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By R. M. Treco

THE thermal expansion of pure beryllium was first investigated by Hidnert and Sweeneyl in 1925 on a single cast specimen stated to be of 98.9 pct purity. A study of the coefficients of expansion by X-ray methods has recently been made by P. Gordon' on powder obtained from the Brush Beryllium Co. assaying 97 wt pct beryllium with about 2 wt pct oxygen as an impurity. The present work pertains to about the highest purity metal obtainable from the Brush Beryllium Co. This metal was in the form of lumps which were remelted and cast in a high-vacuum induction furnace. Expansion data in this paper deal with beryllium extruded into bars of rectangular cross-section 4x1/2 in. and the anisotropic expansivity of a large cast single crystal. Analysis of the cast metal after extrusion indicated a beryllium assay of 99.28 pct. Impurities were 0.170 pct Fe, 0.140 pct Al, 0.014 pct Mg, 0.086 pct Si, 0.020 pct Cu, 0.020 pct Mn, 0.007 pct Ni, 0.007 pct Ca, 0.080 pct C, 0.179 pct 0, (as BeO). Part I—Extruded Metal Thermal expansion measurements were obtained with a fused quartz-tube differential type dilatom-eter3 on specimens cut from the extruded sections in longitudinal and transverse directions. Specimens were machined to a diameter of 0.250 in. and a length of 3.000 in. One sample from each direction was vacuum annealed for 1 hr at 800°C. The dilatometer tube was placed in a vertical tube furnace having a uniform temperature zone which was twice the length of the sample. Average time for a complete thermal cycle to 500°C was 18 hr. Temperatures were observed with two chromel-alumel thermocouples attached to the sample about 1 M in. apart. The accuracy of temperature measure-ment was ± 0.25°C. An argon gas atmosphere sur-rounded the specimen to prevent oxidation of the beryllium. Samples were identified as shown in table I. Results - The original plan included measuring expansion up to 1000°C, but the first two runs on sample No. 5 showed that a permanent contraction occurred from

Jan 1, 1951

By Julian Glasser, Arthur Fleischer

THIS country was faced with the possible necessity of utilizing nonbauxitic ores for producing aluminum during World War 11. Construction of four experimental plants to treat such ores by four different processes was authorized1-4 including one at Salt Lake City, for the conversion of Marysvale alunite to metal-grade alumina and potassium sulphate by the Kalunite process.' An aluminum reduction plant in Tacoma, Wash., with a capacity of 50 tons of aluminum per day, was constructed to handle the Kalunite alumina produced at the Salt Lake City plant. The alumina and aluminum plants were Defense Plant Corp. projects operated by Kalunite, Inc. and Olin Industries, Inc., respectively. Kalunite alumina differs from Bayer alumina in several respects, particularly in that the former contains potash instead of soda. The presence of potassium in the alumina feed to the cryolite bath was stated by aluminum technologists to be undesirable under the usual operating conditions of aluminum furnaces. In 1940, about 20 tons of Kalunite alumina produced in the Kalunite pilot plant, were reduced electrolytically in a 10,000 amp furnace at Battelle Memorial Institute and at the aluminum reduction plant at Neuhausen, Switzerland. These relatively small scale tests indicated that satisfactory commercial aluminum could be produced in a practical manner. The Tacoma plant reduced about 2,500,000 lb of Kalunite alumina to produce more than 1,200,000 lb of aluminum, in accordance with the accepted gractice for reducing Bayer alumina. It was desired to determine whether commercial aluminum could be produced on a large scale and to establish the technological differences in commercial reduction practice between Kalunite and Bayer alumina. In the course of collecting data, the effects of the abnormal chemical composition and physical properties of Kalunite alumina were observed wherever possible. Tacoma Reduction Plant The reduction plant had two pot lines, each with 120 cells in series, operated at approximately 32,000 amp. Each cell was provided with a single rectangular Soederberg continuous anode, with side-pin electrical contacts. Each cell was hooded and ventilated through a stack connected to 14 other cells, with 25,000 cfm blower. When the plant started operation in 1942, all of the cathode linings were of block construction. Rebuilt cells were of rammed paste construction.

Jan 1, 1952

By D. G. Westlake, E. S. Fisher

The habit planes for zirconium hydride precipitation in crystals of a zirconium have been determined at various hydrogen concentrations. The (10 • 0)planes are the predominant habit planes; some (10 • 5) and (10 -1) planes were observed after charging conditions which pevmitted formation of a surface layer of hydride. No platelets zrlere observed parallel to any of the twinning planes. Mechanisms for em-brittlement due to hydride precipitation are discussed. LANGERON and Lehr1 found, in 1956, that zirconium hydride precipitates in zirconium in platelets lying parallel to (10.0) slip planes. In 1960, Kunz and Bibbz reported observing the platelets in three different families of twinning planes, (10.2) {11.1), and {11.2), but never in the slip planes. The present study was undertaken to ascertain the cause of these seemingly contradictory results. EXPERIMENTAL Two specimens of iodide zirconium were used in the experiments. Specimen I was a single crystal, while specimen II contained three grains. Grain growth was accomplished by the technique of Lange-ron and Lehr. Three faces were ground on specimen I; the first was 2 deg from the (00.1) basal plane, a second was 2 deg from the (10.0) prism plane, and a third was 4 deg from the (12.0) plane. One face was ground on specimen II such that the poles of the surfaces of crystals A, B, and C were as shown in Fig. 1. After the faces were ground on 600 grit silicon carbide paper, they were chemically polished by dipping in a solution of 8 parts hydrofluoric acid, 50 parts nitric acid, and 50 parts water. This removed all cold worked metal from the surface. The samples were charged to various levels of hydrogen content by heating in hydrogen gas which had been purified by reaction with uranium powder. The various charging conditions are shown in Table I. Specimen I was heated to the reaction temperature at the indicated hydrogen pressure and allowed to react until essentially all the hydrogen was used up. Then the temperature was raised for homogenization. Specimen II was charged by making periodic addi-

Jan 1, 1962

By C. W. Mason

TIN has long been cited as offering a classic example of polymorphism, second in repute only to the allotropy of sulphur. The notorious "tin disease," which Cohen1 has studied so exhaustively in terms of the enantiotropic transformation of tetragonal white 0 tin to cubic gray a tin, has apparently encouraged the expectation that one or more addi-tional polymorphic modifications might exist. The search for confirma-tion of this idea has, as might be anticipated, led to the accumulation of a body of miscellaneous evidence, much of which would probably never have been sought, or taken seriously even by its discoverers, but for previous assumptions. The ball apparently was started rolling in 1880 by Trechmann,' who reported a new modification of tin (y tin), which was brittle and found in "hard head," a highly arsenical, slaggy material produced in a certain stage of tin smelting. A mixture of two kinds of crystals was obtained from a Cornish tin furnace, and those thought to be y tin were studied crystallographically. The results indicated that these crystals were rhombic and of different density from the tetragonal tin prepared electrolytically by Miller.3 Their analysis was given as 98.7 per cent Sn, 1.3 per cent Fe, and traces of As, Sb, Bi and S. In 1881 von Foullon4 obtained similar crystals from a Bohemian tin furnace. Headden5 examined crystals similar to those of Trechmann and von Foullon and reported them to be monoclinic, but of analysis corresponding to stannous sulphide. Later, Stevanovic,6 by goniometric measurements, proved that these crystals of SnS were really rhombic. Groth7 pictures and describes both "rhombic tin" (Fig. 9, vol. 1) and stannous sulphide (Fig. 84, vol. 1); their faces and angles correspond within the accuracy of measurement. Spencer3 in 1921 examined the above evidence critically; he found similar crystals from Cornish tin furnaces, proved them to be SnS, and even was able to analyze some of Trechmann's original specimens, finding high sulphur content. (Apparently Trechmann's analysis had been based on a second lot of crystals, not described crystallographically.)

Jan 1, 1939

By M. Albertson

AT Cobalt, Ontario, Canada, a lake was drained to facilitate mining, by the Mining Corpn. of Canada, during the spring and early summer of 1915. Previous to pumping out the water, great quantities of sands and slimes from concentrating plants had been discharged into the lake and during and after the lake's drainage, its basin' Was a receptacle for tailing products. As the writer was at work along the shore line as the lake was being drained, he had a good opportunity to observe the changes that took place as the water was withdrawn. Some adjustments between the incoming sands and the mud in the lake had taken place before pumping was commenced. One of the most interesting results was the appearance of a small dome in a path the writer traversed twice a day for several months; he remembers distinctly the difficulty of crossing this. Cobalt Lake owed its existence to the gouging out of a rock basin by glaciation. The long axis of the basin closely follows the strike of a thrust fault of about 500 ft. (160 in.) vertical displacement. The lake was originally shaped somewhat as shown. The length was about 3000 ft. (914.4 in.), the width at the lower lobe was about. 1000 ft., and the, width at the narrows probably. 400 to 500 ft. The original depth of water varied from 20, to 30 ft. (6.1 to 9.1 m.), near where the island later was formed, to 60 to 70 ft. (23.6 to 27.6 m.) in the widest part of the lower lobe. At the narrows, the depth was 30 to 40 ft.. Above the bed rock was sand, with boulders near the bottom, and mud. During the building of the railroad in 1903, considerable filling was done along the right of way. With the commencement of mining operations, about 1905, waste rock and mill tailings were dumped into the lake. One of the mining companies operated a hydraulic giant to remove the glacial debris from several hundred acres of rock surface; much of the sand and clay from this operation was deposited in the. lake. About

Jan 2, 1921

The present paper records a chapter in the history of the development of an electrolytic manganese industry in the United States.l A relatively large pilot plant at Boulder City, Nev., for the production of electrolytic manganese was conceived as part of the national defense program to make this country independent of foreign importation of manganese ore. The first authorization, in November 1940, however, was for a plant of only several hundred pounds capacity. Improvements in process and subsequent additions to some sections authorized by subsequent appropriations have enabled the plant to produce as much as 2000 lb. of manganese a day for substantial periods of time. Since in pilot-plant operation frequent changes are made in the flowsheet, the electrolytic manganese plant was constructed so that equipment could be rearranged with a minimum of expense and time. Several different kinds of the various ¦ types of equipment were installed for many of the operations, so that the one most suitable for the process might be chosen. Pilot-plant operations were begun in November 1941 and have been continuous except for brief shutdowns for installation of new equipment. More than one-half million pounds of manganese have been produced. The improvements in process, selection of equipment, and operational procedure developed are recorded here. Development of the Process The work of early investigators on the electrolysis of manganese solutions has been reviewed by Shelton. Until the method of continuous production of manganese by electrolysis was perfected by SheltonZm4 and coworkers, no practical procedure had been devised. The method as originally developed by the Bureau of Mines will be described here only briefly. The manganese dioxide ore was reduced in a rotating kiln-type furnace at 650°C. in an atmosphere of "city" gas. The calcine was leached with spent electrolyte and enough sulphuric acid to produce a neutral leach solutioil containing 2 5 grams manganese per liter as manganese sulphate and zoo grams per liter of ammonium sulphate. Arsenic was removed from the solution by the addition of 0.0j gram iron per liter as ferrous sulphate followed by oxidation with manganese dioxide, and aeration, which precipitated the iron as ferric hydroxide. The solution, free from iron

Jan 1, 1944

By Rossier W. Raymond

John Birkinbine was born Nov. 16, 1844, at Reading, Pa., the eldest son of H. P. M. Birkinbine, widely known as a hydraulic engineer. The family removed subsequently to Philadelphia, where, as a young man he established with his father the office now, continued by his sons, after more than 60 years. His education was received at public schools, the Friends' High School in Philadelphia, the Hill School at Pottstown, Pa., and the Polytechnic College of Pennsylvania, where his studies were interrupted in 1863-4 by service in the Union Army, which included participation in the battles at and around Gettysburg. Later, he devoted two years to work in a machine shop; and subsequently he became associated with the late P. L. Weimer, under the firm name of Weimer & Birkinbine, operating the Weimer Machine Works at Lebanon, Pa. Much of his work was in mining, metallurgy, and blast-furnace construction. As manager for the South Mountain Mining & Iron Co. he carried on experiments with various fuels for iron-ore smelting while maintaining the furnace in constant operation. The carefully recorded results obtained were widely published, and are referred to in text-books by other metallurgists as most complete. From his Philidelphia office he was sent to nearly every State, and to Canada and Mexico, for examinations, reports, constructions or im-provements in iron-ore mines, blast furnaces, iron works, water supplies, hydraulic development, irrigation projects, etc., and his engineering knowledge was requisitioned by several Eukopean corporations. A number of business trips were made to Mexico, beginning with a visit to the Cerro de Mercado at Durango,,before railroads were established in that. portion of Mexico, to make a critical examination and report on this "Iron Mountain." Later visits covered other localities and engineering problems, familiarizing him with the major part of the iron industry in Mexico. The late disturbed political conditions in that Republic have retarded the probable enlargement, modernization, and improvement of much of the iron and steel industry of Mexico, upon which he investigated and . reported for various capitalists on both continents. One interesting subject included in these reports was a proposed electric furnace, to be operated by energy from water power.

Jan 1, 1916

By A. M. Nicholas

WHEN attempting to lift mill pulp containing a considerable percentage of wolframite, in an ordinary bucket elevator, difficulty was encountered from the tendency of the tungsten minerals to settle, on account of their high specific gravity. Lifts not exceeding 20 ft. (6m.) could be accomplished without particular difficulty, because there was insufficient time for consolidation of the heavy minerals in the bottom of the bucket; but with higher lifts, the heavy tungsten minerals would settle so solidly that when the bucket turned over at the top of the elevator the contents could be only partially dumped. In this case it ,was necessary to lift the material a distance of 34 ft. (10m.); hence some means had to be adopted to prevent settling, at least to such an extent that the material could be dumped from the buckets. To reduce the carrying time to a sufficient extent would have required a belt speed of 475 ft. (144.7m.) per minute, which was not feasible. It was decided to try, by vibrating the belt about midway of its span, to keel) the material sufficiently agitated during elevation to prevent settling. Underneath the rising side of the belt was placed a 12-in. (30.48-cm.) idler pulley, 18 ft.-(5.5 in.) up in the total lift of 34 ft. The idler pulley was set eccentric by 3/4 in. (19 mm.) and it was hoped that the vibration thus imparted to the belt, running at a speed of 280 ft. (85 m.) per minute, would prevent settling in the buckets. It was found that the pressure of the belt on the idler, due to the small inclination of the elevator, was not sufficient to overcome sliding on the idler, and the agitation was insufficient to accomplish the desired purpose. The idler was then connected to the drive shaft of the elevator through an intermediate pulley, gearing down to a speed of 20 r.p.m., so that a positive vibration was imparted to the belt; this imparted enough motion to the belt to prevent settling and the contents of buckets clumped satisfactorily.

Jan 2, 1918

By Edgar S. Cook

At the close of the Bethlehem Meeting, the writer was experimenting with large fuel-charges, 4000 Ibs. basis, as compared with 2000 Ibs., hot had not made sufficient progress to draw any safe conclusions. Previously me had always used 2000 Ibs. fuel, the ore-burden being proportioned to this as a basis. I could never persuade myself that there was any advantage to be derived from following the more popular method of larger fuel-charges. Our men were accustomed to the old way of filling ; and we did not care to run the risk of the errors likely to follow any alteration in routine work, particulary as I could not, by my course of reasoning, discover ally compensating gain. Nevertheless, after reading Mr. Gordon's discussion of Mr. Birkinbine's paper, '' Operations of Warwick Furnace from August 27th, 1880, to September 1st, 1885" (Transactions, xiv., 833), I determined to test by actual experiment the value of large fuel-charges : the change was made in the week commencing March 28th, 1886, and continued until July 25th, about four months. The fuel and ores remained during the trial the same as had been used before, and have been used since. For the first two weeks, the furnace worked with great regularity, giving excellent results, exceeding those of the two weeks immediately preceding. But for my remembrance that the furnace had on former occasions worked with equal uniformity for longer periods without any apparent reason, I should doubtless have concluded that this improvement was due to the different method of filling and congratulated myself that a means had at last been found to prevent inconvenient "dirt" accumulations. Before abjuring my previous skepticism, however, I resolved to pursue the trial further. The fourth meek developed the peculiar conditions that had prevailed previous to the change; and these continued with more or less frequency during May, June and July. At last, finding no improvement over the smaller charges—no change in fact for better or for worse—I commenced filling the 2000 lbs. fuel-charge in the latter part of July, and have continued it up to present writing, September 4th.

Jan 1, 1887

HUBERT INGERSOLL ELLIS Hubert Ingersoll Ellis, who met accidental death on Jan. 6, 1919, in eastern Washington, had already advanced far in the profession of mining engineering and gave promise of a brilliant future. He was born on the Washington coast in June, 1889, and had his preparatory schooling at Menlo, Wash. In 1905; he entered the College of Mines of the University of Washington, and at once made a high record of scholarship. After completing 3 years of his technical course, he went to the interior of Alaska, where he spent 4 years in mining. During this time he was field correspondent for technical-magazines and wrote several important articles. In 1915, Ellis completed his senior year in the College of Mines; his graduation thesis was a comprehensive paper on mining methods at Fairbanks, Alaska, which was published as a series of articles in the Engineering and Mining Journal. On July 14, 1915, he entered the employ of the Bunker Hill & Sullivan Mining & Concentrating Co., Kellogg, Ida., as an underground miner, and was soon promoted to the position of operative on experimental metallurgy and later chemist in the same work. Later, he did exhaustive work on flotation with particular attention to the use of various addition agents. For the past 212 years, his work was largely in the field, examining mining prospects and directing work of investigation, during which time, while located at Sumter Valley, Ore., in 1916, he was elected to membership in the American Institute of Mining and Metallurgical Engineers. During the same year, he was married to Miss Grace Wells, of Arkadelphia, Ark., and besides his widow leaves a young son. In Hubert I. Ellis, there was found the rare combination of executive, administrative, and business ability, together with a temperament exceptionally well adapted and trained for research work and for the careful and exhaustive examination of engineering problems, both practical, and academic. These qualities were in addition to a splendid physique and a personality that made him highly successful in the handling of sub-ordinates and in his contact with his associates and the public.

Jan 4, 1919

By G. K. Manning, W. E. Few

WORK on the effect of vacuum heat treatment of 0.040 in. diam sintered and wrought molybdenum wires has been sponsored by the Office of Naval Research at Battelle for the past several years. An electrical resistance furnace' capable of maintaining a vacuum of less than 0.1 micron of mercury at temperatures as high as 4000 °F was used for heat treating the wires. Early in the work, it was found that the introduction of a few microns pressure of oxygen into the furnace resulted in a rapid increase in the oxygen content of the wire specimens and the appearance of a discrete oxide phase. Subsequent elimination of the oxygen atmosphere caused the disappearance of the oxide phase. This was used to determine the solid solubility of oxygen in molybdenum over the temperature range of 2000" to 3000°F.2 It was observed that, with the disappearance of the oxide phase, the wires regained some ductility. Single-phased wires possessed from 5 to as much as 40 pct elongation in 2 in. Later, attention became centered on determining the cause of this wide range in ductility. Wires containing less than 0.002 pct C, less than 0.0007 pct 0, less than 0.0005 pct N, and less than 0.00003 pct H exhibited the erratic ductility noted above. These percentages represent approximately the limit of accuracy of presently available methods of analysis and thus it became apparent that chemical analysis would be of little help in the study. A number of possible explanations for the wide range in ductility were suggested during the course of the work. It was first suspected that variations in the grain size of the recrystallized wire specimens might be responsible. Wire from several lots of material was available. One of these lots tended to develop very large grains when recrystallized, the others all developed an ASTM grain size of 3 to 4 when heated above 2700°F. No correlation between grain size and ductility could be found. It was thought that back diffusion of oil from the diffusion pump might cause contamination of the wire, principally with carbon, but when wires were treated without cooling the cold trap in the pumping system,

Jan 1, 1956

By John C. Fowle

Having had for many years the management of magnetite mines, and having noted the various admixtures, such as jasper, " green rock," actinolite, etc., that occur so frequently in the deposits and make the fine ore so difficult as well as expensive to sort by hand, I studied the different ways of mechanical sorting, but found none eatisfactory—the universal objections being the expense, the small quantity that could be handled per hour, and the low grade of ore produced after all. Feeling that some means would be discovered ultimately for concentrating the small ore, I began at the Michigamme mine, at Michigamme, Lake Superior, Michigan, to separate it from the larger and richer lumps, by placing in all the shaft-houses screens of round iron bars set 1/4-inch apart, on which the skips were dumped as they were hoisted; the coarse ore going into one stock-pile or into cars, and the small ore, from 2 or 3 inches diameter down to powder, going into a special stock-pile, to be treated as soon as some proper means was found to separate the ore from the rock and ether impurities. Careful investigations showed that neither dry nor wet concentration was the right process for us; and I finally studied the magnetic process. Not knowing of any magnetic separator in this country that would handle such large pieces of ore as I wished to treat, I looked abroad and found in Sweden the Wenstrom separator. One of these machines was brought to the United States and tested in New Jersey and other places. (See the papers of Messrs. Cook and Birkinbine, Trans., xvii., 599 and 728.) This original separator, having 15-inch face of drum, I brought to the Michigamme mines, and, no one having confidence in it, placed it in operation at my own expense. Finding that in this way large ore could be treated much better by magnetic separators than by hand, and with much greater enrichment of the product, I put up a small, crude mill with several series of screens, so as to size the material and

Jan 1, 1891

By Eugene S. Machlin

A classical theory of solid solutions involving neavest-nergkbor intevactions with both central and linked-central forces between atoms has been developed. It has been found that the theory, where it can be checked quantitatively, is in ageement with experiment. The theory encompasses a description of many diverse pkenomena, such as antiphase shift structures, size effect, relative stabilities of various solutions, lattice para,neters, and order-disorder transitions. In particulav. a quantitative prediction not involving adjustable pavameters is made concevning the deviation of the Au-Cu interatonlic distance in long-range ordered (Ll,) Cu-Au I fronl the average distance based on the distances in pure gold and copper. This prediction, which is in agreement with expel-intent, has not been encompassed by any preuious theory. The theory of order-disorder is fragmentary. That is, no one theory exists that can explain the variety of qualitative phenomena observed. Further, many theories are not in good quantitative agreement with experiment. This subject has been reviewed by Muto and Takagi, Tuttman, and Oriani.3 There exists no doubt that the quasi-chemical approximation is not a complete description and that the inclusion of strain energy using macroscopic elasticity theory concepts leads to results in disagreement with experimenL4 The observation of antiphase domains and ordering systems such as Cu-Pt has led to Brillouin zone treat-ment of the order-disorder transition as opposed to the classical Ising model. The objective of this paper is to demonstrate that it is possible to develop a pairwise approximation model that can explain many of the observed order-disorder phenomena that have puzzled investigators in the past. This theory is based upon an empirical model due to ergmman' for the elastic constants of metals. This model is generalized for multicomponent systems. As will be shown, the theory yields a short-range ordering energy for the disordered solution which differs from the ordering energy calculated from the differences in energy of disordered and long-range ordered solutions. It will be demonstrated that there is no necessary correlation between heats of formation and the tendency to order or between size effect and the tendency to order. Also, the existence of antiphase domains and iso-short-range-order systems that form superlattices (Cu-Pt) is predicted on the basis of the theory. Further, the relative stability of competing superlattices is calculable from the theory. If single-crystal elastic-moduli data are available for the pure components and one superlattice then there exists but one adjustable parameter in the calculation of lattice parameters for both the disordered and ordered solid solutions. In one special case, no adjustable parameters are required and a quantitative prediction is made. For the calculation of energies and partial order, there exists but one additional adjustable parameter, the pair-exchange energy V used in the quasi-chemical approximation (or the Ising model.) However, in these calculations, much more precise values are required for the single-crystal elastic moduli than available if the quantitative uncertainties in the predicted values of the energies are to be sufficiently small. THEORY ~er~man' has developed a model with which he was able to obtain fair agreement with experiment for the relations between the elastic constants for metals. This model which we shall call Bergman's model is a linear combination of his models I and 11. In effect, Bergman, in this model, considers that each interatomic distortion is composed of two components: a classical central force distortion with an associated central force constant and what we shall call a linked-central force distortion with an associated linked central-force constant. The linked-central force distortion component obeys the constraint that the sum of such distortions over all the bonds equals zero. No constraint is imposed on the classical central force distortion component. Bergman' derives the constraint on the linked-central force distortion on the basis of application of Pauling's relation between bond distortion and bond number to metals.ga This assumption is not logically necessary, however, and the Bergman model may be taken as a mathematical model for elastic constants, e.g., a purely empirical model without a physical basis. In the present work, the method of Bergman has been applied to two-component systems (solid solutions). In place of an external strain—which would allow a calculation of the elastic constants for the two-component system—it is considered that internal interatomic distortions exist as a consequence of having three potentially unequal distortion-free interatomic distances and but one "average" interatomic distance. It is assumed that the distortion-free interatomic distances between atoms of the same element are those found in the pure element having the same undistorted crystal structure as the solid solution. The distortion-free interatomic distance between unlike atoms is in general not measurable except in the probably nonexistent

Jan 1, 1967

By William C. Sleppy

The nmgnetic susceptibility of heat-treatable aluminuin alloys is sensitive to chanyes such as solution or dissolution of solute and the precipitation of mew phases. By measuring the change in the magnetic susceptibility of aluminum alloys caused by various heat treatments, an empirical relation was found from which atomic arrangements in dilute binary alloys of copper, zinc, and magnesiutn in aluminum have been delineated. The relation predicts the ultimate formation of C1LA12 when copper is precipitated from solid solution in aluminum. Euidexce joy silovt- range order is found for copper in solid solution in aluminum in the sense that copper atoms avoid being nearest neighbors to an extent greater than would result from a purely random arrangertzeizt. Hume-Rothery has predicted such short-range order joy solid solution of copper in aluminum The Al-Zn system agrees with evidence obtained from X-ray scattering at small angles and predicts a tendency for zinc atoms to cluster in solid solution in aluminum. In the Al-mg system, the empirical relation indicates an approach to randor distribution of magnesium in solid solution in aluminum with a tendency for magnesium segvegation which increases with incveasing temperature. ThE magnetic properties of metals are complicated by the fact that contributions are made to them both by electrons of a "metallic" type which belong to the crystal as a whole, and by electrons in states localized on particular atoms. An expression1'2 for the bulk magnetic susceptibility of aluminum may be written as the sum of three contributions: where XA1 is the bulk susceptibility of aluminum per gram of material (in the cgs system, the units are those of reciprocal density); Xa1+3 is the diamagnetic contribution of the electrons localized in ion cores; Xa1 is. the paramagnetic spin contribution of conduction electrons often called Pauli paramag-netism: Xa1 is the diamagnetic contribution of the conduction electrons often called Landau diamag-netism. Ion core diamagnetism arises from the precession of the electron orbits which occurs when a magnetic field is applied to a system of electrons moving about a nucleus. Its contribution to the magnetic suscepti- bility is small, temperature-independent, and unaffected by alloying. The conduction electron diamagnetism is also temperature-independent and arises from the translatory motion of the electrons. For perfectly free electrons this contribution should be exactly one-third of the Pauli spin paramagnetism, but this relation is seldom even approximately true. Blythe2 determined the conduction electron diamagnetism in pure aluminum and found it to be extremely small. Any change in the conduction electron diamagnetism caused by alloying is neglected in this work. The Pauli paramagnetic contribution3 to the magnetic susceptibility of aluminum depends upon the number of electrons that occupy excited states and whose spins can be turned parallel to an applied magnetic field. The number of electrons free to turn in the field is proportional to the temperature and each spin contribution to the susceptibility is inversely proportional to the temperature. A slight temperature dependence of Pauli paramagnetism occurs when the number of electrons occupying excited states cannot increase sufficiently to balance the inverse dependence on temperature of each spin contribution. The decrease of the magnetic susceptibility of aluminum with increasing temperature is attributed to a temperature dependence of the Pauli paramagnetism. Estimates of the Pauli paramagnetism of aluminum have been made by several workers.2,4,5 All of the values are in reasonably good agreement with each other. In this work Xal at 17°C is taken as 0.761 X 10-8 cu cm per g. An expression similar to [I] can be written for the magnetic susceptibility of an aluminum base alloy containing a fractional weight percent x of solute:' Xa = (1 -x)XAl+3 +xXsoluteion * XaPauli +Xadia) [2] where X, is the magnetic susceptibility per gram of alloy, Xal'3and Xsolute ion are the ion core diamag-netic contributions, and xpauli and xdia are the Pauli and diamagnetic contributions of conduction electrons in the alloy. If the components of a mixture are not alloyed but simply mixed together in their pure states without producing a new phase, then the magnetic susceptibility of the mixture is given by the Wiedemann additivity law: Xm =x1X1 +x2x2 + ..xnxp [3] where X, is the susceptibility per gram of mixture and xnXp are the weight fractions and susceptibilities, respectively,-. for the pure components. The additivity law is not applicable to alloys because the outer electronic structures of the components are changed by alloying.' Both the Pauli paramagnetism and Landau diamagnetism are affected; hence the magnetic susceptibilitv of an alloy is usually different from that calculated using the additivity law. In this work the difference, X, -X,, is taken as a measure of the change caused by alloying.

Jan 1, 1968

By H. E. Cline

Mechanical properties of the eutectic between CoAl and cobalt were measured over a range of- temnperatures and strain rates for a variety of microstructures produced by directional solidification and by thermo-mechanical processing. Directional solidification led to rodlike, lamellar, and irregular microstructures. The unusually high volume fraction of the cobalt-rich rods and the lurge spacing of the rods were explained by the phase diagram. The hot-worked structure consisted of fibers of COAL in a cobalt-rich matrix. The roonl- tevlperature strength of the uvrought material increased with decreasing grain size but the 1000°C strength decreased with decreasing pain size. At high temperatures the directionally solidified tnaterial was stronger and less strain-rate-sensitice than the hot-rolled material. The fine-grained hot-worked ma-terial became superplastic at high temperatures, with tensile elongations greater than 850 pct, while at root temperature this material was ductile and impact-resistant because of the ductile matrix. Fracture occurred in the directionally solidified material at elevated temperatures by inter phase separation and at roorn temperature by cracks in the intermetallic phase. Growth of these cracks was impeded by the ductile cobalt-rich phase. It was found that the CoAl intermetallic remains ordered at elevated temperatures. DIRECTIONAL solidification of eutectic alloys has been used to produce structures consisting of parallel rods or lamellae. Although the spacing of the phases depends on the growth rate, it has been observed to be of the order of 1 µ in many eutectics. A strong intermetallic phase has been used to reinforce a ductile matrix in the rod eutectic A1-Al3Ni and the lamellar eutectic Al-Al2cu.1 The microstructure of the eutectics A1-A13Ni and A1-A12Cu remained aligned after samples of these alloys were exposed to temperatures just below their melting points for long times. Stability of the microstructure at elevated temperatures makes directionally solidified eutectics a candidate for high-temperature applications. Recently Thompson4 has developed the Ni-NiMo eutectic containing 40 pct NiMo lamellae, giving a tensile strength superior to nickel-base superalloys. Unfortunately, this eutectic oxidizes rapidly at elevated temperatures. By mechanically processing a two-phase structure, one may reach strengths as high as 700,000 psi, as demonstrated by drawn pearlite.5 In this case the strengthening mechanism was thought to be related to the fine substructure formed during deformation.5 However, a heavily worked structure may recrystallize and coarsen at elevated temperatures. Some worked eutectics such as Al-Al2Cu,6 Pb-Sn,7 and Sn-Bi7 have shown unusually large elongations in tension when tested at elevated temperatures. This phenomenon of large extension, called "superplasticity", was related to the fine grain size of wrought two-phase alloys at elevated temperatures. A mode of deformation of "superplastic" material has been shown to be grain boundary sliding,' which has also been observed during creep of polycrystalline materials.9 The Co-A1 system was chosen for this investigation after examining the phase diagrams of binary eutectics." The high melting point of 1400°C, the aluminum content which was expected to give oxidation resistance, and the properties of the intermetallic CoAl were the chief factors influencing this choice. This eutectic consists of a mixture of the intermetallic CoAl and a cobalt-rich solid solution. The intermetallic CoAl has a large range of solubility and a CsCl structure." From the similarity between CoAl and NiAl one would expect CoAl to be ordered at elevated temperatures; however, specific heat measurements" show a transition at 800°C. West-brookL2 has measured the hot hardness of CoAl and found a rapid decrease in hardness above 600°C. The tensile properties and stress rupture properties of as-cast CoAl-Co eutectic were measured by Ashbrook and wallace13 who report a room-temperature tensile elongation of less than 1 pct. I) EXPERIMENTAL A) Sample Preparation. Experimental materials were prepared by directional solidification, by hot working, and by powder processing. The starting materials were electrolytic 99.9 pct pure cobalt and 99.99 pct pure aluminum. 1) Directional Solidification. A vertical Bridgman apparatus heated by induction was used to directionally solidify cylindrical ingots $ in. in diam and 5 in. long. The apparatus was first evacuated and then an argon atmosphere was introduced to retard evaporation. The ingots were contained in an alumina crucible inside a graphite susceptor that rested on a movable water-cooled base. The base was lowered out of the induction coil at a constant rate. Eight of the ingots were solidified using a drive rate of 2.5 cm per hr, two of the ingots at 1.2 cm per hr, and one ingot at 10 cm per hr. The eutectic composition Co 10 wt pct A1 was used in all but one ingot which had the composition of the stoichiometric CoAl intermetallic, Co 32 wt pct Al. 2) Mechanical Processing. At 1000°C the eutectic Co 10 wt pct A1 is a mixture of an intermetallic phase, Co 21 wt pct Al, and a cobalt-rich phase, Co 5 wt pct Al.10 These phases differ from the stoichiometric CO 32 wt pct A1 and pure cobalt because of the large solubility of this eutectic at elevated temperatures." Four rectangular slab ingots, 4 by 1 by 12 in. high, of Co 10 wt pct Al, Co 5 wt pct Al, Co 21 wt pct Al, and Co 32 wt pct A1 were cast for hot rolling. The cobalt was first vacuum-melted, H2-treated for 20 min,

Jan 1, 1968

By B. E. Eakin, R. T. Ellington

An apparatus and a procedure for determining the viscosity behavior of hydrocarbons at pressures up to 10,000 psia and temperatures between 77 and 400° F are described. The equipment is suitable for measuring viscosity of either the liquid or vapor phases or the fluid above the two-phase envelope for systems exhihiting retrograde phenomena, according no the phase state of the system within these ranges of temperature and pressure. Equations are developed for calculation of viscosity from the experimental measurements, and new data for the viscosities of ethane and propane at 77° F are reported. INTRODUCTION With the advent of higher pressures and temperatures in industrial processes and deep petroleum and natural gas reservoirs, demand has increased for accurate values of physical properties of hydrocarbons under these conditions. Proportionately, more frequent occurrence of natural gas and condensate-type fluids is encountered as fluid hydrocarbons are discovered at greater depths. This increases the importance, to the reservoir engineer, of being able to predict accurately the physical properties of light hydrocarbon systems in the dense-gas and light-liquid phase states. Reliable gas viscosity data are limited primarily to measurements made on pure components near ambient temperature and at low pressures. Few investigations have been reported for high pressures, and except for methane, data on light hydrocarbons are subject to question. This is demonstrated by the large discrepancy between sets of data on the same component reported by different investigators. For mixtures in the dense gas and light liquid regions and for fluids exhibiting retrograde behavior there are very few published experimental data. Viscosity data for methane have been reported by Bicher and Katz,1 Sage and Lacey,12 Comings, et al,3 Golubev,3 and Carr,3 with good agreement among the last three sets of data. Comings, Golubev and Carr utilized capillary tube instruments for which the theory of fluid flow is well established. The theory permits calculation of the viscosity directly from the experi- mental data and dimensions of the instrument alone. Sage and Lacey, and Bicher and Katz used rolling-ball viscometers. The theory of the rolling-ball viscometer has not been completely established, and these instruments presently require calibration by use of fluids of known viscosity behavior before viscosities of test fluids can be measured. To obtain accurate data it is necessary that the rolling-ball viscometers be calibrated by use of fluids of density and viscosity similar to the test fluids, a difficult selection for the gas phase. From the methane data and experimental tests on various natural gases, Carr developed a correlation for predicting the PVT behavior of light natural gases.2,3,4 This correlation was based on data for a very limited composition range; its application to rich gases and condensate fluids is questionable. The object of this investigation is to develop an instrument which can be used to obtain viscosity data at reservoir temperatures and pressures, for rich gases, condensate-type systems above the two-phase envelope and light liquid mixtures. These data will be used in an effort to develop correlations to represent the viscosity behavior of these fluids. APPARATUS In a previous viscosity study Carr2 utilized a modified Rankine capillary viscometer configuration," Fig. 1. In this instrument the gas to be tested is forced through the capillary tube in laminar flow by motion of a mercury pellet in the fall tube, the measured displacement time being that required for the mercury slug to move between the brass timer rings. The viscometer is constructed of glass and mounted in a steel pressure vessel. The test gas pressure in the viscometer is balanced by an inert gas (usually nitrogen) in the vessel. Excellent results have been obtained with instruments of this type, with Carr2 and Comings5 reporting repro-ducibilities of 99.5 to 99.3 per cent and an estimated absolute accuracy of 99 per cent. However, these instruments have limitations which have precluded their use for liquids. The need for maintaining a balance between pressures of the test fluid and inert gas in the viscometer vessel presents operating problems, and requires charging the test fluid to the viscometer very slowly. The principle drawback to the Rankine unit is behavior of the mercury slug which provides the pressure differential across the capillary. When even trace quantities of propane or heavier hydrocarbons are present in the test gas, the mercury tends to subdivide

By A. R. Hendrickson, C. F. Smith

Hydrofluoric-hydrochloric acid mixtures have been successfully used to stimulate sandstone reservoirs for a number of years. Hydrofluoric acid (HF) has a specific reactivity with silica which makes it more effective than HCl for use in sandstone. Kinetics of the reactions of HF have been studied to determine the related effects of reservoir composition, temperature, acid concentration and pressure on the spending rate of HF. Secondary effects from by-product formation are noted and described. Predictions are made concerning the improvement in productivity resulting from HF treatment of skin damage. The kinetic order of HF reaction in sandstone was experimentally determined to be first order, i.e., the reaction rate is proportional to concentration. HF reacts faster on calcite than on clay, which, in turn, is faster than the reaction rate of HF on sand. Static conditions retard the HF reaction rate. As HF is forced into cores, there is a temporary reduction as a function of flow rate and acid concentration. Extensive deposition of calcium fluoride in acidized cores was not observed. Although some CaF, was defected, it was not considered a major source of damage in cores containing moderate amounts of carbonate. Other fluosilicates could be potentially more dangerous than CaF, in reducing permeabiliry. INTRODUCTION Hydrofluoric acid has been widely used in stimulation treatments since 1935, when mud acid was introduced to the petroleum industry. Originally, this hydrochloric-hydrofluoric acid mixture was intended to remove mud filter cake, but it has since been successfully applied to many other oilfield problems. Mud acid treatments have been unusually successful in sandstone reservoirs where hydrochloric acid is unreactive due to a lack of enough calcite in the formation. The relatively small amount of hydrofluoric acid present (2.1 per cent) reacts with sand grains, clays and traces of calcite which are generally present in sandstone reservoirs. Since hydrofluoric acid (HF) is the key to mud acid success, this research effort has been dedicated to gaining a more thorough understanding of the basic chemical and physical principles involved as HF reacts. Hydrofluoric acid's reactivity with silica makes it unique in application. Other mineral acids such as hydrochloric, sulfuric or nitric are unreactive with most silicious materials which comprise sandstone formations. A typical sandstone reservoir may contain 50 to 85 per cent silicon dioxide, more commonly called sand or quartz. Hydrofluoric acid reacts as follows: 4HF + SiO2 + SiFO + 2H2O The silicon tetrafluoride (SiF,) is a soluble gas, in some ways similar to CO2, and is capable of undergoing further reaction when held in solution by pressure. These reactions will be considered in detail later. Kinetics of the reactions of HF have been studied to determine the effect of reservoir composition, temperature and pressure on the spending of the acid. Secondary effects from by-product formation have been noted and described. The individual reactions of HF on quartz, glass and clay are reported. Mathematical correlations have been drawn, then applied to studies of HF spending in cores obtained from actual producing sandstone formations. The research reported herein is only the beginning of a continuing approach to better understanding and use of HF in petroleum reservoirs. THEORY AND DEFINITIONS Through the years, a concentrated effort has been made to understand the effects of many variables on hydrochloric acid (HCI) spending in limestone. Hendrickson el al., have given mathematical relationships for HC1 reactions which made possible the engineered approach to acidizing. The same variables—temperature, acid concentration, formation composition, pressure and permeability-porosity relationships—which affect HC1 behavior in limestone also govern HF behavior in sandstone. Insoluble by-products of HF reaction have been isolated and identified. Their effect on fluid flow has been measured under varying conditions in an attempt to evaluate the extent of possible damage and means of eliminating it. In general, HF follows the same reaction paths as HCI. It will react with limestone and dolomite with speed and ease. Thin sections of acidized cores show the reaction of HF with limestone or calcite faster than its reaction with either clay or sand. When HF reacts with calcite (CaCO,), theoretically, calcium fluoride (CaF2) is precipitated, and has been blamed as a major cause of reduced permeability. On the other hand, pH and pressure such as that encountered in an underground formation under acid treatment definitely retard CaF2 formation,' so the whole question of CaF, deposition in wells is a subject for study.

Jan 1, 1966

By M. A. Goudie

The deposits occur in a large salt basin of Middle Devonian age. The potash, the final deposit in the salt basin, results from several interrupted cycles of evaporation and dessication. The deposits are extensive, and, at first glance, relatively undisturbed. With more and more wells being drilled, it has now become evident that salt solution has played a large part in changing the original deposits, resulting in some cases in partial to complete removal of the potash and the underlying halite. The most dominant factor in the removal of salt by solution appears to have been tectonic movement and consequent faulting, probably of relatively minor dimensions but of major importance. Evidence which indicates the tilting of the evaporite basin to the north and northwest is shown by the changing pattern of the basin during succeeding eras of potash deposition. The potash minerals of most importance economically are sylvite and carnallite. Reserve calculations indicate that 6.4 billion tons of recoverable high grade potash in K2O equivalent exist in the basin. The Devonian salt basin, which contains the Saskatchewan potash deposits, extends from just east of the foothills in Alberta, north as far as the Peace River area, across Saskatchewan and into Manitoba as far east as Range 10 west of the First Meridian and south into Montana and North Dakota (Fig. 1). The basin is closed everywhere except to the northwest. The known potash deposits are confined almost entirely to the Province of Saskatchewan, with the exception of a small area in western Manitoba bordering the Saskatchewan boundary. The following discussion will concern only the Saskatchewan part of the basin. The evaporite series in the basin is defined as the Prairie Evaporite Formation of the Elk Point Group, of Middle Devonian age. Recent work done by potassium-argon dating methods has indicated an Upper Middle Devonian (Givetian) age of from 285 to 347 million years for the potash. The Elk Point Group consists in ascending order of the Ashern, Winnipegosis, and Prairie Evaporite Formations. The Ashern formation, with an average thickness of 30 ft, sometimes called the Third Red Bed, consists of dolomitic shales and shaly dolomites. The Winnipegosis, is a reef-type dolomite, usually with good porosity, and in many cases oil-staining, although to date no production has been obtained. The thickness varies from 50 to 250 ft. The Prairie Evaporite formation, varying from 0 to 600 ft in thickness, consists of halite with interbedded anhydrite and shale, with considerable amounts of potassium salts in the upper part of the formation. The potassium salts are chiefly chlorides, although very minor occurrences of sulfates have been re- ported. The anhydrite beds do not appear to be continuous, although generally one or two bands of anhydrite underlie the lowest potash zone and are used as marker horizons. The shale occurs as seams interbedded with the salts, as large irregular inclusions in the salts and as very fine particles in intimate mixture with the salts. The Prairie Evaporite Formation is overlain by the Second Red Bed member, the Dawson Bay Formation and the First Red Bed Member of the Manitoba Group, listed in ascending order. The Red Beds are shales which vary in color from red to green, maroon, grey, grey-black, and reddish purples. They serve as marker horizons for coring the potash. The Second Red Bed averages 14 ft in thickness, the First Red Bed 35 ft. The Dawson Bay Formation, which everywhere overlies the First Red Bed and the Prairie Evaporite Formation in the area under discussion, is a reef type of carbonate, in some places limestone, in others limestone and dolomite, with vugular to pinpoint porosity averaging 130 ft in thickness. In some parts of the area, it has a salt section near the top of the formation, usually with interbedded shales and limestones. In other parts of the area, it is waterbearing and the salt is absent. Detailed mapping has indicated that the areas in which the Dawson Bay is water-bearing are areas which have been disturbed by faulting. Where the Dawson Bay is salt-bearing, the porosity has been plugged by salt. The total thickness of the salt varies from between 600 to 700 ft in the center of the basin to zero at the northern edge of the basin (Fig. 2).* The salt-free area in the center of the Province is believed to have resulted from removal of salt by solution. Evidence from several wells suggests that salt removal has been a continuing process from the time of deposition to the present day. One well drilled between the Quill Lakes for potash information encountered

Jan 1, 1961

By P. Pietrokowsky, T. E. Tietz, J. E. Dorn

The amount of solid solution hardening in aluminum alloys was found to be dictated by two factors: the lattice strain, and the change in the mean number of free electrons per atom of the solid solution. To obtain this correlation it was necessary to assume that aluminum contributes two electrons per atom to the metallic bond. WHEN the modern scientific method of analysis was first being formulated, Francis Bacon recorded in his "Essays" (circa 1600) that "an alloy . . . will make the purer but softer metal capable of longer life." During the intervening centuries voluminous data have been reported which demonstrate that the additions of alloying elements do in fact increase the hardness and strength of the pure metals. Nevertheless, the significant details of this problem on the unique effect of each element toward enhancing the mechanical properties of alloys only recently have been subjected to systematic scientific scrutiny. The major objective of this investigation is to determine how minor additions of alloying elements affect the plastic properties of polycrystalline aluminum alloys. By means of such studies it is hoped to provide not only data on the solution strengthening of aluminum alloys, but also a body of facts which will supplement the knowledge already available on the factors responsible for solution hardening in general. A review1"10 and analysis1' of the existing data on the effect of solute elements on the plastic properties of solid solutions reveal that our current knowledge on solid solution hardening is somewhat meager, inconsistent, and inconclusive. Many of the inconsistencies are undoubtedly attributable to the influence of unsuspected factors, such as purity; or uncontrolled factors, such as grain size, on the plastic properties of alloys. Nevertheless the following conclusions might be tentatively accepted: 1. Addition of solute elements invariably increases the yield strength, tensile strength, and hardness of the host element. 2. The rate of strain hardening, in general, increases with the concentration of the alloying element. 3. The strengthening effect in ternary alloys is the sum of the individual strengthening effects of the two solute elements as measured in their binary alloys. 4. The lattice strain is one factor that affects the strengthening of the alloy but it is not the only factor. 5. A second factor might be the difference in valence between the solute and solvent metals. All of the available evidence is in complete agreement with the first conclusion; the remaining conclusions, however, are not in agreement with all of the published data, but, in each case, the major weight of the existing evidence favors these deductions. Additional investigations will be required before most of these tentative conclusions can be accepted without reservation. In the following report an extensive investigation of the plastic properties of binary aluminum alloys is described. This work was undertaken in an attempt to shed more light on the general problem of solid solution hardening. Materials for Test: Aluminum was selected as the solvent metal for the present investigation on the effect of solute elements on the plastic properties of alloys. This choice was made for several reasons: (1) There appears to be little fundamental data in the published literature on the effect of solute elements on the properties of high-purity aluminum alloys. In view of the ever increasing economic importance of aluminum, such data would be of basic interest to the metallurgists concerned with the development of new aluminum alloys. (2) Aluminum is thought to be only partially ionized in the metallic state1' and consequently it might provide more complex relationships of the mechanical properties with the concentrations of the solute elements than more simple fully ionized solvents would reveal. (3) The data on aluminum alloys will provide a broader basis for correlations between the mechanical properties of metals in general and the concentration and atomic properties of the solute elements than is now available. Some complications, however, attend the selection of aluminum: The solubility of the various elements in the alpha aluminum phase are quite restricted, and not always well known. Consequently, only dilute solid solutions are available for study. This, however, may be somewhat advantageous because the dilute solution laws presumably are simpler than those applying to concentrated solutions. In addition, strain-hardened pure aluminum is known to recover at atmospheric temperatures. Very likely its alloys exhibit slower recovery rates. Thus, the secondary factor of effect of alloying elements on recovery might complicate the data. Such compli-

Jan 1, 1951

By William H. Breeding

The remarks that follow are based substantially on experience covering 45 years, 80% of which has been in placer work, rather than on a review of available literature. Most commercial placers have been deposited by the action of water. The richer and more- difficult-to-mine placers are those in the headwater areas where gradients are steepest. The most lucrative placers are generally in inter- mediate areas where volumes are greater, fewer boulders are present, and gradients are from 3% to 1-1/2%. The higher volume, lower grade placers are in the lower reaches of river systems where gradients are lower. Where gold-bearing rivers have discharged into the sea, wave action can concentrate values on beaches, past and present. Most of the rich, readily accessible placers were mined by our forefathers. Current opportunities exist: (1) in remote areas where infrastructure has been absent in the past, or development has been prohibited by adverse ownership - political or commercial; (2) in deposits that could not be mined by equipment available to our forefathers; (3) in deposits unidentified by our forefathers; (4) where the-price-of-product/cost ratio is substantially better than in earlier years; or (5) a combination of those factors. When I entered the placer business in the late 1930s, and subsequently, a prevailing opinion believed that glacial deposits should be avoided as irregular in mineral content and composition, and unrewarding to explore and develop; yet an operator has been mining a fluvio-glacial deposit profitably for the past 17 years. Rich buried placer channels, of ten called paleo-channels were worked in the last century, generally by hand methods, and under conditions that would be unacceptable today. Exploration and mining equipment now available make some of these channels attractive targets. Well-known examples are in California and Australia. The formation of a commercial placer requires a source of valuable minerals. Above primary deposits, there may be eluvial deposits formed by the erosion of gangue minerals and the concentration "in situ" of valuable minerals. Down slope from these deposits are the hillside or colluvial deposits, and below them are the alluvial deposits of redeposited material. Most of the great placer fields of the world are the result of several generations of erosion and deposition. Well-known examples are in California and Colombia. Gold is a very resistant and malleable material, and gold placers may extend for 64 or 80 km (40 or 50 miles) along a river system. Platinum is less malleable, but is very resistant to disintegration. Diamonds are extremely hard, and (especially gem diamonds) may be found over great lengths of a river system. Cassiterite is less resistant to disintegration, and tin placers seldom extend over two miles without resupply from an additional source or sources of mineralizaton. Tungsten minerals are generally more friable, and within a few hundred yards of the source disintegrate to the point that they are uneconomical to recover. Rutile, ilmenite and zircon placers generally result from the weathering of massive deposits, and may be encountered over extensive areas; most are fine grained and durable. What does a geologist or mining engineer look for in placer exploration? The old adage to look for a mine near an existing mine is still valid. You need a source of valuable mineral. Then you require conditions for concentration, which means a satisfactory gradient and/or other conditions that will permit heavy minerals to settle. Nicely riffled gravel, often called a shingling of the bars, is conducive to placer formation. Coarser gravel is logically associated with coarser gold. Excessive clay and/or high stream velocities in narrow channels can carry gold far downstream and distribute it uncommercially over a large area. When material is extremely fine, in situ weathering and concentration become more important. Placers frequently occur distant from lode mines, and one must remember that in a larger watershed the exceptional floods that occur once in a hundred or a thousand years can move great quantities of material long distances. The carrying power of water is said to vary with the fifth or sixth power of its velocity. I am not ready to disagree with Waldemar Lindgren and accept that many commercial placers are substantially enriched by the chemical deposition of gold from solutions; however, I have seen crystalline gold in clayey material quite distant from known sources of primary gold that is dif-

Jan 1, 1985