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By Arthur F. Taggart

RECENT jig practice has shown such marked departures from the pronouncements of the textbooks, particularly as to particle size recovered and size range of feed, as to make it desirable to reexamine the mechanism of jig action. This paper presents the results of such a study. The general conclusions of the paper are: I. A jig bed is a bi-functioned as well as bi-parted body. The upper layer comprises a plastic stream moving slowly in a substantially horizontal direction from feed lip to tail board. It serves to rough out tailing and light middling and to pick up heavy middling and lift it out of the jig box. The lower layer acts as the ultimate separating means by absorbing concentrate and rejecting heavy middling. 2. The separating function of the lower layer is performed in three definitely different ways, depending upon the relative sizes of the grains presented to it and those composing it. EXPERIMENTAL The experimental work consisted of close and long-continued visual observations of operating beds in a plunger jig, eccentric driven, and in determinations of the settling rates of various metal spheres through a quartz bed under various conditions of operation. Falling velocities were measured by an ingenious method devised by A. C. Dorenfeld, a student in the Mining Department at Columbia. Spheres of different metallic alloys, Y8-in. diameter, were cast with a short piece of fine copper wire frozen in to serve for suspension. A short piece of black cotton thread was looped to the top of the wire to serve as an indicator. The set-up for a test is shown in Fig. I. The thread should be boiled, if necessary, to make it freely water absorbent. The piece of clean plate glass D is supported rigidly at the proper height in a vertical position. The white scale E is similarly supported behind the glass. At the beginning of a test, D is filmed with water by holding it (best with clean rubber finger cots) under running tap water. It is then clamped in approximate position and C, already wet, is laid across it and drawn straight and vertical with the upper end at or near the top of D, and the ball A slightly above the top of the expanded bed. The water film holds the string to the glass. For a test the string is released, its upper end position noted just after the top of the ball becomes submerged, when the corresponding time is read, and thereafter simultaneous readings of position and time are taken as desired. Results of the visual studies of the bed are given at the pertinent places in the following discussion. Results of the settling tests are summarized in Figs. 2 and 3. DEFINITIONS The name bed as used herein refers to the entire mixture of solids and water filling the jig box. A layer is a stratum of a bed composed of particles of substantially the same specific gravities. A granular product is long-range when it approximates a crushed or ground product limited as to upper size only; a shorlrange product is one closely sized. A bed is loaded when operating with continuous feed

Jan 1, 1943

Prominent among the ore minerals at Mt. Ellison, in the Brock's Creek district, Northern Territory, are a number of copper-bismuth sulphides wittichenite, aikinite, emplectite, in association with nativebismuth, chalcopyrite, bornite, chalcocite, sphalerite and linnaeite.Linnaeite and aikinite formed first and were followed by native bismuth. Wittichenite was later and substantially replaces earlier minerals. Replacement of aikinite by wittichenite has produced secondaryor reaction bismuth.INTRODUCTIONThe Brock's Creek district of the Northern Territory lies to the south east of Darwin and has been the locale of intermittent mining of small but rich deposits of diverse ore type. Gold, tin, and copper ores were recovered especially between 1890 and 1910 with minor exploitation up to the present time. Copper ores were of prior importance, the main production coming from supergene enriched deposits of chalcocite.The mines are situated in strongly folded Precambrian strata comprising slates, sandstones, volcanics and amphibolites with replaced haematitic rocks (Sullivan, 1953). The strata in the Brock's Creek area immediately north of the Darwin-Birdum railway line are domed around a roughly circular granitic mass some 5 miles in diameter. The Mount Ellison mine is located near the N.E. margin of the granite in metamorphosed basic country rock.Study of a series of polished sections from Mt. Ellison revealed the presence of linnaeite, chalcopyrite, bornite, aikinite, wittichenite, emplectite, bismuth, sphalerite, and chalcocite. With the exception of sphalerite and emplectite each of these minerals is prominently developed and intimately intergrown with the other constituents.

Jan 1, 1963

THE refining period of an open-hearth heat blends imperceptibly into the finishing period, during which final adjustments are made in slag composition, in bath action and temperature, and in composition of the steel, in order to prepare it for casting into ingots. Operations must be governed by the consideration that alterations in the character of the heat during the finishing period must be held to a minimum. In a broad sense, the finishing and deoxidation period of a heat may be said to be- gin when the action of the last ore addition has ceased, and to end when the teeming of the ingots is completed. INGOT STRUCTLIRES A survey of the relative advantages and disadvantages of different types of ingot structure is required because deoxidation treatments during the finishing period control the amount of gas evolved during solidification and consequently determine the type of ingot structure. Four classes of ingots are recognized, de- pending upon the degree of deoxidation to which the steel has been subjected. These types are killed, semikilled, capped, and rimmed; typical examples of their structures are represented by ingots 1, 2, 5, and 7, respectively, of Fig 9-1. The actual ingots from which these cross sections were sketched were all poured to the same height (indicated by the dotted lines) in the same type and size of bottle-top molds. The eight drawings of the figure represent selected types of ingot structure in a continuous series from "dead killed" to "wild," resulting from variations in the total quantity of gas evolved, from none at all to copious amounts, during solidification of the steel in the mold. Killed and semikilled steels are adjacent at the "quiescent" end of the ingot structure series where only small amounts of gas are evolved. The term "quiescent" describes the action of the molten metal during and subsequent to the teeming of killed and semikilled steels. Capped and rimmed steels are adjacent at the

Jan 1, 1964

By W. C. Brice

Minnesota contains a major copper-nickel resource. In anticipation of requests by industry to develop this resource, the Minnesota Department Of Natural Resources has developed a computerized resource inventory and analysis system, MINESITE This extensive database is available to regulatory agencies as they evaluate mining proposals as required by law. The Resource Analysis phase of the project allows state mining policy decisions to be evaluated in terms of long-range effects on Minnesota's mining industry and environmental and land use impacts. The analysis also allows for comparison of proposed mine facility sites to a representative range of sites in terms of engineering, site characteristics, and land use and environmental impacts.

Jan 1, 1980

By Caibin Wu, Ali Lei, Ningning Liao, Jingsheng Ye

"The particle size distribution characteristics of ground product can influence the quality of the classification overflow and the next beneficiation indexes in an ore concentrator. Usually, the size distribution of ground product is considered to be determined by that of new ball mill feed. However, based on large amounts of data from industrial grinding circuit surveys, this paper has clearly shown that the size distribution of ground product should be determined by the size characteristics from classification underflow unless the circulating load was small, because the new feed is an important component and occupy a dominant position of mixed ore from belt feed and classification underflow. On the other hand, the correlation coefficient of the size distribution between ground product and classification underflow can be more than 0.99 when the relevance principle and its method are used. Meanwhile, their P80 value also keeps a synchronous correlation. The greater the capacity of classification underflow is, the higher the correlation of size distribution between the ground product and the mixed feed is. Furthermore, the correlation coefficient of the size distribution between ground product and classification overflow which is from primary or secondary can be 0.96. It is another discovery that the correlation coefficient is related to the type of classifier. The coefficient of size distribution of overflow and underflow from hydrocyclone is superior to that of spiral classifier, which can explain the reason why the hydrocyclone is widely used to replace the spiral classifier in concentrator.INTRODUCTION It is well knows that ball mill circuits closed with cyclones or spiral classifier such as a primary grinding circuit, a secondary grinding circuit and SAB mill have become an industry standard. Which grinding process employed will be determined by the P80 value of ground products. When the primary closed circuit ball mill or SAB that it is different throughout between the two processes was employed, a grinding fineness with -200mesh under 68% will be available. However, the secondary grinding circuit with the fineness of -200mesh above 80% can be conducted. Of course, the grinding fineness is determined by the grain size characteristics of the mineral."

Jan 1, 2018

Laboratory electrical resistivity measurements of rocks are reviewed. Inductive and galvanic methods are discussed together with the ten important experimental factors which should be considered in an investigation.These experimental factors are electrodes, sample preparation, measurement errors, temporal current variations, current density, frequency, electrolyte composition, electrolyte saturation, pressure, and temperature.

Jan 1, 1969

By R. J. Smith

Hornestake's Mclaughlin Mine is the first commercial application of pressure oxidation pretreatment of gold prior to cyanidation. Inherent to the autoclave process are several liquid/solid separations. Flocculant consumption represents a significant portion of the consumable reagent costs at McLaughlan. This paper focuses on the efforts of the Operating, Metallurgy and Engineering groups to improve thickener operation and minimize flocculant consumption. An operating philosophy incorporating feed solids control, increasing flocculant dilution water and minimizing flocculant solution shear has resulted in a reduction in 1986 flocculant costs of $0.054/t ($0.06 st) versus 1985 costs. Additional changes are projected to result in a further cost reduction of $0.20/t ($0.22/.st) in 1987.

Jan 1, 1988

By J. Dorsey

In 1910, Colonel Boyce Thompson, who owned Inspiration (now Cyprus Miami) and various other mining interests, formed the Magma Copper Company and leased the Silver Queen claims around Superior, Arizona. At the same time, he purchased other claims around the Silver Queen claims from what was then called the Magma Mine. The mine continued to operate until 1982 when Newmont Mining Company, who owned Magma Copper Company, shut down the operations due to high costs and low copper prices. When Magma was spun off by Newmont as an independent company in 1987, new studies of Superior were started. It was clear from these studies that the mine had been shutdown and over 1400 employees laid off for two basic reasons: first, as a resu1t of a mine plan that was technically flawed and second, be-cause of very high production costs mainly due to the low productivity from a very high cost work force. During 1989 a plan was formulated to re-open Superior with the determination to over-come the problems that resulted in closure. A new mine plan was developed and a management style developed that promotes team work and high productivity.

Jan 1, 1992

By Kurt Oakes, John Williams

Placer Dome, US operates the Bald Mountain Mine. The Bald Mountain Mine is a surface operation located in remote northwestern White Pine County in east-central Nevada, approximately midway between Elko and Ely. The mine is in the Newark Valley along the southwestern flank of Bald Mountain a part of the Ruby Mountain range, at an approximate elevation of 7,500 ft (2,286 m). The geology at the Bald Mountain Mine is highly altered, both mineralogically, and structurally. Highwall stability and control have long been an issue at the operation, due largely to the varying geologic conditions. In some blasts as many as seven distinct geologic unconformities exist. These unconformities affect both final high wall integrities, as well as blast fragmentation characteristics. A 60 million ton (54.5 million tonnes) layback expansion of the existing “Top Pit” as well as development of a new satellite pit, “Sage Flats”, is being undertaken. Design final highwall pit slopes have been steepened from the traditional 47º to 55º in order to reduce overall ore-to-waste ratios, thereby improving economic viability for the expansion over the 4.5 year life of the project. With the increased usage of electronic detonators throughout the mining industry, mine operations staff, as well as representatives from the mines explosive supplier felt that an evaluation program incorporating electronic detonators would be warranted. The areas of focus for this evaluation would be resultant highwall pre-split integrities, peak particle velocity measurements (both near field and far field), frequency measurements, loader productivity, and visual interpretation of the results. The mine incorporates 25 ft (7.6 m) benches and uses separate trim blasts in conjunction with production blasts in order to reduce blast effects along final highwalls. Hole diameters in production blasts are 7? ” (200 mm). Typical production blast patterns are 18 ft x 18 ft (5.5 m x 5.5 m), drilled in a square pattern configuration. Shot sizes vary greatly, ranging from 200 holes to as many as 800. Bulk low percentage ANFO/emulsion blends are utilized as the redominant blasting agent. Non-electric dual delay detonators (25 ms/500 ms), with non-electric surface delays are the initiation system utilized in production blasts. Typical production blast design

Jan 1, 2004

By X. Song, Q. Zhang

"The development of fracture zones in surrounding rock mass has significant impact on the stability of underground mine roadways. Detection of the fracture zones is of compelling importance for maintaining roadway stability as well as for safe and speedy excavation of the roadways. This paper presents a study conducted at Dong Bao Wei underground coal mine, where the roadways were developed in diabase rock mass. The roadways suffered severe damages, including sloughing and excessive floor heaving. The borehole imaging technique was applied in the study to observe and detect fracture zone development surrounding the roadway openings. Based on the borehole imaging studies, new roadway support systems were proposed to improve the stability. INTRODUCTION At the Dong Bao Wei Coal Mine three main roadways of the west wing were excavated. The three roadways had semicircle arch cross sections and were at a depth of 650 meters, each being about 750 meters in length. The roadways were driven through a section of thick diabase intrusion, which was softened by water with reduced strength and may turn into powder form under weathering. Site investigation indicated that the roadways in diabase intrusion zone were badly damaged due to severe deformation, and very serious roadway sidewall sloughing and spalling accompanied by severe floor heave often occurred.(Figures 1 and 2) In order to ensure the normal use of the roadway, undercuts were excavated. However, this operation seriously affected the roadway construction progress and increased the amount of roadway support operations as well as the roadway maintenance costs. Furthermore, a roof fall accident occurred in nearby drilling site. The investigation indicated insufficient support provided for the roadways which imposed significant safety hazards and would have serious impact to mining production and subsequent mining activities.The support of the main roadways is a critical task and is the focus of the underground opening excavation work at the mine, since more than 40 years of service life is required from these main roadways. For these roadways, large cross sections with high degree of stability and minimal amount of deformation should be maintained. Therefore, providing sufficient and appropriate roadway supports is of significant importance to the coal mine. In this paper, in order to optimize the roadway supporting system, studies were carried out on the geological structures, lithological characters, roof bolt anchoring features and suitable anchoring layers. The studies were aimed at ensuring the stability of mine roadways, reducing the roadway maintenance costs and providing a safe mine passageway for orderly production and progressive development of the mine"

Jan 1, 2016

New and more cost-effective methods of haulage and hoisting will be needed to develop the underground mines of the future. A review of the development of technology since the 1950s shows that once mechanised equipment became available it took 25 years for appropriate mining methods to be developed and the equipment made reliable, then a further 25 years to reach todayÆs level of automation and reliability. Suggestions are made about possible areas for ongoing research with the observation that there is little research worldwide into disruptive technologies. A call is made for better organisation and presentation of the opportunities and potential benefits of new underground mining technologies.

Jan 1, 2005

By S. Vela, R. M. McKinley, L. A. Carlton

Johnson et al. have described a new well-testing technique that measures formation flow properties between wells.' The technique, called pulse-testing, requires a sequence of rate changes in the flow at one well and measzcrement of the re.rulting pressure changes at an adjacent well with a very sensitive differential pressure gauge. This paper describes an extensive application of the technique in a producing oil field. Pulse-tests on 28 of 45 possible well pairs in the field provided a picture of the areal distribution of reservoir hydraulic diffusivity, trans-missibility and storage. The primary objective in presenting these data is to demonstrate the potential of the methcid for reservoir description. A second objective is to show in three ways the qualitative and quantitative accuracy of reservoir parameters determined from pulse-tests: (I) pulse-test data show a nonuniformity in the field, closely correlating with the oil-water distribution as given by production data: (2) pulse-test values for permeability are comparable with core va1ue.s; and (3) perhaps most important, the field responds to a conventional interference test in the manner in which pulse-test data predict it should. The pulse-testing technique by Johnson et al.' is an ideal source of data for purposes of reservoir description, for it provides a measurement of formation storage S = +ch, hydraulic diffusivity 91 = k/+cp and transmissibility T — This paper describes an application of this method in a producing oil field. Results were analyzed to give numerical values for the parameters 7, T and S. These values were compared with oil-water production data (for the effect of fluid saturation), with core data and with data from an interference test. The reservoir in which the pulse-test survey was run is the result of a structural trap formed by a fault along the east side of a north-south trending anticline. A down-structure aquifer providcs a natural flank water drive for the pool. The producing formation is a dolomitic lime- stone having mainly vugular permeability; the formation oil has a gravity of 29" API with negligible dissolved gas. The field contains 19 wells, all on pump, arranged on 40-acre spacing along the top of the anticline. Fig. 1 shows the location of all these wells except two at the south end of the field. The dashed line on the right-hand side of the figure represents the approximate location of the fault with respect to well positions. Pulse-Test Survey and Analysis of Data A pulse-test requires a pulsing well and a responding well. In the field, changes were made in the rate of flow at the pulsing well by stopping and starting the pump periodically and measuring the corresponding pressure

Jan 1, 1969

By S P. Young, K R. Monro

Reducing metal prices have forced mining operations to become more efficient and innovate in order to do more with the existing base. Much of this effort has focused on improving the efficiency of load and haul operations. The key to this is to understand and quantify where delays and missed opportunities exist. Metrics such as utilisation of availability, efficiency utilisation and asset availability are helpful indicators of performance; however, uptime-based time usage models and performance analysis tools using productive operating time models help to identify additional improvement opportunities.Phu Kham is a copper-gold mine operated in the Lao People’s Democratic Republic (Laos) since 2008 by PanAust Limited. The mine is a single large open pit of 450 m depth, running a fleet of 51 100 t class rigid dump trucks and 300 t and 200 t shovels controlled with the aid of a fleet management system in order to achieve ex-pit material movements of 56 Mt/a.Commencing in late 2014, a range of initiatives were implemented in order to improve the efficiency of the mine haulage fleet. These include hot seating of all operator changeouts via changeout ramps, split shifting of crews to minimise queuing delays, maximising blast volumes and minimising blast event days to reduce blast exclusion delay events including opportune refuelling of equipment during blasting events, inspections of trucks during refuelling events, implementation of a dedicated haul road services team to help reduce wet weather related delays and infrastructure development for haul path efficiency improvements.These and other initiatives have allowed the mine haulage fleet utilisation of availability (UofA) to be sustainably increased from 85 per cent to 97 per cent (see Figure 1), efficiency utilisation to increase from 85 per cent to 90 per cent, and productive operating time (POT) to increase from 73 per cent to 84 per cent. The corresponding increases in efficiency of the haulage fleet has allowed an equivalent reduction of eight haul trucks from the fleet to meet continuing life-of-mine production requirements.CITATION:Monro, K R and Young, S P, 2016. Truck haulage improvements at the Phu Kham mine – the journey to 97 per cent utilisation of availability, in Proceedings International Mine Management Conference, pp 339-346 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jun 22, 2016

By P. L. M. Wong, N. W. Johnson

Surface analysis by X-Ray Photoelectron Spectroscopy (XPS) of samples taken from the galena flotation section of the Hilton Concentrator of Mount Isa Mines Limited are presented. Flotation rate and pulp chemical data taken during the sampling period are also presented and discussed. Surface analysis suggested that, under normal operating conditions, an overlayer of precipitated calcium sulfate existed at the surface of the sulfide minerals. In particular, there was a decrease in the surface concentration of calcium sulfate for the concentrate samples relative to that occurring on the tailing samples. This suggests that the flotation process was selective against minerals which have calcium sulfate predominating at the surface. Heterocoagulation of hydrophilic calcium sulfate on to the galena surface considerably reduced galena flotation rate. Methods to control calcium sulfate precipitation, which include sodium carbonate treatment of the pulp, are also discussed. Sur- face analysis results of samples taken from the Hilton Concentrator during sodium carbonate addition to the grinding circuit are also presented. This shows clear evidence for the removal of calcium sulfate from the mineral surfaces without concomitant surface precipitation of calcium carbonate. Reasons for the apparent dispersion of precipitated calcium carbonate are discussed. Galena flotation rate was increased by the addition of sodium carbonate apparently due to the removal of interfering calcium sulfate.

Jan 1, 1995

By P. A. Anderson

Innovative solution management is being used at Coeur-Rochester, Inc. to increase bullion production and decrease overall costs. New operating programs call for reduced solution application rates to the heap to increase pregnant stream values at a lower and less costly plant flowrate because silver and gold extractions are equal regardless of leach solution application rate. Solar heating is used in the summer months to increase the core temperature of the heap for use in the winter months thus increasing silver extraction rate. This paper outlines the programs now in effect and the savings incurred because of them.

Jan 1, 1989

By Paula Maria Gomes Cunha Leão

Um modelo matemático tridimensional, via software Fluent 14.0, de modo a descrever o fluxo, em regime transiente e isotérmico dos fluidos escória e nitrogênio, foi utilizado para avaliar o comportamento de slag splashing em um convertedor a oxigênio com o propósito de reparar as regiões desgastadas do revestimento de trabalho deste reator. Para um dado padrão de sopro foi investigou-se o efeito de parâmetros tais como temperatura, densidade, viscosidade e tensão interfacial. Os resultados são comparados com dados de projeção disponíveis na literatura.

Aug 16, 2017

By Narendra N. Khatri, Michael Deutscher, Jozef F. Zurawski

Five sewer connections were required to divert Combined Sewer Overflow (CSO)from existing outfalls to an old underutilized large diameter brick sewer (the Easterly Interceptor). The connections were part of an on-going CSO control program by the Northeast Ohio Regional Sewer District (NEORSD) in the City of Cleveland, Ohio. Each connection was made by pipejacking and hand-mining a fiberglass-reinforced polymer (FRP) pipe through soft glaciolacustrine clays and silts. Jet grouting was utilized to stabilize the soils and fill the voids surrounding the interceptor prior to making the underground connection. Reinforced concrete liners were constructed inside the aging brick sewer to provide structural stability during ground improvements and connection work. The project also involved micro tunneling two approximately400 foot lengths of FRP pipe through soft ground using a slurry pressure balanced machine.

Jan 1, 2005

Sandsloot open pit is situated on the northern limb of the Bushveld Complex, 250 km north east of Johannesburg, South Africa. Sandsloot is currently the largest open pit platinum mine in the world and is one of six potential open pits in the area. The geotechnical strength properties of the Platreef have posed significant mining and processing challenges to the PPRust operation since inception in 1992. In order to optimize the whole business as opposed to isolated cost centres a mine to mill initiative was embarked upon in 1997. Initial work focused on ore characterization and an entire suite of data was collected for each rock type. This included mineralogy, geochemistry, geotechnical, blast ability indices, as well as metallurgical strength data. The second phase involved the clear definition of customer requirements, namely the optimum performance criteria for the plant and mining departments. This involved extensive field trials and data capture to measure the interaction and influence of the mine to mill value chain. Once the design targets were defined, a 3D geotechnical model was constructed to ensure that the targets were consistently achieved. The model is very similar to an ore reserve model; however, it is populated with geotechnical, metallurgical and blast index data. Through software queries the appropriate blast powder factor for each mining block can be obtained, thereby ensuring the correct fragmentation is blasted for the plant and mining operation. The initiative has delivered significant results showing improvements across the mine to mill value chain. These include increased loading rates, reduced electricity and crushing consumables, as well as higher plant throughput. Additionally, the initiative has benefited both brownfield and greenfield projects on the PPRust operation

Jan 1, 2006

By Kris Inwood

"In 1879, when the Dominion government initiated its controversial program of industrial promotion, iron smelting in Canada was limited to one company producing coke iron on the mainland of Nova Scotia and three small charcoal blast furnaces in Quebec. There was no steel production. By the eve of the First World War, iron and steel were being produced in very large quantities, the companies active in 1879 had disappeared and new centres of integrated iron and rolled steel production at Hamilton, Sydney and Sault Ste. Marie had come to resemble the industry as we know it today. The most dramatic change was that at Sydney, Nova Scotia, where in the early 1900s, two steelmaking companies established works. The Sydney developments have been explained as the result of resource discovery and technical change. W.J. Donald, in his authoritative account of the Canadian iron and steel industry, observes:(1) ""The most rapid growth of the Canadian iron and steel industry has occurred since 1897 ... The remarkable growth has been caused largely by the new conditions of the industry. The discovery and use of Newfoundland ores, together with the availability of Cape Breton coal, has made the Nova Scotia industry not only possible but profitable .... It is a safe conclusion that the Canadian industry would not have been an important one, had it not been for the discovery of the Michipicoten and especially the Wabana (Newfoundland) ores:' Donald also argues that metallurgical progress had been necessary to render the ores valuable. ""Newfoundland ores ... contain a considerable amount of phosphorus, and were made available for steel-making by recent inventions:' The purpose of this paper is to re-examine Donald's story. It will be argued that the origin of steel-making at Sydney is somewhat more complicated than Donald has indicated. The difficulty with Newfoundland ore extended beyond its phosphorus content and a resolution required more than the basic open hearth furnace identified by Donald. Moreover metallurgical change was only one of several developments necessary to induce industrial investment at Sydney. Surprisingly, however, the discovery of iron ore in the late nineteenth century does not appear to be part of the explanation."

Jan 1, 1999

By E. Swartzman

THE free-swelling index, a numerical value for the free-swelling properties of coal, is being used to an increasing extent in specifying coal for burning in various types of equipment. The empirical standard ASTM method for determining this index uses, as a source of heat, a gas burner which requires frequent calibration because gas pressures are not constant, relatively small changes in gas pressure resulting in rather wide variations in the temperature attained in a crucible and thus in the resultant size of the coke button. Furthermore, the quartz crucibles specified for the test are not standard equipment, and relatively small variations in dimension and wall thickness from those specified often result in rather wide variations in the resultant size of the button.

Jan 10, 1951