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By R. G. Hudson, H. W. Paxton

The activities of iron and chromium in their binary system have been measured by the Knudsen orifice technique. The system is close to ideal at 1200- 1250 C with slight positive deviations. The effect of this on the liquidus and solidus is discussed and these are calculated for two limiting assumptions. The vapor pressure of pure iron, pure chromium, and one alloy is compared with that obtained by the Langmuir free-evaporation technique. The results agree, indicating a vaporization coefficient close to 1. HERE are no reported data on the thermody-A namic activity of iron and chromium in the solid portions of the phase diagram. It is generally assumed'.' that the liquid solutions of iron and chromium obey Raoult's law. Chen and Chipman" have inferred that the liquid solution obeys Raoult's law. The minimum' in the solidus-liquidus curves for the iron-chromium system shows that there are deviations from ideality in either the solid or liquid or both. Because of the importance of developing reliable techniques for obtaining activity data in alloy systems at high temperatures and of the data so obtained, an investigation of the activity of iron and chromium in the binary at 1200-1250 C was undertaken using the Knudsen cell. Experimental The apparatus and experimental procedures used in this investigation were described in a previous paper." The various materials used for the construction of the Knudsen cell are listed in Table I. The metal used for the determination of the vapor pressure of chromium was 99.9 pet pure, obtained from A. D. Mackay, Inc. The iron was obtained as electrolytic grade from Fisher Scientific Company. The Fe-Cr alloys used are shown in Table 11. The largest error and controlling factor in the accuracy in the experiments reported here are introduced because of temperature uncertainty, which is estimated to be ±3 deg C. This introduces an uncertainty of 26 pet in the measured pressure. Experimental Results and Calculations The vapor pressures of pure iron and pure chromium were calculated from the measurements by the Knudsen equation3 on the assumption that only Cr or Fe atoms were present in the gas phase. For metal vapors, at the high temperatures and low pressures involved in these measurements this should be a reasonable assumption. Whitman" corrections for the cells were made. The data and results of pressure calculations are presented in Table I, and are plotted in Fig. 1. In addition the heat of vaporization at the absolute zero, ?E°°, has been calculated for chromium. These calculations are summarized in Table 111. The data used in these calculations are as follows kelley13 (F° - E°°/T ) Speiser, et al H (F° - E°°/T ) 010 where F" — standard free energy at temperature T It was necessary to calculate the total pressure above the alloys from the total weight loss W of the cell during a run, because of the fact that all attempts to collect and analyze the chromium and iron vapor effusing from the cell in the apparatus available failed. The failure resulted from the re-

Jan 1, 1959

By N. A. Gokeen, M. Ohtani

EFFECT of elements on the solubility of carbon in liquid iron is useful in calculating and correlating a number of thermodynamic properties as shown elsewhere in detail.' Kitchener, Bockris, and spratt2, and later Turkdogan and Hancock3 have investigated the effect of sulfur on the solubility of carbon at various temperatures and concentrations. For any chosen sulfur concentration, the solubility of carbon reported by Kitchener et al. is considerably lower than that by Turkdogan and Hancock. It was therefore felt that a reinvestigation of this problem was necessary. EXPERIMENTAL METHOD An alloy of Fe-C-S .was prepared with electrolytic iron and ferrous sulfide melted by induction in a graphite crucible, 4 in. high 1 1/2 in. ID under a CO-atmosphere. The temperature, held at 1500" ± 5°C in all experiments, was measured with a Pt-Pt + 10 pct Rh thermocouple immersed into the melt. In order to assure saturation with carbon, the melt was stirred with a graphite rod. After approximately 1 hr at 1500 °C, a sample was obtained by sucking the melt into a silica tube, 4 mm ID. The sample was then analyzed for carbon and sulfur by usual methods. RESULTS The results are presented in Table I and plotted in Fig. 1 with the individual values of Turkdogan and Hancock.3 Scattering in the data is equivalent to 3 pct or less in carbon analysis. The broken line represents the empirical equation obtained by Kitchener et al. from their data. It is evident that the present data are in good agreement with those of the former investigators but in disagreement with the latter. The cause for this discrepancy cannot be readily offered since the experimental methods in the three investigations were nearly identical. Additional evidence corroborating the author's results may be presented in the following manner. The difference between the solubilities of carbon in the ternary Fe-C-X melt with a small concentration of any element X, and in the binary Fe-C melt is %?C = %CIII-%CII [1] where %?C is the change in solubility, and %CIII and %CII are the solubilities in the ternary and the binary systems respectively. The value of %Cii

Jan 1, 1961

By Murali Gadde

Among different types of ground control problems associated with underground coal mining, those related to in situ stresses are the most common ones affecting the safety and economy of a mining operation. As a result, this has been the focus of many ground control research works done in the last three decades. This paper summarizes a recent work done on in situ stress related ground control issues of underground coal mine development workings. The approach used in this study was three¬-dimensional finite element modeling by an implicit code, ABAQUS/Standard. In the models, roof stability evaluations were made using Hoek-Brown rock mass failure criterion. Influence of the in situ maximum horizontal stress angle on the stability of both entry and intersection was examined to help determine the best development layout orientation. Also, the effect of in situ stress ratios on the stability of development openings was studied. To make the work more general, both 'low' and 'high' in situ stress fields were considered In general, the modeling results indicated that entries oriented in the direction of maximum horizontal stress were in the best condition while those oriented at 90° had the least stability. For intersections, the maximum and the minimum stability were seen at 0°/90° and 45°, respectively. However, under some combinations of input conditions, the best or the worst conditions were noticed at same other orientations as well. Based on these findings, layout design charts were prepared for both entries and intersections. It was also found that the change in ground conditions with change in layout orientation was more significant for 'low' in situ stress fields than for the higher ones. Change in the average safety factor with change in the ratio of in situ maximum horizontal to vertical stress resembled a lognormal distribution curve. However, the effect of the ratio of in situ maximum to minimum horizontal stress lacked such a clear trend for different input combinations considered.

Jan 1, 2004

By A G. L Pratt, M S. Kemp

BHP has used many innovative techniques when recruiting its workforce for the Cannington Project. Looking for a balance of experience and enthusiasm it was necessary to develop pre-selection tests to reduce the initial number of applicants to a manageable number for first interviews in Townsville. Success at this stage led to an applicant, and their spouse, to go through a second interview at the mine site. The full process from application to job offer took up to six months, but the results were felt to be worth the effort. The approach taken has resulted in a highly motivated and flexible workforce. This paper outlines the philosophies behind CanningtonÆs recruitment process, highlights some of the issues associated with the approach, and offers some measures of the outcomes.

Jan 1, 1998

By Lawrence Veiller, D. Eppelsheimer

D. Eppelsheimer, * Middletown, Ohio.—The housing of employees has so many and so varied aspects that in order to reach even an approximately correct solution it is necessary to have in mind a few fundamental principles; but it is not possible as yet to write these housing principles in the clear and correct form that is possible with many of our natural laws. Manifestly, the problem depends first on the kind of people it is necessary to house. What is suitable for the Southern unattached negro is not suitable for the married skilled American. The influx of colored labor has affected quite a number of what were satisfactorily housed communities. The second important factor is the relative proportion of the number of employees to the total employable population of the community in which the industry is located. The employer of a hundred men in a large city has little responsibility in the matter of housing his employees. If he employs 75 per cent. of the employable population in a community of 27,000, as is the case of the company with which the writer is connected, it means a large responsibility. In the establishment of an entirely new plant in a more or less isolated place, the responsibility becomes greater. As engineers, we design and write the specifications for the machinery to accomplish a definite purpose, and proceed to house it, provide the necessary buildings with their accessories in the way of cranes, or heating systems, or sprinkling systems, as the case may be. There is no reason why the operating force should not be built up in very much the same way: design the organization, write its specifications so that the employment department can secure the proper men, and then house that organization with just as much thought and care as is given the plant. In the plant, the various machines will work along certain definite lines and accomplish certain results; but even if we start with the proper organization it takes considerable time to get that organization working together. One of the most important elements to this end is the proper housing of the organization. A man usually spends more time at home than at work. Proper surroundings and a comfortable, convenient house of good appearance exercise an influence that cannot be denied, and an employee situated in such surroundings is far more inclined to follow the policies of his employer and take an active part in furthering them than one dissatisfied with his home and surroundings, which feeling

Jan 1, 1919

APPROXIMATELY 90 per cent of the steel that is melted and refined in the United States and poured into ingots is made in basic open-hearth furnaces, as shown in Table 1-1. The annual ingot capacity of the steel industry reported January 1,1950, by the American Iron and Steel Institute8* was 99,040,160 tons, of which the basic open-hearth process accounted for 85,896,580 tons, 86.7 per cent of the total. The capacity of the individual furnaces varies over a wide range, a large majority falling within limits of 50 to 200 tons (Fig 1-1). Most of the units constructed [ ] since 1942 are in the larger size groups, between 175 and 225 tons capacity.

Jan 1, 1951

By G. B. Shea

In the search for possible future sources of petroleum products, the recovery and utilization of bitumens from the large outcropping deposits of bituminous sandstones in the United States have been under study by the Bureau of Mines for the past several years. The results of laboratory research in the adaptation of the hot-water separation process to recovery of bitumen from bituminous sandstones were reported in an earlier publication, on the Edna deposits near San Luis Obispo, Calif. This publication included analytical data on the cracked products and asphalts obtained from the extracted bitumen and on the cracking and distillation of the bitumen. Comparable hot-water separation tests have been run in the San Francisco, Calif., laboratory of the Bureau of Mines on quarry samples from the large deposits of bituminous sandstones near Vernal and Sunnyside, Utah. The bitumens were isolated from the extracts of the separation plant and analyzed at the Petroleum and Oil-Shale Experiment Station of the Bureau of Mines, Laramie, Wyo. Part I of this report summarizes the general characteristics of the Vernal and Sunnyside deposits and discusses the hot-water separation process as applied to those bituminous sandstones and the results obtained. The separation tests showed that these bituminous sandstones also respond to treatment by the hotwater method of separation. The bitumen in the Vernal sandstone was extracted more readily by the action of hot water than was the Edna bitumen, which greatly simplified plant operation. The Vernal sandstone contains no water-soluble iron compounds, such as were found in the Edna sandstone, and, therefore, required no preliminary water washing. Recovery of bitumen from the Vernal sandstone was about 96 percent.

Jan 1, 1952

By O. C. Blade

This report on the properties of motor fuels sold through service stations in the United states was made in accordance with a cooperative agreement between the American Petroleum Institute and the Bureau of Mines of the United states Department of the Interior. This paper is a continuation of a series made in cooperation with the Coordinating Fuel Research (CFR) Committee of the Coordinating Research Council (CRC), Inc. The first of this series of reports presented data on motor gaso1ines sold during the winter of 1935-36, and succeeding reports described motor gasolines sold during the summers and winters to and including the summer of 1941.3/ No reports were made on motor gasolines sold during the winter of 1941-42 and during the summer of 1942. However, starting with the winter of 1942-43, the semiannual reports were resumed

Jan 1, 1948

Jan 1, 1944

By James E. Berryman

A method is presented for calculating the pressure depletion performance of a gas-condensate reservoir from the original reservoir fluid composition using the laboratory determined pressure-production history and retrograde liquid accumulation as guides. Equilibrium vaporization ratios for this calculation were modified from published data until the calculated dew point pressure and retrograde liquid accumulation agreed with the values observed in the laboratory. The calculated results are compared with the produced gas composition determined by low temperature analysis during constant volume laboratory experiments of pressure depletion behavior. This comparison shows that the calculation procedure is adequate for determination of gas phase composition. Data from field separation tests in low temperature separators are presented which verify the applicability of published equilibrium vaporization ratios for a wide range of separator conditions. INTRODUCTION A reliable prediction of the pressure depletion performance of a gas-condensate reservoir is necessary in determining reserves and evaluating field separation methods. The predicted performance is also used in planning future operations and studying the economics of projects for increasing liquid recovery. Because the flow of fluid in a volumetric gas-condensate reservoir is usually single phase flow, the pressure-depletion per-formake is primarily a function of the phase behavior of the reservoir fluid. The properties of a gas-condensate system of major importance are: (1) compressibility factor at reservoir temperature and pressure; (2) dew point pressure; (3) composition changes of the vapor phase with pressure depletion; (4) recovery of original in-place hydrocarbons at any pressure; and (5) retrograde condensate accumulation. These properties are most generally determined by a pressure depletion-type experiment on recombined separator gas and liquid samples in the laboratory. ldeally the pressure-depletion performance can be calculated from the composition of the original reservoir fluid if the reservoir temperature and initial pressure are known.1,2,3 It has been reported "... comparison of such computations with depletion-type ex-periments on recombined samples in the laboratory have yielded results that appeared to be entirely adequate.". The success of such calculations is determined by the equilibrium vaporization ratios chosen, especially those for the higher boiling point hydrocarbons. It is the purpose of this paper to present a method for computing the change in composition of the vapor phase during pressure depletion by production using laboratory determined properties of the system to guide the calculation and to illustrate the use of the method with data from the Cockfield "D" sand of Washington field, St. Landry Parish, La. Results of field tests and laboratory analysis are included. As a result of this reservoir fluid study, a cycling program has been evaluated, the fidd has been unitized, and the cycling started in July, 1956.

Jan 1, 1958

By Vasily P. Muravjev, Gennady I. Razgildeev

The theory of reliability is a powerful mathematical tool for determining optimum selection of components and application of electrical power to coal mines. In order to make this tool useful, statistical material on equipment life must be gathered and all failures carefully recorded. Statistical data can be applied to new apparatus design and can be used to determine optimum configuration of network and maintenance to reduce costs. Reference is made to underground power systems in the USSR. Technical progress in the last few years has occurred in the design and application of highly productive coal mining and transporting machinery. One of the most important problems facing mining engineers is to increase the availability of the machine to obtain higher productivity. However, machine failures and breakdowns of electrical power supply components cause serious delays in the coal-winning processes. In spite of the fact that electrical equipment and the power supply contribute only a small percentage of direct mine costs, electrical failures as well as power supply delays can result in severe indirect losses. It is necessary, therefore, to consider reliability and safety in the application of electrical equipment underground. To obtain the best results, it is necessary to investigate and evaluate the reliability of the electrical mining components (starters, breakers, motors, cables, etc.) and optimal methods for minimizing maintenance, the desired result being equipment which is efficient and safe. Electrical equipment reliability directly influences economics: the lower the reliability the more frequently failures occur, causing serious working delays and possibly huge economic losses. By the same token, while increasing the number of preventive maintenance calls per unit time might result in fewer failures, thus reducing delays, the cost of making more frequent maintenance inspections will increase; this is one aspect to be discussed in detail. Obviously, failures of identical types of electrical equipment (starters with the same current and voltage, etc.) are influenced variably by different working conditions, environments, quality of the apparatus, maintenance procedures (personnel, frequency, quality), load, and other factors. Hence, the lifetime of identical types of equipment will vary depending upon usage in terms of the foregoing factors. Thus for a given type of electrical component, these factors must be considered quantitatively; the interaction of all these factors are evaluated quantitatively by a statistical method using probability theory. Equipment reliability must be quantitatively determined from a study of equipment life, since no one laboratory test can reproduce all working conditions and environmental effects. Nevertheless, reliability theory applied to electrical mining equipment is a very powerful mathematical tool for selecting as well as evaluating certain parameters. It is necessary to select several reliability parameters so that one can obtain an expression for the total overall economic situation in terms of cost, taking into consideration damage caused by electrical equipment failure and cost of maintenance. To accomplish this result, such characteristics as apparatus lifetime, breakdown idle time, and losses (damages) can be determined quantitatively on a statistical basis. For identical electrical equipment working under similar conditions, the previously mentioned reliability factors are random variables and therefore can be characterized readily by a probability density function. Investigations carried out by the authors in the Kuznetsk Basin (Kuzbas) in West Siberia, USSR, show that the reliability factors of electrical mining equipment are well described by the exponential, normal, or Erlang's distribution in most cases. Mining electrical equipment life is well-described by the exponential law. The distribution of lifetime density is

Jan 1, 1971

By C. H. G. Bushell, G. Brown, C. J. Krauss

1N FLOTATION, copper sulphate is used universally for the activation of sphalerite and marmatite and, to some extent, for the activation of other minerals. The copper activated surface readily adsorbs standard collectors such as the xanthates and dialkyl dithiophosphates whereas untreated zir~ sulphide does not. With the host of reagents available, making a mineral float is seldom difficult. The problem is to achieve selective flotation. In zinc flotation, the great value of copper sulphate results from its ability to activate zinc sulphide preferentially to gangue minerals. At the Sullivan Concentrator of The Consolidated Mining and Smelting Company of Canada Limited, the most abundant gangue mineral in the lead-zinc ore is pyrrhotite, and the zinc mineral is marmatite of somewhat variable zinc to iron ratio. For this Cominco study, selectivity between marmatite and pyrrhotite was therefore the most interesting aspect of copper sulphate activation.

Jan 1, 1961

By R. S. Rickard

Chemical processing of ores has gained new im¬petus in recent years. The reasons are many. They range from the need to process ores that are difficult to beneficiate to the avoidance of pollution. Although many think of chemical processing as a hydrometallurgical operation there are other techniques. An example is chlorination. Chlorination, although examined and discarded by many investigators, is again being considered as a means of extracting uranium1, treatment of silver-lead ores2, and the recovery of base metals from pyrite cinder and ores3. Segregation roasting of copper and nickel ores, a process similar to chlorination, is another chemical treatment being revived.

Jan 1, 1970

By M. Sears, K. Mohamed, J. Addis, J. Wickline, G. Rashed

To better understand the load shedding and the stress transfer on coal pillars due to room-and- pillar retreat mining in deep cover panels, researchers from the National Institute for Occupational Safety and Health (NIOSH) conducted a monitoring field study. Two sites, at overburden depths of 1,000 ft (304.8 m) and 1,500 ft (457.3 m), were selected in a room-and-pillar mine operating in Southern West Virginia. The deformation and stress changes in the roof and two adjacent pillars at each site were monitored during the retreat mining process. The monitoring results and field observations were used to calibrate large-scale FLAC3D models for each site. The calibrated models were used to assess different sizes of roof bolts installed in deep cover areas. INTRODUCTION Deep cover room-and-pillar retreat mining is an important emerging issue that will intensify in the future as shallower reserves are depleted (Mark, 2009; Chase et al., 2002). During pillar retreat mining, the likelihood of local and/or global instabilities increases due to elevated stress levels near the pillar line because of the abutment loading. In the last decade, approximately 31% of the room-and-pillar mining groundfall fatalities in the United States occurred during pillar retreat mining. Between 2013 and 2017, this proportion increased to 55%, of which 50% of these fatalities were due to falls of roof and rib that occurred during pillar recovery (MSHA, 2018). One interesting piece of information about pillar recovery fatalities was that the victim was nearly always under bolted roof. Sheared and broken #5 (5/8-in), fully grouted rebar bolt failure contributed to three of four fatal roof fall incidents that have occurred in deep cover retreat mines (NIOSH, 2010). This claim raised the following question at the study mine: Is it safe to use a 4-ft long #5 (5/8-in) rebar bolt grade 60 at a depth of cover more than 1,000 ft (304.8 m)? There was some concern about shear failure of the #5 (5/8-in) rebar bolt at a depth of cover over 1,000 ft (304.8 m). To answer the question and to reduce accidents and fatalities caused by ground falls due to room-and-pillar retreat mining in deep cover panels, the National Institute for Occupational Safety and Health (NIOSH) monitored the roof and rib deformation and the change in vertical pressure within two adjacent pillars during pillar recovery. The study was conducted at two deep cover sites in a room-and-pillar mine located in Southern West Virginia that operates in the Lower War Eagle (LWE) seam. The monitored sites were selected at 1,000 ft (304.8 m) and 1,500 ft (457.3 m) depths of cover. In this paper, site-1 represents the monitored site at 1,000 ft (304.8 m) of cover, while site-2 represents the monitored site at 1,500 ft (457.3 m) of cover. For this study, large-scale FLAC3D numerical models were calibrated based on both field observations and instrumentation results. The calibrated models were then used to compare the ground response and the induced stresses of two pillars at instrumented sites 1 and 2. The maximum lateral displacement (roof shift) obtained from the calibrated large-scale FLAC3D models was applied to a small-scale FLAC3D bolted models, the safety factor for axial stresses of the simulated roof bolts was calculated at the deep cover sites.

Jan 1, 2019

By F. W. Bond

Predictive ground-water modeling is currently being applied to a wide range of engineering applications. In recent years models have been used to evaluate the effect of large ground-water withdrawals on regional water supplies; subsidence associated with overpumping; siting and design studies for chemical dumps; siting and safety aspects of nuclear waste storage; and heavy metal migration from disposal sites. Similar modeling techniques could be used to analyze water-related problems in the minerals industry such as mine dewatering (both open pit and underground), environmental and pollution control, and process water supply and disposal The objective of this discussion is to describe how ground-water models are being used to assist in the solution of water-related problems outside the industry and to extrapolate that use to mining problems.

Jan 1, 1980

Low metal prices prevailing at the beginning of 1950 stimulated the search for improved mining methods. More experience was gained during the year with such new developments as the jackleg drill, millisecond delays as applied underground, trackless mining, and Diesel powered equipment. One of the outstanding innovations in mining practice was the starting of the Round Mountain "dry land gold dredging operation." The Government is now inviting the mining industry to open up every available source of new metal supply and this circumstance will undoubtedly speed the development of new machines. New methods will also result but it is doubtful if economic efficiency will be at its peak.

Jan 2, 1951

By T. S. Spicer, C. C. Wright, R. G. Bowman

In recent years considerable publicity has been given to the problem of atmospheric pollution by fuel-burning equipment. Legislation has been stimulated and smoke ordinances have been enacted, the provisions of which show a definite trend toward stricter control of the emissions not only from the stacks of industrial fuel users but also from the chimneys of domestic consumers. As a result of war conditions, some slackening in the enforcement of these ordinances may be noted, but this is only a temporary expediency caused by the changes necessary in the distribution of the nation's fuel supplies and difficulties in securing the necessary equipment. Previous trends may be expected to continue in the postwar period. Largely because of the consumer demand for automatic heat, but partly because of the legislation against smoke emission, there has been a marked increase in the use of domestic underfeed stokers with the past decade. When correctly adjusted and operated, these units reduce the smoke emission materially, so that even the high-volatile bituminous coals may be burned with little or no emission of objectionable smoke. Unfortunately, however, the use of the domestic underfeed stoker introduces another problem; namely, fly-ash. Production of Fly-ash The term "fly-ash" is a misnomer, since the fly material is generally a mixture of small carbonaceous particles varying from green coal to coke, and inorganic particles ranging from fluffy ash to small particles of fused clinker. For want of a more comprehensive name, however, the term fly-ash is used throughout this paper to include all the fly material. Even with hand-fired furnaces a certain amount of fly-ash is produced, which necessitates periodic cleaning of the boiler flues or furnace radiator, the smoke pipe, and occasionally the chimney itself. With stoker operations the amount of fly-ash is increased many fold, because of the higher velocity of air travel through the fuel bed. Frequently the amount of this fly-ash attains such proportions as to constitute a definite nuisance to the householder and his neighbors and distracts very materially from the otherwise automatic or semi-automatic performance of the stoker. Virtually all the boilers and hot-air

Jan 1, 1944

By I Grant

On the 1 June 1978, the Town and Country Planning Act 1953 was replaced by the revised and more comprehensive Town and Country Planning Act 1977. The new act brings in some substantial changes to the law affecting regional and district planning, and for the first time makes provision for maritime planning. The importance of the Town and Country Planning Act 1977 to the Mineral industry is primarily in the relationship between Regional Planning Schemes and District Schemes as the needs and resources identified in a Regional Planning Scheme will override the underlying District Schemes. The mineral extraction industry must be recognised as a regional responsibility which draws on the resources of a region to satisfy the demand of the communities within that region rather than a purely local operation within one District.

Jan 1, 1978

By Paul D. Merica, L. J. Gurevich

In connection with other investigations on the properties and characteristics of chilled-iron car wheels, the question as to the best range of annealing temperatures was raised. Chilled-iron wheels are cast with a chill against the tread and the inside of the flange, the remainder being in sand. The composition of the metal is so chosen that under these conditions the trcad and inside of the flange will show white iron to a depth of from 5/8 to in. (15 to 22 mm.), the remainder of the wheel becoming graph itized or gray. In order to relieve the stresses set up during cooling under such drastic conditions, the wheels are stripped from the mold, while still red hot, piled in a soaking pit, and allowed to cool very slowly from their temperature at stripping. Obviously the most suitable temperature for this annealing is the highest at which no formation of graphite occurs within the white tread and at which the wheels can be stripped from the molds. Inasmuch as no direct determinations have been made of the temperatures at which the formation of graphite takes place in white iron of compositions used in car wheels upon annealing, it was considered worth while to determine these temperatures as a means of establishing the maximum temperatures at which the annealing of the wheels may be carried out. In the course of this work, some incidental observations were made which are of interest in connection with the theory of graphitization in whitc iron. The literature on the subject of the formation of graphite both during cooling at casting and upon annealing is very extensive and can be best studied by reference to a comprehensive discussion of the subject by Hatfie1d.l Perhaps the most important contributions of previous investigation are the following: 1. Whether a given mass of molten iron becomes white, mottled, or gay upon casting, depends on its composition and its rate of cooling through the temperature range of solidification and immediately below. 2. The more rapid the rate of cooling, the less is the extent of graphitization.

Jan 1, 1920

By T. A. Rickard

In a previous paper (ante, p. 411) some description was given of the occurrence of the auriferous alluvium, extensive deposits of which lie among the highlands of the province of Otago, New Zealand. The present paper will describe some of the methods by which that alluvium is exploited. The alluvial mining of New Zealand is not yet hindered by " debris legislation." The mines are for the most part situated in a country of little agricultural value, and large rivers with rapid currents act as tailings conveyors. In time, however, steps will have to be taken to restrict the discharge into the Clutha of the tailings which are slowly raising the river-bottom. The methods of California have been followed in Otago with such alterations as peculiar local conditions require. The distinctive feature of the alluvial mining of Otago is the prominence given to the hydraulic elevator. The all-important factor in this form of mining is the control of an abundant water-supply at a suitable height above the level where it is to be utilized; and in this respect the gold-fields of the south island of New Zealand are most favora-

Jan 1, 1893