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By W. O. Crosby

INTRODUCTION. THE crystalline belt of the Atlantic Seaboard, south of New York, attains its maximum breadth of 220 miles on the northern border of North Carolina; and in this State it is most widely characterized by the occurrence of gold in workable deposits. Half a dozen auriferous belts have been recognized by Nitze and Hanna.1 These are, in the main, coincident in position and trend with the NE.-SW. zones of metamorphic slates and schists, which, more than any other feature, give character to the geological map of North Carolina. The central gold-belts, accompanying the main zone of slates and associated igneous rocks, are much the more important and persistent, and may be regarded as continuous northward across Virginia and southward into South Carolina. Tile eastern belt, on the other band, is the shortest and, economically, one of the least important. Its extreme length does not exceed 25 miles, the narrow band of slaty rocks to which it belongs passing, both NE. and SW., beneath the coastal-plain formations. But, although limited in area and production, this belt is, perhaps, comparable with the central belts or any part of the sea-board crystallines in the variety of conditions under which the gold occurs. It lies chiefly in the NE. part of Franklin county and the NW. part of Nash county, on the watershed of Fishing creek and other tributaries of Tar river. The elevation is between 400 and 500 ft. ; and the Tertiary peneplain has here an exceptionally perfect development, the reliefs separating the slightly incised stream-courses consisting of broad, flat-topped peneplain remnants, bounded by gentle lateral slopes.

Mar 1, 1908

By M. D. Hassialis

THE claim is made in a number of patents1,2,3,4 that some compounds of the class known as aryl sulphides have collector properties. One of these patents generalizes the claim to include all aryl sulphides, whose generic formula is R-S¬R[=]-R’ (where x = r,2, . . . ), with the restriction that if the aromatic radicals R, R' contain substituent groups these groups may not contain nitrogen or oxygen. Moses, Hess, and Perkins cite as evidence for their claims the results of flotation tests on Anaconda and Miami copper ores using Biphenyl sulphide, ditolyl disulphide and dinapthyl disulphide as collectors. The use of alkyl sulphides as collectors has also been reported5 with the conclusion that the alkyl sulphides are better collectors than the corresponding aryl sulphides. The experimental work cited appears to confirm this contention. In order to test these claims with respect to diphenyl sulphide, a sample, purchased from the Eastman Kodak Co., was tested against Anaconda ore. The procedure followed was that of Moses, Hess, and Perkins. A sample of ore weighing 500 grams was placed in a laboratory ball mill. To this was added 220 grams of water, 0.06 grams of commercial diphenyl sulphide (1/4 lb. per ton of ore), and 0.8 grams of lime (3 lb. per ton of ore). The material was ground until 93 per cent passed a 65mesh screen. This pulp was diluted to 16 per cent solids. A sample of the diluted pulp was placed in a Minerals Separation type of laboratory flotation cell. After a 2-min. agitation period, pine oil was added and the froth collected for a period of 15 min. This test recovered 68 per cent of the copper, with a ratio of concentration of 6.8: 1. The tailing assay was 0.3 per cent Cu. Moses, Hess and Perkins attained a recovery of 75 per cent, with a ratio concentration of 12: 1. Although these results do not compare too well with those of Moses, Hess and Perkins, subsequent tests showed an improvement, as judged by vanning of the tails. It is concluded, therefore, that the patent results are confirmed. CONTACT-ANGLE TESTS In order to study the response of the various minerals, found in Anaconda ore, to commercial diphenyl sulphide, some contact-angle tests were made. Polished particles of bornite, chalcocite, chalcopyrite, pyrite and quartz were conditioned for 15 min. in a suspension of diphenyl sulphide in water. The concentration of this suspension was 0.284 grams per liter, this being the concentration of this reagent in the ball mill. The conditioned particles were rinsed with water (not rubbed with filter paper or boiled linen) and then tested against an air bubble in the bubble machine, with the following results: born-

Jan 1, 1943

By M. D. Cooper

For the purpose of obtaining some first-hand data in regard to the shooting down of coal in bituminous mines, it was the writer's good fortune to be employed as a shot-firer for almost one year. In all, 6020 shots were fired by him during this period. All of the work was done in what is known as the South Main section of the No. 2 Mine of the Ellsworth Collieries Co., Ellsworth, Pa., a subsidiary of the Lackawanna Steel Go. Position of Shot-firing in the Cycle of Operations The established practice of the Ellsworth Collieries Co. calls first for the undercutting of the coal by electric chain machines across the face of the entry or room. This is followed by replacing any posts removed by the machine-runners, or the setting of new posts or timber, as may be required. After this has been done the machine cuttings are loaded into cars. Then the coal is spragged, and a shot hole drilled to the depth of the undercut. Next in order, the shot-firer loads the hole and fires the charge. The working place is then cleaned up, timbered if necessary, the sides and face squared up, and loose material taken down. The face is again ready to be undercut. Materials Used Permissible explosives were used exclusively in blasting coal. These were Carbonite No. 2, a nitroglyccrine explosive; and three different makes of ammonium nitrate explosives, Tunnelite, Red H, and Mine-ite 5-D. The last-named was used during the greater part of the period. It is interesting to note that even at the beginning of this work, the gases resulting from the explosions of the charges caused no especial distress on. the shot-firer's part and this continued to be the case except on the occasions when a change was made from one class of explosive to another.

Jan 1, 1918

By H. R. Brannon, J. S. Osoba

The introduction of the scintillation counter into field use for gamma-ray well logging has provided a new tool with special utility for the deternzination of natural radioactivity of sediments. Previous subsurface gamma-ray measurements have indicated only the total amount of radioactivity of the sediments. With the scintillation counter, the relative amounts of the elements which emit gamma radiation can be determined. Sediments logged included 35 zones in wells located in the Teras Gulf Coast, East Texas, and West Teras. Although the data obtained from measurements made to date are not sufficient to evaluate the possibilities of spectral logging, it appears likely that spectral measurements will yield information of geologic value. INTRODUCTION Although variations in the natural radioactivity of sediments were recognized as early as 1909,1 the appli- cation of such variations to borehole logging was not made until almost 30 years later. A group of Russian workers in the early 1930's were successful in making crude measurements of natural gamma activity in an oil well borehole. The first practical gamma-ray logging system was developed by Howell and Frosch2 in 1939. Induced radioactivity, or neutron, logging appeared soon after the introduction of gamma-ray logging. After early work had demonstrated the potentialities of radioactivity logging, development of sensitive and stable logging equipment for field use followed, so that neutron and natural gamma logs are now run routinely and have proved to be extremely valuable in characterizing subsurface formations. Even though tremendous strides have been made in developing radioactivity logging, it is apparent that the ultimate in the method of logging has not been reached, for, until very recently1 in none of the commercially available logging systems has advantage been taken of the fact that gamma radiation is composed of a spectrum of rays, each ray having a distinct and characteristic energy. An individual gamma ray originates in a single element and has energy determined by the element. The inten- sity of radiation, or number of rays emitted from unit volume in unit time, is determined by the concentration of the element. If it were possible to sort out these gamma rays and assign them to their parent elements, thereby essentially analyzing for the elements, a wealth of new information descriptive of formation material and fluid content would be at hand. For example, if in natural gamma logging, the gammas due to potassium and to the thorium and uranium series were measured individually, data would thus be available on the concentrations of each of the three elements, adding materially to the information content of the log. In contrast, conventional gamma logs measure only a quantity proportional to the combined concentrations of uranium, thorium, and potassium. The naturally radioactive elements occur in sediments in concentrations dependent on source material of the sediment, and through their chemical characteristics, on conditions of deposition,' so that the individual concentrations may be diagnostic for particular formations. These concentrations, particularly if measured in situ, could lead to a powerful tool for correlation and for reflecting environmental conditions under which sedimentation took place. As a correlation tool, individual uranium, thorium, and potassium measurements

Jan 1, 1957

By Fred D. Rosi

Introduction There is probably no field in which materials research has played a greater role than that of electronics. However, to trace present and future patterns of materials research in electronics is not an easy assignment, since this industry has a high degree of dynamism in its growth, and is busily engaged today in the scientific improbabilities of only recent yesterdays. On the other hand, this task seems especially appropriate since electronics is a truly frontier industry - one whose place in American industries has advanced from 50th prior to World War II to 6th in 1967, with sales of more than $22 billion. And this growth has been associated with the equally rapid progress of science and technology over the period - in particular with the emergence of materials science as a vital force in underscoring this progress. For several reasons this parallel growth is not too surprising. First, by its very definition electronics is a science that essentially deals with the nature, behavior, detection, generation, control and utilization of electrons in solids or at their surfaces. Second, in the electronics industry, systems are made of an integration of components, and these components with their interconnections are made of materials. Thus, the basic building blocks of systems are materials; and it has been largely the advances in materials research and technology that have led to new and improved devices and systems. It follows, therefore, that the broadening of the frontiers in electronics through the exploration of new territories is tantamount to scientific discovery and materials innovation to a degree found in no other major industrial activity. But to put this in the proper perspective of present and future materials trends, it would be appropriate first to survey historically the progress in electronics by pointing out major scientific discoveries and associated materials research patterns that have led directly to its tremendous growth. Then from this base we can consider recent trends in materials research that could form the basis for future progress in the electronics industry. In my review I shall examine the areas most familiar to me, so I must acknowledge at the outset that this survey is not all-inclusive.

Jan 1, 1971

By M. Guney, A. R. Bell

In Mindola mine on the Zambian Copperbelt, there is a plan to extend the current production level of 1.2- 1.5 km (3,900-4,900 ft) with five additional production levels. Research work indicated that the present total heat output of 38.6 MW will inevitably increase to 63.2 MW in 25 years. Estimated WE and DB temperatures, representing the total heat generation in stope faces and development headings during these same periods are predicted to increase to 33.8/40.2°C (93/104°F) and 35.3/42.1°C (95/108°F) respectively. It is assessed that the nominal refrigeration capacity needs to be progressively increased to 9,000 M W.

Jan 1, 1984

By Paul T. Allsman

Passage of the Mining Act of 1866, superseded by the Act of 1872, was the first major entry of the Federal Government into the problems of mining. Such a law was necessary simply to help re- solve a number of disputes in mining. Now, however, a hundred years later, the extent of government involvement in the mineral industry often comes as a shock to the mining engineer who has reached management level. In fact, he has been poorly prepared for an understanding of the role of government in the industry and he becomes frustrated, even hostile. In our political system, private industry is responsible for producing minerals and the Government sees to it that production will be adequate for a peace-time economy and for any emergency. There have been great social and political changes since World War I1 with the result that the Government's participation in our society has steadily increased. A new dimension in business and government relations has been introduced which should be examined more closely.

Jan 5, 1966

A MINING institute open to all men interested in any branch of the mining industry will be held at the Col-lege of Mines, University of Washington, Seattle, during the week beginning March 5. Prospectors, miners, mine owners, persons interested in metallurgy, investors in min-ing enterprises, and the public generally are invited to at-tend. This institute will take the place of the Winter Min-ing Session which originated at Seattle in 1897 and con-tinued for twenty-eight years. The complete new equip-ment of the Mines Laboratory will be used to give demon-strations of new machines and processes of mining, ore dressing, and metallurgy. This year the ceramic industry, including cement and branches of clay working of special Importance in the Northwest, will be included in the insti-tute. All instruction will be given by specialists. Prominent technical men and managers will give lectures on their special subjects. Among the speakers engaged are G. T. Jackson, formerly superintendent of the Alaska-Gas-tineau and the Chichagof mines, who will speak on the mining of large bodies of low-grade ore; R. F. McElvenny, superintendent of the Tacoma Smelter, on the nature of contracts that a smelter can offer to mines and prospects; M. D. Leehey, mining lawyer, on some popular errors re-garding the mining law; H. H. Townsend, on the explora-tion and purchase of prospects by operating companies; J. L. McAllen, on quartz mining in the Willow Creek dis-trict, Alaska; F. Powell, on gold dredging. In the evenings, lectures illustrated by stereopticon views and moving pic-tures will be given. The week will close with an excursion o mines and plants.

Jan 3, 1928

The problems associated with the processing of the Tilden ore are very much representative of the problems encountered in plants processing fine grained magnetic and nonmagnetic iron ores. I would like to comment on some of the problems mentioned in Dr. Nummela'spaper and add to his list of research opportunities in the processing of iron ores. Grinding, the most important step in the processing of fine grained iron ores, is synonymous with liberation. One grinds to separate discrete grains of minerals from the gangue. By convention- al grinding in tumbling mills, mostly random size reduction is achieved with relatively little preferential liberation of minerals. Not only are discrete particles broken that should not be broken, but damage is done to the mineral surfaces. The combination of over- grinding and surface damage shows up in lower recovery figures and higher grinding costs. What is obviously needed is a better comminution process that is more discriminating and that would permit liberating mineral particles at the coarsest possible size with a minimum production of fines. Laboratory attempts at such preferential grinding have been quite successful, but technological difficulties have unfortunately prevented its use. Impact grinding is a good example of a new comminution process that has not been accepted because of equipment problems. Either these problems have to be solved or new comminution systems have to be developed to reduce grinding costs and improve liberation. In his paper Dr. Nummela mentions the change in the primary mill throughput that occurs during the winter months. Seasonal changes in the operation of the grinding circuit and other unit operations have been observed in many plants, and many explanations for this phenomenon have been advanced. The fact is that we do not fully

Jan 1, 1979

Discussion of the paper of L. C. Graton and Joseph Murdoch, presented at the New York Meeting, February, 1913, and printed in Bulletin No. 77, May, 1913, pp. 741 to 797. THOMAS T. READ, New York, N. Y. (communication to the Secretary *) :-At the meetings of English technical societies it not infrequently happens that, during the discussion of a paper, someone will arise to say that although he highly appreciated the material presented, nevertheless he believed it would have been better if some other phase of the question had been more highly emphasized. Assuming that this form of discussion is permissible in the Institute, I should like to reiterate the point made by Prof. A. J. Moses that conclusive proof of the identity of the minerals in question is an essential feature of the study of ores in this way. This is also expressed by Paul Krusch in his recent valuable paper 1 on the sulphide ores (in which he arrives at conclusions diametrically opposed to those of Mr. Graton), as follows : ?The diagnostic properties of the various ore minerals are known to but a limited circle of investigators." Many earlier investigators began the study of ores beneath the microscope by reflected light, but discontinued their work, in most cases, because they were unwilling to undertake the great amount of preliminary work necessary to securely establish a basis for their inferences. It is evident that Messrs. Graton and Murdoch realize that the promised later paper on diagnostic characters will be the more important of the two, but the point should be emphasized to forestall a flood of literature from other investigators who may gain the impression that the brief survey of polished specimens is a wade mecum to incontrovertible conclusions as to any given ore deposit.

Jan 10, 1913

(The following-list contains the names of those members of the Institute of whose connection with military service we have only recently. become acquainted.) ADAIR, ARTHUR C., Corporal, 4th Co., 1st Tr. Bn., 154th D. B., Camp Meade, Md. BATCHELOR, STILLMAN, 1st Lieut., Co. 6, E. 0. T. S., Camp Humphreys, Va. BATES, BENNETT R., 1st Lieut., Engineers, Co. 3, E. 0. T. S., Camp Humphreys, Va. BJORGE, GUY N., Co. 3, E. 0. T. S., Camp Humphreys, Va. BOAS, Ross, H., U. S. A. BRADLEY, . H., JR., Capt., 408th Engineers, Camp Cody, N. M. BRINTON, OWEN F., Capt., Engineers, U. S. A. BROWN, HAROLD C., 2d Lieut., A. S. A.P.

Jan 1, 1919

By R. W. Armstrong, P. C. Jindal

TABOR1 has indicated for a number of polycrystal-line materials that their hardness should be directly related to their yield strength. For a material showing zero work-hardening, the Meyer hardness, MH, may be calculated in terms of the yield stress, sy, by utilizing slip line theory and the result is: The Meyer hardness corresponds to indenting the surface with a spherical indenter and specifying the ratio of load and projected area of the indentation. The correlation indicated by Eq. [I] is not well-established. It has been verified to some degree by performing hardness tests on materials strained to the maximum nominal stress and taking this stress as the (new) yield stress of a nonwork-hardening material. The dependence of hardness on yield strength for an annealed material capable of showing work-hardening has not been theoretically evaluated but, presumably, the hardness should be greater than that specified above. Marcinkowski, Fisher, and szirmae2 measured the dependence of the Vickers Diamond Pyramid hardness, H,, on yield strength for an annealed Fe-Cr alloy which shows work-hardening and found:

Jan 1, 1968

By Michael J. Messel

The critical shortage of asbestos fiber in the world today brings to the foreground the question of locating and developing new deposits. The object of this paper is to discuss some of the more important factors which should be considered in the examination and valuation of a new asbestos enterprise. Some of the more important uses of asbestos fiber are for textiles, heat insulators, building materials, filters and a series of other uses. The properties of this mineral, such as fibrous structure, color, strength, silkiness and flexibility, coupled with resistance to fire, certain chemical action and decay make its application unique for certain industrial uses which consume over 500,000 tons annually. These same unique properties which make this mineral so valuable also make a deposit one of the most difficult to appraise accurately, because of the many undeterminable and varying factors which must be considered before a deposit can properly be termed commercial. The majority of the asbestos fiber today, having the above mentioned properties, is sold by grades which are based on fiber length. Present day fiber prices vary over a wide range from $800 to $225 for crude fibers and $300 to $20.00 per ton for milled grades. For valuation purposes a careful study should be made of existing fiber prices and markets. Examination of Deposits In carrying out prospecting and examination of a deposit, considerable caution is required to get the necessary information in the form that will have the most value for the final determination. There are two main classes of asbestos fibers, chrysotile and the amphiboles, the chrysotile being, by far, the most important both in abundance and uses. This paper will stress mainly chrysotile deposits, however, the amphiboles have many important uses, especially amosite and crocidalite. Their valuation presents special problems as other factors may be involved, especially as they are not graded according to any well defined and adopted standard but usually according to the use for which they are being supplied. Most chrysotile deposits occur in two main types of rock, (I) mainly in basic igneous, such as dunite and peridotite, (2) to a lesser extent in sedimentary rocks, such as dolomite and limestone. All of these require a certain degree of metamorphism to be favorable to asbestos formation. Approximately 90 pct of the asbestos deposits are derived from serpentinization of dunite or peridotite, whereby the magnesium-silicate olivine was altered to hydrous magnesium-silicate serpentine. Under certain favorable geological conditions, this serpentine takes a fibrous form having a definite crystal structure, probably due to molecular rearrangement, and is known as chrysotile. The fiber veins are usually ir-

Jan 1, 1948

By Michael J. Messel

THE critical shortage of asbestos fiber in the world today brings to the foreground the question of locating and developing new deposits. The object of this paper is to discuss some of the more important factors which should be considered in the examination and valuation of a new asbestos enterprise. Some of the more important uses of asbestos fiber are for textiles, heat insulators, building materials, filters and a series of other uses. The properties of this mineral, such as fibrous structure, color, strength, silkiness and flexibility, coupled with resistance to fire, certain chemical action and decay make its application unique for certain industrial uses which consume over 500,000 tons annually. These same unique properties which make this mineral so valuable also make a deposit one of the most difficult to appraise accurately, because of the many undeterminable and varying factors which must be considered before a deposit can properly be termed commercial. The majority of the asbestos fiber today, having the above mentioned properties, is sold by grades which are based on fiber length. Present day fiber prices vary over a wide range from $800 to $225 for crude fibers and $300 to $20.00 per ton for milled grades. For valuation purposes a careful study should be made of existing fiber prices and markets. EXAMINATION OF DEPOSITS In carrying out prospecting and examination of a deposit, considerable caution is required to get the necessary information in the form that will have the most value for the final determination. There are two main classes of asbestos fibers, chrysotile and the amphiboles, the chrysotile being, by far, the most important both in abundance and uses. This paper will stress mainly chrysotile deposits, however, the amphiboles have many important uses, especially amosite and crocidalite. Their valuation presents special problems as other factors may be involved, especially as they are not graded according to any well defined and adopted standard but usually according to the use for which they are being supplied. Most chrysotile deposits occur in two main types of rock, (I) mainly in basic igneous, such as dunite and peridotite, (2) to a lesser extent in sedimentary rocks, such as dolomite and limestone. All of these require a certain degree of metamorphism to be favorable to asbestos formation. Approximately 90 pct of the asbestos deposits are derived from serpentinization of dunite or peridotite, whereby the magnesiumsilicate olivine was altered to hydrous magnesium-silicate serpentine. Under certain favorable geological conditions, this serpentine takes a fibrous form having a definite crystal structure, probably due to molecular rearrangement, and is known as chrysotile. The fiber veins are usually ir-

Jan 1, 1947

By Michael J. Messel

The critical shortage of asbestos fiber in the world today brings to the foreground the question of locating and developing new deposits. The object of this paper is to discuss some of the more important factors which should be considered in the examination and valuation of a new asbestos enterprise. Some of the more important uses of asbestos fiber are for textiles, heat insulators, building materials, filters and a series of other uses. The properties of this mineral, such as fibrous structure, color, strength, silkiness and flexibility, coupled with resistance to fire, certain chemical action and decay make its application unique for certain industrial uses which consume over 500,000 tons annually. These same unique properties which make this mineral so valuable also make a deposit one of the most difficult to appraise accurately, because of the many undeterminable and varying factors which must be considered before a deposit can properly be termed commercial. The majority of the asbestos fiber today, having the above mentioned properties, is sold by grades which are based on fiber length. Present day fiber prices vary over a wide range from $800 to $225 for crude fibers and $300 to $20.00 per ton for milled grades. For valuation purposes a careful study should be made of existing fiber prices and markets. Examination of Deposits In carrying out prospecting and examination of a deposit, considerable caution is required to get the necessary information in the form that will have the most value for the final determination. There are two main classes of asbestos fibers, chrysotile and the amphiboles, the chrysotile being, by far, the most important both in abundance and uses. This paper will stress mainly chrysotile deposits, however, the amphiboles have many important uses, especially amosite and crocidalite. Their valuation presents special problems as other factors may be involved, especially as they are not graded according to any well defined and adopted standard but usually according to the use for which they are being supplied. Most chrysotile deposits occur in two main types of rock, (I) mainly in basic igneous, such as dunite and peridotite, (2) to a lesser extent in sedimentary rocks, such as dolomite and limestone. All of these require a certain degree of metamorphism to be favorable to asbestos formation. Approximately 90 pct of the asbestos deposits are derived from serpentinization of dunite or peridotite, whereby the magnesium-silicate olivine was altered to hydrous magnesium-silicate serpentine. Under certain favorable geological conditions, this serpentine takes a fibrous form having a definite crystal structure, probably due to molecular rearrangement, and is known as chrysotile. The fiber veins are usually ir-

Jan 1, 1948

By Hugh Spence

THE use of natural feldspathic rocks, as opposed to straight feldspar, for ceramic purposes is not new. "Cornwall stone," a semi-kaolinized granite containing fluorite, has long been used by the English pottery trade instead of feldspar, and "Carolina stone," a similar rock, is now being offered to the American trade. A recent report of the U. S. Bureau of Mines states that trachyte, a glassy volcanic rock, is being used in California instead of feldspar in ceramic bodies. In Germany, phonolite and basalt have been investigated, and possibly also used, as ceramic raw materials, and extensive research has been conducted in Russia in recent years looking to the utilization of the immense bodies of nepheline syenite of the Kola Peninsula, which is the host rock of the apatite deposits now being exploited on a large scale in the Murmansk region; the nepheline is recovered as a by-product of the concentration of the apatite. Long used principally as a raw material for the pottery and allied industries, where, in bodies, glazes, enamels, etc., it serves as a fluxing ingredient and forms, on firing, a glassy bond with the more refractory clay, flint and coloring particles, feldspar has been finding ever increasing employment in glass. In 1936, over half of the nearly quarter of a million tons of feldspar sold in the United States went to the glass trade. Its usefulness for this purpose is due to the resistance to thermal shock which it imparts to glass products, particularly bottles, containers and tableware, because of its alumina content, which averages from 16 to 20 per cent. Active search has been made on the American continent during the past few years for other minerals of feldspathoid type, with comparable or higher alumina content, that may be suitable for glass and other ceramic purposes. One of the most important results of this work has been the delimiting in central Ontario of large bodies of nepheline syenite of excellent ceramic grade.

Jan 1, 1938

By R. E. Reed, R. D. Leggett, Paxton, H. W.

TECHNIQUES have been developed for growing monocrystals and bicrystals of Fe-20 Cr, Fe-20 Cr-20 Ni, and Fe-18 Cr-8 Ni alloys by both the strain-anneal and the Bridgeman techniques. None of the techniques are new but since they are simple and many people have expressed interest, they are described here quantitatively as they could be modified for other single-phase "commercial" materials of high melting point. CRYSTAL GROWTH BY STRAIN ANNEAL Flat tensile specimens with a tapered gage length were initially studied to deduce the approximate critical strain. Normal flat tensile specimens were then used. The optimum procedure for the austenitic steels (Fe-Cr-Ni) deduced from a variety of cold reductions, recrystallization treatments, tensile strain, and growth anneals was as follows: cold reduce 70 pct, recrystallize (after machining tensile specimens) at 1000°C for 1 hr, strain in tension 2.5 pct, and then heat to 1350°C as rapidly as possible. A time of 100 hr at 1350°C is usually sufficient to pro-

Jan 1, 1960

By AIME AIME

THE papers presented at the geophysics session" on Feb. 17 were concerned largely with three aspects of the science. The first ones dealt with the transmission of elastic waves through the earth, then electrical methods came in for their share of attention and finally, the question of the teaching of geo- physics came up for the first time at these meetings. Also, for the first time, there was a symposium of mining men on the practical value of the new science. The paper (T. P. 267) entitled "Seismic Propagation Paths" was presented by Donald C. Barton in the absence of the authors. It dealt with an investigation of the speed of propagation of seismic waves. The latter travel in a straight line when proceeding at a constant velocity, but if the velocity increases at increasing depths, the line of travel becomes a curve. Under the assumption of the authors this curve is found to be the arc of a circle, and their paper gives calculations for reflected and refracted wave paths under these circumstances.

Jan 1, 1930

By Alexander Bowie

In many places throughout the Western mountain plateau regions of the United States coal beds in place have been burned over very extensive areas, the fire evidently originating on the nakedly exposed outcrop of the coal bed and gradually burning its way into the bed for considerable distances under very heavy cover. The surface evidences of the burned-out coal beds are seen in the calcined and discolored rocks overlying the places of the outcrops. The greater the mass of the burned coal the higher the results of its combustion can be seen in the overlying strata. I have noted many instances of this condition in the States of South Dakota, Wyoming, Colorado, New Mexipo, and Arizona. In the lignite fields of Dakota and Wyoming I noted stretches of level country many square miles in extent where the surface rooks were roasted and vitrified by the burning of a great bed of lignite lying nearly level and with a light cover; this is probably the most favorable natural condition for the burning out of a coal bed. The less the depth of the rock covering overlying the coal bed, the better the chance for a continuous supply of air to the fire; but when the coal bed dips heavily into the ground, or even if level, if it passes under a hill or mountain which gives the bed a heavy covering of strata, the fire has more chances of being extinguished from natural causes than in the first condition described. The distance which a crop fire may extend into a coal field is very much influenced by the dip, the thickness of the coal bed, and the nature of the rock covering immediately overlying it. In reasoning on this subject, it would seem logical to assume in the case of a coal-bed cropping at the base of a hill and dipping into it, with an extensive drainage surface above the crop line, that a crop fire would be promptly extinguished by the caving in of the overlying strata and the precipitation of the rainfall from the drainage surface above the outcrop through the breaks formed in the caving strata. This consideration would be more or less effective according to the climate of the location and the nature of the overlying strata. In a humid climate where the rainfall was heavy the water from the natural precipitation alone would probably extinguish a crop fire before it could work its way very far under cover, but in an arid climate this preventive does not seem to be effective.

Jan 1, 1915

By K. W. Smith, E. A. Thomas

Various grades of synthetic mullite have been developed in recent years to replace or supplement natural sources of mullite deriued from the mullite group of minerals consisting of sillimanite, kyanite, and andalusite. Raw materials and heat treating processes used in making synthetic mullite are described. Chemical and physical data are given for typical grades and crystalline structure is illustrated with micrographs. Use of synthetic mullite as a refractory material in the glass and metallurgical industries is discussed. Mullite (3A12O3.2siO2), the only stable compound formed in the alumina-silica system, is usually present to some degree in all aluminum silicate ceramic products. The formation of mullite is considered beneficial to give rigidity to the structure and is dependent upon the ratio of Al2O3 to SiO2 in the original composition, particle size, degree of mixing, firing temperature, cooling rate, and the presence of auxiliary glass-forming fluxes. Mullite may also be formed at the reaction interface of fire clay or alumina-type refractories in contact with glass or slag melts. The term synthetic mullite is commonly used today to identify a class of sintered and fused aggregates or grains in the alumina-silica system having a highly developed mullite structure but derived mainly from raw materials other than the sillimanite group of minerals. Within the past 15 years extensive research has been done to develop economical processes to form sintered synthetic mullite aggregate to replace calcined Indian kyanite in super-refractories. Severa1 brands of such mullite are now being produced in commerical quantity and finding extensive use in refractories. Based on the service results of such refractories in many applications throughout the metallurgical, ceramic, and glass industry these developments have been considered successful and suitable substitutes for Indian kyanite now appear assured. EARLY DEVELOPMENT The conversion of kyanite, sillimanite and anda-lusite minerals of the sillimanite group to mullite and their use in refractories and porcelain have been discussed quite extensively in the literature by peck,' Grieg,' Riddle and Foster,3 Bowen and Grieg,4 and others and will only be mentioned here for reference to compare properties with synthetic mullite. In 1928, curtis5 reported on the development of a high temperature gas-converter process for forming synthetic mullite. The raw materials were derived mainly from lumps of high alumina clay of the correct natural composition or blends of clays and alumina that was interground and briquetted to form a suitable charge to maintain a surface combustion firing within the converter. Curtis was, no doubt, the first to illustrate by micrographs in natural color the crystalline structure of mullite derived from kyanite and mullite derived by sintering clay and alumina mixtures at temperatures above cone 32 (3123°F) and by electric fusion. In 1937, sei16 was issued a patent covering the use of a mixture of alumina-silica minerals and alumina in the proportion to form a mullite-yielding material at temperatures in excess of 3100' F. During the period from 1930 to 1940, economic conditions were not favorable for the production of synthetic mullite mainly due to an adequate supply of good grades of Indian kyanite ore suitable for conversion to mullite. Uncertain conditions on availability of the Indian kyanite during the early stages of World War II fostered further study on the development of synthetic substitutes. In 1943, McVay and wilson7 reported on an extensive investigation of domestic substitute materials. Their work covered essentially the use of mixtures of electric furnace mullite, calcined topaz, and calcined domestic kyanite. Compositions were found that gave equivalent or better hot load strength than Indian kyanite in mullite-type brick compositions; however, the calcining of the topaz presented certain physical and chemical problems on the disposition of silicofluoride and hydrofluoric acid while the high cost of electric furnace mullite was a limiting factor. In this work it was pointed out that water-quenched fused mullite was found to be unstable on reheat and gave poor hot load strength due to excessive glass present whereas the slow cooled or annealed mullite contained large crystals of mullite and corundum with little glass and gave superior results.

Jan 1, 1961