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By K. L. Fetters, F. M. Walters

ALL previous records were broken by the Iron and Steel Division, in the number of sessions, the number of papers, and the attendance. In addition to ten papers (all preprinted) on properties, structure, aid hardenability of, carbon and alloy steels, eight formal papers were presented on one or more phases of steelmaklng, and a symposium on the determination of hydrogen and nitrogen in steel. This last started at 2 p.m. and was going strong with more than a third of the audience still present at 6 p.m.

Jan 1, 1944

By Y. H. Liu, R. Kiessling

The chromium, iron, and tungsten borides have been treated with ammonia at different temperatures. They are attacked, forming metal nitride and boron nitride, and the results are summarized in the tables. In the tungsten-nitrogen system a new phase has been observed, closely related to the known ß phase. THE present investigations were begun to determine whether any ternary phases exist in the transition metal-boron-nitrogen systems for the metals chromium, iron, and tungsten. Attempts to prepare such phases were made by using the borides of the metals as starting materials and ammonia as the nitriding agent. Although no new ternary phases have been found to exist, the results may be of some interest with regard to the technical use of the borides. General Procedure A steady stream of dry ammonia was passed through a silica reaction tube, the central part of which was kept at the reaction temperature while its ends were water-cooled. Weighed amounts of the borides were placed in a silica or porcelain boat and heated at different temperatures for a period of 10 to 24 hr. The boat was then rapidly removed from the reaction zone to the quenching zone, the water-cooled end of the tube, by means of a simple magnetic device. The nitrogen content of the products was determined by the increase in weight of the specimens, and the phase analysis was carried out by X-ray methods. For this analysis a Guinier-type camera, constructed at this Institute, was used with a bent, ground quartz crystal monochromator. The general reaction, which occurred in all the experiments, may be summarized as: metal boride + nitrogen -* boron nitride + metal nitride For the higher temperatures pure metal was formed instead of metal nitride. It is sometimes difficult to Discussi detect boron nitride among the reaction products by X-ray methods. Prolonged exposures of some specimens showed, however, that the strongest reflections of boron nitride were present. Additional evidence for its presence was given by the increase in weight of the specimens after nitriding. This increase was always greater than that corresponding to nitride formation only and was often in close agreement with the formula given above. Finally, a white powder, which was shown by X-ray methods to be boron nitride, was left if the reaction products after nitriding Fe,B at 448°C and FeB at 768°C were dissolved in diluted sulphuric acid. Ch rom iu m - Boron - N itrogen Five phases have been found to exist in the Cr-B system,' , and all were used as starting materials. Investigations on the Cr-N system have shown the existence of two nitrides with ideal composition Cr,N and CrN.".' * The results are summarized in Table I. All the borides are attacked and decomposed into chromium nitride and boron nitride, and the kind of nitride formed depends only on the temperature and not on the boride used as starting material. The lowest reaction temperature, however, is different for the different borides. Thus the 6 phase begins to react at about 735 "C, the r phase at about 800°, the S phase at about 900°, the 7, phase

Jan 1, 1952

By Harry Bapty

LONGHOLE drilling with a heavy type percussion Leyner drill, jointed steel rods, and a tungsten carbide insert bit was investigated while drilling and working a quartz barite brecciated rock. Procedure and practice were developed and its suitability for tackling pillar and sill recovery proven and extended to regular stoping at Torbrit. Torbrit, as the name implies, is a contraction of the Toric property and the Britannia Mining & Smelting Co. Ltd., the former owners. This silver property, with minor amounts of lead, zinc, and rarer sulphides of little or no economic value, was discovered in 1916 from an outcrop in the Kitsault River, 18 miles north of Alice Arm Post Office, in the Portland Canal Mining District, B. C.

Jan 11, 1954

By W. E. Bonini, E. A. Hickok

IN the course of an investigation directed toward expanding ground-water facilities in Essex and Morris counties, New Jersey, the Board of Water Commissioners of the city of East Orange authorized a seismic-refraction survey' for the purpose of de-lineating bedrock topography below unconsolidated overburden. Results of the survey were highly satisfactory and led to the preparation of a comparatively detailed bedrock contour map. Knowledge of the bedrock depth and configuration was an important aid in selection of sites for test drilling. The portion of the East Orange Water Reserve under consideration is in the flood plain of the Pas-saic River about 10 miles west of Newark, N. J. The flood plain is about 175 ft above mean sea level and is bordered by low hills rising to elevations of approximately 250 ft. The bedrock underlying the Water Reserve consists of sandstone and shale of the Triassic Brunswick formation and is covered everywhere by deposits of unconsolidated glacial outwash sand and gravel, lacustrine clay, and recent river silt as much as 150 ft thick. Yield of wells in the sandstone and shale averages 100 to 200 gpm. Since production wells constructed in the sand and gravel aquifer in the buried river valley shown on the contour map (Fig. 1) yield 300 to 1400 gpm, it was proposed to locate additional production wells in this buried valley, where the yields per well would be maximum. In 1939 and 1946 the East Orange Water Dept. had electrical-resistivity surveys made to determine depths to bedrock. From the resistivity data the exploration company prepared a bedrock contour map. A well field expansion program begun in 1955 utilized this information to locate sites for test wells along a predicted northward extension of the buried valley in which existing production wells are located. After several test wells (wells 201-205) had been drilled, it became apparent that the resistivity information was unreliable." For example, test well 201 recorded bedrock at a depth of 72 ft, whereas the resistivity depth determination was 130 ft. As a consequence, the test drilling program was temporarily suspended and a seismic survey was under- taken to determine the topography and extent of the buried valley known from well records to underlie the existing well field. In the first phase of this study, several seismic shot point locations were placed at sites where well logs had been obtained previously. This procedure is necessary in a new area to determine whether the seismic method is applicable and what degree of accuracy is to be expected. At the East Orange Water Reserve, depths obtained from the shot points near test wells 202, 203, and 204 were within 8 to 11 pct of the depths logged (Table I). With this assurance that accurate results could be obtained, additional seismic spreads were located on the Water Reserve. Using a portable refraction seismograph, in the fall of 1955 a crew of four men shot a total of 29 reversed seismic spreads in a period equivalent to six field days. Charges as heavy as 3 1b of 40 pct dynamite were necessary at a few places to overcome ground vibrations caused by traffic on nearby highways. At most other sites, a 1-1b charge was sufficient. Travel-time plots were made for all spreads, and depths and true velocities were calculated according to formulas for multiple sloping layers by Ewing, Woollard, and Vine.' The plot of spread 7 (Fig. 2) is typical of the short spreads in which bedrock was shallow—about 50 ft in this case. Where there were not enough arrivals through the bedrock to define the high velocity bedrock line, the spreads were lengthened. This was done by placing shots on line several hundred feet away from each end of the line of geophones. It was then possible to construct complete reverse plots for both short and extended shot points (see spread 27, Fig. 3). Four individual depths were calculated from each extended spread. Three and in some cases four seismic layers were observed. The surficial layer had a velocity range of 900 to 1200 fps, the lowest velocity recorded. This seismic layer is above the water table and is interpreted as recent river silt. The bedrock had the highest velocities, which ranged from 10,600 to 16,400 fps. Intermediate velocities ranged from 4500 to 6800 fps. In every case the intermediate layer was within

Jan 1, 1959

By Arthur E. Granger

IN the early days of the science, and until the recent past, geologists worked as individuals or in small groups. Prior to 1930 perhaps the largest single group under one administrative head was the Geologic Branch (now Division) of the U. S. Geological Survey, which employed at that time (including temporary help) 100 to 150 geologists. Today that same unit employs some 1500. In industry some companies employ as many as 100 geologists in a single department. These numbers obviously pose a need for administration. The basic qualifications for good administration are the same for any group of human beings, but the administration of geologists presents some special problems. Choosing Administrative Personnel: There are two kinds of personnel needs: 1) technical, which requires professional geologists who have proved their capabilities in the field, and 2) clerical and fiscal, which provide the necessary supporting or housekeeping functions. This discussion will be concerned only with the first category, except to point out the need for competent and understanding help from clerical and fiscal people and close relationship between top administration, technical or professional personnel, and the clerical and fiscal groups.

Jan 7, 1957

By AIME

HAPPILY, a large group of the non-ferrous fraternity have long valued a personal association with the new Chairman of the Institute of Metals Division. Many others who will meet him, either officially or unofficially this year, will find themselves sharing the enthusiasm with which he has been welcomed to his new office. Albert A. Smith, Jr., was born at Butler, N. J., on Dec. 28, 1904, and moved to New Haven in time to initiate his preparation for Yale University on the home grounds. After receiving a B.S. degree cum laude in 1926, he stayed on for graduate work at the Hammond Laboratory under C. H. Mathewson, and was awarded an M.S. degree in 1928.

Jan 1, 1948

Henry D. Hibbard, New York City (communication to the Secretary): The title of Mr. Sargent's paper is somewhat misleading, since the paper itself relates chiefly to various kinds of annealing and their effects, and in very small part only to heat-treatment proper. This term has a well-defined meaning in steel metallurgf, and always includes a rate of cooling faster than the material treated would have in the open air. In bringing about this accelerated rate of cooling, some medium other than air at rest is brought into contact with the heated steel. Usually a liquid (almost always either oil or water) is employed ; but for certain steels a blast of air, and for others an easily fusible or soft metal, such as led (either solid or melted), may be used. Heat-treatment usually includes also subsequent moderate heating, followed, it may be, with another accelerated cooling.

Jan 1, 1902

By William H. Kobbé

THE CHAIRMAN (M. L. REQUA, San Francisco, Cal.).-We have had in California a great deal of trouble from the breaking. off and collapsing of well casings from shifting sand, and it is quite true with us as indicated in the paper, that no casing has been found sufficiently strong to withstand that. I know of wells in which casing that has not been in the hole over 2 or 3 days has collapsed and when that casing has, been pulled out it has been just as flat as your hand. I am also familiar with swelling bed rock in the gold drift mining ground of California. It does swell and keeps on swelling and never seems to stop. Just as long as tunnels are kept open in that kind of material there has to be a gang going through the tunnel constantly cutting out and easing up. They have put in timbers 24 in. in diameter in an effort to hold that kind of ground and it has always filled. The only way to succeed is to keep a gang of men busy all the time cutting out and easing down as it squeezes in. C. NARAMORE, Washington, D. C.-My experience has been very similar to yours in, the same field in the matter of breaking off of casing. I had charge of one well, in which I put in reënforced casing, anchored it in place and got 1 day's production, 150 bbl., out of it. The following morning my lease foreman telephoned that it had broken off. I thought at that time we would have more evidence, so I drove out to the well without ordering a new shoe joint. It had been customary to merely start from town with a new shoe joint, pull the pipe, take off the crooked bottom joint, start the casing back and sometimes never touch any iron (lost casing)- when redrilling the well. Where the flattened joints went

Jan 4, 1917

By P. Somasundaran Discussion by Knut L. Sandvik

Knut L. Sandvik (Mining Engineer, Mineral Dressing Laboratory, Technical University of Norway, Trond-heim, Norway) — The discovery that adsorption at solid-liquid interfaces is influenced by adsorption at other interfaces may prove very fruitful in the further development of flotation theory. Having reached the same conclusions as P. Somasundaran in some experiments with amine hydrochlorides, I would like to offer more direct evidence of the interfacial adsorption mechanism based on surface tension measurements and adsorption studies.' This evidence was derived from flotation tests carried out in a Hallimond tube at neutral pH and 60°C. The amount of amine solution and quartz surface were chosen to insure measurable concentration changes during flotation due to adsorption. Adsorption data for

Jan 1, 1969

By T. Suganuma

Mitsubishi-Cominco Smelting Co. is a joint venture of Mitsubishi Metal Mining Co. Ltd. (M.M.M.) of Japan and Cominco Ltd. of Canada. The smelter, which is located alongside M.M.M.'s Naoshima copper smelter, was completed in May, 1966 and has a capacity of 36 000 metric tons per year of refined lead. The concentrate feed for the smelter from Pine Point Mines Ltd. is high grade with low impurities; particularly silver, bismuth, antimony, and arsenic, which facilitated a simple plant layout and operation. Concentrate, fluxes, recycle granulated slag and return sinter are drawn from bins by automatic control over weigh belt feeders, sintering is carried out on a 20 m2 Lurgi updraught sintering machine, furnacing in a 3.0 m x 1 ½ m water jacketed blast furnace equipped with an Asarco continuous tapper, refining in four 120 metric ton kettles and casting on a 25 metric ton/hour automatic casting machine. The S@ gas from sintering is cleaned in a high temperature baghouse utilizing glass bags and is then delivered to the M.M.M. copper smelter acid plants. The furnace gases after cleaning in a low temperature baghouse are vented to atmosphere.

Jan 1, 1970

By Arthur Phillips, C. H. Mathewson

During the past year considerable work dealing with the mechanical properties and microstructure following the anneal under uniform condi-tions of certain types of commercial rolled brass has been done in this laboratory. Since these experiments were conducted with the active cooperation of the Bridgeport Brass Co., involving free use of its product, and have thus furnished information which is characteristic of some of its special mixtures, full publication of the numerical relationships and comparative results encountered does not seem justifiable. Some of the more general features of this work are, however, available and it is our present purpose to use the material in question, along with some results of special tests, in discussing the characteristics of recrystallization as related to the degree of hardening by strain and the ordinary annealing variables. We desire to make acknowledgment of the many courtesies extended by Mr. Charles Ferry, Metallurgist of the Bridgeport Brass Co., and the value of his cooperation, which has greatly stimulated the study of brass in this laboratory. A clear and systematic presentation of the principal relations between temperature and time of anneal, the changing physical properties and microstructure and the degree of previous reduction by cold-rolling, was first made, in the case of rolled brass and copper, by the French engineer, C. Grard,' in 1909, although much fragmentary information of this general character had appeared earlier and the main facts involved were undoubtedly known to many brass specialists through their own private research. From this work, it appears that in the cartridge mixture (67 per cent. copper, 33 per cent. zinc) the properties imparted by cold-working within the limits, 13 to 75 per cent, reduction of area by rolling Original Area — Final Area 0.13 to 0.75), are not affected by anneal- Original Area " ing for a 50-min. period at any temperature below 200°C. At or in the

Jan 1, 1916

By J. A. Brusset

THE Adanac mine was opened by West Canadian Collieries, Ltd. in 1943, and the question soon arose as to which system of haulage should be selected. Compressed-air locomotives and ropes were rejected on the ground of high cost. Since under the Alberta Mines Act the use of trolley locomotives underground in coal seams is not permitted, the choice lay between storage battery and Diesel locomotives, The preference of the author, who had experience with both in gassy French coal mines prior to 1930, was for Diesel locomotives due to lower cost of installation and greater flexibility and reliability. It was realized that the adoption of Diesels would be somewhat of an innovation since in the United States the mining laws prohibit their use under- ground in coal mines, and in Great Britain in 1943 their use was only in the incipient stage. By 1945, 25 Diesel locomotives were in use underground in gassy mines in Great Britain, and approval had been granted for the use of an additional fifty of two approved types also for gassy mines. Numerous special regulations of the British Coal Mines Act have been formulated to govern the use of Diesel locomotives. For instance, they are not allowed closer than 200 yards from the working face; daily inspections are required; and a weekly checkup and cleaning must be given the engine by a competent engineer. Also, methane content of the air in the roadway can never exceed 1.25 percent, and daily checks must be made if it exceeds 0.75 percent. Under Alberta regulations, we were required to use a flameproof type engine, to be used only in fresh air intake. The engine fumes had to travel along a separate ventilation split where no man was permanently employed. It is forbidden to run a

Jan 1, 1949

THE Council of the Geological Society of America has named its gold medal after R. A. F. Penrose, Jr., who recognized the need of such an award and supplied the endowment. The medal is to be awarded for achievement in pure science and may be given to a worker of any race or nation. Mr. Penrose, whose own professional work has been mainly in applied geology, had previously established a medal fund for the Society of Economic Geologists. This was awarded to T. C. Chamberlin at the meet-ing of that Society at Cornell University in 1924. The new medal is to be given on the recommendation of the G. S. A. Council, but not necessarily every year.

Jan 4, 1927

By H. l. Burghoff, C. H. Mathewson

THE study of the creep of metals under conditions of prolonged loading has received the attention of many investigators for several years and almost innumerable papers have been published on the various aspects of the subject. As it appeared that much could still be learned from a study of single crystals, the present work was carried out to study the effects of temperature and conditions of loading upon the properties and deformation in tension of single crystals of alpha brass containing about 70 per cent copper and 30 per cent zinc. In particular, it was hoped to obtain information from tests below and above the recrystallization temperature of the material, so that properties such as elastic limit, yield point or critical stress, and manner of deformation might be compared for tensile tests at an ordinary loading rate and for prolonged. loading. Accordingly, short-time tensile tests and creep tests were made at room temperature, 300º, 500° and 700°F. The two latter temperatures are above the lowest possible recrystallization temperature of polycrystalline 70-30 brass. PREVIOUS WORK Clarke and White1 have made creep tests of some copper-zinc alloys, including 70-30 brass, and copper-zinc-tin alloys at temperatures both below and above the recrystallization temperature of the materials considered. Hanson and Wheeler have studied the flow and fracture of single crystals of aluminum for short-time and prolonged tensile loading over a range of temperature extending from room temperature to 400°F., their experiments being made without consideration of the orientations of the test specimens. Extensive creep and fracture tests on single crystals of lead at room temperature have been made by Betty3 and by Baker, Betty & Moore.4 Results of the last-named investigation were published while the present work was in progress. Millers examined the elastic limit of zinc single crystals at and above room temperature by means of creep tests, while Miller and Milligan6 reported the results of tests designed to show the influence of temperature on elastic limit of single crystals of aluminum, silver and zinc. The behavior, of iron crystals under static tensile loading at room temperature was reported by Gensamer and Mehl7 while the present investigation was in progress. Their specimens exhibited a well-defined yield point, below which no appreciable creep could be detected. The manner of yielding proved interesting, as the shape of the creep-time curve for the iron crystals differed from the common type of creep curves. Elongation did not begin immediately, or at least was initially very slow. The rate of elongation then increased continuously and finally decreased to zero. This S-shaped type of elongation-time

Jan 1, 1941

By AIME AIME

THE Charleston Section of the A. I. M. E. held a joint meeting with the National Coal Association and the American Society of Mechanical Engineers on May 6 and 7, at which 94 members and guests were registered. Mechanical operation of coal mines was the subject discussed. First on the program was a paper entitled "Rock Dusting in the Coal Mines of West Virginia," by R. M. Lambie, chief of the Department of Mines, and Gordon MacVean. It appears in full in the current issue of MINING AND METALLURGY, p. 290. J. E. Jones of the Old Ben Coal Corp. opened this discussion by describing the method of rock dusting employed in the mines of that company, giving many interesting details, incidentally referring to the use of rock dust in fighting mine fires. He described one case where a number of troughs was brought to within 150 ft. of the fire, and rock dust had been thrown in its direction. After each trough had been thrown the party advanced a few feet, where another trough was discharged. About 10 ft. were gained on each advance, until the party found they had advanced completely over the fire.

Jan 1, 1926

By Robert W. Bartlett

A computer model for predicting the rate of oxidative leaching of copper from fragmented low grade sulfide ores is presented. The model involves the kinetics of the dissolution of chalcopyrite grains and solution diffusion of oxygen within rock pores. Adjustable curve fitting parameters are not used. The model was tested by comparing computed extraction curves with experimental results for a -11 inch ore obtained by block caving and leached at 90°C and 400 psi oxygen for one year at the Lawrence Livermore Laboratories.

Jan 1, 1973

By Walter Miller

DURING the second year of America's active participation in the war the main objectives of the petroleum refining industry were again to provide the four most important product needs for war: 100-octane aviation gasoline, toluene for TNT production, high-quality lubricating oils for the needs of aviation and the armed forces, and petroleum chemicals for synthetic rubber manufacture. All other materials supplied by the petroleum industry took an inferior priority ranking, depending on the degree of essentiality. To accomplish the above objectives the industry initiated and carried on a building program during 1942 and 1943 which will put those two years down in petroleum refining history as the greatest construction years of all time, a record which will hold for decades to come. Led by an estimated total of $900,000,000 going into 100octane and contributory plant investment, it is easy to picture a total of two billion dollars and more going into additional refining-industry plant investment during 1942 and 1943, most of it privately paid for, but a substantial part covered by R.F.C. Government money financing.

Jan 1, 1944

By J. Norman Bulkley

As electrical power is used to a greater extent on the Rand than in any other mining center, it is thought that a short description of the methods used and results obtained may be of interest. In comparing Rand practice with that on other fields, several general factors should be borne in mind: First, the mines are all working on large tonnages of low-grade ore (average. $6.50). The annual crushing rate is about 27,000,000 tons. Second, the mines are all grouped udder the financial and engineering control of mining houses, so that the results of a group, rather than an individual mine, are open for study, and practice follows more uniform lines. Third, coal of fair quality (about 12,000 B.t.u.) can be obtained for $2 to $3 per ton., Good supplies of condensing water are, however, scarce, and have to be carefully stored. Power Supply Power is supplied by the Victoria Falls & Transvaal Power Co., Ltd., and its subsidiary, the Rand Mines Power Supply Co. Both companies, which are practically one from an engineering point of view, operate the following stations, all feeding into the same system.

Jan 2, 1916

Arrangements have been completed in New York whereby the re- sources of The Engineering Foundation, under the auspices of the four principal national engineering societies, are placed at the disposal of the National Research Council, which was appointed by the National Academy of Sciences* at the request of President Wilson. The object of the Council is to coordinate the scientific research work of the country in order to secure efficiency in the solution of the problems of war and peace. The Council was without funds until The Engineering Foundation, established to further scientific and engineering research, offered to place its resources at the Council's disposal, including the services of its secretary, Dr. Cary T. Hutchinson, to act as-secretary of the Council. The offer was accepted and plans for immediate activities have been placed in the hands of an executive committee. In indicating how thoroughly, every branch bf science and engineering is represented, Dr. George E. Hale, Director of the Mt. Wilson Solar Observatory, and Chairman of the Council, when he was in New York attending to the details of the arrangement, called attention to the personnel of the body, saying that it is the purpose to enlist the cooperation, in the solution of our industrial and military problems of a scientific character, of every possible established agency. Medicine, for example, is represented on the Council by Dr. William H. Welch, President of the National Academy of Sciences, Brigadier General William C. Gorgas, , Surgeon Crenera.1 of the United States Army, Dr. Simon Flexner, Director of the Rockefeller Medical Institute, and Dr. Victor C. Vaughan, Past President of the American Medical Society; biological science by Dr. Edwin G. Conklin, Professor of Zoology, Princeton University; chemistry by Dr. A. A. Noyes of Massachusetts Institute of Technology and Dr. L. H. Baekeland; physics by Dr. A. A. Michelson of the University of Chicago; and electricity by Professor M. I. Pupin, of Columbia University.

Jan 10, 1916

By C. H. Mathewson, H. l. Burghoff

The study of the creep of metals under conditions of prolonged loading has received the attention of many investigators for several years and almost innumerable papers have been published on the various aspects of the subject. As it appeared that much could still be learned from a study of single crystals, the present work was carried out to study the effects of temperature and conditions of loading upon the properties and deformation in tension of single crystals of alpha brass containing about 70 per cent copper and go per cent zinc. In particular, it was hoped to obtain information from tests below and above the recrys-tallization temperature of the material, so that properties such as elastic limit, yield point or critical stress, and manner of deformation might be compared for tensile tests at an ordinary loading rate and for prolonged loading. Accordingly, short-time tensile tests and creep tests were made at room temperature, 300°, 500° and 700°F. The two latter temperatures are above the lowest possible recrystallization temperature of polycrys-talline 70-30 brass. Previous Work Clarke and White1 have made creep tests of some copper-zinc alloys, including 70-30 brass, and copper-zinc-tin alloys at temperatures both below and above the recrystallization temperature of the materials considered. Hanson and Wheeler2 have studied the flow and fracture of single crystals of aluminum for short-time and prolonged tensile loading over a range of temperature extending from room temperature to 400°F., their experiments being made without consideration of the orientations of the test specimens. Extensive creep and fracture tests on single crystals of lead at room temperature have been made by Betty3 and by Baker, Betty and Moore." Results of the last-named investigation were published while the present work was in progress. Miller5 examined the elastic limit of zinc single crystals at and above room temperature by means of creep tests, while Miller and Milligan6 reported the results of tests designed to show the influence of temperature on elastic limit of single crystals of aluminum, silver and zinc. The behavior of iron crystals under static tensile loading at room temperature was reported by Gensamer and Meh17 while the present investigation was in progress. Their specimens exhibited a well-defined yield point, below which no appreciable creep could be detected. The manner of yielding proved interesting, as the shape of the creep-time curve for the iron crystals differed from the common type of crcep curves. Elongation did not begin immediately, or at least was initially very slow. The rate of elongation then increased continuously and finally decreased to zero. This S-shaped type of elongation-time

Jan 1, 1941