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R. V. Norris, Wilkes-Barre, Pa. (communication to the Secretary*):—Mr. Stow's paper presents a series of arguments, numbered from 1 to 18, concerning the relative merits of four systems of colliery-ventilation, designated by the author as " plain pressure-ventilation," " plain exhaust-ventilation," " obstructed pressure-ventilation," and " obstructed exhaust-ventilation." These arguments are subsequently compared by means of tables, in which an arbitrary numerical value is assigned to each, and which consequently serve no other purpose than that of showing his opinions and predilections, as indicated by his assignment of the said numerical values. In addition to this general summary, Mr. Stow intimates his preference for a fifth method of colliery-ventilation—namely, what he calls " alternating pressure-ventilation," which consists in the running of the fan at "pressure " during working-hours, and as an " exhaust" between shifts—a system which he proposes as, perhaps, new, yet which he thinks deserves recognition " as a standard form." This proposed " standard form " is not to be found in practice ; and I think it would be impracticable in gaseous mines of large extent, for the following reasons: 1. It takes considerable time to reverse the air-current in a large mine; and the reversal would involve a period of complete stoppage of ventilation, long enough to permit serious accumulations of gas. 2. In shaft- and slope-mines, at least, it is hardly practicable to have " every man out of the mine" during the night, and certainly impracticable to avoid keeping mules and horses inside. 3. The doors necessary to divide and direct the air-current are properly hung to open against the air-pressure; and, unless

Jan 1, 1910

By C. Wert, P. Bunn

Determination of the solid solubility of gases in metals is usually done by one of two methods. The first is an additive method, in which measurement is made at temperature of the maximum amount of gas absorbed by an initially degassed piece of the metal. Gas additions are made until the dissolved gas first comes into equilibrium with a compound. This method is most useful at relatively high temperatures where the amount of gas absorbed is relatively large and where equilibration of the dissolved gas with the gas atmosphere can be achieved in a relatively short time. The second is a precipitation method. A supersaturated solution of the gas in the metal is held at temperature until equilibrium is established between the gas atoms in solution and a compound. The quantity of dissolved gas is then determined by some physical measurement which is sensitive only to the gas in solution. This method is generally useful in low temperatures. This paper describes measurement of solubility of nitrogen in tantalum whereby measurements at low temperatures using internal-friction methods are plotted together with existing measurements at high temperatures. The solubility is thereby known from less than 0.5 at. pet at 350°C to near 13 pet at 2300°C. Several measurements have been reported of the solubility of nitrogen in tantalum. These are collected in Fig. 1. Three single determinations by Ke,1 Andrews,2 and Brauer and zapp3 are plotted along with a series of measurements by Vaughn, Stewart and schwartz4 and Gebhardt, Seghezzi, and Fromm.5 Although not much doubt exists about the solubility being in excess of 10 at. pet above 2000°C, the solubility indicated at low temperatures depends on whose data are selected as being most reliable. The variation is enormous, being at least an order of magnitude at 500°C. Accordingly, a measurement was begun to examine this discrepancy. The method of measurement finally selected was that of internal friction. A solid solution of nitrogen in tantalum was prepared by heating a tantalum wire in a dilute at-

Jan 1, 1964

By Sylvan Cromer

The need for a clear understanding of the physical nature of the flow of gas-liquid mixtures in vertical pipes is ever becoming more apparent. This type of flow is encountered when gas and oil are produced from a well; when water is removed from gas wells with siphon lines and when liquids are elevated by means of air or gas lift. Although a number of investigator1-7 have published data on the flow of gas-liquid mixtures, in only a few cases has the experimental setup been devised to permit visual study. In the fields of heat transmission, such as the boiling of liquids and the study of the critical phenomena of the hydrocarbons, researchers have been able to throw additional light on heretofore unexplainable happenings through actual observation in glass apparatus. This investigation was therefore undertaken in order to obtain qualitative as well as quantitative results for air-water flow. Experimental Apparatus and Procedure The flow column used in these tests was made of standard 2-in. pipe and was approximately 98 ft. in height. Pyrex observation sections 2 ft. long having the same internal diameter as the wrought-iron pipe were placed at 14-ft. intervals in the column. The bottom of the tube was cut off square and terminated in the mixing chamber. No perforated nipple or footpiece of any kind was used. To the top of the column was fastened a semicircular return bend having a 4-ft. radius. The flow column was supported by a standard cable-tool drilling derrick (Fig. 1) into which were built observation platforms at each Pyrex section.

Jan 1, 1940

By Sylvan Cromer

The need for a clear understanding of the physical nature of the flow of gas-liquid mixtures in vertical pipes is ever becoming more apparent. This type of flow is encountered when gas and oil are produced from a well; when water is removed from gas wells with siphon lines and when liquids are elevated by means of air or gas lift. Although a number of investigator1-7 have published data on the flow of gas-liquid mixtures, in only a few cases has the experimental setup been devised to permit visual study. In the fields of heat transmission, such as the boiling of liquids and the study of the critical phenomena of the hydrocarbons, researchers have been able to throw additional light on heretofore unexplainable happenings through actual observation in glass apparatus. This investigation was therefore undertaken in order to obtain qualitative as well as quantitative results for air-water flow. Experimental Apparatus and Procedure The flow column used in these tests was made of standard 2-in. pipe and was approximately 98 ft. in height. Pyrex observation sections 2 ft. long having the same internal diameter as the wrought-iron pipe were placed at 14-ft. intervals in the column. The bottom of the tube was cut off square and terminated in the mixing chamber. No perforated nipple or footpiece of any kind was used. To the top of the column was fastened a semicircular return bend having a 4-ft. radius. The flow column was supported by a standard cable-tool drilling derrick (Fig. 1) into which were built observation platforms at each Pyrex section.

Jan 1, 1940

By Sylvan Cromer

THE need for a clear understanding of the physical nature of the flow of gas-liquid mixtures in vertical pipes is ever becoming more apparent. This type of flow is encountered when gas and oil are produced from a well; when water is removed from gas wells with siphon lines and when liquids are elevated by means of air or gas lift. Although a number of investi-gators1-7 have published data on the flow of gas-liquid mixtures, in only a few cases has the experimental setup been devised to permit visual study. In the fields of heat transmission, such as the boiling of liquids and the study of the critical phenomena of the hydrocarbons, researchers have been able to throw additional light on heretofore unexplainable happen-ings through actual observation in glass apparatus. This investigation was therefore undertaken in order to obtain qualitative as well as quanti-tative results for air-water flow. EXPERIMENTAL APPARATUS AND PROCEDURE The flow column used in these tests was made of standard 2-in. pipe and was approximately 98 ft. in height. Pyrex observation sections 2 ft. long having the same internal diameter as the wrought-iron pipe were placed at 14-ft. intervals in the column. The bottom of the tube was cut off square and terminated in the mixing chamber. No perforated nipple or footpiece of any kind was used. To the top of the column was fastened a semicircular return bend having a 4-ft. radius. The flow column was supported by a standard cable-tool drilling derrick (Fig. 1) into which were built observation platforms at each Pyrex section.

Jan 1, 1939

By William Fink

THE investigation of the phase relations of high-purity aluminum-base alloys is a part of the fundamental research program of the laboratories of the Aluminum Company of America. The results of a number of binary and ternary systems have previously been published in the transactions of this society. The aluminum end of the binary aluminum-titanium system has been studied. This system has received relatively little attention. To the authors' knowledge, there are two previous papers on this subject. E. van Erckelens1 determined the constitutional diagram reproduced in Fig. 1. .According, to this diagram, the liquids represents the separation of TiAl4 (Ti = 30.7 per cent.). He concluded that this is the composition of the compound, because in his work the eutectic horizontal terminated at 30.7 per cent. titanium and the metallographic examination of a sample of this composition revealed only one phase. According to the constitutional diagram developed by W. Manchot and A. Leber,2 reproduced in Fig. 2 from data given in their article, the liquidus represents the separation of the compound TiAl3 (Ti = 37.2 per cent. ). The composition of the compound was derived in a manner similar to that utilized by van Erckelens. Moreover, Manchot and Leber confirmed the composition of the compound by analysis of the constituent left as a residue after dissolving the alloys in weak sodium hydroxide solution. Although these are the only publications describing the constitution of the system, other investigators have studied the composition of the titanium compound. L. Wöhler3 says that there is a compound TiAl3 which was later confirmed by W. Manchot and P. Richter4 and by

Jan 1, 1931

By Harry H. Power

The relative merits of air and natural gas as propulsive agents in pressure drive operations have been discussed for a number of years. When air or gas is introduced into the sand, various factors lead the operator to the selection of what he believes to be the proper propelling medium; but when the question of relative drive effect is raised, several physical and chemical premises must be taken into consideration in arriving at a conclusion as to the superiority of one medium over the other. Dow and Calkins1 and Beecher and Parkhurst2 have contributed fundamental experimental work on the effect of dissolved gas in lowering the viscosity and surface tension of crude oil. Herold; and Tickell' have indicated that whatever type of reservoir control obtains, gas plays other important parts in the movement of oil towards the well, namely: 1. The propulsive and expansive force of the gas. 2. The "Jamin effect," or resistance to the movement of oil in a porous media due to the formation of gas bubbles. When quantitative studies are made, parallel conditions must be selected whereby we may say definitely whether air is superior to gas as a driving medium, or vice versa. Examples of similar conditions are not easy to find in the field. However, in the laboratory we can make determinations which may lead to general conclusions when applied to the field. The experimental and research work described here was started at the laboratories of the University of California in January, 1927, and completed in private laboratories at Tulsa, Okla., in February, 1928. The apparatus used was designed especially for the work.

Jan 1, 1929

By D. L. Gardner, H. L. Barr

The following report covers the history of the development of the mine, present equipment, methods and costs of mining and milling. In addition, a description of the ore deposit is given with emphasis on the origin of the fractures, mode and types of ore occurrence, and mechanics of granite emplacement. An endeavor has been made to present a complete and accurate statement of the San Mauricio mine, the highest grade gold mine in the Philippine Islands. Credit is gratefully acknowledged to the mine staff for descriptions and details regarding their particular field of work. All analyses were made by Mr. T. A. DeVore, head chemist, San Mauricio Mining Co. Messrs. Edward Wisser, J. E. Fyfe, A. F. Skerl and W. B. Meek, geologists, have contributed geologic information and ideas, for which thanks are extended. The Executive Committee of Marsman and Co., Inc., Managers of the Company, has kindly given permission for publication. Mr. J. B. Stapler, Division Manager, Marsman and Co., has had the courtesy to read the manuscript and to give critical and helpful suggestions. Location of Area and Scope of Work San Mauricio Mining Co. controls a group of 113 claims that lie immediately north of the town of José Pafiganiban (formerly Mambulao), Camarines Norte, Luzon, P. I. (Fig. 1). Exploration work commenced in the spring of 1934; active development began in the fall of that year and has continued to the present date. Mill construction was begun Ocl,. 15, 1935, and production started March 10, 1936. Total production to June 1, 1939, is P10,499,105.15 ($5,249,552.57).

Jan 1, 1941

By D. L. Gardner, H. L. Barr

The following report covers the history of the development of the mine, present equipment, methods and costs of mining and milling. In addition, a description of the ore deposit is given with emphasis on the origin of the fractures, mode and types of ore occurrence, and mechanics of granite emplacement. An endeavor has been made to present a complete and accurate statement of the San Mauricio mine, the highest grade gold mine in the Philippine Islands. Credit is gratefully acknowledged to the mine staff for descriptions and details regarding their particular field of work. All analyses were made by Mr. T. A. DeVore, head chemist, San Mauricio Mining Co. Messrs. Edward Wisser, J. E. Fyfe, A. F. Skerl and W. B. Meek, geologists, have contributed geologic information and ideas, for which thanks are extended. The Executive Committee of Marsman and Co., Inc., Managers of the Company, has kindly given permission for publication. Mr. J. B. Stapler, Division Manager, Marsman and Co., has had the courtesy to read the manuscript and to give critical and helpful suggestions. Location of Area and Scope of Work San Mauricio Mining Co. controls a group of 113 claims that lie immediately north of the town of José Pafiganiban (formerly Mambulao), Camarines Norte, Luzon, P. I. (Fig. 1). Exploration work commenced in the spring of 1934; active development began in the fall of that year and has continued to the present date. Mill construction was begun Ocl,. 15, 1935, and production started March 10, 1936. Total production to June 1, 1939, is P10,499,105.15 ($5,249,552.57).

Jan 1, 1941

By Paul Billingsley, Augustus Locke

The mining districts of the first order' of the western United States (and borders) are those named on Fig. 1. These fall into four groups: (1) in the eastern outliers of the Rocky Mountain system; (2) in the Rocky Mountain system itself; (3) in the Great Basin; and (4) in the Sierras and Coast ranges. Of these four groups, the first three are almost entirely of Tertiary age and are within a belt of compressive folding which we shall call the Rocky Mountain-Great Basin thrust arc. The backbone of this belt is shown by the line BAC. The position of the ore districts in this belt indicates a conformance to linear elements of the continental pattern. These are additional to the peripheral elements emphasized by Butler.2 Nature of the Thrust Arc The thrust arc separates regions of contrasted kinds. To the east of it are flat-lying plateaus interrupted by earlier mountain folds; to the west, sunken basins, in which block-faulted ranges lie like an anchored fleet in a sea of desert wash or lava. The. cross-sections are as shown in Fig. 2. The backbone of the belt is the upward and eastward moving block represented by the Glacier Park, the Wasatch, and the Virgin mountains, successively. The structure represented on these sections is the culmination of events which began far back in geologic time and throughout which a contrast has existed between the regions east and west of the backbone line. Before the Pennsylvanian, as Fig. 3 shows, there was a shallow shelf on the east and a deep marine trough on the west; after

Jan 1, 1935

By Paul Billingsley, Augustus Locke

The mining districts of the first order' of the western United States (and borders) are those named on Fig. 1. These fall into four groups: (1) in the eastern outliers of the Rocky Mountain system; (2) in the Rocky Mountain system itself; (3) in the Great Basin; and (4) in the Sierras and Coast ranges. Of these four groups, the first three are almost entirely of Tertiary age and are within a belt of compressive folding which we shall call the Rocky Mountain-Great Basin thrust arc. The backbone of this belt is shown by the line BAC. The position of the ore districts in this belt indicates a conformance to linear elements of the continental pattern. These are additional to the peripheral elements emphasized by Butler.2 Nature of the Thrust Arc The thrust arc separates regions of contrasted kinds. To the east of it are flat-lying plateaus interrupted by earlier mountain folds; to the west, sunken basins, in which block-faulted ranges lie like an anchored fleet in a sea of desert wash or lava. The. cross-sections are as shown in Fig. 2. The backbone of the belt is the upward and eastward moving block represented by the Glacier Park, the Wasatch, and the Virgin mountains, successively. The structure represented on these sections is the culmination of events which began far back in geologic time and throughout which a contrast has existed between the regions east and west of the backbone line. Before the Pennsylvanian, as Fig. 3 shows, there was a shallow shelf on the east and a deep marine trough on the west; after

Jan 1, 1935

The mining districts of the first order' of the western United States (and borders) are those named on Fig. 1. These fall into four groups: (1) in the eastern outliers of the Rocky Mountain system; (2) in the Rocky Mountain system itself; (3) in the Great Basin; and (4) in the Sierras and Coast ranges. Of these four groups, the first three are almost entirely of Tertiary age and are within a belt of compressive folding which we shall call the Rocky Mountain-Great Basin thrust arc. The backbone of this belt is shown by the line BAC. The position of the ore districts in this belt indicates a conformance to linear elements of the continental pattern. These are additional to the peripheral elements emphasized by Butler.2 Nature of the Thrust Arc The thrust arc separates regions of contrasted kinds. To the east of it are flat-lying plateaus interrupted by earlier mountain folds; to the west, sunken basins, in which block-faulted ranges lie like an anchored fleet in a sea of desert wash or lava. The. cross-sections are as shown in Fig. 2. The backbone of the belt is the upward and eastward moving block represented by the Glacier Park, the Wasatch, and the Virgin mountains, successively. The structure represented on these sections is the culmination of events which began far back in geologic time and throughout which a contrast has existed between the regions east and west of the backbone line. Before the Pennsylvanian, as Fig. 3 shows, there was a shallow shelf on the east and a deep marine trough on the west; after

Jan 1, 1935

By Augustus Locke, Paul Billingsley

The mining districts of the first order' of the western United States (and borders) are those named on Fig. 1. These fall into four groups: (1) in the eastern outliers of the Rocky Mountain system; (2) in the Rocky Mountain system itself; (3) in the Great Basin; and (4) in the Sierras and Coast ranges. Of these four groups, the first three are almost entirely of Tertiary age and are within a belt of compressive folding which we shall call the Rocky Mountain-Great Basin thrust arc. The backbone of this belt is shown by the line BAC. The position of the ore districts in this belt indicates a conformance to linear elements of the continental pattern. These are additional to the peripheral elements emphasized by Butler.2 Nature of the Thrust Arc The thrust arc separates regions of contrasted kinds. To the east of it are flat-lying plateaus interrupted by earlier mountain folds; to the west, sunken basins, in which block-faulted ranges lie like an anchored fleet in a sea of desert wash or lava. The. cross-sections are as shown in Fig. 2. The backbone of the belt is the upward and eastward moving block represented by the Glacier Park, the Wasatch, and the Virgin mountains, successively. The structure represented on these sections is the culmination of events which began far back in geologic time and throughout which a contrast has existed between the regions east and west of the backbone line. Before the Pennsylvanian, as Fig. 3 shows, there was a shallow shelf on the east and a deep marine trough on the west; after

Jan 1, 1935

By Harry Power

THE relative merits of air and natural gas as propulsive agents in pressure drive operations have been discussed for a number of years. When air or gas is introduced into the sand, various factors lead the operator to the selection of what he believes to be the proper propelling medium; but when the question of relative drive effect is raised, several physical and chemical premises must be taken into consideration in arriving at a conclusion as to the superiority of one medium over the other. Dow and Calkins1 and Beecher and Parkhurst2 have contributed fundamental experimental work on the effect of dissolved gas in lowering the viscosity and surface tension of crude oil. Herold3 and Tickell4 have indicated that whatever type of reservoir control obtains, gas plays other important parts in the movement of oil towards the well, namely: 1. The propulsive and expansive force of the gas. 2. The "Jamin effect," or resistance to the movement of oil in a porous media due to the formation of gas bubbles. When quantitative studies are made, parallel conditions must be selected whereby we may say definitely whether air is superior to gas as a driving medium, or vice versa. Examples of similar conditions are not easy to find in the field. However, in the laboratory we can make determinations which may lead to general conclusions when applied to the field. The- experimental and research work described here was started at the laboratories of the University of California in January, 1927, and completed in private laboratories at Tulsa, Okla., in February, 1928. The apparatus used was designed especially for the work.

Jan 1, 1928

By Edward Keller

In order to conduct intelligently the sampling of copper of various forms and grades, solid or in molten furnace-charges, a knowledge of this subject is essential. Yet figures and tests have been persistently withheld from publication, and the books at our command give us little or no information in this regard. This gap in our copper-literature has led to a series of experiments, the results of which are given below. Nearly all gold- and silver-bearing copper, destined for shipment, is cast into the form of bars or pigs. For the sampler, the question arises, Does copper, so cast, remain homogeneous ? If it does, sampling should present no difficulties; but, from experience, we know that this is not the case, and we are thus led to study the behavior of the precious metals arid impurities in copper when the latter changes from the molten to the solid state. For the purpose of the experiments here described, all available grades of copper were selected, and all of them mere subjected to the same conditions, an important requisite for proper comparison. The molten copper obtained directly from reverberatory- and blast-furnaces was cast in a cast-iron mould, the sides and bottom of which were 1 inch thick, and would, therefore, give the copper a fair length of time to chill. The inside dimensions of the mould, and, consequently, of the block of copper obtained, were: length, 10 inches; width, 9 inches; and depth, 5 inches. Fig. 1 illustrates the method employed to obtain samples from these blocks. A was cut away, and the face so produced BALTIMORE COPPER WORKS,

Jan 1, 1898

By F. C. Greene

Development work in western Missouri was continuous during 1933, owing to the shallow depths at which production is obtained and the low operating costs. Unfortunately, no statistics covering the total production of oil and gas during the year are available. No new oil-producing pools were opened in 1933, but the Knoche area in 1.46 N., R.33 W., Cass County, was extended. There are probably less than 100 producing oil wells, all in Cass and Jackson counties, with a combined production of possibly around 150 bbl. daily. Several new gas areas were developed and there were several extensions of old areas, in 1933. Production was extended north by an entirely new pool—the Hammond pool, north of Plattsburg in Clinton Co. (sec. 18, T.55 N., R.31 W., and sec. 13, T.55 N., R.32 W.) where 13 wells were completed, the largest producing 2,332,000 cubic feet. In the Bartle and Marshall pool in secs. 3-4-9-10, T.47 N., R.33 W., Jackson County, four wells opened a new area. The largest well was 1,000,000 cubic feet. There were some small extensions near Independence, Jackson County. Two wells of about 300,000 cu. ft. were completed at a depth of 700 ft. in Kansas City and in a deeper sand than is usually productive. The Shaler area, in secs. 27-34, T.44 N., R.33 W. in Cass County, was extended with several wells, the largest of which was 300,000 cubic feet. The production in the pools mentioned is obtained chiefly from the Henrietta and Cherokee formations of the Pennsylvanian age.

Jan 1, 1934

By F. E. Crane, J. Downie

The general application of Darcy's law to natural rocks has already been challenged in the literature.1 The evidence shows that the permeability as calculated from the Darcy equation can be a function of the pressure drop and the salt concentration of the water phase. Most explanations for aberrant behavior involve clays and their properties and have been qualitatively satisfactory.Recently, however, Odeh2 revived the theoretical views of Yuster.3 Since Yuster's concept implies a fundamental error in using Darcy's relationship for two-phase flow, and not merely that conditions may limit its use, Odeh's experimental support arouses considerable interest. However, Odeh's work as presented is thought to to be inadequate. He has omitted important information about his materials and procedures; therefore, acceptance of his conclusions should be withheld. Since a clay effect is possible, Odeh should have been allowed space to present a more detailed account of the rocks which he used and the precautions which he took to avoid confounding the effects of clay and fluid circulation. In addition, it follows from Odeh's discussion that the oil relative permeability should increase as the viscosity ratio increases. Odeh presents data corroborating this deduction. It also follows that the oil relative permeability should decrease as the viscosity ratio of oil to water decreases. However, our results show that a high relative permeability, when once attained by using a viscous oil, may be maintained when that oil is replaced by an oil of much lower viscosity. EXPERIMENTAL PROCEDURE The results are shown in Fig. 1 and were obtained as follows. Sandstone cores. 3-in. long X l-in, in diameter and which contained clays, were saturated with

By Howard W. Dubois, Charles T. Mixer

Only within the past few years have chemists recognized the importance of the fact, that comparatively large amounts of phosphorus may occur in the siliceous residue left from the acid treatment of iron-ores. We know of one case in which an ore contained about three times as much phosphorus in the insoluble, as in the soluble, form. It was disposed of at a premium, as an exceptionally high-grade Bessemer ore containing 0.010 per cent. of soluble phosphorus, while the insoluble phosphorus brought the total amount up to 0.040 per cent. The magnetite and specular hematite of the Lake Superior districts and the fine ores of the Mesabi range, as a rule, contain very small amounts of insoluble phosphorus. But the mining of the soft hematites and the progressive lowering of the phosphorus-limit in a strictly Bessemer ore, have combined to make the determination of insoluble phosphorus one of the routine-requirements in all analyses of Bessemer ores. The insoluble phosphorus is understood to be that pbosphorus which cannot be extracted by boiling hydrochloric acid of 1.1 specific gravity. The time given for the extraction of the soluble phosphorus will vary, of course, according to the nature of the ore. In ordinary practice the boiling is continued until the residue is white or only very slightly tinged with ferric oxide. This ordinarily takes from half an hour to an hour. The prolonged boiling of ores known to contain considerable quantities of insoluble phosphorus has failed to extract any appreciable amount of additional phosphorus. Very fine grinding and subseqnent sifting through bolting-cloth has not increased the extraction. These statements represent the re-

Jan 1, 1898

By S. Wiederhorn

The energy and force of interaction between a crack and a slip band have been calculated. When the distance between the crack and the slip band is greater than the dislocation spacing of- the slip band, the force on the cgrack is perpendicular to the slip band. The energy needed to propagate a crack against this force can be lawe enough to pevmit crack propagation parallel to noncleavage planes. SEVERAL recent experiments have demonstrated the occurrence of crack-slip band interaction in ionic crystals having a NaC1-type structure. Stokes, Johnston, and Lil have studied the nucleation and growth of cracks in MgO. From their observations, they conclude that slip bands have the ability to halt and stabilize cleavage crack nuclei. Gilman2 has shown that a crack, propagating along a (100) cleavage plane in a previously deformed LiF crystal, tends, at certain points within the crystal, to switch to (110) planes. He reasons that plastic deformation reduces the cohesive energy of the (110) planes below that of the (1130) planes, making possible (110) crack propagation. Keh3 has demonstrated that when indentations are made in MgO, crkcks form along (110) planes at the indentations. Gilman2 attributes the formation of these cracks to plastic cieformation. There is some doubt as to the formation of cracks on (110) planes. Kuznetsov4 in his discussion of crack propagation in rock salt, shows that splitting along (110) planes requires 1.76 times as much energy as splitting along a stepped (100) surface. Therefore, the observed (110) cracking in LiF and

Jan 1, 1962

By George J. Bancroft

AT the New York meeting of the Institute, April, 1907, I presented a paper entitled, The Formation and Enrichment of Ore-Bearing Veins,1 in which paper I advanced the following propositions (1) That the majority of mineralized veins are the product of expiring vulcanism ; (2) that most of these veins were primarily mineralized by comparatively rich solutions in comparatively short periods of time; (3) that the solutions gained their metal-values from a comparatively rich source; (4) that there is a barysphere containing large amounts of the useful metals; (5) that eruptions spring from various depths and bring various kinds of magmas towards the surface; and (6) that only those eruptions which disturb the barysphere and bring a magma rich in metals sufficiently near the surface to be leached by vein-making solutions are productive of valuable ore-deposits, other eruptions producing barren veins. Ore-deposits due to magmatic segregation were not included in this general survey. As a result of considerable further study I have modified my views in some respects, while in others I feel more sure than ever of the ground taken at that time. That ore-bodies are infrequent occurrences and born of extraordinary conditions I think is now generally accepted. The theory that persisted for a time-namely, that ore-bodies were formed by the ordinary ground-water, which consists of extremely dilute solutions, derived from leaching extremely lean surface-rocks, and which must occupy enormously long periods of time in concentrating the values so leached, is, I think, now pretty generally regarded as not applicable to the great majority

Jan 1, 1913