Search Documents

By T. S. Jr. Sligh

OF all the qualities that are essential in a good cigar tobacco none is quite so important as the burn. This term is general and includes many points, the most important of which are evenness of burn, color of ash, firmness and coherence of ash, and fire-holding capacity. The fire-holding capacity refers to the length of time the leaf or cigar will continue to, glow after ignition. Chlorides tend to prevent complete combustion and products are formed thereby that are injurious to the flavor and aroma. On the other hand, the carbonates of the alkalies, particularly of potassium, aid the combustion and increase the fire-holding capacity. Barth1 thought that the harmful effect of the chlorides was due to their fusing and coating the tobacco, thereby preventing complete combustion. Schlosing,2 Nessler,3 and Garner,4 suggested widely different theories to account for the favorable action of potassium salts. In order to study carefully the action of the various salts upon the course of combustion of the cigar a knowledge of the temperature of the burning cigar is necessary. Lehmann5 who seems to be the only investigator who has made any attempt to determine the temperature of a burning cigar gives 480° C. as the maximum temperature which he recorded. It is evident, however, that his measurements were in error, probably on account of the method and apparatus used, since the lowest visible red corresponds to a temperature of about 575° C.

Jan 9, 1919

By P. R. Gage, R. W. Bartlett

At high temperatues and reduced oxygen pressuves, molybdenum silicicles oxidize to form SiO(g) vathev than a passivating SiO2 film. This is a sevious problem for low-pressure applications of sili-cide-coated rejvactory tnetals. As oxiclalion pvoceeds, the higher oxidntion potential of silicon initially suppresses oxidation of molybdenum and silicon is depleted near the surface. Eventually, silicon depletion causes secondary passivation (SiO2) mid an active to passiue transition in oxidntion behavior at moderately low pressures. At very low pressures, silicon depletion continues until steady-state oxidation of both silicon and rnolyhdenum can proceed at rates propovtional to their initial stoicliiorrzetvies. Ohsel-vations of 'oxidatiou-rate belzcriliov at temperatures from 1101° to 1700°C and oxygen pressures from 10-7 to 1 at in were made using thermogravimetn'c, X-ray diffraction, and elect?*on-rtric?ro/,vobe techniqrres. The experimental results are in good agreement with calculated lirnits for the various types of behavior that were based on tlievtnochernicnl atzd dffusion rate data for the Mo-Si system. A protective oxide film normally forms during the oxidation of elemental silicon. However, at elevated temperatures and reduced pressures this film is not present and oxidation is rapid. wagnerl has shown that this behavior occurs because SiO(g) is more stable than SiO2. The behavior of the silicides at high temperatures is similar but more complicated. Molybdenum and several silicide compounds are involved and the chemical activity of silicon, or the equivalent silicon vapor pressure, can vary considerably in these phases. Also, diffusion in the silicides resulting from reactions in which a higher silicide is reduced to a lower silicide, or molybdenum containing dissolved silicon, must be considered. EXPERIMENTAL AND ANALYTICAL METHODS Isothermal oxidation experiments were conducted using hot-pressed MoSi2 and Mo5Si3 wafers. Each experiment was conducted at a fixed oxygen pressure by controlling the flow of oxygen in and out of the furnace chamber. Most of the experiments were conducted in a molybdenum-wound tube furnace. Special construction features, including use of a high-purity dense A12O3 refractory tube, permitted operation in high vacuum to 1500°C. Higher temperatures could be obtained at higher working pressures and with a sacrifice of tube lifetime. Temperature was measured with three Pt 6 pct Rh/Pt 30 pct Rh thermocouples and controlled with a proportional controller. Weight changes were monitored with a quartz spring balance. The few experiments, at higher temperatures and low pressures, were conducted in a cold wall vacuum chamber using induction heating with direct susceptance of the sample. Because of the variable levitation effect of the induction coil on the sample, weight changes could not be monitored continuously in these experiments. All samples representing both experimental methods were weighed before and after oxidiation and examined with a microscope and analyzed by X-ray diffraction. The analytical treatment assumes equilibrium at interfaces and uses existing thermodynamic data. For convenience, equilibria are expressed as chemical potentials or as vapor pressures of the gases involved. The resulting differences in equilibrium vapor pressure between adjacent interfaces and between the surface and external atmosphere drive diffusion processes in the solid and gas boundary film, respectively. These diffusion processes govern the rate of oxidation. A bibliography of the sources of thermochemical data for the reactions pertinent to the Mo-Si-O system is given in Table I. Reactions are listed with the sources of free-energy data referenced. Since all of these reactions involve one or more gas species, usually oxygen, a plot of the product-gas chemical potential, -RT In Pg, vs absolute temperature for each reaction is given in Fig. 1. These curves can be used to determine equilibrium vapor pressures or to compare the stability of different compounds in the various gases: O2, Si, SiO, and Moo3,. The data of Table I and Fig. 1 were used to determine the analytical results presented in this paper. EXPERIMENTAL RESULTS The weight changes for three MoSi, samples oxidized at 1500°C are plotted against time in Fig. 2. The treatments were identical except for the indicated variance of oxygen pressure and each curve represents one of three characteristic types of behavior that were observed. The upper curve is an example of passive oxidation, which is defined as

Jan 1, 1965

By W. R. Crane

While professiorlally engaged in the oil- and gas-fields of Kansas, in measuring the pressure and flow of gas-wells, and studying the phenomena attendant upon the production of both oil and gas, I noticed in the flow of gas a peculiar and interesting feature. That there are actual lines of flow in liquids (non-compressible fluids) discharged through an orifice, or a short section of pipe, is shown by the external shape of the discharge—the vena contracts. Such lines of flow are not observable in the discharge of gas from an orifice. It can hardly be questioned that they exist. That they are not apparent is probably due to the very small weight of the gaseous particles, which climinishes the momentum of their movement in a given direction, acquired before they issue from the orifice, and also to the expansion of the gases, which would exert a powerful influence in overcoming any such tendency in their flow. Gas flowing from an orifice, supplied by a large reservoir or blowing-engine, exhibits almost the reverse of what is noticed with liquids. Namely, the gas assumes the form of an inverted truncated cone, of large angle: with its apex-end at the orifice. (See BB, Fig. 1.) This external ahape assunled by the flow of gas shows, however, marked differences under varying conditions of volume and pressure. For instance, a large volume of gas under high pressure, flowing through a 2- or 3-in. pipe, as in the case of a natural gas-well, assumes a more definite conical form, the angle of which increases as the pressure falls. Moreover, outside of the well-defined inverted cone is a thin conical heath or zone of gas, A A, the angle of which is considerably greater than that of the main cone, and increases with +1UNIVERSITY OF KANSAS, LAWRENCE, KANSAS.

Jan 1, 1905

By H. N. Treaftis, J. W. Cahn

THE previous determinations of the solvus of tin in solid lead disagree with one another by as much as 40°C or almost 10 at. pct. Even determinations that appear to be careful differ considerably in both the solubility and its temperature coefficient. Recent kinetic workl -3 on the rate of precipitation of tin from lead-tin alloys and thermodynamic work4 on the heat of solution of tin in lead have given some insight into the time necessary to reach equilibrium in this system. As this time is longer than that used in almost all previous determinations of the solvus, these determinations are questionable. Since the interpretation of recent kinetic results requires accurate values of the equilibrium solubility the present work was undertaken. DISCUSSION OF PREVIOUS RESULTS The methods used in previous studies may be placed into three classes: 1) Several alloys covering a range of compositions are allowed to reach "equilibrium" at a certain temperature.5-7 Some property, such as the X-ray lattice parameter of the lead-rich phase or the re- sistivity of the alloy, is then measured as a function of composition. The solubility limit for that temperature is taken to be that composition at which a discontinuity in the property occurs. However, the recent kinetic work has shown that tin precipitates in two stages. The first stage is rapid but leaves the lead still supersaturated. The second stage is very slow, and it seems from the equilibration times quoted by the investigators of the solvus that the end of the first stage of precipitation was usually mistaken for equilibrium. This is especially true at temperatures below 100°C where the first reaction is still quite rapid (from minutes to months), but where the second stage is so slow that very long holding times are required to reach equilibrium. Alternatively micrographic work8 on several alloys of different compositions seems to have given good results if done carefully. 2) The beginning of precipitation in a homogenized alloy is measured as it cools slowly8-10. Since reactions in solids undercool easily, such determinations will always give too low a temperature for the solvus. 3) Some property of an alloy is measured as a function of temperature while the alloy is above the solvus.5,9,11 The range of temperature can usually be extended slightly into the two phase region. Then the alloy is precipitated at a much lower temperature and slowly reheated. The solvus is taken to be the lowest temperature where the property of the reheated alloy is equal to that previously determined for the homogeneous alloy. Usually one also expects a discontinuity at the solvus in the temperature variation of the property for the reheated alloy. The difficulty in this method is the sluggishness of the dissolution process, and this method may give too high a solvus temperature. EXPERIMENTAL The phase boundary or solvus temperature was determined by a modification of method 3 for a series of chemically analyzed high-purity alloys, ranging from 5.1 to 26.4 at. pct Sn. The resistance, as a function of temperature, of a sample of homogenized alloy (which could easily be undercooled) was compared with the equilibrium resistance which that alloy sample attained after precipitation at room temperature followed by long isothermal anneals at various temperatures. Before each anneal the sample was rehomogenized and reprecipitated. The solvus temperature could be located to within 1°C as the intersection of the resistance vs temperature curves for the homogenized and equilibrium alloys. No attempt was made to locate the phase boundary more accurately since the limiting factor was the precision with which the alloys could be analyzed. This precision was ±0.1 wt pct Sn and corresponds to an error of 1 deg in temperature. This use of isothermal anneals differs from some of the previous investigations in which method 3 was used with baths of slowly rising temperatures. It was found early in the investigation that solvus temperatures tended to be high if the latter method was used even at extremely slow heating rates. For example a

Jan 1, 1961

By J. D. Raulerson, J. M. Williams

This paper presents a comparative evaluation of several system currently being used or proposed for the transport of matrix from an open-pit mine to a large fixed plant. The matrix is a sticky, wet clay to be carried from 8-16 km (3-10 miles) at 910 t/h to 1.8 kt /h (1,008-2,000 stph). The system is complicated by frequent moves of the open-pit mine site and other factors, such as use of the clay component in land reclamation.

Jan 1, 1984

By H. T. Kennedy

The fact that intrusion of water into oil wells can be prevented by treating the sand adjacent to the well seems to have been only recently recognized. Swan1 mentions the process of solidifying naphthalene in strata. R. Van A. Mills2 recommends the use of materials such as sodium silicate and sodium carbonate, which react with oil-field water to form solid plugging agents. When a well is drilled in a new field the oil sands are found essentially devoid of water (Fig. 1). Unless a completely impermeable break exists over wide areas in the field, no water is found above the lower limit of the oil zone and no oil is found below the upper limit of the water zone. After considerable oil has been taken from the well, however, it is almost universal experience that water intrusion occurs. This intrusion may be of two kinds. The water may follow a path parallel to the bedding planes of the producing formation through loose streaks in the pay sand, as shown in Fig. 2, or the water level of the field may rise and enter the well by coning (Fig. 3). Water entering from the side is called "edge water," and that coming in from the bottom is called "bottom water.'' Effectiveness of any method for shutting off water depends not only on the effective treatment of the sand adjacent to the well but on

Jan 1, 1936

By H. T. Kennedy

The fact that intrusion of water into oil wells can be prevented by treating the sand adjacent to the well seems to have been only recently recognized. Swan1 mentions the process of solidifying naphthalene in strata. R. Van A. Mills2 recommends the use of materials such as sodium silicate and sodium carbonate, which react with oil-field water to form solid plugging agents. When a well is drilled in a new field the oil sands are found essentially devoid of water (Fig. 1). Unless a completely impermeable break exists over wide areas in the field, no water is found above the lower limit of the oil zone and no oil is found below the upper limit of the water zone. After considerable oil has been taken from the well, however, it is almost universal experience that water intrusion occurs. This intrusion may be of two kinds. The water may follow a path parallel to the bedding planes of the producing formation through loose streaks in the pay sand, as shown in Fig. 2, or the water level of the field may rise and enter the well by coning (Fig. 3). Water entering from the side is called "edge water," and that coming in from the bottom is called "bottom water.'' Effectiveness of any method for shutting off water depends not only on the effective treatment of the sand adjacent to the well but on

Jan 1, 1936

By L. A. Roe, E. A. Elevatorski

Wollastonite, named after William H. Wollaston, an English chemist, is a calcium metasilicate, CaSiO3; CaO: 48.30%, SiO2: 51.70%. It has a short history as an industrial mineral. The earliest production of wollastonite is reported to be from a deposit near Code Siding, located north of Randsburg, CA. At this locality small tonnages of wollastonite were quarried during 1933-34 and 1938-41, and processed into mineral wool. This operation was largely experimental and virtually no United States production was again reported until the 1950s when a large deposit near Willsboro, NY, was developed by the Cabot Corp. A processing plant was placed onstream in 1953, with nearly continuous production to date. It is currently operated by NYCO, a division of Processed Minerals, Inc. Since 1958, wollastonite deposits in the Little and Big Maria Mountains of Riverside County, and in the Panamint Range of Inyo County, both in California, have operated intermittently for production of both ornamental and commercial wollastonite. During 1980, the United States was the major producing country, furnishing about 75% of the world's output. Current production comes from Finland, Mexico, India, and Kenya. Small amounts have been shipped intermittently from the USSR, New Zealand, Republic of the Sudan, Republic of South Africa, and Namibia (South-West Africa). The principal use of wollastonite is in the manufacture of plastics. Other uses are for paints, ceramics, adhesives, fluxes, glazes, thermal insulation board, and refractory products. Mineralogy Pure wollastonite, CaSiO3, has the composition of 48.3% CaO and 51.7% SiO2. However, it is seldom found in the pure state due to the ease with which it takes into solution the metasilicates of manganese, magnesium, iron, and strontium. Predominantly, wollastonite occurs as a contact metamorphic deposit forming between limestones and igneous rocks. Commonly associated minerals are garnet, diopside, epidote, calcite, and quartz. It has a specific gravity of 2.8 to 3.0, and hardness of 4.5 to 5 on Mohs' scale. When pure, it has a brilliant white color, but with impurities it may be grayish or brownish. Luster is vitreous to pearly. Melting point of wollastonite is about 1540ºC. Wollastonite occurs in coarse-bladed masses, rarely showing good crystal form. It is usually acicular or fibrous, even in the smallest of particles. The most unique property of crushed and ground wollastonite is its cleavage. Fragments of crushed wollastonite tend to be needle-shaped, imparting a high strength, and this property is the basis for many of its uses. The fiber lengths are commonly in the ratio of 7 or 8 to 1, length to diameter. The average diameter of wollastonite is 3.5 µm. Some crystals of wollastonite fluoresce under short-wave or longwave ultraviolet light, or both, with colors ranging from yellow-orange to pink-orange. Specimens may also show phosphorescence. The acicularity of wollastonite is a property of considerable importance to the marketplace. The plastics industry makes utilization of high aspect ratio grades of wollastonite (20:1) for reinforcing thermoplastics and thermoset polymer compounds. The naturally high pH of 9.9 (10% water slurry) is a prime property to the coatings industry. The coatings industry uses milled grades of wollastonite as a pH stabilizer in interior and exterior PVA and acrylic latex systems. Processed wollastonite can have a G.E. brightness of 90 to 93. Chemically, wollastonite is inert and this property makes it useful as a filler and reinforcing agent. There are two polymorphs of calcium silicates: wollastonite, a low temperature form, and pseudowollastonite, a high temperature

Jan 1, 1983

By H. M. Day, C. H. Mathewson

THE constitution of the system silver-mercury has attracted the attention of many investigators during the last two decades, but since their results are for the most part in poor agreement, there is little need for a review of their individual contributions. It remained for the very careful thermal and microscopic investigation of Murphy' in 1931 to give the constitutional diagram in its present and unquestioned form, which is shown in Fig. 1. He devised methods for taking cooling curves on alloys under high pressures and for the microscopic observation of alloys which contained liquid mercury as a structural constituent at ordinary temperatures. The compositions of the intermediate phases were confirmed and supplemented through X-ray analyses by Preston2 and Stenbeck.3 According to Murphy, at 276° C. silver is able to dissolve 44 to 45 weight per cent of mercury, which may increase at lower temperatures to about 50 per cent. Preston concluded that the saturation boundary occurred at 46 ± 2 per cent at 100° C. From the values reported in the literature, these are the only ones that may be accepted as lying even in. the right region. PREPARATION OF ALLOYS The silver used in the present investigation was supplied by the United States Metals Refining Co. through the courtesy of the Committee on Industrial Uses of Silver and, since a complete spectrographic and chemical analysis was furnished, no attempt was made to purify it or to further establish the impurities present. The analyses reported by the company are shown in Table 1. Milligan4 has found that the magnesium content is probably less than 0.0005 per cent.

Jan 1, 1938

By Leo P. Tarasov

Magnetic torque studies of ferromagnetic single crystals have been carried out in a number of laboratories during the last decade&apos;s2 and some work has been reported on polycrystalline material showing preferred orientation. Goss3 used the method extensively in developing electrical sheet with desirable magnetic properties, but he used it as a control rather than as a means of studying the texture. Bozorth4 made a quantitative correlation of a torque curve he obtained from some cold-rolled iron with the texture as determined from X-rays, but did not extend his studies beyond the one specimen. Other studies, which have been reported from time to time2,5 have also been incomplete in the sense that no effort was made to study a whole series of samples, differing only in degree of cold reduction or in the annealing temperature, in order to ascertain the effect of such treatments on the texture as revealed by torque measurements. It is the purpose of this investigation to make such a study, mainly in order to see how useful the method can be made when used under favorable circumstances and to find what kind of a correlation can be expected between magnetic and X-ray studies of texture. Before proceeding further, it is desirable to say a little about single crystals, so as to make clear the concepts involved in magnetic torque measurements. Magnetic Torque Method It is fairly well known nowadays that single crystals of ferromagnetic substances have directions of easy magnetization and of hard magnetization. In Fig. 1 are reproduced typical magnetization curves for a single crystal of iron, which show that in a < 100 > direction saturation occurs at low fields compared to those required to saturate the same crystal in a <110> or a <111> direction. (The magnetization intensity I is defined by the equation B = H + 4pI.) At fields high enough to

Jan 1, 1939

By Leo P. Tarasov

Magnetic torque studies of ferromagnetic single crystals have been carried out in a number of laboratories during the last decade&apos;s2 and some work has been reported on polycrystalline material showing preferred orientation. Goss3 used the method extensively in developing electrical sheet with desirable magnetic properties, but he used it as a control rather than as a means of studying the texture. Bozorth4 made a quantitative correlation of a torque curve he obtained from some cold-rolled iron with the texture as determined from X-rays, but did not extend his studies beyond the one specimen. Other studies, which have been reported from time to time2,5 have also been incomplete in the sense that no effort was made to study a whole series of samples, differing only in degree of cold reduction or in the annealing temperature, in order to ascertain the effect of such treatments on the texture as revealed by torque measurements. It is the purpose of this investigation to make such a study, mainly in order to see how useful the method can be made when used under favorable circumstances and to find what kind of a correlation can be expected between magnetic and X-ray studies of texture. Before proceeding further, it is desirable to say a little about single crystals, so as to make clear the concepts involved in magnetic torque measurements. Magnetic Torque Method It is fairly well known nowadays that single crystals of ferromagnetic substances have directions of easy magnetization and of hard magnetization. In Fig. 1 are reproduced typical magnetization curves for a single crystal of iron, which show that in a < 100 > direction saturation occurs at low fields compared to those required to saturate the same crystal in a <110> or a <111> direction. (The magnetization intensity I is defined by the equation B = H + 4pI.) At fields high enough to

Jan 1, 1939

By Erhard Hornbogen

Twins were propagated into large, well-annealed crystals of a, iron-phosphorous and a, iron-molybdenum solid solutions. Strain fields caused by interaction of these twins were made visible by precipitation. These strain fields can be explained by assuming that transmitted and reflected plastic waves are created when a twin strikes an obstacle with high velocity. The twin front itself can be regarded as a shear wave that may be able to develop a one-dimensional shock front. The occurrence of {WO} fracture by the reflected stress is also discussed. The described effects were not found when twins propagated at lout velocity into disturbed crystals, for example, into crystals previously deformed by slip. DEFORMATION twinning leads to shearing of a crystal lattice under external load. The shear appears to be homogeneous over a large number of crystal layers. In a iron, shear occurs on the (112) planes and in the <1ll> directions. The formation of a twin proceeds by the movement of partial dislocations that change the stacking at the twinning plane.l, In the bcc lattice, this partial dislocation can be created by dissociation of a sessile a/2[111] dislocation that lies in the (112) plane: Cottrell and Bilby&apos;s spiral mechanism can explain the homogeneous shear, but has not been proven experimentally. Nevertheless, this mechanism can explain the possible high velocity of formation of a twin. In Cottrell and Bilby&apos;s model, as in other models of twinning or phase transformation, a much higher energy is required to spread the first stacking fault than to add new layers by further movement of the partial dislocations. The dislocations will therefore become accelerated proportional to the difference between the stress, tN, to nucleate and tp to propagate the twin. It has been assumed3,4 that tn is the stress required to make two partial dislocations of apposite sign pass for the first time. After the first layer of new stacking has been formed, the maximum stress is TN=Gb/4pd where G is the shear modulus, b is the Burgers vector of the partial dislocation, and d is their perpendicular spacing so that the amount of shear is S = b/d. From this formula, a value of 25 kg per mm2 has been estimated for twinning in Zn3. The measured values are smaller, but local internal stresses may help to provide the necessary stress. For a iron, a higher value can be expected, mainly due to the higher value of G. That agrees with the observation that "burst" twinning occurs if the yield strength is in-

Jan 1, 1962

By Dennis A. Clark, Brent Larsson

Tunnelling today is a lot more than drilling and blasting. The developments in drilling and blasting technique have made it pos¬sible to save costs both by increasing the advance per round and optimizing the demands on the final contour. Increasing the hole depth by using longer feeds and bigger dril¬ling rigs make the drilling time shorter compared to the set up time. It is important that the deeper holes are followed up by using a suitable cut. The most common cut in Sweden today is a parallel hole cut with one or more large holes; with a diameter corresponding to the hole depth and wanted advance per round. It is often specified that smooth blasting is to be carried out with a specific drill hole spacing. It is extremely rare, however, for specifications to be issued concerning the alignment of the raw of holes closest to the contour holes. It is very easy to ruin the effect of smooth blasting altogether by firing the rest of the round carelessly with an excessively high charge distribution. The drilling and blasting of the contour holes and the line of holes closest to the contour holes is therefore an extremely important part of any underground work. Accuracy and care in connection with the drilling of contour holes is also extremely important since it is possible to reduce the amount of overbreak, the result being more rapid mucking out, smoother and more durable surfaces and also less consumption of concrete for lining purposes.

Jan 1, 1983

By Folke H. Kihlstedt

Geophysical prospecting for ore has been more or less at a standstill during the present crisis owing to the lack of interest in base-metal exploration. A notable exception is the increased use of electrical and magnetic methods in prospecting for gold, the former in Canada, United States, Sumatra, Africa and Western Australia, and the latter on the Rand. This application to gold prospecting marks a forward step in ore prospecting because it is based upon mapping the geology instead of a direct location of the ore in question, as the amount of gold in an average gold ore is far too small to have any influence upon the physical properties of the rock in which it occurs. The development has thus gone in the same direction as geophysical prospecting for oil; that is, to find geological conditions that are genetically connected with the gold ore as exemplified by known occurrences. Naturally the success of this indirect prospecting depends upon two things: (1) the soundness of the geological conclusions upon which is based the hope of discovering new deposits, because a great many geological "set-ups" are barren, and (2) the ability of geophysical methods to help the geologist to collect the pertinent geological data within reasonable cost, after which favorable structures may be drilled or trenched. The first point is one to be considered by the mining geologist. In the vicinity of producing mines or promising prospects, the chances of finding ore in quartz veins and shear zones are great, and a survey giving the location of these features will materially guide both surface and underground exploration. Even in outside exploration the chances are sometimes favorable. As an example may be taken the Northeastern Ontario-Western Quebec gold zone. Large areas are here covered with glacial and post-glacial deposits and a simple study of available maps reveals the fact that less than 30 per cent of the area can ever be even preliminarily prospected by cominonly used prospecting methods, of which the pick and shovel are the main tools. Considering the number of deposits found, it is evident that many deposits remain hidden below the overburden. The knowledge of gold geology gives a starting point

Jan 1, 1934

By A. B. Hersberger, R. S. Dean

Although it is obvious that in any flotation process we must have a froth, in recent years the development of collecting reagents has caused the possibilities of better frothing agents to be overlooked. Some investigators have even gone so far as to say that the number of satisfactory frothing agents was sufficient. A little consideration will show, however, that the reagents available in the past were far from ideal frothers. The properties of an ideal frother for flotation work may be set down as follows: 1. It must form in low concentrations a copious but not too persistent froth. 2. It must be insensitive to hydrogen-ion concentration of the pulp; that is, it must froth equally well in an acid or alkaline medium. 3. It must be insensitive to salts, even in high concentration. 4. It must be absolutely noncollecting to both sulfides and nonsulfides. 5. Its frothing properties must not be affected by collecting reagents, including soap, the most generally used nonsulfide collector. 6. It must readily emulsify and disperse any insoluble collecting agent that is likely to be used. Clearly the existing frothers do not qualify. Pine oil, for example, is an acceptable frother for many purposes but if used in soap flotation a delicate balance between pine oil and soap must be struck because, as pointed out by Coghill1, these two reagents are incompatible in certain concentrations. The objections to soap itself as a frother are obvious, and the cresols and their substitution products all have some collecting power and very little emulsifying power. The mechanism of frothing in flotation was early explained on the basis of the Harkins-Langmuir theory of oriented molecules.2 These investigators showed that if an organic compound having an unsym-metrical molecule (in which one end of the molecule contained water-

Jan 1, 1939

By R. S. Dean, A. B. Hersberger

Although it is obvious that in any flotation process we must have a froth, in recent years the development of collecting reagents has caused the possibilities of better frothing agents to be overlooked. Some investigators have even gone so far as to say that the number of satisfactory frothing agents was sufficient. A little consideration will show, however, that the reagents available in the past were far from ideal frothers. The properties of an ideal frother for flotation work may be set down as follows: 1. It must form in low concentrations a copious but not too persistent froth. 2. It must be insensitive to hydrogen-ion concentration of the pulp; that is, it must froth equally well in an acid or alkaline medium. 3. It must be insensitive to salts, even in high concentration. 4. It must be absolutely noncollecting to both sulfides and nonsulfides. 5. Its frothing properties must not be affected by collecting reagents, including soap, the most generally used nonsulfide collector. 6. It must readily emulsify and disperse any insoluble collecting agent that is likely to be used. Clearly the existing frothers do not qualify. Pine oil, for example, is an acceptable frother for many purposes but if used in soap flotation a delicate balance between pine oil and soap must be struck because, as pointed out by Coghill1, these two reagents are incompatible in certain concentrations. The objections to soap itself as a frother are obvious, and the cresols and their substitution products all have some collecting power and very little emulsifying power. The mechanism of frothing in flotation was early explained on the basis of the Harkins-Langmuir theory of oriented molecules.2 These investigators showed that if an organic compound having an unsym-metrical molecule (in which one end of the molecule contained water-

Jan 1, 1939

By John A. Meech, J. G. Paterson

Activated carbon is a strong adsorbent for amyl xanthate, capable of removing from solution up to a quarter of its own weight in xanthate. In selective flotation system where depression is unstable, separation efficiency increases with activated carbon additions. The improvements observed are brought about by two mechanisms. First, by removing stripped and residual collector ions from solution, competition between depressant and xanthate is reduced and depression is stabilized. In addition, the texture of the froth phase at high pine oil concentrations is modified by activated carbon such that better drainage between the air bubbles takes place, alleviating the mechanical entrapment of depressed mineral particles. In treating a bulk copper/lead concentrate produced from GECO ore, selectively between galena and chalcopyrite is increased when activated carbon is used. Although the rate of flotation of galena is marginally lowered by activated carbon, a small extension in the duration of flotation allows the lead recovery to increase by 19% at the same recovery of copper. An addition rate of 0.75 kg/ton (1.5 lb/st) of bulk concentrate is suggested as optimum from this testwork. However, the actual level used in the mill is dependent upon the residual concentrations of collector and frother in the bulk concentrate pulp.

Jan 1, 1979

By George Sachs

THE process of recrystallization has not as yet been explained satis-factorily. Some definite conclusions could be drawn from recent investi-gations, such as, for example, that recrystallization is a process of nucleus formation and crystal growth 1and that the orientations of the nuclei correspond to some fragments of the original crystals, which have been considerably distorted during deformation.2 There are, however, a number of metals and alloys crystallizing in the face-centered cubic system, which form a particularly simple orientation if recrystallized as a sheet.3 Such a sheet is almost a single crystal with the cubic axes parallel to the rolling, transverse, and normal directions of the sheet. This preferred cubic or (100) orientation of the recrystallized sheet has been considered to be very different from the rolling structure of the same metals,4 but there are two reasons why this last supposition remains open to controversial discussion. The first reason is academic: In practically all cases except the one mentioned above, close correlations and similarities between rolling and annealing orientations have been observed; for instance, in iron and steel sheet.6 Secondly, no deformed metal actually forms a-simple orientation. In any thoroughly investigated case a number of different orientations and considerable scattering or deviations from the ideal orientations have been found., It is generally true that investigations on single crystals have shown that a definite orientation is approached in stretching or in compression of an originally undisturbed crystal.7 In the special cases, however, where the initial orientation was close to an important crystallographic direction that differed from the final "ideal" orientation, the resulting orientation changed very little by deformation, staying somewhere in the vicinity of the initial orientation." Such deviations

Jan 1, 1940

By F. L. Wolf, G. E. Alderson

The reclaiming of nietallics from slag and sweepings is of vital interest to every brass-foundry man, but the first cost and interest on the investment often make it prohibitive for the small foundry to enjoy the benefits of a complete concentrating unit. However, the cost of such an installation and the cost of operation are often exaggerated to such an extent that foundries dispose of their copper-bearing refuse at a great loss. This paper gives the actual costs and the returns obtained in the reclaiming plant used at the Ohio Brass Co. This plant is divided into two sections—the preliminary treatment and concentrating departments. In the former occur the screening, crushing, and hand-picking operations whereby rnost of the non-valuable and heavy metallic constituents are removed. The concentrating equipment consists of an elevator, bins, jigs, ball-mill, arid table. Preliminary Treatment The preliminary treatment varies, depending on whether the material is slag, foundry-floor sweepings, or brass casting-floor sweepings. Material of the first class is produced from the operation of six Steele-Harvey and six Schwartz furnaces; the second class represents sweepings from an average of thirty-five. molding floors per day: and the last is collected around the sprue cutters and knockout bench. Treatment of Slag The slag, analyzing 30 to 40 per cent. copper, is passed over a 3-mesh yard screen (Tyler standard mesh) stretched on an inclined rectangular frame supported by adjustable legs and equipped with a hopper which directs the undersize into a barrow. The fine product, running about 20 per cent. copper and representing 20 to 25 per cent. of the total slag, goes direct to a storage bin for concentrator frrd. The oversize is charged into a No. 2 Hill cinder crusher, which takes 175 to 200 11,. to a charge and crushes two charges per hour through &apos;a No. 4 riddle. It

Jan 1, 1921

By Charles Barrett

THE orientation of metal crystals and grains, both large and small,. can be determined conveniently and accurately without the use of X-ray apparatus. This seems to be appreciated by so few metallurgists that it may be useful to explain in detail the method we have found most satis-factory in the laboratory the reflection of light from crystallographic etch pits. This note includes a description of a suitable inexpensive instrument and instructions for etching various metals and for plotting the data. As the stereographic projection is used to facilitate handling the data, this note may be considered as an appendix to an earlier review of the metallurgical uses of the stereographic projection.1 Various methods involving etch pits have been used by other investi-gators, Bridgman&apos;s method2 consists of attaching the specimen to a sphere (a transparent sphere is convenient4), holding it at arm&apos;s length, and marking a spot on it when it has been turned so that the etch pits reflect light into the eye of the observer from a lamp standing behind him. It has an accuracy of about 2° and is extremely rapid. A greater accuracy can be obtained by having the reflected light fall on a screen, as has been done by Czoehralski, 5 Chalmers,6 and Schubnikov.7 All of these methods have been intended for undeformed single crystals. Tammann and his coworkers"&apos; developed a method for estimating the number of grains in a polycrystalline aggregate having orientations in a given region of the stereographic triangle and thus obtained statistical information about deformation and recrystallization textures. While the method has had some use in recent years,9 it is not applicable to the majority of problems in physical metallurgy. Smith and Mehl10 determined orientations by plotting the directions of the sides of individual etch pits on a stereo-

Jan 1, 1940