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By D. J. Wynnemer, G. W. Preckshot

Precise electromotive force measurements have been made on the zinc-cadmium system over the temperature range 700° to 900°C. Activity coefficients, partial free energies, enthalpies, and entropies have been determined .for the entire composition range. The integral heat of mixing is positive and compares favorably with calorimetrically determined values. Vapor-liquid equilibrium compositions were determined .for a total pressure of 1 atm and these agree well with previous values determined in other ways. The use of electromotive force measurements to obtain thermodynamic data for liquid metal systems is a simple and well-known method. Several reviews of the various experimental methods and results have been published.2,3,11 However, most of the past work using this technique was carried out at temperatures slightly above the melting point of the alloy system where alloy composition changes due to vapor transport and increased metal solubility in the electrolyte are not important factors. One advantage of extending the electromotive force measurements up to and including the normal boiling point of the alloy is that it is then possible to evaluate the vapor-liquid equilibrium of the alloy at various pressure levels up to 1 atm. A detailed discussion of the thermodynamics of reversible electromotive force cells can be found in most advanced physical chemistry or chemical thermodynamic textbooks. The expression stating the inter-relation of the electromotive force and the thermodynamic functions is the Gibbs-Helmholtz equation.

Jan 1, 1962

By Edgar S. Cook

Portions of this paper repeat in substance the statements made by me in an address before the meeting of the American Society for Testing Materials, held in June, 1903, at Delaware Water Gap, Pa. The views I then expressed, I still hold and believe to be pertinent to the present discussion of this subject. In doing my part, therefore, at the request of our Secretary, towards the further consideration by the Institute of the Physics of Cast-lron from a commercial as well as a theoretical standpoint,—a theme which received interesting treatment in our meeting some years ago, but has been somewhat neglected recently,—I make no apology for reiterating the views I have expressed elsewhere. Indications all point to the substitution of classifying pig-iron by chemical analysis for the old-time method of grading by fracture. Commencing with the larger users, and the makers of specialties, who require more positive information as to the composition than is afforded by the fracture; the use of pig-iron, guided by analysis, has spread with much greater rapidity to all classes of foundry-work than the most sanguine expected. Grading by fracture, as guided by experience with any particular brand of iron, has some points in its favor. The fact that, for so many years, castings of multitudinous forms, and for an endless variety of uses, were made in a fairly satisfactory

Jan 1, 1905

By Frederic H. Wright

The secondary metals industry might well be defined as the group of remelters, smelters, refiners, and manufacturers that convert scrap metals or residues to commercial forms. In this industry, scrap metals and residues are processed to pro- duce refined metals, ingot alloys, fabricated shapes, and chemical products. Secondary metal is defined as metal recovered from commercial scrap, that is, scrap that has entered the processor's plant in scrap form. Metal recovered by a manufacturer from "home scrap" generated in his own plant is not considered to be secondary, because it represents part of the original stock that simply requires additional treatment before emerging as a finished product. In any economic study, a basic point of measurement must be chosen, and in the case of secondary metals, the melting pot or its counterpart represents the stage in which metal is converted from scrap to some more usable form. Beyond this point there is often no means to distinguish between secondary metal recovered from scrap and virgin metal produced directly from ore. In the last fifteen or twenty years the secondary metals industry has grown to major importance. Some consumers distrust secondary metals, but frequently this distrust serves only to prove an inability to keep up with the times. A rapidly decreasing number of manufacturers like to boast that they use only virgin metals, but a little investigation would show them that more than one third of all

Jan 1, 1943

By L. C. Graton

Civilization did not begin until metals became the material of tools, implements and machines. - RICKARD, Man and Metals. HISTORY is no more an end in itself than is a backsight the sum total of a survey. This Institute may view with satisfaction the remarkable development of the mineral industry since its founding three score and fifteen years ago, its own enlarging service to that industry, and the contribution thus made toward the enhanced welfare, opportunity and mutual understanding now in greater or less degree reaching and benefiting all peoples of the globe. But neither this professional society nor the dynamic mining industry as a whole wishes on this anniversary to direct its gaze chiefly toward the past. The foremost purpose of historical review should be to throw into clear perspective the strong points and the defects in the forward march thus far, primarily as the basis for conceiving and designing a still sounder progress henceonward. At various times since the Institute's founding, the theories of ore deposition have been considered from the historical view point.l-7 For the present occasion it seems fitting to lay prime emphasis on the practice and utilization of geology in its varied relations to the problems of the mining industry. It is hoped that the reader will understand and accept the degree to which the whole is sampled by parts familiar to the present writer, and the disproportionate attention to thought and achievement within the United

Jan 1, 1947

By I. L. Greninger

THE property of the Andes Copper Mining Co. is in the central part of the Republic of Chile, Province of Atacama, 147 km. (91.5 miles) eastward by rail from the port of Chañaral. At this point the Andean system is made up of two principal ranges. The mine is on the westerly slope of the outer, or western, range, at a mean elevation of 3250 m. (10,500 ft.). A meter-gage railroad extends from the company's port at Barquito, near Chañaral, to the reduction plant at Potrerillos. This road has a total length of 151 km. (94.0 miles), of which 93 km. (57.79 miles) are owned by the Andes Copper Mining Co. The remainder of the road is owned by the state. The company operates its trains over the portion of the road owned by the state, under an agreement with the Chilean Government. The mine is connected with the reduction plant by a meter-gage railroad, 10 km. (6.214 miles) long, which extends from the coarse ore bins at the metallurgical plant to the underground storage bins at the mine. Tunnels make up 60 per cent. of the total length of this railroad. As is characteristic of the Andean region in Chile, the topography of the locality is extremely rough, and a number of points near the mine have elevations of from 15,000 to 16,000 feet.

Jan 1, 1928

By J. H. Wernick

IN temperature-gradient zone-melting1 a molten zone is moved through a solid or across a solid surface by the establishment of a temperature gradient. This technique has both practical and fundamental aspects. One practical application is to make p-n junctions for semiconductive devices, particularly for devices in which the junctions are desired within the semiconductor. From a fundamental point of view, the technique is being investigated as a method for determining diffusivities in liquid alloys, and preliminary diffusivity results have been reported by the writer." In this paper, the effects of crystal orientation, temperature, and molten zone thickness in temperature-gradient zone-melting, and the bearing of these effects on diffusivity measurements and n-p-n junction formation are discussed. Experimental Procedure An effect of crystal orientation was noted in early experiments. To facilitate its study, movements of wire zones across a surface, rather than through the body of a single crystal, were observed for various surface planes and travel directions. The experirr-entai setup is illustrated in Fig. 1. The graphite end-section for the high temperature heater has an apron about 1/16 in. above the upper surface of the crystal. This apron insures that the surface temperature of the block is equal to or greater than the temperature within the block at every point, Thus, the zone does not penetrate the block and convection in the liquid is minimized. The experi-through a block is shown in Fig. 2,

Jan 1, 1958

By J. J. Brown

Wilkes-Barre Meeting, Julie, runs., THE ore-hearth was the earliest type of furnace used in smelting Mississippi Valley lead-ores, which are very pure, and low in silver-content. The first smelters made no attempts to recover lead from the smoke; and since about 15 per cent. of the lead -in the charge escaped in this manner, early practice with the hearth was decidedly wasteful. At most of the large smelting-plants blast-furnaces with auxiliary roasters were substituted for the hearths long ago. But, upon the introduction of the Lewis and Bartlett bag-process for collecting fume, the ore-hearth was used by companies engaged in the manufacture -of pigments, simply on account of the large percentage of fume made by it. In fact, the extraction of lead was kept down by the use of hot blast and other devices. During recent years, however, several smelting companies have realized that the preliminary roasting of galena for the blast-furnace is not economical, and have, therefore, replaced the roasting-furnace with a modification. of the old Scotch hearth, in which a large percentage of the lead in a charge is recovered directly as pig-lead, while the remainder passes partly into fume and partly into slag low enough in sulphur to be charged into the blast-furnace without further treatment. The results obtained have proved so satisfactory, both As to recovery and operating-expense, that one eminent metallurgist has predicted the universal use of the ore-hearth on non-argentiferous ores. The-ore-hearth, thus employed as an adjunct to a blast-furnace plant, is rather a desulphurizer than a smelting-furnace proper,-the chief object being to make a blue slag suitable for the cupola-furnace. Hence, no special care is taken to obtain from it a large lead-extraction. * Head of Department of Ore Dressing and Metallurgy, Oklahoma School of Mines and Metallurgy, Wilburton, Okla.

May 1, 1911

By J. C. De Haven, Harry Seltz

INTERMETALLIC compounds are formed in many binary metal systems. Some compounds are stable to their melting points, and others decompose at lower transition temperatures. Even those of the first class are dissociated in the liquid state, as indicated by the continuous form of their solubility curves at their melting points'. While the lattice structures of some of these compounds' have been determined, their thermodynamic properties have not been investigated. In this paper is described the determination of the free energy and heat of formation of the compound CdSb, which is of the first class mentioned above, melting congruently at 455° C. This compound shows a rhombic structure, and the lengths of the edges of the elementary cell containing four molecules are: a = 6.52,b=8.60,c=4.16Å2 There are three possible methods of determining the free energy of formation of a compound of this type. The first method, applying the third law of thermodynamics, requires the measurement of its heat capacity preferably to liquid hydrogen temperatures, and a calorimetric determination of its heat of formation. The second method involves the study of the equilibrium of the compound in some gas reaction, such as: CdSb + CO2 = CdO + CO + Sb. From the known free energies of formation of, CdO, CO2 and CO the free energy of formation of CdSb could be calculated. The third method measures the electromotive force of a galvanic cell in which the cell

Jan 1, 1935

By W. H. Emmons

THIS paper is the third of a series treating of the relations of ores of the metals to igneous rocks. The first1 outlined the general problem; the second2 proposed a classification of lode ores, and showed how the distribution of the deposits is in a certain measure controlled by the contour of the roof of the parent batholith. A number of mining districts were discussed, the examples being selected chiefly from group 2 of the classification. The proposed classification of lode deposits, briefly stated, is as follows: 1. Cryptobatholithic: near hidden batholiths which have not yet been exhumed by erosion. 2. Acrobatholithic: in and near cupolas or domes of batholiths-the high points of larger underlying masses. 3. Epibatholithic: on batholiths, near their rims, but below eroded cupolas, or below the highest points of the roofs. 4. Embatholithic: among closely-spaced outcrops which probably are parts of a single batholith. The outcrops of invaded rocks predominate. 5. Endobatholithic: in and near roof pendants of large batholiths. The invading rocks predominate. 6. Hypobatholithic: in deeply-eroded batholiths, where even roof pendants, have been -eroded. Deposits of certain metals on the roofs of the batholiths are much more numerous in some positions than deposits of other metals, and the horizontal zonal arrangements of lodes of different metals are shown characteristically only in certain groups. In a large measure, also, the character of the fracturing and metallization is determined by, the-position on the roof, of the batholith.

Jan 1, 1927

For the first time in its history the Institute will hold a meeting in the State of Arizona. A few years ago Arizona stood third in the copper-producing districts of the United States. Since that time, with the development of porphyry mines, the output has gone up with great rapidity until it not only is the leading district, but its output at the present tune is at the rate of nearly double the Montana output; which now stands second in the list. In connection with this development, most interesting departures have been made in methods of mining, concentration and smelting. Principles of mining and metallurgy of the greatest interest will be covered by papers which will appear in the Bulletin and be presented at Technical Sessions, while ample opportunity 'will ,be- afforded for those who go to the meeting to see all the points of interest to them. In addition, members will be well rewarded by the marvelous natural features to be seen on the trip, including the petrified forests, the cliff dwellings on the Apache Trail and the Grand Canyon of Arizona. It is planned to start the special train from New York, but members and guests may join the special at other points en route as indicated by the following schedule: ITINERARY Thursday; September 14th, Lv New York Grand Central Terminal 5.30 p.m. Dinner in dining car, a la carte

Jan 9, 1916

By David E. Hyatt, Christopher H. Cox, Franklin T. Davis

INTRODUCTION The composition of water used in the flotation process has always been of primary interest to the flotation metallurgist. It is by alteration of the chemistry of the water introduced to the process that flotation separation is effected. In only a few cases has it been necessary to treat available water prior to use in the process. In the past, flotation tailings were treated for the removal of solids via the tailings dam and water decanted from the dam was either recirculated to the process or discharged to the surface water system. The choice of recirculation or discharge was based upon water availability, effect of recycle water on the process, and economic considerations. The Federal Water Pollution Control Act Amendments of 1972 have charged the United States Environmental Protection Agency with establishing effluent limitations from point sources of discharge into the navigable water of the United States. A detailed study, sponsored by EPA, of the water of ore processing plants took place in 1974 and 1975 and guidelines for these plants will presumably have been published by the time this paper has been presented(1). The action of many of the individual states preceded the EPA in this attempt to regulate the quality of the water discharged from industrial point sources. Even with recycle of tailings water, some water is discharged from tailings dams into the substrata and at least one state is currently preparing guidelines for the quality of water discharged into the substrata.

Jan 1, 1976

Henry M. Parks, director of the Oregon. Bureau of Mines and Geology, has supplied the following information regarding a recent discovery .of manganese ore in Jefferson County, Oregon, about seventeen miles southeast of the railroad at Eagle Point, a station on the P. & E. Railway. The occurrence is about five miles southeast of Lake Creek Post Office and near the confluence of Lost Creek with the south fork of Little Butte Creek. The manganese ore occurs as psilomelane and pyrolusite, disseminated through a flat bed of volcanic tuff breccia; at a point where the bed was penetrated by a churn drill hole, the thickness of the ore-bearing stratum was 30 ft. Development thus far has consisted of open-cuts, one of which exposes a face about 40 ft. high and 75 ft. broad. Other smaller open-cuts have followed the bed for a. distance of 400 yards. The nodules of manganese mineral vary from a maximum of 25 to 50, lb. down to the size of beans and others as small as mustard seed. These grains, when clean, average from 55 to 58 per cent. manganese. A 12-ft. groove sample in the face of the main open-cut yielded 14.86 per cent. manganese. The peculiar occurrence of the manganese nodules should present but slight difficulty in concentration. A small experimental mill was built last winter, comprising gyratory crusher, rolls, and jigs, which,

Jan 8, 1918

By Raymond Mancha

WHEN calculating the pressure-volume characteristics of projected mine-ventilat-ing circuits by orthodox methods, certain basic assumptions are required in order to employ the various available empirical data. It is assumed, for example, that the mine air is an incompressible fluid subjected to isothermal flow, an assumption suffi-ciently accurate for practical purposes since pressure and temperature differentials are small throughout the average circuit. A more erroneous assumption, however, is that all air is accounted for as it travels throughout the mine. No attempt is usually made to evaluate stopping leakage as it occurs; instead, the air volume required at the last crosscuts is assumed to enter the mine, travel the vari-ous intake air courses intact, sweep the workings and travel out by the return air courses to the point or points of exit from the mine. Actually, there is a leakage of air from intake to return at every stopping, the quantity of this leakage depending upon the tightness of the stopping and the pres-sure difference across the stopping. Unfortunately, a lack of empirical data and knowledge of the condition of individ-ual stoppings makes an exact analysis of underground stopping leakage impossible. Generally, leakage is most severe through the old stoppings outbye the circuit. These are also subjected to higher pressure differ-ences than the newer inbye stoppings. Therefore the circuit air volume diminishes at a decreasing rate progressing from out-bye to inbye the circuit.

Jan 1, 1940

THE papers by G. F. Loughlin and I. A. Ettlinger discussed the distribution of formations and ore-bodies in two of the main mining districts of the Southwest. The convergence of the deeper orebodies at Cripple Creek points to their common hypogene ori-gin, as do the occurrences of the copper ores of, central Arizona. E. L. Bruce described the areas in southwestern On-tario around Red Lake and Woman Lake, another prom-ising gold district. Of special interest was a series of lantern slides showing the use of power-driven boats and of hydroplanes as means of transportation. Within a few years, no doubt; such devices will revolutionize the mining industry and reconnaissance mapping in these relatively inaccessible areas. Much interest was evinced in the paper by J. W. Finch on "Sedimentary Metalliferous Deposits of the Red Beds." It was written as a caution to people at-tempting to mine these deposits. The discussion of the chemical equations presented in the paper brought out the fact that a large amount of study of such ores is necessary before we shall be able to write equations to explain their formation. Especially pertinent were the discussions by David White as to the relation of decay-ing plant tissue to metalliferous deposits and the color of sediments; also the point brought out by T. S. Lover-ing that chemical compounds produced by bacteria may greatly affect the deposition and reorganization of sedi-mentary metalliferous deposits.

Jan 3, 1928

By M. J. Ginsberg, N. A. Gokcen

THE preliminary study of electrochemical desul-furization performed by Ohtani and Gokcen1 left a number of points concerning the process to be investigated. Two of these were i) the determination of the effect of greater current and voltage on the desulfurizing Flower of acid slags (% CaO/% SiO2- 1) and ii) the possibility of the loss of silica in slag by the reactions 2C (in metal) + SiO2 (slag) = Si (in metal) + 2CO(g) and C + SiO2 (in slag) = SiO(g) + cO(g) proceeding to a point at which the composition of the slag was sufficiently altered toward the basic side so a1.s to noticeably affect the rate of de-sulfurization. The apparatus and the procedure used in the present investigation were the same as those used by Ohtani and Gokcen, except the control circuit was connected to 120 v dc instead of 24 v dc and thereby allowed greater freedom in choosing the values of both current and voltage. The graphite crucible containing the melt and serving as the cathode was 3-in. high, and was of 1 1/2-in. ID with a graphite bar of 3/8-in. diam and 8-in. length threaded into the bottom for electrical connection. This was placed into a magnesja outer crucible with a hole in the bottom and alumina insulation was packed between the two crucibles. A charge consisting of 180 g of

Jan 1, 1962

By Kent E. McElhattan

Selecting efficient machinery for an underground mining operation is a highly skilled art that still depends largely on human judgment and experience. In a coal mine, for example, there is no better way to predict the results of operating with a cutting machine or a continuous miner than to go underground with a sharp-pointed miner's pick. The trained eye can detect the depth of point penetration, cleavage planes, roof and floor strata, and many other conditions impossible to determine in a laboratory. Even so, however, an entirely new set of conditions may lie unexposed just a few feet behind the solid face. The candid truth of the matter is that practically nothing is known of the phenomenon of extracting a mineral from a solid. Consequently, the selection of mineral extraction machinery and systems must be based on results obtained elsewhere under apparently similar conditions. A recent study of the problem of equipment and system analysis was conducted in the coal mining regions of West Virginia. This state was chosen for study because it afforded representative sampling. The 172 coal mines investigated ecompassed seam heights ranging from less than 30 in. to over 84 in. and covered virtually all known coal mining conditions except two. The exceptions are the extreme pitch of coal seams in the western United States and British Columbia and the "bumps" encountered in the Rocky Mountains. Both of these extreme conditions are worthy of individual study.

Jan 7, 1969

By A. Spilners, M. Simnad

The rates of formation of the different oxides on molybdenum in pure oxygen at 1 atm pressure have been determined in the temperature range 500° to 770°C. The rate of vaporization of MOO, is linear with time, and the energy of activation for its vaporization is 53,000 cal per mol below 650°C and 89,600 cal per mol at temperatures above 650°C. The ratio Mo03(vapor.lzing)/MoOS3(suriace) increases in a complicated manner with time and temperature. There is a maximum in the total rate of oxidation at 6W°C. At temperatures below 600°C, an activation energy of 48,900 cal per mol for the formation of total MOO, on molybdenum has been evaluated. The suboxide Moo2 does not increase beyond a very small critical thickness. At temperatures above 725°C, catastrophic oxidation of an autocatalytic nature was encountered. Pronounced pitting of the metal was found to occur in the temperature range 550° to 650°C. Marker movement experiments indicate that the oxides on molybdenum grow almost entirely by diffusion of oxygen anions. USEFUL life of molybdenum in air at elevated temperatures is limited by the unprotective nature of its oxide which begins to volatilize at moderate temperatures. Although the oxide/metal volume ratio is greater than one, the protective nature of the oxide film is very limited. Gulbransen and Hickman' have shown, by means of electron diffraction studies, that the oxides formed during the oxidation of molybdenum are MOO, and MOO,. The dioxide is the one present next to the metal surface and the trioxide is formed by the oxidation of the dioxide. Molybdenum dioxide is a brownish-black oxide which can be reduced by hydrogen at about 500°C. Molybdenum trioxide has a colorless transparent rhombic crystal structure when sublimed, but on the metal surface it has a yellowish-white fibrous structure. It is reported to be volatile at temperatures above 500" and melts at 795°C. It is soluble in ammonia, which does not affect the dioxide or the metal. In his extensive and classic investigations of the oxidation of metals, Gulbransen2 has studied the formation of thin oxide films on molybdenum in the temperature range 250" to 523°C. These experiments were carried out in a vacuum microbalance, and the effect of pressure (in the range 10-6 yo 76 mm Hg), surface preparation, concentration of inert gas in the lattice, cycling procedures in temperature, and vacuum effect were studied. The oxidation was found to follow the parabolic law from 250" to 450°C and deviations started to occur at 450 °C. The rates of evaporation of a thick oxide film were also studied at temperatures of 474" to 523°C. In vacua of the order of 10- km Hg and at elevated temperatures, an oxidation process was observed, since the oxide that formed at these low pressures consisted of MOO, which has a protective action to further reaction in vacua at temperatures up to 1000°C. Electron diffraction studies showed that, as the film thickened in the low temperature range, MOO8 became predominant on the surface. Above 400°C MOO, was no longer observed, MOO, being the only oxide detected. The failure to detect MOO, on the surface of the film formed at the higher temperatures does not militate against the formation of this oxide, since according to free energy data MOO3, is stable up to much higher temperatures. At the low pressures employed, this oxide would volatilize off as soon as it was formed. Its vapor pressure is relatively high and is given by the equations" log p(mm iig) = -16,140 T-1 -5.53 log T + 30.69 (25°C—melting point) log p(mm He) = -14,560 T-1 -7.04 log T+1 + 34.07 (melting-boiling point). Lustman4 has reported some results on the scaling of molybdenum in air which indicate a discontinuity at the melting point of MOO, (795°C). Above the melting point of MOO,, oxidation is accompanied by loss of weight, since the oxide formed flows off the surface as soon as it is formed.5,6 Qathenau and Meijering7 point out that the eutectic MOO2-MOO3 melts at 778C, and they ascribe the catastrophic oxidation of alloys of high molybdenum content to the formation of low melting point eutectics of MOO3 with the oxides of the melts present. Fontana and Leslie -explain the same phenomenon in terms of the volatility of MOO,, which leads to the formation of a porous scale. Recent unpublished work by Speiser9 n the oxidation of molybdenum in air at temperatures between 480" and 960°C shows that the rate of weight change of molybdenum is controlled by the relationship between the rates of formation and evaporation of MOO,. They have measured the rates of evaporation of Moo3 in air at different temperatures and estimated an activation energy of 46,900 cal. This compares with the value of 50,800 cal per mol obtained by Gulbransen for the rate of sublimation of MOO, into a vacuum.

Jan 1, 1956

By Bruce A. Kennedy

The first light of dawn was appearing through the window of the giant Pan American Boeing 747 as we crossed the Irish Coast on course into London's Heathrow Airport While still over Ireland, the plane began its descent and a few minutes later an announcement on the public address system informed us that we were coming up on Lands End. Cornwall, and would then begin our final approach into London. Barely visible below through the WISP). clouds were the Seven Sisters Lighthouse and the rugged cliffs of Lands End and Cape Cornwall, the westcrnmost point of England. Start at Lands End To a displaced Englishman, it seems amazing that technology has brought us to a point where large jet aircraft use Lands End as the starting marker for final approaches into London. It was not so very long ago that we considered the eight-hour car journey or the 12- hour train trip from London to Lands End as a major undertaking. Today, with the 180,000-lb thrust of four engines, this enormous aircraft transports 350 or more passengers that distance in a matter of a quarter of an hour. The incongruity of the situation is that the technology leading up to the development of the powerful jet engines used on: today's aircraft started with the ; invention of the steam engine which found its first commercial use some 300 years earlier in the mines of Cornwall 20,000 ft below.

Jan 1, 1971

By E. K. Landis

The question of magnetic concentration is assuming considerable importance, and the efficiency of the different concentrating-machines is widely discussed. As the amount of iron left in the tails must vary with commercial requirements, and with the nature of the minerals in the tails, the writer feels justified in calling attention to some points often overlooked. In almost every such commercial operation a point is reached beyond which it does not pay to go, the material saved by further operations being obtained at a cost too great. The amount of iron left in the tails from concentration must depend, therefore, upon the cost of crushing, the size to which the ore is crushed, the nature of the minerals in the gangue, and the nature of the ore itself. Some ores are so intimately mixed with their gangue that a large loss of iron in the tails is unavoidable. In many cases the gangue contains hornblende, pyroxene, serpentine, etc., which carry considerable iron as silicate, or otherwise combined, and this iron a magnetic machine cannot extract, since the minerals themselves are not magnetic. It is evidently unfair to charge the machine with this loss of iron; and hence a satisfactory test of any such apparatus would require that the iron present in the ore as magnetite should be determined, and the proportion in the tailings of such iron only should be the measure of the loss, as compared with theoretical efficiency.

Jan 1, 1892

By E. J. Quinn, M. F. Fogler

In a recent paper, Rawdon and Mutchlerl gave some exceptionally interesting results on the Brinell and scratch hardness of severely cold-worked metals. In their work, they found that, on continued cold rolling, the metal hardened up to a particular point and then reversed and became softer; this was true for both Brinell and scratch hardness values. The generally reported behavior2 of metals, with respect to Brinell tests on cold-worked material, is that the metals harden up to a certain point and then, on further cold rolling, no change in Brinell hardness occurs. Jeffries and Archer3 state that there is little difference between the scratch hardness of annealed and cold-worked metals; the work of Faust and Tammann4 also indicated no difference between the hardness of annealed and cold-worked copper. Rawdon and Mutchler found, when they plotted the reduction ratio (initial thickness divided by thickness after rolling) against the hardness value for the cold-rolled material, that the hardness number increased up to a reduction ratio of about 3 and then decreased and became even smaller than that for the annealed metal. This behavior was reported for both scratch and Brinell hardness; Figs. 1 and 2 show their results for Brinell hardness on the metals for which they published data. This is an exceptionally interesting phenomenon, if it occurs under all conditions of rolling, and would have an important bearing on the practice of cold

Jan 1, 1925