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By R. W. Dr. Raymond

(Read at the Philadelphia Meeting, February, 1878.) THE manufacture of ferromanganese in the blast furnace having been the subject of considerable attention in the Institute, I beg to put on record a contribution to the discussion from a quarter hitherto not directly represented, namely, the St. Louis furnaces, near Marseilles in France, belonging to a company of which M. Jordan, a member of the Institute, is Managing Director. These furnaces commenced in 1862 to manufacture specular pig (fontes à facettes) containing from three to six per cent. of manganese. In 1864 the regular production of spiegeleisen (fontes miroitantes), containing seven to ten per cent, of manganese, was inaugurated. At that time the Rhine was the only locality of this manufacture, and the Bessemer works of England and France obtained from Germany all their spiegel. From 1864 to the present time, the St. Louis furnaces have been advancing steadily the percentage of manganese in their product. From ferromanganese of thirty per cent. they had arrived, about two years ago, at a product containing seventy to seventy-five per cent., and for some time past they have been turning out what, as M. Jordan remarks, may fairly be termed fonte de manganese, or manganese pig, instead of iron, since the percentage of iron it contains is not more than 8.5, while the percentage of manganese is 85, or ten times as great. This very high grade material has a peculiar appearance, entirely different from that of ordinary cast iron or spiegel. It is granular, and steely gray in color. The following analyses, communicated to the Société to des Ingenieurs Oivils, by M. Jordan, show the composition of various products of the St. Louis furnaces :

Jan 1, 1878

Edward Keller, Baltimore, Md. (communication to the Secretary*) :—The authors of this paper are to be commended for their industry and congratulated upon the many interesting results which were the fruit of their researches. While thoroughness has marked their work in general, yet on a few points in particular they have touched but lightly, for which reason, it would appear to me, they have hit wide of the mark in their respective conclusions. The work alluded to pertains chiefly to the occurrence of magnetic iron oxide (ferroseferric oxide) in copper-mattes. Because the authors find that the magnetic residue, left by the dissolved sulphides, varies largely in quantity according to the strength of nitric acid used (with potassium chlorate) in dissolving the mattes, they conclude :— "It appears, therefore, that the ferroso-ferric oxide is the result of precipitation by the oxidizing agent, rather than an original constituent of the matte." In this part of their investigation, Messrs. Gibb and Philp have ignored some well-established data,. In the first place, they have overlooked the fact that there are mattes which are strongly magnetic and others which scarcely show any magnetic property. There is nothing in their work tending to explain this variation. They Seem to have tested none of their products for magnetism. Secondly, they have overlooked the fact that magnetic iron oxide probably exists in all ore-charges in the copper-matting furnaces, and, under the given conditions, that this oxide is very difficult to reduce and to combine with silica to form slag. Thirdly, they pay no attention to the varying specific gravity of the several grades of copper-matte, which may exceed, equal, or fall below that of the magnetic oxide. These are .essential points which, I believe, clearly in-

Jan 1, 1906

The Subcommittee on Manganese, of the A.I.M.E. Committee on Industrial Preparedness, prepared under date of Jan. 24, 1924, for and at the request of the War Department, a confidential report on manganese as an element in the problem of national defense. This report was later released and published, in slightly modified form, as a separate pamphlet. After the lapse of eight years, in view of the vital position of manganese in the problem of industrial preparedness agenist a war emergency, the War Department made a request to have the onclusions of 1924 reviewed and brought up to date. To comply wi' this request the manganese subcommittee was reconvened and ex' tive studies were once more made of the entire subject of mang? . A new report, with specific recommendations, was submitted + War Department in February, 1932. This second report, with 4. L specific conclusions and recomrnendations expressed to the War Department omitted, has now been released and is hereby published. Following a rather brief discussion of uses of manganese and classification of manganese ores, requirements and sources are dealt with at some length. Domestic ferro-grade reserves are estimated on the basis of price and are shown by means of a curve where tons of metallic manganese are plotted cumulatively against prices ranging from 50¢ to $1.00 per unit; thereby indicating at a glance the tonnage which the Committee believes would become commercially available at any particular price per unit. Foreign sources of ore are described and foreign prices which the domestic producer must meet are considered. The question of a war-emergency reserve is then analyzed, requirements are balanced against apparent resources, and the principal conclusion that emerges is that a war reserve or stockpile is still vital to national defense.

Jan 1, 1934

By J. E. Pogue

It is the purpose of this paper to attempt to establish three theses which may be stated in advance as follows: 1. The crude oil potential is the accumulation of surplus initial production. 2. The crude oil potential is a semi-inventory and therefore is a causal factor in the price of crude petroleum. 3. The price of crude petroleum no longer correlates with above-ground inventories but does correlate with corrected inventories (i. e., above-ground storage plus the inventory equivalent of the crude oil potential). The factors and principles set forth in this study are thought to yield an approximate answer to a number of questions of active interest in the petroleum industry today, to wit: (a) How long would be required to eliminate the potential if all drilling ceased? (b) What would be the indicated crude oil production of the United States in 1931 if proration were abandoned? (c) What economic change would be necessary to warrant a higher price for crude oil? Definitions For the purposes of this study the following definitions may be stated: The crude oil potential in the United States is the quantity of oil that all the oil wells would make the first 24 hr. if permitted to flow unrestricted. The surplus potential is the above-mentioned quantity minus the volume currently produced. Initial production is the first day's unrestricted flow of an oil well. Aggregate initial production is the sum of the initials of all wells completed during a year. Surplus initial is the initial not needed to bring production into balance with demand. The surplus initial is equal to the crude oil potential minus the current rate of production. The annual production-equivalent of the crude oil potential is the volume of oil that would be produced in one year if all wells were permitted

Jan 1, 1931

By John Blatchford, William T. Hall

The product obtained by roasting stibnite is likely to contain some unoxidized antimony trisulphide and a mixture of antimony trioxide and antimony tetroxide. It was desired to determine, as accurately as possible, the condition of the antimony as well as the total quantity present. Attempts were made to separate the trisulphide and the two oxides by methods based upon their varying solubilities in different solvents, but no satisfactory results were obtained in this way. It was found, however, that by determining the total antimony content, the antimony present as trioxide, and the antimony present as trisulphide, a good idea of the chemical composition of the roasted product could be obtained. The total antimony was determined by dissolving the sample in concentrated hydrochloric acid, reducing the antimony entirely to the trivalent condition by means of hydriodic acid and eventually titrating the antimony back to the pentavalent condition by means of iodine in the presence of sodium bicarbonate1* The details of the procedure are as follows: Weigh out 0.25 gram of the roasted product into a trapped flask (Fig. I), add 4 grams of powdered tartaric acid, 2 grams of potassium iodide and 40 c.c. of concentrated hydrochloric acid. Boil the solution gently f;r 5 min. and then cool to room temperature by shaking the flask while holding it under running water. Then, very carefully discharge the iodine color by the cautious addition of 0.05-normal sodium thiosulphate solution, adding a little starch toward the last. Nearly neutralize the acid with ammonia solution, but leave the solution distinctly acid. Pour the slightly acid solution into 200 c. c. of water containing an excess of sodium bicarbonate and titrate to a permanent blue color with standard 0.1-normal iodine solution.

Jan 1, 1916

By R. W. Brauchli

The author has made a statistical analysis of the relations between recovery and length of cores, diameters of cores and of drill pipe, and cost of coring under different contractual conditions. The data are presented in tabular form. The length of the core appears to play a minor part in the percentage recovered, with a tendency to lower percentages with increased core length; approximately 50 per cent of the length cored is normally recovered if the cores are more than 2 in. in diameter. The diarneter of the core has a more pronounced influence on the recovery; 1 3/8-in. cores average 29.1 per cent, 2 1/8 -in. core 53.4 per cent and 3 1/8-in. cores with 6 5/8-in. drill pipe 68.5 per cent. Where 31/8-in cores were taken with smaller diameter drill pipe, i. e., 4 1/2 - in. drill pipe in 8 1/4-in. hole, the recovery dropped to 49.8 per cent, indicating that the more rigid drill pipe favors good core recovery, a conclusion also borne out by the results obtained in using large drill pipe for smaller diame-ter cores. Surprisingly good recoveries were obtained from both the Johnson and Simpson sands; shale, limestone and dolomite each gave less then average recoveries. No serious fishing jobs resulted from coring operations. Attention is called to the need of a core drill which will make it possible to drill a full-sized hole while coring, and thus reduce the cost of cores. Data pertaining to core drilling should be consistently recorded, such as, diameter of drill pipe and collar, diameter of core, recovery, size of cutter heads, type of core-barrel, coring time, speeds of rotation and of pumps, weight on core-barrel, etc.

Jan 1, 1933

By W. P. Blake

One of the most remarkable iron-ore districts of the world is found in Southern Utah, in Iron County, about 270 miles south of Salt Lake City, and 10 miles west of Cedar City. This region has long been known in a general way; but, being at present somewhat difficult of access, it has been rarely visited by 'any of our members. Professor Newberry has published somewhere a short description. Last year, by the invitation of J. R. Walker, Esq., of Salt Lake City, one of our associate members, I formed one of a party, including Professor G. W. Maynard and W. S. Keyes, to visit and inspect the region. A special car was placed at our disposal by the courtesy of Hon. John Sharp, Superintendent of the Utah Central Railway. From the present southern terminus of the road at Milford, a drive of 55 miles took us to Cedar City, about 10 miles east of the iron region. The ores outcrop in a low range of hills or mountains, and stand out in such bold relief from the general surface, and are so massive and jet black, that they may be seen for miles before they are reached. These outcrops extend in long lines over the hills, and mark very . clearly the course of the beds, conforming generally to the inclosing stratified formations, probably of Palaeozoic age. These rocks are somewhat obscure, but there are large outcrops of limestone without much alteration. This, in places, appears to be the adjoining rock, at others the wall-rocks are porphyry, and at others apparently a quartzite and a fine-grained felsite. The beds of iron-ore are from 10 to 100 feet and more in thick ness, and some of the outcrops extend unbroken continuously for 1000 feet and more. It consists chiefly of magnetite and hematite,

Jan 1, 1886

To the members of the A. I. M. E., who have given much and risked all to fight "Over There" with pick, or gun, or brain, and to the members who have chosen the sometimes more self-denying duty of remaining at home to help produce metals for fighters: Your experience in foreign lands has bred in you that spirit of internationalism which will soon be infused into every corner of our country by virile lads thrilling from a great experience in an old, yet new, land over the seas. To them the East will not seem as far from the West as it was, nor the North from the South. Sectional jealousies will seen despicable to one who has fought for a great ideal shoulder to shoulder with real men of other nations. And they who have willingly sacrificed much on the altar of service will have little patience with an egotist, be he laborer, tradesman, capitalist or engineer. The problems which peace brings to us are more difficult than those of war and their solution requires not only cool heads, tolerance, and wise judgment, but the "getting together" of sections and classes and individuals. The triumph of justice over individualism, represented by the draft law, must be repeated, for there are "slackers" in peace Is well as in war, and the spirit of self-denial expressed in response to Liberty Loans, Red Cross, and Welfare drives and Food Administration appeals must live. We have only just begun to learn how to serve. It is often claimed by our members that the engineer is not given, in the community at large, the recognition which his training should merit; that his reward is not as great nor his service as welcome as it should be. Public service is generally assumed to be a logical activity for a lawyer,

Jan 12, 1918

Doctor David Yang has presented an important new flotation development in the area of fine particle flotation technology; at the same time Dr. Yang presents an explanation for the effectiveness of this improved new fine flotation system in terms of an optimum dispersion state. The same statement is made for the case of carrier flotation (ultraflotation), in the removal of anatase from kaolinite by addition of calcite (selective flocculation of the anatase - calcite system and dispersion of kaolinite). Dr. Yang's data and statements raise some important questions, and I will adress myself to the more fundamental aspects of this new flotation system. The addition of sodium silicate, well known as a good depressant-dispersant agent for siliceous gangue minerals, is proved to be greatly enhanced by the incorporation of polyvalent metal salts into sodium silicate prior to flotation, producing in this manner a condition, as described by Dr. Yang, of optimum dispersion, which in the case of fine-grained oxidized taconite can be described as selective flocculation (coagulation) of hematite and almost complete dispersion of siliceous gangue components. Dr. Yang recognizes that the main mechanism, while not completely understood at this time, seems to operate by modifying the surface characteristics of the gangue slime particles so as to prevent collector from bonding there to, and making the particles strongly hydrophilic so they will become fully dispersed and consequently will not float during froth flotation. At the same time it appears that the conditioning reagent also modified the surface characteristics of the floated minerals (hematite and spodumene in this case) so that they will aggregate and tend to more readily adsorb the collector, resulting in an improved flotation kinetics and selectivity.

Jan 1, 1979

BECAUSE it is necessary that the powders made for casting have a magistery of salt water, I wish now to teach you to prepare the salt that must form this magistery, for without it these powders would not have the toughness to hold themselves together when they are dry. In short, you take the quantity [119v] of salt that you need to prepare and put it in a rough pot, either baked or, if it suits you better, raw but well dried. This is completely covered with a lid or is luted with well- made moulding clay. Then it is encircled with brick ends at a distance of three dita, like a drying furnace. This space is filled with good charcoal; fire is applied and it is left to stand until all the charcoal is consumed by itself* Then you take that quantity of this burned or rather melted salt which you wish to use for moistening the clay and which you think can be dissolved in the water so that it wd remain very salty. It is boiled in a pot with water and then left to stand. After it has settled, your powder is moistened with it and used for moulding. When you see by testing it that the powder stands up as you wish, it is good. If not, give it some more of this water again and continue until you see that it holds enough. For without this magistery it would return to the dryness that it had before as a powder, and you could not use it without fear that it would fall from the Games. In this way this earth, either natural or artificial, is prepared and made ready, and it is used as the need occurs.

Jan 1, 1942

By D. H. Yardley

Diversion of the American Falls of Niagara to permit investigation of ways and means to stabilize the falls while retaining or improving its natrual attractiveness is the geoengineering work that has received greatest public attention this year. The falls are re- treating slowly as rock falls occur while talus de- posits at the base have increased in size. One of the noteworthy questions is whether the talus should be removed-i.e. is it providing support to the base, and so what will happen if it is removed? Certainly the appearance would be improved if the talus were taken away. Geoengineering studies involve mapping of joints, stress measurements, core work and rock sampling and testing, Present work will provide data and interpretation for design of a long term stabilization system, Once basic information is obtained, water will be returned to the normal channel until such time as the detailed design is decided upon. The falls will then be diverted a second time while necessary work is performed. A number of site-environmental studies were carried out for the location of nuclear power plants. These projects involve geology, foundation engineering, hydrology, seismology, meteorlogy, marine geology (in some cases), rock mechanics and occasionally blast monitoring. In one case (investigated by Dames & Moore) the site area was underlain by caverns in limestones at shallow depths but with no surface expression. The geotechnical problems consisted of determining proper spacing of drill holes to locate caverns. Spacing was dependent on the smallest size of cavity that could constitute a support-stability problem for the plant. The finite element method of analysis was used to determine stress conditions around cavities of various size and depths, to assist in determining critical parameters.

Jan 1, 1970

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

Jan 1, 1979

By W. E. C. Coxe

At the meeting of the Institute in Philadelphia, in June, 1876, it was my pleasure to read a paper on the "Manufacture and Endurance of Iron Rails." I then spoke of some trial rails which had been placed in the down track of the Philadelphia and Reading Railroad, over which passed, in addition to merchandise and passengers, most of the heavy coal traffic of that company. One of these rails, made at the Philadelphia and Reading Rolling Mill in 1870, and then placed in the track, was removed in 1876, after having carried about 55,000,000 gross tons, and was on exhibition at the Centennial Exhibition. A piece of this worn rail, twisted cold, was also shown there. One of the same series of rails was allowed to remain in the track until 1878, and short sections of this rail, as well as one not worn, to show its original shape, are presented for your inspection. A comparison of the two will show that the top of the head or tread has morn down 3/16ths of an inch during its nine years of service. It carried in that time 67,000,000 gross tons of freight, passengers, cars, and engines. This rail was made in the usual way of manufacturing iron rails at the Philadelphia and Reading Rolling Mill. The head was made from puddled iron bars, piled, heated, and rolled into bars, 41/2 and 3 inches wide by 1 inch thick, these bars, breaking joints, were made into a pile in section 9 inches square, heated and rolled into slabs 9 inches wide and 2 inches thick; the balance of the rail-pile was made of 41/2 and 3-inch bars, rolled from two-thirds old rails and one-third puddled iron, the

Jan 1, 1880

By L. Dudley Stamp

On April 1, 1937, Burma, formerly a province of the Indian Empire, was formally separated from India and became an independent unit of the British Commonwealth. In future, therefore, statistics of oil production in India will exclude Burma and those for Burma will be separately published. The last few years have been marked by noteworthy, almost spectacular, developments in the oil fields of Burma and the Punjab. In Burma these developments have been the proving of unexpected extensions of the existing fields and not the discovery of entirely new fields. The new extensions are important not only to Burma in giving a new lease of life to her fields, but also in general as stressing some interesting geological aspects hitherto neglected. Production The production of crude oil in Imperial gallons has been: Burma India 1934 254,760,070 67,265,210 1935 251,338,974 . 71,323,362 1936 265,656,393 69,241,504 1937 (eat.) 270,000,000 70,000,000 The Chindwin Fields.—The small field at Indaw continues to produce steadily about 3,000,000 gal. a year, but no really deep test has yet been successfully carried out and resources are thus not yet fully known. The remote location of the field, inaccessible except by river and situated 22 miles from the Chindwin 270 miles up that river from its junction with the Irrawaddy, has not encouraged active exploitation. The field is worked exclusively by the Indo-Burma Petroleum Co., Ltd. (I.B.P.), using now an automatic gas-lift system, and the company formerly refined the oil at a small refinery at Pantha on the river near by. The chief market was for kerosene in upper Burma. The refinery has now been closed. The oil is stored on the field during the low-water season

Jan 1, 1938

A GREAT labor, surely, is that of the coppersmith, since his every work must be hewn from the mass of copper by force of the hammer. At the beginning, middle, and, end all his works are inconvenient pieces and unpleasant to handle. If the work is done on the forge with the fire, it is done in order to refine or compose it into masses again, for drawing these out while hot with the blows of some heavy hammer, or in order to put the works in a condition that allows them to be drawn out while cold and worked. In this he puts all his labor and industry. He who works at this art often makes use of large hammers, sometimes of small ones, and sometimes of those that have a long iron head and a short handle. With these he is obliged ever to proceed in one of these activities, either extending the work lengthwise, narrowing it, or widening it. This is achieved by the manner and direction of striking and therefore it is sometimes hammered on the inside, sometimes on the outside, sometimes with the peen, and sometimes with the flat head. For instance, when he wishes to close it up he strikes it on the outside with the peen, and if he wishes to widen it he strikes it on the inside with either the flat head or the peen. In this way he proceeds to shape it with constant patience, and to make all the vessels that he works graceful. This metal, as I have told you, is soft, flexible, and tenacious under the hammer. It yields with a certain toughness, provided, however, that it is fine and without admixture of a trace of tin or other metal. That craftsman is a good master of this art who best makes every desired work

Jan 1, 1942

By Persifor Frazer

It was my intention to have directed the attention of the members of the Institute to a complete series of rocks representing the older and middle formations represented in Pennsylvania, but time has been insufficient for the purpose, and 1 have been unable, in the first attempts to reduce the sections of those rocks, which I have brought with me to this meeting, to the requisite thinness necessary for exhibiting the peculiarities of their constituent minerals. The rocks represented here belong to the various horizons already mentioned, and include gneiss, ferruginous gneiss, chlorite slate, quartzites, and hydro-mica slates, limestones, dolomites, ferruginous conglomerates, quartz conglomerates, " Potomac marble" (nether member of the Mesozoic series), dolerites, and a syenite. The order in which these are named is, roughly, the order .of geographical position in a section line from southeast to northwest, commencing at the intersection of the Northern Central Railroad with the Maryland line, and ending a few miles from the town of York, and a short distance within the marginal outcrop of Mesozoic red sandstone. In such a geographical section all the rocks above mentioned would be encountered in the given order except syenite, about which a few words are to be said in a moment. (But this is far from representing the rocks in their geological sequence.) There is nothing of unusual interest to present to your notice in these slates and quarteites. The limestones were carefully searched tinder 450 diameters microscopic power, but they show no signs of organic remaius. One section of a fine-grained Triassic sandstone contains a very beau- . tifully banded plate of quartz. But the objects of greatest interest at present are the specimens of trap. The more fine-grained and compact traps were collected from

By C. P. Watson

It is perhaps significant that a few years ago the sessions held here were chiefly occupied with production. In the last two years these sessions have been concerned with production curtailment, unitization and conservation, notwithstanding that production in the United States in 1929 reached a total in excess of 1,000,000,000 barrels. A study of the leading producing units in the United States shows that Oklahoma, Texas and California in 1929 yielded 84 per cent. of the total production from 33.5 per cent. of the total number of producing wells. Production in the United States in 1929 showed an increase of 107,000,000 bbl. over the 1928 figures. This increase in itself perhaps is not enough to have caused the serious situation that is now confronting the industry. However, taking into account the gradual encroachment on the consumption of fuel oil through the greater utilization of natural gas, probably we have reached the point in the United States where prices will determine to a large extent,' in 1930, the amount that will be produced. In the states of Texas, Oklahoma and California, the most significant developmcnt of 1929 has been the desire of operators to reach some agreement to bring production more or less in control with the estimated demand. In November, production in California, particularly in the Santa Fe Springs field, was drastically cut to meet a certain requirement. Similarly, in Texas, the Yates field has been developed and has been producing under an agreement on the part of the operators; and more recently in Oklahoma City, serious efforts have been made to keep produetion in line with consumption. For the year 1930 we can see nothing in sight except drastic curtailment. This is a matter that I am sure is occupying the attention of all the leaders of the industry.

Jan 1, 1930

By J. E. Warren

To clarify the specific questions raised by J. E. Warren's discussion, the following remarks are offered. 1. It is correct that stratification is assumed in the application of the statistical zonation technique, but this does not constitute a limitation. If, in fact, the reservoir is not stratified the zonation technique will show it. The reservoir is then considered as one zone with a particular distribution of permeabilities. 2. The statistical zonation technique was intended as wells may not be an adequate measure of the lateral permeability changes; e.g., if the data presented in Table A-4 of the subject paper are evaluated on the basis of two crossed classifications with interaction, the variation between zones is significant with a probability greater than .99; however, the variation betwen wells is also significant with a probability greater than .87. It is apparent that the technique suggested by the author can be generalized to provide a powerful method for describing petroleum reservoirs. This generalization can be achieved by treating the core data as a two-way classification to determine the between-zones and the between-wells variations; then, the build-up permeabilities can be analyzed, perhaps on at least-squares basis, to establish the probable distribution of the permeabilities within the zones associated with the individual wells. an additional tool for the reservoir engineer to use together with other techniques and all available information. If pressure build-up permeabilities are available, they should certainly be included. Pressure build-up tests were not available for the reservoir considered in the paper. 3. The proposed correlation of zones between adjacent wells was the best of the techniques that I examined. It is not so much a "measure" as an indication of lateral permeability changes, regardless of whether they are seemingly random or form an obvious trend.

By R. F. Mehl, C. S. Barrett, A. H. Geisler

THE mechanism by which the super-saturated solid solution of 20 per cent silver in aluminum decomposes has been reported in two previous publications. 1,2 The analysis of streaks in Laue photograms showed that thin platelike particles (the so-called Guinier-Preston aggregates) form upon {111} matrix planes in the early state of decomposition.1 The size of these particles is larger, the higher the temperature at which they form in accordance with nucleation theory;3 at all temperatures they increase in size with aging.2 When they have grown thick enough to afford three-dimensional diffraction, powder X-ray photograms show that the structure is not that of the equilibrium precipitate y but that of a transition lattice ?'. Since this is also platelike in shape and also lies upon the {111} matrix planes with the {110} direction in the matrix parallel to the {11.0} direction in ?', it seems likely that the original platelet particles are merely ?' in an early stage of formation, and thus finely dispersed. The atomic spacing and pattern on the {00.0} plane in ?' are identical with those on the {111} matrix plane to which it lies parallel, and since comparable directions in the two planes are parallel, the lattices are thus coherent at the interface; an analogous coherence has been found in aluminum-copper alloys.3 The structures ?' and y are both close-packed hexagonal and are oriented alike; they differ only in interatomic distances. Consequently, ? ' is regarded as y strained from its ordinary dimensions by the lattice coherency between it and the matrix.2 The lattice movements that transform the matrix to the equilibrium precipitate appear to be very simple.2 The mechanism of precipitation in this system is simpler and is more precisely known than that in any other system,2,4 hence the system should be a profitable one for the difficult task of correlating property changes with structural alterations. The present report provides additional studies on powder X-ray diffraction from alloys of 10 per cent, 20 per cent and 30 per cent Ag, and presents the correlation of crystallographic changes with changes in microstructure, Brinell hardness and electrical resistivity of the three alloys. PREPARATION OF SAMPLES AND EXPERIMENTAL PROCEDURE The preparation of the 20.2 per cent Ag alloy has been described.2 Alloys containing 9.9 and 29.7 per cent Ag were prepared from 99.97 per cent Al and 99.99+ per cent Ag using a similar procedure. Rolled

Jan 1, 1943

By R. J. Arsenault

The yield drop that occurs in tantalum, Cu-AZ. and Ag-Al was investigated as a function of strain rate and at several temperatures. From the strain-rate dependence of the yield drop an activation volume was calculated and found to agree with that obtained from differential strain-mte tests. The temperature dependence of the yield drop can he explained in terms of the parameter temperature divided by activation volume. The yield drop is attributed to the rapid multiplication of dislocations during their motion. THE yield-point or yield-drop (upper yield stress minus the lower yield stress) phenomenon has been the subject of numerous investigations1-9 in both bcc and fcc metals. Also, there is no dearth of theoretical explanations10-20 to account for the yield-point phenomenon. The present explanations can be divided into two categories: the concept of dislocation locking and subsequent unlocking and the concept of multiplication of dislocations due to their motion. The Vottrell10,11mechanism of locking and unlocking, as applied to bcc metals, is the best known of the three proposed locking mechanisms. The two additional mechanisms, short-range order (SRO)7,16,17 and Suzuki-type locking,14,15 have been employed to account for the existence of yield points in fcc metals. The experimental evidence supporting the locking of dislocations, especially in bcc metals, is well-established. The dependence of the yield point on interstitial concentrations,' the kinetics of strain aging,2 and the observations by electron-transmission microscopy18 are some of these experimental results. The number of experimental observations supporting dislocation locking in fcc metals is not as extensive as in bcc metals. The unlocking of dislocations, which actually is supposed to account for the yield drop, is by no means well-established by experimental results for either bcc or fcc metals. The similar temperature dependence6 of the yielding and plastic flow is one of the experimental factors that cannot be explained in terms of the unlocking of dislocations. The mechanism based on the rapid multiplication of dislocations has been proposed by several investigators. 18-20 Johnston and Gilman19 have proposed a detailed model of yielding, which was later employed by Hahn21 to predict quantitatively the yield drop in iron. This mechanism was discussed in a previous paper22 and several limitations were pointed out. In the same paper it was shown that an activation volume could be obtained from the strain-rate dependence of the yield drop and that a correlation existed between the activation volumes obtained from the yield-drop tests and from differen-

Jan 1, 1964