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By G. W. Healy, W. Craft, D. C. Hilty

By means of a theoretical extension of the Cr-C temperature relation in molten chromium steels to low chromium contents and by a correlation of the ratios of chromium to iron in the slag and metal, a method has been developed for estimating the amount of metallic oxidation during the oxidizing period of a chromium steel heat. Application of this method has indicated that due to temperature limitations metallic oxidation may be excessive for very low carbon steels charged with more than a small amount of chromium. IN the melting and refining of chromium steels the oxidation of carbon to a low level is accompanied by the oxidation of chromium and iron in considerable amounts. For the subsequent recovery of chromium and associated iron from the slag, the amounts of metal oxidized must be known for efficient reduction and control of composition. Further, in order to arrive at an accurate understanding of the process, so that chromium-bearing scrap can be used effectively, information is required on the relation between composition of the charge and weight of metal oxidized to reach the desired carbon content. Crafts and Rassbach1 recently developed an empirical relation between chromium, iron, and manganese oxidized per ton of steel charged, and final carbon content and temperature. This relation did not show any dependence on amount of chromium charged. However, it was felt that such a dependence might be present, so a further analysis of the data was undertaken. Cr-C Relation at Low Chromium Levels Crafts and Rassbach's results were based on temperatures estimated from the Cr-C relation previously established experimentally by Hilty,2 and on a single temperature observation (immersion thermocouple) on a heat made at low temperature from a charge of carbon steel scrap containing only a small amount of residual chromium. The temperatures estimated from the Cr-C relation were for heats charged with chromium-bearing scrap and which contained substantial amounts of chromium (2 to 10 pct) at the end of the oxidizing period. No data, other than that from the low temperature heat just mentioned, were available for the low and intermediate chromium ranges. In order to extend the range in which temperature may be estimated, the Cr-C relation requires further consideration. The Cr-C relation, expressed as suggests that carbon is zero at zero chromium in the bath. This is obviously absurd, because as chromium approaches zero the carbon content must approach the limit established by the Fe-C-O equilibrium. It is evident, therefore, that the Cr-C relation as defined by Eq. 1 is not valid below some minimum chromium content that may vary with temperature. On the other hand, it is probable that any such limiting chromium content is less than 4 pct at 3200°F, since the experimental data from which the Cr-C relation was derived included several observations at that level with no deviation. In any event, it is apparent that further evaluation of the results presented by Crafts and Rassbach is dependent upon a means for estimating the Cr-C temperature relation in the low chromium region. From the observations of Chen and Chipman9 and thermodynamic data given in Basic Open Hearth Steelmaking,4 the following relation can be calculated for melts containing small amounts of chromium and carbon assuming a carbon monoxide pressure of 1 atm: % Cr -21,250 K' = (%C)2; logK1 == —t— +13.88 [2] Moreover, by plotting Eq. 2 for any given temperature on cartesian coordinates, it can be extrapolated graphically to the limiting carbon content at zero chromium for the specified temperature without serious complications. By means of Eq. 2 and its extrapolation, the Cr-C temperature relations originally established experi-

Jan 1, 1954

By R. Floyd Farris

A method is presented for determining minimum waiting-on-cement time, which takes into account the differences that exist between types and brands of cements and such individual well conditions as depth, temperature, and pressure. The basis for the method was determined by laboratory tests. Being a laboratory development, several steps were required to prove its merit. The first step consisted of laboratory tests designed to determine the minimum cement strength required in wells. Basis was found for setting a minimum value of 8 Ib. per sq. in. tensile strength. Next, it was shown by laboratory tests that the time to 8 Ib. per sq. in. tensile strength may be expressed as a function of consistometer stirring time to loo "poises," the approximate relation being "the time to 8 Ib. per sq. in. tensile strength equals the time to I00 'poises' times three." Next, it was shown that the time of maximum temperature development in cement slurries, due to heat of hydration, is also related to consistometer stirring time to loo poises, but only by a factor of approximately two. It was shown also that the shut-in casing pressure will build up after cement is placed and register a maximum pressure at approximately the same time the slurry down the hole attains maximum temperature. From this and the relationships listed above, the general rule was established that minimum waiting-on-cement time (time to 8 Ib. per sq. in.) after casing cement jobs in any well is equal to the time when the shut-in casing pressure reaches a maximum, as measured from the initial mixing of cement, times a factor of 1.5. Cement plugs drilled in the field at the time prescribed by this formula were found to drill "firm to hard," thus confirming the laboratory tests. These tests prove that many of the present regulations for waiting on cement require a longer time than is absolutely necessary. Use of the method herein proposed offers the possibility of a saving of $1200 per well. Introduction The length of time allowed for cement to set after casing is determined either by state-wide rules, field rules, or self-imposed rules written into drilling contracts. In general, the time is dictated by experience and common practice. However, owing to differences in opinion and in experience of the various groups involved, waiting-on-cement time often varies from one area to the next. For example, an operator in an area where no rules exist may drill out of surface pipe at 24 to 36 hr., while another operator in another area may wait 48 hr. or more to comply with state or field rules, although the depth of the well, hole size, type of cement, and other data are identical. An even greater difference in practices will be found by making similar comparisons with respect to oil-string cement jobs. Differences in waiting-on-cement times of 36 to 48 hr. are common. Further complicating the picture is the rather common practice of allowing more waiting time for cement to set at the greater depths than is allowed at the shallow depths. This practice has existed for years in spite of the common knowl-edge1,2,3 that the temperature of the earth at the usual setting depths of surface

Jan 1, 1946

By Charles Y. Clayton

The shank, to give good service, should not upset nor should it cause excessive wear on the various parts of the machine. To fulfill these requirements, the steel must have a certain hardness—that is, resistance to deformation. The hardness is expressed in conventional terms, as Brinell or scleroscope number. Before deciding on the hardness that is proper, several factors should be considered; the most important are: type of drill steel used (whether hollow or solid), length of steel, nature of ground, air pressure, and hardness of hammer or anvil block (usually 600 Brinell). These are not all, but they are the most cogent ones. Without doubt, it would be better to use a shank that is too soft than one that is too hard. Most satisfactory service will be obtained from shanks that are just hard enough to resist any tendency to upset. To express the proper hardness in terms of Brinell numbers would mean a great many tests over a long period of time, or a study of drill steels that are being used successfully in the various districts. To obtain some information along this line, the persons making this investigation requested, a number of companies to send to them drill shanks that had been given the usual treatment at that mine. The results of the hardness tests are given in Table 1. The hardness values given in Table 2 are those of shanks known to have been quenched in water and drawn. These results show that where water quenching and drawing are in vogue the hardness is rarely under 400 Brinell.

Jan 1, 1923

By G. R. Fitterer

NONMETALLIC inclusions in steel have received much attention by metallurgists during the past few years. Many investigators have been emphatic in stating their belief that these impurities are the chief causes of steel failures, while others think that their effects are negligible. One of the main reasons that definite information on the effects of these impurities is lacking is that no reliable method has been developed for the exact determination of the amounts of these different impurities in steel. Some valuable new information has been brought out by a reliable method for nonmetallic inclusions which has been developed at the Pittsburgh Experiment Station of the U. S. Bureau of Mines, in cooperation with the Carnegie Institute of Technology and the Metallurgical Advisory Board. This procedure satisfactorily extracts some of the more common inclusions from steels, thus enabling the investigator to correlate steel failures with inclusion content. Although the data given herein are the first to be published on the subject of the electrolytic extraction method, the interest in the subject is evidenced by the fact that it is already being used by some 20 to 30 steel companies for their various purposes. Some of the comments received from these laboratories indicate that the method is highly satisfactory: the unfavorable comments, when traced to their sources, have been found to be based on some small mistake made in either installation or operation. The chief discrepancy seems to have occurred in attempts to apply the method to the extraction of inclusions from alloy steels. The procedure can be used only for the plain carbon steels and for such low alloy steels as those containing the usual amount of copper (0.2 to 0.3 per cent). Steels containing the carbide-forming alloys such as chromium, tungsten, etc., present far too many difficulties for the accurate determination of inclusions. Luckily, the iron and manganese carbides do not offer any difficulties and no contamination of the oxide-sulfide residue results. It is highly probable that some modification of the following

Jan 1, 1931

By C. M. Wayman, J. F. Breedis

The crystallography of the martensitic transformation in the Fe-30 Ni alloy was reinvestigated. The scatter in the habit Plane as determined from measurements on the mid-rib plane was smaller than reported previously, and the orientation relationship was determined from a martensite plate having known direction cosines. From agreement with crystallographic theory and from observations of the morphnlogy of the martensite plates, it is suggested that the mid-rib plane represents the starting region of the transformation. THE crystallography of the martensitic transformation in the iron-nickel system has been the subject of many investigations.&apos;-7 However, for iron alloys containing approximately 30 wt pct Ni, a wide scatter in the reported habit planes exists. In only one instance has a Laue determination of the orientation relationship been made, but the habit plane of the martensite plate studied was not determined experimentally. Because the most successful thermodynamic and kinetic analyses8 of the martensite transformation have been based on Fe-30 Ni alloys, it was considered desirable to reinvestigate the crystallographic features of the transformation in this alloy. Lieberman9 suggested that the most significant information for use in a theoretical treatment involves the determination of all the crystallographic observables from a single plate of the product phase. This was first done in essence by Greninger and Troiano10 for Fe-22 wt pct Ni-0.8 wt pct C, and is the method followed in this investigation. Some theoretical approaches11-13 in describing the martensitic transformation consider the overall transformation distortion to be comprised of a Bain distortion, or lattice deformation (PI, which produces the structure change, and a lattice invariant deformation (G), such as twinning, which together leave the interface or habit plane un-distorted. The incorporation of a rigid body rotation (R) results in a transformation distortion (E) such that the interface plane is left both undistorted and unrotated. In matrix notation, E = RPG where the lattice invariant deformation has "taken place" in the austenite. Bowles and Mackenzie14-16 in formulating a theoretical approach proposed an adjustable scaler quantity, denoted as 6, which represents a uniform dilation in the interface plane. This dilation acts to adjust the lattice spacings of the parent and product structures at the plane of contact. Using the dilation parameter as a variable, these authors were able to account for a continuous variation of habit planes in steels along a curve in the stereogram between {225}A and {259}A. she invariant line strain14 of the transformation is 6 RP, and the corresponding transformation distortion is E/6.) With the dilation parameter known, the invariant line is computed as the triple coincidence of the habit plane, the shear plane of the lattice invariant deformation, and the initial Bain cone.14 The contraction axis for the Bain distortion can be taken9&apos;17 as [010]A, and the correct permutation of the habit plane indices used. Kelly and Nutting 18 have established the shear plane (of twinning) in the tetragonal martensite of Fe-22 Ni-0.8C to be {112)M by means of transmission electron microscopy. The reasonable shear system is then {112}M which is equivalent to {011}A <01l>A. The as-

Jan 1, 1962

By F. Keller, R. H. Brown

Because of the extensive use of Alclad 24s alloy sheet in aircraft construction, there is much interest in the metallurgical changes caused by heat-treatment of this product.1, 2 One of these changes is the result of the diffusion of soluble elements from the core into the coating during treatment. This paper deals with the thermal treatments that may influence diffusion and with the practical effects of diffusion on the serviceability of the product. As is well known, Alclad 24s-T sheet has a core of high-strength alloy combined with surface layers of relatively pure aluminum. The microstructure of a cross section of this product is shown by Fig. I. Not only does the relatively high-purity coating have a high resistance to corrosion, and hence serves as a mechanical barrier between the core metal and the corroding environment, but in addition this coating exerts electrochemical protection over areas where the core may be exposed, such as cut edges. In addition, the coating affords electrochemical protection to projecting heads of A17s-T, 17s-T and 24s-T rivets, or attached members made from these alloys. Under some conditions of heat-treatment, however, diffusion of copper into the coating will alter the electrochemical relationship between the coating and the core to the extent that only partial protection will be obtained under some corrosive conditions. The reason for the electrochemical protection lies in the fact that the coating layers of pure aluminum are anodic to the alloy core. The addition of copper to aluminum produces alloys in which the potential is lower than that of the pure metal. Moreover, as the amount of copper in solid solution in 24s alloy is increased, the potential of the alloy becomes more cathodic. When heat-treated at 920°F. and quenched in cold water, 24s-T is about 0.16 volt cathodic to pure aluminum. However, copper will diffuse from the core into the coating, and if it reaches the surface the potential will be altered in a cathodic direction. Thus the potential difference between the core and coating may be less than 0.16 volt, depending uponIthe thickness of the coating, and the time and temperature of heat-treatment. Of the methods available for determining the extent of diffusion of copper from the core into the coating of Alclad 24s-T, two are generally used; namely, the metallo-graphic and the solution potential methods.3 Metallographic Methods Metallographic methods will reveal the progress of diffusion of copper into the coating. For instance, the diffusion zone in the coating intermediate between the coating surface and the core is shown in Fig. I. This photomicrograph is of a polished and etched cross section of 0.040-in. Alclad 24s-T sheet. Diffusion proceeds into the coating more rapidly along the grain boundaries than through the body of the grains. Consequently, the diffusion zone is not of uniform width

Jan 1, 1944

By A. A. Burr, D. G. Ebeling

The effects of casting texture, grain orientation and grain size upon the performance of Alnico permanent magnets is described. Single-crystal specimens were produced by special sintering and grain coarsening techniques to study the effect of crystal orientation. In addition to texture and orientation effects, an analysis of the results indicates that the permanent magnet performance is impaired by a refinement of the grain size. AN excellent historical review of the development of Alnico permanent magnets has been prepared by Bozorth.1 The desirable permanent magnet characteristics of Fe-Ni-A1 alloys were discovered in 1932 by Mishima.2,3 The work of Ruder&apos; showed that the alloys were age-hardenable, and Betteridge5 defined the best composition and heat treatment for the magnetically isotropic alloy known as "Alnico 3." Horsburgh and Tetley0 increased the energy product by the addition of cobalt and copper, "Alnico 2," and Oliver and Sheddon7 demonstrated that cooling in a magnetic field improved the residual induction of this alloy. Jonas8,9 then disclosed the great practical benefits of heat treating an alloy of higher cobalt content in a magnetic field and the resulting alloy, "Alnico 5," has become the standard of the industry. This paper describes the fundamental aspects of a procedure which can be used to further improve the properties of these anisotropic permanent magnet alloys. A study of the casting techniques used in the production of anisotropic Alnico permanent magnets indicated that the magnetic quality was affected by the as-cast macrostructure. Improved performance was observed in magnets containing a high percentage of columnar grains whose long axes were parallel to the magnetic axis of the casting. McCaig10 studied the effect of such columnar grain structures upon the magnetostriction characteristics of similar alloys, however no data was presented showing the effects on other magnetic properties. The following paragraphs describe two experiments which were conducted to determine the effect of various grain orientations upon the energy product. Special composite molds were prepared of highly conductive and highly refractive components to remove the heat of solidification from the casting in a controlled manner. Representative macrostructures produced by these techniques are shown in Fig. 1, along with the relative volumes of favorably oriented columnar grains. The alloy, Alnico 5, has the highest permanent magnet performance of any commercial magnet material. It has the nominal weight composition of 8 pct Al, 14 pct Ni, 24 pct Co, 3 pct Cu, and 51 pct Fe. A heat of this material was cast into molds producing the type A and B grain structures shown in Fig. 1 and pairs of the resulting magnets were placed in heat-treating boats so as to eliminate any biasing effects of boat position. After a standard heat treatment the type A magnets, with 16 pct of the volume composed of favorably aligned grains, had a maximum energy value of 3,940,000 gauss-oersteds, while the type B magnets with 73 pct aligned grains averaged 5,090,000. This large im-

Jan 1, 1954

By T. J. Woods

This paper deals with the origin, definition and prevention of scabs on semifinished rolled-steel product. Mold coatings, which are considered essential in scab prevention, were found to be effective only in relation to the ingot surface of semikilled and killed steels and not necessary for the rolled product. That is to say, the scabs on ingots caused by having been cast in uncoated molds are eliminated in the soaking and rolling operations, therefore are not present on the rolled product. This fact, which is contrary to the average opinion, was established after extensive and thorough experiments had proved the ordinary conception of the origin of scabs to be incorrect. This subject may be of little or no concern to steel plants producing small ingots for the manufacture of small billets and bars, except as it may be of interest in showing why their surface troubles with scabs do not exist on the product of heats with normal pouring practice. But to the producer of large ingots to be rolled into slabs for large plates used in shipbuilding, it is a very important subject. Definition of a Scab The generally accepted opinion is that the individual scabs present on rolled products (as shown by Fig. I) are considered to have been individual splashes on the ingot surface. This opinion was found to be incorrect. Experiments showed that there were no individual scabs on the product that had appeared as individuals on the ingot surface. The single scabs seen are either pieces of a shell that is present near the bottom of all top-cast ingots, or a veneer that may be present on any part of an ingot improperly poured, as when the stream strikes the mold wall. This definition is based on a detailed study of scabs and their characteristics in which the following have been found true: Location.—On the product of heats poured without trouble, scabs, if present, are always on the product that corresponds to the bottom end of the ingot, and usually occur in clusters. This is true whether molds are coated or not. Shape.—There is no regularity as to shape, size or thickness. It is sometimes possible to separate a few pieces and place them together, like pieces of a jigsaw puzzle, indicating that at one time they had been united as one piece. If individual splashes were the origin of scabs, the foregoing would not be true. Instead, the splashes, which occur throughout the pouring of the ingots, would be present uniformly over the entire product and there would be considerable similarity in the shape and thickness of the scabs. Experimental Work Our experimental work was conducted on 200-ton heats of semikilled plate steel tapped into an oval ladle 15 ft. high. All ingots were top-cast direct into 24 by 54 by 82-in. molds, straight-sided, set on flat stools. Two separate studies were made about one year apart, each study extending

Jan 1, 1943

By Gregoire Gutzeit

THE development reported in this paper was begun by the author a number of years ago, while he was a lecturer on complex chemistry and metallurgy at the University of Geneva, Switzerland, and in charge of that institution&apos;s research laboratory. Completion of the development and reduction to practice did not occur until last year at the Westport mill, laboratories and testing plant of the Dorr Company, where this method is now in general use for identifying and localizing the mineral constituents of both metallic and nonmetallic ores. It has proved to be a practical tool of the metallurgical staff at the Westport mill, devising unusual milling flowsheets for complex and refractory ore bodies. In a number of instances the findings have been successfully used as fundamental factors in the design and specification of complete metallurgical plants. Seven examples of the use of this method in solving practical milling problems are included in this paper. GENERAL OUTLINE The microscopic study of an ore, at first only of scientific interest, has proved extremely useful both in practical geology and in ore dressing. The binocular magnifying lenses for rough observation of the products of an ore-dressing plant have been in use for a long time; but only within the last few years has a systematic microscopical examination of ore samples become a normal tool of any research laboratory dealing with ore-dressing problems. Such an investigation avoids considerable loss of time as well as empirical trials and useless experimentation. It will generally indicate the correct grinding and often will suggest the proper method of treatment. The petrographic determination of transparent minerals in thin sections, or even in grains, has been perfected, and very accurate methods have been devised to meet any requirement, such as Feodorof&apos;s rotating stage on the petrographic microscope. Almost all transparent minerals can be positively identified by their optical properties; i.e., isotropism, anisotropism, color, pleochroism, refractory index, cleavage, crystal form, birefringence, and others. The identification of opaque minerals is a much more difficult problem and can be done only by using polished specimens. Unfortunately, most of the valuable metallic ores, and even some of the nonmetallic ones, are not transparent; therefore it has been necessary to develop a special technique for the determination of these minerals. Some optical properties-for instance, isotropism, anisotropism, color, cleavage, reflecting power-are often adequate in roughly classifying the mineral. Only "reflecting power" is a measurable value, provided special photometric equipment (ocular photometer or Orcel&apos;s photoelectric cell) is available. The other optical properties mentioned are more or less relative,

Jan 1, 1942

By M. Safiuddin

Within the mining industry, open-pit mining has progressed to a point where a 200-yard walking dragline is as conceivable today as a 35-yard dragline was just a few years ago. This is possible due to the technological advances and efforts of the excavator manufacturers, and the manufacturers of electrical equipment have always stayed abreast with them in meeting their requirements and in making available their experience with the latest control techniques and hardware from various fields for application in the mining industry. An electrician in the coal mines of Pennsylvania who had not heard the word "thyristor" a few years ago now wonders how the old excavators with Rototrols® and magamps could ever work. The thyristors, transistors and operational amplifiers which were considered too fragile and delicate for a rugged and severe application like the mining industry, today constitute the brain of an excavator control taking commands from the operator and giving signals to the muscles of the excavator to move the bucket within a few seconds. A giant 200-yd bucket filled with overburden moves within seconds of the operator&apos;s command. Digging cycles for these excavators range from 40 to 60 sec depending on the swing angle. With these tremendous production capabilities of the excavators, the equipment failures and downtime become very expensive, and the loss of return on large capital investment for such machines becomes intolerable. Even though these failures and downtimes cannot be avoided completely, a good preventive maintenance program can help reduce them, thus increasing the machine availability. As we shall see below, the causes for breakdowns and failures of electrical equipment can be analyzed and a good preventive maintenance program can be drawn up to eliminate most of these failures.

Jan 9, 1967

MINING AND METALLURGICAL SOCIETY OF AMERICA San Francisco Section The San Francisco Section of the Mining and Metallurgical Society of America held a joint meeting with the local section of the American Institute of Mining Engineers at the Engineers&apos; Club, San Francisco, on Tuesday, Apr. 16, 1918. The meeting was preceded by a dinner. Letters from the parent body in NewYork asking for the consideration of the proposed bill before Congress, and an expression of opinion relative to the appointment of a Federal Administrator of Mines justified the joint meeting of the local sections of the two mining societies, in that a more representative opinion of the engineers of California could he obtained. The meeting was called to order at 7:15 P.M. by Mr. Frank H. Probert acting as Chairman. About thirty engineers were present. Mr. Probert read a letter of March 14, from Secretary Huntoon, asking that the meeting be called. He read excerpts from Bulletin 117 of February 28, 1918, of the Mining and Metallurgical Society containing a copy of the proposed bill, so that all present might be advised of its essential contents. He briefly commented on the urgent need of such legislation and invited discussion of the subject. After long and thorough discussion on the part of the members present, Professor Lawson made the following motion: I move that a resolution expressing the sense of the joint meeting of the local sections of the American Institute of Mining Engineers and Mining and Metallurgical Society of America be forwarded to the secretaries of the two societies to the effect that we heartily approve of the purpose and intention of the bill designed to promote and stimulate the production of minerals necessary for the successful prosecution of the war; and that we suggest prices should be fixed for the period of the war and two years thereafter, and that these prices, guaranteed by the Government, should apply at the nearest shipping point to place of production of the minerals. This motion was carried. The meeting then adjourned, and a telegram was sent by Mr. Probert, the Chairman, to Mr. Huntoon, notifying him of the motion that had been carried at the meeting.

Jan 7, 1918

By C. G. Dunn, M. Sharp

IN twinned crystals of the face-centered cubic metals the lattice of one twin is a mirror image of the other in a common twin boundary. When several twins appear within large grain in a sheet specimen, the twin one boundaries form a set of lines at the surface of the specimen which coincide with (111) planes of the large grain. Furthermore, for twins of the same orientation, these lines are parallel. Generally, the presence of identically oriented regions with straight parallel boundaries coinciding with a (111) plane of the surrounding crystal is strong evidence for identifying the island regions as twins of the parent crystal. However, Fig. 1, which shows the macrostructure of a large grain of copper with island regions that satisfy these conditions. is not an illustration of (111) twins. Since the reverse side of the specimen has much the same appearance, it was thought at first that these regions, which appear dark in the macrograph, actually were twins. According to X-ray data, however, these regions are second-order twins of the large crystal. With regard to their formation, these second-order twins formed by secondary recrystallization in a cube texture matrix. Growth occurred in the direction of the arrow (see Fig. 1) as the specimen moved slowly into a gradient temperature furnace as described previously.&apos; Nucleation of the second-order twins occurred, therefore, on the ends facing opposite the arrow. If the origin of the second-order twins were due to repeated twinning, some first-order twin structure should be visible on these ends. This proved to be the case, as very small twins were readily found with the aid of a microscope, and probably could have been seen, in some instances, under ideal lighting conditions without aid of a microscope. Fig. 2 shows a cross-section view taken perpendicular to both the surface and the (111) trace of the parent crystal (visible as a straight boundary in Fig. 1) at the beginning point of growth of a second-order twin and where one first-order twin was relatively thick. In the micrograph, A is the large parent grain; B is the first-order twin of A; and C, which is a first-order twin of B; is a second-order twin of A. Between A and B and between B and C the major straight portions are traces of common (111) twin boundaries. The straight portion of boundary between A and C, however, is not a common crystallographic plane to the two lattices; it is a (111) plane of A and a (115) plane of C. Without considering the mechanism of twinning itself, the origin of the second-order twins may be accounted for in terms of repeated twinning and special growth characteristics. After each nucleation, a selective growth process can be thought of as favoring growth of the first-order twin in local spots only and favoring growth of the second-order twin to an extent comparable with that of the parent grain over relatively large areas in a way similar to that described for twinning in aluminum.&apos; It has already been pointed out that the boundary between the large grain (A) and the second-order twin (C), which is responsible for the straight boundary portions in Fig. 1, involves a (111) plane of A and a (115) plane of C. The same combination of planes is not only possible in first-order twins, but actually appears quite frequently.3 Their prevalence in first-order twins and their presence here in second-order twins, together with the necessary occurrence of a large number of common lattice sites at the boundary, is an indication that this combination produces an "energy cusp"&apos; boundary. (Energy cusp boundaries have been described by Shockley and Read.") The configuration of atoms near a {Ill), (115) boundary in first-order twins is of course different from the configuration near the same type of boundary in second-order twins. References 1 M. Sharp and C. G. Dunn: Secondary Recrystallization Texture in Copper. Journal of Metals (January 1952) Trans. AIME, p. 42. 2W. G. Burgers and W. May: Stimulated Crystals and Twinning in Recrystallized Aluminum. Recueil des travaux chimiques des Pays-Bas (1945) 64, p. 5. aD. Whitwham, M. Mouflard, and P. Lacombe: Discussion of W. C. Ellis and R. G. Treuting, "Atomic Relationships in the Cubic Twinned State." Trans. AIME (1951) 191, p. 1070; Journal of Metals (October 1951). 4 W. Shockley and W. T. Read: Dislocation Models of Crystal Grain Boundaries. Physical Review (1950) 78, p. 275.

Jan 1, 1953

By Merlon C. Flemings, Theodoulos Z. Kattamis

Examination was made of the distribution of tnanganese and nickel in colutrrnar dendrites of a cast low-alloy steel; more limited work was corzducted on chromium. Corresponding "segregrction ratios" were calculnted and shown to be relntivelv insensitive to cooling rate (&apos;&apos;segregation ratio" is defined (Is the ratio of maximum to minimum concentrations within a volume whose dimensions are the order of the dendrite-arm spacing). Isoconcentratiorl curves were determined by the electron micropvobe and by rt7etallografihic studies on specimens subjected to isothermal-transformation treatments. From construction of isoconcentration curves, morphology of columnar dendrites is descvibed as intermediate between Perfect rodlike and sheetlike morphologies. The study is extended to equiaxed dendrites and it is shown that the strcture of these dendrites is sittlilar in many respects to that of columnar dendrites. On the basis of tlze sheetlike morphology of dendrites, a simple model is pvoposed for calculation of honzogenization kinetics. Results of trzatllevlatical analysis brcsed on this utzodel are given. This analysis relates residual segregation to time at homogenization temperature; it is in agreement with experiment. Calculations are given which show that even for relatively rapidly cooled material (of 1-ine dendrite-artn spacing) treatmets at 1200°C or above are necessary to achieve slgxificant Izomogenization of elenlents other than carbon itz reasonable time (e.g., rnangclnese, nickel). Conlplete homogenization of carbon is obtnined at much lowev tenlperatures (below 870°C). IN dendritic solidification of castings and ingots, solute redistribution during freezing results in mi-crosegregation of most alloy elements. The micro-segregation is such that minimum solute concentrations occur at the center of dendrite arms and maximum concentrations occur between dendrite arms. Residual segregation after subsequent therma1 processing (homogenization) depends on maximum and minimum initial concentration, on the detailed geometry of the isoconcentration surfaces within interdendritic regions, on the diffusion coefficient of the solute, and on time of thermal processing. The objective of this work was to determine, for a low-alloy steel, maximum and minimum concentrations, and the geometry of isoconcentration surfaces, primarily in order to permit calculation of homogenization kinetics. Most of the work reported was conducted on Samples from a unidirectionally solidified, fully columnar ingot. This type of ingot is made by extracting heat during solidification from one face; techniques for accomplishing this have been discussed.&apos; Samples were taken at several locations, up to 5.75 in. from the mold chill face; the bulk of the work was performed on samples at 5.75 in. Alloy cast was, nominally, 0.4 pct C, 1.8 pct Ni, 0.8 pct Cr, 0.7 pct Mn, 0.25 pct Mo, 0.3 pct Si, and the balance iron. Brief study was also made on samples from an ingot which solidified with equiaxed grain structure. SAMPLE PREPARATION AND ANALYSIS Samples for electron-microprobe analysis were incorporated in mounts that included pieces of electrolytic nickel, chromium, and manganese, in order to normalize the intensities of these solutes in the specimens; also, a piece of electrolytic iron was included to measure the background. All specimens were polished in the usual metallographic manner. After the microprobe traces were made, the path was revealed by etching the specimens with picral. All microprobe analyses were made by point counting, integrating for 30 sec. The distance between points was fixed from 2 to 10 p, according to the precision desired in each case, the fineness of the structure, and the concentration gradient existing in a given area. (The distance was chosen 2 to 5 p near the maximum-concentration regions and 5 to 10 p near the minimum concentration.) The "take-off" angle for the A.R.L.-Model No. 21000 microprobe employed was 52.5 deg. Samples for metallographic analysis of isoconcentration curves were prepared by austenitizing at 1540°F for 20 min, quenching to the nose of the TTT curves (1200°F), heat treating isothermally at this temperature for a given time 0, and then quenching to room temperature. Due to concentration gradients existing in a dendritic structure, no transformation will take place for a given time 0 of isothermal heat treatment in the regions where the a.lloy concentration is higher than a given limit. Thus, the dendrite appears limited by an isoconcentration curve and can be made to appear to grow by varying the time of isothermal heat treatment.

Jan 1, 1965

By I. J. Hegyi, J. J. Tietjen, H. Nelson, J. I. Pankove

The fabrication of p-n junctions in GaAsl-,P, alloys by a vapor-phase gowth technique has for the first tirne resulted in room-temperature injection lasers capable of operating over a broad range of wavelengths extending into the visible region of the spectrum. The shortest wavelength achieved to date is 6750A at room tetnperature. In addition, at 78°K the threshold current density values for these lasers are generally the lo~vest reported, and the emitted radiation extends to the lozc,est wavelength ever attained (6350A). With lasers fabricated from material containing 14 pct Gap, quanticm efficiencies of 26 pct and peak power outputs of 25 zu were obtained at room temperature. ALTHOUGH room-temperature operation of GaAs injection lasers has been well-documented,&apos;-5 the operation of GaAsl-,P, (x > 0) laser diodes has been restricted to relatively low temperatures.8-&apos;0 This has been previously attributed5, 7, 10-12 partially to the difficulty of preparing single-crystalline GaAsl-& alloys having a high degree of chemical homogeneity and purity. Also, with these materials it has been difficult to prepare high-quality, abrupt p-12 junctions by diffusion techniques; and, in turn, this has made it difficult to obtain optimum electrical properties for room-temperature operationL3 in the resulting laser diodes. As a result, GaAsl-,P, laser diodes have not been efficient enough to permit operation at room temperature. For example, using diffused structures, only a few diodes were obtained which could be operated even close to room temperature (255K)." Recently, a vapor-phase growth method of preparing epitaxial deposits of GaAsl - .P, alloys has been described,14 and the high-purity and homogeneity of these materials has been previously demonstrated. Of special significance, with this technique, n- or p -type doping can be initiated or discontinued at any time and at almost any rate during the crystal growth so that the donor and the acceptor concentrations can be easily controlled to obtain desired impurity profiles. This permits high-quality, abrupt p-TZ junctions to be vapor-phase grown entirely during the crystal growth process, so that diffusion or other p-n junction fabrication processes are unnecessary. After growth, the device does not have to be heated to elevated temperatures, which avoids the possible unwanted introduction and motion of both impurities and lattice defects. Using the vapor-phase growth method cited above, over 300 room-temperature injection lasers have been prepared from GaAsl-,P, alloys having compositions in the range of 0 5 x 5 0.41. These lasers have emitted cohe~ent radiation in the spectral range of 8350 to 6350A at 78°K or from 9000 to 6750A at room temperature. The threshold current densities of the best lasers are independent of the alloy composition over the range 0 < x < 0.2 and compare favorably with values for good GaAs lasers.&apos; MATERIAL PREPARATION Multilayer, epitaxial deposits of GaAsl-,P, alloys are prepared by a vapor-growth technique described elsewhere.14 With this technique, the individual layers which comprise the multilayer structure are prepared sequentially in the deposition apparatus without interrupting the crystal growth. The epitaxial layers are deposited on GaAs substrate surfaces oriented normal to the ( 100) direction. The substrate wafers employed in this study were usually doped with tellurium to an electron concentration of approximately 2 x 10" per cu cm. To avoid strains, the first 10 to 15 p of the deposited material is uniformly graded from pure GaAs to the specific GaAsl- ,P, alloy composition of interest. The GaAsl - ,P, alloy growth is then continued to form a layer of constant composition having a thickness in the range of 25 to 75 p. Both the graded region and the layer of constant composition are doped with selenium to an electron concentration of about 2 x 10" per cu cm. The p region of the diode is then incorporated in the crystal by abruptly changing the dopant concentrations in the vapor phase to facilitate doping with zinc. This layer has a hole concentration of approximately 3 X 1019 per cu cm and typically is 50 p thick. DEVICE FABRICATION In general, the GaAs substrate and the region of graded composition are removed. Ohmic contacts are made to the n-type side by tin evaporation and to the p-type side by an electrodeless nickel deposition. This is followed by an electrodeless deposition of gold on both sides. The crystal wafer is then cleaved along (110) planes and sawed into rectangular parallelepipeds. Typical dimensions are 100 by 300 for the junction area and 100 µ for the diode height. The diodes are either soldered to a copper stud or pressure-mounted in a copper clip. RESULTS AND DISCUSSION Approximately 400 laser diodes having compositions in the range of 0.41 have been prepared by the method described above. Each laser was routinely tested at liquid-nitrogen temperature. The lasers were operated with l-psec current pulses at a repetition rate of 60 pulses per sec. The parameters of greatest practical interest are the photon energy or wavelength of the laser output and the threshold current density. Fig. 1 shows the variation of photon energy with alloy composition at 78°K. The composition was determined from the lattice constant of the material obtained by X-ray back-reflection measurements. Although there

Jan 1, 1968

By R. A. Morse, P. M. Bridges, L. E. Wilsey, Howard N. Hall, P. L. Terwilliger

Theoretical and experimental investigations of a constant pressure gravity drainage system are reported. Experimental data are presented to show that recovery to gas breakthrough by gravity drainage is inversely proportional to rate. The gravity drainage reference rate, which is numerically equal to the so-called "maximum theoretical rate of gravity drainage" is shown to have no particular significance from a recovery standpoint. Before this rate can be used as a basis of comparison for recoveries, it is necessary that the relative permeability and capillary pressure characteristics and displacing fluid viscosities be identical for the systems compared. A method is presented by which accurate prediction of the performance of a gravity drainage system can be made. Close agreement between experimental and calculated drainage performance shows that steady state relative permeability and static capillary pressure data can be used to describe fluid displacement behavior. The very wide range of liquid recoveries before gas breakthrough which result from production rate variation alone demonstrates the importance of this factor in planning depletion of a gravity drainage reservoir. Calculated results are presented which show that little additional recovery can be expected from a high pressure gravity drainage system between the times of gas breakthrough and attainment of such high gas/liquid ratios as to make further pressure maintenance impractical. INTRODUCTION It bas been recognized for some time that gravity forces play an important part in the recovery of oil from some types of reservoirs. Field experience has shown that under certain conditions, gravity drainage can result in very high oil recov- eries. Qualitative reasoning has led most engineers to the general conclusions that: (1) Where gravity drainage is important, the reservoir pressure should be maintained by gas injection at the crest of the structure to prevent shrinkage of the oil in place and to keep a low viscosity so the oil can drain at the fastest possible rate. (2) Recovery by gravity drainage is rate sensitive. A survey of the literature indicates that while considerable work has been done on the effects of gravity in oil production problems, no satisfactory method of calculating the performance of gravity drainage reservoirs has been reported.1,2,3,4,5 In the absence of any proven method of calculating reservoir performance, the level at which pressure should be maintained and the rate of production for most efficient operation has been open to debate. The limits and general character of the recovery us rate relationships are apparent from the following: As rates of production approach zero, oil will drain by virtue of its own weight fast enough that the saturation distribution is always approximately the same as the original static capillary distribution. That is, at the gas-oil contact the liquid saturation goes from 100 per cent to a value of perhaps 10 to 30 per cent in a very short distance, so that as production continues. a relatively sharp gas-oil contact moves down-structure, leaving a very low residual oil saturation in the originally oil saturated zone. At very high rates of production, the oil that drains by virtue of its own weight is negligible and recovery will approach that of a horizontal gas drive, leaving a much higher residual oil saturation. At intermediate rates of production. recovery should be between these extreme*. Despite the lack of quantitative methods, tentative agreement had been reached on the question of optimum producing rate. It has been generally concluded that rather sharp decrease in recovery would occur at rates of production above the "maximum rate of gravity drainage" and hence this rate should not be exceeded. The "maximum rate of gravity drainage" is defined as the rate of production from a 100 per cent

Jan 1, 1951

By W. A. Bruce

Studies of reservoir behavior of 12 Smackover limestone oil and condensate pools are presented. Buckner, Midway, McKamie, Magnolia, Mt. Holly, Schuler (Reynolds) and Village are treated in considerable detail and subjected to analysis with an electrical device for analyzing reservoir behavior. Results and comparisons of these analyses are presented. In addition to these reservoir-behavior studies, an attempt is made to assemble trans-missibility and storage data on the Smackover limestone formation from cores and logs taken in dry holes and producers. This together with the behavior of individual reservoirs leads to a better understanding of the formation as a porous aquifer. The ultimate purpose of this type of study is to improve predictions concerning the future behavior of these pools in such a system. Predictions are presented for several pools. Introduction In 1937 the Phillips Petroleum Co. drilled its J. D. Reynolds No. I to the Smackover limestone formation at Snow Hill, Arkansas. This well found oil in the porous, permeable, upper part of the Smackover, thereafter referred to as the Reynolds lime. Since then, six oil pools and six condensate pools have been discovered in the Reynolds lime, and more than 75 dry holes have explored parts of this formation. By the first of 1943, 44 million barrels of oil and 83 billion cubic feet of gas had been withdrawn from the various reservoirs. The original reserves estimated by the Arkansas Oil and Gas Commission were 342 million barrels of oil and rzoo billion cubic feet of gas. So far all of the production has been from anticlinal structures, most of which are asymmetric and have their axes roughly perpendicular to the dip of the formation top. This is indicated in Fig. I, which shows the pools, dry holes drilled, and contours on top of the Smackover.&apos; These pools are of particular interest for reservoir-behavior studies because the production and drilling has been controlled, and in most cases the records of reservoir data are complete. In addition to the excellent production and pressure information available, more than one half of the wells drilled were cored and all of them were electrically logged. All of the pools show evidence of water drive. While this paper is in a sense a collection of reservoir-behavior studies for several different pools, there has been an attempt to go one step further and to show the importance of the iormation as a porous continuum or a single aquifer in which the withdrawals of fluids from any pool has an important effect on the behavior of all of the pools. An effort will be made to show that the water drives of these pools are dependent upon a much larger area of the Smackover limestone than that occupied by the petroleum accumulations.

Jan 1, 1944

By E. T. Turkdogan, L. S. Darken, R. J. Fruehan

Further consideration is given to the application of the quadratic formalism to evaluate the thermodynamics of binary metallic solutions from experimental data. The use of the thermodynamic relation, in(r1/r2) dN2= 0, in the evaluation of activity data is discussed. The empirical correlations derived previously for enthalpies and entropies of solutions in Part II are shown to be predicted theoretically for a special case. The applicability of the quadratic formalism to the activity coefficients for binary organic solutions is demonstrated. DARKEN&apos; introduced a quadratic formalism describing the composition dependence of the activity coefficient in the terminal regions of binary metallic solutions. In a subsequent paper (Part II) Turkdogan and Darkeen2 extended this formalism to the enthalpy and excess entropy of binary metallic solutions, and showed that the available data for the activity coefficients and heats of mixing of many solid and liquid binary metallic solutions confirm reasonable applicability of the quadratic formalism. Much variation was noted, however, in the extent of the terminal regions from one system to another, commonly from about 10 to 70 at. pct. For the present purpose, equations derived previously need be given only for one of the terminal regions, e.g. region (I), 0 < N2 < N&apos;2: where subscripts 1 and 2 indicate quantities for components 1 and 2 and superscript ° the values at infinite dilution; other terms are: N = atom fraction, y = activity coefficient, = partial molar enthalpy of solution, ?HM = molar heat of solution, ?Sx = excess partial molar entropy, ?Sx = excess molar entropy. The heat and entropy like terms (constants) el, and S12 are defined in the following expression for the temperature dependence of a12, thus a12 £12 — s12 rnl 2.303RT 2.303 R l J Using this formalism, the thermodynamics of binary systems in the terminal regions may be described over a temperature range of experisental interest in terms of eight quantities: Lº1—Lº2, ?Sx1,?Sxº2 , £12 ,£21,fiai, S12, and S21. In the previous paper, these quantities were evaluated for many solid and liquid binary solutions, and two significant correlations were observed between these thermodynamic quantities pertaining to the terminal regions, thus [10] and [11] Combining Eqs. [9], [l0], and [ll] and rearranging gives a12 -a21 = 1.382R log rº2- 0.08(?S2xº- ?S1xº) [12] Since the second term involving entropies is small and Eqs. 1101 and [ll] are empirical relations, the above equation may be simplified to a12 = 2.74 log rº2 [13] Using the values of a&apos;s and y°&apos;s compiled in Parts I and 11, a12 - a21 is plotted against log(rº2/rº1) in Fig. 1; the line drawn has a slope of 2.74. For Hg-K at 300°C, log(yº2 /yº1)= —5.10, not shown in Fig. 1, and from correlation [13], a12 - a21 = -13.97; this is to be compared with -10.76 derived from the activity data (Part II).

Jan 1, 1970

By L. E. Wilsey, R. A. Morse, P. L. Terwilliger, Howard N. Hall, P. M. Bridges

Theoretical and experimental investigations of a constant pressure gravity drainage system are reported. Experimental data are presented to show that recovery to gas breakthrough by gravity drainage is inversely proportional to rate. The gravity drainage reference rate, which is numerically equal to the so-called "maximum theoretical rate of gravity drainage" is shown to have no particular significance from a recovery standpoint. Before this rate can be used as a basis of comparison for recoveries, it is necessary that the relative permeability and capillary pressure characteristics and displacing fluid viscosities be identical for the systems compared. A method is presented by which accurate prediction of the performance of a gravity drainage system can be made. Close agreement between experimental and calculated drainage performance shows that steady state relative permeability and static capillary pressure data can be used to describe fluid displacement behavior. The very wide range of liquid recoveries before gas breakthrough which result from production rate variation alone demonstrates the importance of this factor in planning depletion of a gravity drainage reservoir. Calculated results are presented which show that little additional recovery can be expected from a high pressure gravity drainage system between the times of gas breakthrough and attainment of such high gas/liquid ratios as to make further pressure maintenance impractical. INTRODUCTION It bas been recognized for some time that gravity forces play an important part in the recovery of oil from some types of reservoirs. Field experience has shown that under certain conditions, gravity drainage can result in very high oil recov- eries. Qualitative reasoning has led most engineers to the general conclusions that: (1) Where gravity drainage is important, the reservoir pressure should be maintained by gas injection at the crest of the structure to prevent shrinkage of the oil in place and to keep a low viscosity so the oil can drain at the fastest possible rate. (2) Recovery by gravity drainage is rate sensitive. A survey of the literature indicates that while considerable work has been done on the effects of gravity in oil production problems, no satisfactory method of calculating the performance of gravity drainage reservoirs has been reported.1,2,3,4,5 In the absence of any proven method of calculating reservoir performance, the level at which pressure should be maintained and the rate of production for most efficient operation has been open to debate. The limits and general character of the recovery us rate relationships are apparent from the following: As rates of production approach zero, oil will drain by virtue of its own weight fast enough that the saturation distribution is always approximately the same as the original static capillary distribution. That is, at the gas-oil contact the liquid saturation goes from 100 per cent to a value of perhaps 10 to 30 per cent in a very short distance, so that as production continues. a relatively sharp gas-oil contact moves down-structure, leaving a very low residual oil saturation in the originally oil saturated zone. At very high rates of production, the oil that drains by virtue of its own weight is negligible and recovery will approach that of a horizontal gas drive, leaving a much higher residual oil saturation. At intermediate rates of production. recovery should be between these extreme*. Despite the lack of quantitative methods, tentative agreement had been reached on the question of optimum producing rate. It has been generally concluded that rather sharp decrease in recovery would occur at rates of production above the "maximum rate of gravity drainage" and hence this rate should not be exceeded. The "maximum rate of gravity drainage" is defined as the rate of production from a 100 per cent

Jan 1, 1951

By S. Harries Daddow

IN order to get an idea as to the strength of steel rails, it will be well to review the tests to which iron rails have been subjected. In England, Mr. Ashcroft found that the best 80 pound rails broke under a 300 pound weight, falling 15 feet. In Germany the Society of Railway tyfanage1-s determined 011 and have long applied a test of 1000 pounds falling 101/2 feet, as the standard which all first-class iron rails must reach. In this country no inspection nor test is applied, but tests made show that iron rails fro; our most reliable makers, break under a G foot fall of a 1500 pound drop as an extreme test, most of those tested breaking under a far less test; some breaking with less than a 3 foot fall of the same weight. Everywhere where steel has been used, engineers have come to the conclusion that some test is required to show the regularity and strength of the product. As compared with iron, the tests which steel will stand are wonderful. After numerous experiments partially based on the experience of the rail-mill at Graz, belonging to the Southern Railway of Austria, the Society of German Railway Managers fixed upon a test of 2000 pounds falling 138 feet. They found that this test represented the steel which suited their necessities, and also found that with steel of otherwise average purity, this test represented about one-half per cent. of carbon, and made it a rule to take no steel containing under three-tenths of a per cent. of carbon, because it was too soft. They expressed a hope that a harder steel could soon be made tough enough to stand the same test. I n England, a test was adopted of 2240 pounds, falling 15 to 17 feet on the rail on heavy bearings. This test has been found satisfactory under heavy traffic on average road-beds, and has been invariablyPILLAR of coal, which are designed and left in our mines as the means of supporting the overlying strata of our coal-beds, and securing protection to the miner, are not only insufficient for these purposes, but the most objectionable means of providing the desired security to life and property. Though such pillars are left at a great sacrifice to the owners of collieries and mineral lands, loss to the resources of the commonwealth, and ultimate privation to the public, they defeat the very ends for which they are designed, and not only do not secure life and property, but are as fatal to the one as ruinous to the other. Propositions.-It is eminently desirable that the resources of the Common wealth-particularly our mineral wealth in anthracite coal, which is limited-should be carefully utilized and made available, not only to ourselves but our posterity. Yet, speaking as an anthracite miner, we are wasting our resources of coal with a recklessness which will bring ruin in the end, unless checked, not only to the iron manufacturing interests of the East, whose chief protection, in competition with the iron-masters of the interior, lies in a cheap and abundant supply of anthracite furnace fuel, but to the best interests of the State. It is, consequently, not only desirable, but necessary, that we should realize every ton of coal from each colliery, and every acre of coal area, in order that our resources may not be wasted at present, to breed want in the future, and to realize the greatest present benefit to the mine, the miner, and the public. It is not possible, however, to secure these ends, if we continue to leave, as we do at present, from one-third to one-half our resources in anthracite as pillars in our mines. But our sad bills of mortality, our abandoned collieries, and our yawning mountain-sides, present ample evidence that even this enormous waste of coal, though left for the purpose of protecting life and property, is as totally inade-

By Ancel St. John

During a session on coal and coke at the February, 1926, meeting of the American Institute of Mining and Metallurgical Engineers, the writer called attention to the important work on the X-ray analysis of coal1,2 being carried on in England by C. Norman Kemp and his associates. This aroused so much interest that a paper on the subject was requested for the October meeting. It has seemed advisable to make this paper a preliminary survey of the present status in the application of X-ray methods to coal problems and to follow it from time to time with further articles as the art develops. A survey of this sort naturally divides itself into two parts, radio-scopic analysis of the distribution of constituents through the body of the coal, and diffraction analysis of the state of association of the elementary components. In this article the subject matter concerning radioscopic analysis has been drawn almost entirely from the writings of Kemp and his associates and the illustrations have been sptcially furnished by him. It is a pleasure to record here a great indebtedness for this courtesy and cooperation. The subject matter and illustrations concerning diffraction analysis are taken from the author&apos;s unpublished researches. Nature and Properties of X-rays Before proceeding it is well to recall the nature and some of the properties of X-rays, as well as our present conception of atomic structure According to the accepted theory atoms are composed of electrically-charged particles. A positively-charged center, called the nucleus,

Jan 1, 1927