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By John J. Reed

This paper was prepared as a supplement to the general review by Dr. N. G. W. Cook. His analysis of the problem in terms of the strain energy involved in making the excavation is excellent. It will contribute much towards a clearer understanding of rock behavior and control. Several of the practical applications described herein can be directly related to Dr. Cook's theories and conclusions, and are based on the very same principles. CONTROLLED BLASTING IN ROCK EXCAVATION Generally speaking, the natural rock is a relatively strong and competent structural material, if we conserve its inherent good properties and perhaps reinforce its weak spots. The difficulty often lies in blasting out the tunnel or chamber without damaging the walls and roof we wish to have remain afterwards. Much progress has been made in the last five years in better understanding the controlled excavation of rock. The specialized techniques known as smooth wall blasting and presplit blasting have now developed from the status of curiosities of rock excavation to the point where these techniques are specified in contracts drawn up for such rock excavation projects as tunnels, underground pourer houses, etc. These techniques have been well described and discussed in previous publications; there is no need to reiterate here. It might be well to point out that recent research has demonstrated the effect that inherent rock stress may have on presplitting in certain directions. Material can be presplit most readily parallel to the direction of maximum compressive stress, and this may not always be in the direction desired. Inherent rock stress measurements by stress relief over coring, etc., may have important value in deciding how to best presplit proposed excavations. In addition, recent work at the Colorado School of Mines has demonstrated the feasibility of con-

Jan 1, 1967

The research project on size reduction, sponsored by the mining industry through financial support from individual companies, is now embarking on a second three-year program. The first 3-year program had as its objectives assimilation of the literature on comminution and development of simulation programs encompassing the basic mechanisms of grinding. This involved investigating conditions under which a particle in a mill is captured, the stress to which it is subjected, its break probability, and the resulting particle size distributions. The results were used to obtain the most representative simulation models based on current knowledge of mechanisms. As part of this work a set of computer programs has been developed for the following cases: . Batch mill, by numerical integration for completely general selection and breakage functions. . Continuous open-circuit mill by same method as above. . Continuous open-circuit mill by general numerical integration method, including transient behavior

Jan 1, 1969

By A. K. Mukherjee, John E. Dorn

The effects of strain rate and temperature on the critical resolved shear stress for (321)[111] slip were determined for the silver-rich CsCl type of intermetallic compound AgMg. The flow stress increased only slightly as the test temperature was first decreased below room temperature; a rapid increase in the flow stress was obtained with yet further decrease in temperature from about 250' to 4OK. The effect of both the temperature and strain rate on the flow stress over the low-temperature range could be rationalized satisfactorily in terms of the Peiwls mechanism when the deformation was controlled by rate of nucleation of pairs of kinks. IN spite of the well-documented interest of metallurgists and engineers concerning the mechanical behavior of intermediate phases and intermetallic compounds, very little definitive information is available on this important subject. As recently summarized by westbrook,1 only limited and modest progress has been made thus far in elucidating the details of the mechanism of plastic deformation for the intermetallic compounds; the available information largely concerns phenom-enological descriptions of empirical observations and experimental facts, principally with reference to poly crystalline aggregates. The present report on the elucidation of the rate-controlling mechanism for slip in the bcc structure of AgMg is part of the comprehensive program of a systematic investigation on the mechanical behavior of intermetallic compounds. The intermetallic compound AgMg has a CsCl type of lattice structureZ and is completely ordered up to its melting point of 820c3 This material was selected for our present investigation because of its simple crystal structure, moderate and congruent melting point, ordered structure persisting up to the melting point, and some solubilities of the constituent elements, which could be expected to help in the growing of single-crystal specimens. Whereas previous investigations on the properties of AgMg include hardness,*"6 slip systems,7 tensile flow stress of polycrystalline specimens,' and electrical resistivity,4 the current investigation will be directed principally at elucidating the rate-controlling dislocation mechanism responsible for slip in single crystals at low temperatures. It will be shown that the strain rate is consistent with a model involving the rate of nucleation of pairs of kinks by the Peierls mechanism for plastic deformation. EXPERIMENTAL TECHNIQUES Single-crystal specimens of the AgMg intermetallic compound were prepared and tested as follows: 1) A master alloy ingot of AgMg was produced by melting and chill casting the high-purity silver (99.995 wt pct) and high-purity magnesium (99.997 wt pct) in an induction furnace under a helium atmosphere. 2) Sections of the above-mentioned ingot were placed in a graphite mold containing a spherical cavity in which a single-crystal sphere of 1 in. diam was grown under helium by the Bridgman technique. 3) The operative slip systems were investigated at room temperature on a singlecrystal of AgMg, from measurements of the angles made by the slip traces on the two surfaces of the specimen, which were at 90 deg to each other. The investigation confirmed that the AgMg compound undergoes slip primarily in the (321) plane and in the [Ill] direction, but a small amount of secondary slip was also noticed in the (112) (111) system. No slip was observed in the (110) planes. 4) The single-crystal sphere, mentioned earlier, was oriented in a graphite mold containing a cylindrical cavity of 3/8 in. diam above the spherical receptable to give the angle xo = 45 deg between the axis of the cylindrical bar and the normal to the slip plane (321), and the angle AO = 45 deg between the slip direction [Ill] and the axis of the bar. Oriented single-crystal bar seeds were produced by melting, under a helium atmosphere, a polycrystalline bar in the cylindrical cavity above the oriented spherical seed and by growing an oriented single-crystal bar from the seed. 5) Finally, oriented single-crystal specimens were grown from these cylindrical seeds. 6) The cylindrical specimens were machined in a High-Tension Spark Cutting unit to give a 2-in. gage length. The spark-machined gage section was elec-tropolished in a bath containing 200 ml of H3PO4,

Jan 1, 1964

By H. J. Beattie, G. C. Gould

J. B. Seabrook' recently published properties of a low-alloy Ni-A1 age-hardening steel known commercially as "Nitralloy-N". He mentioned three possible mechanisms of age hardening, viz. order-disorder in the matrix, order -disorder in a precipitate, and a precipitate that goes in and out of solution reversibly without losing coherency. The following results indicate that the last - mentioned of these mechanisms is the cause of age hardening in Nitralloy-N. The reversibility of the age hardening with a sub-critical solution temperature was demonstrated strikingly by Seabrook, whose results are reproduced in Fig. 1. Aging for 22 hr at 975°F (525°C) can reharden the fully-tempered martensite to its original as-quenched hardness of R, 45. A Nitralloy steel was obtained from Seabrook' with the following analysis:

Jan 1, 1962

By Richard Thomas Newcomb

Chapters 5a, 5b, and 6 discuss the long- run supply of minerals and the characteristics of reserve search and production peculiar to extractive industries. It is now necessary to complete the picture by examining supply and demand in commodity markets to show how mineral prices are determined and how both price and production trends might be predicted over long periods of time. These practical interests can be served best by reviewing first some of the characteristics of the short-run static market models familiar to all readers of elementary economic texts, and then extending the theory to models of a more dynamic nature. It is important at the outset to note that economic theory provides a wide variety of economic models based on varying assumptions concerning the behavior of economic agents, the properties of the goods, the time period considered, and so on. Each variety of model offers certain analytical advantages and suffers certain shortcomings. The art of the applied economist or practioner lies in knowing enough both about the technology and practice of his problem and about theory to select the appropriate models for his analysis. In our approach it will be useful first to consider the role of markets for minerals and mineral products in relation to the efficient determination of what and how goods are produced in the whole economy, i.e., a general system of markets, before getting down to the task of analyzing supply and demand conditions in specific markets. The former study is called general equilibrium analysis, while the latter is called partial. By equilibrium is meant a state of the sys- tem under study in which supply equals demand in each market, and the prices which equilibrate the quantities offered and asked are called equilibrium prices. The tendency of prices to return toward equilibrium values if temporarily displaced, or to converge to new equilibrium values if important new conditions for supply or for demand are placed, defines "stable" equilibrium systems. The short-run describes a period in which adjustments to fixed capital are not made, although variable factors such as labor or materials can be adjusted. The long-run envisions a period in which fixed capital and other such constraints can be adjusted. Thus, it may take a sharp increase in price to bring out additional supply of a factor in the short-run with existing plant, while new capacity might permit additional quantities in the long-run without an increase in supply price.

Jan 1, 1976

By F. R. Brotzen, A. R. Troiano, E. L. Harmon

Precipitation processes leading to drastic property changes are a frequent occurrence in titanium alloys containing large amounts of the retained high temperature P phase. In order to establish the kinetics and nature of these precipitation processes, a series of Ti-V alloys was studied. Time-temperature-transformation diqgrams were obtained for 12.5 and 15 pct V-Ti alloys. These diagrams consisted of two intersecting C-shaped curves: one in the high temperature region for the euilibrium transformation P +u+P, and another at lower temperatures depicting the formation of the meta-stable transition phase, o. Presence of the transition phase retarded the precipitation of the equilibrium a phase. Deformation of retained P resulted in the formation of the o phase. Reversion and retrogression phenomena of the transition phase were observed. A negative temperature coefficient of resistance was found in quenched alloys containing from 15 to 20 pct V. CERTAIN titanium-base alloys can be heat treated to produce appreciable changes in properties. For example, remarkably high hardness values may be obtained by aging or isothermal quenching treatments. Most of the information available to date on the hardening of titanium-base alloys has been systematized recently in an article by L. D. Jaffe.' It was pointed out by that author that the hardening was the result of the decomposition of the retained j3 phase to the equilibrium constituents, a and p, and that this decomposition had many of the characteristics of an age-hardening reaction. Recent work by Frost et al.' 3 has contributed much to the fundamental understanding of the hardening mechanism in titanium-base systems. These authors established the presence of a transition phase in the transformation from j3 to a + j3, which they designated o. The transition phase, in their opinion, was at least partially responsible for the hardening and embrittling effects which accompanied low temperature aging. The present investigation of the mechanism and kinetics of the hardening reaction was carried out for the Ti-V system. Ti-V alloys were ideally suited for a study of the decomposition of j3, since age hardening was known to occur readily in this system." Moreover, no intermetallic compounds occur in this system, Fig. 1, thus simplifying the interpretation of the results. Material and Procedure Alloys containing 12.5 and 15 pct V were prepared by Battelle Memorial Institute from iodide titanium furnished by Watertown Arsenal and vanadium of 99.8 pct purity. Ingots of 8 Ib each were prepared by arc melting in an inert atmosphere with a tungsten electrode and water-cooled copper crucible. Each of the ingots was melted once, forged at 1600°, and rolled at 1400°F. Following this, the ingots were remelted, forged, and then rolled to % in. sq bars, which were subsequently grit blasted, pickled, and wire brushed. Another set of alloys containing nominally 17.5 and 20 pct V was produced by the Research Div., New York University. These alloys were arc melted in an inert atmosphere in lots of 20 g each. Heat-Treating Procedure: Whenever feasible, specimens were heat treated in high vacuum resistance furnaces at pressures below 5x10." mm of Hg. Aging and isothermal quenching treatments were generally carried out in salt baths. Specimens were not attacked by the salt, provided the tempera-

Jan 1, 1956

(This list. includes only those who have entered military service within the past month, or whose entry has only recently become known to us; it also includes a few names of those whose titles or assignments have been changed within the month. A complete list will he found in the Year Book mailed with this Bulletin. Another Honor Roll is maintained in the reception room of the Institute.) ALDEN, HERBERT W., Lieutenant-Colonel, Ordnance Dept. ALDER, ALFRED; Engineers' Reserve Corps. ALFORD, NEWELL G., Sergeant, Bureau of War Risk Insurance, Headquarters 84th Division. AMBLER, HARRY A., Lieutenant, 30th Infantry. ANDERSON, GEORGE K., JR., Sec. C, 1st Co.; 3d Officers' Training Camp. AYER, -FRANK A., 1st Lieutenant, 43d Squadron, 3d Prov. Regiment, Aviation Camp.

Jan 3, 1918

By Renato G. Bautista, Robert A. Hard

A comparative study has been made of the ex-tractability of several of the transitim metals from thiocyanate sohtions using methyl isobutyl ketone as the organic solvent. Extractions were made of scandium (III), chromium (III), manganese (II), iron (III), and cobalt (II), of which only the scandium , iron, and cobalt were readily extracted. All extractions were made at pH 2 and at 25.5 °C. A series of extraction experiments was made on scandium, iron, and cobalt to determine the effect of thiocyanate cmcentration added as the ammonium and also as the calcium salt. Also determined was the effect of metal ion concentratim and ionic strength on the distribution ratio. Analyses of the organic extracts indicated the scandium and iron were extracted principally in the uncharged trithiocyanate form, while the extractable form of the cobalt contained the cobaltotetrathiocyanate anion. THE chemical separation of metal complexes in solution by solvent extraction has in recent years been developed for large scale separation as well as bench scale work in the laboratory. It has also found increased application in analytical chemistry. Its extension to extractive metallurgy as a unit operation is best illustrated in the recovery of uranium and vanadium from their leached liquor.5-8 The extractability of some thiocyanate systems have been extensively investigated. The rate earths have been separated from one another using butanol as a olvent. Scandium was effectively extracted in ethyl ether using ammonium thiocyanate as the com-plexing agent.'' Similarly, the separation of hafnium from zirconium has been reported using ether""' or hexone13 as the organic solvent. The extractability of various metal thiocyanates in ethyl ether is given by 0ck.l Sharp and Wilkinson15 prepared nickel-free cobalt slats by thiocyanate extraction. The mechanism of extraction of titanium (IV) thiocyanate with methyl isobutyl ketone was determined by elafosse.''" The characterization of cobalt (TI) thiocyanate complex using methyl isobutyl ketone as the solvent at near neutral aqueous solution and the spectrometric studies of the ex-tractable cobalt complex has been made by Hard." It is noteworthy to mention at this point that the fundamental characteristic of ketone (oxonium) solvent extraction is that the extractable species are uncharged ion pairs solvated by the ketone molecules, but probably still partially hydrated.

Jan 1, 1963

By Reginald S. Dean

THE commercial availability of electrolytic manganese has greatly changed the position of manganese as a nonferrous alloying metal. Manganese metal commercially available up to about ten years ago was reduced with either silicon or aluminum and contained substantial amounts of the oxides of these metals and other impurities. Manganese was accordingly not available as an alloy base and its addition to copper-base and nickel-base alloys was generally limited to a manganese content of a few per cent. Several special alloys like manganin contained up to 12 pct of manganese. A method for the production of electrolytic manganese was developed by the Bureau of Mines in 1936 and commercial production was begun in 1938. At the present time (June 1951), production is about 12 tons per day but appears likely to be substantially increased. Electrolytic manganese is deposited from an aqueous electrolyte containing manganese and ammonium sulphates and is marketed as cathode fragments about 1/8 in. thick. The impurities in its composition are as follows: iron, 0.0015 pct; copper, 0.001; arsenic, 0.0005; cobalt, 0.0025; lead, 0.0025; molybdenum, 0.001; sulfide sulfur, 0.017; sulfate sulfur, 0.014; insoluble, 0.002; carbon, 0.002; hydrogen, 0.015. These figures are from Bulletin 463, U. S. Bureau of Mines. From an alloying standpoint, the most important impurity is hydrogen. This can be removed by heating; 95 pct of the hydrogen can be removed in this way without introducing significant amounts of oxygen or nitrogen. Much of the commercial electrolytic manganese used in alloys is dehydrogenited by the producer, since the amount

Jan 1, 1953

By E. F. Thomas

THE late George S. Rice was active in the inves--I- tigation of bumps, particularly in the last ten years of his career as chief mining engineer of the U. S. Bureau of Mines. Since most of his investigation was carried out in Great Britain, continental Europe, and—to a lesser extent—Canada, his thinking on prevention was influenced considerably by the experience of those countries. It is not surprising, therefore, that when he was called upon a few years before his retirement to investigate bumps in the U. S. and suggest ways to prevent them, he turned to longwall mining. A longwall method had been most successful in combating the bump hazard in mining coal under deep cover, especially in Great Britain, but the prevailing method there at the time was advancing longwall mining, which he knew was uneconomical under U. S. mining conditions. For this reason he proposed a modified retreating longwall system that he believed included the best features of the advancing method. As brought out by Rice,' if the cover is 2000 ft and 50 pct of the coal is extracted, the static load on the remaining pillars will be about 4000 psi, which exceeds the ultimate crushing strength in most instances. If the pillar coal is overloaded before a pillar line is established, then the abutment zone preceding a line of extraction is no place to split pillars or extract them by any method other than an open-end system. Rice therefore advocated open-end mining, preferably by longwall, but he was willing to compromise with long-face mining if the longwall method was not acceptable. Rice's system was put into operation in a mine in Harlan County, Kentucky,3 but subsequent experience has shown that it did not take into account two important factors—avoidance of pillar-line points and maintenance of adequate development in advance of the pillar-line abutment area. For ten years after Rice's retirement the USBM did little investigation and research on bumps, chiefly because so few were occurring that there was not much cause for alarm. But in 1951 there were three occurrences involving fatal injuries, and the Bureau began a statistical survey in that year. C. T. Holland, head of the department of mines at Virginia Polytechnic Institute, was retained as a consultant. The resulting study' of 117 case histories brought out these important conclusions: 1) Almost invariably the bump occurred in a locality affected by the abutment zones of one or more pillar lines. 2) In most cases the locality of the bump was influenced by the abutment zones of more than one pillar line. The term pillar-line point has been used for many years in the Appalachian region for such a situation. Point is used in the geographical rather than the mathematical sense. 3) In pillar-line extraction the following practices are safest in preventing bumps: a. The mine layout should provide for pillars of uniform size and shape along the extraction line. b. The mine layout should be planned so that no development need be done in the abutment zone of a pillar line. c. The layout should permit open-end extraction of pillar lines from the next goaf, so that it will not be necessary to resort to pocket mining, splitting pillars, or any practice that will involve driving in the direction of the goaf within the abutment zone. d. Pillars should be large enough to support area without undue roof and floor convergence before establishment of a pillar line. These are, of course, generalities, and while they are useful in laying out areas where bumps can be expected, they are of limited help in many mines that were committed to a system of mining before it was realized that they were subject to bumps. Under such conditions it becomes necessary to choose between the following alternatives: 1) Abandon the territory, except for pillars that offer no extraction problems. 2) Through experience select the pillars that are most heavily loaded, and, by augering, induce bumps from a safe vantage point so that impinged loads are relieved. This method was first developed at the Gary, W. Va. mines of U. S. Steel Corp. and later adapted to mining thick coal beds at Kaiser Steel's Sunnyside mine in Utah. No scientific method is available to determine where to drill within a loaded pillar. Although this method of unloading has worked very successfully at Gary—with one exception—

Jan 1, 1959

ZAY JEFFRIES, Cleveland, Ohio (written discussion?).-The authors conclude that there is a certain average size of precipitated CuAl2 par-ticle which produces maximum strength and hardness in duralumin; that when the size of particle is smaller or larger than this particular size the hardness decreases. The writer agrees with this conclusion, because it seems to he directly indicated by the facts. Why does duralumin present this apparent discrepancy? Let us con-sider some physical aspects of the precipitation of CuAl2 from a saturated solution on cooling. When a molecule of CuAI3 is removed from the solvent, or matrix, and added to another group of CuAl2 molecules, as is known to occur on slow cooling, the forces of adhesion between the CuAl2 molecule and the solvent have been exceeded. Since a. change in tem-perature only is sufficient to cause precipitation, it must also be sufficient to cause the loss of adhesion bonds between the excess CuAl2 molecules and the solvent, or matrix. Lost adhesion bonds means loss of cohesion of the mass as a whole. When duralumin is cooled from 500° in a furnace, globules of CuAl2, large enough to be seen easily with a high-power microscope, are formed. There are, however, globules so small as to be hardly distinguishable, and others too small to be resolved are suggested by the non-uniformity of the surface appearance of the section. As the smallest globule of CuAl2 resolvable with a high-power microscope contains about 2,000,-000,000 molecules, it is evident that with rapid cooling submicroscopic particles of CuAl2 must be present in large numbers; in fact, after quench-

Jan 12, 1919

ON FEBRUARY 13, 1953 the Miami Copper Company signed a contract with the United States Government, through the Defense Materials Procurement Agency, whereby it under- took, with a base price of 27.359 per lb (subject to escalation based on wage scales and wholesale-price indices), to exploit a new ore body in its mine in Gila County, Arizona. Recoverable ore was estimated at 23,000,000 tons, averaging about 0.677 per cent copper. Moreover, the proportion of oxidized copper, difficult to recover by flotation concentrating, was so high that an average net recovery of only ten pounds per ton (0.5 per cent) was expected. The company proposed to mine the ore by the underground method known as undercut block-caving. Unfortunately the ore body, as has been true of all Miami's ore bodies, lay so deeply buried that no possibility existed of adopting opencut mining as has been done in recent years at Miami's neighbors, Ray and Inspiration. Probably the most distinctive characteristic of Miami's operations has been the extent to which it has developed and improved methods and equipment for underground mining. True, necessity was a potent stimulant, because its available ores since 1926 have been exceptionally low-grade; so, if the enterprise were to survive, it was necessary to keep costs at the minimum. This fact does not detract, however, in any way from the remarkable achievements of Miami engineers in conducting efficient and low-cost underground mining.

Jan 1, 1957

By C. P. Watson, R. E. Collom

Various chapters already written in the history of development of the North Dome of Kettleman Hills are monotonoysly identical in the one underlying' theme of conservation of oil and gas. Discovered on Oct. 4, 1928, by Milham Exploration Co. with its wildcat Elliot No. 1, the field has been subjected to practically every modern form of production restraint in the name of conservation. The record thus far developed shows that conservation was had for a time, at a price; and that unitiza-tion must be blessed by single ownership or 100 per cent participation to be effective. In fact, incomplete unitization places a heavy handicap upon its participants in the competitive development that follows. Shut-in Agreement of July 25, 1929 Not long after discovery at Kettleman but after the Continental Oil Co. and the Standard Oil Co. had completed several producing wells in the discovery group, came the so-called Shut-in Agreement negotiated at the instance of the Department of the Interior. This agreement became effective July 25, 1929. The fundamental purpose of the agreement was to prevent bringing on production of some 30 wells then being drilled and forestall a flood of Kettleman oil on the market. A cooperative scheme was developed whereby wells in the discovery group would continue to produce. Two of them could not be shut in. Drilling wells would be completed to a water shutoff in top of Temblor and operations suspended. Producing wells would contribute the value of 10 to 25 per cent of their production to the owners of suspended qualifying wells. The percentage rate of drainage contribution was left to a committee or umpire. Some acreage was not placed under the agreement. This same acreage later did not come into the Kettleman Unit Agreement. Several wells on this acreage did not contribute to the drainage fund. The total amount of oil produced during the 17 months of the shut-in agreement, by Milham, Continental and Standard from wells in the discovery group, was 5,297,262.22 bbl. The total amount paid out in "drainage" contributions was $2,046,048.18, representing sales value of 1,266,044.06 bbl. of oil.

Jan 1, 1937

By J. S. Blakemore, E. O. Hall

SERRATED yielding, commonly called the Portevin-Le Chatelier effect, is known to occur in a wide range of alloys where the moving dislocations are considered to be locked by the diffusion of solute atoms to them. From the work of Cottrell,1 an approximate relationship between strain rate, E, dislocation density, p , and solute diffusion coefficient, D, giving rise to serrated yielding is: e =Dp

Jan 1, 1969

By C. D. Johnson

Exploration work in 1932 in the Rocky Mountain region, which includes the states of Montana, Wyoming, Utah, Colorado and New Mexico, resulted in the discovery of one new oil field, Cut Bank in Glacier County, Montana; one new gas field, Craig in Moffat County, Colorado; and the definite outlining of a second gas field, Piceance Creek in Rio Blanco County, Colorado, in which there had been drilled but one small gas well prior to 1932. During the year, 95 producing oil or gas wells were completed, giving new initial production amounting to 188,000,000 cu. ft. of gas and 176,420 bbl. of oil per day for the region. By far the largest part of this new production of both oil and gas was developed in southeastern New Mexico, mainly the Hobbs field. However, the Dry Creek field of Carbon County, Montana, contributed over 5000 bbl. of; new oil production. Sixty-two wells were abandoned during the year but of this number only 10 promising structures were nonproductive. The remaining 52 wells had little to recommend their drilling from a structural or strati-graphical standpoint. Eighty-eight wells were suspended in the region' during 1932 before the tests had reached their individual objective horizons. Many of these suspensions were due to financial difficulties and it is possible that several of the operations may be resumed at a later date. At the close of the year, 54 wells were actively drilling, 54 were shut down and there were 20 rigs and locations in the five Rocky Mountain states. The accompanying table gives details of drilling and production.

Jan 1, 1933

By Ossi E. Palasvirta

The authors are to be congratulated for their interesting article, which thoroughly illustrates the variables inherent in filtration of taconite concentrate. The work and the conclusions based thereon largely parallel the test work done by the writer at the Pilotac plant* and the experience gained with a commercial size agitating disk filter in the same plant. At Pilotac, however, a thorough study was also made of the effect of depolarizing (demagnetizing) the filter feed, and it is the purpose of this discussion to comment on the merits of depolarization of the magnetite concentrate prior to filtering. The work at Pilotac was done in three phases: 1) preliminary laboratory testing with a circular filter leaf of 0.047 sq ft, followed by 2) plant testing using a 4-ft diam, single-disk agitating filter that was purchased on the basis of the pilot tests on the 4-ft model. In the laboratory tests depolarization was achieved by slowly withdrawin4 batches of thickened concentrate from a coil producing an alternating field of about 300 oersteds. In plant tests the standard Pilotac procedure1 was employed, wherein the pulp falls freely through the depolarizing coil.

Jan 5, 1958

By P. M. Aziz, I. Markson, C. S. Barrett

The abnormal after-effect in twisted wires that occurs when untwisting is interrupted by etching con be brought under control and used to study the mechanical properties of thin surface films and how they are effected by reagents and heat treatment. Results are given of studies of oxide films on high purity aluminum. IF a wire is subjected to plastic deformation by torsion and then released, it untwists in the normal after-effect, but under certain circumstances the untwisting is abruptly lessened or reversed by the application of an etchant to the wire.1,2 This abnormal after-effect may occur, for example, if there is a coherent oxide film on the surface of the wire which is removed by the etchant. Following a suggestion of A. H. Cottrell that predicted this effect, it is attributed to dislocations that had piled up beneath the oxide layer and represents the rapid release of residual stresses caused by these dislocations. When the layer is removed, the stress relief may be by escape of piled-up dislocations from the metal, or by an activation of latent sources of dislocations located at the surface, together with rebalancing of elastic stresses to compensate for the loss of stressed material, as in a residual stress analysis determination, these mechanisms acting singly or in combination.' The slower the attack of the reagent, the more gradual is the stress relief and the smaller the change in strain rate when the reagent is applied. A study has been made of the factors that influence the magnitude of the normal and abnormal after-effects with the object of developing techniques suitable for a quantitative investigation of the influence of various surface films on dislocations in wires, and of the rate and extent of the attack on the films by different reagents. It was found that reasonable sensitivity and reproducibility could be achieved if a suitable choice of variables was made and if these variables were held constant through a series of experiments. The method was then applied to a study of oxide films produced and treated in different ways on the surface of high purity aluminum wires, and to a study of the damage to these films caused by various reagents. Experimental Procedure The material used throughout this work was prepared from 99.9968 pct Al. This high purity aluminum was melted, cast into 1/2 in. diameter ingots, and then swaged and drawn without intermediate annealing to 0.040 in. diameter wire. A sketch of the apparatus employed for twisting is shown in Fig. 1. The test wires were mounted into the apparatus by cementing one end of the wire to the beaker and the other to the tube with laboratory wax of high melting point. The length of the wire between the waxed joints was 4.2 & 0.2 cm. Extreme care was taken during mounting to avoid cold-working the wire. The wire was twisted through 335" in 2 to 4 sec by rotating the pinion on the gear box until the vertical post on the rotating table, which was initially touching the horizontal stop, was arrested by the stop. All the tests were conducted with apparatus and reagents at the same temperature (about 25°C). In all tests, except those where the duration of the initial torque was investigated, the torque was applied for a period of 2 min. At the end of this time the table was rotated back a few degrees away from contact with the stop and the wire allowed to untwist. The after-effects were measured by reflecting a beam of light from the mirror shown on the apparatus. After the wire had untwisted for 6 min, a reagent was carefully poured into the beaker and thereby applied to the surface of the wire.. In some tests the liquid in the beaker was removed after a few minutes and replaced by an-

Jan 1, 1954

PURPOSE OF STUDY The case study was initiated because of the very real need to provide the best mineral inventory block estimates possible for the relatively new Sacaton mine. Sufficient mining had been done and records kept whereby it was possible to test the various estimation methods against detailed blasthole samples taken during mining. Three estimation methods were selected for testing: (1) the polygonal method, (2) the inverse distance squared method (IDS), and (3) the geostatistical kriging method. The results of the comparative analysis was thought to have very practical application to the selection of extension functions for future estimation of grade for mineral inventory blocks. GENERAL GEOLOGIC DESCRIPTION The porphyry copper deposit of the Sacaton open pit mine is related to small quartz monzonite intrusives of Laramide age which have been intruded into Precambrian granites. Both rock types act as host for the mineralization, which has been secondarily enriched sufficiently to constitute ore. The chalcocite enriched zone has been subjected to postenrichment oxidation processes with consequent partial destruction of the chalcocite blanket. Several mineralogical populations are represented in the total ore zone, but the blocks on the mine benches involved in the study were restricted to the top of the enriched zone. COMPUTATION OF MINERAL INVENTORY BLOCK ESTIMATES In order to make valid comparisons among the three estimation techniques, all of the inventories were prepared from diamond drill assay data used in the original engineering feasibility study. The data was taken from ex-

Jan 1, 1980

By Eugene N. Cameron

Pegmatites occur in abundance in certain areas of South West Africa and in adjacent parts of northern Cape Province in the Union of South Africa. Some of the pegmatite deposits were prospected before World War I, and intermittent mining was done during the period between the two World Wars. The deposits of the Jooste lithium mines became an important source of lepidolite, and beryl, columbite-tantalite, wolframite, and other minerals were produced. Since World War I1 prospecting and mining have been carried on vigorously, with the result that South West Africa produced nearly 3000 tons of beryl during 1949 through 1953, together with more than 40,000 tons of lithium minerals, chiefly lepidolite and petalite. Small amounts of tantalite, columbite, and other minerals have also been produced during the postwar period. Most of this mineral production has come from two pegmatite areas roughly outlined in Fig. 1. One is the Karibib-Omaruru area of north central South West Africa. The second is the northeastern part of the Orange River pegmatite area, which extends into adjacent parts of Namaqualand, in northern Cape Province of the Union of South Africa

Sep 1, 1955

By Otto F. Pfordte

The great advance of the last twenty years in the specialization, delicacy and efficiency of ore-concentrating apparatus calls for a finer system of testing both the qualities of ores and the operations of machines in this department. In amalgamation, lixiviation and smelting, the daily employment of physical and chemical tests has been recognized as necessary, and the cost of the necessary laboratories and employees is cheerfully paid. But while much progress has been made in concentration (due, in a large degree, to the study of the subject in our technical schools), it is still too common in actual practice to follow the loose old method of roughly estimating, once for all, that a given ore " concentrates x tons into one," and resting on this assumption so long as that ore continues to be treated, while assays of the tailings from concentration are made from time to time, without exact determination of their quantity. The first step toward accuracy of control must be a more frequent and precise measurement of the quantity of concentrates from a given operation. This should be expressed in pounds per unit of one ton; and the variations shown in frequent determinations will furnish a constant check upon the character of the ore and the performance of the apparatus. But this is only a part of what should be constantly and systematically done to insure the best work upon a material which must vary continually, even though it come from one mine only. If, in any mill, appropriate laboratory-tests were made at least once a week, the labor and expense involved would be amply repaid by increased knowledge and control of the current operations. A small testing-laboratory, provided with a few gold-pans;

Jan 1, 1902