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By George H. Gilman

THE campaign now being waged to improve the quality of the rock-drill bit is the natural outcome f the scientific development of the drilling machine during the past twenty years. In this development there has been a great increase of power output per unit of weight of machine. But the development of the rock drilling engine has been seriously hampered by the need of a drill bit that would withstand, without undue wear or breakage, the heavy rapid blows of the improved pneumatic hammer. This problem was difficult to solve because an increase in the weight or section of the drill-steel bar resulted in decreased cutting speed and higher operating costs of both the bit and its actuating engine. The solution, therefore, is to make the bit of steel that, for a given weight or section, will be more shock and wear resisting. In the attempt to meet these requirements, many of the drill-steel manufacturers alloyed the steel with vanadium, chromium, nickel, etc., on the assumption that such elements would improve the rock-drill bit but due to the sensitiveness of such steel to forging and heat treatment, higher cost, and lack f continuity of effort on the part of the steel manufacturer to perfect this product, but little progress has been made in the adoption of these steels and the so-called straight carbon steel is today recognized as the standard material for all rock-drill bits. The first step in improving drill-bit efficiency is the determination f the cause of breakage and wear. For this reason, in 1917, certain rock-drill manufacturers, in conjunction with some of the larger mining interests, conducted exhaustive tests in both the field and laboratory. It was then found that, in the main, the cause of drill-steel troubles is not attributable to the duty imposed upon it by the normal operation of the drilling engine, but to improper forging and heat treating of the bit and to the subjecting of the bit to improper use. The fact that it is possible to minimize the troubles attributable to improper heat treatment of the drill steel has been demonstrated and it is recommended that such knowledge be made available by teaching those interested in the production, use, and up-keep of drill bits the principles on which success in this direction may be achieved.

Jan 6, 1921

By Daniel D. Pollock

The il'lott and Jones theory of thermoelectricity predicts that the absolute thermoelectric power of alloys of transition and noble metals should be a maximum when the concentration of the noble metal is approximately 55 to 60 at. pct. An examination of the emf of a series of relatively pure alloys of copper and nickel shows that the predicted maximum occurs at about 57 at. pct Cu. This excellent agreement with the theory is considered to substantiate the Mott and Jones theory of thermoelectricity for binary alloys of transition elements. This theory is extended to show that the emf behavior of dilute, ternary copper-nickel base alloys, which contain approsimately 60 pct Cu and 40 pct Ni, may be described in terms of a scattering mechanism. The scattering effect of a third element is demonstrated to be a function of its valence and its period in the periodic table. Small amounts of solute elements have additive scattering effects upon the emf of the Cu-Ni base. The Mott and Jones equation is modified to include this scattering parameter. This adaptation accurately describes the thermoelectric behavior of ternary and quaternary CLL-Ni base alloys. An empirical form of the modified Mott and Jones equation is derived which permits the calculation of thermoelectric power with an average error of less than 0.4 pct at 500 "C. CONSTANTAN has long been used as a thermocouple element. Its approximate composition varies from 50 pct Cu, 50 pct Ni to 65 pct Cu, 35 pct Ni. Small amounts of manganese, iron, and other elements have been used to modify the composition in order that the resultant emf vs platinum conforms to nationally accepted table. Adjustments of this type are made on a purely empirical basis. Constantan was originally made in Germany and was imported into this country for thermoelectric and electrical resistance purposes. During World War I, the supply of this material became seriously depleted. The work of Bash4 was done in this period in order to develop a satisfactory substitute for the imported material. Bash's empirical work on Cu-Ni alloys is still the basis for all commercial constantans made in this country. No reexamination of the electrical properties of this system has been made, despite the fact that it is now well known that Bash's alloys contained impurities which strongly affected their thermoelectric behavior.

Jan 1, 1962

By L. C. Graton

Although marked by numerous well-known attributes of its own, gold does not possess a kind and range of physical, chemical and geological characteristics wholly different and apart from those of other metals. Instead, it is merely one of the family of metals, with its individual and distinctive traits subordinate to the underlying family relationships and resemblances. The geologist concerned with pure science will pursue, therefore, the same general course and will examine the same broad kinds of facts and interrelations when studying the occurrence of gold as when studying that of copper or cadmium, or any other metal. But when we come to consider the use and economics of the metals, we discover that gold differs strikingly from all the others. Gold, in short, is unique, not by virtue of its inherent characteristics, but because of a peculiar and concerted psychological regard in which it is held. It will be evident, therefore, that the geologist who would deal with gold supply must give far greater weight to economic considerations than is required in his contacts with any other metal. If the geologist be called the scientist of occurrence, and the economist the scientist of use, the economic geologist stands as the necessary link between them. Perhaps it is in part because the economic geologist has made himself more familiar with the science of occurrence than with the science of use and has thus in some degree failed to bridge effectively the gap between the two fields, especially with regard to gold, that the usen1 of gold now appear to be in a state of general concern and even of alarm for the security and adequacy of future supplies. In the case of no other mineral commodity do the users, as a rule, trouble themselves greatly about the adequacy of supply except in so far as that may affect the price which they shall have to pay for the commodity. Oversupply, with resulting low price, they regard as a gift of good fortune. As to long-term undersupply, they are generally content to go ahead on faith, leaving the producer to discover as best he may the means for meeting their requirements or the inventor to find a substitute. But history has shown that for gold a different situation exists. While

Jan 1, 1931

By W. L. Freyberger, R. B. Booth

Froth flotation is a chemically induced method for beneficiating or up- grading an ore, which utilizes a layer or column of froth as a separating medium to segregate and remove the valuable minerals from the worthless gangue components of a finely ground ore suspended in water. The object of this chapter is to discuss the theoretical aspects of froth formation, the various frothing agents employed in flotation, and the effect of chemical structure on froth formation, and to correlate these factors with flotation technology. The flotation method of separation is conducted in three main steps: 1) selective chemical modification of the surface of specific mineral particles to effect floatability or nonfloatability; 2) contact between air bubbles and mineral particles, the selective adherence of floatable minerals to these bubbles, and the rejection of nonfloatable minerals; and 3) separation of the floatable minerals from the nonfloatable minerals. As indicated above, these three operations are achieved by the use of chemicals. Frothers play their most important role in the second and third steps by influencing particle- bubble contact and by affecting the degree of separation obtained in the froth column. Frothers, as defined by flotation operators, are compounds that are used specifically for the purpose of creating a froth in a flotation separation. How- ever, some collectors produce froths that are adequate for some flotation operations. Although this chapter is chiefly concerned with the specific frothers used in flotation, some discussion of frothing collectors is included. Otherwise, collectors (or promoters) and modifiersare not discussed at length; for information on these types of flotation chemicals, the reader is referred to other sections of this book or to other sources.l HISTORICAL DEVELOPMENT OF FROTHING AGENTS Historically, there are two distinct phases in the development of frothing agents and other flotation chemicals: 1) 1860 to 1920-oil flotation, and 1921 to date-chemical flotati0n.2~3 Early in the first period, large quantities of fatty and oily materials, up to 10 to 20% of the weight of the ore, were used as a means of separating the sulfide and oxide components from the gangue minerals in ore pulps. Later, various gases replaced these large quantities of oil as a buoyant and separating medium, decreasing oil requirements to less than 1% of the weight of the ore. With this reduction in oil

Jan 1, 1962

By S. J. Matas, R. F. Hehemann

The existence of two distinct forms of bainite—upper and lower bainite—in hypoeutectoid steels is confirmed by a systematic study of the structure of the product resulting from this mode of austenite decomposition. The transition between these two forms occurs at about 650° F regardless of the alloy content of the steel and their structural differences can be interpreted in terms of the kinetics of carbide precipitation from supersaturated ferrite. In the past few years, a renewed interest has been displayed in the kinetics and mechanism of the bainite reaction in steels. Several rather divergent models for the transformation mechanism have evolved from these studies,'-' however, it is difficult to evaluate these models critically on the basis of the existing experimental data. In particular, a more detailed knowledge of the structure of bainite should be helpful in providing a framework for the construction of an appropriate model. Metallographic studies7-l4 have led to a recognition of at least two distinct forms of bainite—frequently termed upper and lower bainite. Although the morphology of bainite changes with reaction tem- perature, there appears to be a relatively sharp transition between the two forms. This occurs in a narrow temperature range near 650° F. Transformation at temperatures below about 650° F results in the presence within the bainite of small plates of carbides oriented at an angle of 60 deg with respect to the direction of growth of the plate, while at higher temperatures carbides are oriented parallel to the growth direction. There is no generally accepted view regarding the significance of this structural transition. Some authors feel that carbides precipitate from austenite at all reaction temperatures1' while others claim, at least for low-temperature bainite, that carbides precipitate from supersaturated ferrite.14.15 It was recognized many years ago that the nature of the carbide in bainite depends on the reaction temperature. The carbide hase in upper bainite is unmistakenly cementite.16-19 The exact nature of the carbide in low-temperature bainite is less certain. Magnetic measurements of lower bainite reveal no cementite Curie point21'22 and dilatometric studiesz0 produce total expansions which are larger than those predicted on the basis of a ferrite-plus cementite structure. These effects have been attributed to the

Jan 1, 1962

By D. G. Westlake, D. T. Peterson

The saturation solubility of thorium dihydride in thorium was studied by saturation of samples and subsequent analysis. The solubility increased from about 1 at. pct at 300°C to above 20 at. pct at 800 °C. Over this temperature range the log of the solubility was a linear function of the reciprocal absolute temperature for thorium of good purity. The heat of solution of thorium dihydride was found to be 7.9 kcal per atom of hydrogen in crystal bar thorium and 6.6 kcal per atom of hydrogen in Ames thorium, The important effect of hydrogen on the physical and mechanical properties of many metals is receiving increasing recognition. The basic physical and chemical data necessary to help explain the observed effects of hydrogen on the mechanical proper ties of metals are all too often not available. The solubility of hydrogen in thorium metal was determined to provide a portion of this basic data for the thorium-hydrogen system. The absorption of hydrogen by thorium metal and the formation of thorium hydrides was studied by several investigators, beginning in 1891, and their work is summarized in Gmelin's Handbuch.1 No effort was made to determine the extent of solid solubility in the metal in these early investigations and the impure metal available made interpretation of the results uncertain. Nottorf2 reported the results of a careful study of pressure-composition isotherms for the thorium-hydrogen system. The principal interest in this work was in the composition and dissociation pressures of the thorium hydrides. Mallett and campbel13 reported the pressure-composition isotherms for the thorium-hydrogen system up to the composition of thorium dihydride. The saturation solubility of thorium dihydride in thorium was reported to be 13 at. pct at 650°C and 23 at. pct at about 900° C. Mallett and Campbell used thorium metal which had been prepared by the calcium reduction of thorium tetra-fluoride or thorium oxide. The results obtained with thorium of these two types agreed within the experimental error. PROCEDURE AND MATERIALS Procedure—The method used to determine the solubility was to saturate a sample of thorium with hydrogen and analyze a portion of the saturated sample. This method was chosen rather than a determination of pressure-composition isotherms since it was much less time consuming and could be applied at temperatures at which the equilibrium hydrogen pressure was too low to measure. The

Jan 1, 1960

By A. J. Lyon

The stability and permanence of any structural material used in aircraft are of paramount importance. The spontaneous hardening, or age-hardening, which takes place in some of the aluminum alloys under ordinary conditions of temperature and atmosphere, is accompanied by an increase in tensile strength and proportional limit and a decrease in elongation or ductility. Within the last few years the introduction of a number of strong and ductile casting alloys led to a study by the Materiel Division, Air Corps, of the permanence of the physical properties in several of these alloys. It has been found that even though some alloys have good properties directly after casting or heat treatment, they are not satisfactory for stressed parts that require a combination of strength and ductility. It has also led to the conclusion that all alloys that can be hardened by artificial aging—heating in a temperature range below 170" C. (340" F.)—will harden spontaneously if allowed to stand for a sufficient length of time. It follows that, in aircraft work where the factors of safety are limited on account of the necessity of keeping the weight of the structures as low as possible consistent with their safe operation, the properties of the alloys in the stable or final condition should be used as a basis for design rather than the properties obtained on the material directly after casting. The work of Wilm in Germany, Hanson and Gayler at the National Physical Laboratory in England, and Merica, Jeffries, and others in the United States, has shown that the spontaneous hardening is characteristic to a greater or less extent in all aluminum-base alloys in which the solubility in the solid state of the alloying constituents decreases with the temperature. It has been shown that, by heating to a temperature as near as possible to the melting point of the material and soaking at that temperature for a sufficient length of time and then quenching or cooling rapidly, a maximum amount of the soluble constituents can be retained in solution and the condition of maximum hardening effect upon aging can be obtained. Also, in ordinary sand and chill castings, without heat treatment, a sufficient amount of the alloying constituents is held in solution to cause important changes in the final physical properties.

Jan 1, 1929

By Gerhard Derge

THE chemical and physical properties of slag systems are of special interest to metallurgists, for nearly all metals are in contact with molten slags during the primary reduction from their ores and then during the subsequent refining and alloying processes that determine their ultimate use, These processes are carried out at high temperatures and involve such complex chemical systems that fundamental scientific knowledge of the properties and behavior of these slags is inadequate. Various hypotheses have been proposed to explain known slag characteristics. The commonest of these regard the molten slag as constituted of compounds that are dissociated in varying degrees into their constituent oxides, as illustrated by Schenck1 and the recent papers of Chipman and co-authors.2-5 Another proposal is that these compounds dissociate by completes or partial ionization, the evidence for which has been reviewed by Martin and Derge.7 Whatever hypothesis is favored, the exact formulation of these compounds is incomplete. It is based on three principal types of information: I, Studies of solidified slag samples by X-ray diffraction, petrography, and similar methods that can be used at room temperature, The correlation of this information with the high-temperature properties of the molten slag is uncertain, 2. Studies of slag-metal equilibria, which have the advantage of providing observations on the molten slag at high temperature, However, even these data present problems of interpretation because they require a complete knowledge of the metal phase, 3, Direct measurements of properties of molten slag at the temperature of greatest metallurgical interest. Viscosity, electrical conductivity, specific heats, and similar properties have been measured, but the data of this type are widely scattered and frequently difficult to interpret, Additional direct measurements of properties of molten slag that can be interpreted in terms of chemical behavior are required, and this paper shows that the standard physical-chemical measurement of reversible electrode potentials, which measure the activity of specific constituents, is a fruitful source of such information, The purpose of this investigation, therefore, was to find an electrode combination that would yield reversible electromotive force measurements when dipped into the molten slag to be studied. Slags of the systems CaO-SiO2 and CaO-A1203-Si02 were chosen for study because graphite containers could be used and the data could be correlated with those for viscosity, conductivity, and other proper-

Jan 1, 1946

By A. M. Kivari

OPERATIONS at the cement plant of the Permanente Corporation, in the hills about 45 miles south of San Francisco and 12 miles west of San Jose, are interesting to the members because of the adoption of modern hydrometallurgical methods for handling and beneficiating raw materials. Closed-circuit grinding, classification, hydro-separation, flotation, agitation, and thickening are familiar terms at this cement plant. These methods make it possible to process refractory limestone into suitable materials for the manufacture of modern cements. Construction of the plant, having originally a design capacity of 7000 bbl. of cement per day, was started in June 1939, and the first clinker was ground on the following Christmas Day. At present the capacity is about 12,000 bbl. of finished cement per 24 hr., most of the production being low-heat cement.† About 3130 tons of limestone, 620 tons 0f clay and 100 tons of gypsum are required daily for this output. Occasionally iron oxide is added to the clay to obtain the desired composition. This, together with the gypsum, is purchased from outside sources. Up to the present time, the corporation has produced low-heat, normal, moderate heat, moderate-sulphate-resisting, high-early-strength, oil-well, modified-oil-well, and plastic cements. Most of the present production is for Shasta Dam, near Redding, Calif., the total demand being 5,800,000 bbl, of cement. Following are some of the cement requirements of the Shasta Dam specifications: [PERCENT Chemical composition: Loss in ignition2.25 Insoluble residue0.75 SO32.25 MgO5.00 Uncombined lime in clinker (CaO)1 .25 Percentage of iron oxide to alumina ratio1.5 Compound composition: Tricalcium silicate (3CaO.Si02)Not more than 3,5 Dicalcium silicate (2CaO.Si02)Not less than 40 and not more than 65 Tricalcium aluminate (3CaO.Al2O7)Not more than 7 Tetracalcium aluminoferrite (4CaO.A12O3.Fe203) Not more than 0 Fineness:] The average specific surface in the bin sampled shall be not less than 1800 sq. cm. per gram and no individual sample less than 1600 sq. centimeters. Compressive strength: The average compressive strength-in pounds per square inch of three mortar cubes composed of one part cement and 2.75 parts fine testing sand, by weight, shall be equal to or greater than the following:

Jan 1, 1941

By A. M. Kivari

OPERATIONS at the cement plant of the Permanente Corporation, in the hills about 45 miles south of San Francisco and 12 miles west of San Jose, are interesting to the members because of the adoption of modern hydrometallurgical methods for handling and beneficiating raw materials. Closed-circuit grinding, classification, hydroseparation, flotation, agitation, and thickening are familiar terms at this cement plant. These methods make it possible to process refractory limestone into suitable materials for the manufacture of modern cements. Construction of the plant, having originally a design capacity of 7000 bbl. of cement per day, was started in June 1939, and the first clinker was ground on the following Christmas Day. At present the capacity is about 12,000 bbl. of finished cement per 24 hr., most of the production being low-heat cement. [t] About 3130 tons of limestone, 620 tons of clay and 100 tons of gypsum are required daily for this output. Occasionally iron oxide is added to the clay to obtain the desired composition. This, together with the gypsum, is purchased from outside sources. Up to the present time, the corporation has produced low-heat, normal, moderate-heat, moderate-sulphate-resisting, high-early-strength, oil-well, modified-oil-well, and plastic cements. Most of the present production is for Shasta Dam, near Redding, Calif., the total demand being 5.800,000 bbl. of cement. Following are some of the cement require¬ments of the Shasta Dam specifications: [PER CEN'I Chemical composition: Loss in ignition2.25 Insoluble residue0.75 S032.25 M905.00 Uncombined lime in clinker (CaO)T.25 Percentage of iron oxide to alumina ratio1.5 Compound composition: Tricalcium silicate (3CaO.Si02)Not more than 35 Dicalcium silicate (2CaO.Si02)Not less than 40 and not more than 6,5 Tricalcium aluminate (3CaO.Al203)Not more than 7 Tetracalcium aluminoferrite (4CaO.A1203.Fe203) Not more than 20 Fineness:] The average specific surface in the bin sampled shall be not less than 1800 sq. cm. per gram and no individual sample less than 1600 sq. centimeters. Compressive strength: The average compressive strength in pounds per square inch of three mortar cubes composed of one part cement and 2.75 parts fine testing sand, by weight, shall be equal to or greater than the following: [ ]

Jan 1, 1941

By C. E. Lesher

THE Disco* process for the production of low temperature coke and its immediate predecessor, the Wisner or Carbocite process have been described in the voluminous literature of low temperature carbonization.1-4 This paper will describe the development of the process from the first attempt at commercial operation by the American Gas and Electric Co. at Philo, Ohio,' in the 1920's to the successful operation in 1949 by the Disco Co., a division of the Pittsburgh Consolidation Coal Co., of the 1000-ton per day Disco plant near Pittsburgh, see Figs. 1-2. In the 1924 coal industry depression following the hectic post World War I expansion, the northern Appalachian, unionized bituminous coal fields were affected first and foremost, and Western Pennsylvania as hard as any. Competitive market pressure was heaviest on the lower grades of steam coals, notably those from the Panhandle district where ash and sulphur are inherently higher than in the same Pittsburgh coal bed to the east along the rivers. The firm structure of Panhandle coal while favoring the prepared sizes, depressed the usefulness and value of the finer sizes. Panhandle slack and nut slack were marketed with difficulty at consistent, and at times considerable, loss. Many solutions were suggested, and the Pittsburgh Coal Co. investigated all. Lower delivered prices through lower mine costs and more advantageous freight rates were obvious goals, but equally obvious were the difficulties of self attainment of either in any substantial measure. Selling Btu's in pipes was abandoned as an idea after a thorough study of the economics of distribution of what was then, and is even now, the only developed continuous process of complete gasification of bituminous coal-producer gas. Although the coal company purchased huge blocks of electric power, it sold not a car of coal to the central power stations. Public utilities controlled the markets for electric current, and it was found that no matter at how low a cost current might be put on the bus bars by the coal company, distribution to its widely scattered coal mines made such an enterprise practically impossible. Consolidation of underground operations and a huge modernization program of mining operations in the 1920's were but preparation for the introduction of mechanical cleaning of the coal for market, particularly the smaller sizes of steam, gas, and by-

Jan 1, 1952

By A. J. Lyon

The stability and permanence of any structural material used in aircraft are of paramount importance. The spontaneous hardening, or age-hardening, which takes place in some of the aluminum alloys under ordinary conditions of temperature and atmosphere, is accompanied by an increase in tensile strength and proportional limit and a decrease in elongation or ductility. Within the last few years the introduction of a number of strong and ductile casting alloys led to a study by the Materiel Division, Air Corps, of the permanence of the physical properties in several of these alloys. It has been found that even though some alloys have good properties directly after casting or heat treatment, they are not satisfactory for stressed parts that require a combination of strength and ductility. It has also led to the conclusion that all alloys that can be hardened by artificial aging—heating in a temperature range below 170" C. (340" F.)—will harden spontaneously if allowed to stand for a sufficient length of time. It follows that, in aircraft work where the factors of safety are limited on account of the necessity of keeping the weight of the structures as low as possible consistent with their safe operation, the properties of the alloys in the stable or final condition should be used as a basis for design rather than the properties obtained on the material directly after casting. The work of Wilm in Germany, Hanson and Gayler at the National Physical Laboratory in England, and Merica, Jeffries, and others in the United States, has shown that the spontaneous hardening is characteristic to a greater or less extent in all aluminum-base alloys in which the solubility in the solid state of the alloying constituents decreases with the temperature. It has been shown that, by heating to a temperature as near as possible to the melting point of the material and soaking at that temperature for a sufficient length of time and then quenching or cooling rapidly, a maximum amount of the soluble constituents can be retained in solution and the condition of maximum hardening effect upon aging can be obtained. Also, in ordinary sand and chill castings, without heat treatment, a sufficient amount of the alloying constituents is held in solution to cause important changes in the final physical properties.

Jan 1, 1929

By C. E. Lesher

THE Disco* process for the production of low temperature coke and its immediate predecessor, the Wisner or Carbocite process have been described in the voluminous literature of low temperature carbonization.1 This paper will describe the development of the process from the first attempt at commercial operation by the American Gas and Electric Co. at Philo, Ohio, Yn the 1920's to the successful operation in 1949 by the Disco Co., a division of the Pittsburgh Consolidation Coal Co., of the 1000-ton per day Disco plant near Pittsburgh, see Figs. 1-2. In the 1924 coal industry depression following the hectic post World War I expansion, the northern Appalachian, unionized bituminous coal fields were affected first and foremost, and Western Pennsylvania as hard as any. Competitive market pressure was heaviest on the lower grades of steam coals, notably the from the Panhandle district where ash and sulphur are inherently higher than in the same Pittsburgh coal bed to the east along the rivers. The firm structure of Panhandle coal while favoring the prepared sizes, depressed the usefulness and value of the finer sizes. Panhandle slack and nut slack were marketed with difficulty at consistent, and at times considerable, loss. Many solutions were suggested, and the Pittsburgh Coal Co. investigated all. Lower delivered prices through lower mine costs and more advantageous freight rates were obvious goals, but equally obvious were the difficulties of self attainment of either in any substantial measure. Selling Btu's in pipes was abandoned as an idea after a thorough study of the economics of distribution of what was then, and is even now, the only developed continuous process of complete gasification of bituminous coal-producer gas. Although the coal company purchased huge blocks of electric power, it sold not a car of coal to the central power stations. Public utilities controlled the markets for electric current, and it was found that no matter at how low a cost current might be put on the bus bars by the coal company, distribution to its widely scattered coal mines made such an enterprise practically impossible. Consolidation of underground operations and a huge modernization program of mining operations in the 1920's were but preparation for the introduction of mechanical cleaning of the coal for market, particularly the smaller sizes of steam, gas, and by-

Jan 1, 1953

By A. M. Kivari

Operations at the cement plant of the Permanente Corporation, in the hills about 45 miles south of San Francisco and 12 miles west of San Jose, are interesting to the members because of the adoption of modern hydrometallurgical methods for handling and beneficiating raw materials. Closed-circuit grinding, classification, hy-droseparation, flotation, agitation, and thickening are familiar terms at this cement plant. These methods make it possible to process refractory limestone into suitable materials for the mallufacture of modern cements. Construction of the plant, having originally a design capacity of 7000 bbl. of cement per day, was started in June 1939, and the first clinker was ground on the following Christmas Day. At present the capacity is about 12,000 bbl. of finished cement per 24 hr., most of the production being low-heat cement. † About 3I30 tons of limestone, 620 tons of clay and I00 tons of gypsum are required daily for this output. Occasionally iron oxide is added to the clay to obtain the desired composition. This, together with the gypsum, is purchased from outside sources. up to the present time, the ccrporation has produced low-heat, normal, moderate-heat, moderate-sulphate-resisting, high-early-strength, oil-well, modihed-oil-well, and plastic cements. Most of the present production is for Shasta Dam, near Red- ding, Calif., the total demand being 5,800,000 bbl. of cement. Following are some of the cement require ments of the Shasta Dam specifications: Per Cent Chemical composition: Loss in ignition.......... 2.25 Insoluble residue......... 0.75 SO3.................... 2.25 MgO................... 5.'' Uncombined lime in clinker (CaO)......... I.25 Percentage of iron oxide to alumina ratio....... I.5 Compound composition: Tricalcium silicate (3CaO.SiO2)........... Not more than 35 Dicalcium silicate (zCaO.SiO2)........... Not less than 40 and not more than 65 Tricalcium aluminate (3CaO.Al2O3).......... Not more than 7 Tetracalcium aluminofcr- rite (4CaO.Al²O³.Fe²O³) Not more than 20 Fineness: The average specific surface in the bin sampled shall be not less than 1800 sq. cm. per gram and no individual sample less than 1600 sq. centimeters. Compressive strength: The average compressive strength in pounds per square inch of three mortar cubes composed of one part cement and 2.75 parts fine testing sand, by weight, shall be equal to or greater than the following:

Jan 1, 1942

By C. E. Lesher

THE Disco* process for the production of low temperature coke and its immediate predecessor, the Wisner or Carbocite process have been described in the voluminous literature of low temperature carbonization.1 This paper will describe the development of the process from the first attempt at commercial operation by the American Gas and Electric Co. at Philo, Ohio, Yn the 1920's to the successful operation in 1949 by the Disco Co., a division of the Pittsburgh Consolidation Coal Co., of the 1000-ton per day Disco plant near Pittsburgh, see Figs. 1-2. In the 1924 coal industry depression following the hectic post World War I expansion, the northern Appalachian, unionized bituminous coal fields were affected first and foremost, and Western Pennsylvania as hard as any. Competitive market pressure was heaviest on the lower grades of steam coals, notably the from the Panhandle district where ash and sulphur are inherently higher than in the same Pittsburgh coal bed to the east along the rivers. The firm structure of Panhandle coal while favoring the prepared sizes, depressed the usefulness and value of the finer sizes. Panhandle slack and nut slack were marketed with difficulty at consistent, and at times considerable, loss. Many solutions were suggested, and the Pittsburgh Coal Co. investigated all. Lower delivered prices through lower mine costs and more advantageous freight rates were obvious goals, but equally obvious were the difficulties of self attainment of either in any substantial measure. Selling Btu's in pipes was abandoned as an idea after a thorough study of the economics of distribution of what was then, and is even now, the only developed continuous process of complete gasification of bituminous coal-producer gas. Although the coal company purchased huge blocks of electric power, it sold not a car of coal to the central power stations. Public utilities controlled the markets for electric current, and it was found that no matter at how low a cost current might be put on the bus bars by the coal company, distribution to its widely scattered coal mines made such an enterprise practically impossible. Consolidation of underground operations and a huge modernization program of mining operations in the 1920's were but preparation for the introduction of mechanical cleaning of the coal for market, particularly the smaller sizes of steam, gas, and by-

Jan 1, 1953

By A. M. Kivari

Operations at the cement plant of the Permanente Corporation, in the hills about 45 miles south of San Francisco and 12 miles west of San Jose, are interesting to the members because of the adoption of modern hydrometallurgical methods for handling and beneficiating raw materials. Closed-circuit grinding, classification, hy-droseparation, flotation, agitation, and thickening are familiar terms at this cement plant. These methods make it possible to process refractory limestone into suitable materials for the mallufacture of modern cements. Construction of the plant, having originally a design capacity of 7000 bbl. of cement per day, was started in June 1939, and the first clinker was ground on the following Christmas Day. At present the capacity is about 12,000 bbl. of finished cement per 24 hr., most of the production being low-heat cement. † About 3I30 tons of limestone, 620 tons of clay and I00 tons of gypsum are required daily for this output. Occasionally iron oxide is added to the clay to obtain the desired composition. This, together with the gypsum, is purchased from outside sources. up to the present time, the ccrporation has produced low-heat, normal, moderate-heat, moderate-sulphate-resisting, high-early-strength, oil-well, modihed-oil-well, and plastic cements. Most of the present production is for Shasta Dam, near Red- ding, Calif., the total demand being 5,800,000 bbl. of cement. Following are some of the cement require ments of the Shasta Dam specifications: Per Cent Chemical composition: Loss in ignition.......... 2.25 Insoluble residue......... 0.75 SO3.................... 2.25 MgO................... 5.'' Uncombined lime in clinker (CaO)......... I.25 Percentage of iron oxide to alumina ratio....... I.5 Compound composition: Tricalcium silicate (3CaO.SiO2)........... Not more than 35 Dicalcium silicate (zCaO.SiO2)........... Not less than 40 and not more than 65 Tricalcium aluminate (3CaO.Al2O3).......... Not more than 7 Tetracalcium aluminofcr- rite (4CaO.Al²O³.Fe²O³) Not more than 20 Fineness: The average specific surface in the bin sampled shall be not less than 1800 sq. cm. per gram and no individual sample less than 1600 sq. centimeters. Compressive strength: The average compressive strength in pounds per square inch of three mortar cubes composed of one part cement and 2.75 parts fine testing sand, by weight, shall be equal to or greater than the following:

Jan 1, 1942

By Edward A. Capillon

The problem of scrap is probably of greater importance in the pro duction of gold, silver and other precious metal alloys than is the case for base metals and alloys. Remelting of gold and silver scrap in the shop is always a costly process because it involves losses by oxidation of thc base metals in the alloy with a consequent increase in the percentage of precious metal. This is most marked in the case of alloys containing the low-boiling and easily oxidized metals zinc and cadmium. Since it is not generally feasible to assay every shop remelt it follows that the possibilities of lost values arc large. So-called rolled gold and silver plate is made by soldering or welding the precious metal alloys onto base metal. Such plate when defective must be sent to the refinery to recover the gold and silver values, thereby involving additional expense in the form of refining charges. It is obvious therefore that gold and silver alloy scrap is an important item in manufacturing cost and must be reduced to a minimum. The amount of scrap resulting from poor metal will depend on a number of factors in the manufacturing operations, not least among which is the melting and casting practice. The notes which follow are a summary of experiments performed at various times to determine what variables in melting and casting are influential in the production of sound alloys. Metals Used in Alloying Pure gold, that is, gold of 24-kt. value is very much too soft for jewelry purposes and it is therefore always alloyed with other metals to increase its hardness and resistance to wear. For the same reason pure silver is seldom used alone but is alloyed with copper, the standard alloy being sterling silver which contains 92.5 per cent. silver and 7.5 per cent. copper. The metals commonly used for alloying gold are silver, coppcr, nickel and zinc. In addition to hardening the gold and producing alloys of different karat values the use of these metals makes possible the production of gold alloys of various colors such as yellow, red, green and white. The gold-silver-copper alloys vary in color from light greenish-white through green, yellow and red depending on the relative amounts of the three metals. Green or yellowish-green colored golds

Jan 1, 1930

By R. W. Hunt

The old plan was to increase every part of a rail much in the same proportion. But each part should be in proportion to what it ha.; to do. The head should be deep in proportion to tile amount. of traffic and the lowness of the rate of interest on its cost. The body need only he strong enough to carry the head after it is well worn down, and that deperlds on the weight of the machinery, and in the case of steel has little to do with the volume of traffic, except SO far as that affects weight of machinery. Ad on most railroad systems, the same niacliinery is used on main lines with heavy traffic, and bra11ct:es with light, I suggested in 1874 that each systern adopt the same body of rail for both, and make the head deeper on the main lines, shallower on the branches. This plan was adopted on the Pennsylvania Railroad. Bandberg seems to recognize this in his patterns of 1878. E. W. HUNT, TRoy, N. Y.: Again Dr. Dudley preaents to our cousideration a series of most carefully conductetl experiments, and ~llile I fully appreciate the labor and thought this work has cost him, I must still hesitate to accept his deductiono. This paper dilliirs from the previous one in that it denls esclrieively with the wearing qualitiei. of steel rails. Dr. Dudley gives his reason for this change in the following statement: " With the improvement in maintenance of way which has characterized the Pennsylvania Railroad during the last five or six yearn, the remova1 of rails from the track from the first two of these causes (i. e., broken and crushel), has, if I am right, quite notably diminished. This certainly is true with regard to broken rails. And if, as time advances, the number of crushed rails shall diminish, both because of the continued improvement in maintenance of way before referred to, and because, owing to improved and better methods at the steel works, there are fewer crushed rails caused by physical defects in the steel, the question of the wearing capacity of steel rails obviously becomes the allimportant one." Certainly the condition of the roadhd has much to do with mils brealring, crushing, and wearing. If the Pennsylvania and other railroads have done and are doing their part, Dr. Dudley oourteously admits that the steel works have performed part of theirs. But as far as I am informed, the formulas which they have used have been and are still quite wide of the one he continues to recommend. The rails which are not breaking or crushing to so great an extent as formerly, contain higher percentages of both carbon and manganese.

Jan 1, 1881

By R. F. Mehl, C. E. Birchenall

R. E. Hoffman and D. Turnbull—The authors have presented evidence which they have interpreted as indicating that the rate of self diffusion is not intrinsically more rapid at grain boundaries than within the grain. Grain-size effects which apparently exist are attributed rather to impurities concentrated at the grain boundaries. In view of our own experiments and the existing evidence, we believe that the support for this hypothesis is not convincing. We have in progress an investigation in which the rate of self diffusion of silver is being measured over an extended temperature range in both single-crystal and polycrystalline specimens. The results of the single-crystal experiments and some preliminary data on fine-grained polycrystalline specimens have already been reported:' and it is anticipated that a complete report will be published in the near future. The self-diffusion coefficient of large-grained polycrystalline silver (1 grain per sq mm) has previously been measured by Johnson" between 730" and 940°C. The diffusion coefficients which we have measured in single crystals (210 plane normal to diffusion direction) agree within experimental error with values calculated from an extrapolation of Johnson's curve down to temperatures as low as 500 °C. However, it has been demonstrated that the overall self-diffusion rate in fine-grained polycrystalline specimens (initial grain size of 0.003 cm) becomes measurably larger than the overall rate in a single crystal at a temperature of 600°C, and the discrepancy between the two rates becomes greater as the temperature is further decreased. In fact, it has been possible to obtain satisfactory penetration curves for polycrystalline specimens using the sectioning technique at temperatures as low as 400°C. At this temperature, the penetration is 50 to 100 times greater in the polycrystalline specimens than in a single crystal. Fisher" has developed an analysis whereby the ratio of the rate of the unit diffusion process at the grain boundary to the corresponding rate within the grain can be calculated from the penetration curves and an assumption as to the width of a grain boundary. This analysis applied to our data indicates that the unit process at the grain boundary is faster by a factor of 10' at 475°C when the grain boundary width is taken to be 5. The silver used in most of these experiments was obtained from the Handy and Harmon Co. and listed as 99.97 pct pure. Preliminary experiments on 99.999 pct silver from the Jarrel-Asch Co. indicate a grain-size effect of the same order of magnitude as in the less pure silver. Nominally, these purities are as good, at least, as that of the carbonyl iron used by the authors, but of course if an impurity effect does exist its magnitude might be very dependent upon the nature of both major and minor constituents. The authors have cited the work of other investigators who have found no grain-size effects. Neither Steigman, Shockley and Nix" nor Maier and Nelson8 were able to correlate self-diffusion coefficients of copper with grain size. However, all their measurements were performed at or above 750°C; and on the basis of our work with silver, no grain-size effect would be expected at temperatures above about 0.7 of the absolute melting temperature unless the grain size were exceedingly small. Likewise, in the investigation of the self diffusion of lead by Seith and Keil,14 the lowest temperature at which the diffusion coefficient was measured in polycrystalline specimens was 207°C, which is still sufficiently high so that the lack of a grain-size effect is not surprising. Finally, in those experiments on iron from which they concluded that there was no grain size effect, Drs. Birchenall and Mehl seem to have no information as to the actual grain sizes immediately prior to and following the diffusion anneal. Without this information, we believe that their own experiments offer little support for their hypothesis. F. S. Buffington, I. D. Bakalar, and M. Cohen—The results given in this paper agree in order of magnitude with those tentatively reported by us.27 However, significant differences exist in the two sets of data, and it may be well to make an explicit comparison. The diffusion studies at M.I.T. were conducted on somewhat higher purity iron (99.98 pct Fe) than the grades used by the authors, but this is undoubtedly not the answer. Fig. 4 shows the diffusion results of both laboratories for the gamma phase, omitting the authors' data on the commercial steels, while fig. 5 presents a similar comparison for the alpha phase. The divergence is much more marked in the latter case than in the former. In connection with the M.I.T. determinations, all of the runs in the gamma range and those above 800 °C in the alpha range were conducted with specimens having a relatively thick (0.002 cm) electrodeposit of radioactive iron. This practice minimizes any possible error due to extraneous diffusion that may occur during the heating to and cooling from the operating temperature. An exact solution of Fick's law for these boundary conditions was used in calculating the diffusion coefficients. At a later time, three runs were made below 800°C, using very thin electrodeposits similar to those of the authors, and the points fell considerably below the values expected from the extrapolation of the results based on the specimens with the thick deposits (compare dash-dot line in fig. 5). However, in the runs with the thin deposits, deviations of 100 pct were found between the individual specimens, whereas the maximum deviation with the thick deposits was less than 25 pct. Accordingly, it is not known at the moment whether the M.I.T. points below 800 °C should be given as much weight as those above 800°C. If this were done, the frequency factor would be of the order of 400 cm2 per sec, which is quite high. In other metals, the frequency factor for self diffusion lies between about 0.1 and 10 cm2 per sec. As the points below

Jan 1, 1951

Francis Drake, Bulawayo, Rhodesia, So. Africa (communication to the Secretary *):—I should like to place on record some data in addition to those given by Mr. Canby in his paper. I regret that my notes have been destroyed so that I can give no accurate measurements of the water jacket that I am about to describe. This furnace mas erected in Cerro Gordo, Inyo county, Cal., early in 1875, and I think it quite possible that it was the first applied in lead smelting. It was made of plate iron and elliptic in shape, the inner dimensions being about 54 by 42 in. by 48 in. high. The distance between the inner and outer plates was about 6 in. Tuyere holes, one at the back and two on each side, about 12 in. in diameter, were made in this, and in these were placed cast-iron water tuyeres about 16 in. long, the diameter of the blast orifice at the point being about 3 in. The height from tuyeres to feed door was about 9 ft., but the top of the charge was kept about 5 ft. above the tuyeres. There was a space of about 12 in. between the jacket and the top brick-work. This brick-work was supported by a cast-iron plate resting on four cast-iron columns. At the beginning, the jacket was lined with air-dried radial bricks, made of crushed quartz and fire-clay, as it was thought that the jacket would not stand the heat on its bare plates. After a short time the practice was altered and no lining mas put in. The jacket was closed at the top and had a steam drum connected by two pipes at the back. This steam drum was connected to the boiler in which the steam was made for driving the Baker blower, the rock breaker and the pumps. The bottom of the jacket mas also connected to the boiler. The jacket was run under boiler pressure (80 Ib.) for some time, but eventually cracks developed in the inner plate between the tuyere holes,

Jan 1, 1913