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By Jarrell C. Grout

The Bureau of Mines has developed a computer program for use in solving nonlinear regression problems. The program is written in a general form so that, regardless of the functional relationship, the unknown parameters may be evaluated by either the Gauss-Newton or the Newton-Raphson methods of iteration. Variances and covariances of the parameters, as derived from the law for the propagation of errors, are also determined.

Jan 1, 1969

By C. Daniel Kealy

Finite-element,, mathematical models that solve LaPlace's and Richard's equations numerically were used to locate the phreatic surface within tailings pond embankments and to define the subsurface flow of water from the pond. Both must be known to design structurally and environmentally safe tailings dams. The permeability distribution within and beneath the embankment, the fluid potential values upgradient and downgradient from the embankment, and the geometry and elevation of an approximately impermeable layer at some depth beneath the embankment were used as computer inputs in analyzing over a dozen finite-element models of tailings dams varying structurally from simple to complex. Results predicted with the finite-element model were confirmed with measurements in a laboratory model of a tailings pond and in the field. Of particular importance to the design of safe slopes, all data indicated that the phreatic surface within a tailings dam is concave upward, a configuration opposite that in most earth dams. The close correlation between predicted and experimental values confirmed the practicability of using the finite-element technique to design safe tailings dams.

Jan 1, 1971

By Clifford H. Summers

This report describes an experimental program which we conducted on behalf of the U. S. Bureau of Mines, to select from currently available materials two novel systems of construction for air-restraining bulkheads to be used in control of radon-polluted air in underground uranium mines. The program included both laboratory and field tests, the latter conducted in a portion of an operating mine owned and operated by Union Carbide Corporation at LaSal, Utah. The test site was a worked-out, double entry stope having a Volume of about 2000 cubic meters, and was located immediately adjacent to an exhaust airway. The bulkheads were constructed of 15 cm x 1.5 cm timber uprights, 5 cm x 15 cm horizontal members supporting a close-fitted 13 mm plywood curtain-wall., which was covered with a low-permeability membrane to seal in the radon-polluted air. The two membrane materials selected for testing were chosen from a list of twenty-two potentially acceptable candidates using criteria such as strength, flammability, ease of application, adhesion, radon permeability, and elasticity. Thirteen of the candidates were tested in our laboratories for adhesion to plywood and to both wet and dry concrete (simulating wet and dry mine rock surfaces), and for their general physical properties, including radon permeability. The final selections made by the Technical Project Officer, and based on our recommendation, were a pre-formed ethylene propylene diene monomeric rubber (EPDM) membrane 1.12 mm thick, normally used as a roof sealant in industrial construction, and available from Carlisle Tire and Rubber Co., Division of Carlisle Corp., Carlisle, PA, and Aquafas 48-00, a water-based mastic used in a wide variety of commercial applications and available from H. B. Fuller Co., Foster Products Division, Spring House, PA. The EPDM membrane was applied as a single sheet, laminated (dry) between two layers of plywood, and the Aquafas was applied both by troweling and spraying onto a plywood surface. In the field test, radon concentrations were continuously measured before, after, and in the trapped air behind each bulkhead. Temperature, pressure, and velocity of the air in the adjacent airway were also measured and recorded continuously. Radon fluxes at the rock/air interface and through the bulkheads themselves were measured manually on a frequent basis. All continuously acquired raw data were recorded automatically on two USBM Data Aquisition Systems (DAS), and the raw data were converted into engineering units and recorded on magnetic disks by a specially programmed microcomputer that was interfaced with the DAS's. Relatively clean (i.e. low radon concentration) air was pumped into a point near the face of one test bulkhead from a location 170 meters away through vent bag. Several air curtains and two air-restraining bulkheads were erected in passageways adjacent to the test area in an effort to control both velocity and radon concentration of the air flowing past the bulkhead faces. An average concentration of approximately 500 pCi/liter at a flow of 550 m3/minute was attained as the background concentration against which leakage through the bulkheads was measured. The entire field test period extended from October, 1981 to March, 1982, a total of six months, and was subdivided into seven successive time periods: 1) site preparation 2) background measurements prior to bulkhead construction 3) passive restraint, with bulkheads in place and totally sealed 4) open bleeder period of natural convection ventilation in and out of the bulkheaded area through a 10 cm (diameter) opening, with connecting tubing; leading into an Exhaust airway 5) open bleeder period, having forced exhaust through a 1.0 cm opening using a servo-controlled fan 6) charcoal trapping period, using the servo-controlled fan to exhaust air through the charcoal traps, to test the effectiveness of such traps in removal of radon from the exhausted air 7) site decommissioning Each of the two systems tested, one incorporating the pro-formed EPDM-rubber membrane and the other utilizing Aquafas 48-00, was assessed for effectiveness in controlling radon-polluted air by observing the change in the radon concentration in the ventilation air flowing continuously over the surface of each bulkhead. The sensitivity of the observed measurements was limited by the volume flow-rate of the ventilation air and the radon concentration in that air. The data would indicate that the observed increments in radon concentration in the ventilation air moving across bulkheads B-l and B-2 were essentially zero within the limits of sensitivity of the measurements. Data from radon flux measurement taken both on the sealed ribs adjacent to the bulkheads and on the bulkheads themselves did not differ significantly from blank data.

Jan 1, 1982

By W. J. Kroll

This report on the bibliography of zirconium has been confined to those publications and patents that appear to be useful in the commercial development of the metal, both the malleable and the nonmalleable. The methods of production have been stressed and special attention has been given to the alloys. Compounds of importance, like the oxide and chloride, for the manufacture of the metal or of the alloys have been considered. The use of the oxide in refractories anal in the glass and porcelain industries has been omitted. The present survey is critical; that is to say, an attempt has been made to evaluate the effectiveness of suggestions made in the literature. The exhaustive work of Marden and Richy, Bureau of Mines Bulletin 186, published in 1921, has been taken as a base to start from with the intention of bringing the subject up to date with material published in the last 24 years. During this time there was considerable 'advance in the preparation of the metal and Its alloys, and in the development of new uses. On the other hand, there was little progress in the methods of decomposing the ores, so that the chapter on this latter phase is necessarily short.

Jan 1, 1946

By M. Hertzberg

This Bureau of Mines report describes experimental and theoretical studies of diffusion flames in free convection. The cross-coupling between buoyancy-induced flows and the combustion process is explored as it relates to the size, structure, and radiative balance of flames. New data are presented for the size-dependent radiance oscillations of diffusion flames and for the angular distribution of the total radiant intensity from a small methanol pool flame. Both amplitude and frequency of the measured oscillations are compared with theoretical predictions that are based on a new view of the structure of diffusion flames. This new view, which is at variance with the traditional one, assumes uniform reaction in the diffusive mixing zone, and recognizes the significance of the role played by convective buoyancy and its duality in both aiding and impeding flame propagation. Buoyancy quenches propagation at low burning velocities, introducing a real discontinuity in the combustion rate. A "flammable volume" is thus defined as that bound between lean- and rich-limit contours. However, in the flow disturbances generated by combustion waves that consume that volume, buoyancy aids propagation by promoting the convective mixing of a new flammable volume. The measured radiance oscillations are manifestations of these propagation and remixing cycles.

Jan 1, 1978

By Floyd R. Hertweck

This Bureau of Mines publication contains analyses and related source data for 349 natural gas samples from 26 States and 2 foreign countries. The 3 samples from foreign countries and 339 of the U.S. samples were collected during calendar year 1983. The remaining seven samples were collected earlier, but releases granting permission to publish were not received until 1983. All samples were obtained and analyzed as part of Bureau of Mines investigations of the occurrences of helium in natural gases of countries with free market economies. This survey has been conducted since 1917. The analyses published herein were made by the mass spectrometer and chromatograph. The results of these investigations are published annually to make the information available to the petroleum industry and the general public. Twenty-seven publications have presented the results of 13,332 gas analyses made prior to 1983. The first three bulletins (1-3)3 contain analyses and related source data on 5,218 gas samples collected from 1917 through 1960; these bulletins have been supplemented annually by information circulars (4-17, 19-24, 26-27) containing 8,104 analyses of sam¬ples collected since 1960.

Jan 1, 1984

By John Wilson

This report describes the performance of Phase I of a project to design, analyze, and demonstrate a multilift longwall mining method applicable to mining coal seams twelve (12) feet or more in thickness. A non-simultaneous multilift operation is the most viable thick seam mining technique for introduction to the United States coal industry. In the case of the proposed site at Emery, Utah it will result in an increase in coal extraction from 30% with present methods to at least 50% and possibly more. The major technological advance involved in this project is mining a lower lift under a previously mined upper lift. To accomplish this, entries must be developed and maintained beneath the upper lift gob. This will necessitate the use of steel supports at frequent intervals throughout the lower lift' entry system. This has not been done in the U.S. to date. An economic analysis of the project indicates that, while this method will result in a higher than average cost per ton for coal mined, the coal would be competitive with current-operation in the area.

Jan 1, 1976

By John D. Sullivan

In leaching copper ores knowledge of the rate of dissolution of the copper minerals and of the impurities is desirable. With knowledge of these two factors and data as to what minerals are present in the ore the metallurgist has an excellent start on planning a leaching cycle to fit that ore. The rate of dissolution is rather difficult to predict, and the time required to leach a given ore may differ markedly from that required by another ore. The whole study as related to mixed oxidized and sulphide ores is one of relative rates of dissolution of the different copper minerals and the impurities in sulphuric aoid and in ferric sulphate. The aim of leaching is to choose a cycle and strength of solvents to extract a maximum amount of copper and a minimum of impurities. The consumption of reagents per unit of copper dissolved is a function of the strength of the reagents used and the relative rates of attack on copper minerals and impurities. An opportunity may exist of obtaining the kind of electrolyte wanted for electrolytic precipitation and yet of saving on the consumption of reagents by modifying the strength of ferric sulphate and of sulphuric acid during the cycle to fit the time needed for dissolving the sulphide and oxidized minerals present.

Jan 1, 1931

By John D. Sullivan

In leaching copper ores knowledge of the rate of dissolution of the copper minerals and of the impurities is desirable. With knowledge of these two factors and data as to what minerals are present in the ore the metallurgist has an excellent start on planning a leach¬ing cycle to fit that ore. The rate of dissolution is rather difficult to predict, and the time required to leach a given ore may differ markedly from that required by another ore. The whole study as related to mixed oxidized and sulphide ores is one of relative rates of dissolution of the different copper minerals and the impurities in sulphuric acid and in ferric sulphate. The aim of leaching is to choose a cycle and strength of solvents to ex¬tract a maximum amount of copper and a minimum of impurities. The consumption of reagents per unit of copper dissolved is a function of the strength of the reagents used and the relative rates of attack on copper minerals and impurities. An opportunity may exist of ob¬taining the kind of electrolyte wanted for electrolytic precipitation and yet of saving on the consumption of reagents by modifying the strength of ferric sulphate and of sulphuric acid during the cycle to fit the time needed for dissolving the sulphide and oxidized minerals present. Former papers have considered the rate of dissolution of azurite, malachite, tenorite, chrysocolla, cuprite, chalcocite, boruite, and covellite in common leaching solvents. A paper soon to be written will consider some of the less important copper minerals. The present paper considers the rate of dissolution of copper from ores of the Southwest in sulphuric acid of varying strength and the ratio of sulphuric acid consumed to copper dis¬solved. In this study two ores containing the copper principally in an oxidized condition were used. A study of other ores, especially those containing high percentages of sulphide copper minerals, would be desirable, but since consumption of acid has paramount interest,

Jan 1, 1931

By R. S. Dean

A large metallurgical experiment station at Salt Lake City to house the works of the Bureau of Mines in the intermountain area properly has long been projected. It finally became possible when a Public Works Allotment of $300,000 was set aside for building and equipment. With the new building assured, the Bureau of Mines decided to move the headquarters of its Metallurgical Division from Washington, D. C., to Salt Lake City, Utah. It was felt that this move would simplify they administrative work of the chief engineer of the division, as all stations devoted primarily to metallurgical work are west of the Mississippi. These include Rolla, Mo.; Minneapolis, Minn.; Pullman, Wash.; Reno, Nev.; Berkeley, Calif.; Boulder City, Nev.; and Tucson, Ariz. In addition to these stations will groups, of investigators working on metallurgical problem, are maintained at Pittsburgh, Pa., and College Park, Md. Salt Like City was clearly a more central point for the direction of this scattered work than Washington, D. C. The building (fig. 1, A and B) was designed from general plans worked out by the authors of this paper. Contraction was begun in March of 1939, and by the end of the year the Metallurgical Division had moved, into its now quarters.

Jan 1, 1940

By Arthur E. Wells

"The present and possible future commercial production of potash from various sources in the United Status is discussed below under the following heads:1. Potash from the saline lakes.(a) Nebraska lakes.(b) California lakes.(c) Other lakes.2. Potash as by-product from the cement kilns.3. Potash as by-product from the iron blast furnace.4. Potash from silicate rocks.(a) Feldspathic material.(b) Leucite rocks of Wyoming..(c) Sericite slates of Georgia.(d) Glauconite (greensand) of New Jersey.5. Potash from Alunite.6. Potash from organic sources other than kelp.7. Potash from kelp.In this discussion very little more than passing reference, if any, will be given to those projects which up to date have been developed only slightly, if at all, beyond the small scale laboratory stage, or for the development of which there appears to be very little financial and technical backing at the present time. Nether or not many of these proposed projects have merit can be determined only by an actual operating demonstration.Generally speaking, the potash industry of the United States has been hardly more than marking time since the armistice. This is, largely due to the fact that the consumers of potash have been expecting that heavy shipments of foreign potash to the United States would be resumed soon at somewhere near the pre-war prices, and they have not seen owing domestic potash at present prices for many months. The result has been that domestic producers have been unable to sell their product at even cost and many producers of potash have been obliged to close down. Thu Nebraska lake plants were closed down in February. The California saline plants were operating at below capacity, and the only large alunite plant is closed down. Even the cement plants have little or no inducements to recover the potash being lost in their waste gases and the production is very small at present.This condition will doubtless continue until a definite policy is decided upon as to the future importation of potash salts from Germany and. France. If unrestricted importation is allowed at prices even 50% greater than in 1913, only a very few, if any, of the domestic projects will be in position to compete with the foreign potash immediately, and the present industry will probably greatly decline with little or no prospect for a future resumption of the industry."

Aug 1, 1919

By C. E. Brechtel

This project describes the design and testing of large face ventilation systems for oil shale mining. A design data base was generated by reviewing general industry practice, oil shale industry planning, and technical literature. Conceptual designs for seven different systems were developed and evaluated for suitability. A large, free-standing, jet fan and reversible fan with rigid duct were selected for fabrication and testing. The two systems were field tested in a dead-end heading 55 ft wide by 30 ft high and 320 ft long. System performance was optimized using measurements of air flow direction and air velocity. Total system performance was then measured using SF6 tracer gas released to simulate blast fumes, hot diesel exhaust, methane layering and methane from a blasted muckpile. Field testing indicated that both systems delivered similar performance. The jet fan offered some clear advantages because of its mobility, ease of oper-ation and lower power requirement. It also offered some functional advantages in ventilating for methane because of it high average velocity.

Jan 1, 1985

By Homer J. Ballinger

"SUMMARYDuring December 1945, the Bureau of Mines began churn drilling the Winchester zinc deposit, 11 miles south of Joplin in Newton County, Mo. The deposit lies in a virgin area northwest of the Seneca fault. It is one of several deposits partly proven by drilling but never developed.Logs of 28 privately drilled holes had indicated a substantial tonnage without delimiting the deposit. It appeared that additional drilling might increase this reserve sufficiently to justify mining. A, total of 6,33 feet of churn drilling was completed in 17 holes drilled by the Bureau of Mines. Twelve of the holes penetrated minable ore extending the length of the known deposit and materially increasing its estimated tonnage.INTRODUCTIONDuring May 1943, the Winchester property in Newton County, was visited by an engineer 3/ of the Bureau of Mines, accompanied by Dr. A. N. Winchester, owner, and Charles Keith, lessee of the property. At the request and with the assistance of these gentlemen, examination of the property was undertaken. Logs of 28 churn-drill holes were collected, hole locations were surveyed, and available historical data were obtained. It was concluded that although existing drill holes indicated considerable reserves, additional drilling might increase the tonnage substantially. In addition, it was believed that better knowledge of this ore deposit could be obtained by drilling further, and this knowledge could, in turn, be applied to other less proven deposits in the same field."

Jul 1, 1947

By A. B. Campbell

The mines in the eastern part of the now active region of the Tri-State zinc district of Missouri, Kansas, and Oklahoma have unusually acid water, which during periods of moderate or no rainfall As used in the mills to replace losses from evaporation, seepage, and tailings disposal. Its use has caused difficulties by corrosion of equipment and by interference with flotation. The growing importance of flotation- Which requires good water, and the increasing troubles caused by the corrosion of the milling equipment have prompted the Mississippi Valley Experiment Station of the United States Bureau of Mines, in cooperation with the Missouri School of Mines and Metallurgy, Rolla, Mo., to investigate the action of the waters on flotation and to undertake to develop means of obviating their harmful effects.

Jan 1, 1932

By Oliver C. Ralston

The minerals that enter welding-rod coatings and fluxes are the main subject of this report. Few mineral producers know just what minerals and what grades and quantities of minerals are required by the welding trade, and it is for their information that this report has been prepared. The various methods of welding are discussed extensively enough to inform this type of audience. Specialists in welding probably will find little on welding that is of value to them, but they may learn something more about the minerals or mineral products that they use. The authors did not find it easy to prepare this publication, and any needed corrections will be welcomed. Regarding welding, research, Jenks4/ 1 points out that while the process of welding in simple in operation, the phenomena attending its use are extremely complicated, and the efficient and safe use of welding requires an understanding thereof. Although the fluxes and the coatings used have solved many problems, many other problems require the joint effort of the whole industry; therefore, it is hoped that this report will be found of practical value.

Jan 1, 1940

By James P. Rider

Significant advances in longwall mining technology and equipment have occurred over the last decade. By the late 1990s, longwall mine output accounted for 40 percent of all underground output in the U.S., and today longwall mines account for approximately 50 percent of coal produced underground in the United States. A 53 percent increase in average shift production rates has occurred over the last fifteen years. This increased longwall productivity has meant that far more dust is being produced and controlling respirable coal dust provides an ongoing challenge for coal mine operators. The National Institute for Occupational Safety and Health (NIOSH) has completed a series of benchmark surveys at longwall operations across the country to identify current operating practices and the types of controls being used. Gravimetric and instantaneous dust sampling was completed to quantify dust generation from major sources on the longwall section and to determine the relative effectiveness of the different control technologies in use today. Substantial reductions in dust levels were realized at sampling locations on the face when compared longwall surveys conduct in the 1990?s. This paper summarizes the results from the underground dust surveys and discusses current longwall dust control technology and operating practices.

Jan 1, 2010

By K. L. Paciorek

The aim of the present study was to determine the thermal oxidative behavior of materials used in coal mines, with emphasis on the type and relative concentration of the products, in particular the toxic species formed. To supplement this work and to gain understanding as to the type of products possibly formed and also to assess the limitations and advantages of the various analytical methods used a literature survey of the past investigations performed on the compositions of direct interest to the subject program was conducted. The compositions thus covered were cellulose, polyvinyl chloride, neoprene, urethanes, polyamides, polyesters, polyethylene, epoxy, phenoxy, urea-formaldehyde and melamine formaldehyde resins. The results of this review are compiled in the Appendix. The experimental work consisted of thermal oxidative degradation of 36 materials and 4 composites using a stagnation burner apparatus developed in these laboratories which affords a dynamic system approximating somewhat the conditions encountered in underground coal mines. This technique as employed during this program gave only the relative product concentration at specific periods of the decomposition process, The advantage of this approach is that in this manner screening of materials can be accomplished in conjunction with some assessment of the decomposition rate as influenced by temperature and material composition. Limited static tests were performed using a sealed tube method. The materials studied were grouped according to their compositions. The following were the main groups: (a) polyvinyl chloride-containing materials, (b) neoprene compositions, (c) rigid foams (urethanes, isocyanates), (d) miscellaneous materials (including jute, fiberglass, polyethylene and some articles of unknown composition), (e) coal and fluids (phosphate esters, organic esters, oil-water emulsions), and finally (J) composites. The latter comprised a mixture of a phosphate ester fluid with (a) coal, (b) a representative polyvinyl chloride sample, and (c) a neoprene type composition.

Jan 1, 1972

By E. O. RHODES

This report is one of a series written by members of the Solid Fuels Mission to Germany describing wartime developments in the mining, prepara- tion, and utilization of coal. This mission was organized early in 1945 under the auspices of the Technical Industrial Intelligence Committee, which cooperated with a counterpart British Committee. In some instances; engi- neers from other allied countries cooperated. The Solid Fuels Mission operated under the direction of a steering committee headed by Dr. C. J. Potter, Deputy Solid Fuels Administrator. The personnel of the mission consisted of H. F. Yancey, in charge, J. W. Buch, Thomas Fraser, L. L. Newman, and L. D. Schmidt of the Bureau of Minos; H. H. Lowry, Director of the Coal Research Laboratory, Carnegie Institute of Technology; H. J. Rose, Vice-President and Director of Research, Bituminous Coal Research, Inc.; and F. H. Reed, Chief Chemist, Illinois Geological Survey. E. 0. Rhodes, Manager, Development Section, Tar Products Division, Koppers Co., Inc., served on the mission for the Chemical Subcommittee of 1.I.I.C. in Europe. His assignment was the investigation of the coal-tar industry. In this connection he prepared this report on the German Low- Temperature Tar Industry as a companion to his provious report on the German High-Temperature Tar Industry (Bureau of Mines Information Circular 7409). Because of Mr. Rhodes' extensive experience in these fields and the impor- tance of the subject material to the coal producers and those utilizing coal-tar products, both reports are issued by the Bureau of Mines. Over fifty reports were written by the members of the Solid Fuels Mis- elon. These, together with microfilms of supporting data obtained in the course of the investigations, are on file at the Foreign Documents Group, Technical Reports Section, Bureau of Mines, Pittsburgh, Pa., where they are available for examination. Copies of reports available in printed form may be ordered from the Department of Commerce, Office of Technical Services, Washington 25, D. C. Check or money order accompanying order for printed reports should be made payable to the Treasurer of the United States. A Bibliography of Scientific and Industrial Reports, covering all ma- terials and subjects and giving instructions for obtaining the desired items, has been published weekly by the Office of Technical Services. Effective July 1, 1948, the Bibliography of Scientific and Industrial Reports will be prepared monthly instead of weekly and on a more selective basis. issue, which will be the first monthly issue, will be available about July The July month thereafter through June 1949. Annual subscriptions and orders for individual copies starting with the July 1948 issue should be addressed to the Department of Commerce, Office of Technical Servicos, Washington 25, ur, and be accompanied by chock or money order made payable to the Troas- Bibliof the United States. Annual subscriptions for monthly issues of the Bibliography of Scientific and Industrial Roports will be $10. Individual issues will cost $1 per copy. Foreign subscriptions will be $14 per year and $1.50 por copy. tions listed in the Bibliography of Scientific and Industrial Reports should All orders for reports in microfilm or photostatic type of reproduc- ורי

Feb 1, 1949

By R. L. Grant

[Detonators are used to explode permissible explosives, dynamites, or other high explosives. This explosion or detonation is brought about by the energy which is liberated as a combination of concussion and heat when the detonator is fired. In Other words; "The detonator is the key which unlocks the energy of a high explosive" (8)4. Being sensitive and latently dangerous, detonators must meet two primary requirements: They must be safe to handle and must detonate when desired, thereby imparting detonation to the explosive charge.]

Jan 1, 1941

By A. L. Peyton

Manganese-oxide minerals occur in irregular pockets distributed through the residual clays of the Cartersville district, which lies 45 miles north-west of Atlanta in Bartow County, Ga. The district produces, or has produced, limonite, barite, specular hematite, ochre, ferruginous manganese, manganiferous iron are, as well as manganese. Bureau of Mines engineers have visited the district on three occasions - in December 1939, February 1941, and October 1942. During the visit of February 1941, 80 tons of samples of manganese-bearing clays were taken from seven properties for ore-dressing tests, which were conducted at the Bureau of Mines laboratory at Rolla, Mo. The. October 1942 visit was for the purpose of reappraising the district in the light of knowledge gained from the ore-dressing studies and to prepare a plan for the district's development. Exploratory drilling was begun in March l943 and was continued until June 1945. Nine properties were explored that, roughly follow a line beginning near Cartersville and extend to a point 2 miles northeast of the village of White. The work consisted of bulldozer trenching, rotary bucket churn drilling, sampling, and analytical determinations. The manganese district is 18 miles long with a maximum width of 7 miles at Cartersville, which lies at the center of the district. The work of the Bureau was confined to the northern half of the district between Cartersville and Pine Log. The properties explored comprise but a small portion of the Potential producing area.

Jan 1, 1949