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By A. E. Nehrenberg

IN an earlier publication' it was shown that the.. shape assumed by a volume of growing austenite is inherited from the prior structure. The matrix grains of pearlitic microstructures are equiaxed, and austenite grows in an equiaxed manner in these prior structures. Martensite and bainite, on the other hand, have an acicular grain structure, and the austenite produced in such structures grows in an acicular manner. In the discussion of this paper' it was pointed out that in cold-rolled tempered martensite, austenite grows in an equiaxed, rather than an acicular manner. The results of an experiment carried out to arrive at an understanding of this behavior are illustrated by the micrographs. Fig. 1 shows the acicular microstructure produced by heating tempered martensite to a temperature within the Ac1-Ac3 range, 1350°F. When tempered martensite is cold rolled, then heated to the same temperature, the equiaxed structure shown in Fig. 2 is produced. A sample of cold-rolled tempered martensite heated at 1350°F just long enough for the formation of a small amount of austenite is shown by Fig. 3 to have an equiaxed (recrystallized) ferrite grain structure. The small particles of. austenite which formed at 1350°F in the equiaxed ferrite matrix are likewise equiaxed. Thus, the equiaxed growth of austenite in cold-worked tempered martensite is not a contradiction of the principles described in the previous paper, for the growth pattern reflects the matrix grain structure existing at the time of austenite formation. References A. E. Nehrenberg: The Growth of Austenite as Related to Prior structure. Trans. AIME (1950) 188, pp. 162-174; Journal of Metals (January 1950). 2 J. R. Vilella and R. A. Grange: Discussion of ref. 1. Trans. AIME (1950) 188, pp. 1378-1381; Journal of Metals (November 1950).

Jan 1, 1953

By S. R. B. Cooke, C. E. Thurston, G. Kudo

The trend toward utilization of low grade iron ores means that more efficient methods must be developed for their concentration. The collecting ability of fatty acids derived from fish oils has been extensively investigated by Cooke.' Tuna oil, a byproduct of the tuna canning industry, is one of the lower priced fish oils. Utilization of tuna oil fatty acids as collectors in the flotation of iron ore might be economically feasible under certain market conditions, especially if their efficiency were high. Crude or unfractionated tuna oil fatty acids, and five fractions derived therefrom, were tested for their ability to concentrate a commercial specularite ore from northern Michigan. A commercial fatty acid derived from tall oil, and commonly used in nonsulfide flotation, was used as a reference. The crude fatty acids were obtained by simple saponification of tuna oil. Fractions A and B were obtained by acetone precipitation of the crude acids at -5O and -2S°C, respectively. Fraction C was obtained by a partial fractional distillation at 12S°C and at a pressure of 3y in a centrifugal molecular still in order to remove the shortest and longest chain fatty acids of tuna oil as well as oxidation products present in the original mixture. Fractions D and E were prepared by a chilling process in order to precipitate the unwanted saturated fatty acids. Yields and iodine values of the materials used are listed below: The seven samples were used as collectors in a laboratory procedure patterned after the commercial process for flotation of Michigan specularite ore. The outline of the procedure is that previously described1

Jan 1, 1962

By R. A. Jr. Flinn

A CONSIDERABLE number of experiments in recent years have definitely established the fact that the internal friction or mechanical hysteresis of a metal under cyclic stress is a property that is highly "structure sensitive." Because of this fact, it has been suggested that an observa-tion of this property, which often is referred to as "clamping capacity," might he a useful indicator of structural changes taking place when a metal or alloy is subjected to any of a number of metallurgical treatments. Damping capacity is of interest to both engineer and metallurgist, but from a rather different point of view, and the information that each desires from such observations is of a different nature. The metallurgist is in search of various external indications of changes taking place in the interior of a metal; changes which are in themselves not directly observa-ble. Even if the observed phenomenon cannot be explained in funda-mental terms, it may be empirically related to certain characteristics of the material and prove of real value in research. Internal friction or mechanical hysteresis occupies such a position, and, although it is not well understood in terms of basic metallic theory, an observation of its changes can serve in a very useful capacity. Of course, there is nothing new in the measurement of damping, but the use of this property in metallurgical research constitutes a vast field, which has received all too little attention. The present work is essentially of an exploratory nature in this field and is an attempt to evaluate the process as a research tool. The phenomenon of age-hardening was chosen as a typical example of a structural change and one method of measuring damping was examined in considerable detail.

Jan 1, 1938

By H. l. Burghoff, A. I. Blank

J. J. Kanter.*—The authors of this paper have demonstrated that at 500°F their alloy will elongate, under appropriately adjusted stress, one or two per cent over a period of 6000 hr. Then they show that after the alloy has so elongated, it will still elongate anothcr 40 per cent if it is tested at ordinary temperature. I should like to ask the authors how much more than 2 per cent over a period of 6000 hr. their alloy will elongate at 500°F. H. L. BuRghofE.—We do not know, because we have not carried out stress-rupture tests on this material. I believe your point concerning the desirability of stress-rupture testing is very well taken. In the material that we have subsequently tested we have not seen any signs of deterioration. We do not know how much further it is possible to go beyond the 2 per cent before finding grain-boundary separation. We have not encountered any under the conditions of the test. W. E. Kingston.†—IS this particular type of copper susceptible to strain-aging, and if so at those comparatively low temperatures, is that going to affect the shape of the curve? By strain-aging I mean the phenomena that certain ferrous alloys show in which the resistance to deformation increases suddenly during the low-temperature creep cycle, apparently due to some precipitation type of reaction, perhaps analogous to hydrogen embrittlement. H. L. BUrghoff.—I believe that this material is not subject to strain-aging of this type. It is very high in copper content, of course, nearly loo per cent. There are some very minor impurities and it carries a small amount of phosphorus, which, unless it is present as an oxide, should be in solid solution well within the solubility limits. I believe it does not precipitate

Jan 1, 1945

By T. B. Crowe

MucH has been written upon the precipitation of metals from cyanide Solution by zinc. We often read of the many factors that influence precipitation, such as zinc surface, purity of zinc, percentage of lead, temperature of solutions, strength of solutions in cyanide or alkali, etc. -Little do, we hear, however, of the part that oxygen plays in precipitation. Caldecottl says: "As the dissolving of gold is essentially an oxidation process, so its precipitation is one of reduction." All who have studied or worked with cyanide solutions will agree that Caldecott's statement is true.' . In the cyanide work in the mills of the Portland Gold Mining Co., we have always found oxygen to be the greatest enemy to precipitation. Oxygen Antagonistic to Good Precipitation A few years ago, while making some experiments on the effect of pressure upon the dissolving rate of gold from our ores, to prove a point, I made some bottle tests under vacuum. The results were surprising, and showed that under vacuum practically no gold dissolved, which confirmed my belief that Elsner's equation was true and also led me to investigate the amount of dissolved air carried by solutions at atmospheric pressure. The experiment consisted in partly filling an acid-bottle with mill-solution and connecting it by a rubber hose to a vacuum pump. When the vacuum was suddenly applied, a cloud composed of thousands of small air bubbles rose out of the solution, showing qualitatvcily' the amount of dissolved air that was contained in the solution, and also proving that the relief of atmospheric pressure on the solution permitted this dissolved air to escape. In studying literature on the subject, we find Henry's law—"The amount of gas dissolved by a liquid is proportional to the pressure to which the gas is subjected."

Jan 1, 1919

By L. W. Kempf

ALUMINUM alloys, in common with most other metallic alloys, exhibit slight density changes with variations in temper achieved by heat-treatment, which usually are the result of the variation with tem-perature of the solid solubility of the various alloy constituents in the solvent metal. Changes in density are, of course, most marked in conditions that exhibit the maximum variation in solid solubility of the constituents. In aluminum alloys these conditions usually prevail when alloys are quenched from just below the melting point and are subsequently reheated to some lower temperature. Since commercial heat-treatments may be of this type, the density changes, although small (of the order of 0.3 per cent which may be compared with the density change of about 1.5 per cent involved in the transformation, at ordinary temperatures, of gamma to alpha iron during the hardening of steel), may in some specific applications necessitate quantitative con-sideration. This phenomenon has been investigated extensively in the laboratories of the Aluminum Company of America over a period of years. A number of investigators1-5 have observed and measured the density changes accompanying the heat-treatment of aluminum alloys. In general, these changes have not been directly translated to dimensional changes and their significance has been overlooked to some extent by the practical user of aluminum alloys. It is the purpose of this paper to consider some practical aspects of these density and dimensional changes. These density changes were given some consideration in 1917 in connection with the use of aluminum-alloy pistons for aircraft engines. Investigations by Lea and Shakespear were reported in some confidential reports of the British Advisory Committee for Aeronautics, Light Alloys

Jan 1, 1936

By K. Kim

INTRODUCTION A thorough evaluation of the geologic material being considered must be conducted to determine the feasibility of constructing a large-scale underground facility in a deep geologic formation. The design and construction of a nuclear waste repository in basalt, due to the unprecedented nature of the project, adds significantly to the need for thoroughness of this evaluation and mandates that geoengineering data and analysis be of the highest quality. The investigations required to collect the data encompass in situ measurements and observations, as well as laboratory and field tests. Mathematical (numerical) models, which are required to predict the long-term performance of the repository structure, must be developed to evaluate rock mass behavior at canister, room, and repository scale and eventual 1 y must be validated through in situ tests and monitoring. The information generated from these geo- mechanics investigations is essential for assessing site suitability and will be utilized in the development of the repository design, the engineered barrier design, and the evaluation of repository performance. The Hanford Site near Richland, Washington is one of nine sites throughout the nation being investigated by the U .S. Department of Energy as a possible location for the first high-level nuclear waste repository in deep geologic formations. The process of site characterization is currently in progress. If the site is nominated by the U.S. Department of Energy, an extensive program will be undertaken, the culmination of which will be a decision on the suitability of the site for waste disposal. There are a mu1titude of elements to the proposed site characterization

Jan 1, 1984

A self-appointed, committee consisting of J. Waldo Smith, Chairman, Richard S. Buck, J. J. Carty, J. Parke Channing, E. L. Corthell, Alfred Craven, Thomas Crimmins, Gano Dunn, George Gibbs, Alex. C. Humphreys, F. L. Hutchinson, Charles Warren Hunt, D. S. Jacobus, John W. Lieb, William Barclay Parsons, George H. Pegram, Charles F. Rand, Calvin W. Rice, Robert Ridgway, William L. Saunders, Merritt H. Smith, Bradley Stoughton, and William H. Wiley, organized a course of seven free lectures on military engineering, which were given by Captains Thomas M. Robins, Richard T. Coiner, Edward D. Ardery, Corps of Engineers, United States Army, and which was under direction of Major General Leonard Wood. The United Engineering Society presented, without charge, the use of the auditorium for the purpose of these lectures, but the interest proved to be more than three times as much as had been expected, and it was therefore necessary to divide the courses into three parts, one of which was given in the afternoon in the auditorium of the United Engineering Societies Building, one in the evening in the same place, and another in the evening in the auditorium of, the American Society of Civil Engineers. These lectures occurred on Mondays, from Feb. 14 to Mar. 27, 1916. The subjects and speakers were as follows: Feb. 14, 1916: Organization and Duties of Engineers in War, and what Engineers in Civil Life will be called upon to do in the Defence Of the United States. Captain Thomas M. Robins, Corps of Engineers. Feb. 21, 1916: The Service of Reconnaissance Including Surveying, Mapping and Sketching, Photography and Map Reproduction. Captain Richard T. Coiner.

Jan 5, 1916

By AIME

IN the following pages are described the history and present operations of one of the country's great mining and metallurgical organizations-the United States Smelting Refining and Mining Company. Though the articles are largely of interest to the technical man, the success of the Company as a business enterprise should not be overlooked. Almost immediately following incorporation 42 years ago payment of dividends began and the total to date has been about $140,000,000, roughly half to preferred and half to common shareholders. Founders of the Company were Boston businessmen and financiers interested in such diverse enterprises as shoe machinery manufacture, banking, newspaper publications, and stock brokerage. The legal profession also was represented. The Company is one of the few, among the leaders in the mining industry, that has resisted the urge to move its home office to New York and has always remained in Boston. Perhaps for that reason it has been regarded as a "conservative" company. Conservative or not, it has certainly spread out geographically and it has certainly put its eggs in many baskets. In addition to the precious metals and the major nonferrous metals it has ventured into coal and recently in a small way into the field of oil and gas. It seems to have a predilection for the North American Continent; for in addition to Alaska, Canada, and Mexico it has had important operations in California, Arizona, Nevada, Colorado, New Mexico, and particularly in various districts in Utah.

Jan 1, 1948

By AIME AIME

Air transport supplants the old methods. The 3-piece canoe fits in the plane and likewise makes possible not a bad division of labor over a 5-mile portage

Jan 1, 1933

By Robert H. Richards

If one holds up a prism, or wedge of glass, with narrow angle, say l° to 2O, and compares the transmitted image with the image seen above or below the prism, the former will be found to be thrown to one side by an amount varying with the angle of the wedge. Speaking of the two rays as the direct ray and the bent ray, we may say, that when the bisecting plane of the prism is at right angles to the line of sight, the angle between the direct ray and the bent ray will be constant for any given prism. If now we place a prism or wedge of glass in such a position that it half-covers the objective of a telescope, we shall obtain on looking through it two images of every object seen—one image by the direct ray, which comes through the unaovered half of the objective, the other which comes through the prism, and is the image by the bent ray. The angle of divergence of these two raps will be constant and unalterable, whether the telescope is directed to a near object, with its eye-piece at increased distance from its objective, or upon a ' distant object, with eye-piece nearer to the objective. That is to say, if the " throw " or apparent dislocation of the image is one foot in one hundred feet it will be two feet in two hundred, ten feet in a thousand, and so on. The usual form of stadia-telescope has at the focal point of the objective two spider-lines, placed at a definite distance apart and intended, let us say, to represent a throw of one foot in one hundred feet. But as the distance between lines remains the same, while the distance from the objective to the webs diflers with every variation in the distance of observed objects, it follows that the angle between the lines of sight which these two spider-lines define cannot be con stant, but must vary with every increase or decrease of distance be tween the instrument and the object viewed. If in Fig. 1 we represent three positions of the spider-lines by W1, W2, W3, and three objects corresponding to those positions by 01, O2, 0, at near, medium and distant positions, we see at

Jan 1, 1892

By D. W. Jessup

THE handling of native labor is offering an interesting problem that requires diplomacy. It is difficult to induce many of the men to leave their villages and enter into regular work. They do not feel the necessity of manual labor other than to obtain sufficient money to pay the annual hut tax and to buy a little clothing. The ground provides mealies (corn) which means food and beer, he hunts and catches fish, so why work? But gradually, as the native becomes more civilized, his wants increase and his ideas change; he now needs money to supply his desires and eventually he must work more. So in time it is hoped that the labor market will be better supplied.

Jan 1, 1931

By Allen Rogers

TWENTY-FIVE DOLLARS for nothing at all except a sheepskin. That to me is the effect of the New York State law for registration of engineers and the same may be said of any of the state licensing laws. Of course, if one has to practice in more than one state, he must pay a more or less equal amount for every state he works in; and yet there has been little effective protest against these laws. It would seem that the spirit which animated the Boston Tea Party is non-existent amongst engineers. Undoubtedly a good many consider, through their failure to understand the law, that the matter does not affect them. In New York State it is provided that "any person practicing or offering to practice profes-sional engineering or land surveying . . . shall be licensed as hereinafter provided." To quote further from the law: "A person practices professional engi-neering . . . who holds himself out as able to do, or who does, the work that an engineer does . . . " The cunning of the wording of this article can only be appreciated by considering that anyone calling himself an engineer falls within the definition; its liberal inter-pretation (I have not quoted the whole of it) would embrace many who do not consider themselves engi-neers. The state authorities may not construe it to include such individuals; indeed, they may possibly consider it inexpedient to extend it to include engineers of subordinate grade, but the possibility is always there and, even though an engineer be of the grade of assis-tant, he may at any time be called upon to substitute for his principal in responsible charge of the work. It is therefore clear that anyone calling himself engineer and practicing engineering must, for his own protection, apply for registration or run the risk of violating the law. Now, what is the sense of all this? We have done very well without such restrictions on the means of gaining our livelihood. If one only stops to think, there is hardly a minute of his modern existence when he is not dependent for his safety on the engineering by engineers of yesterday or today. How often is one in jeopardy through failure of engineering works, work done under the supervision of those same engineers? If all of us had to wait for our ends by such means, our average life would probably be some thousands of years. Where, then, is the point to the object declared in all these laws that the need for licensing is "to safeguard life, health and property?" Bosh!

Jan 4, 1923

By F. F. Aplan

INTRODUCTION Coal is a solid combustible mineral substance resulting from the alteration of vegetable matter largely in the absence of air. It occurs in nature with varying percentages of mineral matter associated with and incorporated into the coalified material. If the amount of this inorganic mineral matter is sufficiently small, and if selective mining can be practiced so as to avoid the incorporation of ash- bearing material from adjacent strata and/or parting seams, the coal can be used as-mined. Otherwise, it must be given a preparation treatment. In 1980 the bulk of the approximately 525 coal preparation plants were located in the eastern half of the U.S., largely in the Appalachian and to a lesser extent in the midwest coal fields (1). Only 17 of these preparation plants were located in the west; these were in Colorado, New Mexico, Utah, Washington and Wyoming. In the past, however, a great many more preparation plants were operated in these and other western states. The upsurge in both the domestic and world- wide demand for quality coking and steam coal will certainly lead to an increase in the number of preparation plants in the west. In fact, there has been a massive development of coal mines and their associated preparation plants across our northern border in Alberta and British Columbia, largely to serve the export coking and steam coal market. Most of the tremendous increase in newly-mined coal in the western U.S. has come from thick seams of inherently low-sulfur, low- ash coal, easy to mine selectively without significant contamination with ash-forming minerals and requiring no preparation. Because of

Jan 1, 1983

By AIME

IRWIN W. ALCORN, present Chairman of the Petroleum Division, was born Sept. 5, 1899 at Marietta, Ohio, and moved with his family to Robinson, Ill., at the time of the early oil development there. This was in the days of the Star spudders, mud, mules, and Stanley steamers. Al graduated from Robinson High School after participation in basket ball, also attaining the captaincy of the football team of that school. He entered Missouri School of Mines and Metallurgy in 1918 and was ushered by the Army into the S.A.T.C. In 1920 he transferred to the Massachusetts Institute of Technology, later to return to receive his B.S. degree -in metallurgy at Rolla, also joining the AIME. On graduation, he worked for the Skelly Oil Co. at Cushing, Okla., shifting to the Moore Refining Co. at DeNoya, Okla., as superintendent of a small pipe-line system. After an interval of two years with the National Supply Co. in Tulsa, he joined the Independent Oil and Gas Co. of that city, and at various times was chief engineer of the Texas division, superintendent of the West Texas pipe-line system, chief engineer of pipe-line construction, and chief engineer of the refining division. Al organized the Company's production engineering department. In 1930 the Company was merged with the Phillips Petroleum Co. The depression was in and Al was out, 'as was true nine months later when the Smith Separator Co. whose chief engineer he had become, was liquidated. The next few years was spent with Oil Well Supply Co. as a subsurface pumping equipment engineer

Jan 1, 1948

Discussion of the paper of Norman B. Braly, presented at the Butte meeting, August, 1913, and printed in Bulletin No. 80, August, 1913, pp. 1881 to 1906. GEORGE A. PACKARD, Butte, Mont.:-I would like to ask Mr. Braly if he has any information as to the relative efficiency of the sinking pump, using it as he refers to it, discharging the exhaust into the water column or otherwise. MR. BRALY :-I have never gathered any information on that point. It is a question of getting the work done. In driving the shaft, using that method, we find it easier on the men and everything else. In the bottom of the shaft, if you exhaust back into your column, it is a quiet. shaft. Another thing is the freezing: if you are sinking with air in your pump, you will find it is liable to freeze, and in that case as the air is still under compression it will not freeze the pump. The difference is very small if there is any. But, as might be expected, the pump is a little less efficient when exhausting the air into the column. MR. PACKARD :-I suppose all of us know what a pump in the bottom of the shaft is. My experience has been, although I have no figures, that the capacity of a pump is quite considerably decreased if you are pumping, say, from a depth of 200 ft. through a No. 7 Knowles pump, when you exhaust the air into a column, but, on the other hand, it is also my impression that we can raise the water to a little greater distance. I would like to get some figures from somebody who has made actual tests.

Jan 11, 1913

By F. R. Hewitt

THE methods of mining talc are simple, and in western North Carolina are almost entirely by open cut and quarry. The larger part of the talc of this section lies in various-sized "veins" inclosed in quartzitic walls, the majority of which have by folding been thrown into a perpendicular position, or nearly so, and the exposed edges of which have been covered by debris from erosion of the mountain above. This covering of loose rocks and earth is from 5 to 25 ft. thick, and in most cases has to be removed because it is difficult to support. Sometimes the covering is heavy enough to "catch" and timber successfully, and in this case the talc can be worked out by the usual method of following the "vein," using stulls for holding up the walls until the vein is worked out, and then allowing the cut or drift to fall in. In some cases it proves more convenient to sink shafts and run drifts, following the talc "veins" until exhausted. The talc deposits of this section are badly broken and faulted both laterally and perpendicularly, and in some cases are found many feet below the level of drainage, necessitating pumping at considerable expense. . My own experience in mining talc has been that the chief point is to get a reliable "vein," and that then the mining is not as difficult, or any more so at least, than that of any common ore. If the. "veins" are pure talc it is simple; if the talc is admixed with foreign matter, such as tremolite in excess, or stains of iron or manganese, as is often the case, one had better abandon the deposit.

Jan 8, 1916

Dr. Wadsworth's discussion of leaching is straightforward and certainly points out some of the critical areas in regards to the fundamental aspects of leaching. I will address myself to the more practical aspects of leaching. As a couple of general comments, very fine particles are often dealt with only when necessary. In many processing applications the sands and slimes are separated with the sand portion being treated by common metallurgical techniques and the slime portion being treated essentially by any technology that will recover some of the values. Ore treatment techniques such as leach/precipitate/float (LPF) have been used in the copper industry to take advantage of leachable copper preferentially reporting to the fine fraction. The second advantage, of course, is the improved metallurgy associated with the treatment of the sand fraction. Cases can be made for sand/slime separations in the aluminum and uranium industry where most of the value reports to the slime fraction and the sand fraction is rejected In the agitated leach systems, fine particles are often the most readily attacked and leached. In dump, vat and in-situ leaching, fine particles cause considerable problems. The fines will tend to restrict the solution flow from portions of the leach feed. This either causes a significantly reduced solution flow or, more probably, the solution will channel, by-passing much of the ore. In either case the result is a decreased metal recovery from ore. The fine particles of principal concern are clays of a flat plate-like shape which can very effectively compact, swell and cause a decreased solution flow. Discrete silica grains or sulfide grains due to their shape, even though they may be very fine, will not cause nearly the problems clays and secondary precipitates can cause.

Jan 1, 1979

By A. B. Parsons

PUBLICATION of this little volume is a luxury that the Institute itself could scarcely afford. In truth, no engineer nor geologist, no assayer nor metallurgist would be likely to enhance his knowledge, improve his technique, or cut his own operating costs by reading this excellent translation of two booklets first published circa A.D. 1520. It is doubtful if the present enterprise would, in a practical or tangible way, "promote the arts and sciences connected with the economic production of the useful minerals and metals." And such, is the prescribed purpose for which the funds of the Institute should be spent. Fortunately for the Institute, the Seeley W. Mudd Memorial Fund is not so circumscribed; and the Fund Committee enjoys, greater liberty of action. The sponsorship by the Mudd Fund in 1942 of the publication of The Pirotechnia of Vannoccio Biringuccio, as translated by Dr. Smith and Mrs. Gnudi, was an innovation-indeed something of an experiment. Not only was the content of the volume significant mainly for its "cultural" and "scholarly" attributes; -but the format, an outstanding example of the fascinating art of bookmaking, bore no resemblance to the ordinary technical book. The Committee, frankly, was surprised at the enthusiastic reception accorded the volume. When a second edition was required, the Committee became convinced that the publication of material of this type, particularly if printed and bound in attractive form, was an appropriate avenue for utilizing a moderate proportion of the monies available from the Fund. The Bergbüchlein and the Probierbüchlein antedate by some years the first publication of De la Pirotechnia and of De re Metallica; but Georgius Agricola, the author of the latter work, made good use of the material in the earlier volumes. As pointed out in the Introduction, both

Jan 1, 1949

By S. W. Parr

THE low-temperature carbonization of coal involves the carrying out of the coking process under conditions wherein neither the coal mass nor any of the passageways through which the volatile products pass are heated above 700° or 800° C. For convenience in this discussion, the single number 750° will be used to designate the maximum range. This temperature is not selected arbitrarily; it is the result of certain natural conditions that are inherent in the substances involved. Two of these conditions arc sufficiently pronounced to suggest a line of demarcation at this point as follows: (1) Below 750°, all the heavy hydrocarbons are expelled, which means that, at these lower temperatures, the illuminants, the gases of high calorific value, and the condensible oils are discharged; above 750°, there are given off the lean, non-illuminating gases consisting for the most part of hydrogen and marsh gas and having no condensible constituents present. (2) Below 750°, there is substantially no secondary decomposition; above 750°, the volatile products are readily decomposed, forming tars, naphthalene, free carbon, etc. It is not intended to maintain that no secondary decompositions occur below 750°. Many recent studies have demonstrated the practicability, especially in the presence of catalytic substances, of cracking certain of the hydrocarbon compounds; but at these lower temperatures the step is a moderate one, as, for example, from xylene to toluene or from toluene to an anthracene. These changes are moderate in amount. Not only do the reactions proceed slowly but they are subjected to the decomposing conditions for only a short time. This is evident when it is recalled that at these initial temperatures the decomposition, of the coal is very rapid and, if anywhere near a neutral pressure is maintained, the movement

Jan 2, 1920