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By L. Leibowitz, M. G. Chasanov, L. W. Mishler

A drop calorimeter system is described for use in measuring enthalpies to 3600°K. Data are presented for tungsten between 2800" and 3600°K. The enthalpy of tungsten in cal per mole between 2000° and 3600°K can be represented by the equation HºT- Hº298 = - 1.7622 X 103 + 5.7772T + 8.9861 where T is in degrees Kelvin. A tabulation of com -puted values is presented for heat capacity, entropy, and free energy function. A drop calorimeter has been constructed to carry out enthalpy measurements at temperatures to 3600°K. Samples are heated by induction1 and dropped into a commercial adiabatic calorimeter, modified for this purpose. The experimental temperature is limited by the melting point of container materials and compatibility of the container and its contents. Several high-temperature drop calorimeters have been described in the literature1-5 but none has been used at temperatures as high as those in the present work; our measurements of the enthalpy of tungsten range from 2800" to 3600°K. DESCRIPTION OF EQUIPMENT An overall schematic view of the equipment is shown in Fig. 1. Power for the induction coil is supplied by a 25-kw 250 kHz Ther-Monic generator coupled to an iron core RF transformer. The Sample capsule is suspended in the work coil by 10-mil diam tungsten wires which are wrapped around a horizontal 5-mil diam tungsten wire. The horizontal suspension wire is clamped between two massive copper electrodes which are fixed in an x-y motion device that allows adjustment of the position of the heated capsule from outside the vacuum chamber. The copper electrodes are connected by flexible copper straps to a 1250-joule (5 kv, 100 pfarad) condenser bank. When it is desired to release the capsule, the condensers are discharged through the horizontal suspension wire causing it to vaporize rapidly. Very reliable and precise release of the capsule is achieved in this manner. Experiments have shown that no heat correction is required for this discharge energy. As part of the temperature measuring system, two prism holders have been incorporated in the apparatus. The upper prism holder is in the main vacuum chamber itself, whereas the lower one is in a side arm attached to the drop tube below the gate valve. The upper prism is mounted on a rotary vacuum feed-through, and may be moved under a protective shield when not in use. This prevents deposition of vapors on the prism surfaces when temperature measurements are not being made. Similarly, the lower prism is mounted on a push-pull vacuum feed-through, and when not in use may be pulled into its side tube. The prism mountings are fitted with guides and stops so that they may be moved precisely into the desired position. The aim throughout is to minimize the time the prisms are exposed to vapors from the hot samples. At the high temperatures reported in this paper, only the lower prism was used. The upper prism holder in these cases was fitted with an additional radiation shield. By using a prism and viewport, the lower surface of the samples can be observed by an optical pyrometer. The measurements discussed in this paper were obtained with a Leeds and Northrup 8622-C-S series manual pyrometer which is estimated to be accurate to 0.5 pct. Pyrometer calibrations and prism and window corrections were carried out in the conventional manner6 using tungsten strip lamps calibrated by the National Physical Laboratory, Teddington, England. Prism corrections were rechecked after each use. All work to date has been done in vacuum, and no measurable change has been observed in the prism correction below -2300°K for the upper prism and below -2800°K for the lower one. The total time of exposure of the prisms is about 50 sec per run. At high temperature, the final temperature reading is corrected by using the final A value for the prism; see Ref. 6 for details of this procedure. The calorimeter is a modified Parr Instrument Co. (Moline, lll.), Series 1230 adiabatic calorimeter with automatic jacket control. Other authors5 have used a similar calorimeter with good results. The calorimeter jacket cover and calorimeter cover are attached to the drop tube which contains a radiation shield. This shield is a gold-plated copper disc which can be operated manually from outside the calorimeter. The receiver is attached below the radiation shield and is lined with tungsten. In a typical experiment, the calorimeter and its jacket water temperatures were adjusted to 0.000°K temperature difference. The sample was allowed to equilibrate in the furnace at the desired temperature for about 20 min. The initial calorimeter temperature was then recorded, the sample dropped, and appropriate shutters closed. After about 3 min, the drop tube and receiver were filled with helium to 60 torr. The final calorimeter temperature was recorded after it had remained constant over a 5-min period. The equilibration time in the calorimeter was about 25 min. Thermistor probes are used to operate a hot and cold water supply system to maintain the jacket temperature equal to the calorimeter temperature. For actual measurements of the calorimeter temperatures, a quartz thermometer was used (Hewlett Packard Dymec Thermometer, Model #2801A). This thermome-

Jan 1, 1970

By Thomas Varley

IN THE congressional act establishing the Bureau of Mines one of the functions outlined was "to assist I the industry in the prevention of mineral waste." This had not only to do with the waste in mining but in milling and metallurgical practices, including smelting. The organization of the Bureau of 'Mines includes many divisions, each working in a particular field and charged with certain investigative work. The metallurgical division has the above duties under its immediate supervision, and the station located at Salt Lake City is directed by the chief of this division: There are ten experiment stations of the Bureau of Mines, located in various parts of the country, most of them being housed at state universities under cooperative agreements. Considerable care was exercised in locating the stations and in choosing the particular type of work to be investigated at each place. Inasmuch as the Bureau was designed to serve and cooperate with the industry it is only natural that the investigative work be of interest and importance to the territory immediately adjacent to the respective stations.

Jan 1, 1925

By Robert H. Merrill, David W. Wisecarver, Raymond M. Stateham

The US. Bureau of Mines, in cooperation with US. Borax and Chemical Corp. and Kennecott Copper Corp., has investigated the use of the microseismic method to evaluate the stability of large, open-pit slope walls. The method is based on the phenomenon that stressed rock normally emits subaudible rock noises, and the number of rock noises per unit time (noise rate) and the magnitude of the rock noises (amplitude) increase as the stresses in the rock approach the failure stress of the rock. Therefore, the detection and recording of those rock noises serve as a semiquantitative method of predicting the incipient failure of rock. This report briefly describes the three different types of micro-seismic apparatus, the procedures, and the results of microseismic investigations in the slope walls of the Boron mine near Boron, CaL, and the Kimbley, Liberty, and Tripp-Veteran open-pit mines near Ely, Nev. Microseismic monitoring within a frequency band of SO to 5000 Hz indicates noise rates in stable, inactive mining areas are between 0 and 10 noises per hour; the rates in stable, active mining areas are between 10 and 50 noises per hour; and the rate in unstable areas is as high as 2500 noises per hour. High microseismic noise rates in the Liberty pit correlate with the time of nearby earthquakes, indicating that the earthquakes affected the slope wall. The results provide evidence that the microseismic technique is applicable to large pit walls, and that the wide-band, wide-range microseismic equipment appears to be suitable for open-pit investigations. The microseismic method is based on the phenomenon that stressed rock normally emits subaudible rock noises, and the number of rock noises per unit time (noise rate) and the magnitude of the rock noises (amplitude) increase as the stresses in the rock approach the failure stress of the rock. Therefore, the detection and recording of those rock noises serve as a semiquantitative method of predicting the incipient failure of rock. The method has been used for many years to detect incipient failure in roofs or pillars in underground mines. In 1963 the U.S. Bureau of Mines (USBM) started an investigation of the microseismic method in large, open-pit slope walls. The purpose of this investigation was to evaluate the method in open-pit slopes where the rock may be fractured and broken and where the size of the rock mass under investigation is much larger than normally encountered underground. In addition, both the stresses in the rock and the strength of rock near pits are lower than usually found underground. Consequently, there was some doubt concerning the feasibility of the method for open pits, and the economics of such an investigation may have been prohibitive especially if large walls had to be monitored with closely spaced geophones. The successful application of the microseismic method to underground operations has improved safety at little, or no sacrifice, to production or extraction ratios. The anticipated reward in open-pit mining would be the improvement of safety with a minimum sacrifice to mining operations. There is also a possibility that the method could be used to optimize the unloading (stripping) of potential failure areas by the removal of intact rock from the slope wall rather than the cleanup of a slide from the bottom of the pit. This report contains a brief description of three types of microseismic apparatus used in four different pit walls, each of which is different in height, slope, rock types, or has different planes of weaknesses, such as faults, fractures, or joints. Because the geologic features of the pit walls are varied and complex, for brevity, this report dwells mostly on the microseismic apparatus, techniques, the rock noise rates, and the slope movements measured at the various sites. PROGRESS AND DEVELOPMENT The microseismic method was developed over 20 years ago; and the method and examples of investigations in underground mines are summarized by Obert and Duvall. 1 In more recent years, the method has been applied in several underground mines, and an in-situ test under controlled stress conditions is described by Morgan and Merrill. 2 Experience has shown that, on occasions, the microseismic noise rate and amplitude reach a peak value and then start to decrease before a failure occurs in an underground mine; on other occasions, the noise rate steadily increases to a maximum at failure. The method has been applied to slopes by Goodman and Blake,3 and by Paulsen. 4 Goodman and Blake found that the noises corresponded with failures in the slope

Jan 1, 1970

By Lyon F. Terry

ACCEPTED current practice for A the valuation of mineral property is based upon Hoskold's theory and valuation tables first published in 1877, and popularized by Herbert Hoover's "Principles of Mining" issued in 1909. In more recent years the procedure has been developed further in the course of the extensive valuation work required for Federal taxation purposes. The 1-aluation of oil and gas properties and of mines is based upon the same principle-the estimation of the present worth of future net revenues. However, in valuing oil and gas properties the method used for discounting future revenues differs somewhat from that adopted for mines, owing principally to the nature of the re- source. production from oil and gas properties usually declines from year to year, whereas coal and ore de- posits are adapted to a more uniform rate of output.

Jan 1, 1940

By Tilden Cummings

The extractive mineral industries share a number of common characteristics and basic problems which are completely different from those associated with manufacturing and mercantile operations. These industries now supply about 95% of the inanimate energy consumed in this country, and share with agriculture in providing virtually all of our basic raw materials. Mineral producers, like farmers, are subject to the economic hazards of fluctuating markets and prices. Unlike farmers, however, they cannot renew the productivity of the earth, but must seek continually for new sources of supply. The necessity for exploration and development of new reserves, to replace those used up by production, introduces additional factors of economic risk. These operations require the expenditure of large amounts of capital, often well in advance of any assurance of profitability. Commercial banks that understand these special problems can provide a variety of constructive financial services to the mineral industries. The history of cooperation between banks and mining enterprises has yet to be written, but there is every indication that it would encompass a period of hundreds of years. Records refer to depository and lending services by the early European private bankers involving precious metals and jewels. Many of the exploratory voyages to the Far East and the New World were organized with the financial backing of wealthy syndicates, some of which also provided banking services, in the hope of finding new sources of gold and other precious minerals. In the United States many large banks are closely identified with the development of some of the larger mineral deposits such as the Mesabi Range and the gold fields of California.

Jan 5, 1965

Jan 1, 1881

By Lloyd Emory

THE region known as. Guyana or Guiana stretches along the north coast of South America from the mouth of the Orinoco River in Venezuela to the mouth of the Amazon River in Brazil. Politically, it is divided into British, Dutch, and French Guiana, extend¬ ing into Venezuela on the north and into Brazil on the south. Because the area is within the sweep of the northeast trade winds and of approximately the same latitude, plant' and animal life are fairly uniform throughout. The geology is very similar as far as the northern coast is concerned. The drainage is taken care of by a number of large rivers that flow northward directly into the sea. The Courantyne River, which roughly divides the area into half, is the eastern boundary of British Guiana.1 The lower reaches of this river are also the center axis of an ancient bay that at one time indented the coast-line at this point. The old shore-line and, in fact, successive shore-lines can be traced from near the present coast-line in, the northwest district of British-Guiana, south-east and inland, crossing the Essequibo River near Dahli, the Demerara near Christianburg, the Berbice at the mouth of the Kuruduni River and the Courantyne at Vaka-Kuyaha Falls. The line then swings around to the northeast and again approaches the coast near St. Lau-rent in French Guiana. This article will be confined to British Guiana and largely to the valley of the Demerara River, but for geographic names .and topographic details it might, however, apply to Dutch Guiana as well. British Guiana, which comprises about 90,000 sq. mi. and is as large as England, Scotland, and Wales combined, may be divided into three belts, the alluvial belt or coastal plain, the foot-hill area (often spoken of as the sand clay belt), and the hinterland.

Jan 1, 1928

By R. M. Brick, Arthur Phillips, A. J. Smith

A PREVIOUS publication1§ has described the effect of quenching stresses on the lattice parameter values of high-purity aluminum-copper alloys particularly with reference to the solution and precipitation of CuA12. A similar study has been made of the aluminum-rich aluminum-magnesium alloys. Attention has been directed in the present investigation. to the magnitude of the quenching stresses as affected by the specimen size and shape, the number of solute atoms and the quenching rate. The effect of cooling stresses in causing plastic deformation or cracking has been considered in relation to the physical properties of the alloy. On reheating alloys in the two-phase field, the time required for precipitation to occur has been observed in connection with the degree of supersaturation, the rate of diffusion of the solute atoms as a function of the comparative atomic radii, degree of strain, temperature of reheating and grain size. A few qualitative comparisons on the relative effect of these factors have been drawn between the aluminum-copper alloys and the aluminum-magnesium alloys. STRAIN IN SOLID-SOLUTION ALLOYS A 10 per cent magnesium alloy in the form of chill-cast bars was furnished by the Aluminum Company of America through the courtesy of L. W. Kempf. Additional alloys were prepared using aluminum (99.95 per cent Al) and high-grade magnesium. The alloys listed in Table 1 were melted in an Acheson graphite crucible under a flux of fused MgCl2, CaC12, NaCl. Chill-cast rods were sealed under vacuum

Jan 1, 1935

By AIME AIME

INDUSTRIAL Pittsburgh, the center of the coal and iron and steel industry of the world, was host to the Coal Division at its Fall Meeting held there on Oct. 21 and 22 at the William Penn Hotel. The past year has witnessed remarkable progress in new methods of mining and burning of coal and many of the papers on the program discussed these developments. Nearly 100 had registered at the time of the first session on Wednesday morning and this number increased to 168 on Thursday. Owing to the large number of papers on the program, eighteen in all, it was necessary to hold group meetings on Thursday morning, with a capacity attendance at each meeting. . Chairman McAuliffe was on hand early Wednesday morning to open the meeting. George Otis Smith, representing President Lovejoy, came over from Cleveland where he attended the meetings of the Institute of Metals Division. Secretary Parsons arrived later from Cleveland and spent the whole morning with the executive committee of the Division. Doctor Smith, Secretary Parsons, and J. T. Breunich were the official representatives from Institute headquarters.

Jan 1, 1936

By H. H. Taft

IT has long been known that the volcanic area south of Belmont, Nye county, Nevada, had mining possibilities. Some of the old-time prospectors knew that gold existed there. Its remoteness from any source of supplies, its long distances from water, the absence of game, and more, perhaps, the lack of grass for animals to subsist upon, has made this an unattractive region in which to search for mines. The decline of the Comstock mines, the exhaustion of sun-dry large and rich ore-bodies, the high cost of mining, marketing, and particularly the ruinously high freight-charges upon refractory ore that had to be shipped to distant smelters, have kept investors out of Nevada for the last few years; and mining people have hardly yet awakened to the importance of Tonopah, Goldfield and perhaps the newer and less developed districts. The discovery of Tonopah by J. L. Butler, who located the Mizpah Claim in May, 1900, and the fortunes soon realized there, attracted many people. As the boom declined, many went away, some scattering out into the surrounding country, and the population is now about 7,000. In the fall of 1902 a discovery of gold was made 23 miles south, in what is now known as the Sandstorm group, 4 miles NW. of Goldfield. In the winter of 1903-4 the Combination, January and Florence mines were discovered, and shipments of high-grade ore soon followed. In January, 1905, there were 10,000 people in Goldfield. In June, 1904, rich gold-ore was found 85 miles SE., at the foot of the south end of the Kawich mountains, but this discovery was kept quiet until a re-location could be made. On August 10, 1904, the Bullfrog claims, and a month later the Ladd mountain and neighboring claims, were located. The Shoshone group was located September 24. This district is

Nov 1, 1905

By WILLIAM E. NEWNAM

THE molding and loading of pig lead has, in the past, been accomplished mainly by the strong arm method and, as the pigs are usually loaded directly into the cars, it has been a hot and laborious task. Of late years it has been difficult to obtain men willing to perform such labor and the need has been felt for loading and molding machinery which would eliminate all manual handling of the hot pigs and which would be sufficiently compact to permit of installation in existing plants with little or no

Jan 1, 1924

By N. M. Langdon

Spokane Meeting, September, 1909.) THE following corrections to the paper of Mr. Langdon (Bulletin No. 34, October, 1909, pp. 919 to 940), received after the publication of the paper in the Bulletin, will be incorporated in the paper as finally published in the forthcoming Vol. XL. of the Transactions, but are here presented for the information of members:' Page. 921. Table I., furnace M2, item 11. For " 8801 " read "0.8801." 922. Table II., furnace C, item 2, under gas. For " 0.011 C " read " 0.011 0." Furnace G, item 13, under gas. For " 5.074 air " read " 3.074 air." Item 15, 114.269 " should be " 4.289." Furnace H, item 2, under iron. For " 0.04 " read ".0.01." 923. Table II., furnace J, item 1, under iron. For " 0.95 " read " 0.93." Furnace N2, item 6, under gas. For " 0.66 CO," read 0.066 C02." 924. Table III., furnace C, item 17. For " 379 " read " 397." 927. Table IV., furnace C, item 4. For " 0.0124 " read 0.0424." Furnace G, item 15.. For " 4,060 " read " 4,066." 928. Line 2. Items 19 and 20 of heat-supply, should be items 20 and 21. 930. Line 3. Expunge remainder of paragraph after the word " supplied," and substitute the following : "As compared with the fusion-zone, the loss by radiation n C was 25.5 per cent. of the total (2,278 units) supplied to that zone, while in D it was 22.5 per cent. of the total heat (1,824 units) supplied to that zone. Finally, as compared with the reduction-zone, C lost by radiation 36.8. per cent. of the 1,580 units supplied to that zone,

May 1, 1910

By R. W. Raymond

The absence of a convenient glossary- of terms connected with mining and metallurgy has long been felt by the general public. It is to meet this want, not to furnish a technical manual for experts, that the following glossary has been prepared. It originated in an attempt on my part to revise for publication the manuscript of a compilation prepared from the appendix of Yale's work on Mining Titles and one or two other sources, to serve as an appendix to a new work on mining law, about to be published by Mr. H. N. Copy, of Washington, D. C. This revision soon assumed, contrary to my original intention, the proportions of a reconstruction; and with the consent of Mr. Copp, and for the purpose of receiving from my fellow-members valuable aid, I presented my still incomplete work as a paper at the Lake Superior meeting of the Institute, inviting from any quarter suggestions of new terms or better definitions to be incorporated in the glossary before its final publication. This invitation was so widely and generously responded to, that I cannot undertake to make in this place individual acknowledgments to those members of the Institute, and professional colleagues outside of it, who have favored me with assistance and advice. The labor bestowed upon this paper since its presentation at the Lake Superior meeting has considerably exceeded that of its first preparation, as

Jan 1, 1881

By Yuri D. Tretyakov, Robert A. Rapp

The stoichiometry ranges ofNiOl+y and LiFe,O,-d were established by high-temperatwe electrochemical meas7rements in a stabilized-zirconia electrolyte cell. The results were consistent with doubly ionized cation vacancies in NiO,+y and interstitial lithium or iron ions in . The defect structure of the ternary ferrite was derived from the consideration of equilibration with respect to oxygen between the solid and the gas phase. The absolute magnitudes of defect concentrations were calculated. Pavtial molar enthalpies of oxygen in the compounds were calculated and interpreted in terms of the enthalpy of defect formation in these crystals. NICKEL oxide (NiO,,?) is a metal-deficient, p-type, extrinsic semiconductor whose properties are consistent with a structural model based on the presence of cation vacancies as the predominant ionic defect at sufficiently high temperatures and oxygen activities. A survey of previously reported conductivity studies and the presentation of some more recent conductivity measurements will be given in a later paper.' The absolute magnitude of the equilibrium vacancy concentration in NiO has been reported from combined conductivity and thermogravimetric data of ' However, disagreement exists concerning the state of ionization of the nickel vacancies in NiO. Some authors3-' have proposed that the predominant defects in NiO are singly ionized nickel vacancies and positive holes (h') formed by the reaction where, accorhng to the notation of Kroger and Vink,6'7 Oq represents an oxygen ion on its normal lattice site. Other authors"27E have proposed that doubly ionized nickel vacancies (V{i ) and positive holes are predominant and are formed by the reaction One purpose of the present investigation was to establish the nature of the predominant defect in NiO,+? as well as its equilibrium concentration and thermo-dynamic properties at elevated temperatures and known oxygen activities. To accomplish this purpose, the coulometric titration of oxygen into and out of NiO was accomplished using a galvanic cell involving the calcia-stabilized zirconia electrolyte. The ternary oxide, lithium ferrite (LiFe50,-6) is ferromagnetic and has the inverse spinel structure LiFe,O,-d Thus, in the ideal stoichiometric XY204 lattice, Fe3 ions occupy one-eighth of the tetrahedral (A) sites, and i' and Fe3' ions share at random one-half of the octahedral (B) sites within the fcc sublattice of oxygen ions.g The structure and thermodynamics of the spinel structures have been comprehensively decribed.'-' A recent compilation of literature for lithium ferrite is also available. 15 Oxygen-excess LiFe50sis not expected to exist because both i' and 17e3& ions are in their highest normal valency states (positive hole formation is not favorable). As will be discussed, equilibration of the ferrite crystal with oxygen of a surrounding gaseous phase will result in the introduction of equilibrium concentrations of ionic and electronic defects. In the Results and Discussion section a defect model for LiFe50,-d is proposed. This defect model is tested by high-temperature coulometric titration experiments. EXPERIMENT The oxygen activities in nonstoichiometric NiOl+, (and also LiFe,O,-d) were measured by means of coulometric titration with the high-temperature galvanic cell The critical characteristic of a suitable experimental cell is the complete isolation of the phase to be investigated in a minimum sized chamber which is free from extraneous sources and sinks for oxygen (leakage). Then oxygen is only admitted to the chamber or removed from it in known amounts by coulometric titration, which involves the passage of oxygen ions through the solid electrolyte with electrochemical oxidation and reduction reactions at the platinum contacts to the electrolyte. The experimental cell is shown in Fig. 1. The cap of the cell was the tip from a closed-end alumina tube, which was found to be leak-free from a helium leak-detector test. This alumina cap was about 1.2 cm OD and about 1.5 cm high. A Zircoa calcia-stabilized zirconia tablet (crucible lid) of 1.5 cm diam and 0.3 cm thickness served as the solid electrolyte. A Pyrex ring of about 0.1 cm thickness was placed between the electrolyte and the cap. The electrolyte tablet was painted with platinum paste on the entire outer face and on that part of the inner face which would be within the enclosure; these electrodes were further prepared by heating in air at 1000°C for 2 hr. Nickel oxide powder, listed as 99.999 pct pure, was purchased from Leico Industries, Inc. Pills of the NiO were cold-pressed and sintered at 1050°C for 3 hr in a platinum crucible. This poorly sintered NiO was crushed, and chunks were wrapped in 52-mesh Pt gauze (to catalyze the solid-gas exchange) for place-

Jan 1, 1970

By R. H. Harrington

THE definition of precipitation-hardening is well understood and its principles have been subjected to study for some time. However, the variation of properties with double aging, combined with strain-hardening, gives promise of new and useful phenomena. Properly to understand these distinctions, definitions of these terms are necessary. Precipitation-hardening. This reaction usually depends upon an alloy having such a composition that it consists only, or in major part, of but one phase, a solid solution, at a high temperature, so that, upon slow cooling, this solution breaks down into two phases, the solid solution and a compound. By heating the alloy to the temperature for maximum solution of the compound, quenching, and reheating to a suitable lower temperature for critical dispersion precipitation of the compound, useful properties of the alloy may be developed to a maximum. Double Aging.-Dougle aging in part is similar to the process for precipitation-hardening, consisting of heating a precipitation-hardening alloy to the solution temperature, quenching, reheating to the suitable dispersion precipitation temperature, strain-hardening, and again reheat-ing to a suitable temperature to develop certain useful properties to a maximum. The strain-hardening may be induced by two methods: (1) a rate of cooling from the first reheat may suffice to strain the solid solution lattice of the alloy; or (2) the alloy may be cold-worked to a suitable degree between the two reheats.

Jan 1, 1936

Jan 1, 1928

By H. C. Howard

Reaction of oxygen and bituminous coal starts as soon as the coal bed is exposed to air and, with some coals, proceeds with significant velocity even at normal temperatures and at normal oxygen partial pressures of one-fifth of an atmosphere. At higher temperatures, the reaction is greatly accelerated and ultimately a condition is reached where the process is very rapid and we then speak of combustion. It is the purpose of the present paper to discuss the reactions of oxygen and coal at temperatures below those of active combustion. It is these low temperature oxidation reactions which are responsible for heating in storage and for marked changes in agglutinating proper-ties. These reactions may also be employed for the preparation of organic acids, which are of direct interest to the chemical industry. For convenience in discussion, the low temperature reactions of oxygen and bituminous coal can be roughly divided into three stages though there is, of course, overlapping. Stage I is a surface oxidation stage, characterized by the addition of oxygen, with the formation of oxygen containing groups some of which have acidic properties. Carbon dioxide, carbon monoxide and water may be formed con-comitantly and are always liberated at higher temperatures, and in cases where the oxidation is prolonged. Superficially, the coal is little affected by this primary stage of oxidation and usually only minor changes in ultimate composition result. There may be definite changes in coking and coking properties, and heat of combustion susceptibility to further oxidation. The presence of acidic groups can be demonstrated by specific reactions. These groups may show cation exchange properties like the mineral zeolites. The formation of oxalic acid has been reported. If the oxidation is continued, a large fraction of the organic material of the coal is converted ultimately into alkali soluble, acid insoluble products, which have been given the name "regenerated humic acids" and which are the characteristic products of Stage 2. These humic acids, in the solid stage, do not differ greatly in appearance from the original coal, but show large differences in chemical composition and chemical and physical properties. Along with the humic acids, carbon dioxide and some of the water soluble types of Stage 3, are also formed. If the oxidation is carried still further, the humic acids may be degraded completely to the simpler, lower molecular weight acids of Stage 3 which are characterized by solubility in acid as well as in alkaline media, and by their orange, yellow or white colors. Additional carbon dioxide is formed in the transformation from Stage 2 to Stage 3 and, for a number of American coals, a maximum yield of the water soluble types of acids is reached when about 50 pct of the carbon of the coal is converted to carbon dioxide. Primary Oxidation The initial step in the reaction of gaseous oxygen on coal, like that on carbon,

Jan 1, 1949

By Chauncey L. Berrien

The United Verde Copper Company's mine is at Jerome, Ariz. The orebodies arc of the schist replacement type, the main sulfide mass being a large lens-shaped body approximately 7 acres in cross-sectional area. In general, the mineralization is found along the iron schist contact, with the orebodies extending about 1000 ft. along this contact and varying from a few feet to 250 ft. in width. Three types of ore are mined; schist porphyry and the so-called "heavy" or "massive sulfide" ore. Approximately 50 per cent. of the total tonnage mined at present is of the latter class. A representative analysis of this ore indicates 42 to 46 per cent. sulfur. Because of the high sulfur content, blasting in this ore is an extremely hazardous operation. not only does it endanger the lives of men who may be in the mine at blasting time but it also becomes a potential fire menace when timber is in close proximity to shots being fired in these massive sulfides. The origin of the fires of 38 years ago, embers of which are glowing to this day, may perhaps be attributed to dust explosions due to blasting in the massive sulfides of those early square-set stopes. Dust Explosions Dust explosions in coal mines are a common source of mine disasters. That such explosions may be of common occurrence in metal mines is not generally known, but it is known that metal-mine dust will explode and such explosions have been investigated by the U. S. Bureau of Mines at the Pittsburgh Experiment Station. Samples of "heavy sulfide" ore from the United Verde mine were used in the tests. After studying the results of the tests it was concluded1 that: 1. Dust explosions were initiated in sulfide ore dust in the gallery with a charge of as low as 75 g. of 60 per cent. gelatin dynamite. 2. The exploding dust generated considerable pressure.

Jan 1, 1930

Jan 1, 1910