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The Climax Molybdenum Company' s newest operation is the Henderson project, which is located on the east side of the Continental Divide. Ore reserves are estimated at more than 300 million tons at a grade of 0.49% MoS2. For mining the ore a modified panel caving system is used. The ore is transported to the Henderson mill on the west side of the Continental Divide on a 42 in. (1.07 m) gauge railroad through 9.6 miles (15.4 km) of tunnel and 4. 8 miles (7.7 km) of surface track, a total distance of 14.4 miles (23. 2 km). Each train consists of 30 ore cars with capacity of 22 st (20 mt) of ore or 660 st (599 mt) per train. The unmanned trains operate completely automatically. At the 54 in. by 84 in. primary gyratory crusher, the bottom dump ore cars pass over a dump scroll to discharge at a maximum rate of 100 st (91 mt) per minute. Dumped ore falls onto a rock box before passing over a 17 ft long by 46 ft wide (5. 2 m by 14 m) grizzly set at a 40° angle with bar spacings of 7 ½ and 8 ½ in. (191 mm and 216 mm) openings. An estimated 30 to 50% of the ore (which at times is wet and sticky) passes through the grizzly. The operators report that a shallower angle on the grizzly, perhaps 35º to 37º, would have been sufficient and would have prevented impact on the back of the crusher pocket by large boulders. This pocket as well as the crushed ore pocket under the crusher is lined with AR plate. The accompanying drawings show a "future splitter" and the operators are planning the installation of this unit to prevent impact and subsequent damage to the crusher spider. Crushed ore at an 8 to 9 in. (203 mm to 229 mm) size joins the grizzly undersize in the pocket beneath the crusher. This pocket is sized at 660 live st (599 mt) so that it will accept an entire trainload of ore. Crushed ore is removed from the pocket by a four-speed, 84 in. (2. 1 m) apron feeder operating at 9.6 to 29. 3 fpm (2.9 to 8.9 mpm). A 60 in. (1.5 m) takeaway conveyor operating at 480 fpm (146 mpm) delivers the crushed ore to a 58,000 st live and 193,000 st total (52,600 and 175, 100 mt) open stockpile under an A -frame supported tripper gallery. Impact idlers on the takeaway conveyor under the apron feeder discharge are mounted on wood blocks for a cushioning effect and ripped belt detecting bars are located behind each impact idler. The conveyor tunnel is of corrugated and galvanized steel construction rather than concrete. The concrete crusher enclosure is circular in design from its lowest level at elevation minus 110 ft 4 in. (minus 33. 6 m) to elevation

Jan 1, 1978

By George A. Morrison

A deposit Of limestone Was known to exist at a depth of 2000 ft under the property of the Columbia Chemical Division of the Pittsburgh Plate Glass Co. at Barber-ton, Ohio. A 662-acre site was selected for the projected mine, some two miles northwest of the plant and near the main line of the Erie Railway. An electric railway 8800 ft in length connects the mine and the plant. The deposit is overlain by 18 ft of un-consolidated (sand and gravel), 100 ft of water-bearing sandstone, and finally 2080 ft of shale into which thin layers of sandstone are embedded. The limestone bed itself is 345 ft thick and overlies 200 ft of gypsum. A 300-ton-per-hour capacity mine was decided upon. Two shafts were deemed advisable, one for production and the second for service; and these were sunk 550 ft apart, one to a depth of 2323 ft and the other to 2258 ft. Each is 16 X , ft in the clear and timbered with 6-in. steel H-sets on 8-ft centers, using 3/8 X 4 X 4-in. angles as studdles. Twelve inch I-beams were used at 160 ft intervals as bearers set in deep hitches and concreted to a vertical depth of 8 ft. Wooden sheathing was first employed but sloughing of the shale created a pressure on this lining and finally concrete was deemed necessary. Water was encountered only within the first 315 ft, flowing at 60 gpm and by grouting this was reduced to 15 gpm. Temporary wooden sinking headframes were installed with 300 cu ft capacity storage pockets and with doors automatically controlled by air cylinders by hoistmen. Each shaft was operated on four 6-hr shifts. The usual V-cut was drilled at the center of the shaft and the round consisted of 34 holes- A 40 pet gelatin dynamite was employed with some 60 pet in the cut holes. Drilling crews consisted of four to six men. Shale drilled easily but became more bed in depth and sandstone wore away the gauge Of the bits rapidly. A room-and-pillar mining system was adopted whereby rooms turned off on 80-ft centers, each room 40-ft wide and 50-ft high. Rib pillars between rooms were cut into 100 ft lengths by frequent holes. Ventilation is achieved through the two shafts, the down-draft through the service shaft, and the return through the pr0duction shaft. The hoist has a a Of 300 tons per hour and is equipped with 10-ton balanced skips requiring. a 2-min cycle Or 30 trips Per hour- Hoisting is designed to Operate by automatic loading and no hoistman is required for normal Operation. The 48 X 60 in. jaw primary crusher is underground. It is fed through chute and chain feeders and is flood-oil lubricated and cooled. An inclined belt conveyor returns oversized material to the crusher. Tramming is by Diesel-powered trucks.

Jan 1, 1948

By William Loblowitz

A simplified system of flotation testing has been developed recently at the Bureau of Mineral Research of Rutgers University. The technique involves the known principle of skin flotation and can be used with minute quantities of sample and reagents in a beaker. A vessel containing the conditioned sample with added water and flotation reagents is held inclined and rotated slowly. Water-repellent particles come in contact with air and float on the surface of the liquid, while wettable particles are submerged. The float is poured off and filtered whereas the nonfloat remains in the beaker. The filtrate may be returned to repeat the process. This procedure can be made quantitative. Separations are obtained and are remarkably complete and repeatable. The effect of different reagents, optimum quantities, pH and other variables can be determined in a fraction of the time required for conventional testing. However, the method gives no information on the effect of frothers and the quality of froth to be expected in a cell, and it is not practical for particles finer than 200-mesh. Unlike other preliminary tests, separate float and nonfloat products are obtained, and their contents can be determined quantitatively by chemical analysis or grain counts. After the optimum reagent combination has been determined, the effect of fines and frothing may be verified in the conventional flotation cell. On the other hand, agglomeration-tabling can be directly duplicated from beaker tests. Procedure: Five to ten grams of sample are weighed into a 100-ml beaker. Flotation reagents and a small initial quantity of water are stirred together; additional water is then added to produce the proper water-solids ratio. The beaker is then tilted to 45" and rotated slowly. After three to five rotations, liquid and float are poured off and filtered; the filtrate may be recycled until the separation is completed. One test generally requires less than 10 min. Reagent concentration and pH remain quite constant because of the recycling of the filtrate. Two to four tests may be made simultaneously, and the effect of varied conditions may be observed by comparison. Considerable time is saved in preparation and handling since small quantities of sample suffice for a series of systematic tests. Repeatability One test was repeated four times under constant conditions. The sample used was a quartz sand containing approximately 24 pct feldspar and some clay aggregates. The +28-mesh grains had been screened out, and most of those finer than 100-mesh had been removed by hydraulic classification. The results are presented in Table I. For comparison, 500 g of the sample were separated by agglomeration-tabling using the same reagent combination and quantities as given in Table I. The weight percent float was 18.3 pct, composed almost entirely of feldspar and with only traces of quartz. Most of the remaining feldspar was recovered in a middling product with 2.2 pct by weight.

Jan 1, 1952

By R. A. Deju, R. B. Bhappu

The basic structural unit of all silicate minerals is a tetrahedron with a silicon atom at the center and four oxygen atoms at the corners. The oxygen-silicon distance is about 1.6 & and the oxygen-oxygen distance about 2.6 &. The different types of oxygen-silicon frameworks in the various silicates are based entirely on the combinations of the tetra-hedral oxygen-silicon groups through sharing of oxygen atoms. In recent years, infrared spectroscopy has permitted estimation of the ratio of the ionic character of the oxygen-silicon bond to be a few times that of the oxygen-carbon bond and the ratio of electro-negativity of the two bonds has also substantiated this finding. On this basis, it is generally accepted that the oxygen-silicon bond is the strongest one occurring in silicate minerals. As the oxygen-silicon ratio increases from quartz to the olivines, a greater percentage of the oxygen bonding power is available for bonding to cations other than silicon. Hence, with an increasing oxygen-silicon ratio, there is increasing oxygen-to-metal bonding. Upon the fracturing of a silicate mineral crystal, the oxygen-metal bond, which is almost entirely ionic in character, should break more easily than the stronger oxygen-silicon bond, resulting in a greater number of unsatisfied negative forces on the surface. If, then the mineral is immersed in a liquid containing hydrogen ions, these negative forces should tend to be neutralized by hydrogen ions from solution, resulting in a change of the pH of the solution. An increase in the degree of adsorption of hydrogen ions is to be expected as the oxygen-silicon ratio in the crystal structure increases. This study attempted to correlate the oxygen-silicon ratio for various representative silicate minerals to the adsorption of hydrogen ions. Experiments to determine the effect of surface area on this adsorption and to investigate the effect of surface iron were also conducted. It is believed that such studies of the surface properties of silicate minerals will supply pertinent information about their behavior in froth flotation systems. EXPERIMENTAL PROCEDURE Ion Exchange: Carefully selected, hand-picked samples of the minerals investigated were dry-crushed in a ceramic ball mill and sieved to obtain a minus 100 plus 200-mesh sample. The sized samples were then run through the electro-magnetic separator to remove any iron-bearing particles. A 10-g sample of each mineral was placed in 100 ml of freshly deionized water previously adjusted to a pH of 3.50 with HCl. The beaker containing the sample and the water was placed under a bell jar from which the air was displaced at once by nitrogen gas from a tank. All experiments were carried out in a nitrogen atmosphere. The sample and solution were stirred gently but continuously during the entire experiment, the stirring speed being kept about the same for all runs. Changes in pH were followed with a Beckman Zeromatic pH meter and recorded on a

Jan 1, 1967

By Y. A. Topkaya

The placer gold occurrences at Sart Çayl, Manisa, Turkey, the legendary River Pactolus of King Croessus, were evaluated in this study to determine if this deposit contains sufficient recoverable value to justify development and exploitation. The gold occurs both in the upper Neogene conglomerates and the alluvium derived from these conglomerates. The total reserve in the whole region is estimated to be 500 million cubic metres. Samples were taken of the upper conglomerate and in the alluvium in an attempt to determine the amount and the physical nature of the gold. The gold in samples was recovered by screening out barren oversize followed by washing the sand and gravel through riffled sluices. The resulting sluice concentrate was later panned and amalgamated at site. Laboratory cyanidation testing of some samples for control purposes was also done. The average calculated free gold was found to be about 90-100mg/m3 and the size of gold flakes found was quite small. The field as well as laboratory testing of the samples of Sart Çay1 indicated that the potential reserves in this region could only be developed as a sand and gravel operation and the gold could be recovered together with the heavy minerals as a byproduct.

Jan 1, 1984

By A. P., Svenningsen

ECONOMICAL handling of a minimum of 25,000 tons of minus 3/4-in. ore per day, grinding it to 2 per cent on 65 mesh, and effecting a high recovery of the copper at the lowest possible cost were the principal aims in the design of the new Morenci concentrating plant. Dealing with a tonnage of this magnitude, it is obvious that lost motion cannot be tolerated. When ore is carried on a conveyor an unnecessarily long distance or elevated to a greater height than necessary, or when pulp flows in a launder by a circuitous route thereby losing elevation and distance, we have lost motion which is always costly both from the standpoint of construction and operation. In addition to the 25,000 tons of ore which must be handled, 100,000 tons of water per day has to be carried through the plant in the treatment of the ore. Though water is not so difficult to handle as the ore, the combined tonnage represents a figure which could easily run into a considerable monetary loss per day if all phases of the design were not carefully followed with the idea of eliminating any unnessary handing of materials.

Jan 1, 1942

By Joseph Jensen

CURTAILMENT of oil production in California began in 1922 and 1923 when certain of the major companies completely shut down some pumping properties. Efforts of this kind were generally carried on without coordination by individual companies until 1923. From May to August of 1923, oil production in the Los Angeles Basin was curtailed because of lack of pipe-line outlets. This work was handled by a small committee of executives and engineers of some of the pipeline companies without any established. Method such as obtains at present. Not all of the major companies participated in ibis curtailment and the effort was not well organized. The problem then was principally to move the oil. The crisis passed in September of 1923 from then on the major companies each on it own initiative, shut in additional production. At Domiuguez, in 1921, Shell, Union and Associated agreed to limit drilling to a 100-ft. zone for one Near. In the summer of 1925, operators at Ingde-wood agreed to limit developments to a 1300-ft. zone during the 1925 drilling campaign. In the summer of 1927, the Ventura operators cut back their production one-third and deft it thus for 90 day. Drilling in this field has always been at a slow and conservative rate.

Jan 1, 1932

By K. S. Seljesater

SINCE the development of dispersion-hardenable lead-antimony alloys1 in the laboratories of the Western Electric Co., Inc., studies have been made of the effect of various third constituents on these alloys.2 This paper covers a study of the effect of small amounts of arsenic. This element is important since it occurs as an impurity in many commercial antimonial leads and the results obtained are particularly interesting as indicating a class of addition agents which exert a stabilizing effect on dispersion-hardened alloys. EXPERIMENTAL In order to-study the effect ,of increasing amounts of arsenic, a series of alloys were made up containing 1 per cent. antimony, and arsenic varying from 0. to 0.10 per cent., the balance Doe Run lead (99.997 per FIG. 1..-CHANGE OF MICRO-BRINELL HARDNESS WITH TIME OF 1 PER CENT. LEAD-ANTIMONY ALLOY. cent. lead). The alloys were cast into bars 1 ½ in. wide by ¾ in. thick and cold-rolled to about 1/8 in. thickness. Three samples of each composition were annealed 1 hr. at 225° C. and quenched in water. One set was aged at room temperature, one at 50° C., and the third at 100° C., the

Jan 1, 1929

By John W. Vanderwilt

THE Climax district is in northeastern Lake County, Colorado, on Fremont Pass (elevation 11,320 ft.) where the continental divide runs east-west joining high peaks of the Mosquito Range with the Sawatch Range, prominent ranges of the central Rocky Mountains. The mining towns of Leadville and Kokomo are thirteen miles to the south and seven miles to the northwest, respectively. Good highways lead to Denver (100 miles) by way of Kokomo, Loveland Pass, and Idaho Springs, and to Colorado Springs by way of Leadville. The ore deposit and mine are about one mile east of Fremont Pass and 600 ft. higher on the southwestern flank of Bartlett Mountain, a peak in the Mosquito Range. The molybdenite deposit lies within the Colorado mineral belt extending across the Rocky Mountains from Jamestown and Boulder to Silverton and Telluride. (See Fig. 1.) Fremont Pass is a broad open divide separating the drainage of the Tenmile River (Pacific) from that of the East Fork of the Arkansas River (Atlantic) ; but the mountains to the east and west are extremely rugged; altitudes in the vicinity vary from 11,000 to 14,000 ft. A conspicuous topographic feature within the district is the Tenmile Amphitheater, which lies east of Climax and

Jan 1, 1946

By WALTER VOIGTLANDER

FOR nearly 100 years wire rope has been fabricated in much the same way. To the great majority of mine superintendents wire rope is just wire rope, little or no semblance of individuality or identifying characteristics. Such an impression was fairly justified until three or four years ago when a practical means was found of performing or preshaping the wires and strands. This discovery permitted a revolutionary change in wire rope manufacture. Instead of merely twisting a number of wires into a strand, then twisting several strands into a complete rope (which twisting would naturally result in great internal strain, thus reducing the resiliency and over-all efficiency of the completed rope), the preformed wires and strands were laid in place without force or twisting. The obvious result was a rope more nearly approximating mechanical perfection. The applied loads are more evenly distributed throughout the component wires and strands, thus reducing unbalanced wire stresses. This results in a higher safety factor. The fact that preformed rope will not unravel when untied at the ends proves the absence of a torsional stress that exists in ordinary rope. A greater useful allowable stress in the wires is therefore possible in actual operating service.

Jan 1, 1926

To Americans, Alaska occupies a unique position, both geographically and historically. The only integral portion of the United States lying in the sub-Arctic and Arctic regions of the Earth, the early remoteness and climatic conditions effectively combined to impede the economic development of this area. Although Alaska has been a part of our Nation since 1867, its mining industry is still at that stage of development which characterized the West 100 years ago when miners concentrated on high-grade lodes and rich placer deposits. Since World War II, however, there has been a noticeable increase of interest in the raw materials of the North. This concern has been most noticeable in Canada, Scandinavia and Russia, but it has been, and is being shown in Alaska. To the American mining industry, the potential importance of this State can be summed up by the question, "Can Alaskan mining compete successfully with those of other states and countries?" The answer revolves about the vital factors of geography, economics, and the political turmoil of the World. These aspects are among those discussed on the following pages in a series of articles by Alaskans and non-Alaskans alike. We invite you to read "Alaska: Regional Report."

Jan 12, 1961

By R. T. Hukki

IT is no great exaggeration to say that present grinding practice and economics are largely determined by lining design. A record of outstanding liner wear can be achieved with any liner surface pattern that will positively lock the outer layer or layers of grinding media. With no slippage, lining wear is bound to be slight. At the same time, popular practice calls for tumbling loads of about 50 pct of mill volume to obtain maximum grinding capacity. Innumerable parallel grinding investigations have verified that optimum speed for such a mill lies within 70 to 85 pct of theoretical critical speed. If the mill is speeded up to 100 pct of critical, little or no grinding can be accomplished. Earlier Work on Supercritical Grinding: First investigations concerning grinding at supercritical speeds seem to be very old. Remarkable work on the subject has been performed by White,1 and his experiments have been described and summarized by Richards1 White's contributions seem to have passed unnoticed by Fahrenwald, 2,3 whose extensive experiments have been well presented, yet apparently very little appreciated. Additional work on grinding at supercritical speed has been reported, e.g., by Lewenson and Tscherny,4 USSR; Anselm5 and Grunder,6 Germany; and Rose and Evans,[6] Great Britain.

Jan 5, 1958

By Thomas F. Torries, George H. K. Schenck

Crushed and broken stone is used directly in construction as an aggregate and accounts for about half the value and two-fifths of the quantity of natural aggregates consumed in the United States. Sand and gravel provide most of the balance of aggregates except for some lightweight materials such as pumice and expanded shale. Conditions necessary for production of crushed stone from a deposit are : 1) Quality-should pass rigid specifications for strength and durability. 2) Cost-low average total delivered cost. Construction aggregates are hard, essentially inert materials suitable for being formed into a stable mass either (1) by the addition of cementing or binding materials that produce a concrete or (2) by compaction or by natural weight to produce a road base or foundation. Aggregates usually provide about 80 to 100% of the material volume of the construction masses in which they are used. The construction industry utilizes as aggregates about 70% of all crushed stone produced in the United States according to statistics provided by the U.S. Bureau of Mines (USBM) , [Table 1], using definitions as shown below. Nonconstruction uses of crushed stone, [Table 2], are included elsewhere in Industrial Minerals and Rocks because such uses require the special physical or chemical characteristics which are discussed in those chapters.

Jan 1, 1975

By E. Goldin, H. J. Juretschke

THE electrical properties of porous conductors have been studied ever since such materials, usually prepared by pressing and sintering of metallic powders, obtained practical importance. In most cases, however, the results have not been easy to interpret because of the great number of independent variables such as powder size, pressure, pressing rate and temperature, subsequent thermal history, porosity, and so on, which enter into the fabrication of industrially desirable materials. In recent years an interpretation of these properties has become of interest because the electrical properties of many new substances, prepared as fine powders by crystallization from the vapor phase or by reactions in the solid state at high temperatures, have to be determined on porous samples formed from the powder. Since theoretically significant information must refer to the fully dense state of the material, it is important to relate the electrical properties measured on such porous samples to those expected for a sample of 100 per cent density. A simple theory for the porosity dependence of the electrical conductivity and the Hall effect was recently proposed by Juretschke, Landauer, and Swanson.' Their model, assuming a distribution of pores of equal size and shape, sufficiently far apart so that each pore is embedded in a region of uni-

Jan 1, 1959

By M. K. Foster

Ten horizontal retort zinc blocks of a modified Hegeler design are in operation at Nueva Rosita, Coahuila, Mexico, and produce approximately 170 t of spelter daily, or 62 000 t/year. A block consists of two furnaces of 448 retorts each, making 8960 retorts as the plant complement. Each furnace block is fired with natural gas and air maintaining the combustion mixture in the furnace always slightly reducing. No attempt to recover energy through waste heat boilers is made. The spelter moves to market by rail and truck either in palletized bundles weighing approximately 1060 kg, as loose slabs weighing 26.5 kg each, or as 1088 kg ingots. At present 46% of the metal is exported and 54% is consumed domestically in Mexico. The present day trend toward equalized or alloyed spelter, as well as special shaped castings results in sales of 35% of the entire plant's production. Sulfuric acid is also produced by the Contact Process using vanadium pentoxide as the catalyst. The plant is basically a Monsanto contact system, producing approximately 68 t of 100% sulfuric acid daily. Both 98.5% sulfuric acid and 20% oleum are available. All of the acid made is consumed in Mexico. Shipments are made in 26,900 dm3 tank cars.

Jan 1, 1970

By A. E. Gorum, I. Cornet

Fatigrle of ionic crystals has been studied primarily in magnesinm oxide. under cyclic stress dislocations move irrreversibly; they multiply; slip bands form and grow; cracks mucleate and propagnte, and failure occurs. The use of ionic crystals such as MgO is advantageorus in such investigations because they are optically transparent. Individual dislocation Intersections with {100} surfaces may be observed with a standard microscope, using etch-pit techniques. Slip, deformation, crack .formation, and fracture in MgO crystals under cyclic stress are compared with cotrresponditzg processes in metals. ThE effect of cyclic loading in metals has been studied for many years. The appearance of slip lines is readily observed and the ensuing fracture may also be seen. From these observations it is possible to predict the behavior of a material and make an educated guess as to what is happening internally, but the actual changes taking place within the structure are not readily apparent. If one could obtain a material in which the individual glide components could be observed, it would be invaluable in determining the actual slip distribution resulting from cyclic loading as well as the distribution of slip in the neighborhood of a growing crack. Such a material is magnesium oxide. Dislocation arrays may be observed by means of etch pits

Jan 1, 1961

By Felix Wunsch

WHILE the effect of the cold-junction temperature has been known by many, its consideration has been ignored in a number of installations, resulting at tunes in a very considerable error. In fact, the magnitude of this error may amount to over 100° in some cases. While hand-operated correcting devices for portable checking pyrometers may be entirely satisfactory, it is, of course, desirable to have such apparatus en¬ Millivoltmeter Thermocouple Platinum Wire Mercury FIG. 1.-EARLY `METHOD OF AUTOMATICALLY COMPENSATING FOR COLD-JUNCTION TEMPERATURE CHANGES. tirely automatic, when applied to curve-drawing or printing pyrometers, otherwise there is no assurance that the record is correct. Numerous methods for automatically compensating for cold-junction temperature changes of thermocouples have been proposed and used in connection with millivoltmeters. One of the earliest proposed was that shown in Fig. 1. A bare resistance wire was immersed in a column of mercury located near the cold junction of the thermocouple. An increase in temperature near the cold junction resulted in a rise of the mercury column, which short-circuited more of the resistance wire causing an increase in the potential difference across the millivoltmeter, which compensated for the decreased electromotive force of the thermocouple.

Jan 9, 1919

By W. V. Vietti, W. A. Oberlin

Crude petroleum produced in the Texas Panhandle oil field is both an asphalt and a paraffin-base oil and is further characterized by being a high-gravity crude with an extremely high cold test,. An eight-well composite of Panhandle crude showed the following characteristics: Gravity, 36.6° A. P. I. Viscosity: 61 sec. Saybolt at 100° F. 170 sec. Saybolt at 75° F. 1560 sec. Saybolt at 50° F. (stirring) Cold Test, 60° F. Distillation Test: Per Cent. Per Cent. Gasoline........................ 28.8 Wax........................... 19.2 Kerosene........................ 4.8 Asphalt........................ 13 .0 Gas oil......................... 30.7 Sulfur1......................... 0.8 Fuel oil......................... 34.7 Subsurface Conditions The original pressure in the formation in the Panhandle field closely approximated 420 Ib. gage or 435 Ib. absolute pressure. Temperatures taken indicate that the formation temperatures do not exceed 90° F. The temperatures in Table I are typical measurements taken on one lease. * A contribrition from the research department of the Marland Refining Co. of Oklahoma and the production engineering department of the Marland Oil Co. of Texas. 1 Smith [Analysis of Panhandle and Rig Lake Crudes. U. S. Bur. Mines, Circular No. 6014 (December, 1926)] found an average sulfur content of 0.6 per cent.

Jan 1, 1928

By Ingvar Janelid

DURING the last ten years, in the effort to save manpower and costs, methods of drilling and blasting in Sweden have changed and developed in a revolutionary manner. These developments have been accompanied by extensive alterations in methods of tunneling and in mining technique. Since the end of the 1940's there has been a 100 pct change-over in Sweden to the use of tungsten carbide tipped drill steel. Both investigations and practical results have shown clearly that a tungsten carbide chisel bit fastened directly on the drill steel is the most economical for Swedish conditions. This applies to drill steel up to the longest size it is practical to handle. In terms of drilling footage, durability of the drill steel and the tungsten carbide bit is generally the same. In this respect, therefore, a detachable bit offers no advantage over integral steel. Transportation of integral steel to the grinding plant, instead of detachable bits only, involves heavier work, but this is counteracted by placing grinding plants closer together or by grinding at the working place itself. The drilling rate with integral steel is higher, the trouble of changing bits is avoided, and the difficulties which always arise with joints are eliminated.

Jan 6, 1954

By L. J. Gurevich

IN the course of the examination, at the Bureau of Standards, of fusible tin boiler plugs for the Steamboat Inspection Service, it became evident that an investigation should be undertaken to determine the precautions necessary in the manufacture of acceptable plugs. The results of the tests of these plugs show that their manufacture has improved, though at present not all of the plugs tested are satisfactory. Table 1 gives the result of tests of some 1500 plugs from about 100 makers. Records of the tests show that several of the makers were able to produce satisfactory plugs with every pouring. The Steamboat Inspection Service has the following specifications for fusible plugs: "Fusible plugs for use in boilers of steam vessels under the Jurisdiction of the Steamboat Inspection Service shall be made of bronze casing with the bore tapering continuously and openly from end to end, and filled from end to end with tin not less than 99.7 per cent. pure and to contain not more than 0.1 per cent. of lead and not more than 0.1 per cent. of zinc. The small end of the bore may be countersunk not more than 1/32 in. in depth and width, but no recess, thread, or cavity other than this countersink shall be allowed."

Jan 8, 1919