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By H. F. JR. Miller

(Butte Meeting, August, 1913.) THE major cause of the deterioration of the open-hearth furnace as its length of service increases, is the melting down, or rather the slagging, of the checker-brick, together with the deposition of dirt in the form of iron oxide, etc., which helps to close the openings, as well as to slag the brick by chemical action. Any construction that will do away with the necessity of having the waste gases come down through the checkers will eliminate the main reason for their deterioration. There are some other well-defined reasons which are subordinate to the main one given above. Some of the defects of the present type of regenerator chambers are as follows: 1. The checkers cannot be cleaned while the furnace is in operation, nor can they be cleaned at the end of the run without taking out all of the checker-brick. This causes high costs for labor and brick. The labor cost is high because all checker-brick have to be handled twice. The brick cost is high because many of the bricks are spalled in the double handling, rendering them useless because a spalled brick will not stand up. 2. The top courses of brick become coated with iron oxide, etc., melt clown, and large amounts of dirt are deposited throughout the checkers, especially at the bottom. The draft of the furnace is decreased by the closing of the top and bottom openings, especially the top ones, and the entire working of the furnace is affected. If an effort is made to clean the checkers the dirt and brick falling down into the holes still further diminish the draft. 3. The distribution of the air or waste gases through the checkers is in many cases uneven, resulting in a lower temperature of pre-heated air and therefore a slower working furnace. Also, the passage of air and waste gases is so crooked that sometimes the chimney is not powerful enough to overcome the friction.

Jan 6, 1913

By Leons Kovisars

Introduction Competitive analysis is the collection and evaluation of data on a product, a product line or on an entire industry. Much of the focus of competitive analysis centers on production volume and the price targets of the competitors. In actual practice capacity may be used in place of production volume. Similarly, unit production costs and individual producing units - mines, mills, smelters, refineries - may be the targets of the analysis. The purpose of competitive analysis is to provide information for strategic planning. The analysis will locate the position of the company in the industry and define the competitive margin -- or lack of a margin - between the company and other producers. The analysis can show the current situation and may be expanded to examine the outlook for the future. The forecast option is particularly valuable because it will show the opportunities for new project development or the expansion of current production. Similarly, the forecast will show the potential threat from new entrants, and may provide early warning to reconsider operations that may become uncompetitive in the future. Production cost analysis is a clearly understood means to evaluate producers and estimate the outlook for their profitability. The cumulative cost for the industry outlines the supply structure and defines the marginal cost of production used in developing price forecast as explained in the sub- sequent section of this paper. Competitive analysis is particularly important to the mining industry, notably to metal producers. The final product is typically a purified metal conforming to standards, and interchangable with the output of other producers, i.e. a fungible commodity. Brand loyalty is questionable in the mineral industry. Consumers will show a preference for specific brands, but this preference will be limited to a premium of several percent over the general market price. Price and assurance of supply are the keys to marketing success. Assurance of supply depends on geopolitical considerations and production capabilities. Price will be closely related to cost of production and a thorough competitive analysis should describe the cost structure of the industry. This snapshot will locate one's own position and provide an immediate and readily understandable evaluation of the hazards and opportunities inherent in this position. In the following section we shall discuss elements, methods and sources for competitive evaluation. ELEMENTS OF COMPETITIVE ANALYSIS The practice of systematic collection and analysis of data on competition is hardly a new concept; see, for example, Wall (1) or Porter (2). However, most discussions have been in the context of conventional industrial or manufacturing industries, with a focus on product lines and brand marketing. These considerations are not irrelevant to mining but they do have only a limited application. The key to success in the mining industry is minimizing the cost of production. However, this simple concept becomes complex when we consider relevant costs and the planning horizon. Production costs include the factors consumed in production, namely labor, fuel, energy, materials and supplies. The cost also includes purchased and contracted services such as freight, smelting and refining, sampling and sales required to convert ore to the finished metal. Royalties and ad valorem taxes paid on gross production are direct expenses, as is the cost of administration required by the production units. The sum of these outflows is the total cash cost, the expense that has to be paid in cash in order to continue production. Indirect costs incurred by a producer will commonly include allocated headquarters expenses, as well as the capital charges associated with equity investment and debt. Profit is not generally considered an indirect cost even though it represents the cost of using the owner's capital; similarly, income taxes represent the government's participation in the profits of the enterprise. Interest payments are considered as a direct expense in some cost studies, but many competitive evaluations would consider

Jan 1, 1985

THE second operation in the art of casting, and one of the greatest importance, is that of melting and thoroughly liquefying the materials of which you wish to make your casting. On this operation depends the whole outcome of your intentions and the perfection of your work. Without it, even though you had a great abundance of moulds and vast quantities of bronze, your desires, labor, and expense would all be in vain. In this operation I find on consideration that, in addition to experience, there are three necessities-perhaps indeed four-that must be provided without fail. The first is the furnace or other agent which contains the fire and the metal brought together. The second is the wood or charcoal which is the necessary and proper nutriment of the fire, from whose virtues are derived the greater or lesser forces which, according to their kind, are ready to effect what is required. The third is to have the materials disposed to easy fusion by means of corruption, alloying, or by their own nature. The fourth, as the motivating cause of the whole, could perhaps be listed as the first-this is the ingenuity and good judgment of the worker, together with the bodily exertions not only of himself but also of his helpers in addition. For, besides a certain ordinary caution, it is necessary to pay particular attention, first, to see that the furnaces, machines, ladles, hearths, refineries, and other kinds of instruments or similar vessels be made so as to dispose the metals for melting, and, when melted, that they easily maintain them so. These should also be prepared in such a way that they cannot be injured by the fire, for if they should be damaged the operation would fail. In order to do this, it is first necessary that you arrange the instruments with forethought and action so that the power of the fire can operate. Fire operates on things only when brought together with them in long-continued operation, or when driven by a great force of wind. It burns many things and softens others, but it makes the metals as liquid as water.

Jan 1, 1942

By Tell Ertl

TODAY'S mining industry is witnessing a transition in labor utilization. The drill-jumbo operator, the mucking-machine operator, the blasting crew, the scaling and timbering crew are all specialists. The all-around miner is rapidly disappearing. As mechanization has resulted in a higher order of underground skills; specialization of labor has been a natural consequence, as has the need for more supervision and engineering. Mines now are cleaner, neater, safer, and have a greater productivity per man-shift than ever before. Nothing spectacular like the continuous miner has yet come to the underground metal mines, but t a gradual improvement in methods, equipment, and technical knowledge is achieving the increased efficiency. With the exhaustion of the rich ores and large profits and who-cares-about-the-costs, mining has become a business; that of producing low value ores at costs below selling price. Charles A. Chase, patriarch of Colorado mountain mining men, manager of the Shenandoah-Dives, was one of the first to preach and prove his preachings that mining is a business. He has been mining a lead-copper-zinc-gold-silver ore, much from elevations above 1.3,000 ft, for a quarter century without a shutdown.-The ore is of such low value that most engineers and investors still would consider it foolhardy. Yet he has kept Silverton, Colo., alive, has paid wages without a lapse, has produced $25 million of new wealth and maintained a steady return to the investors. This type of responsibility is increasingly apparent in the mining business and is one feather that can be worn proudly. .Much emphasis is being placed on improving, the productive mining operations-breaking, loading and transportation. Breaking in underground metal mining is done by drilling and blasting. To the writer's knowledge, no chain or rotary-type machine has been developed for mining strong, abrasive rock. Drilling Percussion drills are still the standard drilling machines underground. Diamond drills, that: were the rage a decade ago for drilling long holes, are being superseded by the rock drill. The development of the hard abrasion-resistant carbide bit permits full-gage long holes to be drilled by percussion drills at a lower cost than diamonds. The change in the use of percussion drills is chiefly in the method of mounting. The column and arm are disappearing and the jackleg and rubber-tired or track-layer jumbo mountings are taking its place. At the Homestake mine .lightweight jackhammers mounted• on pneumatic legs using 7/8-in. hexagonal drill. rods and 1 1/2-in, tungsten-carbide detachable bits have been found more portable and maneuverable. They have less air consumption, lowered, dynamite consumption, and more footage and tonnage per man-shift than with 3 1/2-in. drifters on a column mounting. Drills now are mounted on longer feed carriages, drilling up to 20 ft without changing steel. These mountings result in great savings because the driller can set up quickly, drill the entire depth of the hole without changing the drill rod or bit using carbide and one-use bits, and can move his machine quickly to the next hole. One man to the machine is becoming general practice. The result is longer rounds rounds drilled at a lower cost than the previously used short rounds. A jumbo developed in the Tri-State can be extended to mine ore left in the roof up to 65 ft above the floor. Drill-rod life was formerly considered to be about 250 min of actual use. The increase in the drilling time per rod per day has gone up considerably with the development of the jumbo and the long-feed carriage, resulting in which is apparently more rod breakage., Consequently, a great deal of research is being done in the attempt to develop an alloy-steel rod with longer service life to offset the greater cost. Some reports indicate that alloy steel or Swedish steel results in cheaper drilling than conventional drill rod. However, several tests have shown only slightly increased life for alloy drill rod. Undoubtedly, the blow of the rock drill, the length of the drill rod, and the resiliency of the rock being drilled are important factors in the life of drill rod, so it follows that alloy steel might work well in some mines and result in no savings in others. The bit forged on the drill rod is seldom encountered and steel detachable bits are not as common as in the recent past. The one-use bit is gaining popularity because of. the difficulty in rehardening reconditioned steel bits satisfactorily. It is thought that the, carbie-insert bit is most applicable to drilling hard 'rock' where the steel bit is unable to drill out a full change, for instance, in extremely abrasive

Jan 1, 1952

HAVING already shown you the methods of making the moulds for casting and how they are to be prepared so that they may receive the melted metals well, it is now necessary, in order to complete the casting with perfection, that I show you not only the operations and instruments by which metals are softened, but also how metals can be made as liquid and fluid as water so they may easily enter into all the hollows of the moulds that you have made. Of these, besides the fire which is the prime agent, there is a very powerful furnace, which is called a reverberator.* I believe this is chosen not only for convenience but also because it is necessary in large casts. This is made of baked bricks, or of crude ones if desired or of suitable fire-resistant stones. Although all masters have the same objective, each one proceeds to make this kind of furnace according to his own ideas so that it can be said that there are almost as many different shapes of such furnaces as there are masters. This can be seen in the place that contains the metal, which is of such a shape that the force of the fire may operate better. Thus some masters are called good who, seeing no farther than what has been shown them, make them circular like a bread oven. Some others make them oval across the fire en- trance, while others extend them lengthwise. Also, there are some who make a single outlet for the flames, some two, and some three. Some make the entrance for the fire high and narrow and others, wide and low. The same is true of the place where the flames are generated, which is called the firebox. Some put the wood in from the side, some lengthwise in the same direction as the entrance for the flames, and some from above by means of a little hole. Also, one makes the vault low, and another makes it high. And while one puts an entrance for air underneath so that the

Jan 1, 1942

By H. K. Shearer

Drilling for oil and gas in Arkansas in 1934 showed more activity than in any year since 1929; with a total of 96 completions, including 36 oil wells, 1 gas well and 59 dry holes. Of the producers, the lone gas well and 35 oil wells were in old fields, and one wildcat producer opened a new pool. Of the dry holes, 16 were in or near fields and 43 were wildcats. The total reported initial daily production of the oil wells was 9013 bbl., averaging 252 bbl. per well. Active drilling operations numbered 65 at the close of the year, compared with 26 at the beginning.

Jan 1, 1935

By S. H. Ash

THE increasing need for the products of our mines, mills, and processing plants, the loss of mine manpower to plants other than those concerned with the mineral industry, and the drafting of our younger men into military service have created an acute situation in many places as to workers and production. This, in turn, has focused attention on the need for conserving manpower by conserving the health and life of our mining people. Health A world-wide tendency is noticeable in the mineral industry toward protecting the health of workmen,-particularly younger workers, as well as older workers who can continue to produce in many places where manpower is lacking. This matter was emphasized at the Geneva Labor Conference for Coal Mines at the Committee's fourth session, held in Geneva, Switzerland, May 7 through 19, 1951. Papers concerning the health of workers were presented at the annual meetings of the mining sections of the National Safety Council, the Coal Mine Inspectors' Institute of America, the American Public Health Association, and other organizations. Safety Conferences Without exception, the attendance at mining-safety conferences in widely separated places throughout the country during the year was the largest to date. What is needed at the safety meetings throughout the country is more-widespread attendance by those who can sell the idea to the workers that they are the focal point in accident prevention and that safety is not going to be achieved alone or even in part by laws, decrees, or commands, but by quiet influence, unconscious suggestion, and personal' guidance. If these are acquired by the workmen, a safe environment and ample, capable supervision supplied by management, accidents will be fewer and less severe. Many safety conferences attempt to develop the foregoing idea by enumerating and describing training programs for supervisors and workers alike. Nothing can replace a course in first aid for all persons employed at any mine or plant as an introductory and basic step to a successful safety program. Even in this, the shoe must fit the foot, rather than applying the order do this or else. In first-aid

Jan 1, 1952

By Carle R. Hayward

LEAD ore smelting plants have been operating in general at reduced capacities and secondary lead has assumed relatively more importance during the last year. Present smelting practice results in a large amount of dross, often over 25 per -cent, from blast-furnace lead. This is usually treated at a fairly high temperature in a reverberatory furnace to remove part of the lead and produce a matte-speiss product which is shipped to a copper plant. Few smelters are satisfied with this 'treatment. The fume losses are high and the matte-speiss contains considerable lead. It would seem that a fruitful field for research was open here.

Jan 1, 1934

By R. J. Cowan

In the art of cementation a controversy has been going on for years as to whether solid or gaseous carbon is the active agent in carburizing steel. More recently opinion has crystallized into a compromise to the effect that carburizing is a gaseous cementation of steel in the presence of solid carbon. The importance of this theory has a particular bearing upon the work to be described. In the art of carburizing, use is commonly made of such words as '' Catalytic" "atomic," "nascent" and "activated," in an attempt to describe the process. These words are used indiscriminately. For instance, the gas is said to be "catalytic" and carbon to be "nascent," or vice versa. In using these expressions, investigators are confirming the acceptance in their minds of the active conditions of both gas and carbon in the cementation process. Reactions at Metal Surfaces For many years attention has been directed to the consideration of reactions that occur on metal surfaces. When heated under the influence of certain metals a complex gas will be broken down and one of the constituents thereof usually found to be very active chemically in combining with the metal. The process of nitriding is an example of this type of reaction. In this case ammonia (NH3) breaks down at the metal surface and the nitrogen which is thus liberated reacts with the surface to form a nitride whereas molecular nitrogen not so liberated is inert and will not react chemically with the metal. Whatever term or terms may be used to describe such reactions, the fact remains that they are highly important and valuable in their commercial applications. Since the metal surface plays so important a part in these reactions, it is evident that any accumulation of reaction products thereon interferes seriously with the progress of the reactions. For this reason it is desirable to remove all such products as rapidly as they are formed in order to bring active gas into contact with the surface and thus facilitate the desired reactions. This is accomplished best by conducting the operation in a continuous manner, thereby causing the reacting gases to pass over the

Jan 1, 1931

By Amos L. Beaty

The oil industry can prosper only if crude production is not excessive. This is true for several reasons. In the first place, the marketing branch of the business is so highly competitive that there is little room for profits in it. There are too many service stations, too many middle men or jobbers, too many refiners eager to press their products upon the market. And the battle is between the strong. If any money is being made in oil today it is by small marketers who buy products from the refining companies and sell on guaranteed margins. In the second place, refineries are overbuilt. There is a large surplus refining capacity. If refined stocks were drawn down they could and would be replenished in short time on short notice. This excessive refining capacity is not serious, however, if the supply of crude is limited to trade requirements. True, it may reflect upon the intelligence of the industry, but if there were a shortage of crude for a few years refining capacities would be readjusted. In the meantime no great harm could result from some idle capacity. It requires no computation to see that refiners could not produce surplus stocks of products from a short supply of crude. I have in mind, of course, the increased yields from cracking. Allowance must be made for that. Still, the picture is the same; less crude is required. I think we can have prosperity in the oil business if too much crude is not produced. A proper limit at this point would be felt all the way down the line. It would slow the refiner and slow the marketer inevitably. Once this constant pressure to make more and sell more is off, operations will be normal and there will be some return on investments. Peices in Relation to Production Potential production at this time is very large, and this condition has existed for many months. As a result the price of crude is low. It is below the average cost of production. Nevertheless, if restraints were withdrawn actual production would immediately increase and the situation would become even worse than it is now. Eventually, of course, the

Jan 1, 1932

The opening session of the Institute was held at Hazle Hall, Tuesday evening, October 27th, with a large attendance of members. President Raymond called the Institute to order, and after a few introductory remarks, introduced Mr. I. Lowthian Bell, President of the Iron and Steel Institute of Great Britain, and Honorary Member of the American Institute of Mining Engineers. Mr. Bell was received with great applause, and made his acknowledgments in a brief speech, of which the following is the substance: He desired to thank the Institute personally for the honor conferred upon him in his election to membership, and also for the invitation extended last year to the body of which he was President. The difficulty felt by many members of the Iron and Steel Institute, of leaving for a long journey the works of which they had charge, aggravated by special industrial troubles at the time of the invitation, had obliged them to conclude that it could not then be accepted in a fitting manner. The iron .manufacture of this country is a subject of great interest to Englishmen, who look with pride upon the achievements on this side the water of the descendants of a common ancestry. His own reception in this country had far surpassed in cordiality even the well-grounded anticipations he had formed from the assurances of the President and other friends. Notwithstanding the flattering manner in which his friend, in introducing him to the Institute, had spoken of his contributions to the science of iron metallurgy, he could not take to himself alone the significance of this welcome. He knew it was a recognition of the services rendered by the body which he had the honor to represent; and he was glad to see present a member of that body, Mr. Thomas Whitwell, who had fortunately been able to make the journey at this time, arid whom he had had the pleasure of meeting on the shores of Lake Champlain. He had been requested to say something of his impressions of the American iron industry. It was not easy to digest so soon the vast

By H. J. Levinstein, W. H. Robinson

A method of chemically polishing silver for metal-lographic examination has been developed. The samples are prepared by polishing on 0, 2/0, and 3/0 paper. They are then polished on 600 micro-cut paper, followed by a final mechanical polish on a cloth containing 5µ diamond paste. The samples are then chemically polished in a solution of 100 cc of saturated chromic acid and 5 cc of a 5 pct HC1 solution. The chemical polishing is performed by swabbing with a cotton ball saturated with the solution. During the chemical polishing, the sample is rinsed frequently in running water. Polishing in this manner for 5 min is sufficient to remove the strained material from the previous polishing operations. The amount of material removed is approximately 4µ/min. The surface obtained is flat and free of pits. Fig. 1 is an interference micrograph of a silver surface polished by this technique. If the solution employed is of improper HC1 content, an interference color film will form on the sample. This film can be removed either by swabbing with a cotton ball saturated with ortho-

Jan 1, 1962

By N. O. Johnson, J. Boyer, D. H. Sargent, R. B. Frahme

Although the Western bentonite industry has grown rapidly, it is facing major challenges to sustained growth. The fundamental penalty of costly overland transportation to both domestic markets and to US seaports is of increasing importance; as both substitute materials and foreign bentonites present more formidable competition in the historic market areas of drilling muds, foundry sands, and iron ore pelletizing; and as foreign demand grows more rapidly than domestic demand. The Western bentonite industry is facing these challenges by altering its transportation patterns, by upgrading of products, and by emphasizing customer service and stringent quality control.

Jan 9, 1979

"Minerals in Transition" is the timely theme of this year's SME-AIME Fall Meeting and Exhibit, to be held September 10-12 at the Salt Palace, Salt Lake City, Utah. Approximately 2000 members and guests are expected to attend the meeting, which will include 117 technical papers, presented during 27 sessions. To complement the technical program, a record number of mining manufacturers and suppliers will be on hand to exhibit the latest in equipment innovation and professional services.

Jan 8, 1975

By Malcolm C. Bridges, Ian A. Goddard

INTRODUCTION Mount Isa mine is a major producer of both copper and lead-zinc- silver ores. During the 1975/76 year, 4.3 million tonnes of copper ore were extracted at an average grade of 3.4%, and 2.4 million tonnes of lead-zinc-silver ore at average grades of 7.0%, 6.7% and 173 grams per tonnes respectively. Systematic lead-zinc mining has continued for just over 45 years and copper mining for just over 30 years. Virtually all mining is underground. The composite and somewhat schematic longitudinal section of Figure 1 shows the overall distribution of ore at the Mount Isa mine. The mine can be roughly divided into two parts about a central shaft complex: to the north there is predominantly lead-zinc ore and to the south there is copper ore. Underground operations are serviced by three shafts in the central shaft complex (P61, R62 andU62) and another to the south in the copper mining area (X41). Mining is spread over a total strike length of 2.9 km and extends to a depth of 960 m. Currently, lead-zinc ore is being extracted between 15 and 11 levels and is hauled to the central ore-hoisting shaft on 13 and 15 levels. Copper ore is being extracted between19 and 13 levels and is hauled to the central shafts on 19 level. The principal lead-zinc mining methods used now, as they have been over the last ten years, are sublevel open stoping and cut-and- fill stoping, with about equal tonnages of ore from each (Figure 2). Since about 1970, there have been several interesting developments in lead-zinc mining methods and procedures, principally: • the development of an effective method for the recovery of pillars between open stopes and • the evolution of safer and more productive cut-and- fill methods. During this period also, the focus of mining has moved 120 m deeper

Jan 1, 1977

By J. N. Houser

THE industrial relations between the Tennessee Copper Co. and its employees have developed a number of interesting things and have been most, profitable to the employees and to the company. It is noteworthy that considerable has been done without a formal organization of any kind built up through the efforts of the company. From time to time there have been discussions regarding the advisability of a formal organization and the decision has always been in favor of the present method. In the year 1919, the company was dealing with its employees through union committees and, after an understanding was reached, satisfactory results began to be obtained, but as time went on the committees did not function and it came to a question of how to reach the men. For the past two years, about once a month, but at no stated time, there has been a meeting with a committee of employees consisting of 40 or 50 men out of 700. This committee is secured by notify-ing the locals. In addition, the Service Department notifies a number of men not represented in the union, so as to have a large representative committee. The meetings are on company time and the men are rotated, so that in time every employee attends , at least one meeting. All department heads and a number of foremen also are present. The operating plans and policy of the company are set out at the meetings and the market outlook for products is discussed. Explana-tions are also given of anything that has come up since the last meeting which affects the employees, and an effort is made to inform them of what will probably happen in the next month or two. Once a week there is a meeting of department heads with the manager, for discussion of all operations as a whole and such depart-mental details as seem advisable. When the depression started, it was necessary to curtail operations and the reasons were carefully explained; before the men were laid off, the employees as a whole were advised of the coming layoffs through these meetings. They were also advised generally who would be retained and given an opportunity to express their agreement or their. disapproval. In fact, an effort was and is being made to keep the employees advised in advance of matters affecting them and to give them full opportunity to express themselves.

Jan 12, 1922

By P. E. Baker

An improved method of logging formation density has been developed in which the formation is bombarded with a collimuted beam of gamma rays. By means of a scintillation detector and pulse height discriminator, the gamma-ray energy band is accepted and recorded which corresponds to deepest penetration into the formation. Laboratory tests on a field tool revealed no borehole diameter effect for smooth holes and no effect of formation chemistry, except insofar as chemistry affects density. In extensive field tests, the density log has exhibited satisfactory agree-ment with core measurements and has correlated accurately with other logs. INTRODUCTION This paper describes an improved method of logging formation density by means of back-scattered gamma rays to penetrate the formation together with energy discrimination to select only that energy (or frequency) range corresponding to deepest penetration into the forma- tion. This method of density logging was developed at the La Habra laboratory of California Research Corp.* Field instruments have been built and tested by McCullough Tool Co. and commercial service has begun in some areas. All of the data discussed here were obtained for the original field tool. The density log can be a valuable adjunct to existing logs because of its use in determining porosity quantitatively. It is useful also in connection with seismic and gravity surveys where formation density information is of interest. PHYSICAL PRINCIPLES The intensity, I, of a beam of gamma rays after traversing a distance, x, in an absorbing medium is given by I = loe -ax where I, is the intensity of the beam entering the medium and a the attenuation constant or macroscopic cross section of the medium for gamma-ray absorption. The macroscopic cross section depends on the number and types of atoms per unit volume and the gamma-ray energy. In brief, it is the sum of the atomic cross sections of all atoms per cubic centimeter. The density of the material is the sum of the masses of all atoms per cubic centimeter. Thus, the density and the macroscopic cross section for gam-ma-ray absorption vary in propor- tion to the number of atoms per cubic centimeter. The density of the material increases, of course, if the atomic masses increase without a change in the number of atoms per cubic centimeter. When the density increases in this latter way, the macroscopic cross section increases also, but disproportionately. This results from the fact that part of the gamma-ray absorption arises from the photoelectric effect and the pair-production effect**, which are proportional to the sixth and to the second power, respectively, of the atomic number of the absorber. The remainder of the absorption results from the Compton effect, and is directly proportional to the atomic number. The gamma rays that undergo Compton scattering are not immediately absorbed. Since these rays are scattered in all directions, a fraction will emerge from the face of the medium at which they entered. If a gamma-ray shield is placed between the source and detector, most gamma rays reaching the detector will be those scattered out of the medium. The intensity will depend on absorption and scattering in the medium, and so indicates the density of the medium. For gamma rays for which Compton scattering prevails, the intensity

Jan 1, 1958

By L. S. Darken

IN the study of reactions occurring in liquid iron, alone or in contact with a liquid oxide or slag phase, it has been found that the experimental data over a limited range of concentration can in some cases be repre-sented satisfactorily by the simple equilibrium expression K - (p1)p1 (p2)p2 . (R1)r1(R2)r2 . where (P) denotes the concentration of a product and (R) the concentra-tion of a reactant in the reaction r1R1 + r2R2 + . . . Some of the reactions for which it holds are listed in Table 1. For others, however, the simple equation apparently does not hold. This has been attributed to an improper method of expressing concentration (for instance, weight per cent instead of mol fraction); or it has been supposed that the solutions are not ideal in the sense that the activity of a com-ponent is not proportional to its true mol fraction, But it may be that the problem has been oversimplified by neglecting some molecular species actually present; that is, by considering only the ostensible simple com-ponents and thus leaving out of account possible compound formation. It is the purpose of the present paper to point out how, in a group of related cases, a reasonable consistent assumption relative to the presence of a compound makes it possible to express the experimental data satis-factorily by the simple equilibrium expression when this compound is taken into account, and to bring into harmony data referring to different reactions in liquid iron. There are several a priori reasons for believing that solutions in liquid iron should not deviate far from ideality, provided that the concentration of solute is not too great and is expressed in proper terms. The factors that commonly lead to nonideality in systems at ordinary temperature as ionization or the occurrence of polar and nonpolar molecules-are presumably less effective in metal and in slag systems at high temperature. Again, the type of equation commonly used to express the value of

Jan 1, 1940

By Rex O. McLellan

The formation of a monovacancy in a metal is simulated in an elastic model by the displacement of the surface of a small spherical cavity in a large elastic continuum. The application of linear elasticity to this distortion results in a well- known formula for the energy and an expression for the concomitant entropy change due both to the shear strain in the continuum and also to the dilation of the solid resulting from the boundary conditions at the surface of the solid. Elastic data (the sliear modulus and its temperature coelficient) are used to calculate the entropy and energy of formation for many metals. Despite the simplicity of the assumptions involved, the agreement between the calculated entropies and energies and experimental values is remarkably good. In recent years there has been a large increase in measurements of the absolute concentration of mono-vacancies in metals as a function of temperature. Hence new data for both the energy and the noncon-figurational entropy of formation of monovacancies has become available. Recent measurements&apos; of the anomalous (non-Arrhenius) self-diffusion in many bcc metals has also focused interest on the prediction of the thermodynamic parameters of mono- and multi-vacancies in those metals for which no data are available. Damask and Dienes&apos; have discussed the various theoretical calculations of the energy of formation EL, of a monovacancy. These include simple models involving the breaking of atomic bonds on moving atoms from the interior of a crystal to the surface, models combining elastic calculations with surface-energy terms and detailed quantum mechanical calculations. The simler models give the correct order of magnitude of &, but tend to overestimate it by a factor of about two. The quantum mechanical calculations4"7 have been carried out for the noble and alkali metals with generally reasonably good agreement with the available Ef data. The calculation of entropy of formation Sfv14 lnvolves a fundamental calculation of the perturbation of the phonon spectrum caused by the creation of a vacancy. Huntington, Shirn. and wajda8 have given an approximate evaluation of sJV by considering an Einstein model for the localized vibrations in the immediate neighborhood of the defect and then using elastic theory to calculate the entropy associated with the shear stress field in the distorted crystal (as originally proposed by Zenerg). They also included a term due to the dilation of the crystal. They obtained a value of 1.47k for copper, in good agreement with the experimental value (1.50k). However, Nardelli and Tetta- manzi1° have recently shown that neglecting the coupling between atoms (Einstein Model) may lead to a serious error so the agreement may be somewhat fortuitous. In this work simple linear elastic theory is used to calculate the entropy and energy of formation of mono-vacancies. Despite the simplicity of some of the assumptions involved, the agreement with the available experimental data is remarkable. However. the reasonable degree of success in the application of linear elastic calculations to the excess entropy of a solute atom in a dilute solid solution1&apos; indicates that the application of elastic theory to vacancies. where the interaction of different atomic species is not involved, may not be inappropriate. THE ELASTIC MODEL The metal is assumed to be a spherical elastic continuum. A small spherical cavity of volume V = 4i;v:&apos;/3 is cut from the center. removed. and dissolved rever-sibly in the bulk of the material. TO a good approximation no net atomic bonds are broken and the material does not undergo a volume change although the externally measured volume of the body would increase by V. The radius of the sphere of metal is much larger than r Next a negative pressure is applied to the cavity causing its surface to be displaced inward by an amount simulating the relaxation of the lattice around a monovacancy. In this model the energy and entropy accompanying the distortion are taken as 4, and <. As a first approximation the equation of state for the solid is taken as: r = ro(i + *~D LiJ where K is the bulk modulus. P the hydrostatic pressure. Vo the volume of the material at 0°K and zero pressure. and d+/dT = 30. where 0 is the linear thermal expansion coefficient. The variation of entropy with hydrostatic pressure is given by the Maxwell equation: These equations give the entropy change resulting from increasing the hydrostatic pressure from 0 to P as: and since • we have: This is the entropy arising from the dilation resulting

Jan 1, 1970

By LE B. GRAY

ALL meeting of the Chemical Section, National Safety Council, in Rochester, N. Y., put his hand on at least ten salient points that apply to safety in nearly any laboratory ; these are as follows : 1. Impress your laboratory worker at the start that he is dealing with powerful and dangerous-forces and that every experimental set-up must be studied from the stand- point of its fiber, electrical, explosive, and health hazards.

Jan 1, 1929