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By H. L. Washburn, G. L. Judy

DURING recent years thermal drying of fine coal has increased at a tremendous rate, but very little discussion of the several excellent units has found its way into print. This is particularly true for operating and maintenance costs, and the operator who is faced with his first fine coal drying installation must depend chiefly on hearsay when trying to determine what his drying costs will be. This article presents the maintenance and operating costs for the seven drying units now installed in preparation plants of Pittsburgh Consolidation Coal Co. and lists other cost information that should be obtained before any particular drying unit is selected.

Jan 10, 1957

By Orson Cutler Shepard

RECENT research work in the flotation concentration of minerals has been concerned mainly with flotation reagents and the mechanism by which collecting reagents are held to the surface of certain mineral particles. The fundamental question of why air bubbles cling to properly prepared mineral surfaces is usually dismissed with the statement that the surface is air-avid or water-repellent. In my article in MINING AND METALLURGY for June, 1932, I showed theoretically that surface tension relationships govern bubble attachment in Rotation. This explanation has not been accepted by many; probably be¬cause the difficulty of measuring solid-solution surface tensions prevented obtaining experimental evidence. If the surface tensions involved in the system [solution, mineral, air bubble] are responsible for attachment of the air bubble to the mineral, any change in the surface tensions should cause a corresponding change in the attachment of the air bubble. An example in which the mineral-solution surface tension could be varied was found with mercury. When mercury is in contact with solutions of certain electrolytes the surface tension at the contact of mercury and solution can be altered by electrical polarization of the mercury. The surface tension rises to a maximum as the mercury is given an increasing negative potential and then decreases with further increase in potential. The theoretical relation between the surface tensions and the attachment of an air bubble is given by the following equation:

Jan 1, 1936

By Marshall D. Himes

The Pima mine, Pima County, Ariz., a 53,500-tpd copper mine, is located 17 miles south of Tucson, Ariz. The mine is in a sequence of Paleozoic and Mesozoic sediments striking east-north-east and dipping southeasterly. These sediments are intruded by a Tertiary quartz monzonite porphyry. The Paleozoic Permian (?) dolomites, limestones, and sandstones have been altered to calc-silicate skarn, marble, and quartzite. The overlying Mesozoic Triassic (?) clastic sediments have undergone some recrystallization and hydrothermal alteration. The clastic metasediments are divided into three distinct lithologic units: lithic arenite, arkose, and interbedded and overlying black argillite. Three types of hydrothermal alteration in the clastic rocks are propylitic alteration (epidote, chlorite, and quartz, with or without sericite), quartz-sericite alteration, and potassic alteration (K-feldspar, quartz, and sericite, with or without chlorite and calcite). The porphyry has undergone potassic alteration. Dominant structures are an east-west postmineral fault in the western part of the pit, and strong low angle faulting and shearing which truncates the ore body at depth. The two joint sets, one parallel to bedding and the other at right angles to bedding are prominent in the mine. Faulting is in two dominant directions, one striking northwest, dipping northeast, and the other striking northeast, dipping northwest. Economic mineralization is prediminantly disseminated pyrite and chalcopyrite, and molybdenite-quartz veinlets. There are less important amounts of magnetite, hematite, sphalerite, galena, tennantite, and bornite. Mineralization is believed to be both structurally and chemically controlled.

Jan 1, 1974

By Andrews Allen

THE large increase in the wages of mine workers makes it imperative that all factors tending to limit production per miner be eliminated, if possible. The trolley and storage-battery locomotive, mining machine, hoisting engine, mining system, etc. have increased the possible output per man. But this output is still limited by the capacity of the hoisting engine and cable and by the size of the mine car. The superiority of skip hoisting in metal mining is shown by its almost universal adoption. By varying the size of skip and the rope speed, any desired hoisting tonnage can be secured and, since only one kind of material is handled and breakage is unimportant, the loading of the skips can be easily and cheaply effected from bins into which the cars are dumped. The cars may then be designed to fit the conditions in the mine instead of being a compromise between hoisting and mining conditions, very likely suiting neither. In coal mines, the usual practice has been to hoist the car to the surface, either on platform or self-dumping cages. Of late years the number of skip-hoisting plants in coal mines has been rapidly increasing, but there is more or less inertia to overcome in establishing so radical a change in practice; also the earlier skip operations were not uniformly successful. As a result, it became evident that metal-mining practice would require radical modification before skip hoisting could be successfully used in coal mining.

Jan 2, 1921

By R. Woodward Moore

A GRAPHICAL method of analyzing the data obtained from shallow earth-resistivity depth tests is presented. The method is based upon empirical results and has no theoretical basis. The usual apparent resistivity-electrode spacing curve is used together with a cumulative resistivity-electrode spacing curve plotted on the same sheet. The greatly reduced scale required for plotting the cumulative values of resistivity together with the effect of the summation of the individual resistivity values serves to minimize the effect of purely local surface anomalies and inadvertent errors of measurement. The point of intersection of tangents or straight lines drawn to intersect at zones of maximum curvature in the cumulative curve indicates the depth to the underlying material. Numerous figures are presented in which data from published reports and from recent field studies are analyzed and the results compared with actual depths established by borings or with depth values obtained by the use of theoretical methods of analysis. Smoothly rounded curves of apparent resistivity such as are often obtained in the field, and which have been a serious drawback to attempts to analyze the data empirically heretofore, appear to be susceptible to rather accurate analysis by the method described. The method is best suited to analyses involving shallow two-layer formations. It has been applied successfully, however, in analyzing the data obtained from tests made over shallow three-layer formations. As with most empirical methods, its chief advantage is its simplicity and ease of application.

Jan 1, 1944

By J. R. Finlay

Every business man who has reached the age of forty, or perhaps even thirty, must know from his own experience that there are occasional periods of "good times'' and others of "bad times "-booms and panics. Those who give to business some complexion of science have invented a semiscientific name for these alternations-the business cycle-indicating that it is a normal phenomenon which by its own nature repeats itself. The longer one lives and the more one enlarges his own experience by the study of history, the more of these cycles he knows and the more disposed he becomes to take their recurrence for granted. If these alternations can be put into the category of common- places, why not treat them as such? We are in a sharp depression right now, why worry about it? Is there not a certain average value for business that can be depended upon in spite of depressions? By way of rejoinder one might answer that war is the great commonplace of history, but when we get into one we generally find it worthy of attention. In the present case, many a man has lost two-thirds of his income, and he is extremely nervous about finding it again. The Southern Pacific Railroad earnings have dropped 75 per cent in the past year; Pennsylvania, 60 per cent; United States Steel Corp., about the same. The drop in current earnings is

Jan 1, 1932

By Frederic H. Wright

The secondary metals industry might well be defined as the group of remelters, smelters, refiners, and manufacturers that convert scrap metals or residues to commercial forms. In this industry, scrap metals and residues are processed to pro- duce refined metals, ingot alloys, fabricated shapes, and chemical products. Secondary metal is defined as metal recovered from commercial scrap, that is, scrap that has entered the processor's plant in scrap form. Metal recovered by a manufacturer from "home scrap" generated in his own plant is not considered to be secondary, because it represents part of the original stock that simply requires additional treatment before emerging as a finished product. In any economic study, a basic point of measurement must be chosen, and in the case of secondary metals, the melting pot or its counterpart represents the stage in which metal is converted from scrap to some more usable form. Beyond this point there is often no means to distinguish between secondary metal recovered from scrap and virgin metal produced directly from ore. In the last fifteen or twenty years the secondary metals industry has grown to major importance. Some consumers distrust secondary metals, but frequently this distrust serves only to prove an inability to keep up with the times. A rapidly decreasing number of manufacturers like to boast that they use only virgin metals, but a little investigation would show them that more than one third of all

Jan 1, 1943

By Eugene Coste

In a recent paper' I took exception to the opening paragraph of Mr. Hill's paper, in which he says:— " In endeavoring to interpret the geological occurrence of oil, the geologist is confronted by the fact that science has not yet solved the problem of its origin, which lies at the root of the subject.... For the present we must consider oil as a material in the rocks, the origin of which is still unexplained." I take this occasion to repeat my objection to the above statement, as well as to the similar statement of Mr. C. W. Hayes and William Kennedy in their recent bulletin2 on the same oilfields :—" The origin of petroleum is one of the most obscure problems by which geologists are confronted." I do not hesitate to say that these statements, which claim we know so little to-day of the origin of petroleum, are not warranted in the present state of geological science, and that, on the contrary, geology can to-day most clearly prove the origin of oil to be inorganic and the result of solfataric volcanic emanations. It has been so long assumed that oil or bitumen is due to the decomposition of the organic remains of the sedimentary rocks, that the words organic and bituminous are used synonymously and, accordingly, without attempt at explanation, the origin of oil is in every case ascribed to some bituminous-shale horizon, more or less full of organic matter. Such falla

Jan 1, 1905

By Victor Lenher

The interest shown recently in selenium and tellurium has brought many requests for an assembling of the analytical chemistry of these two elements. The intention of this paper is to discuss all of the chemical principles utilized in the detection and quantitative determination of these elements, as well as to describe the works methods actually followed by producers of tellurium and selenium in the United States. These methods have been furnished by S. Skowronski of the Raritan Copper Works, H. D. Greenwood of the United States Metals Refining Co., F. F. Colcord of the U. S. S. Lead Refinery, and E. W. Rouse and A. E. Hall of the American Smelting and Refining Company. Occurrence Selenium is found associated with sulfur, to which in many respects it is quite similar. Occasionally deposits of native sulfur, notably those in the Lipari Islands, Kilauea, and Japan, show a red-brown coloration, I which is readily distinguished from that of other sulfur; this red-brown * sulfur contains a small amount of selenium. Not infrequently, the , sulfides of the heavy metals are accompanied by selenium and tellurium, • presumably as selenides and tellurides. The Scandinavian pyrite, which is one of the large sources of European sulfuric acid, when roasted has fur- - nished a large part of the selenium that has come to the United States; it I was in flue dust from the roasting of Scandinavian pyrites that the element was discovered by Berzelius in 1817. Greek and Spanish pyrites also

Jan 1, 1923

By Victor Lenher

The interest shown recently in selenium and tellurium has brought many requests for an assembling of the analytical chemistry of these two elements. The intention of this paper is to discuss all of the chemical principles utilized in the detection and quantitative determination of these elements, as well as to describe the works methods actually followed by producers of tellurium and selenium in the United States. These methods have been furnished by S. Skowronski of the Raritan Copper Works, H. D. Greenwood of the United States Metals Refining Co., F. F. Colcord of the U. S. S. Lead Refinery, and E. W. Rouse and A. E. Hall of the American Smelting and Refining Company. Occurrence Selenium is found associated with sulfur, to which in many respects it is quite similar. Occasionally deposits of native sulfur, notably those in the Lipari Islands, Kilauea, and Japan, show a red-brown coloration, I which is readily distinguished from that of other sulfur; this red-brown * sulfur contains a small amount of selenium. Not infrequently, the , sulfides of the heavy metals are accompanied by selenium and tellurium, • presumably as selenides and tellurides. The Scandinavian pyrite, which is one of the large sources of European sulfuric acid, when roasted has fur- - nished a large part of the selenium that has come to the United States; it I was in flue dust from the roasting of Scandinavian pyrites that the element was discovered by Berzelius in 1817. Greek and Spanish pyrites also

Jan 1, 1923

By Stefan Boshkov, Malcolm T. Wane

THE validity and accuracy of velocity measurements underground have been questioned repeatedly by those in mine ventilation work. The general disagreement on the subject is well illustrated in an AIME publication.' Although the presence of errors is readily admitted, their magnitudes are not known and often are described by practical operators merely as "great," "small," or "of no importance." The belief that errors are of academic interest only prevails because of a justifiable claim that actual volumes of air circulated are well in excess of those required by law and safe mining practices. Poor understanding of the source and nature of errors inherent in velocity measurements, coupled with questionable determination of cross-sectional area, result in faulty techniques for the purpose of expediting ventilation surveys and render doubtful the calculated volume. Often consistency of readings is confused with accuracy. A succession of check readings showing a maximum deviation of 5 pct in the measured value of velocity usually signifies nothing more than diligent application of technique in a stable ventilating current. This article discusses the errors involved in air measurements underground. Where instrument errors are presented, the treatment is confined solely to the rotating-vane anemometer, recognized as a most useful ventilation measurement tool because of its simple design and easy operation. In the following pages a positive deviation is defined as one which has to be added to the registered air velocity to obtain the true air velocity.

Jan 1, 1956

By George W. Maynard

In the course of an examination of some of the California hydraulic mines in November last, I visited the property of the Gold Run Ditch and Mining Company, near Dutch Flat, Placer County. This is one of the most important and extensively worked mines in the district. The gold occurs in the characteristic blue gravel, which averages 175 feet in thickness, the lower 40-60 feet being made rip of cement gravel, which resists the action of water, and can only he loosened by blasting. The specimen which I have the pleasure of laying before the members was presented to me by Mr. I. L. Gould, the intelligent superintendent of the mines, who informs me that he found it in the old river channel, about twelve feet above the bedrock. The flattened water-worn nugget of gold, about the size of a kidney-bean, is imbedded in blue cement gravel, around which quartz has crystallized. When found the projecting portion of the nugget was enveloped in quartz, the core of gravel and gold having only been discovered after breaking the lump of quartz. On the quartz there is a shell of cement. The specimen is a remarkable confirmation of the theory of the deposition of quartz from solution. DISCUSSION. Dr. T. STERRY HUNT, in commenting upon this occurrence, remarked that it is in accordance with what we already know of the recency of some of the quartz of this region, and cited the microscopic

Jan 1, 1880

By George W. Maynard

IN the course of an examination of some of the California hydraulie mines in November last, I visited the property of the Gold Run Ditch and Mining Company, near Dutch Flat, Placer County. This is one of the most important and extensively worked mines in the district. The gold occurs in the characteristic blue gravel, which averages 175 feet in thickness, the lower 40-60 feet being made tip of cement gravel, which resists the action of water, and can only be loosened by blasting. The specimen which I have the pleasure of laying before the members was presented to me by Mr. I. L. Gould, the intelligent superintendent of the mines, who informs me that he found it in the old river channel, about twelve feet above the bedrock. The flattened water-worn nugget of gold, about the size of a kidney-bean, is imbedded in blue cement gravel, around which quartz has crystallized. When found the projecting portion of the nugget was enveloped in quartz, the core of gravel and gold having only been discovered after breaking the lump of quartz. On the quartz there is a shell of cement. The specimen is a remarkable confirmation of the theory of the deposition of quartz from solution. DISCUSSION. DR. T. STERRY HUNT, in commenting upon this occurrence, remarked that it is in accordance with what we already know of the recency of some of the quartz of this region, and cited the microscopic

Jan 1, 1880

The income of the Institute is derived mainly from dues, advertising in MINING AND METALLURGY and sale of publications. These sources fortunately are supplemented by the interest from invested funds now amounting to over $500,000, a considerable portion constituting endowments for special purposes. Aside from the medal funds the principal endowments are the James Douglas Fund for support of the Library, the Charles Hayden Memorial Fund, designated to further the education of Student Associates, the Rocky Mountain Fund, and the Seeley W. Mudd Memorial Fund. The income from the two last named is available for the support of research and a variety of other purposes. It is allocated by the Board of Directors upon recommendation of standing committees in each case. An active effort is being made to increase the endowment funds of the Institute through a standing, committee, of which H. T. Hamilton is chairman, and of which the other members are: W. H. Aldridge, George D. Barron, Cleveland E. Dodge, Henry Krumb and J. V. W. Reynders. This committee feels that there exists a tremendous opportunity for the Institute to be of ever-growing service to the public, to the mineral industries, and to the profession. It welcomes suggestions as to names of men of means who are vitally interested in the mineral industries, and to whom the opportunity to make a contribution or bequest might appeal favorably if presented in the proper light by the committee.

Jan 1, 1940

By Arthur Flagg

(New York Meeting, February, 1913.) THE Elk City mining district of Idaho occupies a position near the geographical center of Idaho county, a region of mod¬erate elevation in the western foot-hills of the Bitter Root mountains. The district comprises an area of approximately 350 sq. miles, bounded oil the west by the Newsome district and on the south by the Dixie and Oro Grande districts. There are no mining districts to the north or east. Elk City, the principal town and the seat of the mining office for the district, is situated in a hydrographical basin surrounded by low hills. The elevation is 4,200 ft. above sear level. Through this basin flow Elk Creek, Red river, and American river, which unite west of town to form the south fork of the Clearwater. The one township is set out from the Bitter Root Forest Reserve. Though a railroad starting from the Stites terminus of the Clearwater Short Line of the Northern Pacific railroad has been under consideration for some years, the camp is yet with¬out railroad facilities. The projected road would follow the south fork of the Clearwater on easy grades, but would be very expensive to build and maintain. While such a road would greatly benefit those who are now operating in the camp, and in a slight degree stimulate interest in its possibilities, there is hardly business enough to warrant its construction.

Jan 4, 1913

By E. J. Roberts, E. B. Fitch

Most classifiers in use today are, in function, settling pools. A fluid suspension of particles is passed through a pool at such a rate that only a fraction of the particles-the coarser fraction-has time to settle out of suspension. The rest are carried on out of the pool as overflow. The most fundamental way in which such classifiers differ is in the mechanism used to remove the settled particles from the pool. The particles may gravitate from the pool, as in the various sand cones, or they may be conveyed mechanically from the pool by drags, spirals, or reciprocating rakes. The mechanism of settling pool classification and its limitations are discussed. A method for calculating countercurrent classifications is presented. The practical validity of the calculation method has been confirmed through 20 years of use within The Dorr Co. During this time it has been used on diverse feeds and has been checked against many types of settling pool classifiers, with close agreement in nearly every case. Excellent elimination of third critical mesh particles and finer ones may be obtained in a countercurrent classifications series where all stages separate at the same mesh, but elimination of first and second criticals is inherently limited. Spectacular elimination of all criticals may be obtained by arranging successive stages to classify at successively coarser mesh. Improvement in elimination is obtained at the cost of an increased internal recirculation, but this may be tolerable in many cases.

Nov 1, 1956

By R. S. Shoemaker, F. W. McQuiston

ECOLOGICAL CONSIDERATIONS IN CYANIDATION PLANT PRACTICES Ecological controls of tailing storage pond effluents are mainly concerned with mercury and residual cyanide and are critical problems for gold and silver recovery plant operators. For example, mercury for direct amalgamation of gold ore was used at Homestake until 1970 when the Federal Government acted to prevent further use thereby forcing the abandonment of this practice. However, mercury is still used at Homestake, in South Africa, and also in some Philippine and Canadian cyanide plants for barrel amalgamation of free gold gravity concentrates. The amount of mercury involved in South African practice is about 150 ounces for every 100,000 tons of ore milled and which reaches the tailings ponds. In South Africa, it is obligatory that no pond effluent be discharged beyond the mining property boundaries and waters containing mercury and cyanide must be evaporated either on the tailings pond or in specially constructed evaporation dams. In some cyanide plants such as Carlin and Cortez in the United States, all supernatant solution from the tailings ponds are returned to the plant for reuse. When all solution cannot be reused, the excess may be evaporated in shallow ponds, or by spray systems inside of the tailings dam. Such plant reuse of tailings effluent depends strictly upon the degree of contamination or "fouling" of the barren solution and tailing water with cyanicides. Foul solutions that cannot be returned from the tailings pond may be effectively cleaned up by cyanide regeneration. Cyanogens in plant solutions exist chiefly as free alkali cyanides, as zinc and copper double cyanides, as sulphocyanides, and as ferrocyanides. From the free cyanides and zinc double cyanides, substantially complete recovery of the cyanogen is easily effected. Part of the cyanogen combined with copper is also recovered; regeneration of the remainder with the cyanogen existing as sulphocyanide and ferrocyanides requires special treatment. At this stage, it would be generally more practical to eliminate the remaining cyanogen by chlorination. Ecologists have also been concerned with pollution of ground waters from cyanidation plant tailings. An accute problem is solution seepage down stream from tailings dams and strict attention to prevent or collect any seepage is a real necessity. The tolerance levels of the total cyanide content in potable water set by several U. S. and State health agencies are 10 ppb, and 20 ppb discharged into ground waters. The cyanide content so established is, strangely enough, based on the survival tolerance of fingerling trout. Decanted waste water from tailings dams may be effectively treated by the use of alkaline chlorination for the purpose of destroying all cyanide compounds. The alkaline hypochlorite used to oxidize the cyanide to cyanate is applied as such or generated within the waste solution by adding caustic (NaOH) and chlorine gas. A second chemical reaction involves complete destruction of the sodium cyanate.

Jan 1, 1975

During the past 60 or 90 days, the metropolitan newspapers have published much concerning unemployment throughout the nation and the efforts of the Army and various other bureaus for finding work for the returning soldiers. The United States Employment Service has 2000 bureaus throughout the country, which Nathan A. Smyth, Assistant Federal Director, states have placed more than 2,400,000 persons in employment. The Engineering Societies Employment Bureau, which, since December, 1918, has been endeavoring to put all returning engineers in touch with employers who need efficient men, has produced results that are very gratifying to the Secretaries of the four Founder Societies under whose direct management the Bureau operates. During this period, 1615 men have registered at the Bureau's office in the Engineering Societies Building; not all of these, however, are unemployed. Many are ex-army and navy men, who in passing through New York on their way home, look over the field in the hope of making a change for their own benefit before returning to their former positions. During this period, 427 positions vacant have been filed, 2300 of which positions have been filled from the men registered. The letters mailed by this Bureau amount to about 1000 a month and the number of personal calls at the office, 1600. The lowest number of positions filled has been in mining, but the lowest number of registrations is also from mining men. While in February idleness throughout the nation was increasing at the rate of 35,000 a week, under date of Mar. 7, Arthur Woods, a special assistant to Secretary of War Baker, states that there is a material improvement in the unemployment situation and that the problem is no longer a serious one. It is recognized that' the improvement wrought in each individual by his military training and experience has so increased his value that it is 'not only unfair, to ask these men to accept their old jobs at the old wages, but it is probably very unlikely that they will be willing to do so. This plain statement of improvement may not carry conviction to everyone but a concrete example will show its validity. Take the example of a young man under 21, bright and intelligent, with only a high-school education who was employed, before being drafted, on purely manual labor. He shows up well under military training and is made a corporal; he makes good and is appointed a sergeant; and finally becomes top sergeant, which requires him in many ways to handle the entire company of 250 men. The result is; even if he has not been tried by the fire of battle, he comes out of the army with a feeling of self-confidence and capacity that was entirely lacking when he went in and he has had actual experience in handling a larger body of men than the average mine foreman at twice his age, and he has had twice the average amount of detail work to take care of.

Jan 4, 1919

By John Charles

The Engineering Method. By John Charles Lou11sbul.y Fish. Stanford University Press. 1950. 186 P. $3.-This book is about the "professional habit often referred to . . . . as 'the scientific method' . . ." It formulates for students the system of logic and reasoning that is the mark of the practicing engineer. The three chapters are, "The Method of Engineering", "Application of the Engineering Method" and "Uncertainties in Engineering." They cover logic and reasoning, terms, nontechnical problems, practical conditions controlling the engineering method, inescapable uncertainties and the method of coping with them. The author is emeritus professor of civil engineering at Stanford. The material presented here formed chapters 9, 10, and 11 of The Engineering Profession, by Hoover and Fish, second edition 1950. Elements of Ore Dressing. By Arthur F. Taggart. John Wiley & Sons, Inc., New York, 1950. $10.- A modern and practical introduction to the subject by the noted author of the Handbook of Mineral Dressing. The philosophy that a mill and all its parts comprise a single treatment process is a continuing theme in the book. Professor Taggart covers hand picking, screening, filtration, and electrical concentration. After introducing sedimentation, he takes up acceleration in free-settling, hindered-settling, sink-float, jigging, film and trough concentrators and shaking concentrators. A discussion of organic chemicals in flotation is followed by a detailed treatment of flotation. Final chapters deal with primary crushing, secondary crushing, grinding, transport, and controls and flowsheets.

Jan 3, 1951

By Raymond Sanford

IT IS difficult to know just when a hoisting rope should be removed from service and a new one substituted. It is desirable to utilize the full life of a rope but, on .the other hand, the damage and possible loss of life, resulting from delay in replacing it may amount to many times the cost of a new rope. In the present methods of inspection the inspector must rely upon accumulated experience and a certain sixth sense or intuition in addition to any rules that may be laid down regarding the number and distribu-tion of broken wires. This condition does not neces-sarily arise from lack of interest among users or makers of rope, but is due rather to the lack of satisfactory or adequate methods for testing ropes to determine their exact condition. The main difficulty in devising a physical test lies in the fact that a number of causes, all operating in different ways, contribute to the deterioration of a rope in service, and affect not only the external conditions but also the inner structure of the material of which the rope is constructed. Wear and broken wires on the outer part of the rope are not difficult to detect, but a test is needed which will clearly indicate the presence of broken wires in the interior portions and the change in strength due to alterations in the structure and properties of the material itself.

Jan 7, 1923