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By Marlin J. Veesaert

Urban quarries offer one of the greatest opportunities for profit in nonmetallic mining with limited financial risk-if properly evaluated, planned and developed to meet market needs. Location, with respect to market, is the prime consideration. Geologic considerations and quality of rock are nearly as important. Cost factors and return on investment (ROI) are the principal financial considerations. Risk of capital is determined by weighing all factors that should be considered and how well judgments are based on information acquired. It is a simple, true axiom of business that an investment must be founded on amount of capital required with its expected return plus profit, expertise required to operate, and time involved. Urban quarries generally offer excellent stone product market opportunities. Costs of land with mineral containment and processing operations are much greater than in rural areas. Environmental problems have become increasingly severe. Competition from other quarries in the market area is usually directly proportional to the profit attractiveness. Risk of capital (initial, developmental and operational) can be evaluated and reduced only by thorough analysis of the entire situation. Time and money expended on planning and preliminary investigations probably represent the most productive investment of available company resources. Basic Reasons to Establish a Limestone Quarry Profit Motive: Certainly the dominant and overriding motive must be that of attaining a reasonable profit. In certain situations a quarry firm may acquire land, necessary rezoning (if required), and satisfy all of the other prerequisites preparatory to beginning operations but delaying the actual development.

Jan 1, 1980

By C. K. Leith

THE purpose of these conferences has been to find some basic principles to guide us in the chaos which confronts us, to arrive at elements of a national policy. None such exists, nor, as a matter of fact, have there been any concerted efforts by the public or the mineral industry to evolve one. In the absence of such a policy the administrative agencies of the government can hardly be expected to be consistent or really effective in their handling of mineral problems, domestic or foreign. Basic Facts MINERAL reserves are unequally distributed among the nations. The principal world supplies are grouped around the north Atlantic, and nearly three-fourths of the world's total is controlled politically and commercially by English-speaking people. No one nation has a complete supply of the minerals necessary for modern industry; specialization, reciprocity, and large-scale movements between the nations are inherent in nature's unequal distribution of them. The principal sources of supply are relatively few compared with the nations to be served-a fact which determines broadly certain natural outlines of the world flow. National isolation with regard to minerals can be accomplished only through backward steps in industry and lower standards of living even in the nations possessing the most of the mineral supplies. A certain measure of unified commercial control, international in scope, is a natural consequence of the limited number of the large sources of supply. Mineral supplies for the world as a whole are so large that there is little need for concern about early exhaustion, but every nation has important problems of early exhaustion of particular minerals, which must affect their policies.

Jan 1, 1933

By Robert C. Linares

Cubic zinc sulfide has been grown from molten salt solutions substantially below the hexagonal-cubic phase transition of 1020°C. Crystals free of birefringence have been grown from molten lead chloride at temperatures from 500° to 800°C. Factors affecting the optical transmission and the birefringence are discussed. CUBIC zinc sulfide is of interest for electrooptic devices and as an optical coating material. However, it cannot readily be produced as large crystals which are free of birefringence. The birefringence arises from the fact that the cubic ZnS is usually grown as the high-temperature hexagonal phase and is transformed to the lower cubic phase by annealing.' This results in stacking faults, stress, and birefringence. A requirement for the growth of cubic ZnS is that it be grown below the phase transition of 1020°C.2 Crystals of cubic ZnS have been grown below 1020°C by the hydrothermal,3 flux,4 and vapor transport5 techniques. However, these all appear to have limitations in size or quality of material produced. It was felt that a new flux method might have a good chance of overcoming some of the previous problems. Mita6 reported the growth of hexagonal ZnS from molten NaCl and wilke7 reported the growth of iron sulfides from molten lead chloride solution, indicating that molten chlorides make good solvents for sulfides. An investigation of a number of possible molten chlorides as solvents showed that molten PbCl2 has an appreciable solubility for zinc sulfide and that crystals can be grown at temperatures from 500° to 800°C. EXPERIMENTAL Crystal growth was performed in open or sealed Vycor or fused silica tubes, in an argon atmosphere or vacuum. There were no deleterious effects due to using vacuum; however, a sealed essentially isothermal system must be used to prevent vapor transport mechanisms from dominating. This will be discussed later in detail. Noble metal containers were not usable as they were severely attacked by these melts. The materials used were: reagent-grade PbC12, reagent-grade ZnS, optical-coating-grade ZnS, and Irtran 2 (ZnS). Crystal growth was accomplished by both slow cooling techniques and gradient growth techniques. In the slow cooling techniques, 15 g of ZnS and 100 g of PbCl2 were used. The components were placed in the silica tube, heated at 800°C for 2 hr, and then slowly cooled (l° to 10° C per hr) to 500°C. The furnace was constructed so that the tube could be inverted, thus allowing the liquid to drain off the crystals at the end of the run. The gradient runs were made by placing the above mixtures in a silica tube at 550° to 600°c, Fig. 1. A temperature gradient was maintained such that the floating mass of undissolved sulfide was 10° to 50°C warmer than the bottom of the tube. Growth occurred on spontaneously nucleated sites at the cooler bottom. RESULTS When using high cooling rates (5° to 10°C per hr), crystals form in thin sheets perpendicular to the {111} face. Crystals 5 by 5 by 1.2 mm, Fig. 2, have been ob-

Jan 1, 1969

By Sherwin F. Kelly

THE geophysical scene shifts and alters, the emphasis changes, and new possibilities loom, but the tendency is always towards widening the field and deepening the analytical penetration. Seismic methods have had their heyday, the torsion balance is being displaced by the gravimeter, electrical methods are showing deeper penetration, soil analysis is the newest tool, and gamma-ray logging appears on the horizon. One of the striking features of re- cent geophysical work in the oil fields has been the marked decrease in the number of seismic crews employed. Although the percentage of company crews is believed to have increased appreciably. the sum total has fallen sharply, as shown by the figures for the Gulf Coast area. About two years ago probably over 100 seismic parties were operating there, whereas now there are only about 35. This decrease may be partly due to the low prices of petroleum with a consequent reluctance to spend money to increase crude-oil re- serves but more probably to the fact that reflection and refraction shooting have been carried on so extensively that they have been applied to a large pro- portion of the areas in which they may reasonably be expected to succeed. Some of the earlier enthusiasm, particularly over reflection prospecting, may have erred on the side of over- optimism; some of the present curtailment may be due to over pessimism; but in the opinion of various observers seismic work at the present rate seems to be at it- optimum. It nevertheless remains pre-eminent as a technique for detailing structures in areas where good reflections can be obtained and is the only method that will give accurate depth to definite beds. Results may be poor in certain areas but many regions still remain wherein it can be applied, so that plenty of structural mapping remains to be done by the reflection seismic method.

Jan 1, 1940

By Edgar A. Scholz, Attilio G. Spat

The rapid worldwide increase in labor costs, prices of goods and services, and the rising tide of economic nationalism do not bode well for the future of mineral exploration and the mining industry. The increasing complexity and difficulty involved in finding economic mineral deposits makes these trends particularly significant. A comparative cost analysis of domestic and foreign exploration projects which developed into mines during the period 1960-74 may be useful in indicating the general nature of exploration expenditures as these trends continue. This analysis is based on a survey of 18 US and Canadian mining companies. Due to the inexact nature of exploration expenditure data, plus the fact that no two mining companies follow the same system of cost allocation, the results of the survey must be considered quite general in character.

Jan 6, 1977

By AIME AIME

The following financial report of the Treasurer of the United Engineering Society is published for the information of members NEW YORK, February 15, 190S. To the Board of' Trustees, United Engineering Society I beg to submit herewith the report of the Treasurer as of December 31, 1907. Your attention is called to the fact that the resources and liabilities, receipts and disbursements statements cover all the financial transactions of the United Engineering Society from its organization up to December 31, 1907. The income and expenses of operating the building during the whole operating period from December 1 to December 31, 1907, somewhat in excess of twelve months, are given. Included in the expenses, amounting in all to $52,647.11, will be found an item entitled "Building Equipment (construction account)." The expenditures under this item were not made for the operating expenses of the building, they represent a construction account, properly speaking, covering expenditures for furnishings and equipment of the building. The Founders' Agreement specifically provides for this class of expenditure under the provision that the Founder Societies shall each be liable for a charge not to exceed $200,000 of principal, which shall include the land and building completed and ready for occupancy, together with the " furnishings, equipment and personal property therein." Certain details of equipment are yet to be supplied, and it. is proposed in the near future to call upon the Founder Societies for an assessment on their respective land and building funds to cover this item of building equipment. Such action would enable the item of $10,039.85 to be transferred to the income account and reduce correspondingly the assessment

Mar 1, 1908

By Walter W. Bradley, OLAF P. JENKINS

IN April of this year the California State Division of Mines (formerly known as the State Mining Bureau) observed its 50th anniversary. The Division serves as a bureau of information and, an encyclopaedia of California's economic minerals. Its primary function is to make economic surveys of the mineral resources of California, their development and utilization. Geological studies also constitute a related part of the work as being necessary in tracing and out- lining ore deposits and the most likely areas in which to find them. The results of the Bureau's data-gathering are published in the form of annual reports of the State Mineralogist, and in bulletins on specific substances. The Division is just completing a series of reports on the mineral resources of the State arranged by counties.. It is now starting .a new series of reports arranged according to substances particularly the so-called non- metallic commercial groups. Of these the following are now available: clays, barite, and mineral paint. These will be followed by reports on feldspar and silica, diatomaceous earth, limestone and others

Jan 1, 1930

By Carl Zapffe

JUST as 85 per cent of the total ore produced annually in the United States comes from the Lake Superior region, so does one of its six producing districts-the Mesabi --dominate that region both as to production and total reserves; also in ore Treatment, Mesabi practice is dominant. Therefore, in discussing future reserves or ore treatment one may visualize one big district with five smaller districts as so many satellites. In considering the future less thought need be given to processes than to, economic policies. For thirty years experimental work has now been in progress and every possible ore-treatment process now known has been given attention. This work was started when there was no recognizable danger of running short of ore because of rapid consumption. Thirty years ago the annual production had just progressed beyond the twenty-million bracket for the first time. Today fifty million tons is considered a small production, and last year the aim was for 65 million. At the recent rate of production the life of the estimated reserves of good ore is about 35 years. All who know the local terrain are convinced that, unlike thirty years ago, the chances for discoveries of new big deposits are nil; treatment of lean ores obviously is to become an all-important topic.

Jan 1, 1938

By W. C. Clarke

An empirical study of the nature of the embrittle-ment which occurs in martensitic and semiaustenitic precipitation hardening stainless steels upon exposure at temperatures of from about 550" to 875°F has been undertaken. This work was aimed at determining cazusation and means of controlling this phenomenon. A commercial copper bearing precipitation hardening alloy was used as a basic material for study. The effect of heat treatment variables was studied as was the effect of variations in analysis. It is concluded from the evidence that martensitic and semiaustenitic precipitation hardening stainless steels are subject to 885°F ernbrittlement similar to that observed in the straight chromium stainless steels. A characteristic of precipitation hardening stainless steels which has limited their use in certain applications is that they embrittle when held at temperatures in the range of from about 550" to 900°F. This is true to a more or less degree in all currently available alloys, either the basically martensitic type or the semiaustenitic type. The rate of embrittlement varies markedly with exposure temperature, being low at 550" to 600°F and in-creasing as the temperature increases. In spite of this embrittlement, these alloys with their unique combination of high mechanical strength, reasonable toughness, and good corrosion resistance are used in many hundreds of applications. Nevertheless, there are potential applications where the embrittle-ment described is a limiting factor. The purpose of this investigation was to study the embrittlement of these alloys and to find a way to control or eliminate it. GUIDELINES USED IN PRESENT WORK The work reported in this paper is based on a study of 17-4 PH*, a very widely used alloy. It has been used *Trademark of Armco Steel Corp., licensor. in pressurized water and boiling water atomic reactors operating at about 550°F for a number of years. As the life of such equipment is extended or operating temperatures are raised, the possibility of embrit-tlement becomes of increasing concern to materials engineers. Much investigation work was done with respect to the use of 17-4 PH at 550°F. K. C. Antony' states "Such estimation" (of an activation energy for the diffusion of chromium in iron) "would indicate W. C. CLARKE, Jr. is Senior Research Engineer, Advanced Materials Division, Armco Steel Corp., Baltimore. Md. This manuscript is based on a talk presented at the symposium on New Developments in Stainless Steel, sponsored by the IMD Corrosion Resistant Metals Committee, Detroit, Mich., October 14-15, 1968. significant secondary aging is improbable at temperatures less than 700°F within normal component service life". This statement is modified however by the recognition of the accelerating tendencies of applied stress and internal stress as well as the possible effect of irradiation. In this investigation of 17-4 PH, the H 1100 (1900°F-1 hr oil quench or air cool + 1100°F-4 hr-air cool) condition was used, partly because this condition is normally used in atomic reactors. As shown later, the precipitation hardening temperature has no real bearing on the rate of embrittlement. An exposure temperature of 800°F was selected since embrittlement at 800°F is rapid, permitting development of relative data in time periods of 400 to 500 hr. For those not familiar, a nominal present day analysis of 17-4 PH is: C Mn P S SiCrNiCuCbN 0.04 0.30 0.015 0.015 0.60 16.00 4.30 3.25 0.23 0.030 TYPICAL BEHAVIOR OF 17-4 PH Figs. 1 and 2 show the behavior of a commercial heat of 17-4 PH under the conditions defined. Characteristically, 800°F exposure causes a rapid drop in Charpy V-notch impact strength. Tensile and yield strengths gradually increase and a gradual loss of elongation and reduction of area occur, accompanied by an increase in hardness. Notched tensile strength increases to 125 hr exposure and then sharply decreases after exposure for 500 hr. The notched vs un-notched tensile ratio remains virtually constant to exposure for 125 hr (1.67 to 1.56) but drops to 1.15 after 500 hr. Tensile ductility is not alarmingly affected even after much longer exposure times than these. For example, samples aged at 1100°F for 1 hr exposed at 800°F for 4000 hr showed a drop in elonga-tion of from 13 to 11 pct and in reduction of area of from 58 to 37 pct. Notched impact is the property SmIgth KSI 3JJ[/__________^UTS-Nrteh 260 ;/- 240 —^ 200 UTS-Smooth________._, o ioo mo Sob" m Too Hours Exposure Fig. 1—Effect of exposure at 800°F for various times on notched tensile strength and smooth tensile and 0.2 pct yield strength of 17-4 PH in the H 1100 condition.

Jan 1, 1970

By B. P. Mulcahy

When the phrase "selection of coal for carbonization" is used, there is always the implied continuance of thought "to make good coke.'' The reason for this, of course, lies in the fact that, in almost all instances, when coal is carbonized coke is the principal product. Under certain conditions the yield of gas may also be a factor, but even here it must be secondary to the coke yield, for in every instance coke represents the largest single product of the process. The importance of coke to the byproduct industry has been considerably enhanced during the past 20 years because of the continuously decreasing financial returns of all the by-products. This fact will account, in part, for the rebirth of interest and investigation in the carbonization process during the past 10 years. Many papers have been written on this subject, with naturally divergent thoughts because of the diversity of interests, but in each instance the common aim was the same—the making of better coke. Scope of Investigation In perusing this literature, the writer was struck with the constantly recurring imposed condition of asking for better coke, but with the distinct unwillingness to make any concession to temperature of carbonization. When there is a high demand for coke, the only means by which the industry can increase the quantity is to shorten the coking time by an increase in temperature, or to increase the quantity of low-volatile coal, or both; and since in many instances the percentage of low-volatile coal can be increased only in small quantities, because of factors to be discussed later, the big increase must come from shortening the coking time. When this is done most of the improvement accomplished by the selection of the coals in the mixture is lost. It is not felt necessary in this paper to discuss the advantages of minimum ash and sulphur and other materials in coal. The value of minimum contents of these materials in coke is well established. When the use of coals high in these contents is dictated, the selection of coals, as we will consider it here, cannot apply to full advantage. The scope of this paper, then, will be to discuss the factors of inherent coal characteristics and operating procedures that influence coke quality, for they are fundamentally related and both must be considered if we are to attain our objective of better coke. A study of either must embrace a study of both simultaneously. To properly evaluate the influence of the coal and to help in the selection, we must first be able to appraise the coke, and interpret fairly the influence of the process in all of its aspects. Appraisal of Coke To refer simply to the quality of coke gives no indication of what is meant, for the term is too general in its implication. An analysis of a coke is divided usually

Jan 1, 1944

By B. P. Mulcahy

When the phrase "selection of coal for carbonization" is used, there is always the implied continuance of thought "to make good coke.'' The reason for this, of course, lies in the fact that, in almost all instances, when coal is carbonized coke is the principal product. Under certain conditions the yield of gas may also be a factor, but even here it must be secondary to the coke yield, for in every instance coke represents the largest single product of the process. The importance of coke to the byproduct industry has been considerably enhanced during the past 20 years because of the continuously decreasing financial returns of all the by-products. This fact will account, in part, for the rebirth of interest and investigation in the carbonization process during the past 10 years. Many papers have been written on this subject, with naturally divergent thoughts because of the diversity of interests, but in each instance the common aim was the same—the making of better coke. Scope of Investigation In perusing this literature, the writer was struck with the constantly recurring imposed condition of asking for better coke, but with the distinct unwillingness to make any concession to temperature of carbonization. When there is a high demand for coke, the only means by which the industry can increase the quantity is to shorten the coking time by an increase in temperature, or to increase the quantity of low-volatile coal, or both; and since in many instances the percentage of low-volatile coal can be increased only in small quantities, because of factors to be discussed later, the big increase must come from shortening the coking time. When this is done most of the improvement accomplished by the selection of the coals in the mixture is lost. It is not felt necessary in this paper to discuss the advantages of minimum ash and sulphur and other materials in coal. The value of minimum contents of these materials in coke is well established. When the use of coals high in these contents is dictated, the selection of coals, as we will consider it here, cannot apply to full advantage. The scope of this paper, then, will be to discuss the factors of inherent coal characteristics and operating procedures that influence coke quality, for they are fundamentally related and both must be considered if we are to attain our objective of better coke. A study of either must embrace a study of both simultaneously. To properly evaluate the influence of the coal and to help in the selection, we must first be able to appraise the coke, and interpret fairly the influence of the process in all of its aspects. Appraisal of Coke To refer simply to the quality of coke gives no indication of what is meant, for the term is too general in its implication. An analysis of a coke is divided usually

Jan 1, 1944

By AIME AIME

A JOINT meeting of the Canadian Institute of Mining and Metallurgy and the American Institute of Mining and Metallurgical Engineers was held at Spokane, Wash., and Cranbrook and Kimberley, B. C., on Oct. 13 to 16, 1926, with a total attendance at one or another or all of the meetings of about 300 members, ladies and guests. At the opening meeting, on Oct. 13, in the Davenport Hotel, Spokane, about 175 were present. The morning was occupied with addresses of welcome by M. H. Sullivan for the Columbia Section, who called on Mayor Charles A. Fleming, President John F. Davies for the Chamber of Commerce, and E. R. Hannibal, president of the Associated Engineers, each of whom heartily welcomed the visitors. Philip N. Moore, former president, and special representative of President Samuel A. Taylor, replied for the A.I.M.E., and Lewis Stockett, president, and Charles A. Banks, chairman, British Columbia Division, Canadian Institute of Mining and Metallurgy, and Henry M. Parks for the visiting A.I.M.E. sections, made appropriate responses on behalf of those they represented. The members and ladies had luncheon with the Associated Engineers. Philip N. Moore addressed the assembly on "The Opportunity of the Engineer"; an excerpt from his address appears on another page. At the afternoon meeting, with Lewis Stockett in the chair, Frank M. Smith was asked to make a brief statement of the proceedings of the Silver Producers Association in Denver. Supplementing his talk by placing a well-prepared statement on "Silver and the Plan of the Royal Commission on Indian Currency and Finance" in the hands of those present, he narrated what had been undertaken by the Silver Producers Association and what they hoped to accomplish.

Jan 1, 1926

By G. C. Stone

AS the term "hardness" is used with many different meanings, it should be understood that it here means resistance to deformation by compression. It was determined by measuring the pressure, in pounds per square inch, necessary to reduce by 20 per cent., the length of cylinders 1 in. (25 mm.) in diameter by 2.6 in. (66 mm.) long. The tests were made at Columbia University on an Olsen 400,000-lb. machine, the load being applied at a constant rate of speed 0.0319 in. per min. The results were obtained by Messrs. Rigg and Williams, and some of them were given in a paper read at the Sixteenth Annual Meeting of the American Society for Testing Materials, in June, 1913. The remainder of the results were obtained in subsequent experiments by the same authors. In all cases, the results given are the averages of three or more closely concordant tests. All of the spelters tested were of standard commercial grades and all were of compositions making them good deliveries. The accompanying table gives the results arranged in the order of increasing hardness:

Jan 1, 1919

By Fred D. DeVaney and

The coercimeter, as its name implies, is an instrument for measuring the coercive forcet of magnetic substances. It was developed by Davis and Hartenheim in the Special Studies Section, Metallurgical Division. A detailed description of this apparatus may be found elsewhere.2 The coercive force determinations of magnetic materials are interesting because of the relationship established by Gottschalk,4 who showed a linear relationship between the magnetization coercive force and the specific surface of comminuted particles. The value of this relationship in determining grinding efficiency has been shown by Dean.3 The determination of the surface contained in the subsieve sizes has always been a difficult problem for investigators. They made approximate measurements of the surface of coarse materials by sizing on screens, but for the determination of the surface of the sub-sieve sizes it was necessary to make detailed grain counts or elutriation tests, or to study dissolution rates. The technical literature contains many references to other methods for determining these surfaces, either by some special apparatus or by mathematical calculations based on distribution lines. Many of the methods are long and tedious, and the results of some, at least, are questionable. he turbidimeter gives quick results on ground cement. By using magnetite as the material to be ground, a simple determination of its coercive force by the coercimeter, requiring 10 minutes or less, can be transposed directly and accurately into units of relative surface. This subject has been pursued further by the U. S. Bureau of Mines in cooperation with the Missouri School of Mines and Metallurgy, Rolla, Mo., and the following is a description of the results.

Jan 1, 1939

By Fred D. DeVaney and

The coercimeter, as its name implies, is an instrument for measuring the coercive forcet of magnetic substances. It was developed by Davis and Hartenheim in the Special Studies Section, Metallurgical Division. A detailed description of this apparatus may be found elsewhere.2 The coercive force determinations of magnetic materials are interesting because of the relationship established by Gottschalk,4 who showed a linear relationship between the magnetization coercive force and the specific surface of comminuted particles. The value of this relationship in determining grinding efficiency has been shown by Dean.3 The determination of the surface contained in the subsieve sizes has always been a difficult problem for investigators. They made approximate measurements of the surface of coarse materials by sizing on screens, but for the determination of the surface of the sub-sieve sizes it was necessary to make detailed grain counts or elutriation tests, or to study dissolution rates. The technical literature contains many references to other methods for determining these surfaces, either by some special apparatus or by mathematical calculations based on distribution lines. Many of the methods are long and tedious, and the results of some, at least, are questionable. he turbidimeter gives quick results on ground cement. By using magnetite as the material to be ground, a simple determination of its coercive force by the coercimeter, requiring 10 minutes or less, can be transposed directly and accurately into units of relative surface. This subject has been pursued further by the U. S. Bureau of Mines in cooperation with the Missouri School of Mines and Metallurgy, Rolla, Mo., and the following is a description of the results.

Jan 1, 1939

By W. F. Boericke, T. H. Garnett

The Wisconsin zinc district, or the Upper Mississippi lead and zinc district as it is also termed, lies in the southwestern corner of Wisconsin, and embraces adjacent portions of Illinois and Iowa. It includes Iowa, Grant, and Lafayette counties in Wisconsin, and Jo Davies country in Illinois. In Iowa, Dubuque formerly produced considerable lead, but there has been little mining there in recent years. The map, Fig. 1, shows the entire district, withroads, railways, streams, and the various towns, or "camps," around which the mines are clustered. The hatchwork indicates the areas in which lead and zinc have been mined. The district is about 60 mi. (96 km.) north and south and about 40 mi. (64 km.) east and west. Not all of the territory is mineral bearing, and there are considerable areas that are believed to be barren. The grouping of the mines is patchy and irregular, though certain broad zoncs of mineralization extend almost the full width of the district, as from Mineral Point west through Mifflin and Livingston, and from Shullsburg west through New Diggings and Hazel Green. It is worth noting that the best mines of the district have, to date, been found within 10 mi. ease or west of the fourth principal meridian line, thus lying within a long, narrow, north-and-south belt extending the length of the district. In a field as large as the Wisconsin, which has only within comparatively recent time been worked intensively for zinc, the chances are good for opening new and important orebodies in parts of the district not yet, or insufficiently, prospected. However; the prospecting has been most successful around, or adjacent to, the old lead diggings of nearly a century ago, and the camps that were well known then are still centers of activity. In their order of importance they are: New Diggings, Ben-ton, Mifflin-Livingston, Galena, Linden, Hazel Green, Shullsburg, and Highland. The district is one of the best farming districts in Wisconsin, with deep fertile soil. The farms are large and well improved, and the towns are modern and prosperous. Railroad facilities are good and proximity to Chicago is an asset. Mining is usually done on a leasing system of 10

Jan 1, 1920

By William L. Fink and

Although age-hardening in an aluminum-base alloy containing magnesium was observed by Alfred Wilml as early as 1911, it was not until 1919 that a theory of the mechanism of age-hardening was proposed. Merica, Waltenberg and Scott12 studying the age-hardening characteristics of Duralumin at the National Bureau of Standards, came to the conclusion that age-hardening of this alloy is caused by the precipitation of CuAl2, which is less soluble at the aging temperature than at the solution heat-treating temperature. It was postulated that the initially precipitated particles were of fine colloidal dimensions but that they gradually grew in size. Maximum hardness was assumed to be attained when the particles reached a critical size. This theory was at first received skeptically, since it was a widely accepted view at that time that the solid solution state should represent the hardest state of an alloy. Shortly thereafter, Jeffries and Archer proposed their well-known slip interference theory.'13 They suggested that age-hardening was accomplished by the precipitated particles acting as keys interfering with slip along crystallographic glide planes. They showed that this mechanical theory led direct,ly to the assumption that maximum hardening would be produced by particles of a critical size, which they suggested would have a diameter approximately 10 times that of the aluminum atom. This contribution amplified and explained so rationally the age-hardening theory of Merica, Waltenberg and Scott that wide acceptance resulted. Objections to Simple Precipitation Theory From time to time certain experimental facts have been cited against the simple precipitation theory. The first of these was the discovery by Fraenkel4 that, although the electrical resistivity of Duralumin decreased during aging at higher temperatures (from 100' to 250' C.), it increased during aging at ordinary temperatures. This was not in accordance

Jan 1, 1940

By William L. Fink and

Although age-hardening in an aluminum-base alloy containing magnesium was observed by Alfred Wilml as early as 1911, it was not until 1919 that a theory of the mechanism of age-hardening was proposed. Merica, Waltenberg and Scott12 studying the age-hardening characteristics of Duralumin at the National Bureau of Standards, came to the conclusion that age-hardening of this alloy is caused by the precipitation of CuAl2, which is less soluble at the aging temperature than at the solution heat-treating temperature. It was postulated that the initially precipitated particles were of fine colloidal dimensions but that they gradually grew in size. Maximum hardness was assumed to be attained when the particles reached a critical size. This theory was at first received skeptically, since it was a widely accepted view at that time that the solid solution state should represent the hardest state of an alloy. Shortly thereafter, Jeffries and Archer proposed their well-known slip interference theory.'13 They suggested that age-hardening was accomplished by the precipitated particles acting as keys interfering with slip along crystallographic glide planes. They showed that this mechanical theory led direct,ly to the assumption that maximum hardening would be produced by particles of a critical size, which they suggested would have a diameter approximately 10 times that of the aluminum atom. This contribution amplified and explained so rationally the age-hardening theory of Merica, Waltenberg and Scott that wide acceptance resulted. Objections to Simple Precipitation Theory From time to time certain experimental facts have been cited against the simple precipitation theory. The first of these was the discovery by Fraenkel4 that, although the electrical resistivity of Duralumin decreased during aging at higher temperatures (from 100' to 250' C.), it increased during aging at ordinary temperatures. This was not in accordance

Jan 1, 1940

By W. N. Carr, J. R. Biard, B. S. Reed

An analysis of the semiconductor injection laser is presented which is based on a phenomenological model using device and material parameters. The intent of the laser threshold analysis is not to predict from theory the actual threshold current density but rather to provide a logical means of interpreting experimental results. The device and material parameters have been selected such that they describe both the threshold conditions and quantum efficiency of the lasev. A technique is proposed whereby the current required to obtain a population inversion is predicted from device 1-V characteristics. Experimental data are presented which support the analysis. THIS investigation is concerned with the characteristics of GaAs lasers fabricated in this laboratory. However, the assumptions used in these calculations should not limit their application to GaAs alone. It is felt that the analysis is sufficiently general to be useful in describing the operation of other semiconductor-laser materials. ANALYSIS heavily doped semiconductors to be considered. The absorption and/or generation of optical radiation may be completely specified in terms of q(E) and the probability functions f,,(E) and f,(E) which define the occupancy of the valence-band and conduction-band levels, respectively. The symbols used in this analysis are listed at the end. Following the approach of all' it can be shown that the effective gain coefficient, g, in the plane of a forward-biased P -N junction is g(E)=-ai@)[1-fv(E)-fc(E)] [1I In particular Eq. [I] holds for the photon energy at which lasing occurs, Ep. Throughout the following discussion Eq. [I] is considered only for the lasing transition E = Ep. For simplicity the functional energy dependence of the various factors is omitted in subsequent equations. Unless otherwise stated the symbols used represent the values at Ep. If the analysis is limited to the P-type side of the laser junction, the function q(l -f,,) is recognized as the band-to-band absorption in the P-type material at thermal equilibrium. Under forward-bias conditions the function f, is determined by the electron quasi Fermi level in P-type material. For sufficiently large forward bias the second term in Eq. [3] will become dominant and net gain will result; i.e., g will become positive. In order to simplify the subsequent analysis several assumptions are in order at this point. a) No conductivity modulation occurs. /„ is independent of f, and therefore go is a constant. b) The P-type material is heavily doped such that the degeneracy of the valence band permits popu-

Jan 1, 1964

By R. W. Newcomb

THE constancy of calibration, and to a great extent the life, of a thermoelement is dependent on the suitability of the primary protecting tube in which the wires are mounted, particularly when used at high temperatures. An ideal thermocouple protecting tube would be com-posed of materials that would not contaminate the thermoelement wires contained in it-one that would remain absolutely gas-tight ,it all temperatures of usage, that will not be attacked by gases, or other surrounding agencies, that is not destroyed by heat, that withstands sudden and extreme temperature changes, that affords a high degree of mechanical protection and does not deform at high temperatures, that is a good heat conductor and obtainable in small diameters so as to keep down lag factors. It has not yet been possible to produce tubes of any known mate-rials that will meet all of these conditions. In selecting protecting tubes, therefore, one should be chosen the characteristics of which best fit it to the particular conditions of usage. Frequently conditions are such that two tubes have to be used, a primary gas-tight protecting tube inside of a secondary protecting tube, because certain agencies will attack the primary gas-tight tube unless it is guarded by the outside tube.

Jan 9, 1919