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By John Jermain Porter

THe value of any particular ore, coke, or limestone, for iron-making, depends upon its effect, first, upon the quality or value of the resultant product; and second, upon the cost of smelting. The factors under the first head are the percentages of phosphorus, manganese, and other elements, which remain in the pig-iron ; while those under the second head are the percentages of iron, carbon, or lime, the slag-forming constituents, which must be fluxed, and any other ingredients which give rise to variations in cost of fuel and flux. The first of these criteria of value is perhaps not capable of being reduced to a general formula embracing all cases, since it must vary to a great extent with market-fluctuations. For example, Bessemer pig is worth sometimes more and sometimes less than foundry-pig; and the premium paid for high manganese varies within wide limits. The second, or smelt-ing-value, however, can be expressed numerically with a fair degree of accuracy; and it is with this phase of valuation that the present paper is concerned. The utility of a means of comparing numerically the relative smeltiug-values of difierent ores, cokes, and limestones, is self-evident, although it may not have importance in Northern practice, where materials are largely standardized. On the other hand, there are, especially in the South, many furnace-managers who must use a great variety of materials of widely varying grade; and it is with special reference to this district, and in connection with the efficiency-methods which I have elsewhere proposed,' that the methods herein described were devised.

Jan 1, 1913

The United States Employment Office of the Department of Labor, of which the division of engineering and education, under the direction of A. H. Krom, maintains an office at 29 La Salle Street, Chicago, Ill., is engaged in a classification of engineers in order to make their services more readily available in case of need. We have received a form used by this division, on which it requires only a very little time to indicate one's particular line of work, his experience and the salary that he desires. We have been asked to impress upon members of the Institute the distinct advantages that come through registration. Filling out the blank entitles an engineer to free employment service, provides him with direct contact with the Government, supplies him with information in regard to engineering affairs, and helps him to become successful in his profession. The Government wishes every technical man to register, so that it may know the strength and location of the engineering reserve. It is therefore the duty of every patriotic engineer, whether he needs a position or not, to register at once. Blanks can be obtained by addressing the office above noted.

Jan 10, 1918

THE CHAIRMAN.-Thank you. Since the papers are rather closely related, I think rather than taking them one at a time we will entertain discussion on any of these problems at this time. W. A. REICH.*-We, of course, quite a while ago got the yellow light that Mr. Cole spoke of, and like everyone else immediately started to study silicon bronzes and brasses. We were interested in the silicon bronzes and brasses because we felt that in order to replace gun metal which makes up a large part of our use we needed something with an elastic limit at least equal to that of gun metal. That means at least 12,000 lb. per sq. in. This study was aimed only at tin conservation. Then we dropped the study of silicon bronzes because high purity copper which is needed in their manufacture became a scarce item. To make a long story short we have recommended to our designing engineers that they use 85-5-5-5 wherever possible because 85-5-5-5 we understand can be made entirely from scrap with little or no tin addition. 85-5-5-5 has a lower elastic limit than 88-8-4, so we felt that we would need another substitute material, a structural alloy with an elastic limit equal to that of 88-8-4, and we immediately turned to the manganese bronze type of alloy. The poor foundry properties of standard manganese bronzes were mentioned by Mr. Thieme and since we feel that high zinc content is largely responsible for this difficulty, our development is directed along the lines of uncovering a material with a lower zinc content and which gains its elastic strength from the addition of other alloying elements, such as, aluminum, manganese and iron. It must be possible to make this alloy entirely from scrap with no additions of scarce high purity material. I would appreciate an expression of opinion on how low we can go in zinc content with this type of alloy without seriously impairing the availability, and how high we can go in aluminum content without making use of aluminum restricted for that use. We assume that the maximum lead content must be placed at 1 ½ per cent to insure good availability and we feel that about I per cent of tin in the alloy would improve salt water corrosion resistance similar to the effect of tin in Admiralty Metal. Has anyone here had experience with the effect of tin and lead on the weldability of such an alloy? C. S. COLE.-What percentage of lead and tin? W. A. REICH.-About 1 per cent of lead and 1 per cent of tin. We are studying the weldability of the alloy but perhaps someone already has the answer. (Pause, no answer) The claim has been made that 1 per cent of lead can be added to certain silicon bronzes without impairing their properties. A silicon bronze with a low zinc content requires high purity copper in its manufacture but if say the 15 per cent zinc, 44 silicon balance copper alloy could be made, with a I per cent lead content, some quantity could be made from scrap. We do not know whether the aforementioned is

Jan 1, 1943

Jan 1, 1971

By H. W. Turner

THE axis of the middle portion of the Ural mountains is made up chiefly of highly compressed igneous and sedimentary schists, considered of Devonian age by the Russian geologists, with large areas of serpentine (peridotite originally) gabbro, etc., intrusive in the schist series. In addition there are large areas of probably older granitic and gneissic .rocks. The nickel deposits referred to in this paper are found in the Devonian schists and their associated igneous rocks. The gabbro-peridotite intrusions probably took place in late Devonian or early Permian time, inasmuch as the Permian and Carboniferous beds lie at gentle angles on the Devonian series on the west slope of the Urals. Perhaps the first attempt to work a nickel deposit in the Urals was made about 1866 in the Revdinsk district, which is situated southwest of Ekaterinburg. I was informed by a Russian that a wet method of extracting the nickel was tried but was not a commercial success. This deposit has been described by Müller,1 Foullon,2 and Karpinski.3 Beck4 gives an abstract of these papers.

Jan 2, 1914

Prof. G. W. MAYNARD, New York City (communication to the Secretary): Prof. Christy, in his admirable paper on "The Growth of American Mining Schools," has overlooked the work done by the Rensselaer Polytechnic Institute in its department of mining and metallurgy. This oversight is naturally due to the fact that the department was, for lack of money, discontinued in 1871. It was organized by the writer in 1867, starting with ten students, who had already completed the first two years of the civil engineering course in the Institute. The course covered two years, specifically devoted to mining, metallurgy and assaying, which, in connection with the two years' drill in the civil engineering department made a four years' course. During the four years of the existence of the department, thirty-five students took the course, of whom twentyfive graduated; and of this number eight have been members of the Institute of Mining Engineers, and the majority of them have occupied high positions in the profession. The equipment of the department was, at that time, second only to that of the Columbia School of Mines. As Prof. Christy has cited other institutions which are not distinctively mining schools, but in which the ruining course was subordinate to other courses, it seems to me that the work in this line carried out by the oldest engineering school in the country may very properly be referred to. In addition to the regular mining course, a special course in assaying was given; and many young men were here prepared for positions in the mines and metallurgical works of the west. PROF. George F. Swain, Boston, Mass.: I have listened with great interest to Prof. Christy's valuable paper, but there is one conclusion at which he arrives that appears to me entirely unjustifiable, and to which I desire to take exception. Prof. Christy finds that of the total wage-earners in the United States in 1880,10.41 per cent. were employed in " trade and transport;" 20.24 per cent. in " manufactures and mechanics," and 1.83

Jan 1, 1894

IN general in making such powders, all kinds of gravel, tuff, washed river silt, and similar earths whose grain is fine and lean by nature are good for this operation of casting, either by themselves or in mixture because they are disposed to receive the metals well on account of a certain dryness which they possess. Many kinds are also compounded by means of art. Of these, I shall proceed to tell of all those that experience [119] has taught me to recognize as good. But first I desire that we return to speak of the natural ones because they are real earths and can always be had wherever one may be, and in the necessary quantity. They please me greatly because they are easy to reduce on account of their disposition. A loam is made from these and mixed by beating with wool-cloth cut- tings, spent wash ashes, and horse dung. This is made into cakes and dried. These are then put to bake in a furnace or in some other way and, in fact, are baked very well. Then it is pounded and sifted with a fine sieve, or it is ground in a potter's color mill, or by hand on a porphyry with water, to the fineness that the craftsman desires, or as fine as he can make it. When it has been ground it is again drained free from water and dried out with fire. Then as much magistery of salt is taken as will moisten it. It is dried and pounded again and passed through a sieve. When it has been made as desired in this way it is moistened again before use with water, urine, or vinegar just enough so that it holds together when it is squeezed in the fist. Then, when it has been brought to this point, it is moulded as you will hear. Powders are also made of crushed brick, tripoli, vine ashes, tiles, and glazed drainpipes, or burned emery, calcined tin, straw, and of burned paper and horse dung as well as of young ram's-horn ashes and many other things. The goodness of all these depends on three things; namely, on receiving the metal well, on being so fine as to be almost impalpable, and on their being made .with a magistery that renders them hard and strong when they are dry. In addition to these powders I have used another when I needed it, and it has succeeded well every time I made it. To make this. I have taken I two parts of pumice and one of iron scale and ground them on the por-

Jan 1, 1942

By O. N. Carlson, D. G. Alexander

THE hardness anisotropy of metals and alloys has been of increasing interest in recent years but silicon ferrite,1 niobium,2 and tungsten3,4 are the only bcc metals about which this type of information has been reported. This investigation was carried out on vanadium and chromium single crystals in an effort to determine to what degree the hardness variations observed in these metals are due to orientation effects and to compare their behavior with other bcc metals. In earlier work the authors had observed a small angular dependence in the Diamond Pyramid Hardness of single crystalline vanadium on the (100) plane but no anisotropic effects were noted on either the (110) or (111) planes. At the suggestion of R. G. wheeler5 it was decided to investigate this effect in greater detail using the more asymmetric Knoop indentor. The vanadium metal used in the study was prepared by the aluminothermic reduction of V2O5 followed by electron beam melting.6 The principal analyzed impurities were 230 ppm C, 230 ppm O, 65 ppm N, 90 pprn Al, Cr not detected, 50 ppm Fe, 60 ppm Ni, and 200 ppm Si. The chromium was an iodide-refined product obtained from the Chromalloy Corporation. Analysis of this material showed the following amounts of impurities present: 10 ppm C, 9 ppm O, 2 ppm N, 0.4 ppm H, 3 ppm Al, 2 ppm Ca, 2 ppm Cu, 20 ppm Fe, 1 ppm Mg, 0.3 ppm Mn, 1 ppm Mo, 3 ppm Ni, 10 ppm Si, and 1 ppm V. Single crystals of both metals about 1 cm in diam and 10 cm in length were grown by an arc-zone melt- ing technique.7 The chromium crystal was annealed at 1600°C for 6 hr in a purified argon atmosphere to remove any strains or inhomogeneities, but the vanadium was tested in the as-grown condition. The crystals were oriented by the Laue back-reflection method and then sectioned with a spark cutter into individual specimens with a (loo), (110), or (111) plane parallel to the crystal surface. They were mounted in Lucite and carefully ground to a flat surface. The vanadium specimens were then electropolished in a 6 pct perchloric acid-methanol mixture while the chromium specimens were mechanically polished on a Syntron vibratory polisher using an alumina abrasive. The orientation of each crystal was then rechecked by the back-reflection X-ray method. All of them were found to lie within 2 deg of the desired orientation with the exception of the (110)-Oriented chromium crystal which was within 4 deg. Microhardness impressions were taken at 10 deg intervals from the common (110) direction by rotating the crystal in the plane of the crystal surface. A Knoop indentor was used with a 400-g load on the vanadium crystals and an 800-g load on the chromium. The hardness values are averages of 6 impressions and standard deviations were calculated for each set of data. The values reported for the (111) plane of vanadium are based on from 10 to 15 measurements for each point. The microhardness results for vanadium and chromium are plotted as a function of the angular rotation of the long axis of a Knoop indentor from the (110)

Jan 1, 1970

By L. V. Wade

Abstract-US Bureau of Mines efforts under longwall research programs to develop the capability to predict support requirements for longwall/shortwall support systems are discussed. Ground control studies are being conducted in conjunction with several longwall/shortwall demonstration projects. Geologic, support performance, and strata behavior are being documented on these projects. A hypothesis is presented for the prediction of support requirements.

Jan 11, 1978

By J. A. Singmaster

IT will perhaps be wise to define my terms in begin-ning to talk about my subject, especially so where the popular and commercial terminology are as con-fused as they are in the case of zinc. While our French friends know zinc by its true name, and we find Balzac, Daudet, and other literary celebrities using it correctly in their novels, it is quite the contrary in English, particularly here in America. The quotation of a definition for zinc recently appearing in one of our leading technical magazines, "zinc is the place where they wash the dishes," will emphasize the difference. Zinc suffered in the first place by becoming an article of commerce long after its alloys with copper were in common use under the name of brass. Then again, when the art of zinc coating iron and steel objects was commercialized, we called it galvanizing, which is really a meaningless term. The French and Germans use the obvious terms-zinguerie and verzinken-for the opera-tion. Since these two uses of zinc, brass making and galvanizing, have been by far the largest consumers of zinc, is it any wonder that the popular knowledge of zinc is as vague as it is? In fact, since the disappear-ance of the sheet of zinc along with the parlor stove, the zinc-lined bath tub and refrigerator, there has been little popular contact in this country with the undis-guised metal zinc. On the Continent, where zinc has been used for over a hundred years under its real name, particularly for roofing and building purposes, the situ-ation is quite different. It is quite refreshing to turn for a moment to the contrast offered by my friend, Dr. Merica's specialty, nickel. They put 2 or 3 per cent of it into steel, and we have nickel-steel, or a larger amount into an alloy, and we have nickel-silver. To be sure there is no silver there, but what need that matter, nickel is used in the alloy and is first in the name. They plate with nickel and call it nickel-plating, no galvanizing about that. And, finally, they take that noble coin which admits us daily to underground New York, composed of three parts of copper and one part nickel, and get away with nickel as its popular name.

Jan 6, 1927

Improvement of drilling operations through the development of new, unconventional drill bits is a prime research target at Sandia Laboratories, Albuquerque, N.M. Sandia is currently focusing efforts on four new bit designs which its engineers believe may eventually improve penetration and reduce operating costs. The Energy Research and Development Administration (ERDA) has budgeted $500,000 in support of this program to date. Two of the drill bits-one that chips rock with high voltage spark discharges, and another which fires small projectiles into the rock ahead of a regular roller bit-are designed to increase both penetration rates and downhole bit life.

Jan 8, 1975

By P. Martinez, A. F. Hoyte, F. E. Senftle

The possibility of applying a neutron activation technique for silver exploration is considered. A mobile positive-ion accelerator type neutron source is used to irradiate a small area of rock or soil in situ. By using a short period of irradiation and gamma ray spectral analysis, a technique is shown for silver exploration. Two different mobile units are described. Laboratory and preliminary field tests both indicate that a sensitivity of less than 1 oz of silver per ton of ore can be achieved. The increasing consumption of silver for industrial uses and also for coinage has caused a serious shortage of silver in this country. The silver shortage has been reviewed and analyzed by kiilsgaard1 who concludes that, "The best hope for meeting future demands for silver is through accelerated exploration for precious ores." As almost all the exposed "bonanza" type silver deposits evidently have been found, it is urgent that some sensitive geophysical technique be found to detect large, extended, but generally low-grade, secondary ores, as well as hidden vein deposits. Silver is easily made radioactive by exposure to slow neutrons; hence a neutron activation method appears promising for locating silver deposits. The principles of mineral beneficiation using neutron activation techniques were discussed some years ago.2-4 Using the same approach, a preliminary description5 has been published of neutron activation as a mineral exploration tool. An exploration technique is described in which silver is made radioactive in situ and detected with a gamma radiation counter. The technique is similar to the well-known method used for uranium exploration. THEORETICAL CONSIDERATIONS Elemental silver consists of two isotopes, Ag107 and Ag109, having naturally occurring isotopic abundances of 51.4% and 48.6%, respectively. For short periods of irradiation of silver by thermal neutrons, the long-lived 250 day, half-life isotope, Ag110m, is not produced in significant quantities. However, significant quantities of 2.3 min half-life Ag108 and 24.5 sec half-life Agl10 are formed by the following reactions. Ag108 and Agl10 emit a 0.44 Mev (million electron volts) and a 0.66 Mev gamma ray, respectively. Ag107 + n + Ag108 (2.3 min) Ag109 + n + Ag110 (24.5 sec). Because of the large capture cross section (110 barns) of Ag109, and short half-life of Ag110 (24.5 sec), the 0.66-Mev gamma ray is the most prominent emission from silver for neutron activation periods of about a minute's duration.* The 0.44-Mev gamma ray from Ag108 will also be present, but will be one or two orders of magnitude lower in intensity. The decay scheme of Ag110 is shown in Fig. 1. If the neutron irradiation time is limited to about 100 sec, the Ag110 activity will essentially reach saturation and can be used to detect the presence of silver. In a neutron flux of 10 8 neutrons/cm2/set, the induced 0.66-Mev activity in 1 g of silver will be about 2 x 107 disintegrations per sec. This is about 1000 times the measurable gamma activity of 1 g of uranium in equilibrium with all its decay products; hence there is ample activity for detection. Under the same conditions of activation, most of the other elements do not reach this relatively high disintegration rate. Although this is in favor of the proposed technique, other problems must be considered. For mobile operation, it is desirable to obtain the largest neutron flux to weight ratio. Hence we have used a small 150-kev accelerator-type neutron source rather than an isotopic source such as an americium-beryllium neutron source. By use of remote control system, an accelerator-type neutron source can be safely used without the massive shield required for an isotopic source. Moreover, an accelerator-type source is more versatile in that it allows one to use a flux of either 14-Mev or 3-Mev neutrons, depending on whether a tritium or a deuterium target is used. With a 14-Mev generator, one can obtain a flux of 10 9 neutrons/cm 2/sec, and with a 3-Mev generator, the flux is generally two orders of magnitude less. Although silver will become activated with either generator using proper moderation, detection may be

Jan 1, 1968

HUDSON MAXIM, Brooklyn, N. Y.-Immediately after the creation of the Naval Consulting Board, Admiral Strauss, Chief of the Bureau of Ordnance of the Navy, told members of the Board that the most important problem for the scientists to solve was erosion in large guns. The Navy, for years, had been working on the problem with marked suceess, but there was much yet remaining to be accomplished. As Chairman of the Committee on Ordnance and Explosives of the Naval Consulting Board, I communicated with several experts in the manufacture of steel, principal among whom was Prof. Howe. He generously agreed to help in every way possible, and the work that he has done and the time that he has spent upon it can he appreciated only by reading his paper. Prof. Howe asked for some rings. from a, certain 14-in. gun which Admiral Strauss had mentioned in particular, and in which, he had informed us, at each shot the bore of the gun, was enlarged about 0.001 in.,' and that after a relatively small number of rounds it was considerably eroded. It has puzzled scientists for a long time to account for the peculiar erosive effect produced by the powder gases in a gun, arid: what Prof. Howe has done in his paper is worthy of Sherlock Holmes. He is a veritable Sherlock Holmes of science.

Jan 4, 1918

By Joseph W. Mills

In 1956 the discovery of nickel on Jumbo Mountain, Snohomish County, Washington, focused attention on this part of the Cascade Range, far more renowned for its timber than for its mineral resources. Hand specimens assaying as high as 13 pct Ni encouraged Discovery Mines Inc. of Mount Vernon, Wash., to stake 12 claims in Township 31 North, Range 9 East of the Willamette Meridian. The property was leased to Climax Molybdenum Co. in January 1957. Trenching, sampling, and geologic studies were carried out during the late summer of 1957 when most of the snow had disappeared. Although the deposits are only about four miles south of the logging town of Darrington and about two miles, as the crow flies, southeast of the end of a good gravel road from that town, all camp supplies and equipment were air-dropped, owing to the extremely rugged nature of the terrain.

Jan 3, 1960

By W. H. Davitt

While it is true that taxes, especially income taxes, whether they be federal, state, or local, are not usually thought of as a "cost" of doing business, it is equally true that these tax costs do reduce the distributable profits just as much as the cost of power, supplies, or labor. Therefore, the consideration given to taxes is often as important as that given to other costs. Hopefully you will recognize that, within certain limits, taxes can be controlled to an economic advantage. The tax laws as now imposed are quite complex. Many of these laws and the regulations thereunder involve many factual determinations, technical considerations, and specialized valuations that can best be made by people trained in the specific area concerned. A substantial amount of a tax liability turns on the proper consideration given to issues involving facts and principles which are peculiarly engineering in nature. The importance of these "engineering" issues in tax administration has been significantly increased in recent years by our rapidly advancing technology, automation, stepped-up mineral and oil exploitation, new industries such as electronics and nuclear power, and the extension of percentage depletion to all minerals. These specialized requirements incorporated in the law are so technical that full consideration can not be given by people with a non-engineering background.

Jan 7, 1974

Jan 1, 1960

1. Healthy and active Local Section or¬ganizations are vital factors in promoting the vigor and growth of the Institute. 2. Activity on the part of Local Sections should be recognized and stimulated by appropriation of funds from the Insti¬tute's treasury; and these appropriations should be as large as is consistent with the relative needs for other activities. 3. As between different Sections, the amount of such appropriations should be based primarily on the extent of activities as reflected in the number and character of meetings held and the attendance of the members at such meetings. 4. In making a request for funds for any year, the officers of a Local Section should submit a report on the printed form approved by the Directors at their meeting on November 19, 1937. 5. A standing Committee on Local Sec-

Jan 1, 1944

By G. R. Fritterer

INVESTIGATORS in the field of temperature measurement have long sought a thermoelectric couple fulfilling the following requirements: 1. It should be useful up to and including high industrial tempera-tures; i. e., 1000° to 1800° C. 2. Its thermoelectric variation with temperature should be linear and be maintained after heating to high temperatures for long periods of time. 3. It should be reproducible; i. e., different couples of the same elements should have similar calibration curves. 4. Its thermoelectric power should be large so as to allow the industrial use of rugged recording instruments. 5. Chemical reactions with, and physical changes within the elements of the couple should not alter its calibration. No thermocouple proposed to date exhibits simultaneously all of these characteristics, whereas the couple about to be described fulfills all requirements to a satisfactory degree.

Jan 1, 1933

By H. A. Wriedt

Zinc-vapor pressures in equilibrium with bcc solutions of zinc and iron at 703.5", 757", 793", and 900°C were measured by an isopiestic method. Thermody-na?nic properties of zinc in these solutions were derived directly and those of iron with a Gibbs-Duhem integration. Zirzc and iron exhibit large, positive, and moderately temperature-sensitive deviations from ideality. Excess enthalpies and Gibbs energies are positive in the ranges studied. It has been establzshed in relating published phase equilibria to the Gibbs energies of forming solid solutions that positive departures from ideality also exist in the fcc solutions. Tlze stability, as defined by Darken, of the bcc solutions is small but positive at 703.5"C. Its decrease with decreasing temperature indicates that a miscibility gap may exist in the stable or metastable bcc solutions at lower temperatures. The changes of thertnodynanlic properties relatable to changes in magnetic state are minor compared to other changes due to alloying. The accuracy with which the relation between lattice parameter and composition of the bcc solutions is known has been improved. Zinc increases the lattice parameter of a iron by O.ZOZA per unit atom action zinc to at least NZn = 0.25. TO our knowledge, only Ciganl has previously investigated thermodynamic properties of the bcc solutions of the Fe-Zn system. He measured zinc-vapor pressures in the temperature range from about 320" to 360°C by an effusion technique. We have measured the vapor pressures of zinc in equilibrium with bcc solutions of zinc and iron at 703.5", 757", 793", and 900°C by an isopiestic technique. This investigation and the pursuant thermodynamic computations are part of a program for studying several properties of these solid solutions. In the appendix we report a remeasurement of the relation at room temperature between the lattice parameter and zinc content. Related work not reported herein embraces measuring the diffusivity2 of zinc in ferrite at 700" to 900°C and the Curie point temperature3 as functions of composition. EXPERIMENTAL METHOD AND APPARATUS Purified iron at a series of constant temperatures was saturated with zinc at a series of constant zinc-vapor pressures, the range of conditions being so limited that the equilibrated solid solutions were ferri-tic. The equilibration was conducted in long capsules, Fig. 1, that had been evacuated, gettered with titanium, and sealed. The purified iron, part of a vacuum-melted ingot of electrolytic-iron stock (Glidden Co. 1044-grade), had the impurity contents listed in Table I. It was used in the form of millings about 0.001 in. thick. A zinc of 99.999 pct purity (United Mineral and Chemical Corp.) and later one of 99.9999 pct purity (Cominco Products, Inc.) were used, with no observed difference in results. Sufficient zinc was placed in the capsule (separate from the iron and kept at a different temperature) to supply the vapor phase and the iron alloy, while leaving a pool of pure liquid zinc throughout the run. The imposed temperature of the residual zinc pool fixed the vapor pressure of zinc throughout the capsule; condensation was avoided at other locations by making this the lowest temperature in the capsule. Two common complications of nonisothermal systems were, we believe, effectively absent from ours: first, molecular species other than monatomic have no appreciable concentration in zinc vapor at 700" to 900~~: second, the development of zinc-pressure differentials in the capsules was suppressed by use of relatively large-diameter tubing and the absence of diluents in the zinc vapor other than desorbed impurities. The specimens and zinc pool were located at two isothermal zones (each ranging within 1°C over several inches) of a wire-wound, 37-in.-long vertical-tube furnace. The required temperature distribution was achieved by external adjustment of the currents in three electrically isolated windings. The temperatures of the isothermal zones were controlled independently by ther-

Jan 1, 1968

By R. Hogg

INTRODUCTION As mineral particles are made smaller and smaller, it follows that their surfaces assume a greater and greater importance. In the extreme, the colloidal systems are characterized by the complete dominance of surface over bulk properties. Surface characteristics and properties will clearly influence any fine-particle processing operation. Comminution, for example, is a process of creating new surface. Agglomeration, on the other hand, may involve the reduction of surface area and the forces involved are generally surface forces. All mineral separations, solid-solid as well as solid-fluid, involve the treatment of two or more phases (solid plus liquid and/or gas). As the interfacial area increases, so will its effects on processing. Both physical and chemical separations are influenced by interfacial phenomena. Gravity separations are usually performed in a liquid phase and may be affected, for example, by the wetting characteristics of the solids. Flotation processes, of course, are based on the exploitation of differences in surface properties. Hydrometallurgical processing usually involves interfacial chemical reactions, e.g. leaching. The rates of such reactions depend on surface area and may be influenced by electrochemical effects in the electrical double layer at the solid-liquid interface, or by adsorption of reactant and/or product species from solution. In characterizing a mineral surface, it is important to consider first the surface area, since this determines the relative importance of the interfacial effects. The structure and chemical composition of the surface, which may depend on segregation of impurities within the solid and on adsorption from the external environment as well as on the bulk composition of the solid, will generally determine such

Jan 1, 1980