Search Documents

By F. V. Greene

This paper is based on my experience in the use of asphalt, for paving and other purposes, during the last ten years, part of the

Jan 1, 1889

By A. Eilers

I PRESENT herewith, for the inspection of the members of the Institute, a specimen of coke, made in gas-retorts from the lignite of Trinidad, Colorado.

Jan 1, 1874

By A. Eilers

I present herewith, for the inspection of the members of the Institute, a specimen of coke, made in gas-retorts from the lignite of Trinidad, Colorado.

By Clarence R. King

Diamond drilling of Cove Creek deposits and development of flotation-refining process may lead to commercial operation of property worked sporadically for almost a hundred years.

Jan 4, 1953

By T. R. A. Davey

A Survey of current and recent research and developmental work is supplemented by predictions for processes which should be developed over the remainder of this century.

Jan 1, 1970

The authors have done a very thorough job in analyzing the factors affecting turndown sulfur performance at Inland's No. 4 B.O.F. While many of the results are not unexpected, it is helpful I am sure to have quantified many of the relationships that the operators rely upon daily. On the other hand, however, the results shown for ladle skimming are very surprising. I do not doubt the statistical relationship shown but I feel, based on our experience at Youngstown, that some other parameter has been ignored in the data on ladle skimming. It was our experience that by skimming our hot metal transfer ladle we could reduce our lime consumption by eleven percent while obtaining sulfur removal comparable to that shown by the authors. I would like the authors comment of similar adjustments on the lime charge that were made on skimmed heats at Inland. If not, it would seem that one could gain more desulfurization in the B.O.F. by raising the hot metal manganese than by installing a skimmer. The author's state that no comparisons are valid between the data sets for the two time periods involved because of the difference in the consumption of No. 2 Bundles. I feel this in fact is one of the important conclusions to be drawn from the paper, as there seems to be approximately a 10-20 percent difference in percent of heats that are under 0.020 percent sulfur for similar conditions, which is an extremely important difference with today's demands for low sulfur. I would like the author's comments on the difference in the amount of 82 bundles consumed. Along this same line I was quite surprised by the relatively low number of heats that had a first turn down of 0.020 percent sulfur or less. Also rather disconcerting are the conditions necessary to achieve a first turn of 0.020 percent sulfur, 50 - 60 percent of the time, as required by today's specifications. It is a problem which we are well aware of, but the numbers are still shocking.

Jan 1, 1972

By William M. Newton, John E. Sherborne

The value of the electric log as a means of interpreting underground structures has been increasingly demonstrated by its almost universal present-day use. It becomes important, therefore, to be able to evaluate the factors that affect the values obtained. By far the greatest number of electric logs are measured today in boreholes filled with rotary mud, the properties of which may exert an important influence on the electric log. In an effort to establish what the order of magnitude of such effects might be, a series of investigations was made in the laboratory and the field. Apparatus suitable for either field or laboratory use was designed and a procedure established for determining the factors that affect the resistivity of drilling muds over a wide variation in mud condition. Five muds representative of the types of clay-base muds employed in California were tested and the following observations were made: 1. The effect of raising the temperature from 8o° to i8o°F. is to decrease the resistivit~ of the mud or filtrate approximately 50 per cent. 2. The resistivity of the mud in most cases closely approximates that of its filtrate. 3. The change in the resistivities of muds caused by the addition of chemical is not the same function of the amount of chemical added for each mud. 4. The effect produced by increased sodium chloride content is to reduce markedly the resistivity of the mud and its filtrate. 5. Weighting materials, such as baroid and limestone, tend to increase the resistivity of drilling mud. 6. Cement and counteracting reagents reduce mud resistivity. The results of the investigation indicate that the mud resistivity is materially affected by the addition of electrolytes whether these are added for the purpose of conditioning the mud or enter the mud when salt beds or highly saline structures are penetrated. It should be observed, however, that the magnitude of the effect produced upon the electric log by changes in mud resistivity is also dependent upon the relative salinity of the water en. countered in the formation being logged. The laboratory data are supplemented by field data, which indicate that both the self-potential and resistivity curves are influenced by mud resistivity.

Jan 1, 1946

By Roy A. Hardy

THE Getchell mine is a comparatively recent discovery in the old Potosi mining district, Humboldt County, Nevada, a district organized in the seventies and eighties, in which some prospecting was done in several metamorphic zones along a monzonite-sedimentary contact. The district had no production in the early days and no further work was done until the same metamorphic zones were prospected for tungsten (scheelite) in 1917 and 1918, when a few small lots were shipped. It again lay dormant until 1934, when prospectors investigated a large siliceous escarpment at one end of the old district where outcroppings were a prominent feature of the topography. Undoubtedly, during the early prospecting of the district, the outcroppings had been investigated for mineral, probably by panning, with negligible results because the gold later found is invisible in the concentrate and is refractory. A fire assay revealed the presence of sufficient gold to warrant development work. The outcroppings were easily prospected by short tunnels having their portals in the siliceous material on the hanging-wall side, with a maximum distance to crosscut to the footwall of 135 ft., or a distance at right angle to dip of 60 to 90 ft. Development work, reaching a depth of over 600 ft. on the dip of the vein, was done by means of various crosscut tunnels, winzes and laterals. A churn-drill hole was also sunk, which intersected the vein at a depth of 1100 ft. on the dip. Sufficient development work of this character was completed by 1937 to justify the erection of a reduction plant to roast the sulphide ore and cyanide the calcine, and to treat the oxidized ore by straight cyanidation, to make a doré bullion for shipment to the mint. The erection of the plant was started that year and finished early in 1938, with a combined capacity of about 800 tons per day. It has operated continuously since erection and recently was enlarged to handle 1000 tons per day. The vein dips with the slope of the mountain, and by stripping the hanging wall the ore may be mined by power shovel for several hundred feet below the outcrop. Thereafter underground methods will be necessary.

Jan 1, 1940

By John E. Sherborne, William M. Newton

The value of the electric log as a means of interpreting underground structures has been increasingly demonstrated by its almost universal present-day use. It becomes important, therefore, to be able to evaluate the factors that affect the values obtained. By far the greatest number of electric logs are measured today in boreholes filled with rotary mud, the properties of which may exert an important influence on the electric log. In an effort to establish what the order of magnitude of such effects might be, a series of investigations was made in the laboratory and the field. Apparatus suitable for either field or laboratory use was designed and a procedure established for determining the factors that affect the resistivity of drilling muds over a wide variation in mud condition. Five muds representative of the types of clay-base muds employed in California were tested and the following observations were made: 1. The effect of raising the temperature from 8o° to i8o°F. is to decrease the resistivit~ of the mud or filtrate approximately 50 per cent. 2. The resistivity of the mud in most cases closely approximates that of its filtrate. 3. The change in the resistivities of muds caused by the addition of chemical is not the same function of the amount of chemical added for each mud. 4. The effect produced by increased sodium chloride content is to reduce markedly the resistivity of the mud and its filtrate. 5. Weighting materials, such as baroid and limestone, tend to increase the resistivity of drilling mud. 6. Cement and counteracting reagents reduce mud resistivity. The results of the investigation indicate that the mud resistivity is materially affected by the addition of electrolytes whether these are added for the purpose of conditioning the mud or enter the mud when salt beds or highly saline structures are penetrated. It should be observed, however, that the magnitude of the effect produced upon the electric log by changes in mud resistivity is also dependent upon the relative salinity of the water en. countered in the formation being logged. The laboratory data are supplemented by field data, which indicate that both the self-potential and resistivity curves are influenced by mud resistivity.

Jan 1, 1946

By Michael J. Messel

W. P. MOULD*—Has consideration been given to the problem of retreating the 4,000,000 ton tailings pile to recover the very considerable amount of asbestos fiber that was lost over the years due to insufficient operation and poor recoveries? Also, what was known about the possible content of chromite and the sulphides of nickel and cobalt? M. J. MESSEL (author's reply)—Consideration was given to the problem but nothing concrete has been done up to this time. W. P. MOULD—I am certain the tail- ings contain a very considerable quantity of fiber, not all of which is in the shortest lengths, because in the milling of talc rock from a neighboring location having a common origin with the asbestos bearing serpentine source of the tailings pile, a concentrate carrying 15 pct Ni and Co in complex sulphides and constituting about 4/10 of 1 pct of the talc rock was recovered. In the belief that the tailings also contained an appreciable content of chromite (then in demand, 1937) it was suggested to the management of the asbestos company that a truck load of the current tailings be sent to the flotation plant of the talc company where it would be put over the concentrating tables in an effort to discover the presence and roughly the percentages of chromite, nickel, and cobalt. Preparations for the test were woefully inadequate and the test was completely snarled up by the surprisingly large quantity of asbestos fiber from 1 in. long down to very short fiber, all of which matted up and plugged launders and pumps with disastrous effects and practically the total loss of the sample. If anything was indicaded by the test, it was that a wet process for milling asbestos was worthy of very serious consideration. M. J. MESSEL—A wet milling process for tailings retreatment only, is at present under study at our plant. One asbestos mining company in Canada has constructed a fairly large test plant for this purpose, but as yet no definite results have been obtained other than in a small test unit plant which were in some respects quite encouraging.

Jan 1, 1950

By Ming-Kao Yen

S. E. MADDIGAN*—I think Mr. Yen should be complimented on doing a very excellent and a very comprehensive piece of work. I was particularly pleased to note the use of X rays in a somewhat less tedious technique than pole figures. In the past I think many workers have been diverted away from the use of X rays in such investigations because of the large amount of work involved in pole figures if one is dealing with a great number of specimens. The same thing, I think, applies to the determination of orientations by counting of twins which is also a very tedious procedure; as a result several papers which have otherwise been of excellent quality have depended upon etching techniques for determination of orientation. The present paper indicates that the results reported in those previous papers were correct, but I think the use of etching techniques alone is a rather shaky basis for setting up theories in the literature. W. M. BALDWIN, JR.*—This discussion will be a short note of correction and apology. In my discussion of Brick, Martin and Angier's paper I incorrectly reported the orientation of phosphorus deoxidized copper annealed at temperatures. When I learned that Mr. Yen was preparing the present paper I asked that he correct this previous error, which he most graciously consented to do. However, through my ambiguity the correction noted on p. 59 of Mr. Yen's paper is still not the proper one. For this I take full responsibility. The orientation which I observed in phosphorus deoxidized copper at high temperatures is the (112) [111] which agrees with the pole figure given in Fig 8a, on p. 65 of Mr. Yen's paper. Our observations were made on the basis of twin counts rather than X ray determinations and therefore serve as an independent confirmation of Mr. Yen's data. M. K. YEN (author's reply)—The author wishes to thank Dr. Maddigan for his comments in regard to the application of glancing technique to textures. As a matter of fact, considerable work has been done recently in connection with

Jan 1, 1950

By I. J. Gardescu

The production of petroleum in Rumania in 1932 totaled 52,560,000 bbl., an increase of 6.8 per cent over 1931. The average daily production rose from 123,000 bbl. at the beginning of the year to 173,000 bbl. at the end of the year, the production in the Gura-Ocnitzei field rising from 38,800 to 80,700 bbl. per day. This increase was due to competitive development during which time the percentage of total production of the various operating companies remained practically unchanged. Chief producers were: Concordia, 30.3 per cent; Unirea, 21.6; Romano-Americana, 13.5; Steaua Romana, 8.3. Boldesti, where production of the previous year was practically doubled, would have produced far greater quantities were it not for the fact that both Astra Romana and Romano-Americana curtailed drilling operations. Of the total daily production of 21,800 bbl. a day, the Astra Romana, Steaua Romana and Romana Americana, produced respectively 67, 25 and 8 per cent. The Moreni field showed a sudden drop in production from the preceding year, due primarily to reduced drilling activities. Its production of only 21,000 bbl. a day removes it from first position for the first time in many years. All the other fields showed a decrease in production, except Ochiuri, 3 miles west of Gura-Ocnitzei, and Ceptura, 12 miles east of Boldesti. Drilling1 During the first nine months of 1932, 116 wells were completed, 8 of which were dry holes. The Meotian (lower Pliocene) is the producing horizon in 73, the Dacian (upper Pliocene) in 31, and the Oligocene in 4 of the completed wells. Three of the Oligocene wells were drilled in the Bacau district and one at Grausor, near Campina. In addition, 47 wells were drilling on Oct. 1,1932. Of the total completions and drilling wells, 92 per cent employed rotary for a footage of 98.5 per cent of the total drilled. Power for rotary drilling was furnished to 105 wells by steam, to 38 by electricity, and to one by gasoline.

Jan 1, 1933

HUBERT INGERSOLL ELLIS Hubert Ingersoll Ellis, who met accidental death on Jan. 6, 1919, in eastern Washington, had already advanced far in the profession of mining engineering and gave promise of a brilliant future. He was born on the Washington coast in June, 1889, and had his preparatory schooling at Menlo, Wash. In 1905; he entered the College of Mines of the University of Washington, and at once made a high record of scholarship. After completing 3 years of his technical course, he went to the interior of Alaska, where he spent 4 years in mining. During this time he was field correspondent for technical-magazines and wrote several important articles. In 1915, Ellis completed his senior year in the College of Mines; his graduation thesis was a comprehensive paper on mining methods at Fairbanks, Alaska, which was published as a series of articles in the Engineering and Mining Journal. On July 14, 1915, he entered the employ of the Bunker Hill & Sullivan Mining & Concentrating Co., Kellogg, Ida., as an underground miner, and was soon promoted to the position of operative on experimental metallurgy and later chemist in the same work. Later, he did exhaustive work on flotation with particular attention to the use of various addition agents. For the past 212 years, his work was largely in the field, examining mining prospects and directing work of investigation, during which time, while located at Sumter Valley, Ore., in 1916, he was elected to membership in the American Institute of Mining and Metallurgical Engineers. During the same year, he was married to Miss Grace Wells, of Arkadelphia, Ark., and besides his widow leaves a young son. In Hubert I. Ellis, there was found the rare combination of executive, administrative, and business ability, together with a temperament exceptionally well adapted and trained for research work and for the careful and exhaustive examination of engineering problems, both practical, and academic. These qualities were in addition to a splendid physique and a personality that made him highly successful in the handling of sub-ordinates and in his contact with his associates and the public.

Jan 4, 1919

By Roy A. Hardy

The Getchell mine is a comparatively recent discovery in the old Potosi mining district, Humboldt County, Nevada, a district organized in the seventies and eighties, in which some prospecting was done in several metamorphic zones along a monzonite-sedimentary contact. The district had no production in the early days and no further work was done until the same metamorphic zones were prospected for tungsten (scheelite) in 1917 and 1918, when a few small lots were shipped. It again lay dormant until 1934, when prospectors investigated a large siliceous escarpment at one end of the old district where outcroppings were a prominent feature of the topography. Undoubtedly, during the early prospecting of the district, the outcroppings had been investigated for mineral, probably by panning, with negligible results because the gold later found is invisible in the concentrate and is refractory. A fire assay revealed the presence of sufficient gold to warrant development work. The outcroppings were easily prospected by short tunnels having their portals in the siliceous material on the hanging-wall side, with a maximum distance to crosscut to the footwall of 135 ft., or a distance at right angle to dip of 60 to 90 ft. Development work, reaching a depth of over 600 ft. on the dip of the vein, was done by means of various crosscut tunnels, winzes and laterals. A churn-drill hole was also sunk, which intersected. the vein at a depth of 1100 ft. on the dip. Sufficient development work of this character was completed by 1937 to justify the erection of a reduction plant to roast the sulphide ore and cyanide the calcine, and to treat the oxidized ore by straight cyanidation, to make a doré bullion for shipment to the mint. The erection of the plant was started that year and finished early in 1938; with a combined capacity of about 800 tons per day. It has operated continuously since erection and recently was enlarged to handle 1000 tons per day. The vein dips with the slope of the mountain, and by stripping the hanging wall the ore may be mined by power shovel for several hundred feet below the outcrop. Thereafter underground methods will be necessary.

Jan 1, 1941

By S. A. Hoenig

In an earlier publication, the application of exoelectron technology to the monitoring of dry grinding in a ball mill was reported. Recently, the author has investigated the ball mill problem in more detail with the system shown in [Fig.1]. Here, some of the current generated in the ore-ball-water mixture was picked up by the metal chains and served as a measure of the rate of grinding. While the mechanism of current generation has not been completely clarified, a parallel study of electrical effects associated with rock drilling indicated that the major driving force is the zeta potential*, while oxidation of the freshly fractured material provides the remainder of the current. Both of these effects are sensitive to the exposed surface area, and it might be expected that the observed currents would provide a measure of the grinding rate. This "surface area" effect allows the measurement system to be used in any type of rock or ore grinding. Some studies with sulfide copper ore indicate higher currents than those observed with silica sand, but the overall pattern of current versus grinding rate is essentially the same. Experimental Studies The experimental system was set up as shown in [Fig. 1]. The initial studies were done with silica sand because of its availability and for comparison with the data of reference 1. The sand was sized to an average of 425 /MI (40 mesh); a typical charge consisted of 2.5 kg (5.5 lb) of sand, 0.85 L (0.22 gal) of tap water and 2.5 kg (5.5 lb) of iron grinding balls 25.5 mm (1 in.) in diameter. For a typical "run," the mill was loaded with a fresh charge of ore and operated for periods ranging from 10-60 min. During this time, the current was measured with a Keithley 417 picoammeter and a chart recorder. At the end of the grinding period, the charge was removed and sieved to recover the 425, 300, and 212 µm (40, 50, and 70 mesh) fractions which were then drained and weighed. A fresh charge was used for each test and every attempt was made to keep the draining and weighing processes uniform.

Jan 1, 1985

By Roy T. Southin*

The finding of Wojciechowski and Chalmers that columnar crystal growth can be stopped by an already existing network of equiaxed crystals is supported by other recently reported work on both static and mechanically stirred ingots.27,28 Support for the dendrite arm fragmentation mechanism, too, can be obtained by comparing the effects of spinning on ingots cast in a material which has a dendritic solid/liquid interface during solidification with one which has a cellular interface, since no evidence of change at the interface, other than a change in growth direction, can be found in the cellular material. But there are alternative ways of producing an equiaxed zone in materials which characteristically solidify with a cellular interface. For example, interrupted spinning of a normally cast ingot can do it. In this case it has been shown28 that the equiaxed zone is caused by the showing of dendritic particles from the top surface of the ingot to nucleate a network of equiaxed crystals which forms a barrier to the continued growth of the columnar grains. This showering has also been shown to be a major effect in materials solidifying with dendritic interfaces. It has also been proposed28,29 that, for an equiaxed zone to form, not only must nuclei be present ahead of the interface but also these nuclei must grow to sufficient size to be a barrier to the further growth of the columnar grains. A further requirement is that a network of these grains continually be produced ahead of the growing interface; otherwise there is a reversion to columnar growth as found by Wojciechowski and Chalmers. In normally cast ingots it is possible for nuclei ahead of the interface to grow since during a large portion of the solidification time there is no temperature gradient ahead of the interface,30 and, in fact, the liquid may be slightly undercooled.29 This then is the major difference between the work under discussion and normal industrial solidification conditions, since Wojciechowski and Chalmers imposed a considerable temperature gradient in the liquid. The statement in the Wojcieshowski and Chalmers paper that one needs to lower the temperature gradient

Jan 1, 1969

By K. A. Lambert

In the Anthracite Region there are considerable areas where the original mining was done 50 or more years ago. In this original mining, the pillars that were left proved inadequate in size for the support of the roof, which has since collapsed as a result of squeezes, and completely filled the original openings. In an endeavor to recover the coal which remains in the pillars in such areas, the reopening cost for development, as well as for pillar recovery, has been excessive in many instances. Various methods have been tried out with a view to lowering the cost, in order that the greatest possible percentage of recovery of the reserve tonnage may be realized economically. Ordinary hand mining necessitates the driving of development road 10 ft. wide in the clear between timber legs, with 6 ft. of clearance over the rail to accommodate mine cars; collars or crossbars on the timber sets have been difficult to maintain in these openings in the heavily caved condition, especially in beds where the overburden is great,. Numerous failures have occurred on these development road timbers because of roof movement resulting from removal of pillars. The actual removal of pillars from this development work has been costly because full-width openings for transporting mine cars to the face have to be maintained by cleaning caved material from alongside the pillars, or skipping up along the pillars where pillars of sufficient width are found. Shaker-chute Methods A method of developing such caved conditions and recovering pillars tributary to this development, utilizing shaker chutes, is being tried out with considerable success at Loree colliery. An outline of the chute and apparatus is shown in Fig. 1, which indicates the location of pillars and caved material. The cost of both labor and material required in the recovery of such coal is considerably less than by ordinary hand methods. In order to try out this method of mining a location was chosen where a tightly caved area had been developed by ordinary hand methods to within 300 ft. of the property line. The original bed height was 12 ft., with an overburden of 325 ft., but on account of the squeezes which

Jan 1, 1931

By Raymond Mancha

TO determine the optimum inside dimension of an airshaft, it is necessary to strike the proper balance between the cost of power for air friction and turbulence losses within the airshaft, on the one hand, and the cost of sinking the airshaft, on the other. An airshaft larger than necessary is extravagant because the increased amortization rate exceeds the reduction in power cost. Conversely, an airshaft smaller than is needed wastes more power than can be justified by the corresponding reduction in amortization rate. The airshaft power is a function of the air volume Q cu. ft. per min. and the air- pressure drop p in. water gauge across the airshaft The airshaft pressure drop is calculated by the formula: [ ] wherein R is the air-friction coefficient for the portion of the airshaft 1 ft. deep, 0 ft. in perimeter and A sq. ft. in area, when passing an air volume of Q cu. ft. per minute. The airpower w kw. dissipated within the airshaft is computed by the formula: [ ] With a combined over-all unit efficiency of the fan and drive of E per cent, the air- shaft power requirements become [ ] There are 8760 hours per year, so with energy at I cent per kilowatt-hour the annual cost per kilowatt for continuous operation is $87.60; therefore, with energy at C$ per kw-hr. the annual airshaft power cost MI dollars per year becomes: [ ] which, expressed by the component parts, becomes : [] The amortization rate a dollars per year per dollar invested includes both depreciation and interest on the investment. These in turn involve the expected useful life of the airshaft and available monetary interest rate. For the purpose of this discussion the cost of airshaft sinking is assumed to comprise a fixed move-in charge Y dollars, which covers the cost of transporting, erecting and removing the shaft-sinking equipment and is independent of the air- shaft size. Also, it is assumed that the cost of shaft lining, if any, is fixed at $X per cu. yd. of lining material and that excava-

Jan 1, 1946

By Roy A. Hardy

The Getchell mine is a comparatively recent discovery in the old Potosi mining district, Humboldt County, Nevada, a district organized in the seventies and eighties, in which some prospecting was done in several metamorphic zones along a monzonite-sedimentary contact. The district had no production in the early days and no further work was done until the same metamorphic zones were prospected for tungsten (scheelite) in 1917 and 1918, when a few small lots were shipped. It again lay dormant until 1934, when prospectors investigated a large siliceous escarpment at one end of the old district where outcroppings were a prominent feature of the topography. Undoubtedly, during the early prospecting of the district, the outcroppings had been investigated for mineral, probably by panning, with negligible results because the gold later found is invisible in the concentrate and is refractory. A fire assay revealed the presence of sufficient gold to warrant development work. The outcroppings were easily prospected by short tunnels having their portals in the siliceous material on the hanging-wall side, with a maximum distance to crosscut to the footwall of 135 ft., or a distance at right angle to dip of 60 to 90 ft. Development work, reaching a depth of over 600 ft. on the dip of the vein, was done by means of various crosscut tunnels, winzes and laterals. A churn-drill hole was also sunk, which intersected. the vein at a depth of 1100 ft. on the dip. Sufficient development work of this character was completed by 1937 to justify the erection of a reduction plant to roast the sulphide ore and cyanide the calcine, and to treat the oxidized ore by straight cyanidation, to make a doré bullion for shipment to the mint. The erection of the plant was started that year and finished early in 1938; with a combined capacity of about 800 tons per day. It has operated continuously since erection and recently was enlarged to handle 1000 tons per day. The vein dips with the slope of the mountain, and by stripping the hanging wall the ore may be mined by power shovel for several hundred feet below the outcrop. Thereafter underground methods will be necessary.

Jan 1, 1941

By R. F. Mehl, W. Batz, C. Wells

L. S. Darken—It is indeed gratifying to find that the results of the two different methods here reported are in substantial agreement with each other and with the earlier work1 of two of the authors. Dr. R. P. Smith, of our laboratory, has been conducting some experiments at 1000°C to determine the diffusivity of carbon in austenite by a third method— the steady state method. This work, which will soon be reported, is far enough advanced that we can say it is in substantial agreement with that of the present authors. The only disparity which might be considered significant is in the high-carbon region, where we find that the diffusivity rises a little less steeply than indicated in fig. 8. F. E. Harris—The authors have presented an impressive arrangement of data concerning the diffusion of carbon in austenite. Of particular interest is the compilation, table IV, which is repeated in col. B of table V for direct comparison with values (col. A. table V) from a formulation using a single Q value of 31,000 cal as the activation energy for diffusion. This comparatively simple formulation has been used quite successfully in the practical application of calculating the carbon added (or removed) through the face in carburizing and decarburizing experiments, where the face concentrations are held quite constant for known times and temperatures. Literally hundreds of tests have been so checked where the computed and experimental values have varied by less than 5 pct. For higher temperatures, where proper carburizing data are hard to obtain, the diffusion couple is treated as a decarburization of the high-concentration bar and as a carburization of the low-carbon member. The analysis has been limited to a maximum of 1.40 wt pct carbon. The agreement between cols. A and B in table V may be considered fair, if a liberal viewpoint is taken. The use of a diffusion couple has one serious drawback, in that comparatively small amounts of carbon pass through planes of concentration close to those of the initial high-carbon and low-carbon members, and hence small errors become important. In addition to the sensitivity at these high and low concentrations.

Jan 1, 1951