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By O. K. Riegger, L. H. Van Vlack

The median angle of relatively few two-dimensional observations provides a satisfactory value for dihedral angle determinations. Those data that contain bimodal or non-equilibriated dihedral angle distributions are readily detected. THIS paper is concerned with a statistical simplification for determining dihedral angles in solids. Microstructures are partially controlled by relative energies of interphase boundaries and grain boundaries. smith1 has shown rather conclusively that such boundaries may be equilibrated to give a vectorial balance at grain and phase edges. Thus if an accurate measurement is made of the dihedral angle associated with grain and phase edges, an accurate calculation of the relative energies may also be made. The accurate measurement is difficult because the dihedral angle involves two planes in three dimensions, and only a two-dimensional cut through the dihedral angle is usually observed. Such a two-dimensional cut is statistically random provided there is no preselection or orientation. Harker and parker2 have shown that the mode of the frequency distribution of observed angles is within 5 deg of the true angle if the true dihedral angle is 120 deg. smith1 had calculations made to show that the same generalization could apply to dihedral angles of 30, 60, 90, and 150 deg. This procedure of requiring the determination of the statistical mode is time consuming because experience has shown that more than 200 angle observations are necessary before the mode is clearly indicated. It is possible to determine the dihedral angle with equal accuracy with only 25 angle observations if the median angle is used in place of the mode angle. Use is made of Harker and parker's2 basic equation tan =2 sin x cos

Jan 1, 1961

By T. D. Yensen

AGING is a term that connotes a slow change in properties under ordinary operating conditions. It can be accelerated by increasing the temperature and by mechanical straining. The magnetic properties of iron and some of its alloys have for many years been known to be subject to such a change. But the cause of the change was not recognized until a few years ago after mechanical age-hardening in non-ferrous alloys of the "duralumin" type had been definitely shown, by means of solid solubility curves, changes in electrical resistance and microanalysis, to be caused by slow precipitation of one or more con-stituents from the solid solution. The similarity between the solid solubility curves of such alloys (Fig. 1) and those for iron-nitrogen (Fig. 2) and iron-carbon alloys (Fig. 3) below the Al transformation point suggested at once that magnetic aging of iron might be caused by a similar process; namely, by the slow precipitation of carbon and nitrogen in the form of Fe4N and Fe3C at ordinary temperatures because of a cooling rate that had been too rapid to permit complete precipitation according to equilibrium conditions. This suggestion has since been amply confirmed, particularly by the comprehensive work of Köster1 on the effect of nitrogen and carbon. Typical curves are shown in Fig. 4 for the relationship between aging temperature and coercive force. Previous to the establishment of the precipitation-hardening theory it was thought that the effect of nonmetallic elements like C, N, 0, etc., on the magnetic properties of iron was greatest when these elements were retained in solid solution, atomically dispersed throughout the interstitial spaces of the iron lattice2.

Jan 1, 1935

By R. G. Ward

The temperature gradient in the subhearth metal or "salamandern of the iron bhst furnace results in the establishment of gradients in the concentrations of silicon, manganese, carbon, and sulfur. The temperature and compositional variations observed in three blast furnaces are analyzed according to irreversible thermodynamics and the systems appear to be close to the steady state condition. Apparent heats of transport, Q, for silicon, manganese, carbon, and sulfur are found to be respectively -17.5, -5, -2.1, and+22k cal per g mol. In conclusion the significance of thermal diffusion in extraction metallurgy is briefly discussed. INCREASING interest has been shown in recent years in the application of irreversible thermodynamics to metallurgical problems. In particular studies have been made of the transport of matter in thermal gradients1-' and under chemical gradients imposed by a binary solvent However, no detailed example in extraction metallurgy has been reported although gradients are the essence of many extractive processes. The case of the distribution of elements in molten blast furnace iron under a thermal gradient is discussed here. DATA In blast furnace operation the hearth bottom is often extensively destroyed by molten metal, and the metal may penetrate perhaps 10 ft into the furnace foundations forming a "bear" or "salamander". Several hundred tons of molten metal may thus exist beneath the level of the conventional tap hole and remain relatively undisturbed for several years under a thermal gradient. This system is subject to little convective stirring because the temperature decreases from top to bottom, and mechanical stirring due to movements in the stack and to tapping operations is unlikely to penetrate far into the metal. The system may thus be regarded as static

Jan 1, 1963

By B. H. Bergstrom, A. P. Cohen, D. W. Fuerstenau

B.H. Bergstrorn (Research Div., Allis-Chalmers Mfg. Co., Milwaukee, Wis.) — Fuerstenau and Cohen have concluded from our study of single particle crushing, which had suggested that the size moduli of the crushed specimens were determined by the specific energy expended independent of feed size, that the same independence with respect to feed size exists for the specific energy-product size relationship for rod mills. They present data supporting this conclusion. Our single particle crushing experiments were on single spheres of soda-lime (type of glass was not given in our study) glass for which the feed size can truly be neglected. However, the feed size cannot be neglected in any case where the effective size modulus of the feed is not too much coarser than the size modulus of the product. This can be illustrated in the second experi- ment of Fuerstenau and Cohen where the feed is considered to be the original -6 +%mesh material. However, one can also consider the product from the 7.5-min grind to be the feed for the 10, 15, 20, 25-min grinds, and the 10-min product to be the feed for the 15, 20, 25-min grinds, etc. If the specific energy-product size moduli curves are drawn for these other feeds, as shown on Fig. 3, the new curves (and some curvature is apparent) are much steeper than the -6 +%mesh feed line. The slopes of these new curves are about -1.5, —1.8 and -3.0. This observation is in accord with the observation by Bond, who states that the net specific energy input to a grinding mill is equal to the specific energy represented by the product less the specific energy represented by the feed. Bond presents, on a diagram similar to Fig. 3, a series of curves which illustrate the effect of

Jan 1, 1963

By H. C. George

CAREFUL- sampling and good judgment as to probable recoveries are important factors in estimates of ore reserves, based on prospecting drilling results, but other factors are equally as important and may be more misleading and perhaps disastrous if not properly interpreted. Some of these are: 1. The case where no, ore is shown in the "sludgings," when, as a matter of fact, the drill has passed through a thick sheet of ore which has been broken up and washed away into open crevices. In numerous cases, later mining operations have shown that this has happened. This condition may be discovered by shooting the drill .hole at the point where the open crevices occur, but shooting should not be done until after the drill hole is completed, because the resulting shattered formation may salt the drill hole at lower levels. 2. The case where rich cuttings are shown for a thickness of 20 or 30 ft., when ore was encountered in only the first sludging. Owing to soft or loose formation, the ore from the first sludging has salted the lower sludgings. The presence of large pieces of ore and a similar ratio between zinc and iron assays in the lower sludgings frequently indicate this condition. In the lower sludgings, the presence of oxidized ore in unaltered limestone sometimes shows this condition. 3. The case where the drill hole shows a considerable thickness of ore; but owing to the presence of a vertical sheet of ore, perhaps not more than 1 in. thick, at the place where the drill hole is located, the good assays resulting might be misleading. If this condition is suspected, the drilling of several more holes within a distance of 10 or 15, ft. will usually show it.

Jan 1, 1921

By Joseph W. Richards

(New York Meeting, February, 1912.) THE Ashio copper-mine of the Furukawa Mining Co. is situated 18 miles from Nikko, and 109 miles north of Tokyo, near the center of Japan. The mine-waters are run over scrap-iron, whereby most of the copper is precipitated as cement copper, leaving iron sulphate with some copper sulphate in solution. After using in the wet concentrating ore-dressing plant, the waste water contains clay and ore-slimes. The only avenue of disposal of this water is the Watarese river; but as this flows through valleys in which the water is used for irrigating the rice-crops, it is necessary to purify and clarify the water before discharge. The water amounts to from 600 to 700 cu. ft. (from 17 to 20 cu. m.) per minute, and averages about 0.00025 per cent. of copper, representing more than 18 tons of copper per month. The water carries H2SO4, FeSO4, Fe, (SO,),, CuSO4 and other metallic sulphates in solution, and clay, ore-fines, slimes and basic. iron sulphates as suspended matters. To purify and clarify the water, precipitation by milk of lime has been used, in three different ways, as follows: I. First Method, Copper not Recovered. Milk of lime was run into the water, and the mixture run through six settling-ponds, and then through a sand filter into the river. Fig. 1 is a view of the settling- and filtering-ponds. In the first pond, sand and metallic hydrates free from copper collected; in the next five ponds, slime, calcium sulphate, and metallic hydrates carrying copper settled out. The effluent carried from 0.1 to 0.05 mg. of copper per liter

Jun 1, 1912

By Ancel St. John

AT THE New York meeting of the Institute of Metals Division in February, 1927, Jeffries and Tarasov presented a paper on Tungsten and Thoria,1 in which the experimental facts were interpreted in accordance with the prevailing point of view that the thorium is present as the oxide, thoria. In discussing that paper the writer of this article stated that his own investigations, which had been unavailable to Messrs. Jeffries and Tarasov, showed that the so-called "thoriated" tungsten filament failed to disclose any sign of the oxide when subjected to X-ray diffraction analysis, but did give plenty of evidence of the presence of metallic thorium and, in certain cases, of a material believed to be an alloy of tungsten in thorium. Since these results were completely at variance with the results reported in the paper under discussion and with other papers which had preceded it from time to time in the past, it was felt that further discussion should be withheld until the new evidence could be presented adequately. Arrangements were therefore made to present that evidence at this meeting. MATERIAL EXAMINED The material examined was high-emission filament such as is used in radio tubes, supposed to contain about 0.75 per cent. thoria. The actual analysis was not stated. SCOPE OF THE INVESTIGATION The investigation was undertaken because of a feeling that the thorium present in filamentary material of this type exists as metallic thorium or as an alloy of thorium and tungsten and not as the oxide. Attention was therefore directed to determining: 1. The minimum amount of thoria detectible in a mechanical mixture of thoria powder and finely divided tungsten. 2. The amount of thoria detectible in the filament. 3. The condition of any thorium present in other form than as thoria. 4. The amount of thorium dissolved in the tungsten.

Jan 1, 1928

By JOHN BIRKNBINE

MR. NEILSON was born Aug. 12, 1842, at Philadelphia, Pa., where he died Dec. 30, 1906. His business career began with his graduation, in the class of 1862, from the Polytechnic College of the State of Pennsylvania. For a short time after graduation he was instructor in mathematics at the college, and then became associated with Messrs. Booth & Garrett, chemists, of his native city: In 1867 he was sent to the Adirondack mountains to care for mining interests of the late Jay Cooke, and spent about three years there, operating the forges at Elizabethtown, Essex county, N. Y. He also prepared an interesting monograph on Catalan forges and their operations. In 1868 he published a chart showing the material progress of the United States, and the cost of certain staple products during a series of years, which is believed to be the first of its kind issued in this country. In 1870 he made a trip to the Pacific Coast, prior to entering the service of the Pennsylvania Steel Company. In 1871, when the Logan Iron & Steel Co., of Burnham, Pa., failed, Mr. Neilson was appointed receiver, re-organized the company, became' its General Manager, and spent more than four years in this work. In the meantime, he became interested in the Freedom forge of the same place, and, with Mr. Wm. Burnham and Mr. Milton Brosius, laid the foundations for what is now the Standard Steel Works. From Jan. 1, 1877, to April 1, 1890, he was General Manager of these works, and closely associated with the Baldwin Locomotive Works. In 1878 he was in charge of the first consignment of Baldwin locomotives to Europe, which, with a picked crew of men from Baldwin's, he took to Eydtkennen, Russia, and placed in service. In 1890 he resigned from the Standard Steel Works and ac-

Jul 1, 1907

By Philip Drinker, R. M. Thomson

In the mining and metallurgical industries, numerous problems arise requiring determinations of solid and of liquid particles suspended in air. Frequently, these problems are of local interest and involve purely economic or operating difficulties; on the other hand, toxic effects from the inhalation or the ingestion of substances suspended in air may be a matter of concern. For checking up process improvements or for determining ventilation efficiencies in problems of this general nature, various methods have been proposed. .Although simpler methods are often satisfactory, precipitation combines several desirable features that other methods lack. This paper is, therefore, devoted to a discussion of portable alternating-current precipitators applicable to the quantitat,ive determination and microscopy of dusts, fumes, and smokes in air. Small particles suspended in gases, such as air, are referred to in the literature as aerosols or suspensoids. Of these terms, suspensoids appears to be preferable as being more nearly in keeping with words in everyday use. In problems involving air pollution by small particles—by suspensoids—it is convenient to distinguish three broad classes based on the size, the degree of dispersion, and the method by which the particles become suspended in the air. Dusts.—Particles or aggregates of particles, 150 to 1 micron in diameter, that are thrown into the air by mechanical agencies are termed dusts. Examples are silica; talc; cement; organic dusts such as hard rubber, starch, and cocoa; flocculated fume, and smoke products. Fumes.—Particles, 0.2 to 1 micron in diameter, formed from chemical or physicochemical reactions are known as fumes. Examples are ammonium chloride, lead and mercury, zinc and magnesium oxides, fogs, and acid mists. Smokes.—Particles, less than 0.3 micron in diameter, formed by incomplete combustion of carbonaceous and other substances are called smokes. Examples are the particles formed from burning tobacco, oil, tar, and gas.

Jan 1, 1925

By Walter White

THE measurement of the reading of a thermoelement is the measurement of an electromotive force extraordinarily small compared to those generally used in commercial work. Of the various possible methods of measuring such a quantity, the most advantageous is always a delicate galvanometer. Since a galvanometer measures current, it is necessary to adopt some scheme by which its current reading shall indicate electromotive force. There are two general methods of doing this. One is to use the delicate galvanometer as a "direct reader," that is, to let the electromotive force of the thermoelement furnish the power and produce the current measured. If the resistance is constant the reading will, after a suitable calibration, give the electromotive force of the thermoelement which, by means of a table or of a suitable scale in the galvanometer itself, will FIG. 1.-SIMPLIFIED POTENTIOMETER. POTENTIAL DROP ACROSS THE PART PIN or CIRCUIT OF BULL CELL BALANCES THAT OF THERMOELEMENT TC WHEN GALVANOMETER G READS ZERO. give the temperature. The other method, that of the potentiometer, is to balance the electromotive force of the thermoelement by means of another electromotive force, using the galvanometer to tell when the balance is made. The usual way of getting this other electromotive force is to have a battery, the "bull" cell, send a current through a series of resistances, which 'may in a special case be the resistance of a single wire. The fall of potential along this circuit will then, by Ohm's Law, be proportional to the resistance; the potential difference between any two points, proportional to the resistance between the two points. This is represented in Fig. 1, where M and N are the two points in the circuit AZ of the battery. If M or N, or both, is movable so that the resistance

Jan 9, 1919

By H. S. Martin

THE Phosphate Recovery Corporation operates three flotation plants, Nos. 1 and 2 concentrators about three miles northeast of Mulberry, Florida, and No. 3 plant at Wales, Tennessee. These plants represent the first commercial phosphate flotation operation and are also believed to be the largest nonmetallic flotation operation in the world at the pres-ent time. The details of this paper will be confined to plant No. 2, this being the newest and largest concentrator in Florida, and the flow sheet being practically the same as at plant No. 1. The No. 3 plant has been oper-ated but a short time and has been shut down since December, 1932, on account of the decrease in phosphate rock production. The phosphate washers usually are located centrally on a known deposit so that about two hundred acres of ground can be mined eco-nomically to each washer location. The washers are moved to new areas when the distance becomes too great for economical pumping. The flotation plants are built either adjacent to a washer, so that current debris may be utilized, or on the site of a former washer where there is sufficient accumulated debris available for mining, and the flotation plants must also be moved from time to time. Most of the water used in the Florida flotation plants is recovered after passing through a circulating system where most of the fine sus-pended matter is settled out, but some make-up water is obtained from deep wells near the plant. Power is obtained from the Tampa Electric Co. through the dis-tribution facilities of the International Agricultural Corporation. Flotation concentrate is hauled from the plant by trolley over the International Agricultural Corporation's trolley system, to the drying plant at Prairie, one mile northwest of Mulberry.

Jan 1, 1933

By Damon H. McFadden

5.1-1. Geographic and Geologic Factors. Surface mines are located where the coal seam can be economically uncovered and where the product can be utilized competitively with other fuels. The planning and designing of a pit may follow various procedures. The sequence for consideration of the influential factors as considered here may not be complete for every pit, nor will it be necessary to be completely used in each design. It is suggested as a check and outline for the engineering approach. Controlling conditions for the layout should be listed and considered with the facilities and equipment for the exploitation. After these items, as listed below, have been discussed and the feasibility agreed upon, then the actual planning and design of the pit can be done. GEOGRAPHIC FEATURES. The location of the coal area sets the climatic stage. The rainfall, the temperature extremes, and the general weather conditions all affect the design of the pit. Overburden soil when wet may not be stackable and may be impossible to move by standard procedures. The coal seam itself may be so soft that it must not be traveled on when wet, as the losses may be the difference between a profitable venture and an unsuccessful one. Some equipment will work well on dry soil only, just as a dredge works only in the wet. The conditions must be checked and analyzed. Some equipment cannot handle frozen soil (wheel excavators), so temperature extremes must be noted. The extreme weather conditions may also govern the expected working days and therefore the ultimate production. The altitude (atmospheric pressure) may affect the equipment, and this should be checked. All of these conditions should be noted on the preliminary map of the area. GEOLOGIC FACTORS. The geologic and surface conditions of the coal field dictate the type of pit generally feasible. Rough terrain, rolling terrain,

Jan 1, 1968

By Wallce E. Pratt

The Philippine Islands have produced no oil commercially; nevertheless, oil is known to be present at various places in the is1ands.l Although all attempts to produce oil commercially have failed, no intelligent, persistent exploration has been carried out. The Richmond Petroleum Corpn. (a subsidiary of the Standard Oil Co. of California) and a syndicate headed by Ralph Arnold are at present engaged in exploring Bondoc Peninsula in Tayabas Province, one of the promising Philippine areas, in a manner that promises to test the petroleum possibilities adequately and intelligently. How can the petroleum resources of an entirely undeveloped area like the Philippines be estimated, where not even the areal extent of the various geologic formations is known? Obviously no calculated figure for assured future production can be derived. Yet a study of the evidence of the occurrence of petroleum, the character of the possible reservoir beds, the probable source rocks, the character and size of favorable structures, and the area over which petroleum-bearing rocks are known to occur, will throw some light on the question. The fact that rocks of the same geologic age and similar composition have been explored and are producing in Borneo, Sumatra, and Java to the south and in Formosa and Japan to the north also affect the problem, so that one can obtain some idea of the quantity of petroleum that may reasonably be expected from the Philippines. It is this measure of the possibilities rather than a definite calculation of petroleum reserves that is presented herewith. This paper will not attempt to describe, nor even to enumerate in detail, the occurrences of petroleum in the Philippines, as such data have already been published. Fig. 1 indicates the localities where

Jan 1, 1923

By Wallce E. Pratt

The Philippine Islands have produced no oil commercially; nevertheless, oil is known to be present at various places in the is1ands.l Although all attempts to produce oil commercially have failed, no intelligent, persistent exploration has been carried out. The Richmond Petroleum Corpn. (a subsidiary of the Standard Oil Co. of California) and a syndicate headed by Ralph Arnold are at present engaged in exploring Bondoc Peninsula in Tayabas Province, one of the promising Philippine areas, in a manner that promises to test the petroleum possibilities adequately and intelligently. How can the petroleum resources of an entirely undeveloped area like the Philippines be estimated, where not even the areal extent of the various geologic formations is known? Obviously no calculated figure for assured future production can be derived. Yet a study of the evidence of the occurrence of petroleum, the character of the possible reservoir beds, the probable source rocks, the character and size of favorable structures, and the area over which petroleum-bearing rocks are known to occur, will throw some light on the question. The fact that rocks of the same geologic age and similar composition have been explored and are producing in Borneo, Sumatra, and Java to the south and in Formosa and Japan to the north also affect the problem, so that one can obtain some idea of the quantity of petroleum that may reasonably be expected from the Philippines. It is this measure of the possibilities rather than a definite calculation of petroleum reserves that is presented herewith. This paper will not attempt to describe, nor even to enumerate in detail, the occurrences of petroleum in the Philippines, as such data have already been published. Fig. 1 indicates the localities where

Jan 1, 1923

By John W. Tieman

Coal is a term applied to vegetable matter which, through geological processes of heat and pressure, has had both its physical and chemical properties changed. Because its chemical composition is variable, geologists classify coal as a rock rather than a mineral. Peat represents the initial stages in the development of coal, although not classified as coal itself. PHYSICAL PROPERTIES OF COAL The physical properties are concerned with the characteristics of coal in its natural state, or prior to its end use as a fuel. For example, the hardness of coal determines the maintenance cost on coal handling equipment; the specific gravity of coal determines the coal preparation techniques used in a cleaning plant as well as the capacity of coal bins, boats and size of cargo, and other coal storage facilities. The physical properties are, of course, dependent upon the chemical constituents that make up coal, and thus all properties are interrelated. Specific Gravity The specific gravity of a body is the ratio of the weight of the body in air and the weight of an equal volume of water. The specific gravity of pure coal ranges between 1.25 and 1.70, generally increasing with rank. The most important use of this physical characteristic is the part that it plays in the cleaning of coal by wet wash methods. The basic principle on which these operate is that the specific gravity of coals differs from their associated impurities and that there is a relationship between the velocity of the fall of particles in water and their density. Since the specific gravity of slate is around 2.5 and pyrite is about 5.0, pyrite and slate will fall to the bottom of a container filled with water more rapidly than coal. If the water is given a pulsating motion by

Jan 1, 1973

By J. L. Stuck

Geological investigation and research have contributed greatly in making industrial minerals the basis of an important industry in the state. North Carolina contains a wide variety of industrial minerals and rock. Mica, feldspar, kaolin, halloysite, talc, pyrophyllite, silli-manite, and spodumene are used to illustrate the progress being made. IN a previous paper1 an attempt was made to indicate the importance of industrial minerals in North Carolina and the wide variety of such materials present. The present paper is concerned with geological investigation and research which have made industrial minerals the basis of an important industry in the state. Geological mapping has gone through three stages in North Carolina during the present century. The first stage is represented by excellent reports of which Corundum and the Peridotites of Western North Carolina,2 Volume I, now a classic, is representative. In this report, a geologic map of the western third of the state is shown on a scale of 10 miles to the inch. The next stage is represented by folios" of the U. S. Geological Survey published between 1902 and 1932. Most of these contained 30 min quadrangle maps on a scale of 2 miles to the inch. The third step is represented by reports prepared during the past 10 years which contain geological maps4 on scales varying from 500 ft to 1 mile to the inch, while many mine maps have been prepared on scales varying from 20 to 150 ft to the inch. As the scale on which geological mapping has been done has decreased, the amount of information secured has increased. Pratt and Lewis did excellent work on the peridotites of western North Carolina, but their maps lacked details. Keith and others added

Jan 1, 1952

By J. Marvin Weller, M. King Hubbert

Preliminary investigations were undertaken with a Megger Ground Tester in 1931 by Hubbert to determine whether the faults in Hardin County, Illinois, could be located by earth-resistivity surveys. The results of these investigations, which were in part presented before this Institute in 1932,1 were sufficiently promising to warrant a more extensive field program in the same general area the following summer. During the second season an apparatus of the Gish-Rooney type was employed because of its greater sensitivity and to avoid the troublesome correction for resistance of potential electrodes necessitated by the use of a Megger instrument. The discussion of earth-resistivity traverses which constitute the main part of this paper is based entirely upon the results of the second season's work. All of the traverses were made with a constant electrode spacing of a equal to 100 ft., and the four-electrode technique was employed. Successive stations in these traverses were spaced at intervals of 100 ft. and the line of electrodes was carried parallel to the line of traverse. The graphs of resistivity profiles presented here (Figs. 1 to 3) are plotted with resistivities in ohm-centimeters as ordinates and with distance divided into stations at 100-ft. intervals as abscissas. After the traverses were run by Hubbert the results were computed, the profiles plotted, and tentative interpretations were made by him. These curves and interpretations were then taken into the field by Wellcr, who made a careful geological examination along the lines of traverse for the purpose of checking and supplementing Hubbert's interpretations. Weller then constructed a geologic cross-section extending along the line of each traverse. The accompanying diagrams graphically illustrate the correlation that can be made between earth resistivity and geology in this area.

Jan 1, 1934

By J. W. Rutter, K. T. Aust

Competitive growth of recrystallized grains into striated single crystals of zone-refined lead produced preferred orientations of the coincidence type after annealing at 175°C, but not at 300°C. This preferred orientation development was found to result from the higher mobility and lower energy of large -angle coincidence boundaries compared to large-angle noncoincidence boundaries. These mobility and energy difference provide a useful basis for explaining many cases of preferred orientation observed in annealed metals. DURING a study1 of the mobility of grain boundaries in zone refined lead, it was observed that the temperature dependence of the grain boundary migration rate is smaller for large-angle, coincidence-type grain boundaries than for large-angle noncoincidence ("random") boundaries. This observation is illustrated schematically in Fig. 1, which shows log rate of grain boundary migration vs reciprocal absolute temperature for two large-angle boundaries. The upper curve refers to a coincidence-type boundary of the sort discussed by Kronberg and Wilson.2 While the mobilities of these two boundaries are similar at 300°C, the coincidence-type boundary has a greater mobility, by a factor of about: four, at 175°C than does the noncoincidence boundary illustrated in the lower curve. The observation described above suggested a simple experiment for testing the role of grain boundary mobility in the development of preferred orientation in annealed, high-purity lead. On the basis of this observation, it would be expected that if a large number of grains of different orientations are growing competitively, and if relative grain boundary mobility is a controlling factor, then the specimen procluced by boundary migration will contain crystals having random orientations if annealing is done at 300°C, while preferred orientations of

Jan 1, 1962

By P. S. Rudman

The allotropic volume changes of the ,metallic elements are reviezoed with the conclusion that in general atomic volume is conserved to better than 1 pct in such transformations. A table of the atomic volumes of the metallic elements is given and its use in considering the size factor in alloys is discussed. The importance of the concept of atomic-size factor, due to Hume-Rothery and coworkers,' is firmly established. Most attempts at quantitative formulations of this concept have employed the atomic radius (half some interatomic distance) as the measure of size and innumerable tables of such radii exist. This is probably, however, an unfortunate choice of parameter. Firstly, discussion in terms of interatomic distances requires a knowledge of the crystal structure. While this is known, except for a few cases, for the elemental structures, there are still many undetermined alloy structures. Secondly, except for the simpler structures, face-centered cubic (Al),* body-centered cubic (A2),* and hexagonal-close-packed (A3).* with ideal axial ratio, there is no unique in- teratomic distance, an m y decision must be made as to which distance, or which average of the distances, should be used. However, the most important point is that for metals the dominant bonding parameter can generally be expected to be atomic volume and not interatomic distance. This is perhaps most explicitly stated in the Wigner-Seitz cellular method.' In this approximation, cellular polyhedra of atomic volume v are replaced by spheres of radius Y,: 4/3 ?rs3 = v. That is, there is no reference to the interatomic distances. If atomic volume is in fact the dominant parameter, then in allotropic transformations we might expect to find atomic volume approximately conserved. For example, in the A1 ? A2 transformation we would thus have

Jan 1, 1965

By A. F. Nylander, J. H. Jensen

Magnesium, in its combined forms, is the sixth most abundant element and the third most abundant metal in the earth's crust, but it is so reactive that it is never found in nature in the elemental state. As part of the rock-forming minerals like magnesite, dolomite, olivine, and serpentine, it is combined in virtually insoluble forms. As part of soluble minerals like kainite (KC1 MgS04 - 3H20), leonite (K2S0, MgSO, 4H20), langbeinite (K,SO, 2MgS04), and carnallite (KC1 . MgCl? 6H20), it is found in evaporite deposits, generally of marine origin, deep within the earth's crust. Since these minerals are soluble, they are found only in deposits protected from the percolation and leaching action of ground waters by an insoluble and impermeable mantle. Usually this mantle is from several hundred to many thousands of feet thick. Finally, as a solute in marine-like brines, magnesium is common in surface and subterranean waters throughout the world. The oceans, which contain 0.13% Mg, illustrate the inexhaustible nature of the reserve. The recovery of magnesium from the rock-forming minerals, usually by thermal decomposition, and from dilute brines such as sea water by precipitation with lime, are frequent industrial practices. But the recovery of magnesium as magnesium chloride from evaporites or natural brines of concentration greater than sea water has been of little industrial significance for economic and technological reasons. The present US capacity is preponderantly based on the sea-water magnesia process with thermal reduction capacity in second place. No present magnesium capacity is dependent on recovery from the stronger natural brines. But projected capacity, although still weighted in favor of the sea-water magnesia process, is partly based on the recovery of magnesium chloride as a byproduct of potash operations.

Jan 11, 1964