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By William M. Kester

INTRODUCTION The Coal Research Bureau of the School of Mines at West Virginia University is presently conducting laboratory-scale tests to determine the technical feasibility of beneficiating pulverized coal and coal fines with high-intensity electromagnetic fields. Interest in magnetic processes for cleaning fine coals was stimulated by results obtained by Yurovsky, et a1 in 1958.1 This work, while not new in concept,2,3 indicated that pulverized coal which had been thermally treated in a rotary drum in the presence of superheated steam and air underwent thermo- chemical reactions. Films of the ferromagnetic minerals magnetite (Fe2O3), hematite (Fe3O4), and pyrrhotite (FeS[3]) were reported to be formed on the surfaces of the pyrite grains associated with fine coal during the foregoing treatment at temperatures ranging from 120 to 360°C. After thermal treatment the coal was magnetically separated in an experimental magnetic device having a field strength of 10,000 oersteds.

Jan 5, 1965

By J. R. Campbell

During the past few years, the writer has had occasion to take several excursions into the realms of the washability of beds 3 and 4 of the Pocahontas coal and the proper handling of these coals in prepared sizes Fig. 1.—Washability curve for 4 by 2½-in. egg, PocahoKtas coal. Note that definite break occurs at about 1.60 sp. gr., and washing at this gravity removes all heavy rock and slate, amounting to about 5 per cent. Curve 2 indicates a bony coal, and washed egg coal might not have a good appcarance, and would be condemned by visual inspection, although it would be well prepared mechanically. to attain the greatest realization for the operator and yet produce a market product acceptable to the consumer. Preparation is not new in the southern field, but some new angles have presented themselves in recent years on account of the progress of mechanical preparation. Mechanical methods are entirely devoid of the five senses given to

Jan 1, 1931

The following are excerpts from the report of the Treasurer of the United Engineering Society, for the year ending Dec. 31, 1915. Finances Due to the growth of the activities of the United Engineering Society, it was found desirable early in the year to consolidate the various accounts and financial records of the Society and of the Library, heretofore kept separately, and to have all the data pertaining to the building and its operation in the charge of one individual. An assistant secretary especially assigned to this work has been appointed, and a separate office has been established. The Finance Committee has had all of the records brought fully to date and has prepared a new set of account books to meet the new conditions. The Real Estate Account now includes the following items: Land $ 540,000.00 Building 1,050,000.00 Equipment 33,171.16 Founder Societies, Preliminary expenses 24,000.00 Total $1,647,171.16

Jan 4, 1916

By J. H. Wernick

IN a study of the rate of decomposition of %-in. cubes of limestone, dolomitic limestone, and dolomite in a sweeping nitrogen atmosphere, Joseph, Beatty, and Bitsianes' found that the zone of calcination advanced at substantially a constant rate at a given temperature. The purpose of this paper is to show that their data indicate at least two processes occurring when the above carbonates decompose. It is suggested that there are two processes occurring consecutively, one the limiting process in a given temperature range and the other the limiting process over another temperature range. The data of Joseph and co-workers have been extended by use of the Arrhenius equation, Eq. 1, a relation beween the velocity constant k of a reaction and the absolute temperature T. d In k A ' dT Rr2 A is the activation energy in calories per mol (additional energy that must be added for an average molecule to react), and R is equal to 1.986 cal

Jan 1, 1955

The next meeting of the Institute, the 113th meeting, will be held in Arizona in the latter part of September, 1916. All papers to be presented, at this meeting must be published in the September Bulletin or previously. Manuscripts must, therefore,' be in the hands of the Secretary of the Institute not later than July 1. In case manuscripts are given by authors to members of technical committees, or others, they must be in the hands of such persons sufficiently in advance so that they may be actually in the hands of the Secretary of the Institute by the date mentioned. In the past, the Secretary has received urgent requests for special consideration regarding manuscripts that come in after the closing date. In view of the obvious unfairness of this, the Committee on Papers and Publications has instructed the Secretary not to accept for presentation at the Arizona Meeting any papers received later than July 1, 1916.

Jan 3, 1916

J: H. POLHEMUS, New York, N. Y. (written discussion*).-The Joplin .mining and milling practice has largely influenced operating methods in the Wisconsin district. Milling equipment is essentially of the same type with the notable exception that no tables are used. The treatment of the flue 'sands has been attempted several times but without commercial success. Table material coming from any one mill is low both in tonnage and zinc content. The iron is comparatively high as the pyrite-line "chat" is much more prevalent than the zinc-lime attached particle. In the finer sizes the zinc occurs mainly as free mineral. These condi-tions make the production of good-grade table concentrates very diffi-cult. The accompanying tabulated results from several mill tests indi-cate the character of the mill tails. I think the average mill tails in the district assay nearer 1.5 per cent. zinc than under 1 per cent., as stated by Messrs. Boericke and Garnett.

Jan 10, 1919

The next meeting of the Institute, the 113th meeting, will he held in Arizona in the latter part of September, 1916. All papers to be presented at this meeting must be published in the September Bulletin or previously. Manuscripts must, therefore, be in the hands of the Secretary of the Institute not later than July 1. In case manuscripts are given by authors to members of technical committees, or others, they must be in the hands of such persons sufficiently in advance so that they may be actually in the hands of the Secretary of the Institute by the date mentioned. In the past, the Secretary has received urgent requests for special consideration regarding manuscripts that come in after the closing date. In view of the obvious unfairness of this, the Committee on Papers and Publications has instructed the Secretary not to accept for presentation at the Arizona Meeting any papers received later than July 1, 1916.

Jan 4, 1916

By E. H. Rennhack

When cast hypoeutectic Zn-Ti alloys are rolled, the TiZn15 compound particles arising from eutectic decomposition form a network of fibers promoting improved creep resistance.' The effect is magnified with increasing titanium content and extends to hy-pereutectic concentrations. Strip produced from the latter-type alloys, however, also contains large, primary crystals of the compound that tend to initiate cracking during subsequent fabrication operations. In a study of the influence of various casting modifications on the size and distribution of these crystals, the phase relationships existing between the eutectic and the TiZnIs intermetallic compound in the Zn-Ti system were of major interest. Although several in- vestigators1 4 have explored the equilibria within this compositional range, their results show considerable lack of agreement. Consequently, with the exception of the solvus boundary, the constitution of this system containing up to approximately 1.0 wt pct Ti was . The findings are reported in the present note.

Jan 1, 1967

By M. I. Sherman, J. D. H. Strickland

PRELIMINARY experiments in these laboratories showed that whereas pyrite1 produced only sul-fate the action of aqueous chlorine solutions on most other sulfide ores resulted in the formation of a mixture of sulfate and elemental sulfur, the production of the latter being favored by a very dilute solution of oxidant. The reactions taking place were obviously complex and only a detailed kinetic study could be expected to clarify the position and enable a prediction to be made of conditions leading to the rapid formation of metal salt and the economically desirable elemental form of sulfur. Galena was chosen for the first investigation as it is of widespread occurrence and is representative of a simple cubic lattice sulfide containing the monosulfide unit, S2-. Experimental Procedure The apparatus and general technique used in this work have already been described.' Analyses for chlorine and sulfate were carried out by the same methods as those used for pyrite. The lead in 1 ml aliquots of solution was determined polarographi-cally, after destroying chlorine with hydrazine hy-drochloride and making solutions 0.5 molar with hydrochloric acid. A large sample of Kansas galena, assaying at better than 98 pet PbS, was crushed and wet sieved to give fractions of —10 + 14, —20 + 28, —28 + 35, and —48 + 65 Tyler screen. The particles were almost perfect cubes and the apparent surface Per gram was calculated assuming each particle a cube Of side equal to the mean mesh opening. A volume shape factor, calculated as for pyrite, was exactly unity. The main apparatus was unsuitable for direct visual examination of the ore particles during the reaction. For this purpose a small cell from a Spekker Absorptiometer optical flats 1 cm apart) was l by a greased microscope slide after filling with oxidant solution. One or two ore particles were placed in the cell and the solution was stirred by a glass covered speck of iron wire activated by an external rotating magnet. The surface of an ore particle was examined under a binocular microscope at between 10 and 40 magnifications. Results Experiments were made under a wide variety of conditions, the form of presentation of the data being illustrated by Fig. 1, where the concentrations of chlorine, sulfate, and sulfur are plotted against time. The fictitious concentration of solid sulfur is used for convenience and is the molarity of sulfur which would be recorded if the elementary sulfur formed during the reaction were dissolved in the liquid iii the reaction vessel. As some lead sulfate is occluded with the sulfur on the ore particles the amounts of sulfur and sulfate formed during a reaction cannot be calculated

Jan 1, 1958

By Walter Crafts, C. M. Offenhauer

IN the course of study of the heat-treatment of low-alloy steels, the behavior of alloy carbides at subcritical temperatures was found to vary from that indicated by published investigations. In order to establish the ranges of formation of carbides in low-chromium steels, a series of steels containing up to 0.60 per cent carbon and 7.5 per cent chromium has been investigated with respect to the type of carbide formed after quenching and tempering at subcritical temperatures. The types of carbide formed as products of austenite transformation to pearlitic and pseudomartensitic structures have also been determined. There have been numerous investigations of the carbides in chromium steels and diagrams of the iron-chromium-carbon system.1 Westgren, Phragmén and Negresco2 identified the following carbides in chromium steels: [Cementite Fe3C (containing up to about 15 per cent Cr) Trigonal carbide Cr7C3 (containing up to about 55 per cent Fe) Cubic carbide Cr4C (or Cr23C3) (containing up to about 25 per cent Fe) Orthorhombic carbide . Cr3C2 (containing only a few per cent Fe)] The most complete information on the iron-chromium-carbon system was supplied by Tofaute, Sponheuer and Bennek3 and by Tofaute, Küttner and Büttinghaus.4 By means of dilatometric and microscopic studies, sections of the diagram were established. This diagram showed the presence of the special carbide Cr7Ca in steels containing about 2.5 per cent to 12 per cent chromium in low-carbon steels and from about 5 to 20 per cent chromium in r per cent carbon alloys from A1 to room temperature. The present investigation has shown that a carbide inversion from Fe3C to Cr7Ca occurs in chromium steels containing more than about 1 per cent chromium after hardening and tempering at subcritical temperatures above about 500°C. The type of carbide observed to be more stable in quenched and tempered specimens was also found to be produced by direct austenite transformation in corresponding ranges of temperature and composition. EXPERIMENTAL PROCEDURE The steels used in these experiments were made in magnesia-lined crucibles in high-frequency furnaces and were poured into 2-in. ingots. The ingots were forged into 1-in. round bars, and all heat-treatments were conducted on specimens of this section .size. Sections of the bar stock 8 in. long were hardened in air, oil or water depending on the composition, after heating to a temperature sufficiently high to dissolve the carbides. The low-carbon and low-chromium steels were not entirely martensitic after quenching, and contained some ferrite and pseudomartensite. No pearlite was observed in the microstructures after auenchine. The quenched bars were cut into

Jan 1, 1942

By P. R. Schmidt, N. J. Themelis

A study zvas made of the deoxidation of copper at 1170°C by injecting a jet of carbon monoxide vertically upwards into the melt. The effects of submersion depth (2 to 20 cm), orifice diameter (& to 5 in.), and gas velocity (100 to 3650 ft per sec) were examined. In the oxygen range 0.1 to 1.0 pct 0, the overall rate was conlrolled by gaseoLcs mass Lransfer. The results were interpreted in terms of a rate coefficient per unit depth which was found to be constant with distance along the jet axis and nearly proportional to the orifice Reynolds number in the range 1000 < NReo < 9100. AS the gas flow rate through an orifice submerged in a liquid is progressively increased, at least three regions of bubble formation may be distinguished. At very low rates, the formation of bubbles is practically a static phenomenon, depending on the orifice diameter, the liquid surface tension, and the densities of the two phases. In this region, the bubble size is constant while the frequency of bubble formation increases with gas flow rate.&apos;-3 At higher flows (500 < NR~, < 2100), the frequency of bubble formation reaches a steady value and the bubble size increases with gas flow rate; when the bubbles issuing from the orifice become so large that they start coalescing to form larger bubbles, the turbulence induced in the liquid by the passage of previous bubbles shatters them into small bubbles of varying size. Finally, for gas velocities in the intermediate and turbulent regions of flow (NR,, > 2100) a tangential separation surface is created around the jet and momentum transfer takes place between it and the surrounding liquid medium. The entrainment of liquid and the resulting deceleration of the gas-liquid dispersion causes the jet to expand forming a characteristic jet cone. The large velocity and density differences between the jet and the liquid result in a high degree of instability and the jet envelope fluctuates rapidly.The characteristic jet cone can be observed by means of time exposure photographs such as those shown in Fig. 1 for an air jet introduced vertically upwards in a water bath. High-speed photography has showns that the gas-liquid dispersion within the cone consists of small bubbles the size of which depends mainly on the jet orifice diameter and Reynolds number. In the laminar region of flow, the following correlation was obtained by Leibson: The results of Liebson et a1.&apos; are plotted in Fig. 2. It can be seen that the region 2000 < NReo c 10,000 is not well-defined experimentally. In the entrance to the fully turbulent region of flow (NR,, = 10,000), the mean bubble diameter decreased to about 0.4 cm and varied only slightly from there on according to the correlation:

Jan 1, 1968

By R. K. McGeary, B. Lustman

Orientation relationships and rates of annealing of 97 pct cold rolled zirconium have been studied by X-ray techniques, metallography, and by hardness measurements. The process of annealing occurring by the formation of domains, and their subsequent growth without recrystallization, is demonstrated. NUMEROUS investigators1-&apos; have revealed sub-grain formation after annealing cold worked metal single crystals and have generally described the results in terms of a dislocation mechanism of polygonization.5,6 in heavily cold rolled polycrystal-line aluminum the first stages of heating cause an apparently spontaneous subdivision of regions of the deformed matrix into a great number of slightly disoriented domains followed or accompanied by rapid growth of certain domains to form a recrystallization texture.7,8 In the present investigation the isothermal rate of annealing of cold worked polycrystalline zirconium has been studied by X-ray techniques, metallography, and by hardness measurement. It will be shown that, rather than by the usual nucleation and growth mechanism,"12 the process of annealing can best be explained by the formation of domains early in the annealing treatment and the subsequent growth of these domains without recrystallization. Experimental Procedure All the experimental work was performed on an arc-melted ingot of high purity zirconium crystal bar made by Westinghouse in a production scale deBoer unit. The weight percentage of impurities in the zirconium were as follows: C, 0.04; Fe, 0.05; Hf, 0.014; W, 0.01; Ti, Ni, and Al, 0.003; Si and N, 0.002; Cr and Cu, 0.001. Metallographically the zirconium showed only a single phase. The 4 in. diarn ingot was forged at 760°C to a 1 1/2x3 in. plate and was then rolled at 760°C to 0.150 in. thickness and annealed at this temperature for 20 min to produce an equiaxed grain structure of about 0.1 mm average grain diameter. The hot rolled plate was roller-leveled, surface ground to 0.135 in., cold rolled 83 pct reduction in thickness on a two-high mill, and then to a total reduction of 97 pct on a Sendzimir mill. The 0.004 in. strip material so produced received no subsequent mechanical treatment. Specimens % in. square were sheared from the rolled strip and isothermally annealed at 104 mm Hg in an all glass vacuum system equipped with a Vycor furnace tube. The temperature data presented are the average temperatures during the runs and did not vary more than about k3"C. X-ray Diffraction Methods: When zirconium is drastically cold rolled, a high degree of preferred orientation results in which prism poles, {1010}, are perpendicular to the rolling direction. After fully annealing this material an entirely new texture develops which corresponds to a 20" or 40" rotation of the deformation texture about hexagonal axes of

Jan 1, 1954

By W. L. Fink, L. A. Willey

DURING the war there was introduced a new higher strength aircraft alloy designated 75S.1,2.3 The properties of this alloy assure extensive applications in both military and commercial aircraft. It is therefore important to understand its limitations as well as advantages. The properties of 75S alloy in the heat-treated tempers, like those of many other aluminum alloys, are affected by the rate of quenching. In general, low quenching rates tend to cause low strengths and to adversely affect the resistance to corrosion. Commercial quenching procedures are usually sufficiently rapid to permit the development of maximum properties. However, in the center of heavy sections, such as large rolled and extruded shapes, the quenching rates may not be rapid enough to develop maximum strength or resistance to corrosion. The investigations of 75S alloy described herein reveal the most critical range of temperature and the effects of quenching sheet and extrusions at different rates through that temperature range, on the tensile properties and resistance to corrosion. PROCEDURE Preparation of Specimens Sheet specimens (3 in. by 9 in.) were prepared from a commercial lot of 75S "as rolled" sheet (0.064 in. thick). The composition° was as follows: Weight Percentage Cu Mn Mg Zn Cr Al with Normal Impurities 1.64 0.16 2.58 5.66 0.27 Remainder The specimens employed for the determination of the time-temperature relations during quenching of sheet were prepared by the following procedure: the hot junction of a 28-ga. iron-constantan thermoelement (asbestos insulated) was brazed to a thin strip of aluminum which was in turn brazed into the end of a 3/16 in. i.d. by ¼ -in. o.d. by 30 in. long aluminum protection tube. Before brazing, the tube was flattened to 0.064 in. thickness over the junction and adjacent lead wires for a distance of 1 ½ in. The flattened end of the tube was fitted into a slot cut from one edge to the center of the 3 in. by 9 in. by 0.064 in. sheet and brazed into place. The brazed joint was dressed to the thickness of the sheet and the entire specimen buffed to approximately the brightness of "as rolled" material. Because of the brazing operations required, these specimens were prepared using 3S alloy. For the investigation of quenching rates in heavy sections, there were used 75S extrusions which had compositions similar to that of the sheet. The specimens consisted of 14 in. lengths of ¾ in., 2 in., 3 in. and 4 in. diam cylindrical rods and a roughly rectangular extruded section which was approximately 4 in. by 7 ½ in. Thermocouples were peened into the bottoms of 1/8 in. diam wells drilled into one end and parallel to the axis to a depth of

Jan 1, 1947

By R. J. Sherman, M. R. Achter

IT has often been reported that coatings may strengthen single crystals and polycrystalline specimens of coarse grain size. This note reports the effect of a surface layer of fine grains on the creep-rupture properties of coarse grained nickel 99.8 pct pure. Sheet specimens were machined from cold-rolled material, finished by surface grinding and annealed at 1230°C in vacuum for 4 hr. Half of them were re-ground on faces and sides and annealed at 925"C for 1 1/4 hr. The double grind-anneal treatment produced a structure consisting of a surface layer of fine grains of 0.02 mm diam on a coarse-grained substrate of grains of 0.40 mm diam. Comparison with specimens which received only the single grind showed that the second grind-anneal did not alter the structure of the substrate. Several modifications were made in specimen design to eliminate erratic rupture behavior outside of the gage length. In the final design the gage section, oriented parallel to the rolling direction, was 1.00 in. long, 0.4 in. wide, and 0.0625 in. thick. End tabs were pinned in place. Although other configurations (welded end tabs, transverse orientation, and wider gage section) showed similar effects of a layer of fine grains, because of the erratic rupture behavior, only the data from the final design are reported here. Creep tests were performed at 650°C in air and in a vacuum of 10~5 mm Hg. Creep rates were measured from the movements of the lever arm. Since the broken sheet specimens could not be fitted together, elongations at fracture measured by means of gage marks, do not include the necked portions adjacent to the fracture. Results of the creep tests with and without the fine grained surface are given in Table I. An explanation for the lower strength in air than in vacuum has been proposed previously in terms of the reduction of crack propagation energy by gas adsorption.l In both environments the fine-grained layer produced a small decrease in minimum creep rate and, except for the shortest test in air, a substantial increase in rupture life. The elongation values at rupture, as they are measured here, do not demonstrate an appreciable effect of the grain structure but do show much smaller ductilities in air than in vacuum. Greater elongations maybe associated with the finegrained layer, however, especially in vacuum, in creep curves such as those in Fig. 1. Duplicate tests were not run to determine the re-producibility of the data. It is felt, however, that, in view of the consistent behavior, the prolongation of rupture life may be attributed to the effect of the fine-grained surface. In the data not reported be-

Jan 1, 1962

By John Chipman

DESPITE the rapidity of chemical reactions at steelmaking temperatures, deoxidation reactions cannot be expected to reach equilibrium immediately after addition of a deoxidizing agent. A considerable period of time may be required merely to obtain complete mixing of the deoxidizing element throughout the volume of steel to which it is added. Evidence in the literature indicates that in some cases the time is long compared with that allowed for completion of the experiment or for teeming of the heat. The great turbulence observed during the filling of the ladle is no guarantee of complete dispersion on a fine scale throughout the heat. During the process there are initially certain volume elements which are high in deoxidizer and others which retain substantially their original oxygen content. Mixing consists of the subdivision and ultimate destruction of these liquid segregates through the process of shear and elimination of concentration gradients by diffusion. The shear process does not continue indefinitely and a quiescent state may be reached in the ladle before all volume elements of divergent deoxidizer and oxygen content are completely eliminated. In furnace deoxidation the time required for complete mixing may be very long unless continuous stirring is employed.&apos; In Fig. 1, let the circle represent one small volume element of aluminum-rich metal surrounded by oxygen-rich steel in which no stirring movement remains. Further mixing requires inward diffusion of oxygen and outward diffusion of aluminum, resulting in precipitation of A12O3 in the diffusion zone. It is important to note that such a precipitate may itself interfere with the diffusion process. Moreover, if the precipitate forms as a film with even minimal mechanical strength, it may interfere not only with diffusion but with shear as well, thus stabilizing compositional differences in volume elements of greater than microscopic size. A film surrounding such a volume element would have little or no ability to rise or to sink unless it enclosed a liquid whose density differed from that of the ambient. Consider now the effect on the overall composition of the melt. Fig. 2 represents the A1-O equilibrium at the temperature of the bath. High-aluminum elements of composition X may exist alongside high-oxygen elements of composition Y in such proportions that the average composition 2 has a much higher A1-O product than that corresponding to equilibrium. The A1-O product supposedly corresponding to equilibrium at 1600 °C was found by Wentrup and Hieber2 to be 10-10, by Hilty and crafts3 to be 2 X 10-9 and by Gokcen and chipman4 to be 2 x 10-14. Only the last named investigators approached equilibrium by means

Jan 1, 1962

By Tell Ertl, Ernest E. Burgh

The Bureau of Mines is operating an oil-shale mine 10 miles west of Rifle, Colo., as part of its Synthetic Liquid Fuels program. The purpose of operating this mine is twofold: First, to supply oil shale to an experimental Processing plant; and second, to develop practices and select methods for mining oil shale on a commercial scale at the lowest practicable cost. The second purpose—that of finding out how to mine oil shale most cheaply—entails considerable mining research. Since the drilling of oil shale probably will be one of the major items of the mining cost, fattors that influence drilling speeds were investigated. One phase of the drilling program was the development of a successful hard-surfaced rock-drill bit1 that can be used for drilling long holes in oil shale without changing bits. During that phase, drilling speeds were measured and drill cuttings were collected for assay and for screen sizing, when the cuttings from the individual tests were compared, a definite relationship was shown to exist between the drilling speed and the coarseness of the drill cuttings. Procedure Measurement of Drilling Speeds All drilling in the tests was done with a Model UMB-D-99W Gardner-Denver wagon drill. Round-lugged drill steel, 141 in. in diameter was used in 6, 12, and 18 ft lengths with 1/8-in. Timken H-type bits hard-faced with acetylene tube borium. The tests were made in the lower adit of the Bureau of Mines oil-shale mine; the grade of the oil shale drilled ranged from 18.6 to 42.7 gal per ton, During the experiments air pressure varied between 75 and go psi while water pressure remained fairly constant at 75 psi. All holes were drilled almost horizontally. Each drill hole was thoroughly cleaned of cuttings after being collared. The advance of the drill along the carriage was measured and recorded as the drilling speed in inches per minute. Method of Collecting Cuttings TO facilitate the collection of cuttings, each drill hole was collared in a smooth, vertical portion of the oil-shale breast (Fig 1). A galvanized-stee1 sheet was fastened to the breast below the area in which the hole was to be drilled. The cuttings washed out of the drill hole by the drilling water were guided by the steel sheet into a wooden box. The cuttings that remained in the drill hole after the drill was withdrawn were scraped out and placed in the same box as the cuttings washed out of the hole. After the cuttings from a I-min. drilling interval were collected, they were placed in flat metal pans. The fines were allowed to settle and the clear water was decanted. The cuttings then were dried in the sun.

Jan 1, 1949

By H. J. Modi, P. L. De Bruyn

IN recent years interest has been aroused in flotation rate studies both from a technical and a more practical aspect. With increasing fineness of grind becoming a necessity in treatment of low grade ores, difference:; in flotation rates of various size ranges will assume importance in the evaluation of overall recovery results. Theoretical analysis of flotation kinetics was initiated by Schuhmann,&apos; who sought to define flotation rate of a given mineral and specified size range in terms of certain physical variables of the flotation system. Using as a basis for his analysis the bubble-particle encounter hypothesis previously advanced by Gaudin,&apos; Schuhmann writes for the rate of flotation (R,.) of particles of average size x, Rx = PcPa(x) V F. [1] In this relation Pc and Pa represent, respectively, the probability of collision between particle and gas bubble in a given time interval and the probability of adhesion of particle to the bubble after collision. Rigorously speaking, the term PC does not have the significance of a probability factor, since it depends on the time interval and therefore can be numerically greater than unity. The term c(x) expresses the concentration of particles of an average size x in the flotation cell in weight per unit volume of pulp, and V denotes the total volume of pulp in the cell. The product, P,c(x)V, defines the frequency of particle-bubble collisl.on, and when it is multiplied by P,, the number of collisions per unit time resulting in successful adherence is obtained. The factor, F, measures the froth stability and is introduced because after fruitful bubble-particle contact some particles may still riot reach the froth launder. Coalescence of bubbles in the froth column or too short a bubble life could account for this effect. Schuhmann also introduced the concept of "specific flotation rate" (Q) to allow for the relative abundance of different mineral species in the flotation pulp. The specific flotation rate, having the dimension of reciprocal time, is defined as Eq. 2: Qx =Rx/c(x)v [2] and it also follows from Eq. 1 that Qx = PcPaF. [31 The theoretical aspects of flotation kinetics were also considered by Sutherland,3 who tried to improve Eq. 1 by expressing the probability factors in terms of such physical variables as particle radius (x), bubble radius (X), velocity of bubble relative to particle (v), the number of bubbles per unit volume of pulp (N) and the induction period (A) necessary for air-mineral adhesion. According to Sutherland&apos;s treatment, the rate equation, Eq. 1, transforms to R, = [3pX x v N] [sech2 (3 v ?/4 X) ] ?c(x) V [4] where the first term in brackets on the right-hand

Jan 1, 1957

By CHARLES F. RAND

PRESIDENT CHARLES F. RAND,1 NEW YORK, N. Y. PAST PRESIDENTS CHARLES KIRCHHOFF,1 NEW YORK, N. Y. JAMES F. KEMP,2 NEW YORK, N.. Y. FIRST VICE-PRESIDENT BENJAMIN B. THAYER,1 NEW YORK, N. Y. TREASURER GEORGE C. STONE,1 NEW YORK, N. Y. SECRETARY EMERITUS ROSSITER. W. RAYMOND, NEW. YORK; N. Y. SECRETARY BRADLEY- STOUGHTON NEW YORK, N. Y.

Jan 2, 1914

PRESIDENT CHARLES F. RAND,1 NEW YORK, N. Y. PAST PRESIDENTS CHARLES KIRCHHOFF,1 NEW YORK, N. Y. JAMES F. KEMP,2 NEW YORK, N. Y. FIRST VICE-PRESIDENT BENJAMIN B. THAYER,1 NEW YORK, N. Y. TREASURER GEORGE C. STONE,1 NEW YORK, N. Y. SECRETARY EMERITUS ROSSITER W. RAYMOND NEW YORK, N.Y. SECRETARY BRADLEY STOUGHTON NEW YORK, N. Y.

Jan 1, 1914

PRESIDENT L. D. RICKETTS,1 NEW YORK, N. Y. PAST PRESIDENTS BENJAMIN B. THAYER,1 NEW YORK, N, Y. WILLIAM L. SAUNDERS,2 NEW YORK, N. Y. FIRST VICE-PRESIDENT SIDNEY J. JENNINGS,1 NEW YORK, N. Y. TREASURER GEORGE C. STONE,1 NEW YORK, N. Y. SECRETARY EMERITUS ROSSITER W.. RAYMOND NEW YORK, N. Y SECRETARY BRADLEY STOUGHTON NEW YORK, N. Y.

Jan 6, 1916