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By H. E. McKinstry

MOVEMENT on a fracture of irregular shape can cause local widening of the fissure and thereby offer freer channelways for circulation of ore-depositing solutions. This influence, coupled with large areas of wall rock available for reacting with ore solutions in brecciated and shattered ground can account for locally active deposition of metals and the resulting ore shoots. Such irregularities in the fracture system may be caused by local variations in the strength of rocks and by pre-existing lines of weakness, especially if these stand at favorable angles to certain components of the fracturing stress. Therefore correct interpretation of the mechanics of fracturing should permit deductions as to structurally favorable places on unexplored portions of the vein system. INTRODUCTION IT has long been recognized that movement on a curved or irregular fault surface is capable of separating the walls in certain portions of the fault, but until very recent years the importance of this mechanism as a factor in localizing ore shoots has escaped proper recognition. A short time ago W. H. Newhouse' presented a careful analytical study of displacements and their corresponding open spaces. For reasons that will be discussed later, it frequently happens that portions of the vein which are favorably oriented are not merely wider but also richer than the average. In many cases the widening with its accompanying richness coincides with very minor changes in the dip or strike of the vein, irregularities that commonly escape notice unless the vein is mapped in detail and a careful geometrical analysis made. While the relationship between the width of the vein and the changes in dip or strike has been recognized as a matter of observation, the irregularities have been accepted as more or less the result of accident. There has been very little effort except in isolated cases to find out the causes of these changes in dip or strike. Yet it is clear that if the causes can be recognized and expressed in terms of geologic structure the geologist will know where to look for repetitions of these favorable conditions either on extensions of the same vein or on adjoining veins. Any lack of understanding of the causes is due to the limitations of our ability to interpret our observations and not to the sheer capriciousness of

Jan 1, 1941

By Magnus Troilius

INTRODUCTION BY C. P. SANDBERG. SINCE the discussion On steel rails in America has forcibly drawn attention to the value of chemical analysis, if not as a necessary stipulation, at least as a guide to control the usual mechanical tests, some doubt has been thrown upon the accuracy of the analytical results Obtained by different chemists. To any One having the least acquaintance with chemistry., it is quite clear that if exactly similar results are to be obtained from the same borings of steel, exactly the same methods must be used by the different analysts. Hence the necessity (if complications are to be avoided) of establishing what I may call standard or normal methods, to be used both by the inspectors and by the chemists at the works. Remembering that the application' of chemistry to steel-rail inspection is yet in its infancy, it is of great importance to possess a perfect acquaintance with the best methods in use. Being myself a grateful pupil of Professor Eggertz, of the School of Mines in Sweden, it Occurred to me, two. years ago, that I could not do better than start a laboratory of my. own, and engage One of his pupils, Mr. Troilius, for the purpose of analyzing the steel borings from mechanically-tested rails, so that I might thus Obtain without delay thoroughly accurate determinations. Moreover, in Order to carry on the, operations in perfect accordance with the methods used at the steel works in England and Germany, where I had to control the manufacture, I deemed it desirable to allow Mr. Troilius to go through a course of training at these works; and I gladly seize this opportunity of expressing my grateful acknowledgments to several works in England and in Germany for affording every facility for such an exchange of information as was found necessary in arriving at the best analytical methods to be used.

Jan 1, 1882

By F. L. Bosqui

INTRODUCTION The history of the development of gold metallurgy in South Africa is divisible into two periods: That preceding the introduction of the cyanide process on a commercial scale in 1890; and the 24 years intervening between that important event and the present time. The period between the discovery of the banket reefs of the Witwatersrand and the year 1890 was one of phenomenally rapid progress in mining development, but of no special interest to the metallurgist. There were no strikingly original or distinctly local advances in the treatment of gold ores. Californian practice in stamp milling and amalgamation prevailed, in mills ranging in equipment between 5 and 50 stamps, operating within a wide range of efficiency, and under the trying conditions usually en¬countered in a new and isolated field. The somewhat incomplete records of gold output of that period show that in December, 1887, there were 20 producing companies in the Witwatersrand district, of which 10 had mills, the largest being of 20 stamps. The only official record of returns for May, 1887, was that of the Wemmer mine, whose modest achievement with a 5-stamp, mill was 100 tons crushed, producing 887 oz. 3 dwt. of gold. This is interesting in view of the .present-day output of this field, which in 1913 reached 8,430,998 oz. The rapid increase of production during this first period (May, 1887, to January, 1891) is shown by the following summary for the year 1890:1 Total tons crushed 702,828 Number of stamps in operation 1,046 Average number of tons crushed per stamp per day 2.36 Yield of gold, ounces 494,817 Yield per ton, pennyweights 13.36 The stamp duty ranged between 1 ½ and 4 tons per day, according to weight of stamp, fineness of screen, and operating skill available. The prevailing weight of stamp was about 900 lb., and the screen, 900 meshes to the square inch.

Jan 5, 1915

THE developments in construction and operation of the basic open-hearth furnace that have taken place in recent years have placed new emphasis on the vital influence played by regulation and control of the combustion system in both furnace production and furnace life. The several factors influencing flame development, such as regulation of fuel supply, air supply, air preheat, furnace draft, and furnace reversal, must be controlled closely if successful furnace performance is to be accomplished. Rugged instrumentation of distinctive design is required to sup- ply dependable information concerning operating conditions, which is requisite to proper regulation of combustion. This chapter attempts to give a practical discussion of the various features of open-hearth practice and instrumentation related to the efficient heating of the furnace, control of temperature, and protection of the furnace structure from accidental overheating. The appended references will be helpful to readers wanting a more detailed treatment of individual topics. OPEN-HEARTH FUELS The most important open-hearth fuels are listed in Table 4-1 together with their compositions and other data useful for combustion calculations. A detailed discussion of open-hearth fuels is not attempted here, but certain factors peculiar to their application to this type of process are briefly indicated on the following pages. Very often an open-hearth shop is forced by economic factors to use a fuel to which its furnaces are not very well adapted, because the general fuel-allocation scheme for the works as a whole seems to demand it. Often a variable marginal supply of coke-oven gas or tar must be consumed by the open hearth, together with another fuel such as producer gas, natural gas, or oil, to fill out total requirements. Most furnaces employ more than one kind of fuel during their useful life; however, the partial redesign

Jan 1, 1964

By Clifford Wilson

SCREENED pipe is designed with the view of restraining the fine, free-running sands of the production zone from entering oil wells. Its successful use is dependent on a number of factors. The nature and effects of some of these factors can be determined through experiment and observation, but some of the elements that have a distinct bearing on the use of screened pipe can be evaluated only by estimate. The important subsurface conditions which affect the use of screened pipe are: 1. Depth of production zone. 2. Extent of production zone. 3. Reservoir pressure. 4. Character and relative quantity of oil and gas. 5. Character of sediments a. Consolidation of beds. b. Variation in beds. c. Grain-size gradation of sands. d. Free-running characteristics of sand from different levels. Aside from the use. of mechanical equipment and tools, the measures to be taken in the installation of screened pipe involve: 1. Size of liner. 2. Length of liner. 3. Design and mesh of screen. 4. Portion of liner to be screened. 5. Manner of setting liner. 6. Preparation of or washing of the well before or during the setting of the screen. 7. Manner of bringing in the well. 8. Manner of flowing the well. Values applicable to the actual subsurface conditions that exist at any well can only be approximated. The accuracy of the estimate will be measured by the amount and quality of the evidence at hand and the personal factor of ability to interpret the evidence fairly, whether

Jan 1, 1932

By V. C. Allen

THE Tri-State Zinc, Inc., Galena, Ill., was confronted with the problem of securing ore from a deposit because the hoisting shaft was several thousand feet from the mill. The orebody is several thousand feet long, averaging 200 ft in width and 60 ft in height and opened up by vertical shafts some 300 ft deep. Mining is by the room-and-pillar method. During the initial operation the ore was loaded by conventional electric 1/2-yd boom-and-dipper shovels and hauled to the shaft by 8-ton diesel trucks. This underground ore loading and hauling was well adapted to the conditions and productive of low costs per ton. However, with the mill situated as mentioned, a triple handling of all broken rock was necessary: l—from the stope to the shaft by truck, 2—up the shaft by skip br can into the surface hopper, and 3—by truck from the surface hopper to the crushing plant at the mill. In addition to the repeated handling, serious troubles were encountered during the winter because of freezing in the shaft hopper. Consideration was given to either moving the mill to the new orebody or to the construction of a second mill. The presence of other orebodies to be mined at a later date made the first alternative impractical while the capital outlay for a second mill, when the present plant of approximately 850 tons per day was deemed sufficiently large for the total reserves, made the second alternative also unwise. It was decided to retain the mill in the originals location and continue to move the ore to it. The idea of driving an inclined adit from the surface to the bottom of the orebody suitable for truck haulage and big enough to allow the passage of all mechanical equipment was conceived. Among the apparent advantages of such an incline were: 1— Direct haulage from the stope to the mill without rehandling. 2—Elimination of virtually all grizzlies. Trucking from underground to the mill would do away with all hoppers, chutes, gates, and skips and make the maximum rock size dependent solely on the size of the shovel dipper at the mine and the crusher opening at the mill. 3—Less secondary blasting would be needed. 4—Ease of transporting equipment and supplies underground. Shovels and trucks could be taken through the incline intact. 5—Equipment could be brought to the surface for repairs and servicing without loss of time. The same advantages of ease in moving would be present in the handling of men, steel, powder, and supplies. 6—There would be far less difficulty in increasing the amount of tonnage that could be moved by truck up an incline than would be found in attempting to increase the capacity of a shaft. 7—All the broken ore in the stopes would serve as bin capacity, as it would take the breakdown of all of the loading and hauling equipment to have the same effect as a delay in shaft hoisting. 8—All danger of men being trapped in the mine as a result of shaft fire or power stoppage would be eliminated. 9— Virtually all trouble from severe winter conditions would be eliminated by the direct haul underground to the mill. The decision was made to proceed with the driving of an inclined adit. The topography of the surface between the orebody and the mill was such that it was possible to locate the portal at a point 170 ft above the mine floor and 1800 ft horizontally from the central point of the orebody to the south and 2500 ft from the mill to the north. A grade of 10 pct was found to be optimum for continuous truck haulage when the various factors of speed, safety, and truck maintenance were all considered. The incline as driven was consequently 1700 ft long on 10 pct grade and 12 ft high by 17 ft wide in cross section. The tunnel-driving equipment was chosen so that it could be used in mining after the completion of the tunnel. Drilling was done with a jumbo with two Joy jibs mounting 3-in. drills, loading with an Allis-Chalmers diesel-powered, front-end loader of approximately 11/4-yd capacity, and hauling by Koehring Dumptor trucks of 8-ton capacity, diesel-powered. The width of the tunnel allowed the end loader and Dumptor to be placed abreast. Since the Dumptors can be driven either forward or backward with equal facility, loading was accomplished without turning around either machine throughout the loading operation. The crew in addition to the tunnel foreman was comprised of three men per shift at the start and in the later work, four men. Each crew could perform any part of the working cycle. If the drilling was completed and the round blasted in the middle of a shift, the same men would proceed with the loading and hauling. Since the mine already had been drained to the bottom levels, no water was encountered. At the halfway point the tunnel was widened for approximately 100 ft to permit trucks to pass. The total cost of the tunnel excluding the capital outlay for equipment, which was all continued in use in the subsequent mine operation, was $60,363.00 or $35.50 per ft. The tunnel was completed at the end of June, 1949 and has been in continuous use since that time. In the five months from July to November inclusive, 106,049 tons have been transported to the mill or an average of 835 tons per day. No unforeseen disadvantages have been encountered and the advantages which had been predicated before the adit's construction have been more than realized. As previously mentioned, the deposit is worked by the room-and-pillar system with occasional faces up to 125 ft high. Except in driving development drifts when diesel-powered, front-end loaders such as were used in the tunnel are employed, all shoveling is done by Yz-yd boom-dipper type shovels electrically driven. These units need a width of 25 ft and a height of 14 ft in which to operate. All hauling is by diesel trucks, mainly Koehring Dump-tors. Roads are maintained with caterpillar tractors and a road grader. The tonnage output from the

Jan 1, 1952

By L. W. Strock

Metallurgists handling lead and zinc ores have long been familiar with the spectrograph as a routine analytical tool, as its earliest regular use by American industry was in controlling impurities of zinc metal and its alloys. This application has been extended to other metal industries on an extensive scale, accompanied by refinements of procedure to such an extent that a large part of some metals produced, especially magnesium, aluminum and steel, are checked only by spectrographic methods for conformity to specifications. The spectrographic analysis of ores and other poorly conducting powdered solids presents difficulties not encountered with metallic samples, which can be arced or sparked as self-electrodes or can be readily dissolved, so that their solutions can be analyzed, as in the American Society for Testing Materials standard methods for zinc and zinc-base alloys. Spectra of powdered solid samples can be prepared by using carbon electrodes provided with a crater of suitable size, into which the sample is packed. Ore samples and many other powdered solid materials usually analyzed in the chemical and metallurgical laboratory are more complex and varied in composition than samples of metals produced in large tonnages. 'lore preliminary work therefore is usually necessary in devising a spectrographic method for analyzing a given type of powdered sample than for analyzing metal samples, in order to use that method with confidence. The howledge that the standard samples and unknowns produce equivalent line intensities at equal concentration is the fundamental basis of any quantitative spectrographic method. On the other hand, powdered samples have an advantage over metals in that any desired number of chemical compounds can be mixed dry in any desired ratio to produce a synthetic standard. Expcrience has shown, however, that spectra of elements in finely divided compounds introduced into a standard in preparing a synthetic ore sample do not always behave in the electric arc in a manner that produces spectral line intensities similar to those observed at the same concentration in a natural mineral. In ore samples minor elements frequently are contained in the crystal lattice of larger particles of an abundant ore mineral. Their dissociation and volatilization from the sample into the arc then proceeds differently in the standard and sample, with resultant differences in intensity. During the past 10 years I have devised and applied several quantitative spectrographic methods for determining various elements in rocks and minerals in connection with studies on their geochemistry,' but the incentive has gradually changed since the summer 0. 1940 to the specific practical problem of searching for domestic sources of rare and stratcgic metals. The

Jan 1, 1949

By John W. Wagner, Robert K. Willardson

Single crystals of Pbl-xSnXTe have been grown from The melt under liquid B2O3 using the Czochralski technique. The PbTe-SnTe crystals were grown from near-stoichiometric melts and from melts with slight deviations from sloichiometry. Crystal growth rates ranging from 1 mm per hr to 1 cm per hr were employed, the latter being generally used. Several investigations were performed to characterize the single crystals grown In this study. The phase diagram of the PbTe-SnTe system was examined. X-ray analyses verified the single-crystal character of the crystals, and powder pattern lattice parameter determinations showed that Vegard's law was followed within the limits of the experimental error. The as-grown crystals were p-type with apparent carrier concentrations of -8 x 1018 to -8 x 1020 carriers per cu cm. Hall coefficients, resistivities, and carrier mobilities were determined as a function of composition. Dislocations were revealed by an electrolytic etch, and the crystals were found typically to contain 2 to 4 x 105 dislocations per sq cm. Microhardness measurements were performed; no maximum in the Vickers hardness us composition curve was seen. Mass spectrometry was used for impurity analyses, and the crystals were found to contain 1 to 2 x 1017 total p-type impurities per cubic centimeter. Distribution coefficients were calculated for the major impurities which were Na, Mg, Al, Si, Cl, and Zn. RECENTLY interest has been stimulated in the preparation and characterization of many alloys of the binary compound semiconductors. This interest is due primarily to the almost unlimited possibilities of adjusting the semiconducting characteristics of these materials by varying the alloy compositions. One alloy system which has been receiving extensive investigation is the PbTe-SnTe system, since these alloys show promise of being useful as emitters and detectors of electromagnetic radiation in the spectral range of 8 to 14 µ. This paper reports on the growth of PbTe-SnTe single crystals by the Czochralski technique and investigations of the general properties of these crystals. The phase diagram of the PbTe-SnTe system was investigated so that specific alloy compositions could be attained. I) CRYSTAL GROWTH The PbTe-SnTe single crystals were pulled from the melt using the Czochralski technique. Generally, the crystals were grown from near-stoichiometric melts, although special growth runs were made from both lead-rich and tellurium-rich melts. Growth of single crystals from up to 5 pct lead-rich melts presented no problems; however, melts with tellurium in excess of -1 pct caused volatilization problems which generally made crystal growth impossible. All melts were prepared from high-purity materials as follows: 1) lead— 6 N— Cominco (Cominco Products, Inc., Spokane, Wash.); 2) tin—5N—Cominco; and 3) tellurium— 5N+— American Smelting & Refining Co., Plainfield, N.J. No further purification of materials was undertaken in this study. The elements were reacted at -1000°C in a vacuum-sealed silica tube for a few hours, a gentle rocking action being used to ensure thorough reaction. The cast ingots were then transferred to a silica crucible for crystal growth. A schematic diagram of the growth apparatus is shown in Fig. 1. The Vycor tube is sealed at both ends by O-ring flanges so that a vacuum or a positive pressure may be maintained in the growth chamber. The pull rod and crucible may be rotated; all crystals produced in this study were grown with the crucible sta-

Jan 1, 1969

By F. T. Selleck, H. H. Reamer, B. H. Sage

An experimental investigation was made of the effect of temperature upon the three-phase pressure associated with the propane-water and propene-water systems when hydrates were present. In addition, the characteristics of the propane-propene-water system were established over a limited range of ternperatureo under conditions such that hydrate was formed. The hydrate phase for this system may he a solid solution and the distribution of propane and propene in it is similar to that found in the coexisting hvdrocarhon liquid phase. INTRODUCTION A knowledge of the characteristics of hydrates of the hydrocarborrs encountered in industrial practice is of importance in connection with the design of process equipment. Villardl.1,2 carried out early studies of hydrates, and de Forcrand1 con-sidered the more probable compositions of the hydrates of hydrocarbons. Hammerschnid1 presented information about the propane-water and the isobutane-water systems. Scheffer5 studied the hydrate of hydrogen sulfide in detail, and de For-crand reported on the hydrates of krypton, argon, and xenon.1 Roberts and co-workers1,2 determined the nature of the hydrates formed in the methane-water and ethane-water systems. Carson and Katz10 studied the methane-propane-water, methane-pentane-water, and the methane-hexane-water systems in the four-phase region. The results of this rather extensive investigation indicated that the paraffinic hydrates formed solid solutions. The experimental evidence now available does not Support the existence of hydrates of the pentanes-antl-heavier hydrocarhons but it cannot be stated with certainty that such hydrates are not formed. Stackelherg. 11,12,13 made extensive studies of the crystal structure of paraffinic hydrate; by means of x-ray techniques and found that hydrates poses; a definite structure and composition. The existence of such a Structure does not preclude the firmation of Solid solutions of hydrates in aqueous systems containing two or more hydro-carbon~. Wilcox, Carson and Katz" reviewrd the information on the hydrates of importance in the processing of natural gas and presented data concerning their formation from natural gas. Kobayashi and Katz1' made studies at high pressure of the Hydrate of methane. and Unruh and Katz"' investigated hy-drates in mixtures of carbon rlioxide and methane. Frost and Deaton contributed to the knowledge of the composition of the paraffinic hydrates The irregularities in the experimental results were several times the expected uncertainties. This experience confirms the behavior encountered by other investigators indicating that hydrates tend to occlude water during their formation, thus rendering difficult the direct measoremeut of their composition. Miller and Strong2 investigated a number. of paraffinic hydrates from the standpoint of their possible application to (, the industrial storage of gas. Powel1 studied the effect of solutes upon the decomposition temperature of paraffin hydrates. Marked lowering of the decomposition temperature at a given pressure may he obtained by the use of such additive agents as ethylene glycol, urea. and sodium chloride. APPARATUS AND METHODS Two method* were here employed to study the behavior of hydrates. The first involved a glass capillary within which the hydrocarbons and water were confined over mercury. The second made use of a double-ended weighing bomb technique." The glass capillary equipment has been described elsewhere.'" A schematic drawing of it is presented in Fig. 1, where the arrangement of the agitator and mercury reservoir is shown in some detail. The lower part of the glass capillary, D, was enlarged to afford space within which the fluids used in the investigation could he stored at low pressures after their introduction through the valve. G. The temperature of the capillary was controlled by the circulation of a hydrocarbon oil of low viscosity from the agitated bath, B, through the vacuum jacketed column. C. The pump, A, was employed for the circulation of this oil. A relatively clear view of the capillary tube, D, was obtained through the vacuum jacket. Mercury was introduced into the lower part of the vessel, E, from

Jan 1, 1952

By Walter R. Hibbard

THE increased strength of a polycrystal-line metallic aggregate compared with that of its individual crystals generally has been associated with complex stress distributions at the grain boundaries resulting from atomic irregularity between grains. This disregistry, together with the necessity for adjacent crystals to deform 'compatibly regardless of the single crystal crystallographic strain mechanism, complicates this mechanism so as to increase the metal's resistance to deformation. Although Taylor1 has shown from purely mechanical considerations the requirement for at least five active slip systems to absorb the complexities during the homogeneous deformation of polycrystalline face-centered cubic metals, experimental studies by Barrett and Levenson2 indicate that this is feasible only in a qualitative sense because of deviations from homogeneous deformation. Seitz and Read in their review3 state: "Unfortunately . . . present knowledge of the grain boundary influence is not sufficient to complement the work in single crystals and provide us with a good foundation for treating polycrystals." The purpose of this investigation was to attempt to clarify the gap between single crystals and crystalline aggregates by an analysis of the effects of deformational stresses. Some of the results were described by C. H. Mathewson in his 1943 Campbell Memorial Lecture.21 PREVIOUS INVESTIGATIONS Since the performance of single crystals deformed under pure stresses has been relatively thoroughly investigated, the most significant researches are concerned primarily with deviations from single crystal behavior of large grained specimens. Qualitative grain boundary effects involving the observed amount of slip were reported by Carpenter and Elam5 in 1921. Individual crystals in a two or three grained aluminum specimen deformed by tension acted in the normal manner described by Taylor and Elam4 except for marked modifications at the grain boundaries. There the power to withstand deformation was considerably increased, leaving a ridge on the specimen where decreased slip occurred, often noticeable 34 in: from the boundary. Adcock,6 Yamaguchi,7 Seumel,8 Hirst9 and others have also reported this phenomenon as a qualitative trend. Yet attempts by O'Neill10 and Ljunggren11 to measure a difference in hardness at grain boundaries in undeformed specimens were unsuccessful. Miller12 measured quantitatively the reduction in slip near the boundary between the single crystal and polycrystalline areas of zinc specimens. These effects consisted of two parts: I. Next to the polycrystalline interface the distribution of stresses was so altered

Jan 1, 1948

By Albert Sauveur

(New York Meeting, February, 1913.) IT is delightful to read a technical paper like that of J. E. Johnson, The Effect of High Carbon on the Quality of Charcoal-Iron, presented in October, 1912, at the Cleveland meeting of the American Institute of Mining Engineers.1 The clear, simple, and straightforward manner in which he describes his experiments and results makes you feel as if you had been, so to speak, at his elbow during the course of his investigations, while his method of procedure is so rational that you can fairly anticipate each step in the logical sequence of the tests performed. The following notes suggested by Mr. Johnson's paper are presented here in the hope that they may help, if only a mite, towards the final solution of a problem of considerable scientific and industrial importance.

Jan 3, 1913

By J. W. Koger, R. E. Hurnrnel

QUENCHED, bcc p brass, P1, transforms to a mar-tensitic phase, when it is cooled below room temperature.' This transformation can be followed using resistance measurements since the resistivity of the martensitic phase is considerably larger than that of the parent phase, Fig. 1.' phillips3 first reported that, when Cu-Zn alloys containing between 37.0 and 39.0 wt pct Zn were quenched from the 0 region to room temperature, variable amounts of a phase could be observed depending on the mode of quenching. If the quench occurs very rapidly, the a phase forms by a "massive transformation". The resultant phase has the same composition as the high-temperature P phase from which it was formed. If the quench is less severe, the alloy is retained largely in the p form; however, some a is formed by precipitation. In this case, a contains more copper than the high-temperature 0 phase from which it has formed. The a phase most probably does not undergo a transformation in the temperature range where p transforms to low-temperature martensite. This can be deduced from the Eesistivity-temperature relation which is linear in this temperature range, Fig. 2. The stable a phase which is present along with R. E. HUMMEL is Assistant Professor, Department of Metallurgical and Materials Engineering, University of Florida, Gainesville, Fla. J. W. KOGER, Junior Member AIME, formerly with University of Florida, is now with Oak Ridge National Laboratory, Oak Ridge, Tenn. Manuscript submitted December 13, 1967. IMD.

Jan 1, 1969

Discussion of the paper of A. P. WATT, presented at the St. Louis meeting, October, 1917, and printed in Bulletin No. 130, October, 1917, pp. 1476 to 1563. THE CHAIRMAN (0. M. _BILHARZ, Miami, Okla.).-Mr. Watt's reference to sorting or hand-picking of the ore in the lead district, which is being introduced at Mine La Motte, is especially interesting. I believe, from my former experience in the district, that hand-picking should be practised to some extent by all the companies in the Lead Belt. I know that a great many thousand tons containing only very small amounts of lead are passed through the mills, which, of course, is not to the advantage of milling machinery. That procedure may be Warranted at times of high prices, but I think that hand-picking should ordinarily be adopted to some extent: ERNEST GAYFORD, Salt Lake City, Utah.-On page 1525, speaking of the settling of slime previous to treatment either on slime tables or by flotation, Mr. Watt states: "The settling area allowed per ton of dry slime varies from 11 to 16 sq. ft.-an average for the district would be about 13 sq. ft. of settling area per ton of dry slime. This figure applies when the, discharge contains 20 per cent. solids." Mr. Ramsey, of the Dorr company, is here and I would like to ask him whether a settling area of 13 sq. ft. per ton of dry slime per 24 hr. is not considerably above the average area of Dorr settling tanks, and whether 20 per cent. solids is not above the general dilution for that' capacity? I should also like to know what is the general average on slimes of that character. E. R. RAMSEY, Denver, Colo.-An allowance of 13 sq. ft. per ton does seem rather large. I am not familiar with the settling characteristics of the dolomitic gangue, but as an average over the country, I should say that 6 or 7 sq. ft. would be nearer correct for discharge at that consistency. L. A. DELANO, Bowie Terre, Mo.-We have had an opportunity to try our tanks at the highest capacity, and-find that by thickening the slime to 30 per cent. solids we average 12 sq. ft. per ton of dry slime. ERNEST GAYFORD.-DO you find any definite ratio between the thickness of the discharge and the settling capacity of the tank? Do you consider that the tank has a larger capacity if the discharge is 3 to 1 than if it is 50 per cent. solids? L. A. DELANO.-I think it has greater capacity with the thinner discharge. It depends a good deal on the density of feed to the tanks; in our case the feed contains 2.5 per cent. solids.

Jan 1, 1918

By H. E. Searle, Robert J. McKay, O. B. J. Fraser

The practical study of corrosion requires consideration of its economic aspects. It must be based on sound scientific principles, but it should be borne in mind that probably the most important object of a corrosion test is to determine what metal in corrosion-resisting construction will produce the greatest operating profit. Thus the corrosion test must be directly connected with money values or it is not a practical corrosion test. This, perhaps unusual, connection between corrosion and economics is partially due to the fact that corrosion deals only with the time factor or duration of equipment, and it is almost the only test which deals with this feature. In these statements a departure is made from the academic definition of the word corrosion and it is done deliberately. The use of the term corrosion is unusual. It is as though we spoke of a tensile test as a "breaking" test. We are not interested primarily in the break but in the strength of the metal. There is no English word which expresses our main interest in corrosion-testing, but let us have clearly in mind that we make corrosion tests to prevent corrosion. Our real interest is in this corrosion-prevention, not in the corrosion. Previous to 1922, it was common comment that "it is impossible to determine the course of corrosion by laboratory testing.'' This statement was true at that time in that the technique of laboratory testing for corrosion resistance was so vague that tests in the laboratory gave untrue results almost as often as true ones. This was so, even in the simple case of determining which one of two metals better resists a given solution. While this is no longer true the number of misleading "corrosion tests" still being ground out by laboratories is too large in the light of our present knowledge. There are two important features of corrosion testing whose neglect is a large contributing factor to misleading results: (1) The economic relations of the corrosion tests to other tests; (2) testing technique. Regarding economic relations J. F. Thompson l has said: "The use of any particular metal is rarely based upon the sole property of resistance to corrosion. In fact, I should like to venture the assertion

Jan 1, 1929

By Robert J. McKay, O. B. J. Fraser, H. E. Searle

The practical study of corrosion requires consideration of its economic aspects. It must be based on sound scientific principles, but it should be borne in mind that probably the most important object of a corrosion test is to determine what metal in corrosion-resisting construction will produce the greatest operating profit. Thus the corrosion test must be directly connected with money values or it is not a practical corrosion test. This, perhaps unusual, connection between corrosion and economics is partially due to the fact that corrosion deals only with the time factor or duration of equipment, and it is almost the only test which deals with this feature. In these statements a departure is made from the academic definition of the word corrosion and it is done deliberately. The use of the term corrosion is unusual. It is as though we spoke of a tensile test as a "breaking" test. We are not interested primarily in the break but in the strength of the metal. There is no English word which expresses our main interest in corrosion-testing, but let us have clearly in mind that we make corrosion tests to prevent corrosion. Our real interest is in this corrosion-prevention, not in the corrosion. Previous to 1922, it was common comment that "it is impossible to determine the course of corrosion by laboratory testing.'' This statement was true at that time in that the technique of laboratory testing for corrosion resistance was so vague that tests in the laboratory gave untrue results almost as often as true ones. This was so, even in the simple case of determining which one of two metals better resists a given solution. While this is no longer true the number of misleading "corrosion tests" still being ground out by laboratories is too large in the light of our present knowledge. There are two important features of corrosion testing whose neglect is a large contributing factor to misleading results: (1) The economic relations of the corrosion tests to other tests; (2) testing technique. Regarding economic relations J. F. Thompson l has said: "The use of any particular metal is rarely based upon the sole property of resistance to corrosion. In fact, I should like to venture the assertion

Jan 1, 1929

By E. S. Leaver

THE presence of soluble base metals in precious-metal ores usually precludes cyanidation as the best method of treatment. The laboratory experiments described in this paper show the possibility of cyanidation of gold-silver ores containing less than 0.5 per cent, of cyanide-soluble copper and the effect of zinc in the cyanide solution. PART I.-COPPER IN CYANIDATION The proposed process of cyanidation of precious-metal ores containing copper is based on the regeneration of about 80 per cent., of the cyanide used in the dissolution of the copper. The method of regeneration involves a combination of the sulfide and the acid precipitation of the copper and silver. The resultant solution is made alkaline with lime, and the gold is precipitated with zinc dust. Solubility of Copper Minerals in Cyanide Solution In order to determine the solubility of copper minerals, including metallic copper, under the usual conditions for cyanidation, experiments were conducted with synthetic ores. Each ore sample was prepared by mixing the particular pure copper mineral with barren sea sand. Both the mineral and sand were ground to pass 100 mesh before they were thoroughly mixed. The percentage of copper in each head sample was determined by direct assay, excepting the metallic copper sample, which was computed on weights before mixing. Table 1 gives the results.

Jan 1, 1929

By Richard H. Bube

Photoelectronic radiation detectors may be conveniently classified as homogeneous intrinsic, homogeneom extrinsic, or junction type. Highly photosensitive homogeneous intrinsic photodetectors may be prepared from a number of different II-VI, III-V, or IV materials. Such materials require the presence of specific imperfections that can act as sensitizing centers to provide long majority carrier lifetime. Homogeneous extrinsic photodetectors are of interest primarity for infrared detection, and consist principully of germaniuim and silicon with suitable inpurities. A vaviety of junction photodetectors exist, with silicon us the most common material for them all. The following extrema in performance are found: 1) highest photoconductivity gain in homogeneous intrinsic photodetectors; 2) smallest response time (highest frequency response) in p-i-n junctions; 3) largest gain-bandwidth product in avalanche diodes. ALTHOUGH the total number of materials exhibiting photoconductivity effects is very large, only a relatively few of these have appropriate properties for a practical photoelectronic radiation detector. In fact if one surveys the commercial detectors currently available, one finds that the field is dominated by some ten or fewer materials. These are summarized in Table 1 in terms of the other important variable in detector fabrication, the structure of the material, i.e., whether the material is used as a single crystal or in polycrystalline form, and whether the material is used as a homogeneous detector or whether the detector depends upon the existence of a junction or barrier in the material. The principal wavelength range for each type of material is also shown, together with an indication of the utilization of intrinsic or extrinsic excitation. For the purposes of the present comparison of various detectors, it will be convenient to discuss two main topics: homogeneous photodetectors and junction photodetectors. The performance of a photoelectronic radiation detector is measured in terms of two parameters: the photoconductivity gain, and the response time of the detector. A convenient figure-of-merit is given by the ratio of gain to response time, often called the gain-bandwidth product. The photoconductivity gain is a device parameter since it varies in many cases with the applied voltage and the detector geometry, and should be distinguished from the actual photosensitivity of the material involved. This photosensitivity can be conveniently given as the product of free carrier lifetime and mobility in the material. The photoconductivity gain is defined as the number of charge carriers which pass between the electrodes per second for each photon absorbed per second, where G is the photoconductivity gain, is the pho-tocurrent in amperes, e is the electronic charge in coulombs, and F is the total number of electron-hole pairs created in the photo conductor per second by the absorption of light. The gain may also be expressed as the ratio of the lifetime of a free carrier to the transit time for that carrier, i.e., the time required for the carrier to move between the electrodes. For a material in which one-carrier conductivity dominates, where T is the lifetime of a free carrier, ttr is the transit time for this carrier, p is the carrier mobil-ity, V is the applied voltage, and L is the electrode spacing. From Eq. [2] it follows that the photoconductivity gain is proportional to the photosensitivity of the material (tP), the proportionality constant being The photosensitivity of a material, and hence the photoconductivity gain of a device utilizing the material, depends on the lifetime of the free carriers as a critical parameter. In a homogeneous material this lifetime is determined by the nature of imperfections in the material, and in an inhomogeneous material the lifetime is determined by the specific junction structure. The speed of response, the other basic photodetec-tor parameter, is determined by factors quite similar to those important for photoconductivity gain. Imperfections are of primary importance in homogeneous materials, and the structure of the junction is a determining factor in junction devices. For infrared detectors it has become common to define another quantity designed to indicate directly how effective the detector is in distinguishing between a small photoconductivity signal and random noise due to the detector and its environment. The detectivity D* is given by

Jan 1, 1968

By Charles M. Rolker

The main tin-producing regions of the world are known to be England, Australia and the Dutch East Indian possessions, chiefly Banca and Billiton. During recent years, the tin of the Malay Peninsula, exported from Penang and Singapore, has been coming prominently to the front. France, Austria, Hungary, Germany, Spain, South America, Russia and China still present insignificant figures. The conspicuous part which the Dutch possessions in the Indian Archipelago have taken in supplying the world with tin, is well known. Tin was discovered in Banca as early as 1710, and has been produced there ever since; but the supply has been most important since Banca came fully into the possession of Holland, in 1821. In Billiton and the adjoining island of Singkep, the existence of tin was known prior to 1822.* The Lingganese knew of its existence in the valley of Embalong, from creeks and streams in the neighborhood of Tima and Simper hills, on Billiton and also on Singkep island, but the prevailing superstition that tin-mining brought misfortune, influenced them to let this industry lie idle. The attempts of the Dutch government to test this question were lukewarm, perhaps by reason of the fear of reducing, through new discoveries, the price of Banca tin, and the island was abandoned in 1826, leaving only a military post. In 1850, Dr. Crookewit, a chemist and naturalist, was sent out to verify the rumors that tin existed in Billiton. His report was unfavorable; but in 1851 Mr. C. De Groot, a mining engineer, found tin readily, and the active work on Billiton dates from that time. Less than 600 tons were produced during the first ten years, and 3000 tons in the next decade. Billiton tin-mining is done by

Jan 1, 1892

By R. M. Rose, K. A. Jones

Resistive measurements ulere made on superconducting niobium single crystals in transverse magnetic fields. Crystals were grouln in both high and ulfrahigh vacua, doped with stnall quantities of oxygen, and annealed in ultrahigh vacua at temperatures from 900' to 1350°C. Maxima in the fluxoid pinr~ir~g force were observedfor the [100] and [210] directions. The increase of the critical current density with dissoved oxygen was seen to saturate at relatively low concentration. This behavior, and the variation of J, and residual resistivity (as a function of oxygen content and annealing) of both clean and dirty gassy) crystals, is seen as a consequence of the formation of clusters with (210)~b habit planes and (200)ffo common boundaries. These suboxide clusters are apparenlly stable at high temperatures and very low oxygen concentrations. It is generally known that dissolved oxygen at concentrations well below the solubility limit sharply increases the critical current density of superconducting niobium.' Such a result would not be expected if Nb-0 solutions were random, not even as the result of segregation on the scale usually encountered in solid solutions. According to the Kim-Anderson theory of flux creep,' the critical transport current density is determined by the pinning force Fp associated with some feature of the microstructure. As the Lorentz force. a or (J X R), of the transport current in the magnetic field approaches Fp, flux creep and then flux flow occur. The pinning force is expected to be quite small if the heterogeneity involved is significantly smaller than tte range of coherency which for niobium is circa 250~.~ Although the strain field of an individual oxygen atom in the niobium lattice is relatively large, it does not seem plausible that individual atoms could be so effective as to account for the data. Also, ~ramer~ found that straining and strain aging specimens containing small amounts of oxygen on occasion decreased the residual resistivity. A possible explanation for the above behavior may be found in the work of van Ooijen and van der Goot,= who found that annealing changed J, for niobium foils containing oxygen, and they attributed the changes to ordering of the oxygen atoms. This phenomenon has been observed by other investigators using X-ray and PROCEDURE Cylindrical 4-in.-diam niobium single crystals with axial orientations [ill], [110], [112], and [oo~] were grown from pure niobium, see Table I for analysis, in an ion-pumped ultrahigh-vacuum system using the electron beam floating zone technique. Total pressure during growth was lo-'9 torr: the oxygen partial pressure was less than lo-" torr, as determined by a mass spectrometer. These crystals will be referred to as the "clean" crystals. Similar crystals were also grown in another system at a pressure of 5 X 10"6 torr. These crystals will be referred to as the "dirty" crystals. Specimens 14 in. long were cut from the as-grown crystals and one end was polished down to no. 600 carbide paper smoothness. A back-reflection Laue photograph was then taken in order to fix the crystallo-graphic directions transverse to the crystal. The critical current density J,, the current density necessary to produce a voltage drop of 1.0 pv between voltage leads placed a in. apart, was determined as a function of the magnitude and direction of the transverse magnetic field and of the oxygen concentration. The technique and experimental arrangement was essentially similar to that of Tedmon et al.' In the remainder of this paper, the azjmuthal angle $ for the field H is referenced to the [ I101 direction in all four crystals, and oxygen was added in small equal increments by anodization and annealing.7 The resistivity ratio, RR, of the resistance at room ternperature to that at 4.2"K (H =7.00 kG) was determined as well.

Jan 1, 1970

By T. Egleston

The manufacture of charcoal in kilns was declared many years ago, after a series of experiments made in poorly constructed furnaces, to be unprofitable, and the subject is dismissed by most writers with the remark that in order to use the method economically the products of distillation, both liquid and gaseous, must be collected. It is asserted with truth that the number of kilns required for a large production of iron would be so great that it is doubtful whether any works would be justified in making the necessary outlay for their constructiou, but it can also be asserted with equal truth that for any such production in a given locality the use of charcoal as fuel would be eqnally unjustifiable. It appears to have been forgotten that there were other manufactures besides iron in which large amounts of charcoal were used, but these consumers seen] to have been guided entirely by the results of the experiments of the iron men, who necessarily made the largest qnantity of it. Some authors speak in a doubtful way of the quality of the charcoal produced, and a few concede that with great care good charcoal can he made in kilns, but that most of the workmen do not like kiln 'charcoal. This is the real secret of the opposition to this method of manufacture. Most of these objections were written when charcoal was the most important fuel used by the iron manufacturer, and when what was a largeproduction of iron for several furnaces was less than that produced by a single modern one, in localities where other fuels can be had. Almost all that has been written on the subject related to the use of the fuel for the manufacture of iron in the blast furnace, where very peculiar properties are required, and where the qnantity produced is limited by the height of the furnace, and this in turn by the crushing resistance of the charcoal. A large production was, therefore, only possible when the best and hardest woods were used. Of all these objections there is not a single one which is not eqnally applicable to any method of charcoal manufacture, whether it be meilers, pits, or furnaces. Until recently, therefore, the manufacturers of charcoal iron

Jan 1, 1880