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By A. Tremari, Paul I. Eimon

Photogrammetrists are studying with new interest the problems of mine mapping and mining engineers are beginning to see what photogrammetry can do for them. Administrators in a number of European and U. S. mines have tried photogram- metric methods and are finding that better maps and data, needed for mine development, can be produced with savings of time, men, and money. In addition to wide use in small scale mapping projects, photogrammetric methods are now used for producing large scale plans and maps in German coal and lignite mines, in some U. S. open pit mines, to inventory TVA coal stock piles, and to compute highway excavation volumes. In each case surveying and map compilation has been made more efficient and accurate by photogrammetry and at significant savings over ground methods.

Jan 5, 1959

By W. L. Kendrick

At Henderson, Nev., Manganese Inc. is mining by open pit methods a low grade manganese ore averaging 21 pct Mn, concentrating it to 42 pct by flotation, and agglomerating it to produce nodules of metallurgical grade-about 48 pct Mn. The striking aspect of the whole operation, and one that has considerable effect on nodulizing, is the use of approximately 250 lb of reagent per ton of mill feed. For many years rotary kilns have been used for drying, calcining, clinkering cement and other products, and burning lime. Their use for nodulizing or agglomerating a metallic ore is new-first reported in this country in 1904, when a small rotary kiln at South Chicago was employed to nodulize flue dust from a blast furnace. After a short time this process was replaced by sintering.

Nov 1, 1956

By Fred C. Bond

DISCUSSION Milton C. Shaw and Donald R. Walker (Massachusetts Institute of Technology)—For many years the two empirical rules of comminution bearing the names of Rittinger and Kick have been applied to grinding processes to account for the energy required to crush brittle materials. The basis for Rittinger's rule was the thought that the energy to grind a substance went largely into supplying the additional energy associated with the new free surface, while Kick's law was prompted by the concept of dimensional similarity and is a special statement of the concept of constancy of strain energy to cause rupture. According to Rittinger the energy to grind a given volume varies as the change in the square of the mean particle size, v - A (D2), while according to Kick this energy varies

Jan 1, 1953

By Fred C. Bond

DISCUSSION Milton C. Shaw and Donald R. Walker (Massachusetts Institute of Technology)—For many years the two empirical rules of comminution bearing the names of Rittinger and Kick have been applied to grinding processes to account for the energy required to crush brittle materials. The basis for Rittinger's rule was the thought that the energy to grind a substance went largely into supplying the additional energy associated with the new free surface, while Kick's law was prompted by the concept of dimensional similarity and is a special statement of the concept of constancy of strain energy to cause rupture. According to Rittinger the energy to grind a given volume varies as the change in the square of the mean particle size, v - A (D2), while according to Kick this energy varies

Jan 1, 1953

By J. Henry Harden

I DESIRE to call the attention of the Institute to a new form of drawing-board trestle. With the ordinary four-legged trestle, commonly used, one has not the means of adjusting the height of the board to the draughtsman. To obviate this inconvenience, and at the same time to enable one to incline the board, I have devised an arrangement of curved and straight slots and thumb-screws, by means of which the board can be raised three or more inches, and placed at any desired angle of inclination on either side. Figures 2, 3 (Plate I) show side and end elevations of the trestle for a single board, and Figure 4 for two boards. The latter form is adapted for use in schools, or where it is desired to economize space.

Jan 1, 1874

St. Joe Minerals Corp. opened a new $30 million mine and mill at its Balmat-Edwards division in September. It will be the largest single zinc mining operation in the United States. St. Joe expects to produce more than 200,000 tons of zinc concentrates from its combined Balmat-Edwards mines and mills in 1972, equivalent to more than 100,000 tons of zinc metal-20% of U.S. mine production. The company has operated in Northern New York since 1926, having commenced zinc mining with its Edwards mine and mill, 12 miles from Balmat. They will continue to operate at a rate of 31,000 tons of concentrate per year. St. Joe started the Balmat facility in 1930 with two mine shafts and a mill, with a capacity of 2300 tpd.

Jan 1, 1971

ENGINEERS AVAILABLE (Under this heading will be published notes sent to the Secretary of the Institute by members or other persons introduced by members.) Graduate mining engineer, with 10 years' experience, having an office in New York, would like to represent a mining company as selling and purchasing agent, and general supervision if desired. Machinery agency considered. No. 259. Member, technical graduate, with several years' experience as engineer for a pyrites company, and as geologist and engineer for copper, nickel, and silver companies, desires a position as engineer or superintendent of mines. No. 260. Member, technical graduate, aged 29, with experience as draftsman, surveyor, and superintendent of iron and gold mines, and as construction engineer, is open for a position as mine superintendent, or in mine examination or construction. No. 261.

Jan 11, 1915

By A. D. Hodges

In 1874 my attention was called to what seemed to me an interesting and new nickel and cobalt combination found in Ludwig and Carter's copper mine, near Mason Valley, Esmeralda County, Nevada. With the assistance of Mr. A. Hebberling I made several partial analyses of the mineral or minerals. I also communicated with my friend, Professor H. B. Cornwall, of the John C. Green School of Science, College of New Jersey, who analyzed a couple of specimens which I forwarded to him. The copper ore occurs in the mine principally as carbonate and to a certain extent as silicate, the latter generally in connection with clay seams or bands. In some places, together with the copper silicate and clay, generally interstratified with them, there occurred a compact shining black mineral (a) containing nickel and cobalt. Occasionally, in cavities, in connection with (a) was found a black substance (b), either massive and in this case very similar to (a) but with driller lustre, or forming an incrustation with rough and botryoidal surface and radial-fibrous structure, or granular and earthy. A few specimens were found having on the surface very fragile black needles (c) sometimes 1/2-inch long, interspersed with needles of malachite. The mineral (a) seemed, according to the analyses, to be of nearly constant composition, and was considered by Professor Cornwall to be a chrysocolla containing nickel and cobalt—a new occurrence to

Jan 1, 1885

By Frank Calvin Roberts

An examination of the various devices employed for operating blast-furnace charging-bells has led me to design the arrangement slrown in the accompanying figure. In order to contribute to the even distribution of stock, the movement of the bell should be in a vertical line, since any tendency to side-thrust which may be in-

Jan 1, 1888

By P. E. Demmler

Phosphorus combines with copper in various proportions, forming true alloys, some of which are of commercial importance. These materials find wide application as deoxidizers and as a means of introducing phosphorus into other alloys, as in phosphor-bronze. Phosphor-coppers containing 10 and 15 per cent. of phosphorus are the commercial grades that are most generally offered. Each has certain advantages when used in making other alloys. The 10 per cent, grade of phosphor-copper has an advantage over the 15 per cent. in that it has a much lower melting point and can be prepared by certain methods with a much lower loss in phosphorus. The 15 per cent. grade has the advantage of lower freight rates per unit of phosphorus and, by the method to be described, a uniform product can be prepared with practically no loss of phosphorus. Alloys of copper and phosphorus containing any desired percentage of phosphorus lower than 15 per cent. can be prepared by melting together the requisite amounts of copper and 15 per cent. phosphor-copper. Processes for making phosphor-copper may be divided into two classes as follows: (1) Those depending on the smelting of phosphate rock or superphosphate of calcium with copper or copper-bearing materials, and coal or other carbonaceous material; (2) those depending on the direct combination of metallic copper and elemental phosphorus. A number of formulas for preparing phosphor-copper according to the first method have been published. The Metal Industry' gives the following: Superphosphate of calcium, 60 lb.; granulated copper, 30 1b.; finely powdered coal, 10 1b. Similar formulas are given by Brannt2 and others, and detail variations are covered by patents, such as those of L. A. Jeffs3 and H. A. Webster.4 Among the objections to this method of producing phosphor-copper are the large amounts of raw material and resulting slag to be handled, and the difficulty of getting a satisfactory fusion. S. Skowronski5 found that at 1300' C. (2372' F.) it was impossible to get a good fusion

Jan 1, 1921

By THEODORE DWIGHT

Members of the Institute have already received a special pamphlet descriptive of the United Engineering Society building, and wilt doubtless be interested in the progress that has been made up to date-February 24th-in erecting this home for the engineering profession. The old buildings on lots Nos. 25 to 33 W. 39th St., New York, were,' removed many months ago, but final contracts for the new, building were not let until the summer of 1905. The size of the building is 115 ft. on 39th Street, and 88 ft. in, depth; the height from, the sidewalk to the top of the parapet is 220 feet. The cubic contents of the building from the. bottom of the basement floor, to the top of the roof, including the pent houses, is 2,290,000 cubic feet. The number of light's, in the building will be between 4,000 and 4,500. The air supply for Auditorium and Lecture. Halls will amount to nearly 10.0,000 cu. ft, per minute, and the exhaust. to 90,000 cu. ft. per minute. In excavating for cellar and foundations, the average depth where good rock was. found was 37 ft.-it varied, however,: from 27 to 65 ft., due to an old water-course having run through the center of the lot; this condition, and the presence of soft rock, which rapidly disintegrated when exposed to air and water, made the foundation-work very difficult. As two of the column-footings of the building have to sustain a weight of 3,000,000 11) each, the most substantial foundations are necessary; 13,000 cu. yd. of earth were excavated for the foundation and basement; and 1,600 cu. yd. of concrete were necessary, to build up the footings. In the completed building there will be about 3,500,000 bricks. Owing to the number of auditoriums, and their location, and the placing of the library on the top floor; where allowance will have to be made for the enormous weight of 300,000 books, the structural steel work has been unusually complicated in this building. For instance, over the auditorium there are two 60-ton plate-girders, made up

Mar 1, 1906

By J. Henry Harden

I desire to call the attention of the Institute to a new form of drawing-board trestle. With the ordinary four-legged trestle, commonly used, one has not the means of adjusting the height of the board to the draughtsman. To obviate this inconvenience, and at the same time to enable one to incline the board, I have devised an arrangement of curved and straight slots and thumb-screws, by means of which the hoard can be raised three or more inches, and placed at any desired angle of inclination on either side. Figures 2, 3 (Plate I) show side and end elevations of the trestle for a single board, and Figure 4 for two boards. The latter form is adapted for use in schools, or where it is desired to economize space.

There's a right way and a wrong way to store diesel electric systems and similar equipment for generating on-site power, according to James Frankow, service manager for Allis-Chalmers Corp's Engine Division. In any event, the less storage the better. Many generating sets are stored before installation, especially when new construction is underway. Improper storage, or mothballing, can create initial reliability problems. Therefore; arrange for inside storage with no drastic extremes in temperature or humidity. If engines and alternators are stored in areas other than inside a dirt-free and temperature-controlled building, the unit or engine should be completely covered and protected against the environment. Before covering it with a canvas or with plastic, the unit should first be sealed at the following critical engine openings:

Jan 3, 1978

FOR two days preceding the Colorado Mining Association annual meeting, officers representing all interests of the lead and zinc producers hammered away at remedies for the ills of the industry behind closed doors at the University Club in Denver. For once in the stormy history of the industry, large and small producers alike came to agreement with an automatic sliding scale stabilization import tax. The proposal set forth in full on the following page, is not new being merely an amplification of the tariff arrangement whereby tariffs are imposed when the price drops below ceiling. Its advocates claim that it is simple, automatic, and flexible. It will give stability to the industry without subsidies and since no government bureaus will be required to administer it, there will be no cost to the taxpayer.

Jan 3, 1953

Established as a Division September 27, 1949 LeRoy Scharon, Chairman C. M. Cooley, Secretary 29 West 39th Street New York 18, N Y

Jan 1, 1952

By E. T. Turkdogan, P. Grieveson, J. F. Beisler

Experimental results are given for the rate of reduction of silica from silicate melts by paphite-saturated iron in the presence of carbon monoxide. It is shown that, when gas bubbles are present at the slag-metal interface, the interfacial chemical reaction is the rate-controlling process in the transfer of silicon from slag to metal. From the silicon-concentration profiles in the metal sample, the diffusivity of silicon in paphite-saturated iron is found to be (5.4 * 0.4) x 10 sq cm per sec at 1600°C. Some consideration is given to the transport of oxygen from the slug-metal interface to the walls of the gvaphite metal container as becoming the rate-controlling process in the absence of gas bubbles at the slag-metal interface. ATTEMPTS were made by Fulton and chipman1 to investigate the kinetics of reduction of silica from calcium alumino-silicate melts by graphite-saturated iron in an atmosphere of carbon monoxide. In these experiments with 400 to 500 g of metal and slag, both phases were stirred in such a manner that the interface was essentially undisturbed. Initially, the graphite-saturated iron contained about 15 pct Si and, after about 8 or 10 hr of reaction time at 1600°C, the silicon content of the metal in- creased by about 0.2 pct. In a written discussion on this paper of Fulton and Chipman, schuhmann2 pointed out the possibility that this observed slowness of the reduction of silica could be due to the transport of oxygen across the liquid metal boundary layer at the slag-metal interface. Although this explanation of Schuhmann is quite feasible for the experimental data of Fulton and Chipman on silica reduction, such a reasoning should not be extended to other rate data on slag-metal reactions unless sufficient evidence is available satisfying the boundary conditions for such a transport process. The hydrodynamics of stirred liquids are very complex and even for a simple method of stirring there is no exact mathematical solution which will predict the mass transfer coefficient accurately. The best available solution of this problem is that given by Lewis' and later modified by mayers~ for a two-liquid system where liquids are stirred by counter-rotating stirrer blades without disturbing the interface. In such a system the mass transfer coefficient is estimated from an empirical relationship using the data on viscosity and density of the two liquids, rate of revolution, the length of stirrer blades, and the diffusivity of the element which is transferred from one phase to the other. It was found in these investigations' that the estimated and observed mass transfer coefficients, in systems containing two immiscible aqueous solutions, agreed within *40 pct. Although this is not considered to be an unreasonable error for the study of industrial processes, uncertainties of this magnitude cannot be tolerated in any theoretical study of reaction kinetics. In view of the complexity of the

Jan 1, 1963

By E. S. Mardock, Robert E. Bush

The object of this paper is to report recent developments in the quantitative interpretation of radioactivity logs. The use of reference lines is described in the application of the new zero radioactivity reference line for the determination of neutron derived porosities is discussed. Illustrated examples are shown of logs from the reef limestone of the North Snyder Field and from the Lansing-Kansas City limestone of central Kansas. A method of using an interrelation factor calculated from the neutron and gamma ray curves, called the neutron Productivity number, for the estimation of productivity from sandstone formations is discussed. When used in a relative manner the neutron productivity number has aided in Predicting whether a given zone will produce gas or liquid or whether it is too shaly to produce. Examples of logs from wells in the Freites District, Venezuela, and in East Texas are shown to illustrate the application of the neutron productivitv number. INTRODUCTION The petroleum industry was introduced to some of the preliminary results of investigations into the quantitative interpretation of radioactivity logs in October, 1949." It was stated at that time that the methods presented were entirely relative because they involved the use of reference points obtained from the radioactivity log, i.e., shale reference lines, dense zone reference lines, or a combination of both shale and dense zone reference lines. These relative methods offered many advantages to the industry in interpreting radioactivity logs in terms of porosity with particular application to limestone and dolomite reservoirs. However, these relative methods did not offer the wide range of applicability desired because the esta1)lishment of reliable reference points from shale in some areas were difficult. It was recognized that a more reliable mean; of establishing reference lines was vitally needed. Such a method is now available through the introduction of an instrumeutal zero device. It is the purpose of this paper to discuss the application of this new zero reference to the quantitative interpretation of radioactivity logs. Previously all applications of quantitative interpretations of radioactivity logs have been made in limestone reservoirs with little or no emphasis placed on sandstone reservoirs. A brief resumé of investigations into the quantitative interpretation of radioactivity logs in sandstone reservoirs is presented here. This discussion deals primarily with the interrelation of the gamma ray and neutron curves and the response of the latter to the density of the fluids filling the pore space in relatively homogeneous sandstones of uniform porosity. The authors believe that the methods presented herein are only applicable locally to specific fields and reservoirs, and that they probably do not offer a wide range of applicability. However, tile authors believe that the wider use of the new instrumental zero references in sand areas will reveal more information about the specific response of the gamma ray and neutron curves to changes in lithology and saturation. Two applications of quantitative interpretation using the new instrumental zero references are presented. Examples are given which show the comparison of logs and porosity in the limestones and dolomites of West Texas and Kansas. Logs of wells in 'Venezuela and East Texas are compared with the drill stem test data, production data, etc.. to illurtrate the interrelation of the gamma ray and neutron curve: and the rise of methods involving these interrelations to determine certain saturation variables. THE QUANTITATIVE APPLICATION OF RADIOACTIVITY LOGS TO LIMESTONE AND DOLOMITE RESERVOIRS Tile theoretical basis for the gamma ray and neutron curves has been discussed elsewhere.9 he method of recording the logs and apparatus involved has also been thoroughly covered and will not be discussed here.'."".'" It has been shown that the neutron curve responds exponentially to liquid filled porosity over the 1 1/2 to 35 per cent

Jan 1, 1951

By Robert E. Bush, E. S. Mardock

The object of this paper is to report recent developments in the quantitative interpretation of radioactivity logs. The use of reference lines is described in the application of the new zero radioactivity reference line for the determination of neutron derived porosities is discussed. Illustrated examples are shown of logs from the reef limestone of the North Snyder Field and from the Lansing-Kansas City limestone of central Kansas. A method of using an interrelation factor calculated from the neutron and gamma ray curves, called the neutron Productivity number, for the estimation of productivity from sandstone formations is discussed. When used in a relative manner the neutron productivity number has aided in Predicting whether a given zone will produce gas or liquid or whether it is too shaly to produce. Examples of logs from wells in the Freites District, Venezuela, and in East Texas are shown to illustrate the application of the neutron productivitv number. INTRODUCTION The petroleum industry was introduced to some of the preliminary results of investigations into the quantitative interpretation of radioactivity logs in October, 1949." It was stated at that time that the methods presented were entirely relative because they involved the use of reference points obtained from the radioactivity log, i.e., shale reference lines, dense zone reference lines, or a combination of both shale and dense zone reference lines. These relative methods offered many advantages to the industry in interpreting radioactivity logs in terms of porosity with particular application to limestone and dolomite reservoirs. However, these relative methods did not offer the wide range of applicability desired because the esta1)lishment of reliable reference points from shale in some areas were difficult. It was recognized that a more reliable mean; of establishing reference lines was vitally needed. Such a method is now available through the introduction of an instrumeutal zero device. It is the purpose of this paper to discuss the application of this new zero reference to the quantitative interpretation of radioactivity logs. Previously all applications of quantitative interpretations of radioactivity logs have been made in limestone reservoirs with little or no emphasis placed on sandstone reservoirs. A brief resumé of investigations into the quantitative interpretation of radioactivity logs in sandstone reservoirs is presented here. This discussion deals primarily with the interrelation of the gamma ray and neutron curves and the response of the latter to the density of the fluids filling the pore space in relatively homogeneous sandstones of uniform porosity. The authors believe that the methods presented herein are only applicable locally to specific fields and reservoirs, and that they probably do not offer a wide range of applicability. However, tile authors believe that the wider use of the new instrumental zero references in sand areas will reveal more information about the specific response of the gamma ray and neutron curves to changes in lithology and saturation. Two applications of quantitative interpretation using the new instrumental zero references are presented. Examples are given which show the comparison of logs and porosity in the limestones and dolomites of West Texas and Kansas. Logs of wells in 'Venezuela and East Texas are compared with the drill stem test data, production data, etc.. to illurtrate the interrelation of the gamma ray and neutron curve: and the rise of methods involving these interrelations to determine certain saturation variables. THE QUANTITATIVE APPLICATION OF RADIOACTIVITY LOGS TO LIMESTONE AND DOLOMITE RESERVOIRS Tile theoretical basis for the gamma ray and neutron curves has been discussed elsewhere.9 he method of recording the logs and apparatus involved has also been thoroughly covered and will not be discussed here.'."".'" It has been shown that the neutron curve responds exponentially to liquid filled porosity over the 1 1/2 to 35 per cent

Jan 1, 1951

By W. A. Tiller

The unidirectional freezing of a semiinfinite liquid from one end has been treated by calculating the solute and temperature distributions in the liquid and solid phases with time, when the solid-liquid interface advances at a rate proportional to (time)lt2. The nucleation probability for new grain formation is calculated as a function of the constitutional and thermal properties of the alloy, the pouring conditions and the catalytic efficiency of the nucleating agents. The transition from columnar crystal formation to equiaxed crystal formation is assumed to occur at a critical nucleation frequency for a particular alloy and the quantitative dependence of the ratio (columnar zone length/equiaxed zone length) upon the freezing conditions has been predicted. The effects of (i) fluid flow in the liquid, (ii) heat transfer through a mold wall, and (iii) a finite ingot length, have been explicitly tveated as departures from ideality. These departures from ideality are found to have very important consequences on the ingot stmcture. In Part I&apos; of this series, a qualitative description of the general ingot structure was developed. The factors that determine i) the ratio of the equiaxed zone length to columnar zone length and ii) the grain sizes in these zones, were discussed. In the present paper, topic (i) will be treated quantitatively, and it is intended that topic (ii) will be treated quantitatively in Part 111. The complete treatment has been split in this manner for ease of development and coherency of presentation. The treatments are quite mathematical in nature and, although some of the conclusions to Part 11 depend upon the treatment presented in Part 111, it was felt that the intended audience would find the material more readable and more useful in its present form. To this same end, it seems worthwhile to reiterate some of the qualitative aspects of grain nucleation during ingot solidification before embarking on the mathematical description. QUALITATIVE ANALYSIS In the conventional method of casting, a liquid alloy with a certain degree of superheat is poured into a mold. The outer rim of liquid metal cools rapidly to the liquidus temperature of the alloy and begins to undercool. As the degree of undercooling increases, nuclei of solid begin to form in this chill layer, this nucleation being catalyzed by certain heterogeneous particles in the liquid. The grains in the chill layer which are generally of random orientation, begin to grow inwards because of heat conduction through the mold. The grains usually develop a columnar shape since the frequency of nucleation of new grains in the liquid ahead of the advancing interface is generally insufficient to seriously impede the growth of the original grains. Due to the slow diffusion rate of solute in the liquid, a solute distribution is formed in the liquid adjacent to the interface which is either an excess or a depletion if the partition coefficient, ko, of the solute is < 1 or > 1, respectively. Thus, the liquidus temperature of the liquid adjacent to the interface is a function of position. The actual temperature in the liquid is also a function of position and the temperature gradient at the interface decreases as the interface moves away from the mold wall. Since the rate of advance of the interface decreases with time, the equilibrium temperature distributions and the actual temperature distributions as a function of interface position, X, can be illustrated as in Fig. 1. Thus, a region of liquid may exist in which the actual temperature is below the liquidus temperature. This liquid is contitutionally supercooled and therefore unstable with respect to the nucleation of new grains. Now, since the supercooling in Fig. 1 increases as the interface moves further away from the mold wall, the nucleation rate of new grains will increase. When the nuclea-

Jan 1, 1962

By M. S. Seltzer

In a previous paper1 it was shown that activation energies for steady-state creep in lead sulfide single crystals varied with the concentration of electronic defects. For n-type lead-excess crystals, values for the creep activation energy, Qc, decreased from 2.9 to 2.2 ev as the carrier concentration increased from 1017 to 1017 electrons per cu cm, while Q, increased from 1.6 to 2.3 ev for p-type sulfur-excess crystals as the concentration of holes increased from 6 X 1017 to 1018 per cu cm. It was also shown in Ref. 1 that the Q, values could best be correlated with the sum of the self-diffusion activation energies in PbS, i.e., for a given concentration of electrons or holes Q, = QPb + Qs, where Qpb and QS are the activation energies for diffusion of pb210 and s35 in PbS. This result suggests that creep rates are controlled by at least two atomic defects, one for lead migration and one controlling sulfur transport. It would be most desirable to interpret these creep energies in terms of an atomic defect disorder model for lead sulfide. Studies of creep rates as a function of sulfur pressure2 indicate that the defects controlling creep rates are singly ionized lead and sulfur vacancies, VPb and Vs. This hypothesis can be more firmly established by determination of Q, under conditions of constant atomic defect concentration rather than constant electronic defect concentration as has been previously done. Therefore, several measurements have been made of Q, on crystals whose con- centration of lead vacancies or sulfur vacancies has been fixed by equilibration under appropriate sulfur pressure and temperature. It was indicated in Ref. 2 that high-temperature isotherms are available which show how the concentrations of various atomic point defects in PbS vary with composition over the entire homogeneity range for the compound. Two such isotherms are shown in Fig. 1 for 900" and 1000°K. Utilizing these isotherms the concentration of a given defect, say Vbb, may be held constant over a particular temperature range by adjusting the sulfur pressure as the temperature is changed. Thus the concentration of one defect suspected of controlling creep rates may be held constant while other defect concentrations vary. The apparent activation energy for formation of these defects can be obtained from the isotherms giving their concentration as a function of sulfur pressure. Activation energies for creep obtained under conditions of constant defect concentration can then be compared with defect formation energies and certain possible atomic defects can be eliminated as creep-controlling species. We have performed creep experiments as a function of temperature at a stress of 244 g per sq mm under conditions which fixed the lead vacancy concentration, V&apos;, at 1016, 3.2 x 1016, and 3.2 x 1017 cm-3, and one were the sulfur vacancy concentration, Vs, was held at lo17 cm-3. The results are presented in Fig. 2 as creep rate, k, vs reciprocal of absolute temperature, 1/T. Specimens 34, 35, and 36 were deformed under constant lead vacancy concentration while specimen

Jan 1, 1969