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By Edgar Shepard

THE interest of the Federal Government in improvement of water-ways dates from 1820, when Congress appropriated $5000 for making a survey of the Mississippi and Ohio Rivers and assigned this work to the Corps of Engineers of the Army. Since that time the Government has gradually assumed increasing jurisdiction in the matter of improvement and control of inland waterways until, by the River and Harbor Act of Jan. 21, 1927, Congress assigned to the Secretary of War and to the Chief of Engineers the duty of making surveys, in accordance with House Document No. 308, 69th Congress, to formulate plans for the most effective improvement of the navigable streams of the United States and their tributaries, for navigation, development of water power, control of floods, and the needs of irrigation. Virtually all the preliminary investi-gations and surveys required by this act have been completed. The reports made to Congress have been published and often are referred to as "308 Reports." The map shown in Fig. 1 is merely a skeleton distribution of the projects covered by these reports, but it serves to indicate the magnitude of the proposed undertaking. In many instances, a single character on the map stands for a major development involving several dams and reservoirs or many miles of canals or levees. The devastating floods of 1936, and the need for worthy public works to take up the slack in employment, gave further impetus to this program and in 1936 led to the enactment of a bill authorizing a large number of these projects.

Jan 1, 1940

By H. Le Chatelier

Jan 1, 1894

By Carl A. Allen

Page Introduction................... 367 FactoRs Affecting the Choice of Method......... 367 Review of Stoping Methods.............. 368 Underhand Stoping................ 368 Overhand Stoping................ 370 Longitudinal or Flat-Back Stoping........... 371 Rill-Cut Stoping................. 372 Saw-Tooth Back Stoping.............. 372 Shrinkage Stoping................ 372 Combination Stoping................373 Side Stoping.................. 374* Breast Stoping................. 374 Sublevel Stoping.........,....... 374 Square-Set Stoping................ 376 Filling Methods................. 376 Caving Methods of Mining......... 376 Top Slicing.................. 377 Sublevel Caving................. 379 Block Caving ................. 380 Back Caving into Chutes.............. 381. Costs of Mining Methods.............. 382 Costs of Willing and Blasting. Comparison of Stoping Methods ... 383 Lighting................... 386 Timbering and Handling Ore in Stopes.. A Comparison of Square-Set and Top-Slicing Methods..............386 Tramming.................... 380 Mining oF the Massive Porphyry CoppeR Deposits ....390 Utah Copper and Boston Consolidated Mines.....391 Ray Consolidated Mine.............. 392 Miami Mine.................. 392 Inspiration Mine................ 395 Ohio Copper Mine...........395 Development.................... 398 Appendix..................... 399 Costs of Mining................. 399 Costs of Development............... 406

Jan 1, 1915

By C. A. Stickels

The preferred crystallographic orientations developed during recrystallization of polycrystalline electrolytic iron sheet, cold-rolled 90 pct, were ivestigated. Recrystallization at 500° or 565° C for relatively short limes produces a texture which is similar to the rolling texture. A duplex partial fiber texture, significantly different from the rolling texture, is found when the annealing time is increased. Recrystallization at 700°C also produces a sequence of textures with increasing annealing time. In order of their appearance, these textures are: 1) the duplex partial fiber texture found at lower temperatures, 2) a four-component texture "near {322}(296)", 3) a {112)(110) +(111)(110) texture, and 4) a two-component "near {554)(225)" texture. Secondary recrystallization, or discontinuous grain growth, accompanies the development of the latter texture. However, the "near {554} (225)" texture was nol observed when secondary recrystallization occurred under other conditions. All of the ideal orientations found in recrystallization textures can be accounted for by the growth of minor components of the deformation texture. IN recent years there has been increased interest in improving the drawability of metals by controlling the preferred crystallographic orientation of the sheet.1-l3 Since more low-carbon steel is drawn than any other material, considerable attention has been focused on the properties of sheet steel. Efforts to improve drawability through texture control have been hampered by the lack of any published systematic study of the recrystallization textures developed in iron annealed below Acl. The purpose of the present work was to supply some of this missing information, specifically, the recrystallization textures obtained by isothermal anneals of polycrystalline iron, cold-rolled 90 pct. LITERATURE REVIEW—DEFORMATION TEXTURES Barrett14 reviewed and summarized the investigations of rolling textures in iron and low-carbon steel prior to 1952. The texture of heavily deformed iron (rolled 90 pct or more) is described as consisting of two partial fiber textures. The dominant fiber texture (designated here as fiber texture A) has a (110) fiber axis in the rolling direction and includes the orientations (001)[110], {112}( 110), and {111}(110). The secondary texture (designated here as fiber texture B) is described as having a (111) fiber axis in the sheet normal direction, and includes the orientations {111)( 110) and (111)(112). Since the publication of Barrett's book, there have been two detailed studies of the deformation texture in polycrystalline iron. In both instances, the more sensitive diffractometer methods of pole-figure determination were used. Bennewitz15 studied the cold-rolling textures developed in polycrystalline low-carbon steel and a 3 pct Si steel. He determined (110), (2OO), and (222) pole figures for specimens reduced 30, 50, 60, and 90 pct and analyzed his results in terms of partial fiber textures. He distinguished three stages in the development of the final deformation texture. 1) Grains rotate to form two incomplete fiber textures, with (110) fiber axes inclined 30 deg to the sheet normal toward the rolling direction (fiber texture B). After 50 pct reduction, the highest density of poles is near an ideal orientation {554}(225), the two components of which are members of this duplex fiber texture. 2) With increasing amounts of reduction, grains rotate about the former fiber axes toward ideal orientations of the type {112)( 110) (common to fiber textures A and B). 3) Finally, grains rotate about their ( 110) axis in the rolling direction, clockwise and counterclockwise from the orientations {112}(110). This produces the range of orientations from (111)(110) to (001)(110) commonly found in the rolling texture of heavily deformed iron (fiber texture A). No significant difference was found between the deformation textures of low-carbon and silicon steels. A few years earlier, Haessner and weik16 had determined (110) pole figures for carbonyl iron rolled to 30, 60, 80, and 90 pct reduction in thickness. heir data agree quite well with the more complete data of Bennewitz, but a somewhat different description of the evolution of the deformation texture was given. The appearance of (110) poles in the transverse direction is ascribed to a (100)[011] component rather than "near {554}( 225) " components, and the (110) fiber axes of fiber texture B are described as located 35 deg rather than 30 deg from the sheet normal. Both of these studies agree that the secondary texture present in heavily rolled iron, the duplex fiber texture B, has (110) fiber axes and not a single ( 111) fiber axis normal to the sheet, as

Jan 1, 1965

ALABAMA Aldrich.-Lloyd, T W Anniston.-Carrington, F G Gerber, A B Heimrod, A A. White, H E Ashland.-Barton, J C Sturdevant, J C Bessemer.-Abbott, C E Ball, T L Hines, H K Hodgkin, W -0. Salmon, H S Thompson, N E Birmingham.-Adams, J H Adler, J. E Aldrich, T H Aldrich, T H, Jr. Ball, E M

Jan 1, 1923

By J. Ellzey Hayden, Lucien Eaton

The Cliffs Shaft mine of the Cleveland Cliffs Iron Co., located in the city of Ishpeming, Mich., is the largest producer of hard hematite ore on the Marquette iron range. The two shafts, A and B, lying 820 ft. (250 m.) apart on the east-west trend of the ore formation, were sunk in the early eighties, and, except for four years, have been steady producers of iron ore. Their location, on a hill overlooking the general offices of the company on the one side and the city of Ishpeming on the other, has made the shaft houses landmarks. In the spring of 1919, as the old wooden shaft houses had become shaky and out of line, and would soon be unsafe, it was necessary to replace them with the least possible delay. Three plans of construction were, therefore, considered: To replace the old shaft houses by somewhat similar structures made of wood; to use steel and radically change the design; or to build reinforced-conerete shaft houses outside of the wooden structures, completely enclosing them. The first plan was disapproved, because it is anticipated that the mine will have a long life and the proximity of other buildings makes the danger from fire rather great. Delay in receiving material, and the necessity for closing the shafts during erection, were other factors in the situation. The second plan was disapproved on account of the high cost of steel, slow delivery, and interference with hoisting during the period of erection. The presence near one of the shafts of a large bed of hard gravel suitable for concrete made the cost of the third plan considerably less than the second, and little, if any, delay in hoisting was expected. Our expectations in this regard were fully realized. Furthermore, the work could be done by unskilled labor, which was plentiful, and the erection could be quickly started. When the proposition was submitted to W. G. Mather, president of the company, he recommended that, on account of the prominence of the buildings due to their location, an effort should be made to combine in the design as far as practicable something of architectural beauty. Following his recommendation, the original plans were submitted to the

Jan 1, 1922

By E. W. Davis

IF the tonnage of merchantable iron ore remaining in the Lake Superior district is divided by the average of the annual shipments for the past 20 years, it will be found that this ore supply will be exhausted in approximately 35 years. This computed exhaustion period would be an indication of the future activities of the iron-mining industry if it were not for the fact that merchantable ore is being manufactured from low-grade ore, of which there is an almost inexhaustible supply in the Lake Superior district. It is true that at present only the simplest of these low-grade ores are being concentrated to any considerable extent, but progress is being made with the treatment of the more complex ores, and now, in addition to 20 washing plants on the Mesabi Range, three plants are equipped with jigs for the treatment of ore that cannot be concentrated simply by washing. The latest addition to the ore-treating plants of the Mesabi Range is a magnetic roasting and concentration plant at Cooley, Minn., in which ore that cannot be concentrated either by washing or by jigging is roasted to the magnetic state and concentrated on magnetic separators. This plant is beginning its third season of operation, and while it is too soon to make definite predictions, there are strong indica-tions that this new process may make commercially possible the manu-facture of high-grade, merchantable iron ore from large quantities of low-grade ore now considered worthless. After the iron oxide contained in an ore has been converted to mag-netite, almost any desired grade of concentrate can be produced, using magnetic-concentration equipment of the types now in general use for the concentration of the natural magnetites of New York, New Jersey and Pennsylvania. The conversion of hematite (Fe203) to magnetite (Fe304) is easily accomplished by heating the ore to a dull red tempera-ture in a reducing atmosphere. The reaction is slightly endothermic, and while it requires 200 B.t.u. to heat to 900° F. one pound of hematite ore containing 45 per cent Fe, it requires only 100 B.t.u. to convert the oxide into magnetite. In the laboratory, using small quantities of ore, this conversion is very simple, but large furnaces suitable for commercial

Jan 1, 1936

By R. S. Archer

The proper representation of equilibria involving graphitic carbon in the constitutional diagram of the iron-carbon system is admittedly an unsolved problem, the complete solution of which will probably require the establishment of more experimental evidence than is at this time available. The object of this paper is to present the author's observations on some of the phenomena in question and his interpretation of this and other recorded evidence. The chief of the recently disputed questions upon which the author has experimental evidence concerns the occurrence of graphitization at temperatures below the Al point. In a paper1 presented at the September, 1919, meeting of this Institute, the following is found: "the results given would seem to indicate that the graphite eutectoid lies at a smaller value of carbon content than has been previously supposed. At least this is true unless there is either a marked formation of graphite eutectoid at these rates of cooling, or a decomposition of pearlite into graphite, both rather unlikely suppositions, but not impossible ones." In a discussion of this paper, H. A. Schwartz2 takes the position that the possibility of graphitization occurring below the A1 point is an open question, but that complete graphitization (to less than 0.10 per cent, combined carbon) commonly occurs above this temperature. Another opinion from the malleable castings industry is found in a recent paper3 by Touceda: "Also the carbide of iron can be broken up into its two soft constituents at the temperature referred to. This temperature is called the critical temperature, or critical range, and for air-furnace hard-iron castings it is in the vicinity of 1440" F. It is the

Jan 1, 1922

By Earl Bardwell

THE structural relations existing between cuprous oxide and copper -were first systematically studied by Heyn1', who suggested that a study of the microstructure of refined copper might be substituted for the analytical methods in vogue for determining the oxygen content of copper coming from the refining furnace. Hofman, Green and Yerxa,2 in their paper A Laboratory Study of the Stages in the Refining of Copper, working along the lines suggested by Heyn, showed that a study of the microstructure could be made to yield a correct estimate of the oxygen content of the specimen of refined copper under examination. In order to determine the oxygen content of the specimen of refined copper under. examination a photomicrograph was first made. From the relative areas of copper and eutectic, the percentage of cuprous oxide and the corresponding percentage of oxygen were then readily calculated. It was found that the values for oxygen thus obtained corresponded closely with the analytical results. With the idea of utilizing this method of determining the oxygen content of each charge dipped from the refining furnaces at the Boston & Montana Reduction Plant, the physical testing laboratory was equipped with suitable apparatus for carrying out the work. It may be of interest to describe certain of the methods which have been worked out in this connection and give such data as have been obtained bearing on the effect of the oxygen content of refined copper upon its conductivity. Apparatus.-For the benefit of those who may be unfamiliar with metallographical apparatus and methods and may be interested to know what equipment is required, a few words with regard to the apparatus is in place at this point.

Jan 7, 1913

By R. Y. Williams

IN the United States, fully 98 per cent. of the anthracite and bituminous coal tonnage obtained from underground operations is mined by the room-and-pillar system. Under this system, the total cost of the coal f. o. b. railroad cars contains as its greatest single item the money paid for "labor." Each labor dollar in an. average bituminous mine may be subdivided into 85 c. paid for work done inbye the gathering turnouts (including all work at the face), and 15 c. outbye that point (including all work in and under the tipple). In an average anthracite mine, the corresponding figures are 70 c. and 30 c., the larger breaker force accounting mainly for the difference between these and the bituminous figures. The next largest single item after "labor" is usually "supplies and power;" and a division of this item inbye and outbye the gathering turnouts shows somewhat the same relative proportions as has been noted under the case of "labor". During the past 10 years, the chief advances made in the coal industry have been to obtain economies through complete mechanization covering that portion of the work which lies outbye the gathering turnouts. These results have been accomplished by applying scientific principles to railroad yard layout, to cleaning and sizing machinery, to dumping facilities, to roller-bearing haulage equipment, and to heavy-rail, well-ballasted trackage. But these improvements, while gratifying in their resulting economies, apply only to 15 to 30 per cent. of the important cost items. Obviously, then, the big problem before the engineers of the coal industry today has to do with the methods of mining and the layout inbye the gathering turnouts. Four years ago, Weston Dodson & Co., Inc., determined to have an exhaustive study made of the conditions which must be met in order to gain complete face mechanization, and in order that such a mining layout would be based on, correct underlying principles. The result of that study, which was made by the writer, led to the adoption of a method of longwall mining wherein the. roof is worked on the caving system and is supported as an overhang along the face by steel jacks.

Jan 1, 1928

By Arthur Taggart

SOME years ago, A. M. Gaudin and one of the authors published a paper showing removal of tar acids from solution by sulfides preferentially as compared to gangues (specifically by galena as compared to quartz).1 The underlying phenomenon was classed as adsorption, and the paper went on to develop the general thesis that so far as water-soluble frothing and collecting agents in flotation are concerned, the phenomenon of adsorption is one of controlling importance. Adsorption was defined in that paper as "a process of rearrangement of a system, which results in establishing a difference in concentration, as between the interfacial layers and the bulk of the phases, of a substance or substances initially uniformly dispersed in one or several of the phases." The paper went on to develop the relation between adsorption and surface energy according to Gibbs' equation (which may be thrown into the form U/c = KdT/dc, where U = excess concentration in surface layer, c = concentration, T = surface tension, and K is a constant), and pointed out that, according to this equation, degree of adsorption and change in surface tension vary directly. The present paper offers a somewhat different definition for the term adsorption; and sets up, in sweeping terms, the generalization that simple chemical reaction underlies the functioning of the flotation reagents which control mineral collection, when these reagents are soluble in and act from solution in the water of the pulp.

Jan 1, 1930

By R. S. Archer

The proper representation of equilibria involving graphitic carbon in the constitutional diagram of the iron-carbon system is admittedly an unsolved problem, the complete solution of which will probably require the establishment of more experimental evidence than is at this time available. The object of this paper is to present the author's observations on some of the phenomena in question and his interpretation of this and other recorded evidence. The chief of the recently disputed questions upon which the author has experimental evidence concerns the occurrence of graphitization at temperatures below the Al point. In a paper1 presented at the September, 1919, meeting of this Institute, the following is found: "the results given would seem to indicate that the graphite eutectoid lies at a smaller value of carbon content than has been previously supposed. At least this is true unless there is either a marked formation of graphite eutectoid at these rates of cooling, or a decomposition of pearlite into graphite, both rather unlikely suppositions, but not impossible ones." In a discussion of this paper, H. A. Schwartz2 takes the position that the possibility of graphitization occurring below the A1 point is an open question, but that complete graphitization (to less than 0.10 per cent, combined carbon) commonly occurs above this temperature. Another opinion from the malleable castings industry is found in a recent paper3 by Touceda: "Also the carbide of iron can be broken up into its two soft constituents at the temperature referred to. This temperature is called the critical temperature, or critical range, and for air-furnace hard-iron castings it is in the vicinity of 1440" F. It is the

Jan 1, 1922

By T. L. McCall

The late Walter Herd1 in 1929 gave a full description of past and present conditions in No. 2 mine, Springhill, Nova Scotia, developed theories regarding the cause of these bumps and made certain suggestions regarding possible methods of future development. Recapitulating briefly from Mr. Herd's paper, the seam is bituminous coal, averages 9 ft. in thickness and has a well defined parting containing fusain about 14 in. from the roof. This roof coal is somewhat stronger than the rest of the seam and has a tendency to cling to the roof. The pitch of the seam where it is now being worked is about 20". The first manifestations of bumps began when the room and pillar workings had reached a depth of cover of 1900 ft. and under continuously increasing depth of cover these bumps increased to such an extent, both in number and severity, that in the year 1924 it became apparent that some change in the system of extraction was necessary. After closely studying all the factors involved and benefiting largely by valuable outside advice obtained by the Provincial Department of Mines of Nova Scotia,2 the system of working was changed from room and pillar to longwall retreating. Mr. Herd's paper described in detail three remarkable bumps in the year 1928 in April, July and October that affected the 5700-ft. and 5900-ft. East levels, the last bump being so severe both in intensity and in extent of damage done that this district was abandoned. The longwall workings to the west of the slope had been stopped in the year 1926 owing to an inbreak of water, coming from the flooded waste of No. 3 seam lying some 400 ft. vertically overhead. This inflow was not excessive, but a large quantity of water being impounded in the old workings it was considered advisable to take the prudent course and not incur the risk of possibly increasing the flow by further working. This district has remained idle ever since.

Jan 1, 1934

THE problem of reaction rates in the open-hearth process is essentially that of trying to form a fairly clear picture of the "chemical mechanisms" in the bath. Quantitative data on reaction rates would not be very useful even if they were available; however, what few , approximate data there are, can be used in combination with data given in Chapters XVI and XVII to sketch a picture of the "chemical mechanics" of the open-hearth process that is consistent with essentially all the present available evidence. The result may later be found incorrect in many details but even so it will illustrate certain useful methods for obtaining a clearer understanding of the process. As discussed in the last portion of Chapter XIII chemical reactions in general involve the following factors: 1. The reacting molecules are mixed together in space in such fashion as to favor collisions among them. 2. A certain number of collisions occur per unit time among the reagent molecules, depending on their concentration and on temperature. 3. A certain percentage of these collisions result in reaction, these being the collisions between those molecules possessing at the moment energy levels above certain minimum values. The temperature factor enters mainly through (3), and its effect is very marked. (What is called temperature is really the mean energy content of all the molecules of the substance involved; at any one temperature a certain proportion of the molecules will have much higher energy content than the mean value.) Various reaction rates measured at around room temperatures have been found to be speeded from 1.6 to 4.0 times by an increase of only 15 to 20°F., simply because increasing temperature produces a rapidly increasing percentage of molecules with energy levels above the minimum needed to produce chemical reaction in a collision.

Jan 1, 1944

By C. G. Dunn, E. F. Koch, K. T. Aust

Strain-induced grain boundary migration was studied in a series of silicon-iron (3% pct Si) bicrystals of controlled orientations. Each bicrystal was given a 7 pct cold-rolling strain rind annealed at 1100°C. The direction of boundary migration was found to depend on orientation; results for several orientations related by a common [110] axis are given. Analysis of the micrographic and X-ray data is made in terms of the residual strain-energy densities within the crystals (energy per unit volurne) and a driving force on the boundary due to an energy density difference across the boundary. Relative strain energies were obtained for the various orientations investigated. A CHROME-acetic acid electroetching method for revealing dislocation sites in silicon iron was previously applied to clarify the structural features and the energetics involved in strain-induced grain boundary migration.',' The present paper is a continuation of this study, but is primarily concerned with the influence of crystal orientation. Sperry, as reported by Beck,3 attempted to determine the factors that influence the preferred growth of one grain over another in aluminum due to strain-induced boundary migration. He found that the particular grain of a pair which work hardened more was invaded, although exceptions to this correlation were noted. The index of work hardening was determined from microhardness measurements of each grain before and after cold-rolling. In the present study, orientation itself was taken as a useful variable for studying the behavior of individual grains in a bicrystal and the direction of boundary migration, since the extent of work hardening is orientation dePendent." The effect of strain on boundary migration is evident from a consideration of driving forces. Thus, in the absence of inclusions, the driving force (per unit area of boundary) for growth of grain A into grain B when a bicrystal is strained and annealed may be expressed as follows:2

Jan 1, 1960

C. W. GENNET, JR.,* Chicago, 111. (written discussion?).-Since the Lehigh Valley accident, transverse fissures have become a source of constant anxiety to railroad officials, because such defects, only infrequently detected by the trackmen, may appear under a moving train entirely without warning. The number of actual accidents resulting from rails containing fissures is no doubt a small proportion of the total, but the serious losses that have been directly attributable to fissures, coupled with the continual possibility of repetition, creates an alarming situation which demands a full investigation of the cause of fissures; apart from other types of rail failures. Mr. Howard's position gives him a field for action and an opportunity for laboratory examination and research that are unsurpassed, and the results. of his investigations must be received with the utmost attention and respect. His admirable paper, summarizing his previously published studies and analyses of the transverse fissure problem, constitutes a convincing treatment of the subject chiefly from the standpoint of stress and strain to which rails are subjected. The intricacies of the problem are so great that seemingly any theory advanced for the cause of fissures may be attacked from some angle; and although Mr. Howard's deductions are logical in the direction followed, it is apparently necessary for considerable work to be done along other lines before his theories can be fully accepted. It is generally conceded that fissures, whether fundamentally clue to fatigue or something else, are of a progressive character, their ultimate size' being the result of growth from an originating nucleus or point of rupture. Abundant proof of this lies in the variable sizes of the fissures found, and there can be no doubt that their development or growth is the result of the strains to which rails are subjected in the track. Obviously, therefore, the most important factor in investigating the cause for fissures lies in determining the conditions that exist at the point or

Jan 4, 1918

By H. P. Greenwald

THE rapidly increasing use in coal mines of portable auxiliary fans, which are generally "blowers" employed in connection with canvas tubing, raises questions concerning the hazards of such equipment, especially where the practices are opposed to established methods of ventilating face workings. Half a dozen or more coal-mine explosions and some fires have been attributed to the use of auxiliary fans; moreover, competent mining engineers have found many dangerous installations and methods of use-for example, intermittent running of the fans in gassy mines with consequent accumulations of firedamp at the faces. These facts have led the U. S. Bureau of Mines to issue this recommendation: "In the interest of safety, the Bureau of Mines, Department of Commerce, recommends that auxiliary fans or blowers should not be used in coal mines as a substitute for methods of regular and continuous coursing of the air to every face in the mine." The comparatively recent introduction of new types of mining machines, mechanical loaders, face conveyors, and slabbing machines has encouraged the trial of new systems of face mining, all of which have for their object the rapid advance of the faces. Although the latter has certain economic advantages, in gassy mines the rate at which gas is given off is generally found to increase in proportion to the speed of advance into new territory, which in turn increases the difficulties of efficient ventilation of the face workings. Some of the systems of advance mining being tried in connection with new mechanizing methods practically compel the use of blower fans and tubing, as single narrow places are now driven, 300 ft. or more without crosscuts. In some instances a series of parallel headings are driven without crosscuts pre-

Jan 1, 1928

By Donald D. Carr, Lawrence F. Rooney

Perhaps no other mineral commodity in this volume has as many uses as limestone and dolomite. These carbonate rocks are the basic building blocks of the construction industry, the material from which aggregate, cement, lime, and building stone are made. Carbonate rocks, and their derived products, are used as fluxes, glass raw material, refractories, fillers, abrasives, soil conditioners, ingredients in a host of chemical processes, and much more. Although the use of limestone and dolomite goes back before recorded history, new uses and products are continually being found. Carbonate rocks form about 15% of the earth's sedimentary crust and are widely available for exploitation. Found extensively on all continents, they are quarried and mined from formations that range in age from Precambrian to Recent. Reserves of carbonate rock are large and will last indefinitely, although high-purity deposits may be absent or have limited avail- ability in certain areas. Limestone and dolomite are so useful and so abundant that in 1972 more than 690 million tons were produced in the United States. In fact, about 75% of all stone quarried or mined in the United States was carbonate rock. Sand and gravel was the only mineral commodity produced in greater quantity. In this chapter we have sought to provide the general reader an overview of carbonate rocks, their composition, distribution, production, and uses, with emphasis on developments since 1960. In doing so we borrowed extensively from our recent report on the applied geology of limestone and dolomite (Rooney and Carr, 1971). The literature on the limestone and dolomite resources of the United States and Canada is so vast and diverse that one can easily become mired down in print. We tried to list those references that are easily accessible and that provide the economic geologist with a starting point for more intensive study. The table listing selected references on limestone and dolomite resources in Canada and the United States reflects our attempt to be selective rather than exhaustive and to direct the reader to the best sources of detailed information.

Jan 1, 1975

By Paul F. Kerr

QUARTZ of a certain kind, is one of our strategic minerals, and Brazil is probably the one important available source. Crystals of quartz of suitable size and perfection for piezoelectrical application are rare; their most outstanding use is in radio work. Clear quartz, or "crystal," free from twinning, cracks, foreign particles of other disturbing lines of growth, and gaseous or liquid inclusions, is cut into plates which provide excellent control of frequency in broadcasting. The squares or rectangles are less than a millimeter in thickness and ordinarily on the order of 1 in. along each side. They are cut at definite angles with respect to the axes of the crystal, and ground with opposite surfaces parallel. Each small slab must be a section of one crystal, uniform throughout in atomic alignment. The thickness of the chip controls the frequency of a broadcast and it is most important to have the plates oriented and ground with utmost precision. Opposite surfaces are parallel to within 0.001 mm. and expansion or contraction due to the temperature is limited to one part in a million.

Jan 1, 1942

By Leonard C. Grimshaw

Diffusion of carbon from gases into iron has been the object of much research, because of its long recognized importance in carburizing processes, but the direct diffusion of carbon from steel into iron has received relatively little attention. Because of the increasing use of clad metals in industry, direct diffusion from steel into iron is becoming of practical importance. Therefore, the object of this investigation was to study the diffusion of carbon from several different kinds of steel directly into relatively pure iron, realizing that elements in the steels other than carbon might influence the rate of carbon diffusion. The previous work on diffusion of carbon into iron has been considerable, and includes many reports in foreign languages. This work has recently been well reviewed by Mehll and Krynitsky12 and the reader is referred to their excellent bibliographies. Methods of Study There are two main methods by which the direct diffusion of carbon from steel into iron may be studied. In one method, steel is first decar-burized in part, and diffusion of carbon then allowed to take place from the steel into the decarburized steel. This method is open to two serious objections: (1) the decarburized steel is not iron, but contains elements such as manganese, silicon, chromium or tungsten, which may be an essential part of the steel under study, and which may seriously influence the diffusion of carbon into the decarburized area; (2) there is from the start of diffusion an unknown carbon-concentration gradient between the steel and the decarburized area. Another method, which possesses neither of these disadvantages, is to study diffusion from steel into a thick plating of electrolytic iron. Herc the chief difficulty is to secure an electrolytic deposit of iron upon steel without introducing an oxide film at the interface that will interfere with diffusion. The author is able to deposit iron upon any kind of steel without introducing an oxide film at the interface, so that diffusion of elements from the steel into the iron is free to proceed unhindered.

Jan 1, 1938