Search Documents

By Robert Y. Lamarche

On exploite le chrysotile dans le sud du Quebec depuis plus de cent ans. Au cours des dernieres decennies, cette variete d'amiante est devenue une des principales substances minerales produites au Quebec. Bien que la production de fibres d'amiante ait diminue de J 365 779 ten /979 a que!que 700 000 ten 1983, le Quebec n'en demeure pas mains une des principa/es sources d'approvisionnement mondial de ce mineral, la valeur des exportations quebecoises ayant ete de l'ordre de 315 millions de dollars en 1983. Dans la presente contribution, nous passons en revue que!ques-unes des notions mineralogiques sur l'amiante, depuis l'etymologie du mot et les proprietes physico-chimiques du mineral, jusqu'd ses principales utilisations commercia/es et industrielles. Un des deux objectifs principaux de noire article est de definir brievement le contexte geologique regional, la lithologie et /'age des roches ultramafiques serpentinisees et de decrire les principales caracteristiques des gftes de chrysotile qu'elles renferment et qui furent exploites a date dans /es Appa/aches du sud quebecois. Nous concluons en dressant un tableau synoptique de la metallogenie et en soulignant le role preponderant qu 'ont joue /es mouvements tectoniques majeurs, a la jonction des plaques et au sein des feuillets et copeaux de la croute oceanique (lithosphere et manteau superieur), sur la genese des gftes de chrysotile dans les roches ultramafiques serpentinisees, et tout particu!ierement dans celles associees aux series ophiolitiques du Paleozaique inf erieur.

Jan 1, 1984

By C. H. Li, R. D. Carnahan, R. J. Stokes, T. L. Johnston

When silver chloride deforms by pencil glide at temperatures of 26ºand 72°C, grain size has no effect upon the proportional limit and the material necks down to a knife edge under tension. At -196ºC, deformation takes place on fewer slip systems to produce straight slip traces, the flow stress becomes sensitive to grain size and fracture occurs by cleavage from an intergranular source without any reduction in area. THERE are significant differences between the appearance of the slip bands formed in silver chloride and in the alkali halides at room temperature. The bands in sodium chloride, e.g., are fine and geometrically straight, whereas in silver chloride they are coarse and wavy.' Such differences in the slip behavior prompted us to inquire what the effects of grain boundaries might be on the mechanical properties of these solids. As an introduction to a general study of ionic poly-crystal behavior, we have investigated the effect of grain size on the stress-strain relationships in silver chloride at different temperatures. We have chosen silver chloride chiefly because polycrystals can be easily prepared free from cracks and macroscopic voids by conventional techniques. Moreover, as we shall see, the slip behavior can be readily modified by changing the temperature. It will be shown that the effect of grain size on the yield stress of silver chloride is strikingly dependent upon the temperature of deformation and that this temperature effect comes about through a change in the number of slip systems which operate at the onset of plastic flow. EXPERIMENTAL PROCEDURES Polycrystalline tensile specimens were made by recrystallizing cold-rolled AgCl sheet. Thirty-gram quantities of AR grade silver chloride powder were melted in a low heat capacity furnace, cast into cylindrical forms 3/4 in. in dim and approximately 1 in. in length and then extruded with a 16:l reduction ratio into rods 3/16 in. in dim. Extrusion temperatures were varied from room temperature to 350°C. In order to impart various degrees of cold'work to the extruded rod. All extrusions were then cross rolled to sheet 0.040 in. in thickness at room temperature and machined to form tensile specimens having a gage length of 0.750 in. with a width of either 0.250 or 0.145 in.* Annealing was carried out in an air oven at 200°C for periods up to 20 hr. specimens having average grain diameters ranging from 0.024 to 0.40 mm were prepared by varying the extrusion temperature and annealing time in the conventional manner. To obtain specimens with grain sizes larger than 0.40mm, lightly deformed thin prisims of silver chloride single crystals (supplied by Harshaw Chemical Co.) were recrystallized. Grain size determinations were made by an intercept method and revealed that the grains were equi-axed. Laue back-reflection X-ray patterns showed little tendency to form a preferred orientation texture. Specimens which were to be used for the slip band studies were polished by immersion in fresh boiling concentrated NH,OH for 60 sec. They were then etch polished for 10 sec on each side by hand lapping on a stationary velveteen lap wetted with a dilute Hypo solution (5 g of Kodak Acid Fixer in 100 cc H20). Finally the specimens were rinsed in warm water and alcohol, blown dry and carefully mounted in the tensile machine for testing. Tensile tests were performed at three temperatures, namely, 26º, -72º, and -196°C. A screw-driven hard tensile machine was used at a constant strain rate of 0.006 in. per in. per min. Loads were determined with a light- proof ring fitted with A-18 strain gages and extensions were measured with a 0.0001 in. dial gage. Constant level baths of alcohol with dry ice and liquid nitrogen were used to maintain the two lower test temperatures. EXPERIMENTAL RESULTS Reproducibility—In view of the light sensitivity and reactive nature of silver chloride, it was necessary to determine whether reproducibility depended upon either exposure to light or to the condition of the surface. However, during the course of the work it became clear that variation of laboratory lighting

Jan 1, 1962

By Wayne A. Greenwalt

A method that determines venture participation when the decision maker's level of risk aversion varies according to venture profitability and risk investment is presented. The decision maker's fundamental aversion to risk is established by the selection of a desired working interest for a venture that anticipates only a discounted payout.

Jan 1, 1982

By E. Ashworth

A thermistor probe has been developed to measure in situ temperature profiles underground. A full description of the probe is given. Data collected from the probe has been used to compare the actual profiles with those predicted from a finite element analysis using laboratory measured thermal properties of the different rock types. This comparison indicates the applicability of laboratory measured parameters in modeling the real conditions. Factors such as applied pressure, moisture content and anisotropy on laboratory measurements is discussed.

Jan 1, 1983

By AIME AIME

CORROSION of tanks, pipes and other equipment in the oil fields is becoming worse as the production of high- sulfur crudes in the Texas panhandle and west Texas areas increases. It has been estimated that .in certain fields of that State one tank out of every five has to be replaced every year because of the high sulfur content of the crude. One suggested method for combating tank corrosion is the use of .materials which have a high resistance to the corrosive action of hydrogen sulfide and high-sulfur crudes; aluminum is one of these materials. As a result, the United

Jan 1, 1929

By Richard L. Sanford

The generalized rail haulage simulator described in this paper is an outgrowth of the need to expand a previously developed single level simulator to permit analysis of production problems where intermediate car storage is used. Many of the ideas of the former single level simulator, which is an integral part of an Underground Generalized Materials Handling Simulator (UGMHS), have been used in model development. In addition, experience gained in applying the earlier model to a variety of operating conditions has been heavily relied on. The generalized rail haulage simulation model can operate as an independent system and, as such, can be used to analyze rail haulage systems using production distributions as data input. In addition, this model is designed to replace the present rail haulage sub-assembly in the UGMHS model and the linking procedure has been integrated into the model. The flow of coal from production sections in UGMHS, for example, fill the mine cars and a condition of no empty cars at a loading station will shut down in by production systems.

Jan 1, 1974

By Frank H. Buchella

Principal factors influencing equipment selection can be grouped into five basic categories. Tonnage Requirements, Ore and Waste Loading, transporting, and ground preparation equipment are largely determined by tonnage requirements. Generally, the greater the tonnage requirements, the larger the equipment size selected. Large size equipment is appropriate for a production of about six million tons (total) per month, medium size for three mil- lion tons, and small size for one million tons or less.

Jan 1, 1973

By H. I. Chesalova, M. Ye. Melnikov, A. M. Asavin

The discovery of iron-manganese ores on the surface of underwater mountains was made more than a half century ago. During this time the basic ideas about the thermodynamics of the processes of hydrochemical reactions in the sea water have been developed by scientists and are revealed in geochemical and mineralogical differences between the deposits from the seamounts and the nodules of the sea bottom. The distribution of the dissolved metals, oxygen, carbonic acid and organic matter in the overlying ocean waters of seamounts in the deep ocean to depths more than 5,000 m has been studied in some detail (e.g. J.R. Hein, P. Halbach. G.B. Baturin, Ye.M., S.I. Andreev, L.I. Anikeyeva, [1-6]). In recent years scientists from YUZMORGEOLOGY have completed detailed geological survey work on the Magellan Seamounts in the Pacific Ocean. The results of drilling the ore body and geophysical and photo surveys have also been described [4]. Previous ideas about the general covering of seamount surfaces with iron-manganese crusts have been changed based on ground-truth surveys. This study examines the complex concentric-zone or spotty arrangement of the most densely covered sections, the strong dependence of the thickness of crust on the geomorphologic features, and the potential influence of the underlying substratum. One established geochemical heterogeneity in the composition of ores, also frequently inversely proportional power dependence on directions was observed. The development of a numerical model of the formation of the ore crust on the seamounts is currently a high priority.

Sep 24, 2006

By Philippe Caudal

This paper presents a case study in which a slope failure was observed on the west wall of the LAB Chrysotile mine in the vicinity of the main ramp in January 2010. Airborne LiDAR results were used to evaluate slope geometry before and after the failure occurred. Back analysis of the failure was performed to assess rock mass properties at the slope scale using various numerical techniques: limit equilibrium, finite elements and fracture networks. The various approaches correlated well with field observations.

Aug 1, 2013

By A. E. Deruyttere, J. Van der Planken, M. Laurent, Van den Bergen

FahRENHORST and schmid1 observed that zinc single crystals work hardened less rapidly when strained in liquid air (- 185°C)than in a bath at -82°C, whereas at higher temperatures the rate of work hardening decreased with increasing temperature, as would be expected. Cadmium and magnesium showed no such decrease at -185°C. At that time the observed anomaly for zinc at liquid air temperature probably seemed insignificant. However it later was confirmed2 by experiments in liquid nitrogen (-196°C) and in the mixture solid carbon dioxide-acetone (-77"C) and therefore appeared to be real. seeger3 then suggested that the anomaly might be due to the different wetting of the zinc crystals by the cooling media. Recently a new confirmation was obtained,4 however the cooling media again were different: the rate of strain hardening was found to be lower in liquid nitrogen and liquid oxygen than in pentane cooled to various temperatures down to -126°C. Ekperiments will now be reported in which the medium surrounding the specimen at the different temperatures was the same, namely gaseous air. The single crystals were made from "Overcor 99.99" zinc. They were grown in a vertical traveling furnace on seeds of nearly the same orientations. The diameter of the crystals was 5 mm and the length between shoulders 140 mm. The brass shoulders were stuck to the crystals by means of araldite. A thin steel wire was fixed to each shoulder and served to fasten the specimen to a Houns-field tensile testing machine. The crystals with the shoulders and part of the wires were surrounded by two concentric cylindrical containers. The coolant. either liquid air or ground solid carbon dioxide, was poured into the outer container only. During cooling the containers rested on a support which was removed when the straining was started. In order to check the temperature which the crystals would attain inside the inner container, a hollow bar of zinc in which a thermocouple was fitted was first mounted in the apparatus as a substitute for a crystal. It appeared that a constant temperature, respectively - 183° and -72°C, was attained inside the bar, if a soaking time of the order of 1 hr was allowed and if the outer container was constantly kept filled. Accordingly, this procedure was adopted for every tensile test. To take account of the large scatter, fourteen tensile tests were performed with liquid air and seven with solid carbon dioxide. The orientation of the crystals and the results are presented in the table, in which the symbols have the following meaning: 1 : temperature x : initial angle between basal plane and specimen axis : initial angle between slip direction and specimen axis a : shear strain at fracture 0: average rate of strain hardening = —-——- 100 t0 and Te representing respectively the critical shear stress and the shear stress at fracture. Despite the scatter of the a- and 8— values which is of the same order of magnitude as in the work reported by Seeger and Trzuble,4 it is evident that the strain hardening rate is significantly lower at -183°C thanat-72°C. The table also contains the average values calculated from Seeger and Trauble's results at the corresponding temperatures: z.e., four results at -183oC and two at-70°, -71°C. These authors calculated 9 in a slightly different way, but this is unimportant. The agreement between the a-values shows that both sets of experiments are comparable despite the differences in experimental techniques. The rates of strain hardening also agree and it may therefore be concluded that the anomaly is not

Jan 1, 1962

For nearly two decades, MINExpo International has held the title to the biggest show in mining. The 2012 MINExpo is expected to be the biggest yet, with nearly 1,800 exhibitors rolling out the newest equipment and services across 12 halls. From September 24 to 26 in the Las Vegas Convention Center, MINExpo will present the newest in everything from automation and robotics to safety and communications equipment to reclamation services, and much, much more. The last MINExpo, in 2008, had nearly 38,500 visitors. The show?s sponsor, the National Mining Association, expects this year will be even bigger, with more than 40,000 visitors over three days. Twenty talks on the issues facing mining today are scheduled for Tuesday and Wednesday mornings, but the real action will happen out on the floor. That?s where ultra haul trucks big enough to carry as much as 363 t (400 st) of rock will be assembled next to underground loaders able to lift more than 20 t (22 st) in one scoop. Caterpillar, Komatsu, Liebherr, Sandvik, Atlas Copco: all the big names in mining equipment will be there. Their massive earthmoving equipment and mining machines are the centerpiece of the show. Preassembly for the largest pieces begins on August 6, 2012.

Jan 1, 2013

The mining industry is an important economical factor in Vietnam. Mining is presently being conducted at about 60 locations and at over 1000 mines. Petroleum extraction and coal mining are the most important parts of industry though metals such as zinc, tin, chromites, iron are also extracted. Last year the sector produced 20 million tons of crude oil, 26 million tons of coal and 500,000 tons of apatite. In particular, Vietnam is one of the world?s largest producers of anthracite, and it is one of the top producers of ilmenite and zircon in the Asia-Pacific region. The government intends to increase the mining production on all levels, however, at present one can observe adverse impacts of the mining activities on the natural environment such as insufficient waste dump rehabilitation, occurrence of acid mine drainage, mining subsidence and emissions as well as lack of appropriate water treatment facilities. This paper describes the current mining situation, future perspectives, the major environmental challenges of the country and approaches to solve these problems. Particular emphasis will be given to the research project ?RAME ? Research Association on Mining and Environment in Vietnam?, a venture carried out by universities, research centres and industry. This project is worked out in collaboration with the national Vietnamese coal and industrial minerals company VINACOMIN.

Jan 1, 2006

By W. R. Tyson

IT HAS BEEN KNOWN for many years that alloy steels can become brittle when tempered in the range of 350-600°C, or cooled slowly after heating to higher temperatures. The metallurgical literature reveals that blacksmiths were aware as early as 1883 that water quenching was necessary after heat treatment above 600°C to avoid brittleness. It has also been known for years that the problem is associated with trace impurities; a paper in the Journal of the Iron and Steel Institute of 1894 refers to the brittle, faceted fractures that occur in steels containing arsenic, phosphorus or sulphur. However, definitive investigation of the mechanism of embrittlement has been possible only within the last decade with the introduction of new experimental techniques to investigate surfaces, especially Auger electron spectroscopy. It is now possible to study in detail the chemistry of surfaces with a resolution of an atomic layer or two, and enormous progress has been made recently in studying the segregation of impurities to grain boundaries by exposing the boundaries by fracture inside the microscope. A clear picture of the processes occurring and their interpretation is now emerging, as was particularly clear at the recent 1977 ASM Materials Science Seminar on Interfacial Segregation held in Chicago in October. Recent research in this area has pointed the way for commercial exploitation of this new knowledge and experimental technology. It is the purpose of this article to trace progress in understanding temper embrittlement and to indicate other areas where control of interfacial segregation and its effects can be important in metallurgical applications.

Jan 1, 1978

By James P. Ludwig

While we are all aware of the need for reclamation of mine sites, few managers and engineers seem to be aware that good reclamation begins with the earliest plans for mining and processing of ores. Far too often the attitude that reclamation is an add-on to worry about at the end of the mining process dominates the thinking of mine engineers and management, A common result is that the reclamationist can be faced with mining and waste disposal designs that are nearly impossible to deal with effectively from an ecological perspective. Everyone of us has been victimized by the down time and maintainence cost that resulted from the purchase of an outwardly attractive, but poorly designed piece of equipment. When confronted by design defects in equipment, a distraught owner can always trade it in, call a consumer advocate, or follow up one of the "lemon laws" at either the federal or state level. A poorly designed mine for reclamation purposes usually cannot be treated either with ease or cost effectiveness. Good reclamation can be effectively prevented by the designs used when the mine was planned. The purpose of this paper is to share some of the experiences our firm has had with reclamation projects at mines in the Upper Midwest as these were influenced or controlled by mine design decisions. My aim is to sensitize mine planners and managers to planning processes they should consider, and hopefully use, early in the mining process to assure successful reclamation during and after mining. Many of the examples I will cite are from experience gained at the recently closed Jackson County Iron Company taconite operation at Black River Falls, Wisconsin. I am particularly grateful to Mr. Vern Metzger, mine manager at JCIC, for his unflagging support of good reclamation practices, employee training programs (which have included reclamation techniques), and his forebearance to put up with our group of ecologists. I realize that this was a time when there were significant internal and external pressures to cut all costs including reclamation efforts. The collaboration has been successful as you will soon see.

Jan 1, 1984

By J. B. Hiskey

Thiourea is a reagent capable of complexing gold and silver. With the proper oxidant, thiourea can effectively dissolve metallic gold and silver. A thiourea leaching system possesses potential advantages over conventional cyanidation including acidic solutions instead of alkaline, cationic complexes in contrast to metal-cyanide anionic complexes, and faster leaching rates with acidic solution of thiourea. Generally, the rate of metal dissolution in thiourea solutions is fastest when ferric ion is employed as an oxidant. Acidic thiourea solutions for certain applications could offer a nontoxic and noncorrosive option for processing gold and silver. This paper provides information regarding the fundamental chemistry of the acidic thiourea system, and reviews the dissolution of both silver and gold in acidic solutions of thiourea. The recovery of gold and silver from acidic thiourea solution is discussed.

Jan 1, 1981

By R. B. Schluter

The objective of this Bureau of Mines investigation was to determine the effects of adding manganese compounds and ores to iron ore pellets. Manganese dioxide, carbonate, sulfate and chloride, plus six manganiferous ores from the Minnesota Cuyuna Range were tested as additives to increase the manganese content of iron ore pellets. One to 5 percent manganese, as a compound or ore, was added to five magnetite concentrates and one hematite concentrate. These concentrates were ballad, indurated (1,300° C), and tested for reducibility. Manganese sulfate and chloride were unsatisfactory additives causing cracking and degradation of the pellets during reduction. Manganese dioxide, carbonate, and the ores were satisfactory additives. The additives increased pellet compression strengths with a corresponding loss of reducibility, as compared to the pellets without manganese additions. The changes in compression strengths and reducibility were caused by the formation of Jacobite spinel and slag within the pellets. However, when the induration temperature was lowered from 1,300° to 1,200° C the reducibility and compression strengths were comparable to the pellets without manganese additions indurated at 1,300° C.

Jan 1, 1974

By Z. D. Hora

"There has been a number of new developments in British Columbia's industrial minerals field over the past few years. Several new industrial operations were started to diversify the line of British Columbia mineral production by magnesite, perlite and fuller's earth. Industry activities and geological projects have identified occurrences of rare earth minerals, niobium, kaoline, fireclay and zeolites. The Geological Survey Branch significantly improved its database on industrial minerals. New geological concepts based on recent work are opening a number of new opportunities f or further industrial minerals' exploration and development in British Columbia.IntroductionTraditionally, the value of industrial minerals produced in British Columbia in any given year comprises between 100/0and 15% of the combined value of minerals, coal, petroleum and natural gas. Over the years a wide variety of industrial minerals has been produced , often with different levels of marketings success. For some products, such as dimension stone and clay or shale products, initial strong demand gradually dissipated; for others such as asbestos and magnesite, new discoveries or new industrial activities created demand and new markets . In some cases, such as fluorite , talc, pyrophyllite and perlite, wider use has been prevented by small size, poor quality or remote location of the deposits. Also, British Columbia , with 2.6 million inhabitant s, provides only a limited market and the industry therefore has to look beyond provincial borders."

Jan 1, 1990

By D. T. White

"Metallurgical extraction processes often call for the heating of aqueous slurries. Indirect heat exchangers are generally not feasible for service with high yield stress slurries because of low heat transfer rates. It is more appropriate to heat the slurry by direct contact, typically with steam as the heating medium. Although having a long and successful history, direct-contact heat transfer to aqueous slurries has been used without the support of pilot plant research. This paper provides results of the needed research, the work being done at a scale large enough to enable direct scale up to commercial operations. A pilot plant heater was constructed and tested to develop an understanding of the slurry heating process and to ensure that commercial scale heaters were appropriately sized.INTRODUCTIONPressure Leaching OperationsPressure leaching operations are often used to oxidise sulphide gold ores, or for extraction of nickel and cobalt from laterite ores with sulphuric acid. Where there is sufficient sulphur available, the exothermic pressure oxidation reactions can be self sustaining at temperatures as high as 225 ºC, without having to preheat the feed slurry. At lower sulphur levels, slurry preheating is required. This is typically achieved by utilising the flash steam released from the slurry letdown stages and contacting this directly with cold incoming slurry ahead of the autoclave. The vessels where this slurry-steam contact is made are known as heaters or condensers, with the number of pre-heat stages varying, depending on how much heat is evolved in the oxidation reaction (Mason, 1990).In nickel laterite pressure acid leaching processes, which operate between 245 and 270 ºC, the only significant exothermic reactions are those associated with dilution of sulphuric acid in the leach. As a consequence, slurry preheating with flash steam is always used commercially. In practice the number of flash steam preheating stages required varies from 1 to 3, driven by a number of factors, including other uses for flash steam and the upper temperature limit at which preheated slurry can be pumped. A diagram of a typical pressure acid leach train is shown in Figure 1.For pressure acid leaching operations and at low sulphur levels in pressure oxidation, boiler generated direct steam addition to the autoclave is required to sustain the reaction temperature. For this reason it is imperative that the flash steam – slurry heat transfer is efficient and the slurry temperature approaches that of the flash steam closely."

Jan 1, 2012

By Ravi S. Bellur-Ramaswamy, Daniel A. Tortorelli, Robert Haber, Nahil A. Sobh

We optimize continuous quench process parameters to produce functionally graded aluminum alloy extrudates. To perform this task, an optimization problem is defined and solved using a standard nonlinear programming algorithm. Ingredients of this algorithm include 1) the process parameters to be optimized, 2) a cost function: the weighted average of the precipitate number density distribution, 3) constraint functions to limit the temperature gradient (and hence distortion and residual stress) and exit temperature, and 4) their sensitivities with respect to the process parameters. The cost and constraint functions are dependent on the temperature and precipitate size which are obtained by balancing energy to determine the temperature distribution and by using a reaction-rate theory to determine the precipitate particle sizes and their distributions. Both the temperature and the precipitate models are solved via the discontinuous Galerkin finite element method. The energy balance incorporates nonlinear boundary conditions and material properties. The temperature field is then used in the reaction rate model which has as many as 105 degrees of- freedom per finite element node. After computing the temperature and precipitate size distributions we must compute their sensitivities. This seemingly intractable computational task is resolved thanks to the discontinuous Galerkin finite element formulation and the direct differentiation sensitivity method. A three-dimension example is provided to demonstrate the algorithm.

Jan 1, 2001

By C. C. Herrick

The vapor pressure of indium has been measured by the torque-effusion technique, as a function of temperature between 1102o and 1422oK. For liquid indium, the vapor pressure (in atmospheres) can be represented by the equation -R In P = 5.782 x104/T - 25.29from 1000o to 1422oK. Extrapolation yields a calculated normal boiling point of 2329°K and a heat of vaporization at 298 oK of 58.09 kcal per mole by the third-law method and of 58.39 kcal per mole by the second-law method. Calculations indicate that the free-energy functions of Hultgren are to be preferred to those of Guruich. BECAUSE of the potential uses of liquid metals, it is important that convenient experimental methods be developed which will lead to a sufficient body of thermodynamic data so that reasonable estimates of properties of liquid metals can be made. Indium is particularly well-suited to investigation, since it remains liquid over a long temperature interval, it alloys readily, suitable containers for it are easily procured, and relatively few investigations of its thermodynamic properties in the region above 1000°K have been made. PREVIOUS RESEARCH The first determination of the vapor pressure of indium was made by Anderson,' using the Knudsen method and silica-lines stainless-steel cells. Kohlmeyer and spandau2 determined the normal boiling point, and a mass-spectroscopic investigation has been made by Lyubimov and Lyubitov.3 (Unfortunately, only an equation representing the data of the latter investigators has been available to us.) Hultgren et al.4 and Gurvich5 have published discordant tables of the free-energy functions for indium. EXPERIMENTAL METHOD The torsion-effusion principle has been described amply in the literature.8,7 With this method, one observes the angular deflection induced by effusion of vapor from a multihole effusion cell which is suspended from a filament producing a small rotational restoring force. The pressure within the effusion cell can be computed from the relation ziaifiai where k is the torsion constant of the filament, 6 is the observed angular deflection, and ai, fi, and qi are the area, force factor, and moment arm of the ith effusion orifice. The force factor f is analogous to the Clausing factor,' and corrects for the reduction in effusive force attributable to the finite geometry of the effusion orifice. Schultz and Searcy' have tabulated the force factors for various tube geometries. EXPERIMENTAL APPARATUS The physical arrangement employed in this study is shown in Fig. 1. The furnace elements are six Globar heat rods with 15-in. hot zones. Temperature is maintained to * 1°K by a Beck mechanism driving two 26-amp Powerstats in parallel. A Pt (Pt, Rh 10 pct) thermocouple serves as the sensing element. Four inner tubes act as vibration isolators; the air pressure required for maximum isolation was determined empirically, and is maintained by a solenoid valve. The tungsten fiber, 9 by 0.002 in., is joined to an 0.008-in. tungsten wire or graphite rod via a machined lightweight chuck.

Jan 1, 1964