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By N. Brown, M. Herman

ORDERING'S effect on the creep strength and other plastic properties of metals is unknown at the present time. Sachs and Weerts' attempted to compare the mechanical properties of the ordered and disordered state by comparing a quenched specimen with one annealed for a long time at a low temperature. This experiment is unsatisfactory because it introduces a possible effect from quenching. Barrett' used a hot impact test, but his method was not sufficiently sensitive to indicate any discontinuity in plastic behavior in the neighborhood of the critical temperature. On the theoretical side, Fisher9 as suggested that short range order would strengthen an alloy, but he gives no conclusions as to the effect of long range order. Cottrell" has discussed the interaction between long range order and dislocations, but does not indicate whether slip in a completely ordered alloy without domain boundaries is appreciably more difficult than slip in the disordered state. Because order exists in so many alloy systems, it is most important to prove experimentally whether long range order weakens or strengthens a metal. This investigation used -brass because: 1) it orders

Jan 1, 1957

By Ralph Schilthuis

SEVERAL investigators1-8 have reported evidence of the existence of native or connate water in oil-and-gas-bearing strata. Both water and salt have been detected in cores of oil sands that yielded oil and gas exclusively when produced. Electrical logs often reveal unexpectedly low resistivity through oil and gas sands, indicating the presence of some material that is a considerably better conductor of current than oil and gas. Furthermore, calculations9 of the oil and gas content of reservoirs based upon production and reservoir-pressure decline data indicate appreciably lower values than are arrived at under the assumption that the pore space is occupied completely by oil and gas. ORIGIN AND OCCURRENCE OF CONNATE WATER IN OIL-AND-GAS-BEARING FORMATIONS The view has been expressed,10-15 and is generally agreed upon, that the expulsion of oil and gas material from source beds and the subsequent migration and accumulation occurred in the presence of salt water. As the strata that usually form reservoirs for oil and gas were laid down by, or in the presence of, ancient seas, the pore space within the strata must have been saturated with salt water before the entrance of the oil and/or gas. Thus, the accumulation of oil and/or gas in the upper regions of structures suitable for reservoirs must have required displacement of the connate water therefrom. In the absence of any forces other than gravitational, it would be expected that the displacement of the connate water out of the zones finally occupied by gas and oil would be complete, and that the vertical distribution of gas, oil, and water in a reservoir would be strictly in the order of their densities. Apparently, however, surface and interfacial forces that will not permit complete segregation of the fluids are active within the capillary spaces comprising a reservoir. The effects of these forces on both accumulation and production of oil and gas have been the subject of study by a number of investigators. 16-37

Jan 1, 1938

By John V. Beall, William F. Haddon

A long the mighty Andean Cordillera, there is splendor beyond imagination-in the natural beauty of the mountains and in daring engineering and lavish investment in the mines. This is the story of the great copper mines of Chile and Peru. Each mine has a special quality which has tested the physical and spiritual resources of the founder. In the early days of the older mines, the mining engineer of song and story was more the rule than the exception. He was physically tough, ingenious and a leader of men. In the current political and social environment of Chile and Peru, the foreign contract mining engineer is still needed; but he must be a different type of man. To John J. Selters at Cerro's Rio Blanco, the principal ingredient is still "toughness," but it is "toughness of mind" that is needed. "He probably should be a teacher." The copper mines are not new. They were, almost without exception, worked by Indians (La Exotica might prove the rule), and later by the intrepid Spaniards. Modern mining began after the turn of the century. In Chile, the first of the big ones was the Braden Copper Co. founded on the El Teniente deposit. This development was followed by Chile Exploration Co. at Chuquicamata and Andes Copper at Potrerillos. These properties have been developed over the years by vast expenditures of money and a monumental amount of labor. None was free of technical problems-metallurgy at Chuqui, marginal grade of the old mine at Andes, avalanches and the great fire at El Teniente. The evolution which has brought the established mines of Chile, and the new ones coming on stream, to their present state of development is in reality the work of wonders of input-money, engineering and responsible management in an atmosphere of political stability. Without any one of these, the result would have been failure.

Jan 11, 1969

By J. L. Bruce

For a number of years, from an economic standpoint, the ventilation of the Colorado mine of the Davis-Daly Copper Co. has been a difficult problem. The development through the main hoisting shaft was pursued for a number of years and to a depth of about 2500 ft.( 762 m.)before large bodies of good commercial ore were opened up. This lack of early success in exploration restricted expenditures for ventilation, with the result that the present orebodies were opened up at a depth of 2500 ft., and in country rock f relatively high temperature, without adequate means f supplying the development faces and the stopes with cool or fresh air of low humidity and suitable velocity. During the progress of development, two or three connections were made at higher levels with the workings of adjoining operations, but these were of a makeshift and unsatisfactory character and afforded no means for carrying downcast air from the surface, in anything approaching a direct course, to the working faces. During the latter part of 1917, arrangements were made with. the Anaconda Copper Mining Co., whereby, during the year 1918 and the early part f the year 1919, a crosscut was driven eastwards on the 2500-ft. level of the Colorado shaft and connection was made by means f an up-raise of approximately 200 ft. to a crosscut driven westwards from the 2800-ft. level of the Belmont mine, this crosscut at the top of the raise being driven at Davis-Daly expense by the Anaconda Copper Mining Co. This connection, in conjunction with a No. 11 Sirocco fan installed near the Colorado shaft, provided the Colorado mine with a maximum of approximately 30,000 cu. ft. per min. of relatively fresh air, most of which came in a fairly direct route from the downcast Belmont shaft through the No. 11 fan to the 2500-ft. level stopes. After passing through these stopes and the stopes of overlying levels, it passed through the main crosscuts on higher levels back to the Colorado shaft, which provided the upcast for this current of air. The improvement

Jan 9, 1921

By N. O. Johnson

THE Hog Mountain mine is a pyritic-gold property in the north central part of Tallapoosa County, Alabama, at an elevation of 800 ft. in the southern Appalachian region. It is 13 miles by a good secondary road from Alexander City, a station on the Central of Georgia Railroad. Since its discovery in 1839, the mine has been worked intermittently. The records of past operations are few and are scattered over a long period of time; however, available information indicates a production of approximately 12,000 oz. of gold prior to the present company's activities, which started in 1933. Additional 7844 oz. has been produced under the direction of the present management. The ore from stopes has averaged 0.200 oz. gold per ton; the ore from development, 0.136 oz. gold per ton. Silver, copper, iron and sulphur are also present but to date are of minor importance. The grade of ore in comparatively narrow veins makes necessary extreme vigilance in the methods of mining. Geology Wall Rock.-Hog Mountain consists of a quartz-diorite intrusion approximately 5000 ft. long by 1200 ft. wide. Its resistance to weathering, as compared to the surrounding schists, has led to the formation of a conspicuous ridge rising 400 ft. above the adjacent country. All the mining operations are confined within the limits of this quartz-diorite formation. . Except where there is excessive shearing, either parallel or at flat angles to the quartz veins, all the walls of the stopes within the limits of the veins are strong enough to make timbering unnecessary. Where shearing exists, there may be a sloughing off of the walls, especially in the process of drawing the ore. When this occurs, stulls are placed in the stope, either while the stope is advancing, or while ore is being drawn from a completed stope. In general, very little timber is required. Veins.-The quartz veins have been deposited along fracture planes in the quartz diorite. There are 20 principal veins, all of which are roughly parallel and strike at right angles to the long axis of the formation.

Jan 1, 1937

By Frederic Carter

THE gold, silver, copper alloys have been the subject of several fairly complete investigations by Jänecke, Sterner-Rainer1 and others, and indeed it would seem as if almost too much labor had been expended on them when one thinks of the numerous other ternary alloys calling for more light; however, the combinations of the three metals are actually so widely used in jewelry that they merit perhaps the work done on them. There are a few properties of importance and interest not treated by the authors mentioned which the writer investigated some little time ago, and therefore he has ventured to put on record the results of some of his tests made at that time. He has chosen, as being the two series of most importance to the jeweler, only the 14 and 18-kt. golds, so the subject is by no means so inclusive as that previously treated. As stated, this paper is merely a record of tests made in a practical manner on two useful series of alloys, and is not at all a critical study of their properties. 14-KARAT ALLOYS These alloys are important because they are the most generally used in 14-kt. jewelry; by changing the proportions of silver and copper there are obtained all shades of color from the green of the alloy containing gold and silver but no copper, to the red of the alloy containing gold and copper but no silver. Many 14-kt. gold alloys are made with the addition of zinc to the three metals mentioned here; the added metal does not appreciably alter the color of the alloy nor has it, in general, much effect on the working properties; it may, however, prove useful as part of the zinc added may act as a deoxidizer and render the alloy free of gas. It is not a necessary addition because with proper precautions all the 14-kt. gold alloys containing only silver and copper in addition to the gold can be made free of gas and capable of being cold rolled without cracking. The alloys in which approximately equal quantities of silver and-copper

Jan 1, 1928

By F. C. Blickensderfer

THE CHAIRMAN (B. B. GOTTSBERGER, Miami, Ariz.).-On your trip today through the Inspiration and Miami mills you have seen in actual operation the machines which represent the changes adopted in grinding methods in the Miami district from the beginning of operations in March, 1911. In one section of the Miami plant are three Chilean mills not yet discarded, representing the first machines adopted. In another section, pebble grinding is still in operation, while in the balance of the plant, pebbles have been replaced with iron balls. In all cases these machines are handling a feed which is the product of roll, grinding down to about ¼ in. in, size. The latest step in grinding in the district, You saw at the Inspiration plant, where in Marcy mills a filed, the larger pieces of which remain on a 2-in. opening, is being reduced in one operation to a product of which only about 3 per. cent. remains on the 48-mesh screen. A detailed comparison of the methods used at the two plants would be very instructive but our own work at Miami has not yet reached a point where such a comparison is possible, the reason being that our final product is not yet fine enough. By means of larger Hardinge mills operating in closed circuit with Dorr classifiers soon to, be installed in one section of the plant, we hope to obtain, under properly balanced operating conditions the same end result as at Inspiration. It, might interest you, however, to know some of the results we have obtained here by the substitution of balls for pebbles. With pebble grinding, using three 8-ft. by 22-in. mills, followed by one 8-ft. by 66-in. mill for regrinding the coarse product of the primary mills, we handled 636 tons per 24 hr. in one section of the plant. Substituting balls for pebbles in the first operation and using two mills in place of three we obtained a tonnage of .714 tons to the section. With the use of balls both in the primary mills and in the regrinding mills, the tonnage for one section was raised to 822 tons per day. Coincident with this increase in tonnage, we also obtained a greater efficiency. The use of pebbles in all mills showed 21.5 per cent. plus 48-mesh material in the final tailing, which figure was reduced to 13.9 per cent. for balls followed by pebbles, and to 4.6 per cent. with the use of balls both in the primary and regrinding mills.

Jan 12, 1916

By Samuel Shallcross

THE principal function of the Bell limestone mine, of the American Lime & Stone Co., at Bellefonte, Pa., is to supply raw material to the company's modern rotary kiln plant at Bellefonte. Because mining costs are naturally higher than many open quarries with more favorably lying strata, it cannot compete, except to a limited extent, in the markets for road material and fluxing stone. In the broad sense, mining does have an advantage over the average open quarry when the end products are designed for and controlled by process and final inspection for the exacting demands of the industrial and chemical markets. Approximately 80 per cent of the output of the Bell mine is sold in the industrial and chemical markets. And as higher standards are set each year for construction and agricultural work, the remainder of the mine output goes to these two classes. Mining produces more fines than open quarries, and these fines are difficult to market; on the other hand, owing to absence of contaminating clay and impure rock, a greater percentage of the output of a mine is marketable. Because of the great production of fines, rotary kilns for lime burning are necessary when the stone must be mined. In 1921 the American Lime & Stone Co. operated 19 quarries and 72 lime shaft kilns spread over an area of 40 miles between Bellefonte and Altoona, Pa. At that time the line-production capacity of the 72 kilns amounted to approximately 700 tons per day. After 15 years the company operates three rotary kilns and six shaft kilns, with a combined output of approximately 500 tons of lime per day, concentrated in its single Bellefonte plant (Fig. 1). Its only stone-producing plants are now the limestone mine at Bellefonte and a construction-stone open quarry at Union Furnace, near Tyrone, Pennsylvania.

Jan 1, 1936

By Walter L. Rice

It is a pleasure to report that the light metals industries are running well ahead of the growth schedule projected by the President's Materials Policy Commission. In the compilation of this survey on the five-year growth of our light metals industries, some gratifying facts come to light. By 1956, for instance, light metals consumption had increased more than 20 pct beyond Paley report expectations-a growth not anticipated by the study until the year 1960.

Jan 9, 1959

By Arthur Taggart

A GENERAL awakening of interest among mill men concerning the mechanical efficiencies of their crushing machines is evident from a perusal of the recent files of mining publications. Considering the large part of the power bill which must be debited to the crushing department, such. interest is natural. When, however, the articles on the subject are read, the only statement upon which the writers agree is that fine grinding consumes a large amount of power, and that the machine which, from a concentration standpoint, offends as a slime producer is, for that reason, a serious offender in wasting power. When the mill man attempts to find a method for measuring the power wasted, or to compare the efficiency of one machine with that of another for the same work, he is confronted with a choice of methods which lead to conflicting results. There are two reasons why the work of crushing is not more generally understood. In the first place, experimental data are difficult to obtain; and in the second place, before these data can be put in general form certain assumptions must be made. A difference in these assumptions by different investigators has led to conflicting conclusions. This conflict has resulted in the proposal of two laws. The first of these is the so-called Rittinger's law, which is variously stated as follows: . "The work of crushing is proportional to the reduction in diameter."-R. H. Richards: Ore Dressing, p. 304 (1903). "The Work required to crush rock is very nearly proportional to the reciprocals of .the diameters crushed to."-A. Del Mar: Engineering and Mining Journal, vol. xciv, No. 24, p. 1129 (Dec. 14, 1912). "The Work done in crushing is proportional to the surface exposed by the operation, or better expressed for this purpose, the Work done on a given mass of rock is proportional to the reciprocal of the diameter of the final product, assuming that all the mass has been reduced to one exact size, which is only theoretically possible."- A. 0. Gates: Engineering and Mining Journal, vol. xcv, No. 21, p. 1039 (May 24, 1913).

Jan 1, 1914

By H. J. R. Way

The work to be described was undertaken at various periods from 1937 to 1939 on the Busia gold field, in the eastern province of Uganda. It was decided to examine the possibility of reef prospection by the resistivity method, for it was not known how far the usually disintegrated nature of most reefs in the ubiquitous laterite near the surface would obscure indications obtained by resistivity traverses. The work at the commencement was therefore largely experimental, but the results obtained thereby were satisfactory, and a survey was started at the Government closed area at Amonikakine. With the limited time and resources at the writer's disposal, it was not possible to complete the survey to his satisfaction or to follow up exhaustively all the geophysical indications, but some of the results of the experimental work and the survey were of sufficient interest to be worth recording; in particular the relation between the width of reef, electrode separation and shape of the curve, and the interference effect of constant separation curves over zones of float are significant and useful. Three new veins were located, but only one contained sufficient gold to warrant detailed prospection. This was called the Geophysical reef, and was uncovered over a strike distance of 1140 ft., and there are indications that it extends over a distance of 1990 ft. These results and the recom- mendations consequent therefrom were embodied in a special report to the Uganda Geological Survey. History OF the Field The Busia field is in the southeastern corner of Uganda near the Kenya-Uganda border, and is about 17 miles north of the northeastern corner of Lake Victoria. Gold was first discovered in the area in the stream beds by Davies1,2 in 1932. Subsequently numerous small alluvial claims were worked by prospectors and the area was prospected for reef by a company for periods varying from three to nine months, but was finally abandoned, as the results were considered unfavorable. Further prospecting by the Geological Survey in 1935-1936 under Davies8 and later under the writer4 uncovered three reefs with sufficient gold values to be of economic interest. These were finally taken over by a company known as Borderland Syndicate, which still owns the area, and from September 1937 to the end of 1941 about 13,000 oz. of gold was extracted from reefs of the area proved by the Geological Survey. Opencast mining operations are still proceeding (February 1943). The Amonikakine area lies to the immediate north of that of Borderland Syndicate. A certain amount of prospecting had been done when the writer started work there. As a result of his report, this area was taken over by another syndicate, but little further work was accomplished before it ceased operating because of difficulties of wartime working.

Jan 1, 1946

By H. J. R. Way

The work to be described was undertaken at various periods from 1937 to 1939 on the Busia gold field, in the eastern province of Uganda. It was decided to examine the possibility of reef prospection by the resistivity method, for it was not known how far the usually disintegrated nature of most reefs in the ubiquitous laterite near the surface would obscure indications obtained by resistivity traverses. The work at the commencement was therefore largely experimental, but the results obtained thereby were satisfactory, and a survey was started at the Government closed area at Amonikakine. With the limited time and resources at the writer's disposal, it was not possible to complete the survey to his satisfaction or to follow up exhaustively all the geophysical indications, but some of the results of the experimental work and the survey were of sufficient interest to be worth recording; in particular the relation between the width of reef, electrode separation and shape of the curve, and the interference effect of constant separation curves over zones of float are significant and useful. Three new veins were located, but only one contained sufficient gold to warrant detailed prospection. This was called the Geophysical reef, and was uncovered over a strike distance of 1140 ft., and there are indications that it extends over a distance of 1990 ft. These results and the recom- mendations consequent therefrom were embodied in a special report to the Uganda Geological Survey. History OF the Field The Busia field is in the southeastern corner of Uganda near the Kenya-Uganda border, and is about 17 miles north of the northeastern corner of Lake Victoria. Gold was first discovered in the area in the stream beds by Davies1,2 in 1932. Subsequently numerous small alluvial claims were worked by prospectors and the area was prospected for reef by a company for periods varying from three to nine months, but was finally abandoned, as the results were considered unfavorable. Further prospecting by the Geological Survey in 1935-1936 under Davies8 and later under the writer4 uncovered three reefs with sufficient gold values to be of economic interest. These were finally taken over by a company known as Borderland Syndicate, which still owns the area, and from September 1937 to the end of 1941 about 13,000 oz. of gold was extracted from reefs of the area proved by the Geological Survey. Opencast mining operations are still proceeding (February 1943). The Amonikakine area lies to the immediate north of that of Borderland Syndicate. A certain amount of prospecting had been done when the writer started work there. As a result of his report, this area was taken over by another syndicate, but little further work was accomplished before it ceased operating because of difficulties of wartime working.

Jan 1, 1946

By A. S. Nowick, W. A. Goering

INspite of considerable interest in the kinetics of ordering of the alloy Cu3Au there is no direct information available on the activation energy for atom movements in this alloy, such as that obtainable by radioactive tracer-diffusion studies or by internal friction measurements. Accordingly, this alloy was examined to find out whether it displays an internal friction peak resulting from stress-induced ordering, similar to that studied extensively in other alloy systems.1-3 Measurements of the internal friction as a function of temperature were made in a torsion pendulum similar to that described by Ké.8 Wire specimens 0.032 in. diam and 11 in. long were used. The wire, obtained in the cold-drawn condition,* was annealed at 900C in a quartz tube to obtain a large grained sample, and then mounted in the torsion pendulum furnace. Internal friction is reported here as the lag angle, 4, which is equal to the logarithmic decrement divided by .ir. Fig. 1 shows the internal friction at three frequencies (the frequency given for each curve is the value measured at the peak). The data for these curves were obtained on cooling one specimen from 460C to just above the critical temperature for long-range ordering, which is about 390C for this alloy. In this way, the internal friction is measured under conditions where the alloy is in the disordered condition throughout the run. The curves obtained at frequencies of 2.15 and 1.29 cps show peaks in the range of measurement. The corresponding peak for the 0.78-cps curve is estimated, from the shift of this curve relative to the others, to be located slightly below the critical temperature (at 385C). The fact that the peak can be observed above the critical temperature is good evidence for the belief that it is a stress-induced ordering phenomenon similar to that which is observed in other disordered alloys. The fact that the peaks in Fig. 1 are not the same

Jan 1, 1959

By L. L. McDaniel

DURING the past few years a number of improvements in smelting and power equipment have been made at the Douglas smelter of the FIG. 1.-GENERAL PLAN OF SMELTER. Phelps Dodge Corporation at Douglas, Ariz. In the summer of 1935 work was started on the first unit of a new reverberatory waste-heat boiler plant which ultimately was to furnish steam for a modern high-pressure power plant. A second reverberatory waste-heat boiler unit

Jan 1, 1939

By John C. Smock

The fire-clays of New Jersey belong in two geological ages, the cretaceous and quaternary, or post-tertiary. Three very small deposits of plastic clays have been discovered within the limits of the Archæan rocks. These are not refractory and of little importance, excepting in a geological consideration. They have resulted from a decomposition of the feldspars of the rock in situ, and they have been classified as inferior kaolins.

Jan 1, 1879

By E. L. Mooney, D. F. Gibson, T. E. Lehman

This paper outlines the features of a computerized planning system, which was developed to aid surface mining and reclamation evaluation. Essential features of the system include three main modules: production, reclamation, and impact analysis. In addition, the system incorporates a large number of computerized data analyses and display features, which are described and illustrated in this paper.

Jan 1, 1983

Jan 1, 1906

By Sidney Powers, Alfred C. Lane

This paper aims to present the results of an investigation concerning gravitative differentiation in lava flows, based on a quantitative microscopic and chemical study of a Triassic basalt from Nova Scotia, and confirmed by data secured from a study of certain Keweenawan ophites. At Cape d'Or, Nova Scotia, near the head of the Bay of Bundy, marine erosion has exposed a series of Triassic basalt flows in which copper has been sought for a number of years. Studies of the thickest flow of the series with regard to volumetric composition, specific gravity, and grain have been made by the junior author, and measurements by students at Tufts College, together with confirmatory observations of the same nature on this and other flows by the senior writer, and chemical analyses made by the Division of Chemistry, Mines Branch, Ottawa,' all show differentiation in lava flows comparable to that in intrusive bodies. The work was made possible by the availability of the drill-cores, the property of Tufts College, and emphasizes the desirability of the study of drill-cores from other localities. Measurements of the specific gravities of certain Keweenawan lava flows of Michigan by the senior author, from material collected in 1915, will be given as a comparison to those of the Cape d'Or flow. It has been found that the specific gravity of drill-cores, or volume per cubic foot, can be readily obtained by measuring their dimensions. This can be done to an accuracy of within 1 per cent. in pieces of core over 100 mm. in length by using a micrometer gage for the diameter, and taking the average of six measurements of the diameter; and the average of four measurements of the length made with a finely graduated ruler. Then, after weighing them, the weight in grams per cubic centimeter, or what is practically the same thing, ounces per cubic foot, is obtained. System-

Jan 1, 1916

By E. W. Krampert

The oil industry was very active in Wyoming in 1936, in contrast to the several quiet years preceding. Production for the year again increased about 7 per cent, following an 8 per cent increase in 1935. During the year, 85 oil wells were completed, compared to 55 in 1935. Three gas wells were completed in 1936, and three in 1935. At the end of the year 45 wells were drilling, as compared to 55 drilling at the end of 1935. Two new oil fields and one new gas field were discovered in Wyoming during the year. In the year 1936 Wyoming produced 14,475,431 bbl. of oil, a gain of 1,001,081 bbl. over the 1935 figure of 13,474,350. This increase, in the main, was due to the taking of light oil from the newly developed Sundance sand pool at Lance Creek, and from the new fields, Quealy and Medicine Bow, which contributed their first production this year. Most of the other old fields either were partly shut in in competition with the new fields, or showed a normal decline. This was especially noticeable in the black-oil fields, where production had been slowly but steadily increasing for a number of years. During 1936 black-oil production decreased approximately 100,000 bbl. as compared to 1935. The only black-oil field to show marked increase was Garland, which managed to take the market from less favorably located fields. The production of Wyoming in 1936 was 11,358,757 bbl. of light oil and 3,116,674 bbl. of black oil. Salt Creek, with a production of 6,015,000 bbl., is still the largest single oil-producing field, accounting for 42 per cent of the year's total production. Lance Creek, an old field, with newly developed production in the Sundance sand, reached second place this year for the first time in its history, with a production of 1,878,486 bbl. Lance Creek production will almost equal that of Salt Creek in 1937, if the present rate of production is maintained during the coming year. Oregon Basin, a large black-oil field, held second place in 1935, but owing to a greatly lessened demand for its production, dropped back to third place in 1936. This was in part due to greatly increased light oil available, and in part to the greater supply of black oil available at

Jan 1, 1937

So commonplace that they are seldom noticed, mining-machine bits have a defi-nite and important bearing on the cost of coal production. At the average mine many thousands of bits are used during the year. The actual cost represented by the pur-chase of the bits used, as well as that of sharpening and handling them, represents a considerable sum of money. From the point of view of indirect costs they are im-portant, as the lack of good bits at a mining machine can seriously impair production. Good bits tend to ensure an adequate supply of coal.

Jan 1, 1940