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By F. Q. Su

Underground Coal Gasification (UCG) is a promising environmentally acceptable clean-coal technology. A typical UCG system has two wells drilled from the surface into a coal seam with some separation of injection from production. The wells are connected underground by various linking techniques. After creating a combustion reactor in an underground coal seam, air and oxygen flow through the injection well. Heat energy and gases are collected from the production well. As gasification progresses, the combustion reactor is moved along the linking hole. Using this process, the fracturing activity inside the coal seam serves an important role for enlargement of the gasification zone because the surface area oxidization increases continuously by coal cracking. For effective coal gasification, fracturing activity must be controlled. Moreover, excess fractures inside the coal seam and surrounding rock can induce gas leakage, underground water contamination, subsidence, etc. Therefore, monitoring and control of fracturing activity in underground areas constitute key technologies for efficient and safe UCG. To monitor fracturing activity, we conducted laboratory and small-scale field experiments of UCG using acoustic emission (AE) measurements. UCG model tests were conducted for linking and coaxial types UCG models. Coaxial UCG systems are compact and are anticipated for application in underground coal seams having a complex geological structure. The UCG model consists of a coal block molded in a steel canister (20 liter capacity) with heat-resistant mortar, with a linking hole or a coaxial-hole passing through the coal block. During coal combustion, coal temperatures, production gas contents, and AE activity were monitored under the control of injection-air and oxygen flow rates. Results show that the combustion propagated inside the specimen along the linking hole. Many AE events were generated during coal combustion. The AE activity was related closely to temperature changes inside the coal block. This AE generation apparently results from crack initiation and extension around the coal combustion area under the influence of thermal stress. However, comparing the results from UCG models of linking and coaxial types, the gasification of the linking type model showed an average calorific value as high as 11.3 MJ/m3. The coaxial type yielded an average calorific value of produced gas as only 5.79 MJ/m3. In the coaxial type of UCG model, the combustion region was limited to the area around the coaxial hole. The AE activity was lower than in the linking type model. For small-scale UCG field experiments, linking and coaxial types were tested at an open pit coal mine in Hokkaido, Japan. Using a linking type UCG, 58.2 kg coal was processed in 39 h, with the calorific value estimated as 11 MJ/m3. However, the coaxial type UCG processed 7.0 kg coal in 9 h, yielding an estimated calorific value of 6.0 MJ/m3. These tendencies resemble those of results of laboratory UCG experiments. Results of these experiments demonstrate that AE monitoring is a useful tool to evaluate combustion reactors for efficient and safe UCG systems. To develop a coaxial UCG system, results show that fracture control around combustion reactors is indispensable.

Aug 1, 2013

By H. J. Rowley

THERE are many varieties of limestone, but for the general purposes of the pulp and paper industry, two classifications are sufficient: (1) High-calcium stone, which should be quite free from impurities and contain not less then 90 per cent calcium carbonate. (2) High-magnesium stone, containing not less than 25 per cent of magnesium carbonate. Before proceeding with detail on the use of limestone and lime in the industry, a few words regarding the pulp products made in Canada are desirable. By far the largest tonnage is made by grinding spruce and balsam logs on rotating sandstones or on artificial abrasive stones of the Norton or Carborundum types. This mechanical or groundwood pulp finds its largest use in the production of newsprint paper, of which it comprises about 80 per cent of the total fibrous substance employed-the remaining 20 per cent being unbleached sulphite pulp. No limestone or lime is directly employed in making groundwood pulp, as contrasted with the chemically prepared pulps, all of which require one or the other form of the base for their processing. Sulphite pulps comprise the next largest tonnage group. They are produced by boiling, under pressure and at elevated temperatures, spruce and balsam wood in chip form in solutions of bisulphites and sulphurous acid. The usual bisulphites employed are those of calcium and magnesium. Sodium, potassium, and ammonium bisulphites give progressively better pulps, but to date, in the absence of efficient recovery methods, cost has precluded their use.

Jan 1, 1939

By G. F. Miller

ONLY IN THE Province of Saskatchewan is natural sodium sulphate found in Canada in amounts large enough to make recovery economically sound. Geologists have estimated that the numerous deposits within the Province contain upwards of 200 million tons of Glauber's salt. There are twenty-one deposits in the Province which contain 500,-000 or more tons and about two dozen with lesser amounts. The first recorded production of sodium sulphate in Saskatchewan was in 1918. The company concerned, and others that attempted to develop the industry in its early stages, were unsuccessful. Their failures were caused by two main factors -lack of knowledge of efficient operating methods and the unstable market situation for the finished product. Today, the situation is changed in both respects and the product, commonly referred to as 'saltcake", is a very important chemical requirement of many industries throughout the world. Before proceeding with remarks on manufacturing methods it should be stated that, although this is a general paper on the manufacturing methods and end uses of the saltcake produced in the Province, the writer is, of course, more familiar with the plants operated by Saskatchewan Minerals than with other operations and perhaps may be excused for dealing more particularly with the plants of that Compa11y.

Jan 1, 1958

The effect of long term exposure of full size bolts to corrosive environments is presented. A special test rig was used to test four bolts under different loading conditions. Four, X-grade identical profile bolts, each of 21.7 mm core diameters (23.7 mm full diameter) were subjected to prolonged corrosion testing using acid sulphate water. The pH value of the circulated water varied between 3.4 and 4.3. The corrosion exposure test period lasted three and half years. Two bolts were axially loaded to 10 and 20 tonnes force respectively, the third bolt was subjected to a 360 Nm torsion load and the fourth bolt was left unstressed to act as a reference bolt. After the test period ended, the bolts were stripped of their corroded coatings and weighted for weight loss. The diameter of each bolt was subsequently measured, and the loaded bolt samples were first tested non-destructively for tensile cracks and then tested for tensile failure. No cracks were found on post corrosion bolts tested non-destructively. The failure strength reduction on all four post-corroded bolts was significant, varying between 21% and 39%. The onset of corrosion was not confined to the targeted mid-section length of the bolt, however, the severest corrosion occurred at the anchored ends of the bolts.

Aug 1, 2013

By Navid Bahrani

The grain-based model (GBM) has resolved the difficulty of matching both the directtension (sc) and unconfined-compressive (st strengths of typical brittle rock by providing a synthetic material that mimics deformable, breakable polygonal grains cemented along their adjoining sides with deformable, breakable interfaces modeled as smooth-joint contacts. In this paper, a GBM utilizing a parallel-bonded base material is calibrated to match both st and sc of Lac du Bonnet granite and then used to simulate a Brazilian test. The Brazilian strength (sB) is slightly overestimated and the failure mode includes ductile post-peak response that is not representative of what occurs in laboratory Brazilian tests. By reducing the grain tensile strength, grain failure occurs during the Brazilian test and a more realistic failure mode that includes brittle post-peak response is obtained. However, the unconfinedcompressive strength of the modified material is too low. Sensitivity analysis on the grain and grainboundary strength properties demonstrates that the grain tensile strength controls the sB/sc ratio. Because the grain strength is controlled by the parallel-bond properties and the lowest achievable st/sc ratio in a parallel-bonded material is ~0.25, it is concluded thatsc, st and sB for a typical brittle rock cannot be matched with a GBM that utilizes a parallel-bonded base material.

Jun 1, 2012

By J. Y. Kim

This paper presents a novel action recognition method for observing human workers using interactions between actions and related objects on an internal construction site. This method can be used to measure work rates for labour productivity monitoring. This monitoring is critical because the performance of a construction project is significantly impacted by labour productivity. However, construction sites are generally crowded with a large number of workers and objects. Such congestion disrupts the accurate, automatic recognition of construction workers? actions. This congestion is one reason that existing automatic action recognition studies of construction areas mainly focus on workers? actions themselves. However, the crowded conditions mean that sites could offer a great deal of clues that could be used for automatic action recognition. According to psychological studies, interactions clearly take place between human actions and related objects, such as between hammering and a hammer. Humans use these interactions to recognize actions or objects more accurately. On the construction site, workers, materials, tools, and equipment are carefully planned out ahead of actual construction. The categories of workers and objects are pre-defined and, as noted, specific interactions define relations between worker actions and objects. In this paper, the interactions are limited to human workers and their hand-held objects. Action recognition results can be combined with hand-held object information to improve recognition accuracy. With the limited interactions, experiments in this paper show a significant improvement in action recognition. This paper describes the utilization of these interactions to improve construction action recognition accuracy based on human skeleton data and 2D color video from Microsoft KINECT sensor.

Aug 1, 2013

By N. Sarmady, Mei Li, N. C. Parson, W. J. Poole

"The mechanical behaviour of AA6082 is a function of the extrusion conditions and in particular, the quench rate after extrusion. It is well known that precipitation of Mg-Si phases on grain boundaries during quenching can negatively affect the ductility of the alloy. In this study, AA6082 alloys containing 0.5 wt. % Mn and 0.15 wt. % Cr were direct chill (DC) cast, homogenized and then extruded to produce 3 mm x 42 mm strips. The microstructure in the as-extruded strips was unrecrystallized due to the Zener-Smith drag from the Mn/Cr dispersoids. It was shown that a solution treatment of 5 minutes at 560°C did not significantly affecting the as-extruded microstructure but if the as-extruded strip was cold rolled prior to heating, recrystallization occurred concurrently with the solution treatment. As such, 3 initial microstructures were produced, i.e. unrecrystallized and recrystallized with a grain size of 9 and 40 µm. After the solution treatment, controlled cooling experiments were conducted using the Gleeble 3500 thermomechanical simulator with cooling rates of 10, 25, 80°C/s as well as water quenched. The mechanical properties (e.g. yield stress, fracture stress and fracture strain) were determined from tensile tests for the different combinations of initial microstructure and cooling rate. The relationship between the quench rate and precipitation of Mg-Si phases on grain boundaries was examined by FEG-SEM. It was found that the yield stress decreased as the cooling rate decreased and that there was complex relationship between the fracture properties and the microstructure.INTRODUCTION As the automotive industry strives to reduce fuel consumption and CO2 emissions with the goal of reducing the environmental impact, there is a need for lighter vehicles. As a result, aluminum alloys are gaining popularity to replace steel parts as structural components. An exemplar of this is the Ford F-150 pickup truck which has an aluminum body and is ˜750 pounds lighter than the previous steel version of the vehicle. The structure includes a mix of aluminum sheet, extrusions and cast alloys. The current research is concerned with the performance of aluminum extrusions in applications such as side rails, crash tubes and other structural parts. These components experience a combination of bending, stretching and folding both during the forming of the part and in service, e.g. crash of a vehicle. There is a need to have detailed information on the influence of processing on final material performance, in particular the cooling rate after extrusion."

Jan 1, 2018

By Michel Ruel, Ali Soltanzadeh, Benjamin Légaré

High fidelity commercial process simulation packages can be used at different stages of a greenfield project, from initial plant design to operator training in the later stages. However, there are several factors that make the software less attractive for small and medium size brownfield projects, such as the licensing cost and the fact-finding manpower required for model design and simulator maintenance. In this paper a different approach is described. The knowledge gathered from operating personnel was used to implement higher level models based on plant data, operating heuristics, and experience rather than detailed component-level models. The computing platform used was a low-cost, well-established, control system vendor-independent software. Throughout this paper we demonstrate the success of implementing this model-based approach using two industrial examples. The first example is a simulation of the carbon monoxide (CO) distribution system at a metallurgical complex. The purpose of this simulator was to test new control strategies and PLC programs prior to implementation. CO being a toxic combustible gas, validation of the suggested control system changes was necessary for plant safety. Simulation of specific operating conditions helped alleviate concerns and improved plant-wide acceptability of the new operating philosophy. The second example is a boiler simulator at a petrochemical plant. The operator training simulator (OTS) was designed as a platform for experienced operators to practice handling rare or abnormal conditions. A customized medium-fidelity model was developed for this targeted application where the cost of a full scale high-fidelity model could not be justified.

Jan 1, 2016

By R. E. Bou Serhal

Many miners are exposed to dangerously high levels of noise on a daily basis. Over the past 15 years, a continually increasing number of occupational hearing loss has been reported from the mining community in the United States, of which, more than 95% is attributed to prolonged noise exposure. Although the noise exposure levels may differ between coal miners and metal and non-metal miners, in the absence of noise control at the source, the solution is the same: use of personal hearing protection devices (HPD). While protecting the miners? hearing it is also essential to no longer hinder their ability to communicate. With access to an advanced HPD that is customized to the miners? ears we are able to combine these two requirements. Using an intra-aural instantly custom molded HPD miners are protected from high levels of noise. The HPD is equipped with wireless capabilities, and contains both a speaker and an In-Ear Microphone (IEM). Therefore, the miners? speech may be captured from inside the ear and transmitted to the remote listener. This IEM signal is relatively noise-free since it is isolated from the background noise. The IEM speech signal, however, is ?boomy? and is missing some high frequency content, making fricative consonants hard to understand. Nonetheless, the IEM speech signal is correlated with the natural speech signal and may be manipulated through statistical techniques to more closely resemble natural speech. By improving the intelligibility and quality of the IEM signal, numerous applications may be enabled. One use of the enhanced IEM signal will be for radio communication. Using wireless radio communication in a noisy mining environment is sometimes the only practical and affordable solution to allow communication between miners equipped with personal hearing protection devices. Traditionally, one of the weaknesses of such wireless radio communication lies in the lack of designating receivers: whether they are the intended receiver or not, all those carrying a radio receiver are subjected to the broadcasted signal. The current work will detail a new concept of a "radio-acoustical virtual environment" where the radio signal will only be received by miners within a given spatial range, such range depending on the user?s vocal effort as well as the ambient and perceived background noise levels.

Aug 1, 2013

By W. T. Gotheridge

The principal sources of coal-dust underground are, of course, coal, and the working of coal. Coal-dust is most dangerous when it is in the finest state of division. This class of dust is found mostly on the roads, being blown or shaken off the loaded trams in transit, or carried in suspension by air currents. The air current passing from the working faces may also carry dust in suspension into the return airway, and the air current from the surface may carry dust from the shakerscreens into the intake airways. The mosl dangerous dust we have to contend with is, (a) that which is most finely divided, and (b) that which contains the most volatile matter, including the inflammable occluded gases, and also oxygen absorbed from the air. According to experiments, coal-dust in a fine and dry state would intensify an explosion, in air free from fire-damp carrying in excess of 3 ozs. of fine dust or 6 ozs. of coarse dust per cubic yard. The volatile matter in the dust must be between 12 and 31 per cent. in the ash-free coal, the latter percentage giving the highest flame velocity. It is vary difficult to propagate flame where coal-dust contains a large percentage of stone-dust, (say 50 per cent.). Shale-dust or other incombustible dust containing no volatile hydro-carbons or carbonaceous matter will prevent the extension of an explosion if mixed with coal-dust in proportion of say 70 per cent., and if the dust is finely divided and dry.

Jan 1, 1924

By Forrest A. Kerr

Northern British Columbia is a term which probably conveys to various individuals quite different meanings. To the average person it signifies an area of indefinite size and indefinite position which may start at Prince Rupert, Stewart, or somewhere else, and end at Alaska or .the Yukon. Many people, in their conception, fail to encompass in their mind's eye that vast tract of land lying ~o the east of the panhandle of Alaska. Few realize that the area north of an east-west line through Stewart represents more than one-third of the Province and is, of course, the part most appropriately designated as northern British Columbia. This section, more especially the northernmost 100,000 square miles, from political, geographic, and economic viewpoints stands isolated perhaps more than any other part of British Columbia. Unlike the rest of the Province, it has no coast line, being cut off from the Pacific ocean by a narrow strip of Alaska. It is bounded on the north by the Yukon, and on the east by Alberta. In the south this northernmost 100,000 square miles is limited by a divide of rugged mountainous country separating the drainage basins of the Stikine and Liard rivers from those to the south.

Jan 1, 1929

By W. Kempson

"As has been noted on numerous occasions, the vertical shafts being sunk around the world are all tending to get deeper as we seek to take advantage of higher grades of minerals which can sometimes be found at greater depths. One of the challenges with these deeper shafts is the requirement to supply services to the mine’s operations at depth as well as the requirement to dewater the mine. Both the supply of water and the dewatering of mines is generally done using piping. With the greater shaft depths, this piping is now required to contain higher pressures as well as to accommodate changes in temperature resulting from normal mine operations. This paper will discuss the requirements for the design of high pressure piping in deep vertical shafts. The discussion will start with the general definition of the systems and the detailed design requirement. Once this is clearly outlined, we will discuss the options available for fulfilling these requirement as well as the advantages and disadvantages of each of the systems. We will finish with the installation recommendations and provide a basis for the maintenance of these systems. INTRODUCTION Piping in vertical shafts is used to provide a number of services in underground workings. These services vary depending on geographical location and the type of the ore body which is being mined. For example, in the Zambian Copper mines, one of the largest requirements for in shaft piping is for dewatering. Similarly in the Gold deposits in the West Wits basin as well as the deep level Copper deposits in Arizona, one of the largest uses for the piping is the supply of a cooling medium to underground workings to create a safe working environment (this can in the form of water or of glycol depending on the application). In South Africa, systems were installed which used the hydrostatic head which is generated from supplying chilled water to mines whose depths exceeded 2,000 m below surface. This chilled water was supplied as a closed system, allowing for high pressures to be generated which was then used to supply useful work (for example, Rock Drills, Face Cleaning and other ancillary services) whose power was traditionally supplied by compressed air or electricity. This system was initially researched by Chamber of Mine in South Africa. The design pressure range of these systems is 14 MPa to 18 MPa."

Jan 1, 2019

By William James Kempson

This paper discusses ore handling systems in shafts. These are considered from the loading facility at shaft bottom all the way through to the discharge mechanism in the headframe. These systems will be discussed from the following perspective: i. Intrinsic safety of the systems ii. The efficacy of the systems to perform consistently iii. The maintainability of the systems iv. Overall system cycle times Particular emphasis is placed on the following specific areas: 1. The Shaft Bottom Loading Facilities The various shaft loading systems currently in use are discussed, the selection parameters surrounding these are quantified and the specific selection criteria are outlined. 2. The Various Skip Configurations In this section the various skip configurations in use around the world will be described and the specific design details associated with these will be highlighted. The advantages and disadvantages of these systems will be compared and the overall efficacy of these will be discussed. 3. The effect of the loading and skip configurations on the Load Cycle Times. The overall cycle time which can be achieved by a shaft system is strongly dependant by the speed and efficiency with which the ore can be loaded and transported out of the mine. The potential of the various systems to be optimized will be discussed. The emphasis of this paper is to highlight the lessons which have been learned with respect to ore transport system design and provide a common basis against which these can be compared in future applications.

May 1, 2013

By A. West, F. Mohammadi

Growing awareness of selenium bioaccumulation has resulted in selenium management becoming an important environmental issue for mining operations. Selen-IX™ is a novel ion exchange based technology developed by BioteQ to provide an effective solution for removing selenium oxyanions from mine impacted water to single-digit µg/L levels. The technology offers significant potential benefits when compared to incumbent biological treatment processes, including substantially reduced capital and operating costs and significantly reduced production of a selenium-containing sludge for final disposal. This paper reviews the key features of the Selen-IX™ process and presents the results of recent pilot testing on selenium impacted water.

Jan 1, 2014

By William C. Browning

An economic drilling programme is one which costs the !east in chemicals, equipment, and time. The basis for such a programme with rotary drilling techniques is a drilling fluid in which bentonites do not swell. This is recognized in the growing trend toward gyp and other inhibited mud systems. Therefore, even though the mechanism of thinner action is a subject of applied colloid ,chemistry, the understanding of this mechanism is of economic importance in controlling the flow properties of inhibited muds. In phosphate, or sodium tannate, conditioned muds that are relative-!y free of contaminating-electrolytes, the thinner, or dispersing agent, is adsor.bed, ?creating an electrical double layer about the clay particles. The mutual repulsion of these charged particles effects colloidal stabilization, or deflocculation of the suspended clays, as discussed by Norton and others. In inhibited muds, however, the electrolyte concentration in the filtrate is sufficient to collapse the double layer and flocculation of the mud solids occurs, as evidenced by increased viscosity and gel values. Chemicals to control the flow properties of inhibited muds, therefore, are vital to the successful use of these systems as it is not always economical to adjust flow properties by watering back. Flocculation of suspended particles, as indicated in the work of Vervey, Overbeek, and others, is due primarily to gravity-like, long-range Van der Waals forces. Prevention of flocculation may, therefore, be secured by the interposition of any barrier between the particles, the thickness of which approximates the extension of the Van der Waals at-traction. Organic polyelectrolytes, such as Kembreak, Rayf!o, and Q-Broxin, may act to increase the double layer charge when used in small amounts in fresh-water muds. More important, however, is the fact that in inhibited muds an increase in concentration of the polyelecholyte permits the formation of a condensed film adsorption layer of the polyelectrolyte about the clay particle. When this occurs, the extremely viscous condensed adsorption layer creates a mechanical. barrier that prevents flocculation of clays, even in the presence of inhibiting concentrations of elecholytes. Rheological evaluation of the degree of deflocculation, or colloidal stability, may be made by utilizing the known effects of particle inter-action and volume concentration on the flow properties of suspensions. Rheological evaluation should be supplemented by direct microscopic or ultra-microscopic observation.

Jan 1, 1958

By W. G. Worcester

THE chief object in presenting this paper on bentonite is to attract general attention to one of the least known and most neglected industrial minerals of Canada, a mineral of extensive commercial possibilities, as evidenced by its development and exploitation in other countries, principally in the United States and Germany; countries upon which some of our most important Canadian industries are dependent for their supply of special clays, such as Fuller's earth and activated bentonite. It was in view of these conditions and the knowledge of the presence of large quantities of bentonite in the Canadian West that the work here reported on was under-taken. While the investigational studies have not been completed, the results indicate that among the many samples tested there are some of real merit and industrial importance. While it has been the author's privilege to examine deposits and samples of bentonite from all of the Western provinces, his chief activities in the field and in research studies have naturally been confined largely to Saskatchewan materials. Notwithstanding this, however, this paper is presented in the hope that it may stimulate a more general interest in, and study of, Canadian bentonites as a whole, a matter of such importance that provincial boundary lines should be overlooked. GENERAL CHARACTERISTICS OF BENTONITE According to Schurecht and Donda (1), bentonite is commonly composed of the mineral montmorillonite, (Mg,Ca)O.Al203 5SiO2 .nH2O, though some are known to consist of beidellite, Al2O3 3SiO2.nH2O: where n is approximately 4, and in certain cases the Al2O3 may in part be replaced by Fe2O3. For present purposes, however, it may be sufficient to state that, in general, bentonite is a "soapy' clay-like mineral or group of minerals composed largely of hydrous aluminium silicate, but frequently carrying small percentages of the alkalies, alkaline earths, and free silica, as well as silicates, gypsum, and other admixed detritus such that purification is usually necessary.

Jan 1, 1937

By Richard W. Herzer

Introduction Thermal methods have been predominant in the metallurgy of the base-metals ever since the foundation of the industry thousands of years ago. Development in hydrometallurgy has been confined largely to the past six or seven decades. It was at first necessarily slow, then for a number of years rapid progress was made. At present, the uncertain state of the metal industry has curtailed research on the subject; however, in the next few years one may assuredly look forward to an ever increasing use of wet processes. Leaching methods have attained the dominant position in the case of certain metals, notably zinc. For others, they have made no headway at all. Copper presents a situation all its own. Due to the varied nature of its ores and to the large number of localities in which it is mined, a great number of processes have been developed, each suitable in its own particular field. In the case of this metal, therefore, it is more difficult to arrive at definite conclusions. It is the purpose of this paper, first, to review the outstanding developments of base-metal hydrometallurgy, and, secondly, to consider possible Canadian applications of some of the processes in use. The discussion will be confined to the three metals, zinc, lead, and copper, with particular reference to the last mentioned. Zinc General Note At present, zinc is produced by two principal processes, the older retort process and the electrolytic process. The latter is a development of the last twenty years and, judging by its present progress, bids fair eventually to supplant older methods in a large proportion of cases. It is certain, at least, that in the erection of a new plant, a hydrometallurgical process would be given the most serious consideration

Jan 1, 1934

By J. A. Reid

THE views and observations expressed herein on this old but constantly recurring question are our own, no effort having been made to align them with standard texts. Therefore, while they may find general acceptance amongst fellow engineers, they must stand as personal opinions and as such are open to debate and discussion. In order properly to consider the subject, it should first be 'set in proper perspective. Why are Prospects Examined? Prospects are examined to determine whether they may contain economic concentrations of metals or minerals, the legitimate mining business being run, pretty largely, to make money. Next to food and clothing, modern civilization is based on metals, with which are included in this discussion minerals, oils, and fuels. A constant and increasing demand for the common metals requires the location of replacements for depleted orebodies, while the use and appreciation of new metals brings increasing demand for them. Aluminium is a good example of a metal which has, within recent years, made great progress. Today, we are becoming increasingly aware of magnesium, chromium, tungsten, thallium, and other lesser known, metals.

Jan 1, 1945