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By Hui-bin Wu, Rui Yuan, Yang Gu, Peng-cheng Zhang, Zheng-zhi Zhao

The corrosion behavior of three kinds of medium-Cr rolled steel pipeline steels in carbon dioxide collecting and transporting environment at different temperatures was studied. The results shew that the 5Cr sample was most affected by temperature. When the temperature rised from 30 °C to 90 °C, the corrosion rate increased from 0.12 mm/a to 1.87 mm/a, which was increased 15.6 times. The corrosion rate of 7Cr steel at 30 °C was similar to that of 5Cr steel. However, as the temperature increased, the corrosion rate rised slowly, increasing by 2.4 times at 90 °C. The corrosion rate of 9Cr steel was not obvious with temperature, and it was always below 0.06 mm/a. The thickness of the corrosion product film of the three samples gradually increased below 70 °C, and suddenly increased above 70 °C. This was related to the negative temperature coefficient of the solubility of FeCO3, and the thickening of the product film also affected the ion exchange of the cathodic reaction. An increase in the Cr content contributed to grain refinement and increased the proportion of the small-angle grain boundaries. More fine grains mean an increase in the total length of the grain boundaries, which could provide a diffusion channel for the free Cr element; on the other hand, the low-angle grain boundary structure was more orderly, with a lower free volume and lower interface energy. Under the combined effect of both, 9Cr steel and 7Cr steel had high volta potential and better corrosion

Oct 1, 2019

By Cengiz Karagüzel, Ömer Canıeren

The mobility of gold and silver metals from refractory ores is very low due to free metal ions in their bodies that bind the transportable and free metal molecules or they are encapsulated in minerals such as sulfides, arsenosulfides, carbonaceous, and clayey materials which make it difficult to extract them. As known from the literature, the enrichment of oxide refractory gold, silver ores, Ag, and Au-rich flotation concentrated from sulfur refractory ores can be leached in the chloride-hypochlorite solutions. In this work, the leaching approach was studied to extract silver ions from refractory ores in the presence of hypochlorite media under high pressure. The mineralogical and scanning electron microscopy analysis of the sample indicated that the silver was encapsulated in barite and quartz minerals in fine sizes. In order to obtain the optimum leaching conditions for the silver ore, the effects of several parameters, namely, temperature, leaching time, NaCl and NaOCl concentration, solid ratio, and particle size on the leaching recovery were investigated in detail. The leaching experiments showed that the highest silver recovery of 62.35% was obtained under the following conditions: temperature of 150 °C, oxygen pressure of 1800 kPa, leaching time of 2 h, concentrations of 2 mol/dm3 and 0.4 mol/dm3 for NaCl and NaOCl, respectively, the solid ratio of 30%, and particle size (d80) 15 μm. The results obtained from this study indicated that the enrichment of refractory silver ores to extract the silver encapsulated in barite and quartz minerals could be possible in the chlorite-hypochlorite under high pressure, a relatively shorter leaching time compared to conventional cyanide leaching.

Jan 28, 2021

By A. G. Roach

MILLING of Nova Scotia gold ores began in 1862 with arrastras and wooden stamps and has progressed to heavier stamps followed by tables and other forms of concentration for the recovery of the sulphides. Chlorination and cyanide leaching of the concentrates has been practised, and in 1936 the combined amalgamation and all-sliming cyanidation plant of Seal Harbor Gold Mines was built. It has since been found that it is not necessary to cyanide the full tonnage and now only the concentrates are being so treated. From his experience in this enterprise, the writer presents the accompanying flow-sheet and supporting comments. While he has not the temerity to maintain that it is the best or only flow-sheet for Nova Scotia gold ores, he feels that it warrants thoughtful consideration by members of the milling fraternity of the Province. THE ORE The gold in Nova Scotia ores occurs both free and intimately associated with sulphides-chiefly arsenopyrite. Much of the free gold is quite coarse and crystalline. This is especially true when it occurs in white quartz. When in the slate, it is usually in thin plates and scales, frequently coated and discoloured. The values bound up in the sulphides are not amenable to amalgamation and must be recovered by other methods-concentration, followed by smelting or fine grinding and cyanidation. While high freight and treatment charges apply on concentrates shipped from the Province to smelters, a considerable quantity has been so disposed of in the past. However, it is hoped that a customs cyanidation plant will soon become available to producers of these auriferous concentrates in Nova Scotia.

Jan 1, 1938

By C. Beckennann, C. Y. Wang

"Computer simulations of structural and compositional development in equiaxed dendritic alloy solidification are performed using a recently developed multi phase model. The model not only accounts for the transport phenomena occurring on the macroscopic (system) scale, but includes also the grain nucleation and growth mechanisms taking place at various microscopic length scales. In this paper, a numerical technique consisting of a fully implicit control-volume based finite difference method and a multiple time step scheme is developed for accurate and efficient simulations of both micro- and macro-phenomena. Sample numerical results are presented to reveal the effects of liquid now and crystal sedimentation on segregation and the final grain size distribution. In particular, the importance of the interplay between the dendrite microstructure and multiphase now patterns is shown.IntroductionIn recent years, modeling of equiaxed dendritic solidification without convection has experienced considerable progress (1,2]. Nucleation and growth kinetic laws have been coupled with transient heat conduction calculations to determine the solidification microstructure. However, modeling of equiaxed dendritic solidification with melt convection and solid movement has not been attempted so far, largely because of the complications associated with the transport of free equiaxed crystals in the melt. The gravity-induced transport of free crystals is fundamental to the development and extent of the equiaxed zone and also greatly affects the columnar to equiaxed transition. Another possible effect of crystal sedimentation or floatation is to cause severe macrosegregation as well as structural inhomogeneities. The only study available in the literature that accounts for both liquid convection and solid transport is by Ni and Beckermann (3], but deals with globulitic structures (as opposed to dendritic)"

Jan 1, 1994

By John L. Burnett

Field criteria are needed to help the prospector recognize a potentially expansible shale, clay, or slate. Certain criteria have proven useful in California even though the physical-chemical mechanisms of expansion are not thoroughly understood. Three conditions must be satisfied before expansion can take place, The raw material must partially fuse at a low temperature (1800-2000°F.), Concurrently a gas must form. The raw material must be sufficiently impermeable to trap the gas within the particle. Low temperature melting, which is controlled by bulk chemical composition, is difficult to assess in the field but most common shale, clay, and slate is suitable in this respect, The presence of organic carbon, the most common source of an expanding gas, is indicated by dark color of the rock, A large proportion of clay-sized particles promotes impermeability; fine grain-size is indicated by conchoidal fracture, The shape of the expanded particle is commonly indicated by the texture of the raw material. Rocks with well-developed slatey cleavage produce accordion-shaped particles; massive rocks tend to form rounded particles. Undesirable materials commonly present with expansible shale include: weathered shale; sandstone and other coarse-grained sediments; and limestone, Weathering, which is indicated by color, reduces or eliminates expansion; therefore, surface samples seldom are representative of the shale found at depth. Sandstone does not expand and will increase the average weight of the finished product, Limestone or particles of carbonate minerals can be actively harmful because they are converted to free lime (CaO) during the firing process, If free lime is present in concrete, hydration will cause expansion of the lime particles which result in surficial ?popouts.?

Jan 1, 1963

By G. W. Jones, R. E. Kennedy

Most gasolines and naphthas are mixtures of paraffin- series hydrocarbons and comprise such substances as pentane , hexane , heptane , octane , and others up to perhaps dodecane . Many of these hydrocarbons , when mixed with the proper proportions of air and ignited , are highly explosive . It is due to this characteristic that gasoline has become so important as a fuel in internal -combustion engines . Gasoline and naphtha also are used in the industry as solvents and cleaning agents . Because of their explosive properties they are dangerous to use unless the composition is so chosen that the vapor pressure of the mixture is not high enough to produce explosive mixtures with air at the temperature at which they are used . Hydrocarbon mixtures may be made less hazardous by adding some incombustible liquid , such as carbon tetrachloride . Barrier reports the amount of carbon tetrachloride that must be added to different naphthas to render such mixtures free from fire and explosion hazards . He found that the amount of carbon tetrachloride that must be present in the final mixture of naphtha and carbon tetrachloride varied with the density of the naphtha . Of the naphthas tested the amount of carbon tetrachloride necessary to render such mixtures free from fire and explosion hazards ranged from 30 to 70 percent . .. Determination of the fire and explosion hazards of carbon tetrachloridehydrocarbon mixtures would be easy if the boiling points and vapor pressures of the two were the same at any given temperature . The fact that carbon tetrachloride boils at 76° C. while the boiling points of the hydrocarbons found in gasoline and naphtha may range from 37° , the boiling point of pentane ,

Nov 1, 1934

By Willy Persson

A common feature of the kinds and amounts of impurities present most pyrometallurgical, processes is injection of oxygen to, remove various in the feed. The degree of success of a specific process step relies critically on control of the instantaneous oxygen potential/oxidation stage, throughout the step as well as upon termination of the step. This will, for instance, determine the distribution of impurities between metal and slag. As long as the operation is perturbation free -detailed analysis of all additions and application of advanced models often yield satisfactory control means However, a pyrometallurgical process is seldom free from disturbances, which reduces the accuracy of the static models and leads to inconsistencies in scheduled route might be uncontrollable changes in quality and quantity of feed, operator interventions and shift changes, timing of cranes, lining wear and accretions etc. The implementation of dynamic, control to correct for disturbances and, more generally for process optimization, requires continuous on-line information on, the actual status of the process. The implementation of sensors for continuous process monitoring, e.g., as regards the instantaneously prevailing oxygen potential or oxidation stage, has been hampered by the highly aggressive environment in smelters; This is. where remote-sensing techniques based on optics and spectroscopy, have proven to form invaluable, tools towards the realization of dynamic production control. Since about 15 years Semtch has developed and industrialized a remote-sensing technology, based on ,optics and spectroscopy, for continuous on-line process monitoring and production control of various pyrometallurgical processes. The presentation will discuss applicability aspects with examples and experiences from installations and tests in ferrous and non-ferrous industry. Keywords: Applied spectroscopy, Metallurgy, Process monitoring, Production. Control

Jan 1, 2003

By R. C. Good

Slag control for any kind of steel, rimming, straight carbon or alloy, should start with the charge and be developed well in advance of the tap because its composition, viscosity and temperature will unquestionably govern the physical and chemical properties of the steel when tapped. In the majority of plants producing alloy steels, primary consideration is given to the chemical specifications; physical characteristics usually occupy secondary place in the melter's mind. Recently, however, buyers have indicated limits of machinability, hardenability, grain size and, of course, always wanted steel free from foreign nonmetallic inclusions. It is these latter specifications that require the attention of the operator to the slag and its control. The slag must act as a vehicle for oxidized elements originating from the metallic portion of the charge; it should hold the oxides of phosphorus, silicon, manganese, iron and chromium that come into contact with it either before or after the refining and finishing stage of the heat. It must be used as a transferring medium of oxygen from the atmosphere or oxide additions to the metal and should permit a free escape of gas generated within the charge. Finally, the slag is the principal controlling factor in regulating the rate of oxidation which in turn eventually determines the quality of the steel as measured for the various characteristics mentioned above. With pig iron of uniform composition, the iron oxide in the slag increases as the limestone is increased but with the same addition of stone in every heat, the iron oxide decreases as the silicon is increased in the charge, and vice versa.

Jan 1, 1935

By Andrew S. McCreath

THE manufacture of pig iron for conversion into steel by the Bessemer and open-hearth processes, is now one of the most important industries of the United States. It is necessary that iron intended for this purpose should be very pure, and especially must it be comparatively free from phosphorus. Great care must therefore he exercised in the selection of proper ores, flux, and fuel. Only such ores as are practically free from phosphorus can be used, and pure fuel is as much a necessity as pure ores; though hitherto iron men have paid comparatively little attention to this point. During the course of my work as chemist for the Second Geological Survey of Pennsylvania, I had occasion to examine some of the bituminous coals of the State for phosphorus, and the results obtained are so interesting that I venture to present them to the notice of the members of the Institute. The coals are arranged in geological order according to the different beds, and the table shows the percentage of phosphorus in the coal and also in the coke. The greatest number of specimens have been selected from the Pittsburgh bed, because it is the principal coal-bed of Southwestern Pennsylvania, and most of the mineral fuel which is mined along the Youghiogheny and Monongahela rivers, to be used in the coke ovens of the Connellsville region and in the blast furnaces and mills of Pittsburgh and its vicinity, and to be shipped to Western and Southern markets, comes from this bed. It will be noticed that many of the specimens examined contain

Jan 1, 1880

By R. C. Good

Slag control for any kind of steel, rimming, straight carbon or alloy, should start with the charge and be developed well in advance of the tap because its composition, viscosity and temperature will unquestionably govern the physical and chemical properties of the steel when tapped. In the majority of plants producing alloy steels, primary consideration is given to the chemical specifications; physical characteristics usually occupy secondary place in the melter's mind. Recently, however, buyers have indicated limits of machinability, hardenability, grain size and, of course, always wanted steel free from foreign nonmetallic inclusions. It is these latter specifications that require the attention of the operator to the slag and its control. The slag must act as a vehicle for oxidized elements originating from the metallic portion of the charge; it should hold the oxides of phosphorus, silicon, manganese, iron and chromium that come into contact with it either before or after the refining and finishing stage of the heat. It must be used as a transferring medium of oxygen from the atmosphere or oxide additions to the metal and should permit a free escape of gas generated within the charge. Finally, the slag is the principal controlling factor in regulating the rate of oxidation which in turn eventually determines the quality of the steel as measured for the various characteristics mentioned above. With pig iron of uniform composition, the iron oxide in the slag increases as the limestone is increased but with the same addition of stone in every heat, the iron oxide decreases as the silicon is increased in the charge, and vice versa.

Jan 1, 1935

By Andrew S. McCreath

The manufacture of pig iron for conversion into steel by the Bessemer and open-hearth processes, is now one of the most important industries of the United States. It is necessary that iron intended for this purpose should be very pure, and especially must it be comparatively free from phosphorus. Great care must therefore he exercised in the selection of proper ores, flux, and fuel. Only such ores as are practically free from phosphorus can be used, and pure fuel is as much a necessity as pure ores; though hitherto iron men have paid comparatively little attention to this point. During the course of my work as chemist for the Second Geological Survey of Pennsylvania, I' had occasion to examine some of the bituminous coals of the State fix phosphorus, and the results obtained are so interesting that I venture to present them to the notice of the members of the Institute. The coals are arranged in geological order according to the different beds, and the table shows the percentage of phosphorus in the coal and also in the coke. The greatest number of specimens have been selected from the Pittsburgh bed, because it is the principal coal-bed of Southwestern Pennsylvania, and most of the mineral fuel which is mined along the Youghiogheny and Monongahela rivers, to be used in the coke ovens of the Connellsville region and in the blast furnaces and mills of Pittsburgh and its vicinity, and to be shipped to Western and Southern markets, comes from this bed. It will be noticed that many of the specimens examined contain

Jan 1, 1880

By H. C. Kenny

THE annealing or softening temperature of cold-worked copper is appreciably increased by almost unbelievably small amounts of silver. As indicated by some data in this paper, the softening temperature of high-conductivity, tough-pitch copper may be increased from 200° to 350° C. by the addition of only 15 oz. per ton (0.052 per cent) of that element. Because it has this higher annealing temperature as compared with the silver-free metal, silver-bearing copper finds considerable use in industry. For example, when hard-rolled copper is used in operations that involve soldering or tinning, silver-bearing copper insures against loss of strength, whereas silver-free copper becomes "dead soft." Yet-though several investigators, beginning with Caesar and Gerner1 in 1916, have shown that small amounts of silver do definitely raise the softening temperature of copper-data are lacking on the problem: What is the specific influence of different amounts of silver on this tem-perature? It was to help in filling this gap in the knowledge of what might be termed "alloy coppers" that the data given herein were obtained. The softening of cold-worked copper depends, of course, on a number of factors, of which the composition of the material is only one. Other highly important factors are the degree to which the material is cold-worked and the time it-is held at the annealing temperature. The method of cold working and the grain size of the metal produced are also signifi-cant. All these variables were taken into account in the investigation reported here, and the influence of silver on the electrical conductivity and on the working was also considered.

Jan 1, 1934

By Claude H. P. Lupis, John F. Elliott

QUITE generally an increase in the temperature tends to bring a system closer to ideality. It is reasonable as a first approximation to consider that the excess free energy will vary linearly with the temperature, or: where t may be defined as the "characteristic temperature" of the solution, or the temperature at which the system would become ideal if the results at T were linearly extrapolated. It must be emphasized that consideration of this hypothetical property is an appeal to intuition rather than an established physical concept. The order of magnitude of 7 for dilute solutions will depend on the nature of the solvent; a value of 3000° + 1000°K may be suggested for ordinary metallic solutions. In terms of free energy, entropy, and enthalpy first-order interaction coefficients, differentiation of the above equations with respect to composition leads to The concept of t offers a simple and plausible interpretation of Chipman and corrigan's3 recent empirical correlation between and a for a number of groups of ternary systems 1-24. The authors found that in each group the ratio was approximately constant. The corresponding calculated from their data by Eq. [4] are listed in Table I. The expected order of magnitude is obtained for 7. As noted by Darken,4 if a regular solution is not assumed, thus if utj) # 0, Chipman and Crrigan's results imply that, as T is increased, ultimately changes in sign, Fig. 1. Clearly Eq. [4] is valid only in a limited range of temperatures since at the temperature 7 at which the system becomes ideal not only should become null but also and . Thus, both and are functions of

Jan 1, 1967

By John G. Viets, J. Robert Clark

A multielement extraction system is being used successfully to provide essentially interference-free geochemical analyses to aid in gold exploration. The Methyl isobutyl ketone-Amine synerGistic Iodide Complex (MAGIC) extraction system separates Ag, As, Au, Bi, Cd, Cu, Ga, Hg, In, Mo, Pb, Pd, Pt, Sb, Se, Sn, Te, T1, and Zn from interfering geological matrices. Quantitative extraction of these elements is accomplished over a broad range of acid normality, making it possible to economically determine all 19 elements from a single digestion or leach solution. The resulting organic extracts are amenable to analysis by inductively coupled plasma atomic emission spectroscopy (ICP-AES) and flame atomic absorption spectroscopy (FAAS). For many years the principal shortcoming of ICP-AES was the complex spectral and stray-light interferences that were caused by the extreme variability of components such as Fe. Na, and Ca in common geological matrices. The MAGIC extraction allows determination of the extracted elements with enhanced sensitivity, from a virtually uniform matrix, by ICP-AES and FAAS. Because of its simultaneous multichannel capabilities, ICP-AES is the ideal instrumental technique for determining these 19 extracted elements. Ultratrace (sub-part-per-billion) determinations of Au and many of the other extracted elements can be made by graphite furnace atomic absorption spectroscopy (GFAAS), following back stripping of the extracts. The combination of the extraction followed by stripping of the organic phase eliminates 99.999% of potential interferences for Au. Gold determination by GFAAS from these extracts under the specified conditions yields a fourfold improvement in sensitivity over conventional GFAAS methods. This sensitivity enhancement and the interference-free matrix allow highly reliable determinations well into the parts-per-trillion range.

Jan 1, 1990

By Richard R. Klimpel

INTRODUCTION The purpose of this paper is to summarize the current status of reagents used in the mineral industry plus present some current challenges and possible new technologies of the future. Table 1 lists the important families of reagents which, when taken together, constitute at least 95% of the current commercial reagent market. A very approximate estimate of the free world reagent market size in mineral applications is about 1.5 to 2.0 billion dollars (U.S.) using 1985 data. Obviously, to serve such a large market requires the effort of many different types of commercial supply sources. It is estimated that there are over 300 industrial firms in the free world that have a dedicated business/technical structure for supplying reagents related to the mining industry. There are a number of characteristics which are associated with the product families listed in Table 1. Understanding these characteristics helps to provide a realistic economic/technical basis for outlining future challenges in mining chemicals. 1.Essentially all of the products listed are old chemistry in the sense that the molecules have been known and manufactured for at least 25 years. This has not been a highly dynamic field of endeavor from the viewpoint of new product introduction. 2. The greater majority of the products listed can be viewed in commercial terms as "commodity" chemicals, that is, they are available from many sources and the pricing of a some- what generic product generally dominates differences in product quality or uniqueness. With commodity pricing, reagent suppliers significantly reduce research expenditures, loosen product quality somewhat if the applications of the reagents allow, etc. in order to be cost competitive.

Jan 1, 1989

By U. C. Tainton

FOR the last 15 years lead has been the standard material for anodes in electrolytic zinc production and it has been generally accepted that this lead should be as free as possible from impurities. Laist1 says, "Next in importance to the purity of solution is the purity of the electrodes and tank lining material. The purest lead obtainable should be used for anodes." The same conclusion is expressed by Ingalls2 and by two German investigators who say that experiments have demonstrated that the purer the lead, the greater is its resistance to corrosion during electrolysis.3 Pure lead, however, while the best material hitherto available for anodes, is not entirely free from objection. The plain lead anode gradually disintegrates under electrolysis, so that the life of an anode, say ¼ in. thick, is frequently not more than two years. Part of the lead from the anode finds its way to the cathode, lowering the purity of the deposited zinc and decreasing the hydrogen overvoltage. The rest of the lead that comes from the disintegration of the anode goes into the manganese dioxide which is precipitated in the cells, rendering unsaleable what might otherwise be a valuable by-product. Yet a further disadvantage of plain lead anodes comes from their tendency to bend or buckle during electrolysis, as a result of intercrystalline oxidation. This makes it necessary to use a fairly wide spacing between anode and cathode to avoid short circuits, and thus leads to a higher power consumption than would otherwise be necessary. The power consumption is also affected by the high decomposition voltage at a lead peroxide surface.

Jan 1, 1929

By A. G. Taylor, H. P. Ehrlinger, U. C. Tainton

FOR the last 15 years lead has been the standard material for anodes in electrolytic zinc production and it has been generally accepted that this lead should be as free as possible from impurities. Laistl says, "Next in importance to the purity of solution is the purity of the electrodes and tank lining material. The purest lead obtainable should be used for anodes." The same conclusion is expressed by Ingalls2 and by two German investigators who say that experiments have demonstrated that the purer the lead, the greater is its resistance to corrosion during electrolysis.3 Pure lead, however, while the best material hitherto available for anodes, is not entirely free from objection. The plain lead anode gradually disintegrates under electrolysis, so that the life of an anode, say 1/4 in. thick, is frequently not more than two years. Part of the lead from the anode finds its way to the cathode, lowering the purity of the deposited zinc and decreasing the hydrogen overvoltage. The rest of the lead that comes from the disintegration of the anode goes into the manganese dioxide which is precipitated in the cells, rendering unsaleable what might otherwise be a valuable by-product. Yet a further disadvantage of plain lead anodes comes from their tendency to bend or buckle during electrolysis, as a result of intercrystalline oxidation. This makes it necessary to use a fairly aide spacing between anode and cathode to avoid short circuits, and thus leads to a higher power consurnption than would otherwise be necessary. The power consumption is also affected by the high decomposition voltage at a lead peroxide surface.

Jan 1, 1929

By Earl Bardwell

IN his paper entitled, Development of Hindered-Settling Apparatus, Dr. Richards has related the history of the development of the hindered-settling classifier and given illustrations of the several types of this apparatus which lie has designed.1 An earlier paper,2 Close Sizing Before Jigging, shows the nature of the hindered-settling phenomenon and the results which it produces. In the first-mentioned paper Dr. Richards describes the method of getting hindered settling and shows the relation that the constriction bears to the classifier. The question of proper ratios between the area of the sorting column and the area of the constriction opening Dr. Richards leaves open, aside from certain statements as to the ratios which have been found to give good results in practice. While working with a hindered-settling classifier of the type now in use at the Boston & Montana Reduction Plant of the Anaconda Copper Mining Co. a number of interesting facts were brought out which have thrown considerable light on the question of proper ratio between the area of the sorting column and the area of the constriction and which will be made the subject of this paper. Free and Hindered Settling. -If a, mineral particle be dropped into a vessel containing still water, the particle will sink in accordance with the laws of free settling in water, which are as follows: 1. Of two grains having the same specific gravity but differing in size, the larger will settle in still water at the greater velocity. 2. Of two grains having the same size but differing in specific gravity, the heavier grain will settle at the greater velocity.

Jan 8, 1913

By W. F. Wheeler

In the study of the coals of Illinois now being carried on by the State Geological Survey, an attempt is being made to determine the most satisfactory basis of comparison between different coals. The following discussion is based upon work done for the Survey in the laboratories of the State University and under the general direction of Prof. S. W. Parr. "Pure coal" has been defined by Mr. A. Bementl as ash- and moisture-free coal, and the use of this pure coal" as a basis for comparing different bituminous coals has lately been much discussed among engineers in the middle West. By some the B.t.u. of the pure coal is being used to check calorimetric results, and to calculate the calorific value of different coal-samples from the same seam, for which purposes it is necessary to assume—first, that the composition and calorific value of pure coal from different parts of the same coal-seam are uniform, and, second, that these values remain constant after the coal is mined, both of which assumptions there are reasons to believe are inconsistent with the facts. Certain variables are included in pure coal, as ordinarily defined, and disregard of them may lead to serious error. In any event, where delicate shades of difference are involved, no sure interpretation of results car] be made, unless these variables be eliminated. As a basis of comparison between coals, ash- and moisture-free coal is much to be preferred to " dry coal," and still more is it to be preferred to moist coal," as ordinarily reported in analyses. There are, however, two constituents other than ash

Jan 1, 1908

By C. A. Stetefeldt

In May and June, 1885, I was engaged in examining the goldores of Las Minas, in the State of Vera Cruz, Mexico, with a view of finding a cheap and efficient method for extracting the gold. The following minerals could be plainly seen in the ore : magnetite, pyrites of iron, pyrites of' copper, quartz, and garnet. Neither galena nor zinc-hlende mere visible, but the ore contained a trace of lead, and in some samples of ore from the Muertos mine, 1.19 per cent. of zinc mas found. Antimony and arsenic were not present. Native gold could scarcely be seen in specimens of' the ore, and it only appeared—mainly in extremely fine particles—after pulverizing and washing. Magnetite was in every instance the most prominent mineral, its quantity varying between 43 and 67 per cent. Determinations of copper and sulphur showed that from 3.5 to 7 per cent. pyrites of copper, and from 3 to 22 per cent. pyrites of iron were present. The gold-value of the ore varied between 0.3 oz. and 0.8 oz. per ton. I do not speak of specimens, but of average samples of large quantities of ore put through the battery. In ore that had been crushed through a No. 40 screen, the gold appeared, in part, as free gold, the rest being thoroughly mixed with the magnetite and pyrites, both minerals containing about the same percentage of gold. If this free gold was brought in contact with pure quicksilver it (lid not amalgamate readily, even if the quicksilver was charged with sodium amalgam.

Jan 1, 1886