but Little interest in physical metallurgy-indeed, it is striking how thoroughly process metallurgy absorbed attention until quite recent years. The first volume carries no article that can be strictly described as physical metallurgy, unless one on the rolling and hammering of ingots be doubtfully so described. Nor does the second volume contribute more the interest then was in mining, and in production methods, both ferrous and nonferrous, with much attention to the new methods of making steel. The third volume records papers on: the condition of carbon in gray and white iron, a paper devoted to chemical rather than microscopic analysis; the annealing of spiegeleisen; phosphorus and carbon in iron and steel, similarly chemical. Much attention was given, and continued to be given for years, to the manufacture and behavior of rails. The question of the nature of steel appeared early (Vol. 11)-What is Steel, by A. L. Holley-where arguments on nomenclature were already active; and Holley also bemoans, in modern spirit, the Inadequate Union of Engineering Science and Art; Pearse wrote on cast iron for guns (reflecting again the ironic beneficence of war in metallurgy), and said that Captain Walbach was the first to insist on chemical analysis of gun irons; he quotes Major Wade's study of comparative hardness, using penetration hardness measurements (Brinell was to come later), and quotes the important Reports on the Strength and Other Properties of Metals for Cannon, by H. C. Baird, Philadelphia, 1855, in which the advanced state of tensile testing at the time is shown. Hewitt, in Vol V, comments upon the function played by technical schools and technical societies upon the growth of metal-

Jan 1, 1948

By I. N. Knap

Discussion of the paper of HOWARD R. HUGHES, presented at the Now York meeting, February, 1915, and printed in Bulletin No. 99, March, 1915, pp. 629 to 635. I. N. KNAPP, Ardmore, Pa.-The claims made in the paper for the Sharp & Hughes cone bit are modest. I have used it with satisfactory results. It is a wonder for eating through hard, brittle rock; it will drill through iron pyrites that the fish-tail bit cannot enter. Soft ground is apt to contain concretions that are much harder than the containing ground. ?We have at times in drilling with a fish-tail bit thought the hole was partly in such hard material and partly in soft, thus making a difficult place to drill past in the ordinary way. By changing to a Sharp & Hughes cone bit such obstructions were easily overcome. This cone bit has greatly widened the range of work that may now be profitably accomplished by the hydraulic rotary method of drilling. It is not, however, adapted to drill soft or sticky ground, the old fish-tail bit being better for such purposes. The fish-tail bit usually scrapes its way through the material drilled, but not always. I believe at times it cuts and chips in soft friable rock. That is, the bit seems to bite into the rock, and when sufficient torsion is put on the drill stem it breaks its hold and jumps around and chips the rock from the bottom of the hole, like a stone cutter's chisel, and then takes another hold. This condition occurs only in friable material when the bit is sharp and the feed properly controlled. The Sharp & Hughes cone bit is a most valuable -tool for the rotary driller.

Jan 5, 1915

By Iley B. Browning, R. E. Strouder, Coleman D. Hunter, Ralph N. Thomas, George M. Straughan

Activity in the oil fields of the state was at a low ebb during the year because of the longest period of low prices that has yet prevailed, which has been detrimental to both the eastern and western sections of the state. Production for the state as a whole shows a drop of 209,192 bbl. during 1939, the total being 5,356,963 bbl. The loss is in the production of the western division, where a loss of approximately 300,000 bbl. more than offset a gain of approximately 100,000 bbl. in the eastern division. The loss in the western division can be attributed to decline in drilling activity due to the low prices prevailing, which were caused by flooding of the normal markcts with cheap Illinois crude. The gain in the eastern division is the result of repressuring operations begun in previous years and now showing results, and not to any renewed drilling activity. Gas development in western Kentucky during 1939 was of minor importance. In eastern Kentucky approximately 50 producing gas wells were drilled, which were sufficient for present market with excess reserves already developed. With the severe winter and additional industry load every gas well connected has been on line for the past three months. Although all demands are being met, development will be greatly increased during 1940 to meet depletion. From the geological point of view, the drilling activity in the western division developed additional information of benefit. Several wells on blocks of acreage assembled in previous years were drilled in the deeper parts of the Western Coal Basin—southern part of the Illinois Basin— giving for the first time accurate information about the Pennsylvanian and lower formations down to and through the Devonian.

Jan 1, 1940

By G. Campbell

The paper by M. Lonoff looks at the importance of byproduct prices on copper production. The paper develops several interesting points on this topic, but there are some points in the theoretical discussion that could use further development. A couple of these theoretical topics will be considered here using the paper's framework of assumptions without concern about how realistic the assumptions are for the copper industry. Lonoff’s theoretical model is based on a static, homogenous world where all copper/byproduct deposits are identical, and these deposits are the main source of these metals. Due to the importance of the byproducts to the production decision, the term coproducts will be substituted for the term byproducts to reflect more accurately this condition. The conclusion is drawn that a rise in coproduct prices necessitates a decrease in copper prices because copper production is increased as a consequence of increased coproduct production. The observation that real world behavior does not always follow this pattern is dismissed as "speculation." However, it can be easily shown that within this simple framework market forces might create the observed behavior. The key question to be answered is what causes coproduct prices to rise. Three possible cases will be used as illustrations. The first case is the one implicity assumed by Lonoff. Here, the demand for coproducts increases at all prices (an outward parallel shift of the demand curve) with the demand for copper remaining constant. As reported in the paper, the results are higher coproduct prices, an increase in coproduct production, and lower copper prices due to the resulting increase in copper production. The second case is when the supply of coproducts are constrained-leading to higher market prices. Copper production, as required by the simple model, is also reduced which

Jan 1, 1984

By W. E. Thorne

The object of this graphic method is to estimate the weight of the casting, which is to be made from a given pattern, when the cross-section is not a uniform geometrical figure. Such an estimate is a very important guide to the foundryman, who would otherwise guess at the probable weight of a casting of new design, and, in trying to be on the safe side, would probably melt an unnecessary amount of iron. It is also an aid to the designer of a new car-wheel pattern, who must otherwise estimate from general experience the probable weight, have test-wheels made, and correct the pattern afterwards, so as to obtain the weight prescribed. For the method here described, an accurate drawing of the pattern is employed. This gives a closer result than a drawing of the wheel itself, for the following reasons: 1. Calculations based upon the actual dimensions of the wheel involve the erroneous assumption that the specific gravity of the casting is uniform throughout; and upon that basis the calculated weight would be wrong, because the amount of metal poured has shrunk in the mould, acquiring the highest density in the outside chilled portion, and growing less dense through the mottled to the gray portions. 2. Calculations based upon the dimensions of the pattern or " chiller " assume that the cooled metal will not have shrunk, but will have the volume of the pattern and a uniform density. These assumptions, though erroneous, counterbalance each other. For instance, the patterns and the chiller which give a wheel 33 in. in diameter when cold, are respectively 33.5 in. in diameter. This shows a shrinkage for wheel-iron of about & in. (ordinary gray pig is commonly assumed to shrink about 1/8 in.) per foot. Wheels cast in 33.5-in. chillers do not always have the

Jan 1, 1903

WHAT was certainly the greatest event of January, and perhaps it will prove to be the greatest of 1923, or even of the next decade, was the meeting of the premiers of the principal Euro-pean powers in Paris on Jan. 2, to consider what should be done with respect to German reparations. The French and British were unable to come to any agree-ment, and the conference broke up on Jan. 4. The French and British parted friends, but each with the determination henceforth to pursue its own economic and political way. This event was profound in its significance and perhaps will be calamitous) in its consequences. Following the disruption of the Conference at Paris, the French immediately began preparations to occupy the Ruhr district on the ground that Germany was in default on coal deliveries, without waiting. for Jan. 15, the next due date for reparation payment. This action by the French led to orders being issued by President Harding on Jan. 10 for the withdrawal of the remainder of the American troops on the Rhine. Thus ended the physical participation in. European affairs by the American army, whose vanguard landed in France in June, 1917. The French occupation of the Ruhr Valley, i.e., the great industrial region of western Westphalia, was made with a large military force. The Germans offered no physical resistance, and passed under French control with sullen resentment. The coal miners to a con-siderable extent refused to work and there was more or less disorganization of railway service. Before the end of the month the opinion was expressed that the French occupation was an economic failure and there were reports of French blast furnaces being blown out for lack of coke.

Jan 2, 1923

By John W. Chang

Introduction Automatic control of primary ball mill circuits has received much attention over the past decade, primarily because its advantages ultimately can be translated into economic terms. Apart from such obvious benefits as improved product quality, increased throughput, and more stable operation, less direct benefits such as easier operation, more orderly maintenance scheduling, and timely management reports all can be realized with the application of modern automatic process control equipment and techniques. Software configurable digital computer-based control systems offer ease of change in control strategies. Occasional control strategy changes are necessary whenever control objectives change or circuit modifications occur. The dependency of control strategies on control objectives and circuit equipment to effect optimal circuit operation is an important, but often neglected issue. Because of the potential for even better control, research and development work continues. [See (Ulsoy & Sastry, 1981) and (Hulbert & Braae, 1981).] Some of the possibilities are discussed later in this presentation. A few preliminary remarks may be in order concerning the relationships among control objectives, control strategies, and circuit equipment. Generally accepted control objectives for primary ball mill circuits include: 1. Maintaining a desired percent solids in the mill. 2. Maintaining a desired measure of particle size distribution at the cyclone overflow. 3. Maximizing throughput. Control Objective I is a requirement for proper operation of the ball mill, especially if it is a grate mill. It concerns smooth movement of material through the mill. Control Objective 2 is a product specification - one of the requirements for proper flotation operation. Control Objective 3, an expression of the desire to get the most out of the circuit, is the easiest to evaluate in economic terms. It assumes that the processes downstream

Jan 1, 1982

By AIME

The following corrections (in italics and bold face) were received too late for the September issue of Transactions: Page 270, Abstract, line 1, spelling should be goethite. Page 270, column 1, authors' box, authors' affiliations should read: L. A. BAKER, formerly Principal Research Scientist, is Pellet Plant Superintendent, Cliffs Western Australian Mining, Cape Lambert, W. A., Australia. C. G. THOMAS is Experimental Officer, Minerals Research Laboratories, C.S.I.R.O., North Ryde, N.S.W., Australia. R. J. CORNELIUS and K. S. LYNCH are General Superintendent, Product and Process Development, and Superintendent, Pellet Plant, respectively, Hamersley Iron Pty. Ltd., Dampier, W. A., Australia. G. J. ARMSTRONG, formerly Chief Metallurgist, Hamersley Iron Pty. Ltd., is Mill Superintendent, Samin Ltd., Burra, S. A., Australia. Page 271, column 2, line 41, should read "highest possible spalling temperature and to adjust the. . :' Page 275, column 1, line 1, should read "(LOI) figures are shown in Table 1 and vary from 2.61..." Page 275, column 1, line 16, spelling should be goethite. Page 276, column 2, line 6, should read "Predicting Grate Speed and Production Rate: The cor-..." Page 276, column 2, line 8, should read "basis of Blends A, B, C, D, and Plant Ore 1, shown in Table..." Page 276, Table 3, heading under "Prediction Method" should read Blend E. Page 277, column 1, line 38, should read "=293 tph of specification pellets (see Table 1 for loss-..." Page 277, column 2, replace caption for Fig. 14 with the following: Fig. 14-Example of calculation of hood temperature profile during downdraft free-water drying, given plant free-water drying time. Page 277, column 2, replace caption for Fig. 15 with the following: Fig. 15-Example of calculation of hood temperature profile during drying, given plant goethite drying time.

Jan 1, 1974

1. Any society of undergraduates at a technical school, comprising students in any branch of engineering, metallurgy, chemistry, geology, etc., may be recognized by the Board of Directors in its discretion as an Affiliated Student Society, and its name, together with the names of its president and its secretary, may be published in Mining and Metallurgy or the Directory of the Institute. The members of such a society will not be named individually on the membership list of the Institute, but may at any time be proposed for election as Student Associates or Junior Members of the Institute, in the usual way. 2. Membership in an Affiliated Student Society, certified by the official representative thereof, and accompanied by suitable testimony as to character and qualifications, will have special weight with the Membership Committee of the Institute, in its consideration of the proposal of a candidate for membership. The Affiliated Student Societies receive the following privileges: 1. A copy of Mining and Metallurgy free; 2. The use of Employment Service; 3. The use of Mining and Metallurgy for publicity purposes, such as printing notices of their activities, etc.; 4. Assistance in obtaining speakers for their meetings, lists of moving-picture films, etc. To retain the privileges of the Affiliated Student Society, its officers must keep in touch with the Secretary of the Institute and advise him of its activities. The foregoing plan is not confined to students in mining engineering or metallurgy. Any undergraduate society of engineers may avail itself of the privileges offered. Societies desiring to be recognized as Affiliated Student Societies are requested to make application to the Secretary of the Institute, giving particulars as to the nature, membership and officers. The following list gives the names of the Affiliated Student Societies as of December 1, 1929, and their presidents and secretaries.

Jan 1, 1929

By William Laird

The predominent method of coal mining in the United States for years has been room-and-pillar mining. The reason for this has been the advantages of room-and- pillar method which is a relatively flexible system and its capital investment. The room-and-pillar method permits some selectivity in mining, especially where gas wells, faults and possible coal quality may be a factor. The mobility of continuous and conventional mining equipment used to develop entries may also be used for retreat mining of rooms and pillars. Longwall mining of coal takes place along a long straight face, or wall, blocked out between two butt or panel entries. The long faces or walls are normally projected in lengths of 61 to 183 m (200 to 600 ft) in this country. The longwall method of mining had its beginning in the United States during the 1800's. During that period, pack wall and wood posts were used for roof support. The longwall face was mined by miners using picks to undercut the coal. To keep the coal face from turning over, short wood posts called sprags were set in a slant position as the coal face was undercut to the depth of two to three feet. When the under-cutting cycle was completed, the sprags were removed to permit the coal to fall from the roof pressure. The longwall mining of coal did not take a firm hold during the 18009s, and room-and-pillar prevailed. In the early 19009s, steel jacks were introduced, and along with it, the modified caving theory. In March of 1950, a retreat longwall mining system, utilizing a plow, manually operated props, wood cribs and chock releases, was installed in one of Eastern Associated Coal Corp.'s mines.

Jan 1, 1981

By Gernot Kostorz

In a recent paper, Raffo and itcheell1 compared solid solution hardening of various bcc alloy single crystals at room temperature and concluded that the expression for localized elastic interaction between dislocations and solute atoms2 that gives the critical resolved shear stress (CRSS) 7,: to = Z . µE3/2 C1/2 where c = concentration, e = misfit parameter, (µ = shear modulus, Z = numerical constant Fig. 1—The slope dT0/dc1/2 for niobium alloy single crystals deformed at 570°K plotted against the misfit parameter € = In' I + 1616 I. from Ref. 6, •estimated from Ref. 7. Table I. Plateau Hardening and Alloy Parameters for Niobium Alloys dT0/dc1/2, kg/mm2 Solute Ref. 6 Tantalum 3.7 ± 0.3 1.9 0.73 + 0.06 9 0.0 ± 0.5 15 Vanadium 16.1 ±1.4 - 0.69 i 0.01 9 -7.4 ± 0.5 16 Tungsten 12.5 ? 1.5 20.9 0.92 i 0.05 10 -5.0 t 0.4 17 Rhenium - 25.9 1.24 11.12 -8.5 ± 0.4 I5 Molybdenum - 14.6 1.04 13,14 -4.6 s†±?˜µ?fF?? 0.5 17 Hafnium - 13.9 0.37 12 4.8 ± 0.5 17 Table 11. Solid Solution Hardening and Alloy Parameters for Tantalum Alloys i)' dTo/dc1/2 kg/mm2, dTp/dc1/2 kg/mm2, Ref. 22 1006 Solute ˜570°K Ref. 7 See Text Ref. 25 Rhenium 44.3 32.5 0.65 -8.5 Tungsten 32.1 24.3 0.34 -4.6 Molybdenum 29.3 19.1 -0.19 -5.9 Niobium 5.8 5.5 -0.43 0.I

Jan 1, 1970

By Craig R. Barrett, Oleg D. Sherby

The creep characteristics of four pure metals with widely Varying stacking-fault energies (silver, copper, nickel, and aluminum) were evaluated above 0.5Tm. Creep tests were performed under conditions of constant atomic diffusivity and constant stress over the elaslic modulus. The sleady-state creep rate, Es, was found to he a funclion of the THE most common empirical representation of the steady-state creep rate, Es, at high temperatures and intermediate stresses is of the form where a is the applied stress, E is an elastic constant, A and n are constants (n is typically stacking-fault energ, y, such that Es is proportional to y3,5. In addition, it was uncovered that the primary creep strain and the strain to fracture increased with increasing y, and that the ratio of initial to steady-state creep rate decreased with increasing y. about 5), Q is the activation energy for creep (usually equal to that for self-diffusion), and kT has its usual meaning. sherbyl and McLean and ale' have used this expression to correlate creep data for a number of pure metals. An interesting aspect of Eq. [I] is the absence of any dependence on the stacking-fault energy. While most creep data seem to obey the stress and temperature dependence predicted by Eq. [I], when data for several metals are put on a master plot they do not fall on a common line but form a band. The width of this band corresponds to a variation in Es of 102 to l03. sherbyl attempted to explain this band by assuming that a grain-size effect was present which led to the observed variation. On the other hand, Felt-

Jan 1, 1965