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By D. W. Fuerstenau, J. H. Brown

The paper by Professors Sun and Mitchell illustrates the value of ultrasonics as a tool for the mineral engineer. In particular, it opens up a number of possibilities to those interested in the field of comminution. The provision of desliming technique, which is thorough as well as rapid, is a distinct contribution, but the data of the paper suggest applications beyond desliming, in that the same treatments may be useful for size determination purposes. Fig. 1 shows that a marked dependence exists between particle size and the height to which it can be elevated by ultrasonic vibrations. While the curves are only extended down to a size of about 100 u, the fact that they appear to be increasing in slope in this range suggests that the separation may be even more marked here. This, we feel, is very strong evidence that a nlethod for fine sizing could be developed to use ultrasonic waves as the separating force. Professors Sun and Mitchell indicate that floccula-ti~n will present no difficulty: "During the investigation it was found that ultrasonic waves were able to dislodge the adhering gangue particles from the min- era1 surfaces and to disintegrate the soft particles into fine sizes." Thus, it appears that the use of ultrasonic waves as the power behind a size separation process may eliminate the problem of flocculation encountered in most wet sizing techniques. It would be interesting to size a fine material under conditions in which particles are known to be flocculated and under conditions where they are known to be dispersed. Use of a sizing technique of this nature may solve several problems that have long persisted in the fine sizing field. The flocculation problem may be overcome; the continuous production of closely sized fractions may be possible with a device similar to the one described; and with photoelectric methods, rapid analyses in the subsieve sizes may be possible. In general, we suggest that this paper be followed by a study of the sizing applications of the apparatus described. We feel that such a study would not only be rewarding in providing a new sizing technique, but also that the present paper almost requires such work to complete the picture of particle motion in a field of ultrasonic waves.

Jan 1, 1958

By Frank C. Appleyard

The two calcium sulfate minerals-gypsum and anhydrite-occur in many parts of the world, and gypsum has long been of economic importance in the family of industrial minerals. Gypsum, the dihydrate form of calcium sulfate (CaS042H20) and anhydrite, the anhydrous form (CaSO4) are frequently found in close association, and it is seldom that a calcium sulfate deposit will consist exclusively of one mineral or the other. Although known gypsum deposits are extensive, anhydrite makes up the largest part of total calcium sulfate reserves. However, it has very minor economic use, and most of the following discussion will be devoted to gypsum. Calcium sulfate is one of the principal con- stituents of evaporite deposits, and when pure, has the following composition: [ ] Deposits of pure gypsum or of pure anhydrite which are large enough to be considered commercial have never been found because of both the metastable relationship between the two minerals, and the presence of impurities such as calcium or magnesium carbonates, chlorides, other sulfate minerals, clay minerals, or silica. As a result most mine production of gypsum will range between 85 and 95% pure. Often it is used as mined, although in certain cases, one or more forms of mineral beneficiation are employed to upgrade the product.

Jan 1, 1975

By William B. Stephenson

IN the pumping of sands, slurries and slimes, practices developed over the years are the real keystones of successful operation. These practices are necessarily based on modifications of familiar theories. Practical methods used in the solution of problems involving the pumping of materials are set forth in the following discussion. BASIC REQUIREMENTS To pump sands and slurries economically, a few basic requirements must be met by the pumping system as a whole. A pipe-line velocity must be established that will move the fluid mixture throughout the entire system without any possibility of the solids settling out. To accomplish this, the velocity of flow must be slightly in excess of the critical velocity of the mixture. The critical velocity of a mixture varies from 3 ft. per sec. to 18 ft. per sec., depending on the screen analysis, concentration, and specific gravity of the solids in the mixture. Most tailings are pumped at a minimum velocity of 4 ft. per sec. if they include slimes, whereas the pipe lines of sand and gravel dredges require velocities as high as 18 ft. per second. A number of articles have been written on the determination of the minimum velocities required to maintain solids in suspension. Studies have also been made on the friction and pumping heads developed when handling solids in suspension.1-4 Our experience so far has shown that, within the normal operating limits of a pumping system, the friction factor follows more nearly the basis described by Howard,1 who says, among his conclusions: " ... values of ƒ (friction factor) .. . will decrease with an increase in velocity." This conclusion is borne out by our actual experience. When the velocity in a pipe line is not sufficient to keep the solids in suspension, the total friction head is greater than when the velocity is increased to a point where the solids are in suspension. A slight increase in the volume of feed to the pump and a slight increase in the pump speed are usually all that is necessary to put the system in balance. MAINTAINING CONSTANT VOLUME Within reasonable limits, the volume of mixture to be handled through a pipe line should be held constant, so that the required velocity will be provided at all times. There are several ways in which this can be accomplished. The commonest is to provide a sump of sufficient capacity to take care of slight surges in the volume of mixture being fed to the pumping system. This sump, however, should not be as large as a settling chamber. The use of a float-controlled, fresh-water make-up valve in a sump will guarantee a constant volume. Where variations in volume are slight,

Jan 1, 1946

By James Boyd

All mining and milling enterprises must be based on adequate ore reserves. Reserves must be established by physical exploration, and the orebody should be of sufficient size and grade to insure recovery of capital invested in mine purchase, development, and mill construction and to provide a reasonable profit. Determination of these economic factors is so complicated, and present costs of mine development and construction so great, that analysis can be made only by competent persons qualified by experience in this field. What rate for maximum efficiency? Unfortunately, even today mills are built before deposits have been adequately outlined, and there are rusting monuments to such folly in nearly every mining region. Also there is a tendency to be guided by the philosophy that "if a little is good, a lot is better," which leads to the conclusion that mining at a given rate and making so much per ton will yield a profit of so many dollars per day. Consequently, why not build a mill to treat twice as much per day and make twice as much money?

Jun 1, 1956

By Stephen E. Merritt, John W. Straton, T. Carl Shelton

Surveying and mapping are used to locate and visually portray objects, lines, or areas in relation to a reference point or line. The actual making of the measurements to locate the objects and points falls under surveying while mapping is concerned with putting the survey information into a graphical form. Generally, the type or class of proposed survey depends on the precision required. Some surveys may need only approximate measurements which can be obtained by simply pacing or by using an ordinary measuring tape; others may require much accuracy, thus calling for the use of an engineer's transit or theodolite along with a graduated steel tape for horizontal measurements, or a level and a graduated rod for measuring vertical distances. Mapping is likewise dependent on accuracy requirements. For example, a general layout showing the relative position of surface facilities may not call for a large scale of dimension or great precision whereas for detailed work, a large scale plus care in plotting points and drawing lines and curves are important factors. SURVEYING METHODS There are many kinds or types of surveying methods. Some examples include : land surveying for determining boundaries of land areas; route surveying for locating roads, highways, right-of-way, and haulways; city surveying for laying out lots, streets, and alleys; and mining surveying for projecting mine openings and locating mining operations. See Fig. 1. There are other types of surveying than those named, but in general, the type of method to be used will depend on the purpose for which the survey is to be made.

Jan 1, 1981

By B. Pitchumani, D. Venkateswarlu

INTRODUCTION The characteristics of feed and product of any size reduction operation are normally expressed as mean size, the size corresponding to 80 percent undersize or the percentage below a specified size or specific surface area. But the feed has a distribution of sizes and quite often it becomes essential to obtain a product of desired distribution. In such cases, size distribution of feed is related to product by matrix methods. The technique of matrix representation of crushing operation was proposed by Broadbent and Calcott (1 to 4). They divided the complete crushing mechanism of coal into breakage, selection and classifying functions for a closed-circuit system to establish relations between the feed and product distribution. Ellis, Ray and Venables (6) suggested an empirical method of determining the breakage matrix by combining the characteristic functions and proposed the following hypotheses: 1. The breakage of individual size fractions passing through the mill at a given rate is the same whether passed separately or as part of a mixed feed. 2. The breakage of a mixed feed may be estimated from the products of individual size fractions passed through the mill separately at a rate at which they would be crushed as part of the mixed feed. This method is stated to be applicable when there is no interaction between the individual sizes.

Jan 1, 1980

By J. C. Bokros

At temperatures above 950°F, zirconium which has been strained a critical amount will experience critical recrystalli-zation. The large grain size thus formed can result in a reduction in the fatigue life by a factor of 2 to a factor of 9 at both high and low temperatures. The critical strains for zirconium vary from 15 pct at 900°F to about 2 pct at 1125°F, while those for zircaloy III vary from 15 pct at 1050°F to 5 pct at 1200°F. Zircaloy II ,experiences no critical recrystallization up to 1200°F. ZIRCONIUM has become increasingly important for nuclear applications and is being employed in reactors at temperatures where recrystallization can occur. Recent work' on the fatigue properties of zirconium has shown that coarse-grained structures developed in zirconium during recrystallization have much lower fatigue lives than fine-grained material. The development of these large grain sizes under such conditions is well known to be the result of critical recrystallization.2-4 Briefly, critical recrystallization occurs when a metal is strained a critical amount and annealed in the recrystallization range. The critical strain is defined as that minimum strain necessary to promote nucleation in the time unit and temperature considered. The maximum grain size occurs at the critical strain, since at this strain the fewest stable nuclei per unit volume grow into new grains. Recrystallization is not evident below this; strain since the nucleation rate is vanishingly lolw, and metal strained more than the critical amount has a higher nucleation rate per unit volume which results in a finer grained structure. This paper describes the critical recrystallization observed in reactor-grade zirconium, zircaloy 11, and zircaloy I11 as a function of annealing temperature and temperature of strain. EXPERIMENTAL The zirconium used was hafnium-free, double arc-melted sponge obtained from the Bureau of Mines. The ingots were forged and hot reduced to 0.08 to 0.10-in. sheet and subsequently cold reduced to 0.035-in. sheet with intermediate and final anneals at 1200 OF for 15 min. The zircaloy II and zircaloy III used were 0.035-in. sheets in the annealed condition. Compositions of these materials as tested are given in Table I. To determine the critical strain at a given temperature, tensile specimens having a0.065-in. taper in a 2-in. gage length were machined from the sheets parallel to the rolling direction. The specimens were polished, etched, and examined metallographically to ensure that all of them were strain-free, initially. Tukon indentations were made every half millimeter along the gage length of each specimen. These served as fiducial marks enabling the plastic strain to be measured with a microscope and micrometer stage. The specimens were pulled to failure at a rate of 0.002 in. per min in an Instron tensile-testing machine. Three temperatures were used for straining: room temperature, 500 ºF, and 900 ºF. The 500º and 900 ºF tests were run in an argon atmosphere. Since the rate of work hardening changes with temperature, a different critical strain was obtained for each temperature of strain. Specimens, prepared in the manner described, were annealed in vacuunl at various temperatures ranging from 900" to 1200 F for up to 1000 hr, after which they were examined metallographically. The critical strain and the recrystallized grain size as a function of strain were determined for each specimen. Results for the same temperature and time indicated that the critical strain measured was reproducible to within 5 pct of each other. RESULTS AND DISCUSSION Since increasing the time of anneal increases the probability of the nucleation of a new grain, the critical strain decreases with time at a decreasing

Jan 1, 1961

By D. P. Harris

This paper surveys a few of the quantitative exploration models that might be of interest to an ex-plorationist seeking to apply methods of operations research to mineral exploration. A general development of each model is presented, and the model is evaluated relative to the exploration activity. Finally, a philosophy of exploration and mineral resources is presented, and a possible exploration strategy incorporating concepts of some of these models consistent with this philosophy is proposed. The high cost of conducting an effective exploration program has generated an increasing interest in methods of optimizing the allocation of the resources of a firm engaged in mineral exploration. As a step towards this, mathematical models have been formulated which are designed to quantify those variables of mineral exploration in such a manner that they can be integrated with all phases of the firm's operations so as to optimize its profit objective. QUANTITATIVE MODELS General: Exploration models express at least two concepts: mineral occurrence and effectiveness of search. In simplest terms, an exploration model might be formulated mathematically as follows: P(X) = F(X) . G(X), where P(X) = the unconditional probability of discovery of X deposits, F(X) = the probability of occurrence of X deposits, and G(X) = the probability of discovery of X deposits, conditional upon their existence in the search area. With these general models as a basis of reference, some of the specific exploration models are examined below. The Allais Model: DEVELOPMENT - M. Allaisl performed the first study in which a philosophy of exploration was formulated into a probability framework. His objective was to estimate the economic profitability of the exploration of the Algerian Sahara. Allais divided the Algerian Sahara into blocks of land (called cells) 10 km square and defined the random variable, X, as the number of mining districts per cell. Thus, F(X) would describe the probability of 1, 2, or n mining districts occurring within any cell of the search area. Allais reasoned that his best information as to the form of the distribution, F(X), was the number of mining districts per cell that had been found in well explored areas in the world, such as the Western States of the U.S. He found that the Poisson function produced a reasonably good fit to the distribution of districts in these explored areas: where? is a parameter, such as the average number of districts per cell. Thus, by determining the value

Jan 1, 1968

By Ben L. Seegmiller

Roof, pillar and floor stability is a most important requirement in underground coal mines because it represents the leading cause of fatalities. In future coal mine planning the geotechnical aspects must often be minimized owing to unavailability of data. It is, therefore, very important to include a geotechnical investigation as part of the coal exploration program. Data which should be collected basically include the geological discontinuity characteristics, the rock strength characteristics and the groundwater aspects. Many times the only source of such data is the exploration boreholes. Therefore, an emphasis must be made to extract the maximum information from the core and the borehole. Data collection methods can include the preparation of detailed geotechnical logs for the roof, coal and floor. Laboratory strength testing will provide estimates of the mechanical properties of the various lithologic types. Slaking and swelling tests provide an insight into the stability characteristics of the rock materials immediately enclosing the coal seam. The boreholes may be used to provide permeability and pressurization data. Having developed a suitable geotechnical data base allows various stability prediction methods to be used. These include a geotechnical appraisal of the roof and floor units, depositional environment methods, multiple overlay techniques, hazard analysis techniques and classification/rating systems for roof and floor. The basic geotechnical data and the stability prediction methods form a basis upon which preliminary rock mechanics designs may be developed. Of particular importance to future coal mining are those designs relating to longwall mining because most companies are thinking in terms of the greater safety and greater productivity offered by longwalls. Items which should be ad- dressed when considering a longwall system include the panel layout in terms of a total mining plan, strata mechanics, roof/floor bearing capacities, face support requirements, face length, entry and pillar

Jan 1, 1983

By I. Iwasaki

The steel industry is facing an unprecedented challenge. I would like to point out the role that flotation technology could play in meeting this challenge by providing high quality raw materials to the steel industry. Of all the technology available to a blast furnace operator, raw material preparation is by far the most important. Raw material preparation has been a key to the success of the Japanese steel industry. The foremost proponent of better raw material preparation was Professor Joseph at Minnesota. He gave a Howe memorial lecture to the AIME audience in the early 1950s, prepared from the lecture notes that he gave in his classes. At about that time he was invited to Japan. It is ironic that the Japanese steel industry listened and made it a success. In order for our steel industry to be competitive, first we must supply high quality and uniform quality raw materials to improve the efficiencies of our blast furnaces. Where does flotation fit in to the iron ore industry then? First, as a primary means for concentrating for oxidized iron ores. Second, to touch up magnetite concentrates for the removal of the last few percent of silica. And third, in the preparation of super-concentrates for direct reduction.

Jan 1, 1984

By George Cole

WHILE many parts of Canada's pre-Cambrian shield are well served by railway, it is frequently necessary for prospecting purposes to proceed farther into areas in-accessible by rail. To such areas in summer the canoe was at one time the accepted means of travel for the prospector while the dog team was much used in winter. Al-though summer travel was much improved by the development of the outboard motor, the lack of facilities for cheap transporta-tion has been a serious hindrance to the employment of capital in opening up the distant fields. The pre-Cambrian surface of Manitoba, like that of Ontario, is hummocky, with rounded hills and ridges of rock alternating with basinlike depressions and valleys oc-cupied by lakes and rivers or by many low-lying portions covered with muskeg. Routes to the mines have not usually been direct or easy and seasonal vagaries have presented problems in themselves. In summer, water transportation may be the cheapest method for the longer dis-tances but it is not every water route that will satisfy the conditions of loading freight onto a boat or scow and of conveying it without interruption to its destination. By its location, a mine may require a large program of boat transportation in summer over part of its route, to be followed by winter freighting for the remainder. In order to carry on development and produc-

Jan 1, 1940

By G. W. Jr. Jarman

THE purpose of this paper is to present briefly a description of some of the special methods of separation or concentration, either singly or in combination with others, and to give certain operating data and examples. Explanation of the usual methods of large-production mill treatment, such as flotation or wet tabling, or of chemically treating industrial minerals, is not included in the scope of this paper, although one of these methods might be, in certain instances, augmented by one or more of the special methods that will be enumerated herein. Description of these special methods will be centered on magnetic separators, electro-static separators and air flotation or air tables.

Jan 1, 1938

By John M. Kelly

This report covers the development, exploratory drilling, and production of oil and gas in New Mexico during 1945. The statistical information was gathered from state regulatory agencies and other sources believed to be reliable; it is presented here in combined form for general information only, and the author assumes no responsibility for its accuracy or completeness.

Jan 1, 1946

A PAPER on "Iron and Steel Scrap in Blast-fur-nace Burdens," by W. C. McKee, general super-intendent, Federal Furnace plant, By-Products Coke Corp., Chicago, was published in the October issue of MINING AND METALLURGY, and written discussion by Richard Moldenke was published in the December issue. Following is the stenographic report of the oral discus-sion that took place when this paper was presented at Pittsburgh. J. N. REESE, Monessen, Pa.-I came to the conclusion that Mr. McKee must be using a poor grade of scrap, therefore his loss was high. Mr. Franchot said that there was ex-cess heat in the stack. There is no excess heat in the hearth, therefore, any heat that is used to melt this scrap must come from the stack. By using scrap in a blast furnace you can utilize this excess heat in the stack. The amount of scrap that can be used in any particular furnace involves a direct relation to the efficiency of that furnace. If a furnace is running on a very low-coke rate, you will not be able to use much; if on a high-coke rate, you can use considerable scrap, probably several times as much as that mentioned in these papers-without using any additional coke. This excess heat can be utilized with-out practically any serious mechanical and operating diffi-culties such as might be occasioned by removing gas from a point other than the top of the furnace. I do not think, scrap has any effect on the iron, although I think some foundrymen are trying to prove that it has, and perhaps some open-hearth men may have that idea.

Jan 1, 1927

By D. O. Noel, E. B. Gebert, J. D. Shaw

IT. is, of course, expected that manufacture of the various metal powders should involve numerous methods adapted to the specific characteristics of the metals themselves. Several methods for powdering a particular metal may be available, but the physical characteristics of the powder as produced by the several methods may be quite different. In the final analysis, the application of the metal powder dictates the physical properties that the metal powder must possess, and this, to a very large extent, will determine which of several possible methods of. manufacture is adopted. Sometimes powder of the same metal is produced by more than one method, each powder having specific characteristics .that make it particularly suitable for its application. For purposes of classification, the various methods of powdering metals can be grouped as follows: 1. Machining. 2. Milling (by ball mills, stamps, attrition mills, etc.). 3. Shotting (pouring molten metal into water, air, etc.). 4. Granulation (by stirring molten metal while solidifying). 5. Atomizing (disintegrating by steam, compressed air, etc.). 6. Condensation of metal vapor. 7. Reduction of oxide powders. 8. Chemical precipitation. 9. Electrolytic deposition. 10. Sintering (for producing alloy powders). 11. Formation of an alloy followed by dissolving or otherwise removing one of the alloying constituents. MACHINING Turnings, cuttings, filings, etc., are, of course, produced as by-products in machine work of various kinds, and find certain applications as metal powders. For example, iron powder so produced is used extensively as a reducing or precipitating agent and as a constituent in certain hard-finish cements.

Jan 1, 1938

By Brij M. Moudgil

Disposal of fine coal refuse is one of the major technical problems which could adversely affect growth and development of the coal industry. At present one of the most: common methods for disposal of fine coal refuse slurry involves impounding the slurry behind dams. However meeting new federal and state government regulations for building, maintaining and reclaiming these impoundments in addition to terrain and space considerations render this technique to be only marginally competitive with other disposal methods. The coal industry has been actively engaged in developing alternate disposal techniques which are economically feasible and environmentally acceptable. A review of coal refuse disposal problem and current refuse disposal practice both in the eastern and western coal fields is presented. Various promising techniques being developed for economical and safe disposal of fine coal refuse slurry are also discussed.

Jan 1, 1980

By P. W. Bakarian

PREVIOUS determinations1,2,3 of the texture of magnesium and its alloys have shown only slight variations in the principal features of the structure. This investigation presents pole figures for magnesium and two of its alloys, in which differences of some magnitude will be shown. Schmid and Wassermann have considered the texture of magnesium in analogy with that of zinc-also a hexagonal lattice. Whereas the zinc texture is said to be derived primarily through basal slip and secondarily through {102}† twinning, the {102} twinning is considered impossible at the later stages of the rolling in magnesium because of its smaller axial ratio. This state of affairs appears reasonable for pure magnesium, but for alloy textures the situation is more complex. A double orientation similar to that found in zinc has been reported by J. D. Hanawalt,4 and the addition of small amounts of calcium to magnesium and its alloys to produce a double texture was noted by J. C. McDonald.5 The pole figures of this investigation, using an improved X-ray technique, show these various textures. The dependence of directional properties of rolled sheet on modifications of texture is well recognized. Correlation of physical properties with existing texture should be even more significant if quantitative valuations are attached to the various areas on the pole figures. Such a quantitative technique is developed herein. EXPERIMENTAL METHOD Two alloys were used, besides high-purity magnesium. In each case, the metal was extruded to bars 32 in. thick and hot-rolled to a thickness of about 0.075 in. It had been established previously that such a reduction was more than sufficient to eliminate the extruded structure. The rolling proceeded in the same direction as that of the extrusion, without any cross rolling. The temperatures corresponded to normal commercial practice, averaging around 600°F. A unique method of preparing the sample was developed in this work. Instead of using a flat specimen, a stem of the metal was cut out of the rolled sheet in the desired direction (rolling direction) as shown in Fig. 2. From a sheet of 0.075 to 0.065-in. gauge, the stem was cut to a square cross section with a jeweler's saw, rounded with a file and polishing paper to a diameter of 0.060 in, and evenly etched in dilute hydrochloric acid to a diameter of 0.038 ± 0.001 in. In this way, a cylinder of the original sheet with its axis in the desired direction was produced. By using this type of specimen for the pin-point pictures, any variance in the absorption of the diffracted beam at the various angular settings of the specimen, was completely eliminated.*

Jan 1, 1941

By E. J. Roberts

Prior to 1916, thickening was an art, and any accurate decision as to what size of machine to install to handle a given tonnage of a specific ore must have been one of those intuitive conclusions, based on both intimate and extensive acquaintance with thick-ners and ore pulps. Then in 1916 "knowledge of acquaintance," became "knowledge about" with the publication of the Coe and Clevenger paper.' The unit operation of thickening had graduated to the status of an engineering science. The fundamental similitude relationships for the two major phases of the operation were defined so clearly that batch tests on models as small as liter cylinders could serve to specify protypes as large as 325 ft in diameter. It is quite apparent from reading the literature that Coe and Clevenger's contribution is not generally appreciated. In so far as the basic engineering relationships are concerned, the only real advance which has occurred in the 30 odd years which have elapsed since the Coe and Clevenger paper is the recognition of the effect of the rakes on the thickening process. Bull and Darby2 noted this in 1926, and the extensive use of the "gluten type" thickener, in which the effect is magni-fied, bears witness to its importance. Comings3 further verified this effect of the rakes. As a matter of fact, a number of papers show an apparent regression from the Coe paper in that the area determinations are made on the basis of a single test from One concentration of solids. Coe and Clevenger amply demonstrated that this is unsafe, since the controlling zone may be one other than that of the feed dilution. Comings3 neatly demonstrated this without apparently realizing it. Of course there have been significant advances in the application of the operation to industry. Open tray thickeners were introduced to save area; balanced tray thickeners, washing thickeners, and multifeed clarifiers were developed with all of their special hydraulic and mechanical problems. Combinations of all kinds have been introduced, such as combination agitators and thickeners, combination flocculators and clarifiers, combination thickeners and filters. With the establishment of the operation on a firm engineering foundation, installation was facilitated and expansion proceeded. There are still problems, of course, functional as well as mechanical. Sometimes the moisture in the underflow obtained in practice is not as low as is expected on the basis of the test data. Sometimes the underflow is so "thick " that its discharge and subsequent handling requires special attention. Island formation plagues some operators. The use of the thickener as a surge basin and blending tank in the cement industry poses unusual problems. Design of rakes and the drive mechanism must be continually im-proved. Corrosion problems must he overcome. Power requirements for raking the settled solids occasionally is the controlling factor as it was in the case of the all American Canal desilting installation. Other similitude relationships and design problems come into the picture when we enter the field of clarification or nonline settlement. We have an energy dissipation problem in introducing the feed and any models must satisfy the Froude model relationships. Autoflocculation requires detention which involves the same similitude laws that we encounter in the compression zone. Approach to an Exact Science The next step beyond having control of the similitude relationships is to understand the why of these relationships right back up the line to first principles. The ultimate might be that, if given the mineralogical composition of the solids and their size distribution together with an analysis of the suspending liquid, we could calculate the entire thickening behavior of the system. Then we could say we had reduced the operation to an exact science. True it might be more trouble getting this basic analytical data than to make our empirical determinations for area and volume, and we would need an ENIAC to calculate the results, but that does not detract from the desirability of such understanding. Considerable work has been done by the chemical engineers with this end in view. Comings,3 Egolf,4 Work,5 Kam-mermeyer,6 Steinour,7 and others have studied the problem. The writer has no final answer to the thickening story but would like to propose a picture of the mechanics of the two phases of thickening which has been found useful in understanding the subject and which leads to some convenient relationship in treating the compression step and arriving at the compression depth.

Jan 1, 1950

By W. C. Knopf, G. Samsel

For several years International Minerals & Chemical Corp. has used a radiation method to assay potassium content of products from potash and feldspar beneficiation. The procedure is rapid, accurate, and inexpensive and is easily handled, if necessary, by nontechnical personnel. Data are presented to show the accuracies that may be expected if the technique is used for control of pilot plants or large- scale plants. Natural potassium is composed of three isotopes -K39, K40 and K41. Five other isotopes, artificially produced, have been detected. In natural potassium only the K40 isotope, with a half life of 1.4 x 109 years, is radioactive. Its modes of decay are beta and gamma rays, positrons, and x-rays. Only the more abundant beta rays, however, are important in radiation measurements using geiger tubes.

Jan 10, 1958

By Gerald Edmunds, R. K. Waring, E. A. Anderson

Brass is liable to failure under the combined influence of stress, certain corrosion media, and time, a phenomenon commonly termed season cracking or stress-corrosion cracking. The consequences of this are serious in applications of brass generally, including the important field of cartridge cases. Cartridge cases (70 Cu: 30 Zn) that fail from this cause may allow the escape of gas from the gun breech, a hazard to the shooter, and may not eject, thus temporarily putting the gun out of action. In loaded cartridge cases, the stress present is partly residual from the, drawing and necking operations and partly applied by the insertion of the projectile. Ammonia, present as a decomposition product of smokeless powder, air and moisture constitute corrosive media. The prevalence of season cracking has been reduced considerably, but not eliminated, during the past quarter of a century by low-temperature annealing to relieve stresses residual from fabrication, a method suggested by Diegel 38 yr. ago(I).2

Jan 1, 1945