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By E. Miller, N. Chou, K. Komarek

The solid solubilities of the compounds PbS, PbSe, and PbTe have been determined by equilibrating single crystals with two phase alloys. The solubilities were determined by measuring the Hall coefficient of the equilibrated samples. The observed maximum deviations from stoichiometry on the lead rich and the chalcogen-rich side of the phase fields were: at. pct excess Pb at pct excess S at 850°C; PbSe--4 x 10'" at. pct excess Pb at at. pct excess at 800°C; and PbTe-2.8 x 10 4 at. pct excess Pb at 780°C, 10"1 at. pct excess Te at 720°C. The previously developed theory of retrograde solubility has been expanded to include intrinsic disorder in the compounds, and the experimental results are in agreement with the theory. THE solid solubility limits of intermetallic semiconducting compounds are of considerable interest, since many of these compounds have potential use as thermoelements in thermoelectric devices, as infrared detectors, or in semiconductor devices. The solidus curves of a significant number of these compounds have been reported to be retrograde with the maximum solid solubility occurring between the eu-tectic and the maximum melting temperatures. In a previous paper,' equations were derived which permit calculation of the maximum solid solubility of an AB compound exhibiting retrograde solubility. Derivation of these equations was based on the assumption that the compound is a nondegenerate semiconductor at the temperature under consideration, that the defects were unassociated, and that the vibrational contribution to the entropy of the compound could be evaluated by the Einstein approximation. It was shown that at the temperature of the maximum solid solubility The entropy term ASS is composed of the entropy of formation of the solid stoichiometric compound (AS$)*, and the entropy due to deviations from stoichiometric composition which is the sum of a con-figurational term (aS*), a vibrational term (AS,), and an electronic term (AS,). In the previous paper the positional entropy was evaluated considering the con- N. CHOU, Member AIME, formerly Graduate Student, New York University, N. Y., is with IBM, Yorktown Heights, N. Y. K. L. KOMAREK, Member AIME, formerly with New York University, is Professor, Department of Inorganic Chemistry, University of Vienna, Vienna, Austria. E. MI LLER, Member AIME, formerly with New York University, is Associate Professor of Mechanical Engineering, California State College at Long Beach, Calif. The paper is based on a thesis submitted by N. CHOU to the Graduate Division, School of Engineering and Science, New York University, in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Materials Science. tributions from defects arising from deviations from stoichiometric composition. The derivation is generalized in the appendix to include intrinsic disorder. The electronic entropy term is also recalculated in the appendix. Of the various semiconducting compounds, the solidus curves of Pbs,' and ~b~e,~ have been most extensively studied. The solidus of PbSe has also been determined, but the temperature of maximum solubility has not been accurately established.5129 The present investigation was undertaken to compare the experimental solid solubility data for these systems with the values predicted theoretically. Since the temperature and composition of the maximum solubility of PbSe has not been accurately determined, experimental emphasis was placed on determining the solidus curves for PbSe in the region of maximum solubility, although experiments were also performed on PbS and PbTe at several temperatures. X-ray diffraction studies were also made on carefully prepared powder samples of PbSe to determine the variation of lattice parameter with composition. EXPERIMENTAL PROCEDURE The procedure of Brebrick and Allgaier was employed for determining the solidus data. Monocrystal-

Jan 1, 1970

By J. E. Campbell, G. D. Calkins, N. M. Ewbank, M. Pobereskin, A. Wesner

GRINDING for size reduction affects the economics of many processes and products. It is essential as the first step in many industrial processes and is also a finishing step for materials with properties depending on particle size, such as talc, cement, and silica sand. Intermediate and fine grinding are vital operations in the U. S. cement industry, which is producing more than 250 million bbl of cement per year.' Wear of the grinding media is a large part of the grinding operation cost. Problems encountered in grinding cement are so complex that evaluation of efficiency and economy of grinding media is difficult.2 It has been especially difficult to evaluate the relative effectiveness of different types of balls because there are no good testing techniques. Many other industrial operations can be evaluated on a laboratory scale with reasonable accuracy. This does not hold true for evaluation of grinding balls. The consistent results obtained in a laboratory test under a given set of conditions are not always borne out in field application. Rough evaluations of the effectiveness of various compositions and types of grinding balls have been made in the field by using a full charge of one type in a mill and comparing the production record with another run using another type of ball. This method is time-consuming and not very precise, as the second run may not have been carried out under identical conditions. Laboratory-scale tests, on the other hand, have yielded inconclusive results, and many investigators have turned their attention to the development of a field testing technique. Field testing small sample lots of grinding balls has been impractical because it is difficult to identify and recover the test specimens from the grinding mill, and individual groups of balls that have undergone different heat treatments can not be separated.".4 To overcome these difficulties, previous investigators have identified the balls by distinctive marks, notches, and drilled holes, but this procedure has three serious drawbacks: 1) Grinding characteristics and quality of the steel balls may be affected. 2) Physical markings may be worn away in the grinding process, especially during a prolonged run. 3) Recovery from the bulk of the charge will be extremely difficult because the markings are hard to see and may be masked by a coating of the product. To circumvent these difficulties, a radioactive-tracer technique was proposed for recovery and separation of steel grinding balls and subsequent evaluation of the various compositions of the balls. The proposed technique involved five basic operations: 1) Thermal-neutron irradiation activation5 of each group of test grinding balls to a different level of specific radioactivity. 2) Addition of groups of radioactive steel-ball specimens into a ball tube mill. 3) Recovery of radioactive steel-ball specimens from the bulk of the mill charge. 4) Separation of the various groups by their specific radioactivity. 5) Evaluation of actual grinding ball wear. Before any physical tests were performed, required neutron irradiation intensity and time were calculated. Probable composition of the steels to be used was ascertained. An examination was made of the radioactive nuclides8 to be formed which would contribute measurably to the radiation level immediately after irradiation and during the test operation. The radioisotopes formed, their types of radiation, and their half lives are listed in Table I. Of these radioisotopes only iron-59 and chromium-51 were significant for the actual wear test. The intensity of radiation that could be detected by a Geiger counter when the test was completed was the basis for the minimum activation level established. The intensity of radiaton that could be safely handled at the beginning of the test was the basis for the maximum activation level, although this was not considered a major problem. Ten groups of grinding balls of various composition and/or surface or heat treatment were to be tested. One group was designated for the minimum irradiation time. The remaining groups were designated for irradiation periods that increased by increments of 33 pct from that of each preceding group. This difference was considered enough for separation and identification of the groups by comparison of specific activity. Potential Hazards: Possible radiation hazards that might be encountered during this experiment were evaluated for the three important phases: 1) the radiation hazard of placing balls and removing them from the mill, 2) contamination of the product cement by radioactive material worn from the balls, and 3) contamination of the steel by the radioactive balls left in the mill. The radiation intensity expected from the whole group of radioactive balls was calculated to be 250 milliroentgen per hr at 1 ft. This meant the balls would require special shielded packaging and warning labels on the shipping containers. In a radiation field of 250 mr per hr a man can work for 1 hr without exceeding maximum permissible weekly exposure. Since the balls could be dumped into the mill in a matter of seconds, relatively little radiation exposure was anticipated at this stage of the operation. If the weight loss in the balls was 7.7 pct per month and the cement feed through the mill was

Jan 1, 1958

Jan 1, 1899

SOUTHERN CALIFORNIA LOCAL. SECTION Executive Committee SEELEY W. MUDD, Chairman C. COLCOCK JONES, Vice-Chairman FREDERICK J. H. MERRILL, Secretary-Treasurer, 631 Higgins Bldg., Los Angeles, Cal. RALPH ARNOLD A. B. CARPENTER In. order to make the meetings of the, Section more interesting and fruitful, the Executive Committee has formed a sub-committee on programs for. Section meetings, which announces for the coming autumn and winter season, four dinner meetings, at intervals of two months, in which the co-operation of all Section members is urgently. requested. The subjects chosen for discussion at these meetings, with the proposed dates, are as follows: Sept. 28, 1915. Mining Geology of Mojave County, Arizona. Dec. 14, 1915. General Geology and Mining Conditions in Southern California. Feb. 1, 1916. Petroleum, its Geology and Technology. April 4, 1916. General Mining Conditions in. South America. F. J. H.. MERRILL, Secretary.

Jan 10, 1915

By R. Stefanko

The use of strain gauges and compression pads for an underground bolt installation in a central Pennsylvania coal mine revealed that satisfactory anchorage could not be maintained in the shale stratum that constituted the immediate roof. Comprehensive laboratory tests resulted in a new shell designed with an increased area of contact and smaller surface serrations. Retightening of the bolt was also found to be beneficial for maintenance of high load values. Roof bolting in coal mines has progressed very rapidly in the last decade, and today this method of support is in general use. There are many theories concerning the functions of roof bolts, but the importance of beam building is indisputable. Proper tension in the bolts minimizes shearing along bedding planes and creates a thick, competent beam from individually weak layers. Bolting must be accomplished immediately upon exposure of the roof, and bolt tension must be maintained if roof failure is to be prevented. Seams are being mined today with roof bolt support where conventional timbering was not effective.' The widespread use of continuous mining equipment was made possible by roof bolts which permit long supported spans free of obstructions. Since adequate anchorage is the key to successful bolting, better methods for determining the efficiency of anchorage are continually being sought. Attempts have been made to measure bolt loads, thus assessing anchorage efficiency by employing sensing devices between the bolt head and roof. 3-s None of the techniques appears to be very accurate, and all have at least one serious deficiency. The greatest efforts are being directed toward the standardization of the pull test.6" Nevertheless, the author believes that the pull test is only one criterion for establishing the efficiency of anchorage and not necessarily the most important one. The conventional pull test involves the short-term application of forces, whereas the success of roof bolt installations is dependent upon the ability of anchorage to sustain relatively long-term forces. Therefore, it would appear that the time-dependent function of the anchor is the single most important parameter for the success of roof bolting in many types of rocks. UNDERGROUND TESTS Strain gauges and compression pads were employed to measure bolt loads in a central Pennsylvania coal mine.8 Bolting had been employed only sporadically in the shale top since dubious benefits were obtained with this type of support. Table I shows some typical results from this investigation. Anchorage losses were extremely variable among the bolts, but all showed a considerable degree of bleed-off. The tests indicated that anchorage efficiency was extremely low in this type of shale. The results confirmed that bolting under these conditions was practically worthless, and thus a waste of material and labor. Probably even more important, bolting constituted a hazard when reliance was placed upon it for support. Certainly the complete lack of confidence in roof bolting, which was apparent in the mine personnel, was justifiable since the bolts did not accomplish their purpose. PRELIMINARY LABORATORY BOLT TESTS The extreme losses in bolt tension that were detected in underground installations prompted a comprehensive study to assess the causes. However, preliminary studies were first made to determine the combined stresses in a roof bolt and to prove conclusively that the observed bleed-off phenomena were due to anchorage: slippage and not to some other physical manifestation. In all of the ensuing tests

Jan 1, 1962

By M. W. Fabjanczyk, E. G. Alexander

INTRODUCTION The purpose of this paper is to summarise development of design processes used in the 1100 oreoody as a result of experience encountered. Design methods have been developed as a result of the history of ground behaviour, free-standing qualities of cemented back fill and mass blasting techniques. This paper contains an historical review of design methods previously described by Matthews ( 1972 ) , Hornsby and Sullivan (1977 and 19781, Kirkby, Blair and Hutton (19781, and Stewart (1980). The reasoning behind design philosphy changes are discussed and placed into context with methods now adopted. The 1100 orebody is Mount Isa's main producer of copper ore (5 million tonnes per year ) . Proven reserves are 120 million tonnes at 3.2% Cu. Location of the 1100 orebody in relation to overall mine geometry was well described by Dayton (1976). Geology The orebody is located in a series of massive brecciated shale lenses, in either a siliceous or dolomitic matrix, surrounded and separated by a uniform shale sequence. The whole formation is truncated at depth by a faulted contact with a greenschist facies metamorphic sequence below (Figure 1 and Figure 2) Mathias and Clark (1976). The breccia is known locally as silica dolomite and contains nearly all the economic mineralisation. Interfingering of shale and breccia often results in irregular boundaries to the silica dolomite and the ore limits. Geometry The geometry of the orebodies is shown by Figures 1, 2 and 3. Figure 3 also shows the location of the copper orebodies in relation to the lead orebodies. Structure Although the orebody is contained within the massive breccia (u.c.s. 150-250 MPa), it is cut by shear zones sub-parallel to the regional bedding (north-south striking, dipping approximately 60o to the west), and diagonally by major transverse faults (Figure A). These major faults have continuity in excess of 300 metres, with varying amounts of displacement up to 200 metres, and are zones of potential movement.

Jan 1, 1981

By H. B. Northrup

Mineral Industries Extension instruction was pioneered by The Pennsylvania State Colleges Extension work was organized in 1893 and constituted what is believed to be the first vocational adult educational effort in that field in America. From 1894 to 1899, twenty-seven extension bulletins were printed and distributed free for the benefit of classes in the coal-mining industry and the records show that free lectures wore delivered by a corps of teachers of the mining department of the College "to the mining employees at their customary lace of assembly upon matters of interest to them in their occupation." In 1899, the State Legislature reduced the appropriation to the College and therefore the extension pamphlets and lectures were discontinued. Several sporadic attempts were made to resume the extension services in mining through industrial grants for travel and publications, and through voluntary contributions by members of the resident staff. The work. consisted mainly of lectures and demonstrations and served the purpose of creating the desire for more training and information of a more formal character. In 1928, the nave of the school was changed, by trustee action, from School of Mines and Metallurgy to the School of Mineral Industries and the working structure of the school was organized under the three functional collaborating headings: Resident Instruction, Correspondence and Extension Instruction, and Mineral Industries Research. The three functional bodies are separate, yet interdependent. The Federal Smith-Hughes law, passed in 1917, made Federal and State funds available for vocational educational work. Mining extension was revived in 1919 and the College employed one full-time extension professor to reorganize the work and instruct the classes. In 1923, the State Department of Mines and the State Department of Public Instruction entered into, a formal agreement with the School of Mineral Industries to assist the College in its extension program.. Classes were organized to study the State mining laws and State Department of Mines' previous examination questions and answers, in preparation for coming state examinations for certification of competency as underground officials. Mimeographed lesson material was used at first, and in 1947 and 1929 mining instruction and mining teacher-training lessons were printed. In 1931, the extension activities of the school were placed on an organized basis compatible with the newly formed school organization and a director was appointed to tale full charge of the work. During that year, at a conference in Harrisburg, an agreement was consummated between the State Departments of Public. Instruction, Mines, Labor and. Industry, and the College whereby extension classes in the field of the, mineral industries could be organized by the College, throughout the State, under "public supervision and. control," in close cooperation with the State Department.

Jan 1, 1941

By C. D. Hunter, I. B. Browning, Ralph Thomas

Production of oil in Kentucky during 1938 was 5,566,154 bbl., showing a substantial increase over that of the year 1937; while in the gas areas development was somewhat retarded although deliveries were similar to those of 1937. In eastern Kentucky there was an oil increase during 1938 of over 150,000 bbl. above that of 1937. No new pools were developed and the increase was almost entirely due to the installation and expansion of secondary recovery methods and to the further development of the Maxon and Big Lime, Mississippian pools in Floyd and Martin Counties. With this development eastern Kentucky reached a level near that of 12 years previous, when the development of several large producing areas had just been completed. In eastern Kentucky during 1938 not over 50 gas wells were completed. Although the pipe-line deliveries were approximately the same as during 1937, development was retarded because of an excess of gas already developed and the intensive development of the Oriskany fields in West Virginia. In western Kentucky, in the part of the Illinois Basin lying in the state and known in Kentucky as the Western Coal Basin, the increase was due to the discovery of a number of new pools, the largest and the one producing the biggest wells being known as the Birk City pool. In fact, the discovery of this pool with the McClosky "sand" (St. Genevieve limestone) as the producing formation was in a large measure responsible for the increased activity, which in turn brought the discovery of the other areas. The discovery well in this pool is the C. T. Blackwell, which came in flowing 1000 bbl. daily from the McClosky sand at a depth of 1870 ft., drilled in April 22, 1938. This discovery, coming at a time when the major companies and many others were conducting an intensive leasing campaign and making extensive subsurface and geophysical surveys in the deeper part of the basin, resulted in renewed activity over the entire area and brought much new drilling. It also brought to Kentucky for

Jan 1, 1939

By G. A. Bole, F. W. Davis

The purpose of this paper is not to report, to the Institute, the results so far obtained in the survey, by the Bureau of Mines, of the metallurgical requirements for open-hearth refractories, but to present an outline that we hope will serve as a basis for discussion. The systematic survey that the Bureau proposes to make has not been outlined, although considerable preliminary work has been done in the way of interviewing open-hearth superintendents in several of the larger steel plants from the Chicago district eastward. At the several conferences so many of the opinions were diametrically oppoeite, when considering the same point, that it was thought that such an opportunity as the Institute offers in the way of a clearing house for moot metallurgical topics should not be overlooked. For this reason, the paper has been prepared as a basis for a discussion which, it is believed, will be of value in outlining the program of the Bureau. D. A. LYoN, Assistant Director. The importance of securing suitable refractories for metallurgical operations is daily becoming more universally recognized; particularly in the manufacture of open-hearth steel, where the life and earning power of the furnace depends largely on the judgment and care exercised in the selection of the correct quality of refractory for each of the parts. Any innovation that would make available to the steel manufacturers refractories with longer life or better suited to their needs than those now employed, and at a cost that would permit of their use, would be of enormous value to the industry at large. It is quite probable that revolutionary changes would not be necessary. Material now used in some parts of the furnace might, by more suitable preparation, be made of much greater service; in other parts, possibly entirely different material would be necessary in order to effect much improvement. Inasmuch as different parts of the furnace structure perform different functions and are subjected to different service conditions, a refractory suitable for one part will be entirely unsuited for another. For this reason, to make a comprehensive study of the refractory requirements of the processes, we should consider the furnace as built up of a number

Jan 1, 1924

By Sergio G. Jarpa

A mining project is, at one and the same time, capital intensive and highly risky. Besides, because of its usual long projected life, the operating cost is more difficult to predict and offtentimes exceed, during the life of the project, the first investment manifold. The objective of this study was to evaluate the applicability of cost-capacity relationships as used in the chemical industry to mining operations and, when necessary, to develop new ones. With the aid of a computer library program available at the Computation Center of the Pennsylvania State University, the total investment in mining equipment was determined to vary exponentially with production capacity, and the scaling exponents for each class of equipment, i.e., drills, shovels, trucks and earth moving equipment, as well as for the total operation were calculated. Since the scaling exponent for the whole mining operation happened to be equal to 0.94, it was concluded that more significant economies of scale are achievable in processing plants than in mining operations. From the operating cost point of view, unit material cost was found to decrease more rapidly than unit labor for the same increases in production capacity. The analysis of cost centers revealed that drilling and blasting, which are materials-intensive operational stages, were the most favorable in achieving significant economies of scale. Hauling unit cost, on the other hand, decreased only slightly when production capacity increased.

Jan 1, 1977

The following is an incomplete list of members and guests who called at Institute headquarters during the period Feb. 10, 1919, to Mar. 10, 1919. R. H. Allport, Cleveland, Ohio. R. R. Landon, Philippine Islands. I. H. Bergstein, New York. Alfred 0. Law, Cambridge, Mass. Capt. R. S. Burdette, San Antonio, Tex. James M. Little, Towanda, Pa. William R. Chedsey, State College, Pa. F. E. Marcy, Salt Lake City, Utah. L. R. Clapp, Philadelphia, Pa. H. F. Nash, Bartlesville, Okla. J. Murray Clark. L. S. Panyity, Columbus, Ohio. E. H. Claussen, San Francisco, Calif. W. C. Ralston, Reno, Nev. George E. Collins, -Denver, Colo. T. A. Rickard, San Francisco, Calif. George L. Collord, Sharpsville, Pa.. W. A. Rigby, Mt, Vernon, Iowa. William M. Corse, Mansfield, Ohio. H. H. Rowatt, Ottawa. Frank R. Crampton, Los Angeles, Calif. P. H. Royster, Pittsburgh, Pa. Capt. E. 0. Daue. Alan B. Sanger, Dorchester, Mass. A. E. Eddy, Butte, Mont. J. S. Shaw, Pittsburgh, Pa. N. H. Emmons, 2d, Lynchburg, Va. S. B. Shutts, Lynchburg, Va. E. W. Engelmann, Hayden, Ariz. Henry B. Smith, New Britain, Conn. F. A. Fahrenwald, Cleveland, Ohio. W. C. Smith, Roselle, N. J. 0. S. Finnie, Ottawa. Harry M. Spoor. John T. Fuller, Honesdale, Pa. D. M. Stackhouse, Johnstown, Pa. Major C. C. Griggs, Eureka, Utah. F. D. Stay,. Cleveland, Ohio. H. F. E. Gamm, Rutherford, N. J. D. B. Sterrett, St. Cyr, Que. A. W. Hackwood, Butte, Mont. R. H. Thayer, Yonkers, N. Y. C. L. Horne, Roanoke, Va. Kirby Thomas,. New York. B. B. Hood, Chrome, N. J. Henry Traphagen, Toledo, Ohio. R. E. Hore, Toronto Ont. H. D. Trounce, San Diego, Calif. Ross B. Hoffmann, Oakland, Calif. Henry J. Volkin, Ossining, N. Y. G. A. Joslin, Salt Lake City, Utah.. A. T. Ward, Bellefonte, Pa. John Johnston, Washington, D. C. Major L. W. Wickes. Paul S. King, Wilmington, Del. Horace V. Winchell, Minneapolis, Minn. E. William Kohl, Jr., Philadelphia, Pa. Fred L. Wolf, Mansfield, Ohio. W. H. Landers, San Francisco; Calif. J. Carson Adkerson, of the Stockwood Realty Corpn., Inc., of Woodstock, Va., writes that they are discontinuing their operations in Virginia on account of the conditions in the manganese market following the end of the war.

Jan 4, 1919

By R. P. Smith

The carbon content of a number of alloys ranging (before carburitation) from purified iron to purified cobalt was determined for fixed activities of carbon by equilibration with each of six CO-CO2 atmosphere at 1000°C. At fixed carbon activity, the carbon content decreases continuously with increasing cobalt content. For concentrations of 0 to 50 at. pct Co the results can be expressed by a linear interaction equation of the type In y2 = 7.76n2/(n1+n3)+ 2.30 n3/(n1+n3) where y2 is the activity coefficient of carbon (standard state such that y2— 1 as n2 — 0 in the Fe-C binary) and n1, n2, and n3 are the number of atoms of iron, carbon, and cobalt per unit weight of alloy. The results are also given in terms of the a functions. In the same concentration range, the results are in accord with the regular solution theory of Alcock and Richardson. THE carbon content of Fe-Si, Fe-Mn, and Fe-Ni alloys at fixed activities of carbon has been reported previously.'-, The present work extends R. P. SMITH, Member AIME, is Research Chemist, E. C. Bain Laboratory for Fundamental Research, United States Steel Corp., Research Center, Monroeville, Pa. these measurements to a series of Fe-Co alloys. These alloys, like the Fe-Ni alloys, are fcc ("aus-tenitic") over the entire range of composition at 1000°C. EXPERIMENTAL PROCEDURE The alloys were made from electrolytic cobalt and Plast-Iron in a small vacuum-melting furnace. A small amount of graphite was added to each melt to keep the oxygen content low. The ingots were analyzed for iron and carbon: the amount of cobalt was obtained by difference. Analysis of the top and bottom of the ingots indicated that they were uniform in alloy content. Except for the pure cobalt the ingots were hot-rolled to approximately 0.15 cm thickness, cleaned by sandblasting, then cold-rolled to about 0.045 cm. We were not successful in cold rolling the pure cobalt; therefore it was hot-rolled to the final thickness. The last traces of surface oxide were removed by acid pickel, then the samples were treated in a hydrogen-2 pct water vapor mixture at 1100°C to remove carbon and most of the oxygen. The carburizing procedure was similar to that previously described.1,2,4 The alloys in the form of strips about 1.7 cm wide, 7.5 cm long, and 0.04 cm thick, together with a similar specimen of purified iron, were equilibrated with each of six CO-CO2 mixtures of fixed composition, then quenched in the

Jan 1, 1965

Jan 1, 1948

By A. W. Fahrenwald

CELL depth has been for many years a controversial question in a flotation-machine performance. In the impeller type of machine, we are really talking about impeller submergence-i.e., the depth in the pulp at which the impeller is required to produce aeration. THE FLOTATION MACHINE A COMPRESSOR A flotation machine can be considered as an air compressor or blower in which the aeration mechanism takes in air under atmospheric pressure[t] (14.7 lb. per sq. in.) and blows it into the pulp (the pulp being the receiver) against a head of 14.7 plus cell depth in feet times 0.4333 lb. per sq. inch. In commercial machines the impeller is submerged in the pulp to depths ranging from about 2 ft. in the smaller machines to as much as 5 ft. in some of the larger ones. In the 2-ft. cell, the hydrostatic head on the impeller is (2 X 1.25 =) 2.50 ft. (assuming a pulp density of 1.25), equal to (2.50 X 0.4333 =) 1.078 lb. per sq. in. For the 5-ft. cell, the hydrostatic head against which the impeller must make air is (5 X 1.25 X 0.4333 =) 2.708 lb. per sq. inch. In the small 2-ft. machine, the volume reduction is (1.078 [-] 0.147 + 0.01078 =) 6.85 per cent and in the large, 5-ft. machine, the volume reduction is (2.708 [=] 0.147 + 0.02708 =) 15.5 per cent. It is obvious that for unit volume of free air intake the larger machine receives a lesser (8.65 per cent less) volume of aeration* than the smaller machine. The bubbles in escaping from the pulp expand and are greater in volume at the surface than at the moment of their formation in the pulp; 7.33 and 18.4 per cent larger, respectively, in the small and large machines. Just how this situation affects flotation is not known. It is interesting to note, however, that the bubbles are smaller in the zone of the coarsest particles and largest in the upper zones of the finer, more easily suspended mineral particles. It would seem that the relationship might be reversed advantageously. The deep cell is at a greater disadvantage in this respect than the shallow cell. Nothing, however, presumably can be done about this situation. The shallow cell is a partial corrective. Not only does the compression ratio of aeration increase with impeller submergence but the hydrostatic head against which the impeller must operate also increases. THE FLOTATION MACHINE AS A PUMP Since, in impeller machines that rely upon their own operation to produce aeration, pulp passes through the im-

Jan 1, 1946

By W. E. Crawford

The Fresnillo Company's mill at Fresnillo, State of Zacatecas, Mexico, treats oxide ores from the Fresnillo mine, dump ores and underground ores from the Plateros district, company leases and custom ores from the Zacatecas district, custom ores from other districts and tailings from old dumps at Fresnillo. The normal capacity of the mill is approximately 2600 dry short tons per 24 hours (a ton of 2000 lb.). The final product of the mill is a precipitate containing gold and silver, which is smelted and shipped as doré bullion to the refinery of the Compania Minera de Penoles, S.A., at Monterrey, State of Nuevo Leon, Mexico. The geology of the district was described in 1923, by T. C. Baker,' from whose paper the following data have been taken: The mineralization of the district was effected in the Tertiary period, following the intrusions and preceding the appearance of the flows. The area within which productive veins have been found is 1 mile long by 1/2 mile wide. The important units of each of the four general fracture systems meet in the central portion of Proano hill, which is an outcrop of graywacke, and where the rock was also intensely fractured by subsidiary movements, resulting in a shattered zone 1200 ft. long by 400 ft. wide. The mineralization was more intense in the immediate vicinity of the principal channels through which the solutions rose. The valuable metals are silver and gold, the ratio by weight of the former to the latter being 1000 to 1.5. Argentite is the predominant silver mineral, and is associated with pyrite and manganese mineral. The sulfides are primary throughout. A slight secondary action is represented by small quantities of native silver and silver halides, principally cerargyrite, which are found in the upper part of the mine. Oxidation has penetrated with great thoroughness to the lowest horizon so far exposed, this being 420 ft. below the present ground-water level. The shattered mass within the central portion of the hill and near the surface was sufficiently mineralized to produce a large stockwork

Jan 1, 1935

By J. W. Putman, N. J. Grant, D. S. Bloom

SEVERAL recent determinations of the melting S point of pure chromium have been reported which give values of 1845°C1; 1895°C,² 1930°C,³ 1860°C,' and 1890°C.5 because of this wide spread of values, it appeared desirable to make one additional attempt to obtain a more accurate, reliable figure. bloom and Grantx recently reported a phase transformation in chromium:.--- it was desired to check this, too, in the course of checking the melting point. To accomplish this, a much higher purity chromium was required. Electrolytic chromium containing about 0.5 pct 0 was crushed to a finer size and was then annealed in highly purified, dried hydrogen at 1375°C for 100 hr. This treatment produced chromium with about 0.008 pct 0, 0.002 pct N, and negligible carbon. The balance of the impurities was 0.3 pct Fe, 0.03 pct Si, 0.004 pct S, and less than 0.001 pct Mo. This chromium was melted in a stabilized zirconia crucible under pre-purified argon, using induction heating. Temperature measurements were made with annealed wolfram-molybdenum thermocouples and a Leeds and Northrup Speedomax Recording Potentiometer. The thermocouples were annealed for 1 min in hydrogen at a temperature of about 2400°C. Each leg of the thermocouple was immersed in an ice-water mixture using mechanical connectors to the lead wires. The thermocouple tip was immersed in the molten chromium in a zirconia protection tube which introduces an error of about 3°C as a temperature drop through the walls of the tube. The weight of chromium was about 183 g. The dimensions of the melt in the crucible were about 1.25 in. diam x 2 in. high. The tip of the thermocouple was held about ½ in. from the bottom of the crucible. Two new thermocouples were used with the above set-up giving the results shown in Table I. Since this chromium is purer than that used by Greenaway, Johnstone and McQuillan,' by Carlile et al.,4 and other investigators,²,3 it is believed to be the more accurate. Thermocouple aging effects which are believed responsible for the high value of 1930°C³ were avoided in this work. This value of 1903°C is correct to about ±10°C. The right hand column lists the temperature of the a ? ß transformation on heating and the ß ? a on cooling.3 A sample curve is shown in Fig. 1. The value so determined is 1840°C + 15°C. Fig. 1 gives adequate evidence that there is a transformation in chromium at high temperatures.' References 'H. T. Greenaway, S. T. M. Johnstone, and M. K. McQuillan: High Temperature Thermal Analysis USing the Tungsten-Molybdenum Thermocouple. Journal Inst. Metals (November 1951) 19, p. 109. ²J. W. Putman, R. D. Potter, and N. J. Grant: The Ternary System Chromium-Molybdenum-Iron. Trans. A.S.M. (1951) 43, p. 824. ³D. S. Bloom and N. J. Grant: Chromium-Nickel Phase Diagram. Trans. AIME (1951) 191, p. 1009; Journal of Metals (November 1951). ' S. J. Carlile, J. W. Christian, and W. Hume-Rothery: The Equilibrium Diagram of the System Chromium-Manganese. Journal Inst. Metals (1949) 76, p. 169. 5G. Grube and R. Knabe: Ztsch. Elektrochemie (1936) 42, p. 793.

Jan 1, 1953

1. What Effect Has Sulfur Or Vanadium (In The Oil) On The Steel With Your Burner? 2. Also, what is the decibel rating on the floor when your burner is on? AUTHORS' REPLY 1. There is no effect. 2. The decibel rating is 98-99 decibels.

Jan 1, 1972

By S. R. Smith, W. M. Voorhis, J. D. Young

The Tennessee Valley Authority (TVA) has conducted investigations to identify the major causes of coal pile inventory adjustments. This paper describes past and current attempts to improve inventory survey accuracy and reduce costly inventory adjustments. The unique interaction between accountants and engineers is also reviewed. Data and results of a recent field test wing downward-looking radar developed by Ohio State University are presented. These show great promise in determining coal pile depth and density, thus improving inventory accuracy. This electromagnetic remote sensing technique, if successful, would provide an optimum technical and economic method of surveying all 12 TVA stockpiles without costly borehole drilling or disrupting stockout and reclaim activity. The effect of changing coal quality to meet environmental standards has made accurate coal pile density measurement more important than ever in reducing the costs of electric power generation from coal.

Jan 1, 1984

By Foster Fraas

That variations in the humidity of the air and in the moisture content of a mixture of broken solids being separated electrostatically cause trouble is not new.' Much of the reputation for unreliability commonly ascribed to the electrostatic separation processes is probably due to this one factor alone. Some operators dry thoroughly before separating; and while this is good in many instances, there are others in which it is not the remedy for trouble. Some mixtures behave best in very dry air and with the mixtures fed to the separator while hot to reduce the adsorbed water content. On the other hand, an overdried mixture on coming to equilibrium with more humid air, has been known to take up moisture selectively on one family of particles, as of coal in the presence of slate and clay, and give sharper electrostatic separation. From these observations it is concluded that there is a permissible moisture content for a particle and also for the atmosphere surrounding it, if in equilibrium, at which the particle will have a conductivity or cntact potential2-4 that is ideal for electrostatic separation. This permissible moisture content varies between a wide range of limits for the different materials that are are and with the kind of electrostatic separating process used. Water can be present as a result of adsorption and condensation from the atmosphere, as an accumulation before or during mining, or as a residue from a previous process step. The water may exist as a liquid film or as an adsorbed layer of vapor. If the water exceeds permissible limits it must be removed. Its state determines the method. Drying by evaporation is necessary for adsorbed water, for part of the liquid-film water (that is, up to several percent of the dry weight), and for free water in the internal structure. Large water contents may be removed by drainage Or filtration. At just what point mechanical removal should cease and drying by evaporation begin depends upon the method of mechanical removal and its cost. Particles can also be separated according to their differences in dielectric constant when suspended in a liquid of intermediate dielectric constant. Recovery of this liquid presents a a problem' Permissible Moisture The adsorbed moisture on the outer surface of minerals can be quickly removed or replaced. Accordingly, in speaking of adsorbed moisture contents, either that of the solid or that of the surrounding air may be considered, the two values being connected by a distribution coefficient which varies with the temperature. However, such a condition does not necessarily exist in processes where an initially dry material is suddenly introduced into an atmosphere having a partial pressure of water vapor or where a moist material is suddenly introduced into a dry atmosphere. Here the resultant differences in the

Jan 1, 1949

Jan 1, 1939