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By Richard Pearce

IN looking around me for some subject on which to frame an address for this meeting, it has occurred to me that some results of observation and investigation, in regard to the varied conditions under which gold is found, may possibly prove of interest. The subject is one which frequently crops up in discussions at our meetings, but there is always an immense amount of uncertainty expressed as to the actual condition in which the gold exists in any particular ore. It follows, therefore, that any light which might be shed on this rather complex subject, would be of value to science and of service to mining and metallurgical practice. In some investigations which I have, from time to time, been led to make, for the purpose of determining to what extent an ore might be concentrated, I have been astonished at the very varied and apparently inexplicable results encountered, and have been naturally led to inquire into the causes for such seeming inconsistency. The mines of Gilpin county, Colorado, where gold was first discovered in that State, furnish an infinite variety of examples of its occurrence, and it was here that difficulties first presented themselves to the Colorado miners, in the sudden transition from what is called " free-milling gold-ore " to an ore characterized by properties which make the ordinary treatment by amalgamation stamp-mills utterly impracticable. So long as mining was limited to what might be called the zone of oxidation in the veins, just so long might amalgamation be conducted without difficulty; but directly the miner reached a point beyond the influence of the oxidizing power of the surface waters, the gold resisted all attempts at amalgamation, and recourse • was had to smelting.

Jan 1, 1890

By H. Herbert Hughes

THE trend in modern building construction is definitely toward the use of weight-reducing materials. The basic advantage of lighter structural weight is obvious; reduction of dead load with retention of equivalent strength affords the possibility of increasing the live load, or if this is not desirable or necessary it makes feasible a reduction in size of structural steel members and corresponding savings in other phases of construction. Among the weight-reducing materials and practices rapidly gaining favor are the use of light-weight patented insulating board to replace back-up tile or units, particularly in home construction; introduction of aluminum alloys to replace steel for many purposes; manufacture of porous brick, the use of which materially reduces the weight of masonry walls and partitions; and the use of self-rising vesicular concrete, diatomite and sawdust tile, porous gypsum, or gypsum tile for nonload-bearing partitions and walls. Even building accessories are being designed to save weight and space; one of the most striking examples of this is improved radiator construction. Concrete technique is keeping pace with the rest of the industry. Burned shale aggregates now available in many sections of the country will make concrete weighing only 100 lb. per cubic foot, saving roughly 35 per cent. in weight and sacrificing none of the strength of a rock-sand mix. It may be more expensive, but actual experience has shown that the saving in dead load will effect a reduction in structural steel which in many instances will more than offset the increased cost of the aggregate. The vesicular nature of most light-weight aggregates gives the concrete especially good insulating, fireproofing and soundproofing properties; yet absorption is comparatively low. Strangely enough, however, the increased use of light-weight aggregates appears to have augmented the demand for ordinary aggregates in concrete construction rather than to have decreased it. Light-weight aggregates have widened the field for concrete structures and, since the producers do not attempt to recommend the use of their material except where weight or other special properties are important factors, impetus- has been given to sales of other aggregates.

Jan 1, 1931

By John B. Cook

Most of today's open pits take the form of conical-shaped excavations in the relatively flat or undulating terrain surrounding them. Ore is usually hauled uphill from the pit bottom by truck, rail, or skip to crushing, beneficiation, railroad loading, and stockpiling facilities near the edge of the pit. There are, however, a few orebodies whose locations in mountainous terrain causes special problems that generate different technical solutions. LAMCO's 10.5 million metric tons per year high-grade iron mine in the Nimba Range in tropical Liberia is probably one of the most extreme of these exceptions (Fig. 1). At Nimba there is a 2,000-ft difference in elevation between the upper- most levels of the orebodies and the start of the railroad below at the foot of the mountain. Haulage to the crusher is usually downhill at grades of up to 12% dictated by the topography of the rugged terrain. Ore is transported from the crusher down the mountainside by a conveyor sys- tem 10,096 ft long, whose average grade is 18%. The belt is braked by asynchronous generators, feeding power into the local network. The original crusher must be relocated at a lower elevation outside the final pit limit to allow that part of the mountain on which it now stands to be excavated. HISTORY The LAMCO Joint Venture is owned 75% by the Liberian-American- Swedish Minerals Co. (LAMCO) and 25% by Bethlehem Steel Corp. LAMCO is comprised of a 50% interest by the Liberian Government and 50% interest by Liberian Iron Ore Ltd (Fig. 2). This joint venture was launched to develop the high-grade iron ore deposits of the Nimba Range.

Jan 1, 1969

By AIME AIME

AMONG the industrial motion pic¬tures released in the last year of possible interest to people in the mining industry are the following: "A New World Through Chemistry," made by the public relations department of E. I. du Pont de Nemours & Co., Wilmington, Del. This film, which is in sound and color, interprets in twenty minutes of narration and ingenious photography many of chemistry's newest developments. It may be borrowed either in 16-mm. size on an 800-ft. reel, or 35-mm. size on a 2000¬ft. reel, the only charge being the cost of returning the film. Douglas D. Rothacker, 729 Seventh Ave., New York City, is prepared to loan free of charge except for transportation each way several films prepared in the plants of the International Nickel Co., 16 mm. with sound. These include: "Nickel High Lights," 35 minutes; "Nickel Mining," 18 minutes; "Nickel Smelting," 18 minutes; "Nickel Refining," 9 minutes; and "Copper Refining," 6 minutes.

Jan 1, 1941

By Charles Himrod

In presenting this paper it is not intended to enter into any discussion of the theory of the blast-furnace, but simply to give the results of a number of determinations of CO and CO 2 in furnace gases, and some conclusions arrived at, and the result of an experiment made in hopes of increasing the production of CO 2. In the first table, on page 198, is given the averages of a number of analyses of gases of different furnaces, and in the second, of two stacks of different sizes under varying circumstances. The conclusions arrived at as to what influences the production of CO2 are as follows: lst,. Kind of fuel. Bituminous coal not permitting the formation of as much CO, as coke. 2d. Kind of ores. Rolling-mill cinder being much less favorable to formation of CO2 than hematite ores, magnetites probably less than hematites, but more than cinder. 3d. Length of time of contact of gases with ore. Small furnaces and too rapid driving both waste fuel by riot allowing enough time for conversion of CO into CO2. 4th. The temperature of blast. The hotter the greater the quantity of CO2. 5th. Regularity of passage of stock through the furnace. The hanging and dropping of the stock, however slight, seems to pack it more solidly in the hearth, increases the resistance to the blast, and decreases the quantity of CO2. These are the most common causes noticed which influence the production of CO2, unless we except the one that might be considered the greatest of all, the one that has spoiled so many tons of iron, and the amiability of so many furnacemen, the one most dreaded, the great unknown. It would seem a self-evident proposition that the better the contact of the gases with the ore and the less with the fuel, the greater would be the amount of CO2 produced. To prolong the contact of gas with the ore furnaces are enlarged with advantage, and pains are taken to charge the stock in such a manner as will best promote it. Still, with furnaces of most approved construction and most skilful manipulation, the gases leave the furnace so rich in CO, that not half the heating power of the fuel is obtained, and the highest

By C Gunther

The term metamorphism as commonly used means any change in a rock in either form or composition, from whatever cause. By metasomatism, according to Lindgren, is meant a metamorphism that involves a change in the chemical composition of a rock by the addition or subtraction of substance. Certain types of metamorphism are due to the action of mineralizing solutions, and are closely connected with ore deposition; they form, therefore, valuable guides in the exploration for ore-deposits. Other types of metamorphism are due to regional processes, and are not connected with ore deposition. By dynamo-regional metamorphism is meant a primary alteration of rocks over large areas under conditions of pressure, flow- age, and heat. This process produces schists and gneisses from either sediments or igneous rocks. It is thought that there is little migration of minerals or of elements in dynamo-regional metamorphism, and that the changes are due chiefly to recrysallization and rearrangement of original minerals in bands with their major axes oriented normal to the direction of greatest pressure. Under these conditions limestones are commonly altered to marble, and sandstones to quartzite, basic igneous rocks to greenstone or serpentine, while rocks of normal or acid com- position commonly yield the usual types of schist or gneiss. Dynamo-regional metamorphism, extending over large areas, has no connection with mineralizing processes, and is, therefore, no guide to ore deposits; while this process has certain features, such as characteristic mineral associations, in common with contact metamorphism, the results of the two processes may usually be distinguished without difficulty.

Jan 1, 1932

By Lewis E. Dr. Young

MINING engineers in the United States understand that mining conditions in the British coalfields are much more difficult than in most of the mines now being operated in the United States. We realize also that in the near future we must face some of these same difficult problems. Early Mechanization The progress made in mechanical loading in the United States is the result of a long struggle in many coalfields to mine with power tools safely and to increase output per man-shift. Attempts to use power to loosen coal and to transport broken coal in the U. S. may be said to date from the Stanly Header, or Entry-Driver brought from England in 1888. The principle of this boring machine was used in the McKinlay Entry-Driver, almost continuously used in the U. S. since 1920. Since 1888 experimental loaders, scrapers, and conveyors were installed with more or less success. Beginning in 1918, considerable progress was made with mobile loaders, and in 1920 the first wage agreement for the operation of mechanical loaders was made in Indiana. In 1923 the Pocahontas Fuel Co. loaded nearly 1 million tons of coal using 23 Coloders. Labor Policy The United Mine Workers of America have never officially opposed the Mechanization movement. On December 10, 1945, in a statement before the House of Representatives Labor Committee, John L. Lewis said, regarding the policy of the United Mine Workers of America: "We have welcomed progress; we have welcomed machines. We have told our people that they had to accept that condition; that it was the process of progress, and that they would have to take their chances." Recent Development In 1951 about 71 pct of the tonnage mined underground was mechanically loaded. Over 4000 shuttle cars are in service and it is estimated that much more than half of the tonnage loaded underground is produced by trackless mining. In 1947 roof-bolting was introduced extensively and it is estimated that more than 2 ½ million bolts are now being used per month in about 600 mines. The use of roof bolts has permitted the more effective and safer use of loaders and shuttle-cars. Continuous Mining The McKinlay Entry-Driver could have been used for continuous mining, but for many years it was used only .for entry driving. In 1946 the Silver machine was developed in Colorado, and in 1947 this was acquired by the Joy Mfg. Co. and called the Joy Continuous Miner. Other types of combination mining-loading machines which eliminate drilling and blasting operations are the Marietta Miner, the Colmol, the Lee-Norse Miner, the Junior Miner, the Goodman and the Konnerth machines. There are several other types in the process of development. Probably by January 1953 there will be about 250 continuous miners in operation in the U. S. Payment of Mine Labor One of the most important problems in mechanizing was the establishing of rates of pay that would be attractive to the best men. Prior to the installation of mobile loaders the hand loaders and cutters have been paid by the ton. It was felt that a system of a day's pay should be established and that piece and tonnage rates should be abolished completely. Without exception, all coal loaded in mines equipped with mobile loaders is prepared and loaded by men paid an hourly rate. Trends in Mining Research There are two diverse approaches in coal production research; to try to design a mining machine to fit current methods, or to adapt mining practice to take advantage of proven machines. A great deal of credit must go to the mine operators who have been enterprising and dynamic enough to use available equipment intensively and to discard it as soon as an improved or new machine is available. Effect of Changing Markets Formerly there was an important demand for lump and prepared coal in the larger sizes for domestic use. The use of bituminous coal for house heating has decreased so that not more than 19 pct of the annual tonnage goes to retail trade, only 12 pct is used by the railroads, and much of the retail and most of the railroad coal is in stoker size. As a result of this decline in the market for coarse coal most of the large mining operations have crushers installed in the tipples or preparation plants. Mass production at the face requires increased preparation facilities. Another important trend is in connection with complete seam mining with mechanical loading. In many mines where the immediate roof is apt to fall with the coal no effort is made to separate roof material from coal prior to

Jan 1, 1952

By M. C. Leverett

THE behavior of mixtures of immiscible liquids in porous solids is of rapidly increasing interest to those engaged in the production of petro-leum. The operation of artificial water-floods and the control of natural ones immediately raise questions concerning the fundamental nature of such processes. Moreover, it is now recognized that often water occurs dispersed throughout the rock from which the oil issues into the well,1 and thus tends to move toward the well simultaneously with the oil. The work reported here is a laboratory investigation of the simultaneous, steady-state flow of oil and water through the same column of uncon-solidated sand. It is thus directly related to the situation in which water occurs in oil-producing sands; it may have less direct implications for the displacement of oil from sands by water. However, it is to be clearly understood that the experiments to be described were performed pri-marily to obtain information of a more or less fundamental nature, and are not an attempt to reproduce, on laboratory scale, any part of an oil field. The dynamic behavior of a system in which oil and water are flowing simultaneously through sand is best described in terms of its "effective permeability" to either phase. For incompressible fluids flowing through a system of uniform cross section, the effective permeabilities to the two phases, in darcys, may be defined by the equations:

Jan 1, 1938

By A. C. D. Chaklader, Ashok K. Kakar

The basic density equation originally dericed ' to predict the increase in density of a compact of spherical particles with the progressive deformation at the points of contact has been further modified to include the yield strength of the material. This has been done by assuming that the contact areas grow to stable sizes under a fixed stress which is equal to three times the yield strength. The final equation has the form: where Do and D me the initial and final bulk densities of the compact, u is the applied pressure, and Y is the yield strength of the material. This equation was tested with the data obtained on spheres of lead, K-Monel, and sapphire. The calculated yield strength t~alues for lead and sapphire are within the range of values reported in the literature. A few of the earliest hot pressing models proposed to explain the mechanism by Murray, Livey, and williams2 and then by McClelland3 are based on a plastic flow mechanism. However, more recent investigations suggest that the overall densification process is a combination of several mechanisms, such as particle rearrangement, fragmentation, plastic flow, and stress-enhanced diffusional creep. While fragmentation and particle rearrangement are considered to be responsible for the densification in the early stages,"475 it has been concluded that the final stages of hot pressing are controlled by stress-enhanced diffusional creep.516 The manner in which the densification takes place, i.e., by fragmentation, particle rearrangement, plastic flow, or stress-enhanced diffusional creep, would depend upon the type of material, the temperature, and the stress level used during the hot-pressing experiments. Metal compacts can be expected to have a much greater contribution from plastic flow than ceramic oxides. Also, plastic flow would be a significant contributing factor to densification at high temperatures and high stresses. Most of these works, directed towards elucidation of densification mechanism, have dealt with kinetics of the process. The results of most of the authors vary from one another and they have proposed either new empirical or semiempirical equations to fit their data. The densification rate was found to vary with the type of the powder, shape and size of the powder, initial packing density of the compact, and a few other factors such as rate of heating, pressure, and so forth. Beyond the initial stages, the densification process has been considered to be as time-dependent flow, controlled by a diffusional process, e.g., Nabarro-Herring creep. Palm our, Bradley, and johnson' have attempted to use modified creep rate equations to interpret the data of densification under hot-pressing conditions. Beyond the initial stages, however, the densification would be controlled by a process depending upon the temperature, pressure, and size of the powders. It is the authors' belief that such densification cannot be exclusively controlled by a single process and so attempts should be made to study some observable phenomenon like microstructure, yield strength, and so forth. The emphasis of this work has been toward studying the densification problem from a more fundamental point of view. Some of the principal variables, like initial packing density, mode of packing, and size of the powders, have been controlled to a great extent. The total strain produced on pressure application (instantaneous) in such a case can be considered to be due to plastic and elastic deformation. The elastic component of the strain can be determined by decreasing the load to the initial value. The strain remaining then can be correlated with the contact areas produced by deformation and the corresponding applied load. In a previous paper,' the possible deformation behavior of spheres in a compact has been theoretically analyzed and experimentally tested. The change in contact area radius a relative to the particle radius R was related to the bulk density and the bulk strain for simple and systematic modes of packing. Tt was found that a density equation relating the above parameters can be represented by: where D and Do are the bulk densities of the compact at any value of a/R and a/R = 0, respectively. This basic equation should hold for any material as it was derived from geometrical considerations alone. An attempt has been made in this work to include the yield strength in the above density equation, so that a knowledge of the properties of any material can be used in predicting the densification behavior during the hot-pressing process. THEORETICAL CONSIDERATTONS The deformation of two spheres in contact under a static load can be compared to the deformation occurring between a hard spherical indentor and the flat face of a softer metal. Tt has been shown theoretically by both ~encky~ and lshlinskyg and experimentally by ~abor" that, for a material incapable of appreciable work hardening, the mean pressure required to produce plastic yielding (for deformation occurring between flat face and a hemispherical indentor) is approximately equal to three times the elastic limit, Y, of the material (in tension or compression experiments). Tabor has further observed that the same relationship is valid in the case of work-hardening materials, if the elastic limit at the edge of the indenta-

Jan 1, 1969

By W. C. Ellis, M. E. Fine

In the iron-cobalt system there are several property-composition relationships of theoretical importance. The alloys are ferromagnetic exhibiting a maximum saturation at approximately 33 at. pct cobalt;' the interatomic distances at room temperature show large positive deviations from Vegard's rule;2 and in the region of 50 at. pct cobalt there is an order-disorder transition2 which has a large effect on other properties. The thermal expansion data for the system have been reported only from room temperature to 100 C and for this temperature range a minimum in coefticient in the rcgion of 50 at. pct cobalt is well established.3,4,6 This paper reports the expansion properties in the iron-cobalt system for temperatures from 30 to 850°C, shows the correlation with other physical properties, and proposes an explanation for the tcrrelation. Experimental Procedure The thermal expansivities of iron-cobalt alloys in 10 pct steps in composition were determined from 30 to about 850°C. The major series of alloys was prepared by induction melting from Armco iron and cobalt rondelles with the addition of about 0.6 wt pct manganese. This series was supplemented by three compositions: high purity electrolytic iron, high purity electrolytic cobalt, and an alloy of 52.1 wt pct cobalt prepared from the high purity electrolytic iron and electrolytic cobalt by vacuum-melting. The compositions of both series of alloys are given in Table I. The specimens for measurement were prepared from the cast ingots by first hot-swaging followed in most instances by cold-swaging to 0.180-in. diam rod. Some alloys in the region of 5c pct cobalt, because of inherent cold-brittleness, were swaged hot to the final diameter. The expansion specimens were approximately 2 1/2 in. long with flat-ground and polished ends. Before measurement they were annealed in hydrogen for I hr at 900°C. In the apparatus used for the thermal expansivity measurements (Fig I), a modification of that designed by Hidnert and Sweeney,? the differential expausion between the specimen and vitreous silica was measured by a dial micrometer reading to 0.001 mm. An invar fixture supported the dial gauge, and this fixture, in turn, was connected to a split invar collar which supported the outer silica tube. A pyrex "T" was placed over the outcr silica tube and was sealed to the invar collar by Apiezon Q sealing compound. A movable hollow vitreous silica rod which rested on top of the test specimen slid through a flexible rubber diaphragm cemented to the top of the pyrex "T." The specimen rested On a vitreous silica pedestal fused into the outer tube and was kept centered by a silica sleeve. A nonoxidizing atmosphere was obtained by admitting hydrogen into the

Jan 1, 1949

By Charles Hart

The art of electric smelting came with the turn of the present century and owes its existence to the introduction of alternating current, which found its first wide use in the establishment of the great power plants at Niagara Falls, N. Y. Prior to that time current was largely direct. The furnaces were electrolytic in nature and found their first metallurgical use in the production of aluminum, and this process still prevails. The normal production of pig iron up to that time was carried on in blast furnaces in which charcoal, coke and anthracite were used as the fuel. This new electric process called for sufficient carbonaceous material to reduce the oxides and impregnate the pig iron with sufficient carbon, but the remainder of the energy was to be supplied by electric power. The chemical reactions are essentially the same in electric smelting as obtains in the older blast furnace. All of these data are so well known in both methods as to need no discussion at this time, for they can be found in scientific : publications and books written during the first two decades of this century. Types of Furnaces The 40 years devoted to the practice of electric smelting may be divided into two . periods of 20 years each. The first was devoted to experimentation with furnace types and with many publications on theories and processes. The second half of this term was devoted to perfecting the types of furnaces and their active commercial operation. The arc furnace may be found in three types: (1) the direct-heating arc furnace with the positive electrode included in the bottom and the other electrode suspended above; (2) the independent arc furnace with its electrodes entirely above the charge, which of necessity depends upon heat reflected from the roof; (3) the direct-heating series arc furnace equipped with two or more electrodes suspended from the roof. Of these three types, only the last is used in electric smelting of iron ore at the present time. The elimination of the other types automatically removed many of the early designs, to the end that there are now only two general types in operation: (I) the " Electrometalls" or high-shaft furnace of Sweden, and (2) the low-shaft or pit-type furnace as offered by Tysland-Hole and Siemens-Halske. The "Electrometalls" furnace takes its name from the corporation formed by the engineers that had undertaken its perfection. After trying several designs they brought forward the furnace shown in Fig. I, which by the way is the highest development of this type of furnace as of today.l Note the trend in the lines, which have kept pace with modern blast-furnace design. The high-shaft furnace lends itself to skip filling and is fitted with tuyeres immediately under the crucible roof, whereby the gases are recycled and the roof preserved. The failure of the Electrometalls furnace in Norway, because of its inability to meet

Jan 1, 1941

By Charles Hart

The art of electric smelting came with the turn of the present century and owes its existence to the introduction of alternating current, which found its first wide use in the establishment of the great power plants at Niagara Falls, N. Y. Prior to that time current was largely direct. The furnaces were electrolytic in nature and found their first metallurgical use in the production of aluminum, and this process still prevails. The normal production of pig iron up to that time was carried on in blast furnaces in which charcoal, coke and anthracite were used as the fuel. This new electric process called for sufficient carbonaceous material to reduce the oxides and impregnate the pig iron with sufficient carbon, but the remainder of the energy was to be supplied by electric power. The chemical reactions are essentially the same in electric smelting as obtains in the older blast furnace. All of these data are so well known in both methods as to need no discussion at this time, for they can be found in scientific : publications and books written during the first two decades of this century. Types of Furnaces The 40 years devoted to the practice of electric smelting may be divided into two . periods of 20 years each. The first was devoted to experimentation with furnace types and with many publications on theories and processes. The second half of this term was devoted to perfecting the types of furnaces and their active commercial operation. The arc furnace may be found in three types: (1) the direct-heating arc furnace with the positive electrode included in the bottom and the other electrode suspended above; (2) the independent arc furnace with its electrodes entirely above the charge, which of necessity depends upon heat reflected from the roof; (3) the direct-heating series arc furnace equipped with two or more electrodes suspended from the roof. Of these three types, only the last is used in electric smelting of iron ore at the present time. The elimination of the other types automatically removed many of the early designs, to the end that there are now only two general types in operation: (I) the " Electrometalls" or high-shaft furnace of Sweden, and (2) the low-shaft or pit-type furnace as offered by Tysland-Hole and Siemens-Halske. The "Electrometalls" furnace takes its name from the corporation formed by the engineers that had undertaken its perfection. After trying several designs they brought forward the furnace shown in Fig. I, which by the way is the highest development of this type of furnace as of today.l Note the trend in the lines, which have kept pace with modern blast-furnace design. The high-shaft furnace lends itself to skip filling and is fitted with tuyeres immediately under the crucible roof, whereby the gases are recycled and the roof preserved. The failure of the Electrometalls furnace in Norway, because of its inability to meet

Jan 1, 1941

Since its organization, in July, 1917, the War Minerals Committee of the Institute, of which William Y. Westervelt is chairman, has been studying important phases of the mineral industry and its relation to winning the war. From this has come a realization of the imperative need for more definite coordination than is possible without direction by some governmental agency. No privately controlled industry can have the detailed knowledge of war needs or the control of all its supplies and markets necessary to effect the adjustment of its activities for war purposes. Inevitable shortages of certain essential minerals confront us unless immediate steps are taken to stimulate and develop. the mining

Jan 2, 1918

By R. P. Rothwell

THE first difficulty mentioned is that in some instances two or more beds of coal separated by sandstone or slate rocks of considerable thickness in one part of a basin, are found running together in another part. Of course, we may happen to strike first the part of the basin where there is but a single seam, and in this case the bed would appear to divide into two or more branches within a short distance. Such cases are not rare in the anthracite coal-fields. I would suggest as an explanation of this phenomenon the gradual sinking of the peat-marsh-the embryo coal-bed-on one side, and the moving forward of the marsh, so that on one part of the bed the formation of peat would still be progressing, while another part, being under water, would be covered with mud and sand. Thus we have different portions of the same bed of different ages. Now if the sinking of the marsh be stopped for a time, the bed will become thicker in the portions left exposed, and if the sinking now changes in direction, so that the part that had previously gone down com¬mences to rise, we should have the phenomenon of a bed, continuous throughout, with one portion overlying another, and separated from it by rock strata. These are exactly the conditions observed in splitting beds. While one side of the lake is sinking, and the peat-marsh moving on in that direction, the other side may be rising,

Jan 1, 1873

By Fortunato Pereira Gamba

The Department of Narino (formerly included in the Department of Cauca) is a narrow band about 170 km. (100 miles) wide in the southern part of the Republic of Colombia, near the boundary of Ecuador, as showu in the sketch-map, Fig. 1. Its capital is Pasto, a small city of 25,000 inhabitants; the pri~icipal towns are T?querres, Cumbal, Ypiales, Barbacoas, and Tumaco. The port on the Pacific ocean is Tumaco, and traffic in the interior is carried partly on the Patia river (steam navigation to the fluvial port of Barbacoas), and afterwards overland over poor roads by human bearers or on mule-back.

Jan 1, 1913

By E. B. BESSELIEVRE

THE great work of Gorgas in stamping out yellow fever in Panama during the construction of the Canal was one of the chief factors contributing to the ultimate accomplishment of the task, two previous attempts having failed largely through the demoralization of workers by epidemics of contagious diseases. Mining camps, rapidly constructed during the boom days of the rushes to new fields, have been frequent sufferers from typhoid when, as so often used to be the case, little or no attention was given to bacterial examination of the water supply or to the method used for disposing of the sewage.

Jan 1, 1930

By Evan Just

Attempting to analyze a 25-year forecast after less than a third of the time has elapsed may seem premature. The President's Materials Policy Com- mission's report necessarily painted with a broad brush and made no claim for pinpoint accuracy in its predictions. More importantly for present purposes, it made no attempt to predict the detailed courses of production and consumption during the period forecasted. Several statistical highs and lows may very well lie between now and 1957, so comparing recent figures with points taken from the report on a straight-line basis would be illogical. Moreover, the report assumed that the general trend of consumption-domestic and foreign-would be upward. Contrarily, domestic figures were lower in 1957 than in 1950. Therefore, to project curves from 1950 through 1957 leads to conclusions that are probably false. Many in the industry would feel more uncertain about forecasting 1975 domestic conditions now than they would have been in 1950, even though nearly a third of the 25 years has elapsed. In making comparisons, several statistical problems are encountered. The Paley report figures for 1950 were estimated in several cases and corrected figures vary as much as 10 pct. For example, the report placed 1950 lead consumption at 800,000 tons, whereas actual consumption was 885,000 tons. Obviously, in comparing more recent figures with the report's projections, adjustments must be made for positions taken in error from the start. Over the long pull, such discrepancies will probably be insignificant, but they must be noted in comparing short-term changes.

Jan 10, 1959

By Francois E. Heuze

INTRODUCTION Rock slope stability typically is governed by the geological discontinuities. This stability can be improved by drainage, unloading, adjustment in slope orientation, adjustment in slope angle, and also by reinforcement such as bolts or tendons. This paper addresses the modeling of bolt reinforcement in rock slopes. Most geological discontinuities such as joints have rough surfaces; they dilate during shear displacement. Their shear strength is characterized by two envelopes (Fig. 1); the peak envelope is distinct from the residual envelope when the joints can dilate. If the dilation is restrained transversely, such as with bolts, the normal stress will increase and the joint strength also will increase. It has been demonstrated that this increase may be considerable (Obert et al., 1976). The new normal stress at peak strength is a com- posite function of the properties of the rock mass and of the steel (Heuze, 1979). Hence, the dilation and its resultant effects on joint shear strength must be included in the analysis and design of the reinforcement. We present a model which can be used to perform such an analysis. Early studies of rock reinforcement in mining and civil applications (Lang, 1957 - Panek, 1962 - Osen and Parsons, 1966 - Lang, 19721, did not consider the specific effects of bolts on joint shear strength. In 1973, Heuze and Goodman reported direct shear tests on rough sandstone joints with bolts perpendicular to the joint plane (Fig. 2). The peak shear strength of such joints was greatly in excess of the shear strength of the unbolted joints. The excess

Jan 1, 1983

By K. E. Manchester, A. H. Clark

Hall measurements have been made on three groups of silicon samples, which were implanted with boron, aluininunz, and phosphorus ions. Boron and phosphorus implants show essentially bulk properties when annealed under previously determined conditions, i.e., 15 min at 80O°C for boron and 10 mirz at 600°C for phosphorus. Bulk properties were also observed in alu?rrilzum-implanted samples when ion concentrations were below 1015 cm-'; however, strange low- terrzperalure behavior and a falloff in cavrier concenlralion was observed for sarnples with ion concenlration abozle loL5 ern-'. This can be attributed to solid-solubility effects since the average bulk concentration f0.r the sample exhibiting bulk properties was below the reported solubility limit for aluminum, while the other samples were above the limit. A detailed study of the annealirzg process indicates that mobilities reach bulk c~alues in phosphorus implants at 250DC, in alutninurn ivnplanls a1 500°C, and in boron implants at 700°C. A simple rnodel has been proposed to fit the annealing data. THE technique of semiconductor doping by direct injection of energetic ions is being actively investigated at this Center. Previously published results from this laboratory have been concerned with the investigation of implanted profiles in silicon and the electrical properties of the resultant p-n structures.1'2 Diode properties have been reported for junctions produced by implantation of boron ions and aluminum ions in n-type silicon and phosphorus ions in p-type silicon. Reverse current characteristics, as well as electron diffraction data, have indicated that the damage to the structure produced by the energetic ions during the stopping process can be minimized by a gentle anneal. The time-temperature conditions for this process have been determined by sheet resistivity studies.3 Electrical profiles of implanted phosphorus ions which have been determined by a differential sheet conductivity technique are based on the assumption that the carrier mobilities and activation energies for ionization are the same as in bulk silicon. These assumptions have been substantiated experimentally by measurement of Hall constants and resistivities of these implanted structures and the results are presented herein. After establishing the bulk property equivalence of the annealed layers, a more detailed examination of the annealing process was undertaken. The sheet resistivity technique initially used to determine anneal conditions has been broadened to include Hall constants and mobility behavior with anneal conditions. PROCEDURE The three groups of samples prepared for Hall measurements were implanted with mass-separated beams of boron, aluminum, and phosphorus ions. Ion concentrations are equivalent surface concentration and they have been determined from beam current measurements during implantation. Implant conditions for the samples are shown in Table I. In all cases, the samples had previously been angle-lapped on one edge and the junction delineated with an HF-copper sulfate solution. The surfaces of the implanted regions of the samples were exposed to the delineating solution and in the case of the "n"-type phosphorus-implanted areas it was later discovered that a finite amount of surface could be etched by this solution. This is discussed in the section on results. The implanted samples were ultrasonically cut into the conventional six-probe configuration shown in Fig. l.* In the annealing studies, for which the meas- urements were taken at room temperature, the sample holder was a Bakelite jig incorporating tungsten mechanical probes. The other measurements were taken using a conventional liquid-nitrogen cryostat, in which the temperature could be varied from 77" to about 400°K. For these measurements, 10-mil aluminum dots were evaporated onto the samples and alloyed with the silicon at 530°C for 15 min. The samples were then mounted in flat-packs, and gold wires were bonded to the aluminum dots. The electrical measurements were made with either a Leeds & Northrup K-5 Potentiometer, a Keithley 147 Nanovolt Null Detector, or a Keithley 601 Electrometer. No external bias was applied to the substrate. There is an inherent self-biasing arrangement at one or the other of the current contacts (depending upon the polarity), and this suffices to limit the current flow to the implanted layer. The magnetic field was generated by an A. D. Little electromagnet. Except for occasional checks of linearity of the Hall voltage with

Jan 1, 1969

By Wm. E. Milligan

LEAD stocks at the beginning of 1943 were comfortable when compared with those of other base metals such as copper, zinc and tin. This situation was early recognized by W.P.B. and other Governmental agencies and every effort was made to encourage the substitution of lead for these latter metals in all essential uses. Despite this apparently healthy condition, lead was not denied participation in the various measures inaugurated by the Government to relieve metal shortages. Thus in the Mexican trade agreement, effective Jan. 20, the tariff on two important classes of lead importss was halved. Similarly, in the setting up of B quota premiums, a B base was allotted to lead, with all pro¬duction above this figure receiving an additional payment of 2.75c. per lb., or a total payment of 11.75c. per lb. At about the same time it was announced that all quota transactions would be based upon the lead content as shown by the smelter settlement sheets. This basis was 86 percent of the lead content for all ores shipped to custom milling plants and 95 per cent for ores and concentrates shipped to custom smelting plants. The importance of this action can be appreciated when in the Coeur d'Alene it was estimated as equivalent to a 5 per cent increase compared to the previous base.

Jan 1, 1944