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By W. S. Weeks

In coursing the ventilating air through a mine it is often necessary to restrict a comparatively open split in order that it may carry exactly the desired quantity of air. Such a restriction is known as a regulator, and usually takes the form of a partition with a hole in it. The quantity of air circulating is controlled by the size of the hole or orifice. For example, it is desired to force a quantity q I cu. ft, per min. through split a (Fig. 1) and the quantity q2 through split b. It requires a pressure of 2 in. water to force the desired quantity through a, and a pressure of 1 in. to force the desired amount through b. The pressure drop between points A and B must be 2 in and a pressure of 1 in. must be destroyed in split b. This is done by inserting a regulator in b, which causes the velocity to increase in the orifice and results in a change from pressure-head to velocity-head. If the air, after passing the orifice, is slowed down in a turbulent manner, all of the velocity-head does not change back into pressure-head, so a permanent loss of static pressure results. A classic formula for computing the area of an orifice to destroy a certain amount of static pressure has been handed down from early days: 0.0004Q a =2 This formula is based on the assumption that all velocity-head in the orifice is "destroyed;" that is, does not reappear again as either velocity-pressure or static pressure. The derivation of the formula is as follows: h = head lost in regulator in fect of air. v = velocity in regulator in fect per second. q = quantity circulating in cubic feet per second. Q = quantity circulating in cubic feet pcr minute. a = area of orifice in square feet.

Jan 1, 1928

By William R. Webster

An investigation has been made of 500 samples of universal and sheared plates of basic Bessemer and basic open-hearth steel manufactured by the Pottstown Iron Company, the carbon-limits being 0.07 to 0.18 per cent. Through the courtesy of Mr. W. H. Morris, President, I am able to lag before the Institute the results of these tests. The samples tested were all taken from the finished material, and the chemical determinations were made on drillings from the broken test-pieces, which were sent to the chemist without giving him the heat-numbers. The results are such as to encourage me to keep on with the work, and, if possible, to have it carried out on other steels. It is kith this view that I now offer my tables in their incomplete form. My first table mas constructed by grouping the tests according to chemical analysis in various. ways, and making a rough tabulated statement, from which the ultimate strengths were worked out and carefully compared with the actual results of the tension-tests. From data thus obtained, one table after another was worked out, and by this method of "cutting and trying" I finally arrived at the results which I now present in Table I. (p. 771). I do not claim absolute accuracy, but my approximations have proved to be so close that the figures are practical data for current use at the works. The indications are that a pure iron, without carbon, phosphorus, manganese, or silicon, if it could be obtained, would give 38,000 pounds ultimate strength. This is assumed as a base, and to it is added the effect of each of the above elements, as explained below. The upper part of Table I. gives the ultimate strength due to carbon and phosphorus, and is the same for both basic Bessemer and basic open-hearth steels. The lower part gives the increase in ultimate strength due to manganese. By adding this to the amount obtained from the upper part, we have the ultimate strength of basic Bessemer

Jan 1, 1893

By E. E. Malouf

With the continued development of low-grade porphyry copper deposits by open pit mining, substantial amounts of copper-bearing strip material have been accumulated in waste dumps adjacent to the many large mines. Since the end of World War II, the production of copper from leaching these copper-bearing wastes increased from approximately 4% of the total copper production to 10% by the early 1960's. Projected increases will probably raise this figure to 20 to 30% by the early 1970's. Furthermore, a gradual recognition of the economic feasibility of leaching mined-out areas is evident and will undoubtedly contribute additional production. Waste dumps in canyons and gulches on the periphery of open pit mines, mine stopes, caved areas, and abandoned open pits often contain substantial quantities of leachable rock ranging in concentration from 0.1 to 0.4% copper. Recent developments in the leaching of copper, mainly the recognition of bacterial oxidation of sulfide minerals combined with better under- standing of the control of the salt content of the leach solutions, both by adjusting the pH and/or by hydrolysis, are resulting in a greatly expanded recovery of copper from these hitherto uneconomic mine rejects. 11.5-1. Mechanism of Leaching. Leaching processes for the extraction of metal values from mine ore or waste may be classified for convenience as either chemical leaching or bacterial leaching. Chemical leaching is considered to be the extraction of soluble salts by metathesis in acidic, basic, or neutral water solutions. The reactions involved may be evaluated by chemical thermodynamics. Bacterial leaching, although a chemical process, is dependent on biological catalysis and this is generally a much more complex process. This justifies its separate treatment in the application to leaching. Acid ferric sulfate solutions are commonly employed in the mining industry to leach valuable metals from metal sulfide ores. The leaching mechanism is a reduction-oxidation reaction in which minerals are oxidized at the expense of ferric sulfate. Such chemical leaching is profitable when

Jan 1, 1968

A GREAT and incomparable speculation is whether the discovery of A compounding the powder used for guns came to its first inventor from the demons or by chance. With this invention he certainly far surpassed all men of every age from the creation of the world up to that day when it was announced by him-men so very learned, indeed like angels and of divine intellect, powerful in every knowledge and power. These had not only revived-arts and sciences and discovered new ones with their intellects, but they had information about all natural

Jan 1, 1942

By E. M. Frizzell

Introduction In 1956, the first mobile crusher was installed in a limestone quarry in Hover, Germany. These early mobile crushers solved the problem of wet and soft ground conditions that did not permit the use of haulage trucks due to the high cost of building and maintaining the haulage roads. Quarry operators also wanted to take advantage of continuous belt conveyor haulage systems and the resulting cost savings. European mines, particularly the coalfields, are in soft materials that allow use of bucket wheel excavators and their following continuous haulage system of belt conveyors. Quarry operators, with this background knowledge of belt conveyors in mining, easily accepted the conveyor concept, once in-pit mobile crushing solved the problem of size reduction of mine-run-rock required for conveyor application. Four years after the initial mobile crusher installation, the first report published on the subject appeared in the December 1960 issue of Mining Engineer (Kochanowsky, 1960). With this early background and basis for direction, mobile in-pit crushing and conveying have increased to more than 74 installations. The capacity, type of crusher, and material being processed appear in Table 1. These data in Table 1 indicate that experience to data has been heavily influenced by limestone installations of less than 1 kt/h (1102 stph). Most of these installations were directly fed by a mine face excavator because of the limestone quarry ground conditions. Crusher Configurations Crushers systems developed to date have varying mobility capabilities. These range from fully mobile units that are used continuously in this mode to fixed, permanently located in-pit crushers. The following terms are presented to help distinguish the range of mobility within the configurations of "mobile" crusher systems planned or now in use. Mobile Crusher The crusher works at the mine face, is directly fed by an excavator, and moves in unison with the excavator on its own transport mechanism as the mining progresses. An example is the unit delivered in 1976 to Yamama Cement Co. in Reyadh, Saudi Arabia.

Jan 1, 1986

By William D. Mayercheck

Introduction of continuous mining machines in the late 1940s created a new production bottleneck in room-and-pillar sections-the shuttle car. While continuous miners could cut and load coal at a nearly constant rate, the mining sequence was repeatedly interrupted as fully loaded shuttle cars changed places with empty ones. This wait-for-the-shuttle delay period forced the coal industry to reassess the shuttle's batch-type procedure with an eve toward continuous haulage systems that would allow uninterrupted coal flow from face to portal.

Jan 7, 1979

By William B. Plank

IN my studies during the past twenty years of the enrollments in the mining and metallurgical schools of the United States and Canada, I have been struck with the great diversity in the curricula offered by these schools. In 1933 when I made my first complete study of the schools (Mining and Metallurgy, May 1934, p. 211), I discovered 19 different curricula or programs of study, leading to almost as many different bachelor degrees, in the 49 schools in the United States and the 4 schools in Canada. These were: (1) Mining Engineering, (2) Coal Mining, (3) Metal Mining, (4) General Mining, (5) Mining Administration, (6) Mining and Metallurgy, (7) Metallurgical Engineering, (8) Metallurgy, (9) Petroleum Engineering, (10) Petroleum Refining, (11) Petroleum Geology, (12) Petroleum and Natural Gas, (13) Ceramic Engineering, (14) Ceramics, (15) Geological Engineering, (16) Mining Geology, (17) Economic Geology, (18) Geo- physics, (19) Fuel Technology.

Jan 3, 1950

By W. S. Ayres

[Secretary's Note.—At the Spokane meeting of the Institute, in discussion of President Brunton's address on "Modern Progress in Mining and Metallurgy in the Western United States," and at the request of members present, Mr. Ayres gave an oral account of his new separator, which is here published as an independent paper, partly because of its inherent importance and partly because it describes an improvement which did not originate in the Western United States, and therefore does not fall, strictly speaking, under the title of President Urunton's address.—R. W. R.] A brief history of the growth of the anthracite-coal preparation will give a better view-point from which to judge the present problem of separating slate from coal. At the beginning of the commercial value of anthracite, 70 years ago, only the pure portions, or " splits," of the veins were mined and shipped to market, and without any preparation or screening other than the selection, while loading, of the glassy lumps, and the rejection of the fine material and the slate that had strayed accidentally into the coal. The next step was the crushing or breaking of the coal (hence the name "breaker" as applied to the preparation-building), and the sizing of it by means of bars or revolving screens. This stage of its development marked the advent of the " breaker-boy " as a slate-picker, with his ever-increasing capriciousness. As the richer veins or a splits " became exhausted and the market demanded a still greater output, the less-pure " splits " and the thinner veins were utilized to produce the coal. Carrying as they do a far greater percentage of impurities, particularly when removing the pillars, it became necessary to build new and better equipped preparation-plants. Finally, we are now at the highest stage of complicatioii yet known to the art of coal-preparation. We are dealing with varying specific gravities, frictional difference, hardness, structure, and form in the pieces of coal and slate coming from many different veins, and

Jan 1, 1910

By Roswell H. Johnson, W. E. Bernard

To know the rate of declinc of oil wells is very important, yet ordinarily we are prevented from getting this rate because the oil from several wells is put into one or a few tanks as soon as the wells have been connected to the power. The object of doing this is economy of tanks, pipes, labor, and accounting. But we are making a great sacrifice for this small economy. The advantages of the individual records are that we would know better: 1. When the well has ceased to be profitable. 2. When a well has gotten into bad condition. 3. The real record of the yield per acre and the rate of decline of the wells. The lease total is too mixed as to age of the wells for existing records to have much significance. To obtain such individual well records and more accurate logs are the great desiderata of satisfactory management of oil properties. 4. Which wells show the slowest decline—information which is valuable in locating new wells or purchasing adjoining leases. The truth of this statement is evident, when we reflect upon the large number of purchases of producing property. Intelligent appraisal is of the utmost advantage and it is impossible without individual well-pro-

Jan 1, 1918

By L. C. McCabe

THE object of the present investigation was to discover a physical basis for rank differentiation of coals, particularly the coals of the Illinois basin. Vitrain1 was selected as the most appropriate coal material to use in the investigation, because of its homogeneity and ease of acquisition and handling. Previous Investigations.-Hoffman and Jenker2 have shown that their index of reflection is a characteristic of coal rank and that the Leitz slit microphotometer may he used in determining the different intensities of reflection. Zhemchuzhnikov3 measured the luster of several Russian coals with a color analyzer and found that the degree of luster was indic-ative of rank. Luster-volatile matter curves based on data from Sucan and Donetz coals were satisfactorily used for determining the rank or volatile content of other coals after the luster strength was determined. In 1934 Fisher4 reported refractive indices of 1.76 for bituminous vitrain and 1.87 for semibituminous vitrain. Investigation of Angle of Polarization.-Early in the present investiga-tion several determinations of the refractive indices of the vitrains were made by immersing the minus 150 plus 200-mesh powder in oils. It was found that all the samples fell within the range 1.6 to 1.8. However, difficulty was encountered in securing oils in this high index range that were closely enough spaced to separate some of the coals. The writers made a number of determinations of the angle of maxi-mum polarization from the polished surfaces of the vitrains and derived their refractive indices by the procedure described in the follow-ing paragraphs.

Jan 1, 1937

By P. E. Demmler

The apparatus in which the process of bright annealing of copper wire was carried out consisted of a section of iron pipe, 6 ft. long and 3 ft. in diameter. The pipe was provided with flanges to which were bolted the end plates for sealing, also with inlet and outlet tubes to allow for the displacement of the air in the pipe by natural gas. After charging with copper wire, sealing and displacing the air, the pipe was heated to 350' C. (662" F.). It was expected that the natural gas would furnish a neutral atmosphere which would prevent oxidation and give a satisfactory bright-annealed product. It was found, however, that the outer layers of wire were discolored and not suited for the use for which they were mtended. To obtain an idea of what was taking place in the annealing furnace, skeins of the hard-drawn wire were placed in a glass tube so that all changes in appearance could be observed as they were heated to different temperatures and under varying conditions. The temperature in each case was determined by means of a thermocouple placed in the tube close to the wire. Following is a summary of the results of these experiments: 1. When the wire was heated for 1 hr. in a current of natural gas at a temperature of 350") 400") or 500" C. (662", 752", or 932" F., respectively), there was a marked darkening of the wire throughout the skein. 2. When heated for 1 hr. in natural gas at a temperature of 600" C. (1112' F.), there was no coloration, the wire remaining clean and bright. 3. When heated in natural gas to 350" C. until darkened and the treatment continued with the temperature raised to 600' C., the coloration disappeared and the wire became clean and bright.

Jan 1, 1923

By P. E. Demmler

The apparatus in which the process of bright annealing of copper wire was carried out consisted of a section of iron pipe, 6 ft. long and 3 ft. in diameter. The pipe was provided with flanges to which were bolted the end plates for sealing, also with inlet and outlet tubes to allow for the displacement of the air in the pipe by natural gas. After charging with copper wire, sealing and displacing the air, the pipe was heated to 350' C. (662" F.). It was expected that the natural gas would furnish a neutral atmosphere which would prevent oxidation and give a satisfactory bright-annealed product. It was found, however, that the outer layers of wire were discolored and not suited for the use for which they were mtended. To obtain an idea of what was taking place in the annealing furnace, skeins of the hard-drawn wire were placed in a glass tube so that all changes in appearance could be observed as they were heated to different temperatures and under varying conditions. The temperature in each case was determined by means of a thermocouple placed in the tube close to the wire. Following is a summary of the results of these experiments: 1. When the wire was heated for 1 hr. in a current of natural gas at a temperature of 350") 400") or 500" C. (662", 752", or 932" F., respectively), there was a marked darkening of the wire throughout the skein. 2. When heated for 1 hr. in natural gas at a temperature of 600" C. (1112' F.), there was no coloration, the wire remaining clean and bright. 3. When heated in natural gas to 350" C. until darkened and the treatment continued with the temperature raised to 600' C., the coloration disappeared and the wire became clean and bright.

Jan 1, 1923

By Eugene S. Perry

The only outstanding development in Montana oil or gas fields during 1935 was the extension of the Cut Bank oil and gas field 7 miles southward. This field is now about 20 miles long and 3 to 8 miles wide, with 218 producing oil wells and 39 producing gas wells. Average daily production of the oil field during December, 1935, was about 6700 bbl.; total production for the year 1935 was approximately 2,020,770 barrels. The Cut Bank field in northern Montana is in a flat to rolling glaciated area used mainly for grazing purposes. Oil and gas occurs in sandstones and shaly sandstones in the Kootenai (Dakota) formation of Lower Cretaceous age at depths ranging from 2700 to 3000 ft. Prominent anticlinal or domal structure is not present, but small plunging anticlines occur locally. Strata dip westward from 75 to 200 ft. per mile. The field lies on the western flank of the Sweetgrass arch, a broad gentle upwarp over 150 miles long. Localization of oil and gas appears to be due either to pinching or lensing out of the sandstone beds, or else silting of the sandstones with clay minerals so that porosity becomes low. Within the field offset wells show marked variation in initial production, which suggests that differences in porosity of sandstone is the controlling factor. The gas-producing portion of the field is entirely updip (east) from the oil-producing portion, and the producing horizons are the same. Initial production of oil wells ranged from about 50 to about 200 bbl. per day, and initial open flow of gas wells ranged from about one million to about 37 million cubic feet per day, with an average of 11 million cubic feet. Initial gas pressures were slightly greater than 700 lb. per sq. in. Oil is brought to the surface by pumping. Both rotary and standard churn-drilling equipment are used. In the remaining 14 oil and gas fields but little new activity took place other than the drilling of offset wells and wells in proven territory. Continuation of "acid treatment" of wells in the Kevin and Pondera oil fields led to reconditioning of many old wells and the drilling of a number of new wells within these fields. Acid treatment of the oil-bearing horizon, which is the dolomitized and silicified Madison limestone of Mississippian age, has proved quite satisfactory, and some "bone dry"

Jan 1, 1936

By Eugene S. Perry

The only outstanding development in Montana oil or gas fields during 1935 was the extension of the Cut Bank oil and gas field 7 miles southward. This field is now about 20 miles long and 3 to 8 miles wide, with 218 producing oil wells and 39 producing gas wells. Average daily production of the oil field during December, 1935, was about 6700 bbl.; total production for the year 1935 was approximately 2,020,770 barrels. The Cut Bank field in northern Montana is in a flat to rolling glaciated area used mainly for grazing purposes. Oil and gas occurs in sandstones and shaly sandstones in the Kootenai (Dakota) formation of Lower Cretaceous age at depths ranging from 2700 to 3000 ft. Prominent anticlinal or domal structure is not present, but small plunging anticlines occur locally. Strata dip westward from 75 to 200 ft. per mile. The field lies on the western flank of the Sweetgrass arch, a broad gentle upwarp over 150 miles long. Localization of oil and gas appears to be due either to pinching or lensing out of the sandstone beds, or else silting of the sandstones with clay minerals so that porosity becomes low. Within the field offset wells show marked variation in initial production, which suggests that differences in porosity of sandstone is the controlling factor. The gas-producing portion of the field is entirely updip (east) from the oil-producing portion, and the producing horizons are the same. Initial production of oil wells ranged from about 50 to about 200 bbl. per day, and initial open flow of gas wells ranged from about one million to about 37 million cubic feet per day, with an average of 11 million cubic feet. Initial gas pressures were slightly greater than 700 lb. per sq. in. Oil is brought to the surface by pumping. Both rotary and standard churn-drilling equipment are used. In the remaining 14 oil and gas fields but little new activity took place other than the drilling of offset wells and wells in proven territory. Continuation of "acid treatment" of wells in the Kevin and Pondera oil fields led to reconditioning of many old wells and the drilling of a number of new wells within these fields. Acid treatment of the oil-bearing horizon, which is the dolomitized and silicified Madison limestone of Mississippian age, has proved quite satisfactory, and some "bone dry"

Jan 1, 1936

By David Reger

ONLY a few small pools of oil were found in West Virginia during 1924. The price of oil was so low that there was no incentive for active effort toward the discovery of new pools or the exploitation of reasonably certain productive areas. At present, several encouraging edge-pool developments are being held in reserve in the hope that a more favorable market is not far distant. In the old pools, wells are being carefully tended; there being little tendency toward abandonment. even in cases where production is temporarily unprofitable. In natural gas, however, the total value of which at the well mouth is now more than that of oil, the year has been busy and profitable. , The decline of old pools, together with the increasing demand, has caused the large operators who carry their gas to the consumer to make great efforts to preserve or increase the rate of production; while the small operators, who sell their product to the large companies at the well mouth, have been stimulated toward the same effort by more favorable prices. These conditions brought about the completion of a greater number .of gas wells in 1924 than in 1923. Few pools of gas have been discovered during the year, the principal production having been obtained in old areas and in the unusually large new territory that was revealed as potentially productive by the drilling of 1923. Some of these latter areas are still without pipelines but definite plans for getting most of this gas are now being executed.

Jan 3, 1925

By F. C. Bond

Since the Third Theory of Comminution was presented eight years ago (I) it has found increasing use in crushing and grinding problems. The practical utility of its wok index equation is quite generally acknowledged (2). However, its theoretical basis has been questioned in at least three technical articles (3) (4) ('). The purpose of this paper is to present experimental proof that it is scientifically correct. Particles under compressive stress are strained and deformed. They absorb strain energy, and when this locally exceeds the breaking strength, a crack tip forms. The surrounding strain energy flows to the crack tip, which rapidly extends and splits the rock, releasing the strain energy as heat. The initial energy flow causes additional crack tips in highly strained areas. If the compression is rapidly applied by impact, crack tips may form before the strain energy has reached equilibrium in the particle, thus decreasing the total work input required for breakage. The energy necessary to break is essentially the energy necessary to produce crack tips, since the energy necessary to extend the cracks to breakage is already present as strain energy in the deformed particles. After breakage nearly all of this energy appears as heat. The crack length cannot be measured directly. However, in particles of regular and similar shape the crack tip length is considered as equal to the crack depth, or crack extension necessary to break, so that the crack length equals the square root of one-half of the surface area. The Third Theory states that the useful work done in crushing and grinding is directly proportional to the total length of the new cracks formed. It can be confirmed by showing that a constant work input produces a constant length of new cracks when reducing the same material to different product sizes. This is done in the present paper on a wide variety of material. The constant work input was supplied by one revolution of the 12" x 12" laboratory ball mill used in making grindability tests by the Allis-Chalmers method (12) (13) The new crack lengths produced per mill revolution were measured from all available grindability test results at 28, 35, 48, 65, and 100 mesh on fifteen different ores, and were found to remain substantially constant for each ore at all mesh sizes. A new technique is used for the measurement of crack lengths. Size distribution plots of the mill feed and product are made by the Third Theory method (9) and the crack lengths are obtained from these plots by the procedure described in the present paper. The energy input required to produce a unit length is of fundamental importance in the size reduction of brittle solids. The crack length Cr is expressed in centimeters per cubic centimeter of solid material. It bears a definite relationship to the external surface area of the crushed or ground solid. A uniform particle shape must be assumed before the surface area and crack length can be evaluated. In this paper it is assumed that the relationship between the surface area and the particle volume of a particle d microns in diameter is the same as that of cube d microns on a side. The external surface areas of particles with a cubical breakage probably agree approximately with this rule, and correction factors can be applied when physical measurements of the surface areas are available for comparison. However, the assumption of equivalent cubes has been found satisfactory for most calculation purposes. Assuming equivalent cubes, one cubic centimeter of particles d microns in diameter will have a crack length Cr of v30.000/d centimeters, and a surface area of 60,000/d square centimeters. The specific crack length is thus equal to the square root of one-half the specific surface area. Where Sa is the surface area in square centimeters per gram and Sg is the specific gravity of the ground solid, then Cr = vSg . Sa/2 = 173.2/ vd (1)

Jan 1, 1961

By Evan Just

Engineering education for the mining industry has been undergoing a gradual change in recent years, to an extent that many employers may not realize. The result of this change is that the new graduate comes to his first employment with very little knowledge that is immediately valuable in operations. He is in fact, simply "half-baked" and needs much education on the job before his schooling will pay out in any significant way. To the employer who fails to recognize this, and fails to give the necessary training to finish the educational job, the modern graduate is likely to be unsatisfying. Moreover, the young fellow's future competence will be impaired. However, to the employer who assumes the educational burden, the effort should pay out as the half-baked products, after a few years, ought to be more useful than their predecessors and should have a greater potential to solve problems or cope with change. The reasons for this development are given below in the foreword to a questionnaire survey circulated by the SME Committee for On-the-Job Training.

Jan 6, 1964

By Oliver Bowles

WHEN a new type of equipment revolutionizes methods of quarrying one kind of stone, producers of other kinds focus their attention on its potentialities in their particular fields. The purpose of this paper is to discuss the accomplishments of the wire saw in slate, to show its more limited attainments in other kinds of stone, and to point out the possibili-ties of much wider application. A wire saw consists of a 3/16-in. or 1/4-in. three-strand wire cable that runs as a belt and cuts the rock by abrasion. (Fig. 1.) The teeth of the saw are sand grains carried in the grooves between the strands.

Jan 1, 1936

By A. U. Seybolt

A. U. Seybolt (General Electric Research Laboratory)— As pointed out in an earlier paper,41 it appears to be very difficult to nucleate Si3N4 in Si-Fe of silicon content up to around 5 pet. Therefore, one observes, as did Pearce, that equilibrations with nitrogen gas yield only nitrogen in solid solution at temperatures above about 700°C, or, as Pearce found, 770°C. Evidently, the free energy of formation of Si3N4 only becomes high enough at -770°C to overcome the reluctance of Si3N4 to nucleate. However, as mentioned in Ref. 41, if some Si3N4 is first formed by a mixture of ammonia and hydrogen, one can then replace this gas mixture by nitrogen gas, and either increase or decrease the amount of Si3N4 present at any temperature by suitable adjustment of nitrogen pressure: that is, to equilibrate with Si3N4. In the equilibration experiments cited in Ref. 41, equilibrium was approached from both sides, and it was found that samples up to 944oC, at least, were in equilibrium with Si3N4. Higher temperatures were not employed, as this would have necessitated a redesign of the apparatus for using nitrogen pressures in excess of 1 atm. To summarize, the results of Pearce's experiments and those of Ref. 41 cannot be directly compared because two quite different equilibria were studied. Therefore, the statement by Pearce on p. 1398 indicating apparent error in Ref. 41 is unjustified. M. L. Pearce (author's reply)— There was limited evidence obtained in the current investigation which would indicate that excessive "supercooling" did not occur. A small piece of the same resulting from heat treatment No. 5 in Table III was subsequently held at 800°C for 16 hr in 95 pet N-5 pet H. Isotope-

Jan 1, 1964

By N. E. Grosvenor

Several methods have been proposed for determining the tensile strength of rock. These have been tried out over the past several years, but the results have been erratic and of doubtful value. The tensile strength of rock is its weakest property, and this property apparently enters into all failure phenomena, whether underground or on the slope of an open pit. Therefore, it is essential that detailed quantitative information is known about the tensile strength of rock if the design engineer is going to select the proper pit slope, pit orientation, or orientation of underground workings so as to give the most economical and safest mining condition. This quantitative information may be used to orient the pit in such a manner as to allow steep slopes along two sides. This information possibly may be used to orient the direction of either underground workings or open pits so as to decrease powder consumption and to increase blasting efficiency. Hence it is of prime importance that a method of determining accurately the tensile strength of rocks be developed. The U. S. Bureau of Mines states' that no standard methods have been proposed by the ASTM for testing the tensile strength of rock. The method described in the Bureau publication is said by them to be unsatisfactory. A similar test that has been used in our laboratory in place of the USBM test is shown in Figs. 1 and 2. h this test the core is placed in a set of grips that has been designed for one particular size core. The grips are designed to distribute the stress around the core if they are tightened correctly. A universal joint or a flexible cable may be used in conjunction with the apparatus to prevent bending or twisting of the specimen. The main difficulty encountered with the system shown is the failure of the specimen within the grips. The possible cause of the failure within the grips may be due to a stress concentration set up by the uneven tightening of the grips. This method can be used only for tests on cores, and even then has been found to be totally unsatisfactory because of the failure within the grips. The U. S. Bureau of Reclamation has been using a test similar to the sketch shown in Fig. 3. Sulfur is cast around each end of the specimen to form a bearing surface and then a ring grip is used to apply a tensile stress. The grips are in contact with the sulfur cast and do not touch the specimen. This method is unsatisfactory, apparently because a large number of the specimens appear to break within the sulfur cast. Professor Wuerker of the University of Illinois uses the test shown in Fig. 4.' Professor Wuerker states2 that this method has given definite and reproducible results with the weakest as well as with the strongest rocks. The test is a supplement in all cases where cores cannot be obtained. The principle and equipment are the same as for the test for tensile strength of hydraulic-cement mortar. Soft

Jan 1, 1961