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By K. C. Carriere

INTRODUCTION The purpose of this section is to introduce the reader to the concepts of computer control of grinding circuits, and to flag some of the opportunities to be encountered, but without becoming overly involved in details of process, equipment or software. It is assumed that the reader has some familiarity with computer hardware and software, and in particular with the grinding process. The paper is organized into four parts: a general commentary of the need for computer control of grinding, a discussion of the process considerations involved, a more detailed elaboration on the current state of applicable computer technology, and a case study indicating one approach towards such a project. A brief installation survey and references for further reading are also given. This section will primarily deal with supervisory computer applications. Direct Digital Control and microprocessor systems are generally used as replacements for analog controls and thus are not considered in depth. Many configurations of grinding circuits exist, necessitating certain assumptions. Since many new concentrators use an open circuited SAG mill feeding a closed circuit ball mill, this configuration is used as a model although the principles stated can be extrapolated to any circuit. Motivation The use of computers for industrial control has been one of the dreams of control engineers and operators alike for many years. The concept of a plant running at optimal conditions with minimal operator involvement is very attractive from economic and technical standpoints. Accomplishment of this goal has been a long struggle, but today likelihood of success of such a project is very high, considering the reliability of modern hardware and the sophistication of available software. The primary motivation of any control system must be economic, i.e. it must pay for itself and make money for the owner, directly or indirectly. In grinding control the benefits which can be expected include: a) Higher through-put b) More uniform product in particle size, density and volumetric flog: c) Reduced operating costs including media consumption, power consumption and liner wear

Jan 1, 1982

By L. S. Reid, R. L. Hunntington

The study of the flow of oil and gas mixtures through oil-bearing formations has received special attention from the petroleum industry within the past few years, and has resulted in a series of research projects based upon various phases of the flow of heterogeneous fluids through porous media. Obviously, the low cost of producing oil during the flowing life of a well makes it desirable to obtain production by natural flow as long as possible and to effect a maximum recovery of oil and gas by the utilization of reservoir energy through efficient methods based upon a thorough knowledge of reservoir characteristics. Despite the extensive research that has been carried out, there is little information available on the behavior of oil and gas mixtures flowing through reservoir formations. This makes it impossible to predetermine the optimum operating conditions for flowing wells. A differential pressure must exist in the reservoir in order to induce flow toward the well. It is a well established fact that with homogeneous fluids the relation of pressure drop to linear distance traveled is a straight-line function as long as the flow is viscous. However, in regard to gas-saturated oils, a number of investigators1l,2,3 have reported that the flow characteristics are materially altered as some of the lighter hydrocarbons are liberated from the oil to form gas while the fluid passes through the reservoir. Most of the work done has been concerned primarily with steady-state flow of liquid-gas mixtures. Cloud1 has studied the effects of saturating crude petroleum oils with various gases, together with the resultant pressure gradients under steady flow conditions, noting that unsaturated oils flowed faster and yet maintained lower pressure gradients than saturated oils. The work of Wyckoff and Botset4 has constituted a major step in the interpretation of heterogeneous fluid flow; especially their concept of

Jan 1, 1938

By John Birkinbine

Through the partiality of my fellow-members I have been able, during seven years' service on the Council of the American Institute of Mining Engineers, to note the development of technical societies, a subject which commends itself as an appropriate theme for me, in retiring from the office of President, at a time when we meet in convention with Canadian technical societies. Our next assembly, called at Chicago at the time fixed for an International Engineering Congress, offers additional reason for the selection of this topic. If subsequent statements appear to give to the American Institute of Mining Engineers greater prominence than to kindred organizations, they may be excused upon the ground of long association with and loyalty to its members, and to a personal knowledge of their work. Besides, data as to its growth and development are more accessible; and at a meeting of the Institute features connected with it may be considered as of greater immediate interest than those affecting other organizations. The purpose of this address is, however, to use the record of the Institute as indicating a similar development of other technical societies, rather than to claim preeminence for any organization; the work of each must speak for it. There is a general tendency to form associations at the present time. Organizations have been created and are active in every profession and in all branches of labor, trade, industry, commerce, manufactures, science and art. A record of such associations and their aggregate membership would be startling, and would show how large a percentage of the population of North America is connected with one or more of them; but the figures cannot be even approximately estimated. The class of associations representing national, state, or local trade interests, such as boards of trade, chambers of commerce, etc., may be used as an illustration. A late report shows that in the

Jan 1, 1893

By Alexander Gakner

Since the end of World War II the Soviet Union has made great strides toward economic development of the country. Today it is firmly established as the world's second largest industrial power after the United States and it has committed itself before the people on both sides of the Iron Curtain to catch up with and to overtake us within a few decades. No nation could achieve such a degree of industrialization or aspire to become the world's industrial leader without a large supply of many basic mineral raw materials or at least easy access to such resources. In addition, it requires technical competence, a large skilled labor force, and a high rate of capital investment. Why should we concern ourselves with these Soviet aspirations? The Free World's yardstick of measuring a nation's well-being is the standard of living of the people in that country. Presumably even Communist governments are committed to some, however gradual, improvement in the standard of living of their people. The population of the USSR is 20 pct greater than that of the United States. Hence, if they ever achieve a standard of living equal to ours, they must by all logic reach a greater overall industrial output. However, in the U.S.S.R. the standard of living of the masses has not kept pace with the expanding industrial production and is still far behind that of the United States. Our concern, therefore, is with what the USSR intends to accomplish with its expanding industrial power: Will they produce large mineral raw-material surpluses and manufacture products to compete with us for world markets and attempt to put us out of business if not use it directly to wage war; or will they use their resources merely to produce more consumer goods for the Soviet people; or will they, along with other Communist nations in the not-too-distant future, compete with us for the world's sources of mineral raw-materials to maintain a high level of mass consumption?

Jan 6, 1960

By Herbert Dlaska

The BBU - rotary hearth treats lead concentrates and battery scrap by the roast-reaction process. It corresponds in principle to the long-known Newnam hearth, however its hearth-basin is not straight but curved to a closed ring. In operation this annular hearth is filled with liquid lead and rotates around a central blast-box. The charge, heated to a glowing-red, floats on top of the lead bath, into which air is blown from the blast-box through a horizontal slot-type tuyere. Ore pellets and brown coal are continuously charged onto the reacting mass from two storage bins. Lead is set free by the roasting reactions and trickles through the charge into the lead bath from where it is tapped from time to time. The reacting mass is continuously stirred by a mechanical agitator and backed, by a mechanical shovel, against the water-jacketed wall of the blast-box. The gangue of the charge forms lumps of scorified character, the so-called hearth slag or grey slag, which are discharged from the hearth. The waste gases are collected in a hood and conducted to a baghouse from where the fumes and dust are automatically transported to the pelletizing installation and are recycled with new material. The daily output of lead bullion depends mainly on the lead content of the charge. With lead concentrates containing 74% lead, about 24 tons of lead bullion per day are produced on the hearth at a direct lead recovery of about 89 per cent. Approximately 10 per cent of the lead content of the new material passes into the hearth slag from where it can be recovered in a blast furnace or in a rotary furnace. For small lead smelters the BBU-process represents the most economical way of melting high-grade lead concentrates. The process requires a relatively small capital investment, consumes little fuel, utilizes cheap fuel and is very flexible. Further, of great importance, is the fact that battery scrap can be treated by the BBU-process with very good results.

Jan 1, 1970

By T. E. Kihlgren, N. B. Pilling, E. M. Wise

Systematic data are presented on the relation of composition of nickel silvers to color, tarnish resistance, hardness and liquidus temperatures, for alloys containing up to 30 per cent nickel and 50 per cent zinc, further modified at certain nickel and zinc contents by 0 to 8 per cent of tin and 0 to 10 per cent of lead. Attention has also been directed, using a still more limited range of alloys, toward a study of tensile properties and such casting properties and characteristics as fluidity, shrinkage and pressure tightness. In some of these, rather broad ranges of composition are dealt with; in others, it has been expedient to focus attention on the Federal Specification 20 per cent nickel silver casting alloy, WWP-541. Introduction The demand for an alloy essentially white in color, which could be cast and worked by simple methods and which possessed strength and corrosion-resisting properties superior to the usual brasses, led to the discovery and early use of cupronickel alloys containing zinc, and sometimes tin, lead and other metals. This type of alloy was generally known as 'German silver until the war, when the term "Nickel Silver" became generally accepted. The element principally responsible for the white color of the alloy and for its strength and corrosion resistance is nickel, which may constitute from 8 to 30 per cent of the alloy. The functions of the other elements will be described later. The manifold uses of nickel silver are largely due to its color, corrosion resistance, ease of casting, fabrication, joining and rather moderate cost. In many instances the alloy is finished by grinding and polishing while in others it may be finished with a silver or nickel plus chromium plate. Electroplates applied to a nickel silver base behave more satisfactorily than those applied to the softer and less resistant alloys, and owing to the white color of the underlying metal the article will retain a pleasing appearance despite local failures of the plating.

Jan 1, 1935

By E. M. Wise, T. E. Kihlgren, N. B. Pilling

Systematic data are presented on the relation of composition of nickel silvers to color, tarnish resistance, hardness and liquidus temperatures, for alloys containing up to 30 per cent nickel and 50 per cent zinc, further modified at certain nickel and zinc contents by 0 to 8 per cent of tin and 0 to 10 per cent of lead. Attention has also been directed, using a still more limited range of alloys, toward a study of tensile properties and such casting properties and characteristics as fluidity, shrinkage and pressure tightness. In some of these, rather broad ranges of composition are dealt with; in others, it has been expedient to focus attention on the Federal Specification 20 per cent nickel silver casting alloy, WWP-541. Introduction The demand for an alloy essentially white in color, which could be cast and worked by simple methods and which possessed strength and corrosion-resisting properties superior to the usual brasses, led to the discovery and early use of cupronickel alloys containing zinc, and sometimes tin, lead and other metals. This type of alloy was generally known as 'German silver until the war, when the term "Nickel Silver" became generally accepted. The element principally responsible for the white color of the alloy and for its strength and corrosion resistance is nickel, which may constitute from 8 to 30 per cent of the alloy. The functions of the other elements will be described later. The manifold uses of nickel silver are largely due to its color, corrosion resistance, ease of casting, fabrication, joining and rather moderate cost. In many instances the alloy is finished by grinding and polishing while in others it may be finished with a silver or nickel plus chromium plate. Electroplates applied to a nickel silver base behave more satisfactorily than those applied to the softer and less resistant alloys, and owing to the white color of the underlying metal the article will retain a pleasing appearance despite local failures of the plating.

Jan 1, 1935

By J. L. Gregg, C. W. Kuttner

ReceNtly there has been considerable interest in the production and use of extra hard alloys composed primarily of tungsten and carbon. Dr. Hoyt's recent paper1 gives a good description of these alloys and describes their performance when used as tools. There are a number of these alloys on the market sold under various trade names, and it is the purpose of this paper to describe the results of an investigation of the structure of five of these alloys by means of microscopic and X-ray methods. The samples studied were in the form of small tools or wiredrawing dies, which were either purchased or supplied as samples. They were in some cases not supplied by the original makers but were furnished by the agents in this country, and we wish to call attention to the fact that they may not be truly representative of the materials supplied under the various trade names No performance data are given and no inference as to the inferiority of one alloy as against any other is made. K. Schröter2 recently described methods for polishing alloys of this type for microscopic examination and has presented photomicrographs of several alloys. However, he did not identify their constituents or describe methods for their identification. Constituents and Their Identification As far back as 1915 attempts were made to utilize tungsten carbides commercially, but the great brittleness of these carbides made these first attempts unsuccessful. Later, successful dies were made by sintering the powdered carbides with small amounts of iron, nickel, or cobalt. Due to the high melting points of the tungsten carbides (2600" to 2800" C.), it is difficult to melt the carbides without volatilizing almost quantitatively the added element of the iron group. Inasmuch as the added metal does not exceed 20 per cent. and is usually present in much smaller amounts, some understanding of the tungsten-carbon equilibrium dia-

Jan 1, 1929

By C. W. Kuttner, J. L. Gregg

ReceNtly there has been considerable interest in the production and use of extra hard alloys composed primarily of tungsten and carbon. Dr. Hoyt's recent paper1 gives a good description of these alloys and describes their performance when used as tools. There are a number of these alloys on the market sold under various trade names, and it is the purpose of this paper to describe the results of an investigation of the structure of five of these alloys by means of microscopic and X-ray methods. The samples studied were in the form of small tools or wiredrawing dies, which were either purchased or supplied as samples. They were in some cases not supplied by the original makers but were furnished by the agents in this country, and we wish to call attention to the fact that they may not be truly representative of the materials supplied under the various trade names No performance data are given and no inference as to the inferiority of one alloy as against any other is made. K. Schröter2 recently described methods for polishing alloys of this type for microscopic examination and has presented photomicrographs of several alloys. However, he did not identify their constituents or describe methods for their identification. Constituents and Their Identification As far back as 1915 attempts were made to utilize tungsten carbides commercially, but the great brittleness of these carbides made these first attempts unsuccessful. Later, successful dies were made by sintering the powdered carbides with small amounts of iron, nickel, or cobalt. Due to the high melting points of the tungsten carbides (2600" to 2800" C.), it is difficult to melt the carbides without volatilizing almost quantitatively the added element of the iron group. Inasmuch as the added metal does not exceed 20 per cent. and is usually present in much smaller amounts, some understanding of the tungsten-carbon equilibrium dia-

Jan 1, 1929

By J. R. Long, C. E. Armantrout, A. H. Roberson, T. R. Graham, R. S. Dean

THE general program of the Federal Bureau of Mines on the study of alloys made with electrolytic manganese has been extended to copper-manganese-aluminum alloys. The initial results of the work are presented in this report and concern a determination of the mutual solubilities of these three metals to form the alpha solid solution. The principal studies of this system, reported in the literature, have been focused on the Heusler alloys containing 10 to 30 per cent Mn with 9 to 15 per cent Al. These investigations concern the ferromagnetic properties and the determination of the crystallization contours, with little emphasis on the phases present in the solid state outside of this area. Heusler1 recognized a breakdown of the beta solid solution of the magnetic alloy, which he says decomposes into the alpha, beta, and gamma phases of the copper-aluminum system, somewhat modified by the presence of manganese. Rosenhain and Lantsberry2 examined alloys ranging up to 10 per cent Mn and io per cent Al but were unable to reach definite conclusions concerning the phase boundaries in that area. Krings and Ostmann3 made magnetic studies and examined the system by thermal analysis. They present contours of the liquidus surface but do not place any of the phase boundaries. Corson4 [ ] has drawn a hypothetical boundary for the alpha field with few data to support such construction. The binary systems involved have received considerable attention by numerous investigators, and their general features are well established. The hopper-aluminum system (Fig, I) has been thoroughly examined by Stockdale,5 who places the limit of solubility of aluminum in copper at 7.4 per cent at the liquidus and 9.5 per cent at room temperature. Smiths established the eutectoid temperature at 570°C. by a study of isothermal decomposition of the beta phase. The copper-manganese system (Fig. 2) has been recently reviewed by Dean and co-workers.7 Using high-purity alloys, they place the solubility of alpha man-

Jan 1, 1946

By Myron K. Rodgers

In rock- or ore-crushing tests all data, in order to be valuable for study and comparison, should be obtained and tabulated under conditions as uniform as possible. The results of many such tests have no value for comparison, because of incomplete data and the lack of uniform conditiops, screens and scale of sizing, etc. The purpose of this paper is to suggest a form of standard specifications which may be developed by the Milling Committee and approved by the A. I. M. E. for rock-crushing tests. It is not intended to discuss any theories of rock crushing. Reports of rock-crushing tests should include the following details: 1. Description of the machine employed (jaw or gyratory crushers, rolls, stamps,tube mills, Chilean mills, etc.), 2. Method and material (timber, concrete, etc.) of foundation. Much power is dissipated in the vibration of poor foundations. 3. Locality from which the rock or ore was obtaincd, and geological, mineralogical, and physical characters of the material. 4. The power consumption of the machine running with no load and with full load, the unit of power being 1 hp. per 24 hr, 5. The capacity of the machine in tons (of 2000 Ib.) per 24 hr. 6. The duty in tons per horsepower-day. 7. The screen analysis of feed and product by the proposed A. I. M. E. standard screen scale. On the foregoing statement, the following remarlrs are offered. Toughness of Rock Table P shows the relative crushing duty of the same machine on three different characters of rock, all other crushing conditions being the same. This table indicates that the specific resistance of the rock to crushing, may affect the crushing duty of a unit of power as much as 300 per cent. Perhaps this quality may be called toughness. It is not a function of hardness only. For comparison of tests, rocks should be divided into

Jan 1, 1916

Commonwealth of Pennsylvania, Department of Internal Affairs, Topographic and Geologic Survey, Harrisburg, Pa George H. Ashley, State Geologist All available printed Bulletins may be obtained through the Commonwealth of Pennsylvania, Division of Documents. Where a price has been set on the publication, checks should be made out to the Commonwealth of Pennsylvania. A Syllabus of Pennsylvania Geology and Mineral Resources has recently been published by the Survey as Bulletin G1, and consists of a general survey of the state An appendix of this bulletin also gives a complete bibliography of Survey publications It will be sent upon request. The State Geological Survey has gone through several phases and reorganizations, publications of three of them being numerous and important A fire, in 1927, destroyed supplies of many of the papers of the present Survey. Available bulletins of the present Survey are: Bulletin M6: Bituminous coal fields of Pennsylvania, in 4 parts available as follows: pt 1, General description of coal, 50 cents; 3, Bituminous coal resources, 25 cents, 4, Analyses of bituminous coals, 25 cents Bulletin M10, Fire clays of Pennsylvania; Mll, Molding sands of Pennsylvania; M12, Anthracite culm and silt (1928); M13, Feldspar in Pennsylvania; M14, Magnetite deposits of French Creek (1931); County Report C1, Adams County, pt 1, Geology and geography (in press), County Report C2, Geology and mineral resources of Greene County (in press); Topographic and Geologic Atlas A5, New Castle Quadrangle (1929), $1; Topographic and Geologic Atlas A27, Pittsburgh Quadrangle (1929), $1; Topographic and Geologic Atlas A168, Lancaster Quadrangle (1930), $1. The present Survey has also issued a number of short mimeo¬graphed bulletins any of which will be sent upon request Briefly they are: No. 15, Mineral resources of Pennsylvania; 20, Iron ores; 28, Magnesite; 40, White clay deposits, Monroe County; 45, White clay deposits, central Pennsylvania; 47, Manganese, Eastern Pennsylvania, 48, Pyrite from bituminous coal mines; 59, Bog

Jan 1, 1933

Foreword—H. Foster Bain........................ 7 Officers and Committees......................... 9 PAPERS Growth of Metallic Crystals. By C. H. Desch...............13 Aluminum Castings of High Strength. By R. S. Archer and Zay .Teffries (With Discussion).............................35 Constitution of Alloys of Aluminum, Zinc and Tin and Aluminum, Zinc and Cadmium. By V. Jares.......................65 Exudations on Brass and Bronze. By W. B. Price and A. J. Phillips (With Discussion)..................•..........80 Preparation of Metallic Single Crystals and Twinning in Zinc and Zinc Single Crystals. By 0. E. Romig (With Discussion).............90 Plastic Deformation of a Zinc Single Crystal. By S. L. Hoyt (With Discussion) 116 Plastic Deformation of Coarse-grained Zinc. By C. H. Mathewson and A. J. Phillips (With Discussion)......................143 The Solidus Line in the Lead-antimony System. By E. E. Schumacher and F. C. Nix (With Discussion)........................195 Note on the Distribution of Energy in Worked Metals and the Effect of Process Annealing Temperature on the Final Annealing Temperature of Fine Copper Wire. By L. Zickrick and R. S. Dean (With Discussion)........207 Note on the Relation of Annealing Temperature to Conductivity of Copper Wire. Ry J. C. Bradley (With Discussion)..................210 Beryllium-copper Alloys. By W. H. Bassett (With Discussion)........218 Some Comparative Properties of Tough Pitch and Phosphorized Copper. By W. R. Webster, J. L. Christie and R. S. Pratt (With Discussion).....233 A Study of the 470" C. Transition Point in Cast 60:40 Brass. By Frances Hurd Clark (With Discussion).......................253 Strldy of the Heat Treatment, Microstructure and Hardness of 60:40 Brass. By Frances Hurd Clark (With Discussion)...............276 Corrosion and Physical Properties of Some Alloys of Aluminurn, Zinc and Tin. By N. 0. Taylor (With Discussion)..................302 Equilibrium Relations in Al-Mn Alloys of High Purity. By E. H. Dix, Jr., and W. D. Iieith (With Discussion)....................315 Deformation of an Aluminum Alloy by a Constant Load. By C. B. Sadtler and J. L. Gregg (With Discussion)....................336 Still Casting of Metals. By P. H. G. Durville (With Discussion).......343

Jan 1, 1927

By Albert R. Ledoux

I am indebted to The Kaolin Co. of West Cornwall, Conn., and particularly to its engineer, Mr. M. Wanner, for permission to make public, through the Transactions of the American Institute of Mining Engineers, the interesting results of his experiments, having in view the winning of kaolin from deep deposits without shaft-sinking or removing of the overburden. So far as I am aware, nothing like it has been accomplished heretofore, although it reminds one of the methods successfully employed in Louisiana for the winning of sulphur from deep beds by the sinking of pipes one within another, injecting superheated steam under pressure through one pipe, the heat of the steam liquefying the sulphur and the pressure forcing it up through the other pipe to bins at the surface. The kaolin-deposit at West Cornwall is an alteration in situ— that is, it is not sedimentary. A series of clay-veins, dipping about 50" from the vertical, lie between a foot-wall of' limonite and a hanging-wall of gneiss and hornblende schist. The clay-veins alternate with veins or seams of more or less broken quartz, and unaltered feldspar. The deposit, which occurs at a point about 600 ft. above the Housatonic river, was opened five years ago, and about 5,000 tons of a superior grade of washed kaolin have been extracted from open pits, and sold. It soon became evident that this mode of extracting the product would prove unremunerative, by reason of the dip of the vein and the intercalary strata and lenses of quartz, and a more satisfactory method of working the deposit was sought. It is well understood that, in the preparation of all clays for market, especially residuary kaolin, the most important as well as the most difficult step is the washing of the crude product. The dificulties increaee with the percentage of foreign matter, especially quartz and mica, contained in the product. Hence, a system

Jan 1, 1907

By Edward H. Robie, E. J. Jr. Kennedy

his volume records the "clay symposium" that featured the geology side of the Annual Meeting of the Institute at St. Louis, February 19-22, 1951. The symposium consisted of four sessions held under the joint sponsorship of the Geology Subdivision and the Industrial Minerals Division AIME and the Society of Economic Geologists. Its main purpose was to define or outline certain problems of clay and laterite genesis, and the papers herein, which were presented at the first three sessions, deal for the most part with individual deposits or special problems. The fourth session was a seminar concerned almost wholly with a discussion of "problems." The discussion follows the papers in the volume. The clay symposium was not the work of an appointed committee. It was thought up and inspired by John J. Collins, who so ably supervised and co- ordinated the mining, geology, and geophysics program for the 1950 annual meeting of the Institute. After requesting Dr. A. F. Frederickson to get material together on clay and laterites for the St. Louis meeting, Mr. Collins visited Dr. Frederickson and discussed this project with him in greater detail. By that time their interest and enthusiasm had spread to others in the field. The Geology Subdivision, the Industrial Minerals Division, and the Society of Economic Geologists by common consent turned over the organization of the program to Dr. Frederickson. Mr. Collins continued in active touch with Dr. Frederickson and gave him every assistance. Dr. E. C. Harder and Dr. W. D. Keller read all the material comprising the symposium, and their comment was made available to Dr. Frederickson, who did much to put papers and discussion in final shape for publication. To the Karl Eilers Memorial Fund--one of the Funds that enables the Institute to publish books of this kind, to the authors of the various papers, to the contributors to the discussion, and to Messrs. Collins and Frederickson the Institute and readers of this book are indebted.

Jan 1, 1952

SINCE I promised you above when speaking of the melting of metals to teach you to make small crucibles and shells for melting, I do not wish to fail in my promise. For, in truth, since they are instruments that are much used for this procedure, they increase the work if they are not good, and often cause great extra expense as well as necessitating repetition of the work. If they are good they save everything. Therefore, if you have to make them, do it so that they, are greatly aided by art. It is first necessary to have the clay of a good nature, that is, resistant to the force of the fire by its own natural virtue, either when it is lean or when its viscousness is mixed with much talc, and whether it is yellow or white. This should be well freed from small stones and beaten well with an iron, and then thoroughly mixed by hand. With this should be mixed an eighth part of finely ground and sifted iron scale,* and also some [145] young ram's-horn ashes. These things should be well mixed together by hand and by beating them. If this clay should not be strong enough by itself, it is mixed with another lean clay, with crushed peperino, flintstone, or some other stone that in your judgment seems to be arid and resistant. Crucibles are worked on a low potter's wheel turned by hand, or on a high one turned by foot, just as plates are made. Both large and small ones are made. Most of them are given a triangular shape at the mouth, and the shells have a kind of spout for ease in pouring out the metal. This done they are well dried, and baked in furnaces like pots or other vessels. At the end, when they have been thus made they are used for melts.

Jan 1, 1942

By J. B. Dilworth

In estimating the investment-value of a mining-property or plant, the value of which decreases with operation, it is often necessary to know the sum which must be set aside periodically from earnings either to renew the plant at the end of its life, or to return the capital involved when the earningpower of the investment has ceased. In such cases it is manifestly incorrect simply to divide the total amount to be retired by the 'number of periods (usually years) during which the investment shall be active, as the sums periodically withdrawn have a certain interest-earning power varying with the length of time they are held and with the opportunities afforded for their investment. But though the interest may be considered to accumulate regularly year by year, yet the rules and tables for compouiid interest do not apply, owing to the addition of a fixed amount of new money to the total at the beginning of each period. Briefly stated, the problem of sinking-funds is, to find the amount of money which must be periodically set aside at a certain rate of interest, regularly compounded, to yield a certain sum in a given length of time. In most practical cases the interest is compounded and the fresh amount added at the same time—usually once a year—and on this basis the problem may be solved as follows : Let S = total amount to be retired, Let T = interest rate : R = 1 + r, Let n = life of tlie sinking-fund or the amortization-period, Let L = the sum set aside at the end of each year. Then the amouilt of the sinking-fund at the end of first year is 2, which at the end of n years will have illcreased by compound interest to IRn-l. Similarly, another amount, x, will be set aside at the end of second year, which will in turn increase

Jan 1, 1911

By M. Albertson

The purposes of this statement are to define a problem that exists in regard to the estimation of developed petroleum reserves, to analyze the problem in an abstract manner, and to discuss it as an introduction to certain papers that follow. The problem is to devise and develop a suitable procedure to permit more accurate estimates of developed petroleum reserves. Part of the problem is to make such estimates available earlier in the life of any particular pool. The problem of securing more accurate estimates of developed petroleum reserves existed prior to curtailment of production. With curtailment, however, the problem became acute, some of the more prominent reasons being as follows: 1. The standard method of estimation depended on production-decline curves. This method is inapplicable while curtailment prevails and available methods arc insufficient. 2. The retarding influence imposed by wide open flow conditions upon overdevelopment is absent. Great losses of capital by overdevelopment can now occur before realization of the true situation occurs, or before effective steps can be taken to stop such wastage. This increases the need for early, accurate estimates. 3. Above-ground stocks have diminished and the equivalent of such supply tends more and more to be retained underground in the natural reservoirs. It becomes increasingly necessary to know accurately the amount of these stocks. To direct attention to an additional point of different nature: improved accuracy of reserve estimation can be obtained only by closer scrutiny of the factors that determine recovery. This examination and the resulting efforts to measure the effect of these factors in terms of ultimate recovery must tend to improve ultimate recovery. The statements regarding the acute nature of the problem also indicate to some extent the importance of the problem and the necessity of finding a solution. Developed reserves of the industry, and of individual opera-tors, are one of the great factors that properly should determine explora-

Jan 1, 1936

By D. I. Cameron

A graphical method has been developed and tested for separating the effects of grain boundary and lattice diffusion in polycrystalline materials. The method is based on the assumptions that for unidirectional diffusion from a plane source of radioactive material, the penetration of activity far into the specimen from the source is due solely to grain-boundary effects, and 2) pure grain-boundary penetration is described by a linear plot of log activity vs the perpendicular distance x from the source. The former is based on the fact that at any temperature the grain-boundary diffusion coefficient is always very large relative to the lattice diffusion coefficient; and the latter is based on the derivation of Fisher.1 Using these criteria along with appropriate penetration data (in this case, data for the diffusion of Cb95 in pressed and sintered UO2) one first plots the data as log activity vs x2 and as log activity vs x, as shown by curves 1 and 2, respectively, in Fig. 1. A tangent line to curve 2 for large x (curve 3) is then transferred to the x2 plot as curve 4. The subtraction of curve 4 from curve 1 yields curve 5 which represents only lattice diffusion and may therefore be related to the diffusion coefficient by using the appropriate solution to Fick's second law. It should be noted that the method has inherent inaccuracies for small and large values of x2 and only the subtraction at intermediate values can be used. For the illustrated specimen the calculated diffusion coefficient is 3.4 X 10-11 sq cm per sec at 1445°C while data using a single crystal of UO2 at the same temperature yielded a value of 2.9 x 10-11 sq cm per sec.2 The same method of subtracting grain-boundary diffusion effects to obtain lattice diffusion coefficients has been successfully used to determine self-diffusion coefficients of Th230 in polycrystal- line thoria.

Jan 1, 1962

By A. J. Strane

PRACTICALLY all explosives may be classified as those that burn and those that detonate. Explosives of the first class include .black blasting and smokeless powder and are broadly known as low explosives, or propellants, because they merely burn and do that comparatively slowly. Their action is as if some power behind the projectile or other material were exerting a shoving or pushing action. The high, or detonating, explosives produce a smashing or shattering effect upon the material. In using military- explosives of the propellant class, the breach of the gun, or cannon, is proportioned to hold the pressure, so that the projectile will be blown out. Exactly the reverse is true in commercial work; then it is the "breach" or the hole that is to be broken. The projectile and the explosive are therefore chosen that will rupture the largest "breach" possible. With the high explosives, it is easy to break out the breach (that is why they are of no value as military propellants)" but with some of the low explosives it is necessary to plug up the muzzle very carefully before shooting. Doubtless the use of incendiary mixtures of oxidizing and combustible materials led, in the 13th century, to the perfection of the mixture which is practically the same as our commercial black blasting powder of today. About 600 years later, nitroglycerine was discovered, but for years its great potential energy could not be used because, in its liquid state, it could not be safely handled or transported. The accidental discovery that kieselguhr would absorb, and hold fairly well, three times its own weight of nitroglycerine, however, made it available. "Guhr dynamite," as the combination nitroglycerine and kieselguhr was termed, was soon displaced by dynamites having an active base, such as wood pulp and other carbonaceous combustible materials. These do all that kieselguhr will do and, in addition, increase the chemical reaction and add materially to the effectiveness of the blast.

Jan 8, 1920