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By Will Mitchell, T. G. Kirkland, C. L. Sollenberger

BENEFICIATION of a Korean scheelite ore has been studied during the past year in the Basic Industries Laboratory at Allis-Chalmers Manufacturing Co. A flowsheet has been recommended including flotation, gravity separation, and a final cleaning by a magnetic separator. The investigation was continued in the field of flotation in order to establish the effect of certain variables on recovery and grade of rougher concentrates. The results of this investigation are recorded here. Mineralogy The scheelite ore was obtained from Korea and was mined from the Sang Dong deposit. This deposit is described as lying in gently dipping metamorphosed sedimentary beds of Cambrian age.' The metamorphism was probably either metasomatic replacement or recrystallization, or both, with subsequent hydrothermal deposition. Igneous bodies in the form of granite porphyry have been found within 7 km of the main shaft and are considered to be a possible source of the mineralizing solutions. The Myobong formation, the host for the Sang Dong deposit, was laid down in middle Cambrian times and consists of series of mudstone, siltstone, shale, and marl, with local stratification of mica schists, hornfels, and tactites. The scheelite is found in quartz bands in the tactites. Although there are six of these bands, only one, the "main bed" averaging 1.75 pct WOs, has been mined to any extent. The ore sample as received in the laboratory was the product of a cone crusher and was all —2 in. The rock appeared to be even textured, medium to fine grained, and gray green in color. No scheelite could be recognized by the unaided eye. However, under ultraviolet light of 2537 A, the scheelite fluoresced and could be distinguished from the gangue. Under the black light, the scheelite showed no definite vein structure but was disseminated throughout the specimen. The raw ore had a specific gravity of 2.96 and weighed about 125 lb per cu ft at —20-mesh Tyler. The —2-in. material was stage crushed through 20-mesh, and samples were cut for mineralogical, chemical, and spectrochemical analyses. Several polished sections were cut from hand specimens. Figs. 1 and 2 show quartz to be the matrix for scheelite. It was reported by Kim2 that the greatest scheelite concentration in the mine is found with a high concentration of quartz and a decrease in the abundance of garnet. Diameters of scheelite particles ranged from 1.2 mm down to less than 50 microns. Spectrochemical analysis showed the ore to be high in aluminum, bismuth, calcium, iron, magnesium, manganese, silicon, tungsten, and with lesser amounts of beryllium, chromium, lithium, sodium, and titanium. Chemical assays showed the —20-

Jan 1, 1952

By John Chipman, A. M. Samarin

It has been long known that the gas evolved during the boil in the open-hearth furnace is mainly carbon monoxide associated with smaller quantities of other gases. A number of attempts have been made to determine the precise effects of carbon and oxygen content of the bath, and of other factors, such as temperature, upon the evolution of carbon monoxide. In his investigation of the carbon-iron oxide product in liquid steel, Hertyl showed that the value of this product at equilibrium could be approximated by plotting the value of the product observed in open-hearth reactions against rate of carbon elimination, and extrapolating to zero rate. The results of this study showed a slight but definite effect of temperature upon the carbon-iron oxide reaction. Experimental studies of the evolution of gases from rimming-steel ingots have not yet attained the degree of precision necessary for an exact understanding of the effects of pouring temperature, carbon content, and iron oxide in the metal upon the composition of these gases. Klinger2 showed that the gas consists mainly of carbon monoxide, and that considerable variation in its composition occurs during the solidification of the ingot. In order that these variations may be understood in their proper relationship to the progress of solidification of the ingot and the segregation that accompanies solidification, it is essential to have a knowledge of the condition of equilibrium in the several chemical reactions by which the gases are being formed. It is also necessary to understand the effects of temperature upon the equilibria, and further, to know the manner in which the temperature of the liquid metal within the ingot changes as the skin of the ingot is being built up. The reactions in which we will be chiefly interested are those involving in the one case the oxides of carbon, and in the other case steam and

Jan 1, 1937

By James Pollock

SUMMARY THE possibility of colloidal deposition of cinnabar has been neglected. In opalite deposits cinnabar exists in particles within or near the colloidal size range. Colloidal processes have been admitted to be operative in hot springs and low-temperature deposits similar to most cinnabar deposits. Mercuric sulphide sols are stable to elevated temperature and pressure, and in nature probably are chiefly affected by the electrolytes in solution, dilution of colloid, and presence of protective colloids as silica. The stability of mercuric sulphide sols to electrolyte is measured, and shown to be greatly increased by dilution and by the protective action of silica. Mercuric sulphide sols follow the Schulze-Hardy valency rule, therefore the precipitating power of complex mixtures of electrolytes can be computed roughly. The stability of mercuric sulphide sols is shown to be greater than the equivalent precipitating power of the electrolytes in a hot spring depositing mercuric sulphide. It is concluded that finely divided or earthy types of cinnabar are colloidally deposited. POSSIBILITY OF COLLODIAL DEPOSITION While colloidal solution has been suggested as a means of transport for a number of minerals, such as the sulphides of antimony, arsenic, and iron, it has been neglected in connection with mercury. This is surprising because there exists positive evidence that cinnabar is present in certain deposits in particles of colloidal or near colloidal size. Colloidal transport could result from either the rapid dilution or neutralization of alkaline sulphide solution bearing mercury coming in contact with deep ground waters, or from colloidal solution near the original source and subsequent flow to the point of deposition unchanged. That the dilution of a mercuric alkaline sulphide solution will precipitate mercury sulphide in colloidal form has been demonstrated a number of times and is easily confirmed. The dilution hydrolyzes the alkaline sulphide Na2S to the corresponding hydroxide and hydrosulphide NaOH and NaHS, and the diminution of the concentration of alkaline sulphide reduces the solubility. It is not the contention of this writer that colloidal deposition is the mode of transport of mercuric sulphide in all mercury deposits, but that the stability of a mercuric sulphide sol, as demonstrated below, in waters that are similar to those that have deposited mercuric sulphide necessitates consideration of this possibility in many deposits, especially those of the hot-spring and so-called opalite type. EVIDENCE OF COLLOIDAL DEPOSITION Ross1 has shown that most deposits of quicksilver are formed at low temperatures and pressures, and probably by solutions that have relatively simple chemical compositions. In most cases the solutions are probably similar to those observed in hot springs, and in two instances-at Steamboat Springs, Nevada, and Sulphur Bank, California-hot springs have been reported by Becker as actually depositing cinnabar.2 Opalite deposits were believed by early investigators to be surface phenomena

Jan 1, 1944

By John J. Croston

IN the closing months of 1936 the copper industry gave every evidence that it was at last on the threshold of an improved era. At the beginning of the year prices stood at 9 ¼ ¢, which in itself was a great improvement over prices prevailing for the three previous years. Industry generally was showing signs of moving forward in this country, and business was definitely good in certain foreign quarters. The threat of war and preparations for rearmament in Europe and Asia acted as a further stimulus to purchasing. By midsummer the situation had so improved and stocks had been so reduced that the cartel of foreign producers (including American producers with foreign mines) decided to increase the production quota to 75 per cent on Aug. 1. Large-scale buying gave continued strength to the price and by Oct. 1 the quota was increased to 80 per cent, and again on Oct. 15, to 85 per cent. Notwithstanding this the price of copper continued its advance and on Nov. 1, with stocks declining continuously, the cartel increased operations to 95 per cent, then to 105 per cent on Nov. 5. In the meantime the domestic producers, because of the great increase in home consumption, had increased their production by nearly one-half. At the close of the year copper sold at 12¢ per pound, and since the turn of the present year has reached 17¢. This rapid increase has not been wholly justified. Much of the increase was due to the legitimate demands of recovering industry, but rearmament orders plus accumulation of reserve stocks in case of war, purchases in anticipation of labor strikes and purely speculative activities on the London Metal Exchange accounted for the balance. Certainly in view of the state of industry and the general world price level, it appears unnecessarily high. Talk of a copper shortage is sheer nonsense, the recent condition in the market being created by overbuying, leaving but a small volume for speculative supplies. It takes some months for an increase in mine output to reach the market, but production is again overtaking apparent consumption, stocks have begun to increase, and this, together with the reopening of many small

Jan 1, 1937

By Carl Zapffe

A Rise in less than ten years from obscurity into great prominence economically, tersely summarizes the history and status of the Cuyuna manganiferous iron ores. The Cuyuna district produces and ships mostly high-phosphorus iron ore, but the annual production of manganiferous iron ore is increasing rapidly and productions from individual mines are becoming more regular and more dependable as to grades and tonnages. This ore bids fair to become, shortly, the principal product of the district and is responsible for its present economic prominence. The iron ores of the district have been described, by the author and others, in many publications and will not be discussed here. Lately the manganiferous iron ores have been given some attention, but the range and variations of chemical composition of the ores, the principal physical characteristics of the ores and their deposits, the relative importance of the different ores and their possibilities in future developments, and the life of the respective reserves have not been discussed. It is impossible to give all of this information with the positiveness necessary for it to constitute a reliable guide for investment or even for future mine development. Each property and each party presents a special case and deserves critical consideration. We are dealing with special ores and always with a set of new conditions. Sufficient information of a general nature can be given, however, to indicate the reason for and the trend of the presently augmented developments in the district. In a great thickness of a big variety of sedimentary rocks, probably of Upper Huronion age, prevailingly of green, schistose phases of slaty and volcanic material intricately intermixed, lies a thin bed containing lenses of iron-bear ing formation. These lenses occur singly or in groups, thus causing the variation in the thickness of the formation; or they are separated at their ends and give rise to discontinuity or they overlap and display continuity with lateral offsets. Intense folding has added to the complications.

Jan 1, 1925

By Alan Morris

The investigation of the hot-working properties of metals and alloys furnishes a problem which has been attacked in many ways. Tensile, impact and hardness tests on heated specimens have furnished interesting data, but in most cases either the tests are difficult to make or the results hard to translate into terms of practical value. Some investigators have used the drop hammer to advantage. It furnishes a rapid and simple method of comparing the plasticity of metals at elevated temperatures. The indications obtained by its use are of value only in so far as their significance is understood and they can be intelligently used to predict the behavior of a given metal under given hot-working conditions. The work reported here was undertaken not only to add something to the existing volume of such data but also to contribute to our understanding of the results. Doerinckel and Trockels1 used cylindrical specimens and determined the work required to reduce the specimen to one-half the original height. Ellis2 studied the effect of constitution on the malleability of steel at high temperature. His method and that of Kent3 were similar to the one used in the present work. The tests described by Kent were made on samples of tin, zinc, aluminum, copper, lead, 70:30 and 60:40 brasses, with and without a small quantity of lead. He concluded that the test would "indicate whether a material can be forged at a given temperature without cracking." This interpretation must be used with caution. While it is probably true within limits, one must consider the severity of the forging operation. Again, it will not apply strictly to forms of hot working other than forging. For instance, an alloy running 61.0 per cent. copper, 3.25 per cent. lead, remainder zinc, will crack badly in the test, yet, it is extruded commercially. When the possibility of hot-working a new alloy is being considered a study of its drop-hammer test should help

Jan 1, 1931

By William Sharp

Discovery of new ore in the Eureka district, Nevada, as a result of bold and persistent exploration based on a geologic interpretation of structure has recently aroused wide comment in mining circles. It may therefore be of interest to the profession to have a summary of the historical background and an account of the recent program of development. The mines of Eureka, discovered in the late 1860's, were the first important silver-lead mines in the United States. They have a production record of more than fifty-one million dollars.' After the ore bodies were apparently bottomed in the 1880's, repeated attempts to find new ore were unsuccessful until 1940, when a diamond-drill hole cut a 40-ft width of sulphide ore 1409 ft below the 841-ft level of the Locan shaft. The next hole cut 30 ft, of ore and three additional holes drilled in 1943 and 1944 showed the ore body to be continuous, Shaft sinking to reach and open up the ore body has been in progress since 1945. Geology Stratigraphy The ore in the Eureka district occurs in a series of Cambrian sediments which is exposed through a thickness of over 6000 ft. The stratigraphic column is as follows:2 Thickness. Ft Ordovician : Pogonip limestone (upper part). Thin bedded limestone with some chert. Upper Cambrian: Pogonip limestone (lower part). Thin-bedded limestone (with shaly limestone and chert).... 425 + Dunderberg shale. Shale (clay and calcareous shale) and thin-bedded limestone............. 34°+ Hamburg dolomite. Dolomite and limestone.................... 900+ Middle Cambrian: Secret Canyon shale. Shale and thin-bedded limestone........ 1,035 Geddes limestone. Carbonaceous, flaggy limestone with some shale partings................ 335 Middle (?) and LoweR Cambrian: Eldorado dolomite. Dolomite and limestone.................... 2,000 Lower Cambrian: Prospect Mountain quartzite. Quartzite with occasional intercalated conglomerate and shale 1,660+ The Prospect Mountain quartzite has been subdivided into two formations: Upper part, Pioche shale. Shale, quartzite with some intercalated limestone (Lower Cambrian fossils)-200 ft. Lower part, Prospect Mountain quartzite proper- 1,460Sft. Total thickness................ 6,695 + Much the most productive of these formations has been the Eldorado dolomite, which yielded more than $42,000,000 at Ruby Hill and an additional amount

Jan 1, 1949

By Harold Markus, Arthur H. Grobe, Gerhard Derge

The high corrosion resistance possessed by tin under most circumstances, combined with its generally satisfactory appearance and useful physical properties, has led to many and varied uses for the metal. These uses have been partly limited by the fact that tin is an expensive metal, therefore many applications have been developed in which tin has been employed in combination with lead, either by coating, as in tin-lined collapsible tubes, or by the formation of alloys containing various proportions of tin-rich and lead-rich phases, as tcrne plate. A detailed knowledge of the corrosion characteristics of the tin-lead couple therefore is of general interest and has become specially important at the present time, when every effort is being made to conserve tin as much as possible. The present study has been limited to carbonate solutions with a pH range from 8.4 to 11.2 so that the results may be related to earlier work on the corrosion of tin and its alloys. 1-3,6 In these papers, the effects of a number of anion and cation additions to these solutions have been observed. Apparatus and Method The electrodes for the corrosion cell were cut from rolled sheet about 1/16 in. thick. The length of all specimens was held constant at 7 in., while the width was varied from M to 2 in. These electrodes were fastened to brass electrode supports, which were attached to rubber stoppers fitting into tall-type one-liter Pyrex beakers that contained the electrolyte. The lead electrodes were prepared from Omaha pig* and the tin was rolled from a slab of Chempur.† After cutting to size, the sheets were polished with No. I emery paper and cleaned with carbon tetrachloride. The edges, back and upper parts of the specimen were coated with a synthetic lacquer, which was supplemented with beeswax for the lead electrodes. The binding posts were coated with beeswax after the electrodes had been clamped. The pH of the electrolyte was controlled by adjusting the ratio of carbonate to bicarbonate. Approximately 600 ml. of electrolyte was used in each beaker. The entire assembly was placed in an oil bath thermostatically adjusted to operate at 30°C. + 0.1". Potentials were measured against a saturated calomel electrode connected to the cell by an agar-agar salt bridge. The carbonate solution used in the salt bridge was the same as that used in the corrosion cell. Currents were measured with a milliam-

Jan 1, 1942

By J. E. Tobey, David R. Mitchell, J. H. Kerrick

DETAILED knowledge of purchase specifications established by coal consumers is essential to the successful design and operation of a coal preparation plant. ANTHRACITE Specifications should be considered by both the consumer and the producer as guide posts outlining a certain path for both to follow. Plants differ, therefore specifications must differ to meet the varied requirements. Specifications are not of themselves a "cureall" or an assurance of complete satisfaction in fuel utilization. Specifications should not be regarded as a license to engage in an orgy of buying any and all coals that may happen to fall within their limits. This would lead to the indiscriminate mixing of coals which may vary in their burning characteristics. Different coals of equal grade tend to be individualistic in their burning characteristics. Rather, specifications should be used to help simplify coal selection, to reduce the actual number of coals used over a given period; in other words, to have a stabilizing influence on coal or customer turnover. In the final analysis, the use of too many coals per year in a plant is costly to both the consumer and the producer. Too many sources usually result in higher operating and maintenance costs for the consumer and higher sales costs for the producer. Finally, the statement included in the report accompanying the comprehensive Coal Selection Charts prepared by the Coal Committee of the National Association of Purchasing Agents, and released in 1938, is significant. This Committee worked diligently for a period of 15 years seeking to find a scientific and reliable method for selecting coals. The two following paragraphs are quoted from its report: More important is the fact that no ready-made classification or set of specifications can possibly replace the judgment and resourcefulness of an experienced combustion engineer or fuel technologist, nor the usual need for full scale plant tests under the exact conditions of use before a final decision is made.

Jan 1, 1950

By Hoyt Stoddard Gale

Recent work on borate deposits near Kramer in the extreme southeast corner of Kern County, California, is of special interest because of the information it seems to give concerning the mode of origin of the borate minerals colemanite and ulexite, especially when considered in conjunction with the valuable clue to the mode of origin of colemanite in its present known deposits given in a paper by W. F. Foshag,1 of the United States National Museum. Colemanite is found in or near original deposits of ulexite, from which it is supposed to have been derived by a change in the character of the ground water or rate of its movement or both. Indications that an alteration of this sort had produced colemanite were first recognized by the writer2 in specimens collected in the Kramer district in 1920, and sent to W. T. Schaller, at U. S. Geological Survey, for identification. The identity of the two borate minerals in these specimens was suspected when collected but not at once determined, but the relations of the minerals as seen in the specimens seemed to afford a manifest clue to the origin of the deposits. Similar specimens were obtained by the writer from deposits in Death Valley soon after he had examined the deposits near Kramer. After studying the specimens submitted to him Dr. Schaller wrote as follows: " I have finally positively identified the boron minerals you sent me with your letter of Sept. 27. The 'white fibrous mineral like ulexite, is ulexite; the 'harder nodules' in the clay are colemanite, apparently formed from the ulexite as a result of leaching, with recrystallization in place—a theory that Foshag is working on." The present paper is a report on the facts observed at the depo its near Kramer, and some general observations on the geological relations noted, which, unfortunately, still form only a very incomplete record. The intimate association of deposits of colemanite and ulexite in California and Nevada with certain volcanic rocks affords a strong pre-

Jan 1, 1926

By W. G. Matteson

In 1915, the State of California passed a law of great scope and importance. This law has been in successful operation for a year and may be briefly described as an act " establishing and creating a department of the State Mining Bureau for the protection of the natural resources of petroleum and gas from waste and destrucbion through improper operations in production; providing for the inspection of petroleum and gas wells; requiring all persons operating petroleum and gas wells to make certain reports" and providing the necessary officers and assessments to carry out the provisions of the act. The statute provides for a separate department of the State Mining Bureau, under the general supervision of the State mineralogist, with a staff composed of a "state oil and gas supervisor" and four deputies. It rules that all petroleum and natural gas wells shall be drilled, operated or abandoned under the supervision of the State supervisor, who shall order such tests or remedial work as seems to him necessary to protect the interests of property owners and the general public. It also provides for a board of arbitration to consider orders given by the supervisor which are not acceptable to the well owner. Section 18 of the act, which is the provision that is directly related to this paper, requires ('the owner of any well referred to in this act to keep a careful and accurate log of the drilling of such well," and further requires that this log shall show the character and depth of the formations passed through or encountered in the drilling, particularly the location and depth of the water-bearing strata; the character of the water encountered (so far as ascertained); whether the water was shut off, and, if solat what point; that it shall show completely the amounts, kinds and size of casing used; the depth at which oil-bearing strata are encountered; the depth and character of the strata, and whether all water was successfully and permanently shut off so as to prevent percolation or penetration into the oil-bearing strata. This log is to be kept in the local office of the owner or operator, subject to the inspection of the supervisor or any of his deputies at any

Jan 1, 1917

By John Birkinbine

IN the spring of 1878 the Pine Grove Furnace, located in Cumberland County, Pa., was blown in after lying idle for several years. The furnace was constructed in 1770, and for over a century it has been in almost continual operation. The plant consisted in 1877, when the writer was first called there, of a stone stack 32 feet in height, inclosing a shaft and boshes, the latter being 8 feet in diameter. The blast was supplied by two wooden blowing-tubs discharging into a third, having a floating piston sustaining a box weighted to give the desired pressure, the power being furnished by a waterwheel. A small 18-pipe hot-blast stove heated the blast. The furnace was remodelled during the winter of '77-78, and a Weimer blowing-engine with a blowing-tub 5 feet in diameter and 2 feet stroke, and the necessary boilers, were substituted for the wooden tubs and water-wheel. The stack was raised and enlarged, and provided with a bell and hopper having a central drop. Water dam and tymp were added, and general repairs were made. The hot oven, however, was riot increased. The furnace had always been operated with charcoal as fuel, and its reconstruction was made with a view to continue the use of charcoal, but provision was made for ample blowing capacity should other fuels at any time be employed. Although liberal arrangements had been made in cutting wood, the stock of charcoal supplied in 1878 was insufficient for the increased requirements of the remodelled plant, and notwithstanding the purchase of some 80,000 bushels from an adjacent idle furnace, there was riot enough to keep the furnace in constant blast until a new supply could be obtained, particularly as the season was unusually backward. Instead of following the established precedent of many charcoal furnace managers, i. e., blow out every February, it was determined to continue in blast, using coke as fuel. Accordingly, when the charcoal stock was exhausted, on March 22d, 1879, Connellsville coke was substituted, the change of fuel being made at once; that is, the coke charges followed immediately upon the last charcoal charges. After working a few days,-the strike in the Connellsville coke region cut off the supply, and anthracite coal was obtained, a mixture of the two fuels being employed. The strike continuing,

Jan 1, 1880

By Clare B. Carlson, C. P. Proctor

THE history of the froth flotation of coal is relatively short. The flotation process was applied to fine-coal cleaning about the time of the end of World War I. Coal flotation finds more widespread use in Europe than in the United States and is used on a commercial scale in nearly all major coal-producing countries in the world. In Fig. 1 the general arrangement of a froth-flotation plant at a British colliery is shown. GENERAL FEATIJIEES OF THE PROCESS Application The flotation process is applicable to the cleaning of the fine sizes, particularly minus 48-mesh coal, although it may be used on sizes as coarse as 1/8 in. Since most cleaning processes usually are not effective on sizes smaller than 48-mesh and certainly not effective on minus 100- mesh, the froth-flotation process offers a solution to the problem of cleaning these sizes. This process consists-of agitating the feed pulp with a small amount of reagents, usually 1.0 to 2 ½ lb. per ton of feed in the presence of water and air; the reagents help to form small bubbles that collect on the particles having a greater affinity for the bubble surface than for the water surface, in this case the fine coal, and the bubbles buoy these particles to the surface to form the frothor concentrate. Slate and shale particles remain wetted and suspended in the water to be drawn off as tailing. The frothers commonly used in coal flotation are cresylic acid, pine oil, and alcohols. More expensive frothers, used in ore flotation, work satisfactorily but do not compare with these cheaper reagents for over-all cost. Collectors- used are low-grade petroleum fractions, such as cheap, partly refined fuel oil, or lubricating oil, sometimes mixed with small amounts of kerosene. Other collectors used are the fatty acids and their

Jan 1, 1943

By Thomas C. Atchison

An understanding of the physical processes involved in breaking rock with explosives will lead to better blasting techniques. In this chapter known rock breakage principles will be outlined, some conjectural ideas will be discussed, and areas needing further study will be pointed out. The principles outlined will serve as a basis for the design of blasting rounds described in the following chapter. 7.2-1. Factors Important to Rock Fragmentation. The efficacy of explosives as tools for rock fragmentation lies in their ability to deliver almost instantaneously large amounts of energy to a limited portion of the rock. When an explosive charge is detonated in a drill hole, its energy is released in a very small fraction of a second in the form of gas at extremely high pressure and temperature. The mechanics of the transfer of this energy to the rock and the resulting breakage are complex and not completely understood. Factors that have been identified as important to the fragmentation process may be grouped in three categories: explosive parameters, charge loading parameters, and rock parameters. EXPLOSIVE PARAMETERS. Explosive parameters known to influence breakage are density, detonation velocity, detonation impedance, detonation pressure, gas volume, and available energy. Detonation pressure is probably the best indicator of an explosive's ability to break solid hard rock. Detonation pressure is roughly proportional to the product of density and the square of the detonation velocity. The relative ability of different explosives to transmit their pressure to stress in a given rock is function of their detonation impedances. Detonation impedance is the product of density and detonation velocity. The volume of gas released in the explosive detonation undoubtedly is of importance, at least in the later stages of breakage, and is probably

Jan 1, 1968

By P. F. Gnirk

Consideration is given to creater formation with shallow, contained, chemical explosions in rock masses which exhibit different inherent physical and mechanical properties as determined by standard laboratory techniques. The primary purpose is to determine whether or not a simple but useful generalized correlation can be established between explosive crater formation and one or more common rock properties. Such a correlation could be beneficial in predicting with some degree of reliability the size of a crater which could be expected in a particular rock type for a given input of explosive energy. A series of crater formation experiments employing constant weight charges of Gelex 2 explosive was conducted in five submembers of the taconite formation at the eastern end of the Mesabi Range in northeastern Minnesota. Five mechanical and physical properties-unconfined tensile and compressive strengths, Young's modulus of elasticity, longitudinal wave velocity, and density-were determined by conventional laboratory techniques using core samples from the taconite submembers. Although insufficient data were obtained to warrant the use of mathematical methods in the determination of empirical relationships, the results provided a fairly strong indication that with an increase in magnitude of any one of the five rock properties definite decreases in the optimum crater volume and surface area occur. Furthermore, for a constant explosive energy input, the presence of bedding planes and joint systems in a rock mass influences the formation of craters in such a manner as to increase the volume of rock broken substantially above that expected from the same rock mass without joint systems and, in particular, without bedding planes.

Jan 1, 1968

By J. B. Austin, R. L. Rickett

Measurements of the rate of decomposition of austenite at constant temperature are commonly represented by plotting the percentage transformed on linear coordinates against time on either a linear or a logarithmic scale, a method that yields a curve that in shape resembles an integral sign (Fig. 1). A graph of this kind is not always convenient because extrapolation to the beginning or end of the transformation, or even intebrpolation, may be uncertain unless there are a large number of observations, which seldom happens; furthermore, the degree of consistency of a set of measurements is difficult to judge from such a curve. It is desirable therefore to find some mode of plotting, or even better to find a standard variety of graph paper, that gives a straight line instead of the integral shape. The straight line has many advantages; the number of readings required to fix the position of the curve is greatly reduced, interpolatiorr is easy and rapid, extrapolation can be carried out with greater confidence and, finally, the consistency of the measurements is readily estimated from the scatter of the points. The last advantage is particularly valuable when the data are obtained by direct microscopic examination alone, because they are influenced by the skill of the observer in estimating the relative size of areas, possibly also by undetected inhomogeneity of the specimen. A search for ways of representing the observations as a straight line yielded two methods which are described in this paper. The paper also includes an account of some interesting relations brought to light in applying these methods to the available experimental data. Usually the best way to derive such a method of plotting is to base it on established principles of chemistry and physics, as has been done, for example, for the temperature variation of the equilibrium constant of a chemical reaction. But so little is known of the mechanism of the decomposition of austenite, and so little is available in the way of well established background for changes of this kind, that it is simpler to rely upon purely empirical means. The general plan therefore is to study existing data with a view to finding some function of the direct observations that will

Jan 1, 1939

By Blake M. Caldwell, Thomas C. Poulter

A new approach to an old problem has made it possible to do in a a tively short period what has not been accomplished in the past three quarters of a century using strictly experimental methods. A theoretical study was made of the underlying principles whereby a jet is formed by a shaped charge and of the mechanism of the penetration of the target by that jet. It was found that there are more than 10, and perhaps as many as 15 variables affectin!? the performance of the shaped charge. Only a few calculations are necessary to show that it is physically impossible to investigate all of these variables experimentally. The shaped charge theory has been extended to include a previously little-understood mechanism in high explosive phenomena; namely, low order detonation. By superimposing a high order detonation on a zone already undergoing low order detonation, all appreciable improvement in performance is accomplished. The development of a design wherehy these phenomena are coordinated in such a way as to develop a jet which is tailored to meet the specific target requirement will be described in detail. The shortcomings or even impossibility of strictly experimental techniques will be illustrated by a discussion of the development of a special-purpose explosive charge. INTRODUCTION In an article appearing in the May, 1888 issue of Scribner's Magazine, Charles E. Monroe described his early experiments with gun cotton (Fig. 1) which led to his name being most fre-quently connected with our present-day shaped charge. Although the sunken letters or "cavities" in Mon- roe's gun cotton were not lined, they produced some penetration of an iron plate. The credit for the lined shaped charge, however, should rightfully go to Dr. R. W. Wood of the Physics Dept. of Johns Hopkins University, who was responsible for first discovering the fact that a metal liner in a cavity of explosive gave high velocity fragments and/or jets of metal. This discovery was made by Dr. Wood inadvertently while investigating an accidental death resulting from an electric blasting cap. He discovered that a jet of high velocity copper particles was ejected from the dimple

Jan 1, 1958

By H. S. McQueen

THE central Ozark region of Missouri has inter-ested geologists and mining engineers for many years. Of particular interest are the mineralized sink-hole type deposits, some of which have produced large quantities of iron ore. Deposits of coal are also known in this part of the State, and in mode of occur-rence are similar to the iron ore deposits. Occurring in the same general area, and often associated with coal, are deposits of high-grade non-plastic flint fire clay, and high alumina or diaspore clay. At present these clays are the most important materials being mined from the sink-hole type deposits. Deposits of high-grade flint fire clay have been known to occur in this region for many years, the Kelley pit near Rolla, Phelps County, being discovered in drilling for iron ore shortly after the close of the Civil War. Mining operations had disclosed at an early date masses of rough, open-textured "sandy" clay associated with the flint fire clay. Some of the hard flint clay also con-tained rounded shot-like particles of "sand." Both types of clay were considered of inferior grade and unsuited to the manufacture of fire brick. These clays were discarded in mining as value-less, in some instances being used for road metal. Some knowledge of the high alumina content of this sandy material had been obtained by 1908 1, and by 1917 the high alumina content was gen- erally known, and commercial shipments of what is now called diaspore clay were being made. These deposits of diaspore clay associated with flint fire clay form the only known deposits of commercial importance in North America. The production of diaspore and flint fire clay at present exceeds that of any former year. Statistics covering the production and value of the former were not collected prior to 1922, and the figures given below do not cover the tonnage of clay mined by companies and used in their own plants, so that the total produc-tion probably is much larger than that indicated. The figures were collected by the U. S. Geological Survey and the U. S. Bureau of Mines in cooperation with the Missouri Bureau of Geology and Mines.

Jan 6, 1928

By H. R. Fife

AN extended study of dustproofing Freeport-seam coal has empha-sized several fundamental features in the successful treating of bituminous coals. The extent of the exposed surface area and its absorption proper-ties for the dust-retaining film were found to be the most critical factors affecting the efficiency of fly-dust prevention. From recently published screen data and specific surface-area measure-ments on United Kingdom coals, an approximation of the surface exposed by mine-run coal and by 1-in. slack was made. The total surface area exposed by an average ton of this mine-run coal was estimated at 3768 sq. yd., while a ton of 1-in. slack represents a total surface area of 8779 sq. yd. with no additions for porosity. It is important in coal treating to consider that in mine-run coal the fraction above 1/4 in. in size represents 79.5 per cent of the total weight, but only 4 per cent of the total surface, while the fraction below 150 mesh contains 47 per cent of the total surface and only 1.2 per cent of the total weight. Also, one should appreciate that, in a 1-in. slack, the domestic stoker fraction (1 in. to 8 mesh) contains 76.3 per cent of the weight and 8.2 per cent of the surface, while the fraction below 150 mesh represents 3.3 per cent by weight and 54.8 per cent by sur-face area. Wax extraction data on 1-in. to 0 slack from mine-run treated Free-port-seam coal showed that the coating was distributed uniformly as a function of exposed surface; hence, nonuniformly on a weight basis. This distribution of the coating on mine-run coal therefore limits the extent of treating that is desirable on bituminous coal at this point in the preparation. The treatment of Freeport mine-run coal before it reached the tipple gave a 70 to 80 per cent reduction of fly-dust in the tipple, a satisfactory treated commercial slack coal, and an indicated change in the trend of tipple degradation. The premium-treated domestic sizes required a supplemental treatment for complete dustproofness.

Jan 1, 1937

By C. B. Foraker

THE Magma mine, of the Magma Copper Co., at Superior, Pinal County, Arizona, is 68 miles east of Phoenix and 21 miles west of Miami, Arizona, on highway U. S. 180. TEMPERATURES AND UNDERGROUND WATERS Surface Temperatures.-The average surface dry-bulb temperature at Superior is 72.4º; wet-bulb, 57.4º; with an indicated relative humidity of 38 per cent. The average yearly rainfall from 1921 to 1936, inclusive, was 18.74 in. The maximum condition of the atmosphere is in June, July and August, and the minimum is in January and February. The surface temperatures, of course, influence the temperatures of the down- cast shafts; however, the variation between winter and summer causes a difference of only 2º to 3º in the stopes and working places that are not close to the intake shafts. Average atmospheric conditions are shown in Fig. 1. Rock Temperatures.-Rock temperatures on the deeper levels of the mine are as follows: [ ] There appears to be no difference in rock temperature for any particular horizon of the various formations or in the vein. Water encountered is always the same temperature as the rock from which it flows, and for this reason it is thought that the water is heated by the rock; not the rock by the water. The country rock apparently has been heated by the various intrusions, perhaps the vein itself, and has not yet had time to cool off. The geothermal gradient (Fig. 2) as indicated by the rock temperatures given above is 1 ½ º per 100 feet. Underground Waters.-The underground water varies from 350 to 565 gal. per min., depending on the rainfall. The limestone and other

Jan 1, 1938