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By C. S. Barrett, D. F. Clifton

THE transformation that occurs in lithium and its solid solutions containing magnesium1,2 is similar in many respects to other diffusionless transformations of the martensitic type. This general similarity makes it desirable to investigate the transformation curves in detail. The current interest in the phenomenon of stabilization in martensitic transformations has created a need for a careful appraisal of possible stabilization effects in both cooling and heating transformations in lithium alloys. The effect of prior heat treatment on the temperature at which transformation begins and the effect of various temperature cycles in partially transformed alloys also merit attention. Limited data on some of these features were presented previously,' but the present studies have been made with improved apparatus, in which erratic fluctuations were smaller than in the earlier work, and include many independent determinations of certain critical observations. Material and Methods Geiger counter X-ray spectrometers were used: a Norelco instrument, original model, and a General Electric XRD-3. The low-temperature specimen holder has been described elsewhere." Specimens 10 mm in diam and 1.5 mm thick were held in firm contact with a copper block which was attached to the lower end of a stainless steel tube that extended up to a reservoir of liquid nitrogen. A heating coil on the tube permitted a controlled temperature gradient along the tube, so that desired temperatures and rates of heating and cooling could be obtained by controlling the heating current. The specimen was surrounded by an atmosphere of evaporated nitrogen in an insulated chamber having double cellophane windows. The temperature of the specimen was read by a thermocouple imbedded in it close to the irradiated area; the specimen could be held at constant temperature within 1°C for long periods. The body-centered cubic 200 reflection near 8 = 26" was used as the index of the amount of b.c.c. material present; occasional checks were made using the most suitable line of the low-temperature phase, the close-packed hexagonal 110 line near 8 = 29". Copper radiation was used throughout. A continuous record was made of the reflected intensities on a strip chart recorder, both when the peak intensity of a line was being followed and when the lines were being scanned at constant temperature. On the continuous recordings of peak intensity, periodic checks were made on the background intensity between the lines, and on the setting of the spectrometer for maximum intensity. The lithium-base solid solution containing 12.4 atomic pct Mg (33.3 wt pct) that had been used previously' was chosen, as it had a transformation range at relatively high temperatures, so as to permit wide temperature cycling within the range. Just prior to use a pellet was cut from the ingot,

Jan 1, 1951

By Carle R. Hayward

SulphuR has long been one of the banes of the steel manufacturer and often no effort and expense have been spared in order to reduce it to a small per cent. in the finished product. This condition is due to a general conviction that in many cases where steels have failed in service, sulphur has been the cause. But there has been a growing feeling in recent years that the verdict against sulphur has been unnecessarily severe. In cases of segregation it was present in. augmented amounts along with other impurities, but it had not caused the segregation. High sulphur in pig iron is caused by poor furnace conditions and the sulphur is merely one indication of an iron that has not been properly reduced. No amount of subsequent treatment under oxidizing conditions in the open-hearth furnace can remedy the defects, although the per cent. of sulphur may be considerably reduced. In other words, the causes of bad steel can frequently be traced back to bad pig iron, and sulphur is merely one indication that the pig iron is bad. The writer recently visited a steel plant where a mass of evidence had been accumulated which substantiated this fact, and the superintendent was emphatic in stating that high sulphur was not harmful provided the steel was not otherwise poor due to insufficient reduction in the blast furnace. The presence of a moderate amount of sulphur is desirable from the standpoint of the man who machines the steel. The low-sulphur material drags and the production of a smooth surface is very difficult. A slight increase in sulphur enables the machinist to produce a smooth surface without difficulty. Since, therefore, such large quantities of steel are subjected to machining, it becomes highly important that the sulphur controversy should be settled, and if its presence is proved to be harmless the ban on it should be lifted. Among the recent papers on the effect of sulphur on steel is one by Dr. J. S. Unger, Manager of the Central Research Bureau, Carnegie Steel

Jan 1, 1917

By Russell A. Carter

Alaska is a land of immense proportions and resources. Its very name, derived from an Aleut term, means "The Great Land." Yet, in a state slightly larger than Texas, California, and Montana combined, there are presently only two-large scale mines in production, excluding dredge operations. Once referred to by its territorial governor as "a storehouse of minerals," Alaska is, in the opinion of many industry observers, at least 20 years away from a healthy, productive mining industry. The mineral potential of the state is tremendous: coal deposits on the North Slope alone have been hypothetically pegged at 1.5 trillion tons. Copper-zinc deposits on the south flank of the Brooks Range are conservatively estimated to be worth $4 billion to $6 billion. However, the problems facing mineral development are of equal magnitude, and include:

Jan 11, 1976

EXECUTIVE COMMITTEES OF LOCAL SECTIONS New York L. W. FRANCIS, Chairman, WILLARD S. MORSE, Vice-Chairman. THOMAS T. READ, Secretary, Woolworth Bldg., New York, N. Y. P. A. MOSMAN, Treasurer. LOUIS D. HUNTOON. WILLIAM A. POMEROY. Boston HENRY L. SMYTH, Chairman. ALFRED C. LANE, Vice-Chairman. AUGUSTUS H. EUSTIS, Secretary-Treasurer, 131 State St., Boston, Mass. ROBERT H. RICHARDS, ALBERT SAUVEUR. Columbia F. A. THOMSON, Chairman. GEORGE W. RODDEWIG, Vice-Chairman. LYNDON K. ARMSTRONG, Secretary-Treasurer, P. O. Drawer 2154, Spokane, Wash. R. S. McCAFFERY, S. H. RICHARDSON.

Jan 11, 1914

EXECUTIVE COMMITTEES OF LOCAL SECTIONS New York L. W. FRANCIS, Chairman, WILLARD S. MORSE, Vice-Chairman. THOMAS T. READ, Secretary, Woolworth Bldg., New York, N. Y. P. A. MOSMAN, Treasurer. LOUIS D. HUNTOON. WILLIAM A. POMEROY. Boston HENRY L. SMYTH, Chairman. ALFRED C. LANE, Vice-Chairman. AUGUSTUS H. EUSTIS, Secretary-Treasurer, 131 State St., Boston, Mass. ROBERT H. RICHARDS,. ALBERT SAUVEUR. Columbia F. A.. THOMSON, Chairman. GEORGE W. RODDEWIG, Vice-Chairman. LYNDON K. ARMSTRONG, Secretary-Treasurer, P. O. Drawer 2154, Spokane, Wash. R. S. McCAFFERY, S. H. RICHARDSON.

Jan 12, 1914

By W. M. Peirce

WITH the supply of zinc, like that of most other nonferrous metals, inadequate to meet the demand, efforts to increase domestic ore supplies and production capacity have been of primary interest. No major sources of new ore have been disclosed during the year but improvements have been reported in facilities for mining and concentrating ores from existing mines. The American Zinc, Lead and Smelting Co. has announced its intention of erecting a new mill in the Ouray district of Colorado. The Consolidated Mining and Smelting Co. of Canada is reported to be planning improvements costing $3,000,000 to its Sullivan mine and concentrator at Kimberley, B.C., where the sink-float process is to be used for preliminary ore treatment. In the reduction field, the St. Joseph

Jan 1, 1947

By Robert H. Richards

OF the several professions-the chemist, the civil engineer, the mining engineer, the mechanical engineer-the courses of instruction, as arranged at the scientific schools, differ considerably as to the amount of practical information which the student is able to gain. The analytical chemist has facility for a very thorough review of the processes which he will be called upon to perform. The student in civil engineering by his field practical learns the use of his tools and the art of taking field-notes. The mechanical engineering student is in the vicinity of machine-shops, which he can visit, and at which . he can work. The student in mining engineering has no such advantages. The mines are at a distance, and the railroad fare to get to them is oftentimes an insuperable difficulty. The aim of these laboratories is essentially to give to the student in mining and metallurgy a chance to study on a small scale the practical parts of his profession. We cannot, in a small laboratory, build a mine to timber, to work, and to survey; we cannot make artificial quicksands and other impediments to mining. In short, we cannot study exploration; but we can study the mechanical preparation and the subsequent smelting of ores. Before presenting the plan of these laboratories it may be interesting to indicate the progress of the idea from its beginning. During the summer of 1870 President Runkle visited the mines of Colorado, and while there, conceived the idea of making an expedition with the mining students to some of the Western mining regions. He talked over the scheme with many railroad and mining men, and everywhere received encouragement. In the summer of 1871 the Institute party visited the mines of Colorado, and spent six weeks in taking notes of them. President Runkle here conceived the idea of building up a mining and metallurgical laboratory ; and by the aid of Booth & Co. of San Francisco, a stamp-mill was obtained, with the Washoe silver-working apparatus. During the year

By Hugh P. Nicholson

IN view of the many articles that have been written on the proper classification of mining systems without so far having produced any particular tangible results it might seem that the subject is hopeless of solution. I do not believe that is so, and my intention in contributing the following outline is to present a slightly different viewpoint. Too much attention is often focused on unnecessary details and not enough on general principles. Too much attention and emphasis is often given to the system employed at one particular mine or in one particular district. In addition, names that are entirely misleading are applied to mining systems, and their adoption by the coming generation perpetuates a condition that needs clarification badly. The following classification is the result of several years of practical experience in mining and also several years' practice in teaching the same subject. It therefore represents a broad picture of the entire field of mining systems from the viewpoint of the miner as well as the teacher. It seems that the difficulty in the past has been in reconciling these two viewpoints. The need of such a reconciliation requires no explanation.

Jan 1, 1934

By H. Merton Ruth

THE northern anthracite fields, although facing the same economic problems as the southern fields, are confronted with the additional problem of fast dwindling reserves of anthracite which can be conventionally and economically won. The mining of coal which remains in thin beds and the recovery of pillars from areas heretofore considered unrecoverable, either by reason of cost or surface restriction, pose problems of in- creasing importance to the economic life of the northern field operations. Successful approaches have Been made to this problem and other work is being performed that holds promise. There exists in the northern anthracite field millions of tons of solid coal, the recovery of which has not been too successful due to the following inherent operating faults: inability to concentrate producing areas; the great quantities of rock to be cut and handled, lack of consideration of proper sequence and speed of second mining, and the continued use of the mine car as the basis of payment. A mining system that has successfully solved these major problems has been in operation in the Scranton area since 1944. Over 1% million tons have been produced from veins varying from 3 to 4% ft thick by this method, which is known as the multiple panel-triangular system-conveyor mining.

Jan 1, 1950

By H. E. Mills

THE local auditorium of a little Alabama mining town was crowded with expectant men, women and children, as the bulletin board had announced the addition of visiting entertainers to supplement the local talent and motion pictures which usually made up the program of the regular monthly safety meeting. In the audience, near the stage, sat a group of bright-faced boys in boy scout uniforms, discussing the picture just completed. As the lights flashed on a crash and scream was heard from the outside, a shrill whistle and word of command from the scoutmaster, and five of the scouts ran out of the hall, while the mine super-intendent stepped on the stage and requested everyone to keep their seats. The scouts returned, three of them carrying a limp figure in their arms, while the other two cleared the doorway and aisle of excited spectators. They marched to the stage and, placing the apparently badly-injured boy on the floor, proceeded to give an expert demonstration of first aid to the injured. The scoutmaster then explained to the audience that the whole affair had been arranged for their benefit, and invited the local first-aid men to come up on the stage to examine and criticize the boys' work. This gave an opening for several talks on the value of first-aid training and accident prevention, which is the main object of the monthly meetings. This demonstration was given by the first-aid team of Troop One, and the entertainment was provided by members of Troop One and Twenty-eight of the Bir-mingham Scout Council, organized by the writer for the purpose of promoting interest in the welfare and safety meetings in the mining villages of the State. During the past year they have visited a number of such meet-ings and presented programs similar to the one men-tioned above. However, in order to assure a good attendance, entertainment features must also be pro-vided, and the serious part of the evening program was interspersed with excellent vocal and instrumental mu-sic, dancing and novelty acrobatic acts furnished by the visiting scouts. In addition to the numerous first-aid teams of the Birmingham Council, there are hundreds of scouts scat-tered throughout the mining district whose knowledge of first aid, safety first, life-saving, personal health and public health are a constant source of protection to their community. All of these subjects are covered by merit badge pamphlets and are required of an eagle scout.

Jan 2, 1927

By Milton E. Wadsworth, R. Ted Wimber

Cobalt sulfate solutions containing ammonium acetate and chloroplatinic acid were reduced by hydrogen in a pyrex-glass lined autoclave in the temperature range of 170o to 232°C and hydrogen partial pressure range of 115 to 830 psia. The reduction rate was directly proportional to the hydrogen partial pressure and surface area of the pyrex glass and was independent of the quantity of chloroplatinic acid added initially. Experiments involving the variation of the relative concentration of ammonium acetate indicated that the reducible cobalt complex was probably the diacetate complex of cobalt, Co(AC)4H20, or a new mononcetate complex Co Ac, which was in solubility equilibrium with a pink precipitate of CO(AC)-4HzO. THE reaction in which a metal is dissolved by an acid to produce gaseous hydrogen and a salt solution was discovered early in the history of chemistry. In 1859 Beketoff found experimentally that this reaction could be reversed; i.e., a salt solution could be reduced by gaseous hydrogen to produce a metal and an acid. A review of work done on this phenomenon since that time may be found elsewhere., The hydrogen reduction of a cobalt salt solution is facilitated by complexing the cobalt ion. An ammonia complex of cobalt has been reduced commercially in the recovery of cobalt metal. A new reducible complex of cobalt was discovered5 when it was found that a co-baltous sulfate solution containing ammonium acetate could be reduced by hydrogen at temperatures in the region of 200°C. When a cobalt sulfate-ammonium acetate solution was heated to a temperature below its normal boiling point, a violet color became apparent, indicating complex formation. The nature of this complex was investigated5 by the addition of NH4Ac to a CoSO4 solution maintained at 85o. During the first additions of NH, Ac, the pH of the solution remained fairly constant at about 5.85. However, as the ratio of NH,Ac to CoSO, approached two, the pH rose and then leveled off at about 6.05. The absorption spectra of a Co(Ac), solution and a CoSO,, NH Ac solution were obtained at 85°C and were compared and found to be the same. These findings suggested that the diacetate complex of cobalt, Co(Ac),.4H20, was formed at 85°C. When a cobalt sulfate-ammonium acetate solution was heated to a temperature above about 165o, a finely divided pink precipitate appeared. The X-ray diffraction pattern of this precipitate indicated that it was Co(Ac), - 4H,O. In addition, it was discovered that when chloroplatinic acid, H,PtCl;, was added initially to the cobalt sulfate-ammonium acetate solution, a faster reduction was obtained. The roles of the solution complex, pink precipitate and chloroplatinic acid in the reduction process were then investigated. APPARATUS The experimental work was carried out in a two-liter stainless-steel autoclave. Adetailed description of the autoclave and the auxiliary equipment used in maintaining constant temperature and pressure may be found elsewhere.= Because the stainless steel was corroded, and also because it acted as a hydrogena-tion catalyst, an all-glass liner was fabricated such that the solution came only into contact with flame-polished pyrex glass. EXPERIMENTAL PROCEDURE The solutions used in the experimental work were prepared by dissolving reagent grade chemicals in distilled water. Although variation of the brand of ammonium acetate appeared to have no effect on the experimental results, CoSO, 7H O from the J. T. Baker Chemical Co. of Phillipsburg, N. J.,was found to give faster reductions than that prepared by Allied Chemical and Dye Corp., N. Y. The former was used throughout the course of the experimental work and was weighed up at the outset of each experiment. The ammonium acetate was dissolved to form a 6M stock solution, which was stored under refrigeration. A 10 pct solution of chloroplatinic acid (J. T. Baker Chemical Co.) was diluted to a 1.15 x 1Q2 M stock solution, which was standardized by precipitation of K,PtCl, as outlined by Scott. The appropriate volume of the chloroplatinic acid, H,PtCl,, solution was pipetted into the clean, dry glass liner. The cobalt sulfate-ammonium acetate solution, which had previously been saturated with

Jan 1, 1962

NEW MEMBERS The following list comprises the names of those persons who became members during the period Nov. 10 to Dec. 10, 1915: BARTH, ERNEST, Petroleum Geol Box 552, Tulsa, Okla. BEROLZHEIMER, D. D.,.Chemist; Librarian, Barrett Mfg. Co., 17 Battery Pl., New York, N. Y. BLIEK, PIERRE FRANCISCO, Mgr., Compania Minera de Oruro, Oruro, Bolivia, So. Amer. BLOCS, JAMES A., Met 1076 1st Ave., Salt Lake City, Utah. BULKLEY, RALPH G., Mine & Mill Supt.; The Montezuma Mines & Mills Co., Montezuma, Colo. BURRAGE, ALBERT CAMERON, JR., Met. Engr.; Director, 85 Ames Bldg., Boston, Mass. CABELL, CHARLES ARNOLD, Vice-Pres Carbon Coal Co., Carbon, W. Va. CHAPMAN, LEWIS CARL, Economic Geol Producer Oil Co., Houston, Tex. CHOFFEL, FLAVIEN AURELIEN, Mgr Ingersoll-Rand Co., Paris, France COY, HARLEY A., Mine Supt American Zinc Co., Mascot, Tenn. DITTMANN, C. 0. ADOLF, Cons. Engr., Beer, Sondheimer & Co., Inc., Santiago, Chile, So. Amer.

Jan 1, 1916

By R. A. Hadfield

It seems a specially fitting opportunity to present a paper on the alloys of iron and aluminum at the New York meeting of this Institute, owing to the fact that America has, more than any other country, originated and developed the manufacture of cheap aluminum. The Cowles, Castner, and Hall systems have all originated in the ever-busy brain of our cousin across the water. The problem of cheaply producing this valuable metal has been a difficult one, but to the writer it seems that the more arduous the task the greater the delight with which our American friend attempts to overcome the difficulties surrounding it, and the more vim he throws into the work. Another and equally striking proof of this is to be found in the recent appearance of the already wellknown remarkable work, The Mefallurgy of Steel, by Mr. H. M. Howe, of the Institute of Technology, Boston, Mass. It is to be hopel that this Institute will not be slow to recognize by some special mark its appreciation of this signally valuable and original work. The writer has been led to describe the following experiments, believing that so far no full and exact report has yet been presented to this Institute as to the effect of aluminum alloyed or combined with the metal iron. It has been a special object to make the material as far as possible a true alloy or combination of aluminum and iron, with as small quantities as possible of other disturbing ingredients, such as silicon, manganese, etc. In the material described in these experiments, the total amounts of other elements present (sulphur and phosphorus being disregarded as present in such small quantities) do not exceed about 0.5 per cent. Such material may therefore be probably taken as fairly illustrative of the effect of the metal aluminum upon iron. Since completing the experiments the writer

Jan 1, 1891

THOSE MARKED THUS * ARE MEMBERS, MARKED THUS t ARE ASSOCIATES THESE SIGNS DOUBLED INDICATE LIFE MEMBERS AND ASSOCIATES RESPECTIVELY THE FIGURES AT THE END OE THE ADDRESS INDICATE THE YEAR OE ELECTION HEAVY FACED T1 PE SIGNIFIES HONORARY MEMBERSHIP *ABADIE, EMILE R , Min Engr P 0 Box 83, Berkeley, Cal '76 *ABBE, CLEVELAND, JR, Geol Aid, U S Geological Survey, Washington, D C '00 *ABBOTT, AI ARTHUR, Cerro de Pasco Mining CO , Cerro de Pasco, Peru, So America '95 *ABBOTT, ARTHUR V , Electrical Engr , Westinghouse, Church, Kerr & Co , 8 Bridge St, New York, N Y '82 *ABBOTT, CLARENCE E, Chief Min Engr, Care Fayal Mine, Eveleth, Minn '04 *ABBOTT, JAMES W , Min Engr , Special Agent, Rocky Mountain and Pa¬cific Coast Division, U S Dept of Agriculture, "Tile New Markham," Denver, Colo '94

Jan 1, 1910

EXECUTIVE COMMITTEES OF LOCAL SECTIONS New York LOUIS D. HUNTOON, Chairman. ARTHUR S. DWIGHT, Vice-Chairman. THOMAS T. READ, Secretary, Woolworth Bldg., New York, N. Y. E. MALTBY SHIPP, Treasurer. GEORGE F. KUNZ, W. DE L. BENEDICT. Boston ROBERT H. RICHARDS, Chairman. ALBERT SAUVEUR, Vice-Chairman. AUGUSTUS H. EUSTIS, Secretary-Treasurer, 131 State St., Boston, Mass. TIMOTHY W. SPRAGUE, HENRY A. WENTWORTH.

Jan 2, 1914

Jan 1, 1935

By AIME AIME

THOUGH born in England-on Nov. 23, 1372 William Wraith was brought to this country at the age of ten. Eight years later he entered the University of Illinois, transferring to the Michigan College of Mines where he got his E.M. in 1894. For the next three years he was a mine surveyor for the fuel department of the Santa Fe Railroad. Then he got into the copper-mining industry, which has occupied his attention for the last forty years. First he was engineer, at Butte, for the Boston & Montana company, and then helped to build the Washoe smelter at Anaconda, of which he was assistant superintendent from 1906 to 1913. The Anaconda company then sent him to Salt Lake City as manager of its subsidiary.

Jan 1, 1938

By Cyril Stanley Smith

Somewhat over ten years ago the author described studies1'2 on the constitution of the copper-silicon system. The copper-rich portion of this diagram is shown in Fig. 1. The experimental points freely dotted about the diagram seemed to justify an otherwise unconvincing diagram and for several years the curious reverse bend in the alpha-phase boundary was accepted as substantially correct, even by later investigators3 of the system who introduced changes in the high-silicon phases. The binary diagram has been used as a base for several ternary systems5-9 without any suggested changes. Voce10 suspected the existence of another phase from his study of the cast alloys in the copper-manganese-silicon system, but evidently hesitated to extrapolate this to the binary diagram, particularly in view of the too ingenious explanation that was advanced1' to account for the pools of constituent clearly visible in castings; namely, that they were secondary alpha of twinned orientation deposited from beta. Von Schwarz,12 in 1932, called attention to the fact that this micro-constituent in copper-silicon alloy castings was anisotropic under polarized light and asserted that a new phase, not cubic, should be placed in the diagram .adjacent to alpha. Sautner,l3 on the basis of investigations with the polarizing microscope and with X-rays, introduced this phase into the diagram at about 6 per cent Si. The relevant part of his diagram is shown in Fig. 2. Sautner called the new phase beta, renaming the old beta phase zeta. To avoid confusion, in redrawing Fig. 2 the phases have been renamed in accordance with the terminology adopted in the present paper, in which the new phase is called kappa and the other phases retain the designation given them by Arrhenius and Westgren.4 The thermodynamic impossibility of Sautner's diagram and the paucity of experimental data left the exact location of the new phase field most uncertain, although his work proved beyond doubt that an additional noncubic phase exists. Because of the industrial importance

Jan 1, 1940

By Cyril Stanley Smith

Somewhat over ten years ago the author described studies1'2 on the constitution of the copper-silicon system. The copper-rich portion of this diagram is shown in Fig. 1. The experimental points freely dotted about the diagram seemed to justify an otherwise unconvincing diagram and for several years the curious reverse bend in the alpha-phase boundary was accepted as substantially correct, even by later investigators3 of the system who introduced changes in the high-silicon phases. The binary diagram has been used as a base for several ternary systems5-9 without any suggested changes. Voce10 suspected the existence of another phase from his study of the cast alloys in the copper-manganese-silicon system, but evidently hesitated to extrapolate this to the binary diagram, particularly in view of the too ingenious explanation that was advanced1' to account for the pools of constituent clearly visible in castings; namely, that they were secondary alpha of twinned orientation deposited from beta. Von Schwarz,12 in 1932, called attention to the fact that this micro-constituent in copper-silicon alloy castings was anisotropic under polarized light and asserted that a new phase, not cubic, should be placed in the diagram .adjacent to alpha. Sautner,l3 on the basis of investigations with the polarizing microscope and with X-rays, introduced this phase into the diagram at about 6 per cent Si. The relevant part of his diagram is shown in Fig. 2. Sautner called the new phase beta, renaming the old beta phase zeta. To avoid confusion, in redrawing Fig. 2 the phases have been renamed in accordance with the terminology adopted in the present paper, in which the new phase is called kappa and the other phases retain the designation given them by Arrhenius and Westgren.4 The thermodynamic impossibility of Sautner's diagram and the paucity of experimental data left the exact location of the new phase field most uncertain, although his work proved beyond doubt that an additional noncubic phase exists. Because of the industrial importance

Jan 1, 1940

By R. C. Gifkins, K. U. Snowden

The value of the index n in power ktivs for the stress sensitivity of minimum creep rale at lead is derived front results drawn from lite literature and from previously unpublished nork on commercial (99.99 pel) and high-purity (99.999 pel) lead polycryslalline and hi crystal specimens. In tests al 0.5Tm (22 to 50'C) for slvesses below 250 psi, n fulls to mily for poly-cr,yslullirle specimens, single crystals, and bicrystals, and toy grain boundary sliding in bicrystals. Between 250 and 500 psi there is a tyansilion range and, for the polycrystalline specimens al least, u high-stress regime for 500 to 1500 psi where n is 5 or 6. These results are such that none of the suggested stress taws can he used to extrapolate to very loir stresses. Meclianisms for deformation in Ike grains and toy grain boundary sliding in the low-strcss regime are outlined. In particular, the mechanism for grain boundary sliding involves sliding controlled by diffusion from tensile to compressire Ledges. predictions based on this model give promising numerical agree-nicul with experiment. II is suggested that the mechanism for grain boundary sliding may he important in other circumstances, e.g., in creep of ceramic materials or superplaslicity, because it can operate with lille or no dislocation aclirity. WhEN the stress dependence of secondary creep rate is represented by a power law the values taken by the stress exponent n are found to vary between 1 and 7, see, c.g., Garofalo.' In Eq. 1 11 u is the applied stress and A a constant. The case for accepting values of v = 1 rests principally upon tests at high temperatures (>0.9Tm) and there have only been isolated tests at lower temperatures (rather than plots of creep rate against stress) for which the creep rates are such that some form of Nabarro-Herring creep with n = 1 is applicable. Hanson5 and Greenwood and cole6 plotted creep rate against stress for tests made in the vicinity of 0.5Tw, and found a "creep yield", so that below a certain low stress the creep rate was linearly related to stress: these observations appear to have been subsequently ignored. Various models have been proposed which agree with a large body of experimental results in which n equals -5 at high stresses (e.g., weertman7 and McLean8). Various alternatives to Eq. [1] have been proposed principally as a means of unifying creep data, but sometimes, it seems, in order to obviate the necessity for assuming a series of regimes of deformation associated with the various values of n; further refer- ence to these will be made in the section on stress laws. This paper calls attention to extensive results which show n = 1 for the creep of lead at room temperature (0.5 T,). RESULTS Fig. 1 is a composite diagram based on figures in the literature6,9,10 with additional results obtained by the present authors and their colleagues11,12 in the course of a number of investigations not directly concerned with stress sensitivity. In Fig. 1 In creep rate is plotted against In stress. The curves show results for two kinds of material. Lead I is of commercial purity (99.99 pct Pb) and lead IT a specially refined material, hydrogen-purified to remove oxygen; it contains 99.999 pct Pb. Curve A is for lead I in polycrystalline form (grain diameter 0.02 to 0.05 cm) at room temperature (22' to 26°C). Curve B1 is for lead I, polycrystalline, tested at 50C. Curve B2 is for lead 11, polycrystalline (grain diameter 0.02 cm), tested at room temperature (22 O- Curves C to F relate to tests made of bicrystals of lead 11: all of the same nominal orientation ("Y" in Ref. 12). Curves C and V are for creep within the component crystals of the bi crystals at 22°C (AB and CD in Fig. 2). Curve E is for creep measured in a gage straddling the boundary, approximately 0.15 mm either side (BC in Fig. 2). Curve F shows rates of grain boundary sliding (as distinct from strain rates in the other curves), obtained by averaging the offsets of six marker lines on the bi-crystal boundaries. The principal feature of the results is that the stress sensitivity falls into two distinct regimes, according to whether the stress is below approximately 250 or above 500 psi (there is a transitional range between 250 and 500 psi). The new result is that below -250 psi two of the curves (A and BI) give a value of n 1, and the other curves also drop below n - 2 to -1.5 but do not extend to low enough stresses to show clear evidence of n 1. At very high stresses the curves tend to give values of n - 6, as previously determined in other investigations. Curve R2 for the high-purity lead in polycrystalline form at room tenlperature almost merges with B, and thus gives new significance to the values for stresses of 150 and 200 psi; previously'3 these points had seemed to fall away from the curve of slope -3, but they now can be seen as almost completing a transition to n = 1. It should be noted that there was originally considerable apparent scatter in the results for the high-purity lead. However, this was found to be associated with annealing conditions or variations in residual content of oxygen and curve B2 was constructed using the highest rate (i .e., the rate for the purest lead) determined for each stress during the course of various investigations over the years: altogether, some forty tests were used in constructing curve R2.

Jan 1, 1968