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By C. Golumbic

Most early research on solvent extraction of coal has been concerned with the molecular structure of coal. Although rush work is continuing, practical aspects of the subject also are being emphasized. For example, development of the Pott-Broche extraction process resulted from the discovery of very efficient solvents for the pressure-extraction of coal. Recently, Orchin and Storch reported the use of even more efficient solvents under similar conditions. In addition to the discovery of more effective solvents, the possibility of efficient extraction at atmospheric pressure is obviously of practical interest. H. J. Rose observed that phenanthrene at its atmospheric boiling point readily dispersed 80 percent or more of Pittsburgh-bed bituminous coal. This fact served as the starting point of the present investigation, ill which determination of the chemical specificity of this solvent and the chemical nature of the resulting extracts was undertaken. This paper represents a progress report of the results obtained to date.

Jan 1, 1950

By M. Cohen, D. J. Blickwede

Quantitative observations concerning the carbide phases in high speed steel are of importance for two general reasons: (1) the carbides, being inevitable constituents of the final structure, exert a direct influence on the properties of the steel; and (2) a substantial proportion of the total alloy content is tied-up in the carbides, and hence the extent of their solution on austenitizing governs the composition of the steel matrix. The latter relationship has a vital bearing on the response of the steel to tempering as well as on its performance in subsequent service. Accordingly, in the course of a long-term study of the behavior of high speed steels, the authors were confronted with the problem of securing quantitative data on the carbide phases. The obvious method for acquiring such information is to isolate the car-bides from the steel and subject them to chemical, X ray diffraction and other measurements. There are well-known extraction techniques which involve the chemical or electrolytic solution of the less noble matrix (ferrite, marten-site or austenite), thus leaving a residue of the carbide phases. However, the results obtained must be scrutinized carefully1,2 since the carbides may be affected by the chemical or electrolytic action. It is the purpose of the present paper to describe the experiments leading to an electrolytic-extraction technique for quantitatively isolating the carbides from both I and hardened high speed steel. Particular attention is paid to the amount, as well as the composition, of the carbides so that the matrix analysis becomes ascertainable by subtraction from the overall steel composition. Illustrative results are given for the M-2 grade of tungsten-molybdenum steel. Review of the Literature The chemical method of dissolving the matrix selectively with respect to the carbides makes use of dilute non- oxidizing reagents such as hydrochloric or sulphuric acid. Although this simple procedure has led to the determination of the cementite composition,3,4 it achieved only limited success because of the interaction between the acid and the carbide residue. Some of the carbides may not only be destroyed in this way, but the hydrogen released is likely to remove part of their carbon as hydrocarbon gases. The electrolytic technique of isolating carbides has the advantage of rapidly dissolving the specimen (anode) in the presence of less reactive solutions than are practicable with the chemical method. This reduces the possibility of chemical attack on the carbides, and furthermore, the hydrogen evolved during the electrolysis is released at the cathode which is not in close proximity to the carbides. The common electrolytes adopted for this purpose are hydrochloric and sulphuric acids.5-l1 Aqueous solutions of ferrous salts have also been used.12,13 A considerable advance in experimental technique was introduced by Treje and Benedicks14 who developed a double-compartment cell for electrolytic extraction, the anode and cathode chambers being separated by a porous diaphragm. A solution of 15 pct sodium citrate, 2 pct potassium bromide and 1 pct potassium iodide was selected for the anolyte, while the catholyte consisted of a 10 pct solution of copper sulphate, with copper serving as the cathode. This type of cell has a number of desirable characteristics: 1. The anolyte has a pH value close to 7, at least at the beginning of the run. 2. The iron that dissolves from the anode-specimen forms a water-soluble complex ion with the citrate, thereby preventing the precipitation of iron hydroxide (which would contaminate the carbide residue) despite the neutrality of the solution. 3. Copper deposition instead of hydrogen evolution occurs at the cathode, and this avoids an increasing concentration of hy-droxyl ions which (in an otherwise neutral solution) might cause the precipitation of insoluble hydroxides. 4. Contamination of the anode chamber by copper sulphate is inhibited by the porous diaphragm. Houdremont and coworkers15 applied the above method (with the further refinement of excluding oxygen during the electrolysis, washing and drying) to the extraction of carbides from a series of plain carbon steels after various heat treatments. They had quantitative success only with specimens in the annealed condition, and concluded that the size and shape of the carbide particles play an important role in the isolation process, with large spheroids exhibiting the least tendency to decompose during the electrolysis. Up to the present time, the citrate double-cell has not been used to any extent for isolating the carbides of high alloy steels, apparently on the grounds that the complex carbides are more resistant than cementite to attack in the simpler acid electrolytes. In particular, Bain and Grossmann7 and Gulyaev10.10a have employed the hydrochloric acid cell for their investigations of the carbides in high speed steel.* It will be demonstrated here that this type of cell is capable of yielding quantitative results in the case of high speed steel, and actually has certain advantages over the more complicated double cell. However, in order to provide a rigorous test of the quanti-tativeness of electrolytic procedures for the problem at hand, both methods were studied in considerable detail.

Jan 1, 1950

By C. T. Anderson

In July 1947, the U. S. Bureau of Mines, in cooperation with the Air Materiel Command, started an investigation of zirconium alloys with the object of determining the suitability of such alloys for high-temperature applications. This report covers the preliminary study of about 25 zirconium-rich alloy systems with respect to preparation, fabrication, tensile properties, metallographic structures; constitution, and heat resistance. Obviously, each system could not be investigated thoroughly, and this publication can be regarded only as a first approach. The more promising individual alloy systems will be studied in greater detail and reported in subsequent publications. The study of zirconium alloys on such a scale has been made possible by the U.S. Bureau of Mines developments in the past 5 years On producing zirconium metal. This basic process is similar to that developed by Kroll for producing ductile titanium metal and consists essentially of reducing zirconium chloride by means of molten magnesium. The Northwest Electrodevelopment Laboratory at Albany, Oreg., has produced several thousand pounds of ductile metal in this manner and has a pilot plant producing over 300 pounds of metal per week. Alloys were prepared by melting Bureau of Mines zirconium and the best available grade of alloying element in graphite, with suitable provisions for preventing oxidation. The ingots were quartered longitudinally and sheath-swaged at 850° c. to 3/8-inch diameter rod. Two of those rods were send to Wright Field for room-temperature and 1,200° F. tensile properties. The remaining two sections were used for metallographic, hardness, heat-treatment, and heat-resistance studies. The salient features of this investigation are summarized in table 1.

Jan 1, 1950

By Worner H. K

Education has always been a topic to rouse the interest of mining and metallurgical engineers, but the recent activities of the Education Committee of the Australasian Institute of Mining and Metallurgy 1, 2, together with the moves throughout the Commonwealth to extend the field of technological education, have made the subject a very live one at the present time. The authors have felt it would be appropriate that on the occasion of the First Ordinary Meeting for 1950, in Victoria, some contribution should be forthcoming concerning the history, present status and possible future trends of mining and metallurgical education in this State. As for the past, the time approaches when there will be none having personal recollections of the beginning of Victorian mining schools or of the men who started them. As for the future, it is obvious that rapidly expanding metal-producing and metalconsuming industries will demand a greater output of competent graduates and diplomates. The era immediately ahead seems to be bristling with opportunities, but mining educators need to temper their enthusiasm for various policies and programmes with the realisation that they are helping to train men who will be leaders 15-20 years hence when the problems of industry and trials of life generally may be very different from what they are to-day.

Jan 1, 1950

By P. R. Tisot

This report discusses the waxes made from shale-oil wax distillate, a specific fraction obtained- from crude shale oil. The plate wax crystals Were exceptionally well suited to solvent extraction. Methyl ethyl ketone was the preferred dewaxing solvent.' The quantity of wax recovered at 32°F was 18.8 percent of the wax distillate, or 6.6 percent of the crude shale oil. The laboratory batch processes used for separating the wax from the distillate and subsequent refining were based .upon conventional petroleum methods. Three grades of shale-oil waxes were made and designated as crude, semirefined, and fully refined. The solvent-extracted wax consisted mainly of paraffin and olefin hydrocarbons. The physical Properties of the fully refined shale-oil wax were the same as er corresponded closely to those of Billy refined petroleum paraffin wax. Inasmuch as the crude and semirefined shale-oil waxes can be separated and refined in much the same manner as petroleum waxes, the cest of manufacture should be about equal to that for making petroleum paraffin wax. The cast of making a fully refined shale oil wax will be somewhat greater than for making .a fully refined petroleum paraffin, due to the loss of the oleofinic material from the shale-oil wax by acid treatment and the increased quantity of acid required for its removal. An analytical method for the determination of wax in shale-oil dietillates, a list of the physical properties that wore determined for the waxes, and the method for testing those properties are given in the appendix to this report

Jan 1, 1950

By E. A. Clarke

The vapor-phase section of the Coal Hydrogenation Demonstration Plant at Louisiana, Mo., was operated for the first time in April 1949. The run lasted only 10 days because of time limitation (pending plant dedication in May) and the small amount of charging stock available. The primary purpose of the operation was to break in and determine the operability of the equipment and to supplement the operators' classroom training with actual practice by operating the plant under mild conditions. A secondary aim was to obtain data on the hydrogenation of petroleum oil and lignite tar distillate at approximately 10,000 p.s.i. while making gasoline and Diesel fuel oil. Although the operations were carried out under conditions considerably below those used in the plant design, a great deal of experience and data was obtained. As it is not feasible at this time to conduct further vapor-phase operations on similar stocks, this report has been prepared to present and summarize the data obtained through this operation.

Jan 1, 1950

By Irving Hartmann

Rock-dusting of coal mines is a most important safety measure for preventing or limiting the propagation of explosions. The Bureau of Mines has recommended for many years that rock dust be distributed on the top, ribs, and floor of mine entries and other workings of all bituminous coal and lignite mines in sufficient quantities to maintain the incombustible content of the dust above the minimum requirements. Rock-dust barriers constitute a secondary safeguard used occasionally to complement generalized rock dusting at entrances to panels and side entries or at other locations. In general, rock dust can be applied effectively with modern rock-dusting machines. However, in thin coal beds, in certain back entries, and in some other areas, rock-dusting machines cannot be used conveniently. Furthermore, many small mines find the purchase of machines costly. In such cases, rock dust is not used at all, or else it is distributed by hand, a relatively slow and costly procedure. In recent years some coal mines have started applying rock dust with the aid of permissible explosives. This may be done in various ways. One method consists in placing a stick of explosive on the floor of a room or entry midway between the ribs and covering the stick with two bags of rock dust that are slit on top and set crosswise one above the other. The explosive is then fired, causing the rock dust to be distributed on the nearby roof, rib, and floor surfaces. The procedure is repeated at desired intervals until the entire area is rock dusted. The method is claimed to be rapid, safe, and inexpensive.

Jan 1, 1950

By B. W. Gandrud

In July 1948, the Bureau of Mines, United States Department of the Interior, in cooperation with the University of Alabama and mine operators, published Report of Investigations 4306, "A Combination Cleaning and Dewatering Process for Treating Fine 'Sizes of Coal, Preliminary Report In this report a new process, referred to as kerosene flotation; was described, and results of experimental work with the process Previous to the fall of 1947 were given, The contents of the report. were summarized on pages 19 and 20' as follows: In coal-preparation plants using wet methods of cleaning, the most difficult problem is the cleaning and dewatering of the "fines" from about 10-Mesh to 0. A combination proceed is now under investigation that shows promise of practically and feasibly solving this problem. The process is similar to froth flotation, but a generous quantity of kerosene is used as one of the reagents, and the feed is from approximately 10-mesh to 0 considerably coarser than the usual froth flotation feed. The kerosene and the coarseness of the reed result in a floated product that, under certain circumstances, can be dewatered satisfactorily by a simple process of mechanical squeezing, Squeezing is accomplished by means of an ordinary conveying' Auger-and trough assembly with a section of pipe easing at the outer end of the trough. The bottom of the trough and. casing is fitted with wedge-wire sections to permit escape of the water freed by the squeezing action of the auger. On account of the important role of the kerosene, the process has been referred to in this report as kerosene flotation. Up to now, the investigative work has been divided about evenly between the laboratory and commercial plants. Nearly all of the work has been done on sludges containing the solids from the underflow of dewatering screens. A few runs have been made on 10-mesh to 0: fines from raw coal, but in some of those runs the dewatering mechanism, failed to function.

Jan 1, 1950

Approximately half of all the fuel energy used in the United States is now pro-vided by oil and natural gas. A persistent and rapid growth in energy demand during the last 3 decades has been absorbed largely by the liquid and gaseous rather than solid fuels. In 1948 the energy provided by coal was substantially the same as in 1920. Meanwhile, the use of oil and natural gas each had increased fivefold. On a per capita basis, the change is more significant. Coal consumption has dropped from about 6 tons per person to 4-1/2 tons, while oil has increased from 4-1/3 barrels to 14-1/3, and natural gas from 7,500 cubic feet to about 35,000. These facts would have only academic interest if the United States had unlimited supplies of all fuels. However, while the Nation's reserves of coal are adequate to meet our needs for centuries, those of oil and natural gas appear limited. It is obvious, therefore, that the security of our liquid-fuel position would be greatly enhanced if the supply could be based in an increasing degree on solid fuels, such as coal/and oil shale, which make up more than 95 percent of our fuel reserves, instead of natural oil and gas. In addition, this would create new employment and help to stabilize the market for coal, which may be facing comparatively bleak prospects in the near future unless its position with respect to other fuels is improved.

Jan 1, 1950

The Third Session of the Forty-Sixth Meeting of the Rocky Mountain Coal Mining Institute convened at the Hotel Colorado, Glenwood Springs, Colorado, June' 20, 1950, at 9:30 a.m., G. E. Sorenson, President, presiding. PRESIDENT SORENSON: The meeting will come to order. To refresh your memory, I will read off the names of the people on the various committees. President Sorenson read off the names on the committees. Mr. Whiteside, do you wish to make an announcement? MR. WHITESIDE: Yes, I would like to 'say a word. .4s you know, this afternoon you will be on your own, and I think some would like to go to Rifle. I wonder if we could get a vote on that now as to how many would like to go to Rifle, as they at Rifle would like to know so they can provide conveyances. There seems to be about 14 or 16 that would like to go to Rifle.

Jan 1, 1950

By Edward Thomas

Note. - Securing mine roof through consolidating thin or otherwise incompetent strata to increase overall thickness of the immediate roof beam is a new method of roof support and control which has aroused great interest amongst mining engineers and which is now being experimented with and thoroughly investigated by the United States Bureau of Mines. A paper on Roof Bolting, illustrated by photographs and motion-picture films, will be presented by Edward Thomas, of the U. S. Bureau of Mines, at the forthcoming Annual Meeting of the Mining Society of Nova Scotia. In the following pages, Mr. Thomas describes the methods used in roof bolting as illustrated by the photographs that accompanied his paper. The photographs are supplied through the courtesy of the United States Bureau of Mines, whose willing cooperation with miners and mining engineers in Canada is very well known and even more greatly appreciated. This method of publishing Mr. Thomas's paper is adopted because few, if any, Canadian mining engineers have actually seen installations of roof bolts and it is felt that the best possible presentation of such an interesting subject through the medium of the Bulletin will be attained by publication of the photograps over explanatory captions. - Ed.

Jan 1, 1950

By Clarke P. E

At the end of the recent war, reports became available from Europe of the use of tungsten-carbide inserts in percussion rockdrill bits. These bits were used with small size rockdrills, so that the only advantage gained from the use of the harder, abrasion resistant, tungsten-carbide appears to have been the greater life of the bit. Larger machines, such as used in Australia in conventional practice, had to be discarded to protect the relatively brittle tungstencarbide inserts and the vulnerable bonding with the bit body.As it had been found in machine shop practice that some grades of tungsten-carbide had been produced with considerably improved toughness, it was decided by Gold Mines of Australia Ltd. that drilling practice with tungstencarbide bits warranted detailed examination under Australian conditions, and that drilling tests should be undertaken at Morning Star (G.M.A.) Mines N.L., for which it acts as General Manager and Consultant.These investigations progressed through three stages:1. Preliminary Investigations and Tests.When the investigations were initiated no commercial bits were available in Australia, and manufacture was commenced with improvised equipment from virtual scratch. These early tests indicated that the use of 3 in. bore rockdrills in conjunction with tungsten-carbide insert bits was a 'possibility, and that it was unlikely that a small bore...

Jan 1, 1950

For the purposes of this discussion it is assumed that contributors should express the thoughts that arise from their personal experience. So wide is the range of mineral deposits, and so varied the methods employed in their discovery and development, that no two geologists are likely to have been impressed with the same applications of their science. The author's own personal experience has been, during recent years at least, very largely concerned with the broader aspects of the employment of scientific method and geological knowledge to the problems of exploration and exploitation, for the guidance of the general public and governmental authority rather than of mine executives and directors. The view-point thus reached is likely to differ in many respects from that of men who are much more intimately concerned with the mining problems of a single metal or a single mining field, and for this reason a statement may perhaps supplement those from others whose experience has been markedly different.It may well happen that, at some not distant date in the future, when systematic and comprehensive instruction in economic geology is embodied in the courses- prescribed for mining engineers during their years of training, the author's comments will be quitesuperfluous; but at the present time they appear to him to call for expression.The Need for Training of Mining Men in Economic Geology.Contact over a period of many years with mining men who have had different kinds of training and experience has been convincing that there is a general reluctance to acquire a full rational understanding of the geological factors involved in exploratory and developmental problems. The correction of this attitude is regarded as vital to the industry and it is necessary to insist that the outstanding requirement of the present day is the utilization of all branches of geological, investigation in the field and the laboratoryby men who have had systematic and specialized training in these matters. The science of geology is many-sided, but is, nevertheless, whole and essentially indivisible. No one can afford to disregard any fraction of its content 'or any of its methods of investigation.The greatest advances have been made in the understarnding of the occurrence of mineral deposits by those whose knowledge Qfbasal principles, has been soundest, whose endeavour has been to ascertain all their relationships in space and time, whose attention to detail of all kinds has been keenest, and at the same time, whose capability to distinguish between major and minor features has been most marked.With the passage of the years and the accumulation of data from many lands, it has been possible to build up a great body of information regarding the primary deposition and secondary alteration of mineral occurrences, which is of the utmost value in guiding thesearch for new deposits to take the place of those that become exhausted. This heritage is due not only to the efforts of gifted in...

Jan 1, 1950

By H. C. Gunning

Introduction The invitation to contribute a discussion on some of the broader features of the mineral deposits of our Cordillera seemed acceptable enough when presented several months ago. More mature consideration has impressed upon me the difficulty of making any constructive or very helpful contribution in the short time available and with my limited inspiration. Dr. Lang deserves our real gratitude for his general paper of nineteen pages at the beginning of the Volume. Into it, with the help of two diagrams and seven tabular summaries, he has packed a lot of useful information and has analyzed along several lines the data of the Volume's twenty-eight detailed papers on our mines and camps. He has added additional facts from his own knowledge of the region. I am sure that, like myself and the whole fraternity, he feels especially grateful to the eleven company geologists who found time to contribute detailed descriptions of mines they have studied. The Regional Situation With the Jubilee Volume and two recent publications of great value from the Geological Survey, we are more up-to-date on Cordilleran geology than we have ever been. But I would like to emphasize that we still have but fragmentary information. Brief study of G.S.C. Map 932A will illustrate this. Our knowledge of the Rocky mountains is limited to two narrow sections along the main railway lines, a somewhat larger area from the border north along the Mesozoic coal-bearing basins, and some reconnaissance along Peace river and the Alaska highway. There is some additional information on old maps, particularly those by G. M. Dawson, but it is very much of the 'exploratory' type. The other mapped areas are chiefly in the accessible region south of 'fifty-one', in the central part adjacent to and spreading north, recently, from the Canadian National railway, and along the edges of the Coast Range.

Jan 1, 1950

By Holmes, George H. Jr.

The Cherry Creek tungsten district was explored by the Bureau of Mines from April 16 to August 13, 1942. This district is in north-central White Pine County, Nev., 50 miles north of Ely. Principal work was done on the property of the Cherry Creek Tungsten Mining Co. and at the adjacent Chance mine, although the entire district was examined and mapped. The exploratory work was done in cooperation with the Federal Geological Survey and comprised surveying, trenching, sampling, long-hole and core drilling, rehabilitation of mine workings, road building, drifting, and shaft sinking. The more important tungsten occurrences were explored by trenching and diamond drilling. Sixteen holes, having a total length of 2,515 feet, were drilled. The project resulted in partial development of three new tungsten deposits and small increases in the reserve tonnage of two scheelite-bearing lenses that were being mined by the company. The following pages summarize the history of the district, outline the ownership of the properties explored, and describe the physical features and mineral deposits. Mining and milling practices at the Cherry Creek tungsten mine are outlined, and the plan and results of project work are presented in detail together with surface maps, assay maps, and drill-hole logs.

Jan 1, 1950

By M. G. Driessen, H. E. Criner

Possible applications of cyclone thickeners for: (1) clarification of the washery water and, (2) recovery of fine coal from the plant bleed. The paper shows: (1) that it is possible to remove all particles including the very finest, from the circulating water, thus obtaining a closed water system and, (2) that reduction of the ash content of the solids of the plant bleed is feasible by means of cyclone thickeners. Performance data for different size cyclones is given in the form of graphs.

Jan 1, 1950

By Jr. Holmes

The Bureau of Mines drilled and sampled the more important magnesite deposits in the Currant Creek Mining District, White Pine County, Nev. The properties of the Ala-Mar Magnesium Co., Inc., and the Nevada Magnesite Co. were examined in August 1942 by D. W. Butner, engineer of the Bureau of Mines, to determine the advisability of investigating the deposits under the strategic minerals program. Development involving diamond drilling, trenching, and sampling was started September 1, 1942, and was completed in the latter part of November 1942. The deposits are on unsurveyed public land in T. 12N., B. 59 E., M.D.B.&M., in an area of high relief ranging from 7,300 to 8,100 feet in altitude. Both properties are situated northwest of the Tonopah-Ely Highway, U.S. Highway 6, from which a dirt road extends about 4.6 miles northwesterly, about 35 miles southwest of Ely, to the Ala-Mar property, and another dirt road extends about 10 miles westerly, about 26 miles southwest of Ely, to the Nevada Magnesite property. The magnesite occurs as irregular nodules, veins, and lenses in a bedded calcareous tuff formation, which overlies a group of volcanic rocks, and which is capped by remnants of rhyolite flows.

Jan 1, 1950

By L. R. Burdick

Anthracite barley is considerably cheaper than rice. Its use, therefore, is attractive from a cost standpoint, - but its smaller size (through 3/16 inch over 3/32 inch round-mesh screen) makes it more difficult to use on some equipment when fairly high combustion rates are necessary to carry plant loads. Tests wore made in one plant to determine the performance of rice and various types of barley on a chain-grate stoker in a two-arch refractory furnace. In general, the efficiency and capacity increased with increased fuel size and volatile content. This performance is presented in tabular and curve form, together with a short review of the ignition and burning process on chain-grate stokers and a discussion of the operating procedures and limitations during the tests. In this particular installation, higher combustion rates and efficiencies could have been obtained with barley if the grate links had been designed for more uniform air flow through the grate surface. Careful maintenance and operation are particularly necessary for satisfactory results with barley on equipment not especially designed for its use.

Jan 1, 1950

By Robert H. Bedford

As a result of the Bureau's general survey of quicksilver deposits in California, the Guadalupe mine area was among those chosen for exploration. Exploration, such as that at the Guadalupe, was aimed primarily at maintaining or increasing production of quicksilver during the critical wartime period. The project as originally planned contemplated sampling the dumps and prospecting some promising surface exposures by bulldozer trenches. Salvage was the objective in the first case and new ore in the second. Later, a program. of diamond drilling was added, designed to add both to ore reserves and to geological information. This report summarizes the history, notes the location and physical features, mentions property and ownership, and presents a brief description of the mine. The geology is outlined, and the work done by the Bureau of Mines is explained and supplemented with accompanying maps. The work involved repairing 1-1/4 miles of roads; bulldozing 13 trenches by removing 2,345 cubic yards of dumps to provide for sampling; digging and sampling 9,284 linear feet of hand trenches, digging and sampling numerous test pits; and drilling 7 diamond-drill holes, totaling 1,000 feet. A total of 419 samples, including 10 percent check samples, were taken. Exploration work in California at the time of this project was under the direction of Spangler Ricker, supervising engineer of the California field office, the late Robert Bedford was in charge of the fieldwork on this project.

Jan 1, 1950

By H. Stuart Auvil

Twelve samples of run-of-oven coke were taken at coke plants in the United States and Canada. Sampling procedure was directed toward obtaining the highest possible degree of uniformity in the gross samples, so that variations in results caused by sampling variations were at a practical minimum. Under these conditions the standard deviation of the screen analysis test on 500-pound samples is found to range from 1.2 percent for the 1-inch screen to 4.5 percent for the 5-inch screen. At present, the A.S.T.H. standard method of test requires that results be reported to the nearest 0.1 percent. This implies a higher than actual degree of precision, and revision of the report required by the method is suggested. Much larger Samples than are generally tested are required to reduce normal testing errors to a point where they are not appreciable fractions of the total variations found in a smoothly operating plant. For example, it is deduced that over 100,000 pounds of coke must be screened to determine if ordinary day-to-day variations in screen analysis have appreciable effects on the performance of a blast furnace.

Jan 1, 1950