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By M. L. Bleiberg, L. J. Jones

THE changes induced in metals by subjecting them to heavy particle bombardment have received widespread attention in recent years and results of such investigations have been reviewed by Slater, Dienes, Seitz, Siegel, and Seitz and Koehler.1-5 Of particular significance are the property changes that occur in uranium-base alloys due to neutron bombardment. These changes are generally very severe since fission occurs within the sample, resulting in the formation of heavy, highly energetic fission fragments, as well as additional neutrons born in fission, which serve to intensify the damage generally associated with fast neutron bombardment of nonfissionable metals. The property changes in uranium and uranium alloys due to neutron bombardment have been summarized by Paine and Kitte16 and Billington.7 It has also been shown that neutron bombardment of

Jan 1, 1959

By Raymond Wilson

GRINDING costs are an important item in cement manufacture, and the cost of power is one of the large items in grinding costs. Even where power is of secondary importance, cost items dependent on mill capacity are influenced by the efficiency with which the mill uses power. Tube mills typify the grinding mills most generally used in cement plants, though other types are in use. Tube mills have been widely criticized as being extremely inefficient, and this feeling regarding them has led to many attempts to design more efficient grinding equipment. Other types may be an improvement over tube mills, but the improvement has certainly not been revolutionary, at least as applied to clinker grinding. The very fact that there is doubt regarding the relative efficacy of various types of mills is an indication that an adequate basis for an analysis of performance is lacking. The development of methods of analyzing mill performance has been hampered by the lack of a suitable method for measuring the work actu-ally done in pulverizing. There has been no acceptable standard to which mill performance might be compared. As a consequence, it was not known whether the margin of possible improvement in pulverizing operations was large or small. Even direct comparison of different types of mills was seldom possible because most plants had only one type of mill for each type of service. Comparisons between plants were difficult because of differences in the grinding characteristics of various clinkers. Some recent developments complete a chain of circumstances that place the cement, industry in a particularly fortunate position for the study of its clinker-pulverizing operations. Modern investigators of grinding phenomena have generally agreed that the best measure of mill performance is the production of new surface. For most materials this measure of performance is largely theoretical and has a rather remote connection with the practical aims of the grinding operation. In clinker grinding, on the other hand, surface area is intimately connected with the properties conferred on the cement by grinding. Moreover, the determination of surface area is rapidly coming into routine use as a test

Jan 1, 1937

By B. O. Pickard

With more than a score of shafts and numerous stope openings to the surface, all inter-connected underground; with underground temperatures high, often exceeding 100' wet bulb; with an ore presenting a dust health-hazard; with certain rocks giving off inert gases; with an altitude of 6000 ft. above the sea level and a dry desert climate, the Tonopah mines offered an interesting problem to the student of metal-line ventilation. Tonopah is not an old mining district, relatively speaking. It was discovered in 1900 and Tonopah soon was a boom camp. Ry 1910 the mines of this district had paid many millions of dollars in dividends. At the time of the 1921 ventilation study, mining had passed its peak of production and the operators were striving to reduce costs, to discover new orebodies, and to attract desirable workmen. In 1925, the camp was operating on a still less prosperous basis, but the several managements had not relaxed in their efforts to keep the mines on a paying basis, neither had they lost their faith in the ability of the mines and the price of the silver to "come back." Early in the fall of 1921 the Bureau of Mines was invited by the mine operators at Tonopah, Nev., to make a detailed study of the underground air conditions in the Tonopah silver district. D. Harrington, chief engineer of the Safety Service Division of the Bureau, who was then directly supervising the ventilation studies, detailed district engineer B. 0. Pickard, mining engineer E. D. Gardner, surgeon C. E. Kindall, and petrographer IT. Insley to carry on the study. G. S. Rice, as chief mining engineer of the Bureau of Mines, was in general charge of the work. Upon the completion of the study each operator was furnished a report on conditions in his mine. In 1925, a supplemental study at Tonopah was made by the district engineer at the request of several of the operators, and each operator advised on the changes in his respective air conditions and recommendations for improvements. Recently, several of the operators gave the

Jan 1, 1927

By C. Hirayama

THIS investigation was undertaken to determine some of the factors contributing to the embrittle-ment of glass-coated silver wire on heat treatment. The materials used in this investigation were 22 and 23 AWG silver wires obtained from Handy and Harman as "fine quality, soft temper." A wet analysis of one sample showed 99.8 pct Ag. The 23-gage wire was covered with a double layer (2.5 mils thick) of electrical grade fiber glass (aluminum borosilicate glass containing a relatively high concentration of calcium, and a very small amount of

Jan 1, 1960

By C. Willard Hayes

Introduction.—The recent developments in the metallurgy of aluminum and its consequent rapidly growing use in the arts are at present attracting considerable attention to its ores. The success of the Hall electrolytic process, by which the metal is obtained directly from the oxide, has removed bauxite from the position of a rather uninteresting mineral to that of an important ore. Its production on a commercial scale is so recent, particularly in this country, that little attention has yet been paid to its mode of occurrence and origin.. Any investigation, therefore, which throws light upon these points should be of interest to mining engineers- at the present time, especially if the conclusions afford a basis for estimating the probable extent and value of deposits already known and a mane of directing search for others. Two localities in the United States have so far yielded bauxite in commercial quantities. These are in Arkansas and in the Coosa valley of Georgia and Alabama. According to descriptions of the Arkansas deposits by Branner, they bear little resemblance to those in the Southern Appalachians and their geological relations appear to be entirely different. Only the latter deposits are considered in the following paper. These have been briefly described by McCalley† and Spencer.† They were visited by the writer during the past summer and somewhat carefully examined, in connection with the study of the areal geology of the region. Location of the Deposits.—The ore is found irregularly distributed within. a narrow belt of country extending from' Adairsville, Ga.,

Jan 1, 1895

By L. A. White

IN this paper it is proposed to follow the developments in the design of the lead blast furnace at Port Pirie from the time The Broken Hill Associated Smelters Pty. assumed control in 1915 to the present time, with special reference to the development of the system using two superimposed rows of tuyeres as is now in operation. Lead smelting operations first commenced in 1889, when the British Broken Hill Pty. Ltd. started its first furnace. This was followed by installing two more furnaces during the same year and another the following year. In 1892, Broken Hill Proprietary Co. Ltd. acquired the smelting works and combined operations with those at Broken Hill, New South Wales; by 1897, the whole of the smelting operations had been transferred to Port Pirie and thirteen blast furnaces were built to treat the Broken Hill ore production. In 1915, The Broken Hill Associated Smelters Pty. Ltd. took over from the Broken Hill Proprietary and have carried out operations since that time. From its inception, the present company started on a long range program of reconstruction, in which the development of the lead blast furnace has played a prominent part. A definite trend in plant development has been towards the simplification of plant control by a reduction in the number of operating units. The great advantages of technical control which resulted from the very simplified flowsheet established in the continuous refining process stimulated the desire to extend the principle to the smelting operation. Thus in the sequence of furnaces described here, it will be noted that the trend has been towards larger and, of course, fewer units. With each such development it is significant that the operating conditions and metallurgical results have shown steady improvement. Standard Furnace In 1920 there were seven furnaces operating, five of a type subsequently called the standard furnace and two of the original thirteen smaller furnaces, the latter type being used for the treatment of drosses, etc. produced from the refinery section, while the standard type carried out the main, lead-smelting operations. The standard furnace (figs. 1 and 2) had the dimensions given in table I.

Jan 1, 1951

By John S. Bell, J. M. Shepherd

pressure difference of 280 psi measured initially on opposite sides of the major fault in the Hawkins Field led to pressure determinations in the Woodbine sand throughout the East Texas basin. Considering the large area, there is unusually good correlation between pressure losses and points of major withdrawals, these losses indicating that the basin pressure has been materially reduced by withdrawals, primarily from the East Texas Field and secondarily from the old fault-line fields of Limestone and Navarro counties, with the pressure loss varying inversely with the log of the distance from these two main areas of basin withdrawals to the measurement points. Apparently faults located throughout the basin serve as local blocks to continuous pressure gradients. INTRODUCTION The pressure anomalies found in the Hawkins Field, Wood County, Texas,' shortly after discovery have led to an area-wide investigation of the pressure distribution within the Woodbine sand of the East Texas basin. These pressures were obtained by drill-stem tests made for that sole purpose while drilling wildcat wells to deeper horizons. The Woodbine sand of Gulf Cretaceous Age is or has been productive of oil and gas in 42 different fields, with the 28 oil fields currently active having produced 118,000,000 bbl of oil during 1949. With one exception, producing energy for all Woodbine reservoirs has been from water drive provided predominantly by expansion of the tremendous volume of water contained in the Woodbine sand. This producing mechanism was recognized at an early date and was described mathematically by

Jan 1, 1951

By John S. Bell, J. M. Shepherd

pressure difference of 280 psi measured initially on opposite sides of the major fault in the Hawkins Field led to pressure determinations in the Woodbine sand throughout the East Texas basin. Considering the large area, there is unusually good correlation between pressure losses and points of major withdrawals, these losses indicating that the basin pressure has been materially reduced by withdrawals, primarily from the East Texas Field and secondarily from the old fault-line fields of Limestone and Navarro counties, with the pressure loss varying inversely with the log of the distance from these two main areas of basin withdrawals to the measurement points. Apparently faults located throughout the basin serve as local blocks to continuous pressure gradients. INTRODUCTION The pressure anomalies found in the Hawkins Field, Wood County, Texas,' shortly after discovery have led to an area-wide investigation of the pressure distribution within the Woodbine sand of the East Texas basin. These pressures were obtained by drill-stem tests made for that sole purpose while drilling wildcat wells to deeper horizons. The Woodbine sand of Gulf Cretaceous Age is or has been productive of oil and gas in 42 different fields, with the 28 oil fields currently active having produced 118,000,000 bbl of oil during 1949. With one exception, producing energy for all Woodbine reservoirs has been from water drive provided predominantly by expansion of the tremendous volume of water contained in the Woodbine sand. This producing mechanism was recognized at an early date and was described mathematically by

Jan 1, 1951

By A. T. Tye

REGARDING the results of preferential flotation at Cananea, Weinig has stated that "The concentrating mill of the Cananea Consolidated Copper Company at Cananea, Mexico, furnishes an excellent example of modern flotation practice. The complete figures are given because they present so forcibly the advantages of modern selective flotation."' L. O. Howard notes that "Perhaps the outstanding example so far published of improvements in results through the use of selective flotation is that at Cananea, Mexico." The following notes indicate the conditions under which the results were obtained at Cananea; also the effect of preferential flotation at the concentrator and at the smelter. In the majority of cases the full benefit of selective flotation is not fully realized, as the concentrates are shipped from the mill to smelters owned by other companies. The saving made at a certain concentrator by this method of flotation may be well understood but the saving resulting at the smelter from the results of preferential flotation at the mill is not so apparent, as the data are contained in the smelting records of some other company. Even at the smelter the great gains following preferential flotation may not be noted, as a variety of ores and concentrates from various sources are received and the difference from the changed concentrator operations of a certain mill may be obscured. As noted by Professor Weinig and Professor Howard, the results obtained at Cananea brought about a veritable metallurgical revolution at the smelter. There are probably plants at which a better preferential separation is being made than at Cananea. Many ores contain barren iron pyrite which, when depressed, does not carry copper into the tailing. Some concentrators use clean uncontaminated water for milling and in others the ore is ground much finer than at Cananea. All of these items are concerned in perfect separation. The details of preferential flotation at Cananea, therefore, are not presented on account of the perfection of the

Jan 1, 1928

By Eric J. Jette

In thermodynamic studies of gas mixtures and liquid solutions, the respective problems have been greatly simplified by the use of two general limiting laws; Dalton's law of partial pressures and Raoult's law. It is generally recognized that these two laws have a common physical and chemical basis which may be stated as follows: The law may be expected to be strictly valid only for systems in which the different molecular species are so nearly the same in their physical and chemical properties that a molecule is unable to recognize whether its neighbor is one of its own kind or not. Positive and negative deviations from both laws are frequently encountered. The occurrence of negative deviations in both gases and liquids is ascribed to attractive forces which, in the more extreme cases, may be so large in magnitude and so highly specific in character as to lead to the formation of definite chemical compounds. Positive deviations in gases develop only at higher pressures where the intermolecular distances are so decreased that factors such as molecular size and shape, which ultimately become concerned with the repulsive forces, come into play. In liquid mixtures, positive deviations are generally considered as due to differences in the symmetrical (nonpolar) fields of force which surround the various molecular species and which are supposed to give rise to a tendency for each species to associate with its own kind and thus to "squeeze out" the other variety. Fundamentally this also involves the existence of repulsive forces between unlike molecules. If the fields of force are unsymmetrical (polar) a tendency towards compound formation results. Stated in more exact terms, strict adherence to the law means that the "activity" (or any adequate measure of this quantity) of a component in a mixture is a linear function of the molecular (or atomic) fraction of that component between the mol fraction limits 0 and 1. A positive deviation means that the activity is greater than corresponds to the law; a negative deviation that the activity is less. The deviations from Raoult's law have been fully discussed by many writers1

Jan 1, 1934

By Rufus J. Foster

During the discussion on the Preparation and Utilization of Sniall Sizes of Anthracite (page 613 of present volume), several inquiries were made concerning the use of the McClave grate, which was mentioned by Mr. Coxe as having proved satisfactory in the generation of steam at his collieries, and also at a large number of industrial estal)lishments in Scranton and elsewhere. For a more satisfactory repIy to such inquiries than could be furnished in the oral discussion, I have prepared the following paper to be included in the published proceedings. And, as the use of the fuel under consideration necessarily requires the employment of a blower to change the fire, from a condition giving an incandescent radiant heat only to one giving a hot gaseoua flame as well, I shall add a description of the McClave Argand blower and its method of action. The grate and blower combined form a complete and effective system fcr burning small fuels, such as anthracite culm, birdseye, buckwheat, bituminous slack, etc., in boiler and other furnaces; while the grate alone is now extensively used with the larger sizes of hard and soft coal in furnaces where blast is riot required. Fig. 1 is a view of the RlcClave grate as built in two sections. It is constructed on the principle best approved by practice to prevent warping and burning out; that is, it presents no long lines of

Jan 1, 1892

By Chung Wang

CHINA now leads the world in antimony production, having contributed during recent years something over 60 per cent. of the world's production. The history of the antimony industry of China dates back to 1897 when the Tai Shing Co. was formed, under contract with the Hunan. Bureau of Mines, for the smelting of the ore to crude; and in 1908 the Wall Chang Mining & Smelting Co. was formed for the smelting and refining of the ore and crude to regulus. The writer was then asked to take charge of the erection and control of this first plant for regulus production in China and has, since then, been more or less connected with the antimony industry in this country. This paper contains the results of many years' experience in connection with the Wah Chang Mining & Smelting Co., Changsha; the Pao Tai Mining & Smelting Co., Wuchow; the Loong Kee Smelting Works and the To-Cheng Smelting Works, Hankow; as well as information gathered from various other small smelters, scattered in different parts of the Provinces of Hunan, Hupeh, Kwangsi, and Kwangtung. An idea of the growing importance of regulus production in this country can be gleaned from the fact that, within a period of about 8 years, the export of regulus from Hunan alone jumped from 3 tons in 1908 to about 6000 tons in 1915; that a production of about 23,000 tons of regulus per year could easily be effected from all the smelters, as tabulated below, most of which were erected a year or two ago under the stimulus of the war booms, if the price at Hankow were to stay somewhere about $900 (Mexican) per ton, half of what it was at its height, thus enabling the utilization of ores from the hinterlands of the provinces; and even under the present ruling of prices and the closing of the less-favored smelters, the production of regulus should not be less than 12,000 tons per year.

Jan 4, 1918

By William Phillips

THE earliest mention of the sulphur deposits in what is now Culberson County, Texas, seems to be contained in "Explorations and Surveys for a Railroad Route from the Mississippi River to the Pacific Ocean, United States War Department, 1853-54." Captain John Pope (he was not commissioned Captain until 1856) had charge of one of the divisions of the Survey. In his report on the geology of the route, William P. Blake noted the analysis of a greenish earthy powder from the bed of Delaware Creek, at the springs, which contained 18.28 per cent. of free sulphur. The report states: "From the chemical examination of the waters of the spring, by Dr. Booth, it appears that chloride of sodium is the principal solid ingredient, but considerable quantities of sulphide of sodium are present. * * * * * The waters from the springs examined by Dr. Booth were alkaline, but it is possible that some of the springs are acid; and in this case the precipitation of sulphur would ensue on the mixture of the acid waters with those charged with alkaline sulphurets and the origin of the deposits of sulphur would he thus explained." This is the first reference to the existence of sulphur in that region, the first mention of the character of the water found there and the first suggestion as to the' origin of the deposits. The possibility of the existence of acid waters was confirmed by E. M. Skeats, nearly 50 years later.1 In this publication, Skeats says that the water from the sulphur deposits in Section 11, Block 114,, Township 5, contains 79.08 grains of free sulphuric acid per gallon. This locality is about 13 miles (21 km.) south of Delaware Creek and about 35-miles (56 km.) east of the Delaware Springs. The next published reference to the existence of sulphur in Trans-Pecos Texas is in the First. Annual Report of the Geological Survey of Texas, 1889, page 226, where W. H. von Streeruwitz mentions that sulphur is found in that region, but gives no further information. In the

Jan 9, 1917

By John Mathews

SOMEONE has divided mankind into two groups: (1) those who have the willingness and imagination to weigh the future gain over against a present indulgence, and (2) those who cannot do so. The former have self-control, patience, foresight and a capacity for sustained effort. Those having these homely virtues become the, possessors of capital and hence employers of others. Those lacking these qualities and owning no capital must seek it from those of the first class, and therefore are employed by others. The human qualities, which divide men into two classes-employers and employed-are, however, capable of change by education, training, environment and by all agencies which tend to develop character. These words of the economist have stuck in my mind for many years and the more I see of men in my business contacts the more firmly I am convinced of their truth. The earth in some respects resembles its inhabitants. When we stroll over the fields and hills we are impressed by the unorganized masses of sand and rock which make up the ground beneath our feet. When by chance we come upon a bit of mineral matter in crystalline form we are impressed by its beauty and symmetry and probably have it polished and call it a gem. Gems constitute a minute portion of the earth's crust, and those intellectual gems, worthy of polish, who brilliantly reflect the incident rays of education and experience that have fallen upon them are few among the masses of mankind.

Jan 1, 1931

By Charles H. Eldridge, Robert J. Anderson

When a metal or alloy is poured into a mold, internal stresses are set up by the cont,raction in volume on passing from the liquid state at the temperature of pouring to the solid state at the ordinary temperature. It is assumed by the writers that all castings are internally stressed. That any casting is internally stressed is shown by its warping or distortion on maturing at the ordinary temperature, by warping or cracking on heating, or by cracking or distortion on machining. In the investigation made by the writers, the internal stresses in cast non-ferrous alloys were studied with a view to examining the effects of heat treatment (i.e., simple anneal) on the release of such stresses. Data have been obtained that show quantitatively that internal stresses can be removed by appropriate heat treatment. The investigation was limited to a study of the effect of heat treatment on stress release in cast rings of the 87:7:5:1 copper-tin-zinc-lead alloy. The writers are indebted to E. G. Fahlman for the method used for inducing stress in cast rings; to M. E. Boyd for microscopic examination and for other aid; and to G. B. Dalrymple for the chemical analyses. General Information While casting stresses have been discussed considerably, they have usually been treated in a general way, and so far as the writers know no measurements of the magnitude of internal stresses in castings have been reported. It has been suggested by many investigators, particularly in the case of steel castings, that castings are internally stressed, and that these stresses can be removed by annealing. In a casting, the internal

Jan 1, 1923

By Robert J. Anderson, Charles H. Eldridge

When a metal or alloy is poured into a mold, internal stresses are set up by the cont,raction in volume on passing from the liquid state at the temperature of pouring to the solid state at the ordinary temperature. It is assumed by the writers that all castings are internally stressed. That any casting is internally stressed is shown by its warping or distortion on maturing at the ordinary temperature, by warping or cracking on heating, or by cracking or distortion on machining. In the investigation made by the writers, the internal stresses in cast non-ferrous alloys were studied with a view to examining the effects of heat treatment (i.e., simple anneal) on the release of such stresses. Data have been obtained that show quantitatively that internal stresses can be removed by appropriate heat treatment. The investigation was limited to a study of the effect of heat treatment on stress release in cast rings of the 87:7:5:1 copper-tin-zinc-lead alloy. The writers are indebted to E. G. Fahlman for the method used for inducing stress in cast rings; to M. E. Boyd for microscopic examination and for other aid; and to G. B. Dalrymple for the chemical analyses. General Information While casting stresses have been discussed considerably, they have usually been treated in a general way, and so far as the writers know no measurements of the magnitude of internal stresses in castings have been reported. It has been suggested by many investigators, particularly in the case of steel castings, that castings are internally stressed, and that these stresses can be removed by annealing. In a casting, the internal

Jan 1, 1923

By Fred E. Wright

In a recent paper1 a detailed discussion is given of the possibilities of using polarized light in the examination of opaque substances. The factors underlying the problem are there treated from the viewpoint of the electromagnetic theory of light and the presentation is necessarily mathematical in form. The practical methods resulting from the discussion are, however, relatively simple and promise to be of value in the determination of certain ores and metals when studied in reflected light under the microscope. The results of the theoretical investigation referred to may be summarized by stating that in general the optical constants, such as refractive indices and absorption indices, cannot be satisfactorily ascertained on small, random, polished sections; that the use of polarized light enables the observer ordinarily to determine whether the crystal plate is iso-tropic or anisotropic, and also to ascertain the degree of anisotropism; that for this purpose methods based either on the contrast in intensity between the two reflected components of non-polarized light, or on the amount of rotation of the plane of polarization, on reflection, of vertically incident, plane-polarized light, may be employed; that methods based on the phase difference between the two reflected components are in general of little value because of the small differences in phase which ordinarily result for a relatively large change in birefringence or biabsorption. The measurement of the optical properties of transparent minerals, even in minute irregular grains, is a simple task with modern petrographic microscope methods and is accomplished by petrologists as part of their ordinary routine work. But the determination of the optical constants of opaque substances is difficult and is rarely attempted; all observations are necessarily made in reflected light and are restricted commonly to the determination of color, of hardness, of the character of crystallization, and of the behavior of the mineral or metal plate toward reagents and abrasives. With practice, the observer becomes expert in recognizing details of this kind and determines with a high degree of certainty the different

Jan 1, 1920

By S. F. Emmons

In a report upon the geology of Ledville and vicinity, which is till in the hands of the Public Printer, I hare given, at some length, my conclusions as to the genesis of the remarkable silver-lead deposits of that region, and the data, gathered during a long and careful consideration, upon which my views were founded. In the brief abstract of this report, published in 1881, the bare conclusions are given, with but few of the facts upon which they were founded. Since that time, these conclusions have been variously criticized, and it has even beer] assumed that the views I expressed with regard to these deposits were intended as a theory of ore-deposits in general.

Jan 1, 1887

By Maxwell Gensamer, Vsevolod N. Krivobok

It is generally recognized that "low temperatures" have a definite effect on the properties of metals and alloys. Furthermore, it is also generally understood that the effect is decidedly adverse. The possibility that the same low-temperature treatment might be employed for the purpose of improving certain properties of the alloys has received less attention until recently, and the experimental and theoretical knowledge consequently is meager. The effect of low temperatures may be studied in two ways: by studying such properties as tensile strength, hardpess, impact resistance, etc., at low temperature, and by studying the properties of alloys at room temperature after these alloys have been subjected to a low-temperature treatment. Even in the latter case, certain properties will differ materially from the same properties obtained on identical material but without cold treatment. In other words, subjecting alloys to cold treatment results in an irreversible change in mechanical properties. Changes of this character are usually indications of the appearance of a new phase or phases, and would be likely to occur in alloys which, either by virtue of their composition or by heat treatment, are retained at room temperature in a metastable condition. Consequently, studies of the effect of low temperatures logically should be conducted from the physicochemical point of view, since the results of such studies not only would furnish metallurgists with interesting theoretical data but would clearly indicate the classes of alloys that would hold promise of improvement, and, possibly, of new applications. As the present investmigation deals with chromium and chromium-nickel alloys of iron of the stainless variety, it has been thought desirable to present the data concerning low-temperature properties of these alloys, available from the most recent and most comprehensive work of H. S. Russell.l A summary of these data is given in Table 1. The data are confined to a limited number of alloys of the type dealt with in the present

Jan 1, 1931

By T. C. Atchison, W. I. Duvall, D. E. Fogelson

Dr. Clark has given an excellent resum6 of the recent theoretical re- search work that has been done on the generation and propagation of stress waves in various types of media.1 Unfortunately the dynamic properties of rock do not fit the assumed properties of the idealized media. As a result, none of the theoretical solutions for the generation of stress waves by applied pressures to interior boundaries of the spherical or cylindrical cavity appear to be completely satisfactory to explain experimental data. This fact does not mean that the theoretical work is in error. It simply means that the appropriate dynamic properties of rock have not been taken into account in the present theoretical derivations. Because of the difficulty of theoretically accounting for the crushing and cracking that takes place when explosives are detonated in spherical or cylindrical cavities, it seems advisable that future theoretical studies should attempt to separate the generation of stress waves from the propagation of stress waves. Perhaps if these two problems are separated, we may be able to solve one of them satisfactorily so that theory and experimental data agree. Dr. Clark's resumé of the research work on scaling and crater formation by point charges is aimed at obtaining a basic understanding of the physical theory of rock breakage, wave generation, and wave propagation. A cursory reading of Dr. Clark's paper shows that there is very little information summarized that can be used by the practicing engineer in the field of blasting. When problems become too difficult to solve theoretically it is always helpful to take the empirical approach and collect experi-

Jan 1, 1967