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By John Gross

THE method of measurement of surface on quartz particles was given in a previous paper.1 With such a method the relation of surface produced in crushing quartz can be compared to the work in crushing without recourse to sieve sizing or microscopic measurement. In crushing, the work input must be known with a fair degree of accuracy. With crushers, rolls, ball mills, and similar apparatus the measurement of the work in crushing is subject to possible errors, due to friction in .the transmission as well as in the machine itself. Moreover, relatively large quantities of material must be crushed to get an average figure. In the selection of a method of crushing, simplicity in design and operation was desired and this was most readily obtained by the use of a free-falling body. A description of the apparatus embodying this principle is given herewith. THE CRUSHING DEVICE The apparatus used is shown in Fig. 1 and in cross-section in Fig. 2. The material to be crushed is placed in the crushing chamber C in the steel mortar M. The mortar is 3 in. dia. by 3 in. high. Two mortars are used, one having a crushing chamber 1-in. dia. by 1/2 in. deep, with a capacity of 4 g. of quartz, the other having a crushing chamber 1 ½ in. dia. by 3/4 in. deep, with a capacity of 12 g. of quartz. The position of the mortar is adjusted by means of three centering screws A. The steel plunger P, which fits neatly into the chamber, is placed on top of the material to be crushed. Plungers of different lengths were tried and as they were found to give practically identical results the length adopted was equal to the depth of the chamber.

Jan 1, 1928

The Development of Research and Quality Control in the Modern Steel Plant. By Leo F. Rein-artz. (Metals Technology, April 1943) Blast Furnace and Raw Materials Essential Considerations in the Design of Blast Furnaces. By A. L. Foell. (,Metals Technology, December 1942) Results Obtained from Surveys of Gas at Furnace Tops. By James M. Stapleton. (Metals Technology, January 1943) Physical Aspects of the Dust Catcher, Gas Washer and Precipitator on No. 3 Furnace at Carrie. By C. P. Clingerman and C. J. FleiscH. (Metals Technology, January 1943) Slag Control by Introduction of Flux through Blast-furnace Tuyeres. By Carl G. Hogberg (Metals Technology, January 1943) The Electrical Conductivity of Molten Blast-furnace Slags. By A. E. MaRtin and GerRard Derge. (Metals Technology, August 1943) Some Physical Characteristics of By-product Coke for Blast Furnaces. By CEarles C. Russell and MichaeL Perch. (Metals Technology, December 19+2) Pyrometry at the Coke Oven. By Robert B. Sosman. (Metals Technology, December 1942) Calcination Rates and Sizing of Blast-furnace Flux. By T. L. Joseph, H. M. Beatty and Gust Ritsianes. (Metals Technology, December 1942) The Low-temperature Gaseous Reduction of a Magnetite. By M. C. Udy and C. H. Lorig. (Metals Technology, October 1942) Steelmaking Problems of Total Operation in Steelmaking. By William C. Marshall and Frank G. Norris. (Metals Technology, April 1943) Silicon-oxygen Equilibria in Liquid Iron, By C. A. ZapFFe and C. E. Sims. (Metals Technology, September 1942) Equilibria of Liquid Iron and Simple Basic and Acid Slags in a Rolating Induction Furnace. By C. R. Taylor and John Chipman. (Metals Technology, September 1942) Rapid Analysis of Oxygen in Molten Iron and Steel. By Gerhard DeRGe. (Metals Technology, January 1943) Silver Chloride as a Medium for Study of Ingot Structures. By Karl L. Fetters and Margaret Dienes. (Metals Technology, August 1943)

Jan 1, 1943

The Development of Research and Quality Control in the Modern Steel Plant. By Leo F. Rein-artz. (Metals Technology, April 1943) Blast Furnace and Raw Materials Essential Considerations in the Design of Blast Furnaces. By A. L. Foell. (,Metals Technology, December 1942) Results Obtained from Surveys of Gas at Furnace Tops. By James M. Stapleton. (Metals Technology, January 1943) Physical Aspects of the Dust Catcher, Gas Washer and Precipitator on No. 3 Furnace at Carrie. By C. P. Clingerman and C. J. FleiscH. (Metals Technology, January 1943) Slag Control by Introduction of Flux through Blast-furnace Tuyeres. By Carl G. Hogberg (Metals Technology, January 1943) The Electrical Conductivity of Molten Blast-furnace Slags. By A. E. MaRtin and GerRard Derge. (Metals Technology, August 1943) Some Physical Characteristics of By-product Coke for Blast Furnaces. By CEarles C. Russell and MichaeL Perch. (Metals Technology, December 19+2) Pyrometry at the Coke Oven. By Robert B. Sosman. (Metals Technology, December 1942) Calcination Rates and Sizing of Blast-furnace Flux. By T. L. Joseph, H. M. Beatty and Gust Ritsianes. (Metals Technology, December 1942) The Low-temperature Gaseous Reduction of a Magnetite. By M. C. Udy and C. H. Lorig. (Metals Technology, October 1942) Steelmaking Problems of Total Operation in Steelmaking. By William C. Marshall and Frank G. Norris. (Metals Technology, April 1943) Silicon-oxygen Equilibria in Liquid Iron, By C. A. ZapFFe and C. E. Sims. (Metals Technology, September 1942) Equilibria of Liquid Iron and Simple Basic and Acid Slags in a Rolating Induction Furnace. By C. R. Taylor and John Chipman. (Metals Technology, September 1942) Rapid Analysis of Oxygen in Molten Iron and Steel. By Gerhard DeRGe. (Metals Technology, January 1943) Silver Chloride as a Medium for Study of Ingot Structures. By Karl L. Fetters and Margaret Dienes. (Metals Technology, August 1943)

Jan 1, 1943

The following is an incomplete list of members and guests who called at Institute headquarters during the period July 10, 1919, to Aug. 10, 1919. Howard C. Arnold, Washington, Pa. J. S. Lane, New York City, N. Y. L. M. Banks, Denver, Colo. H. W. Lawrie, Washington, D. C. George S. Blair, Pittsburgh, Pa. J. L. McAllen, Latouche, Alaska. Richard H. Catlett, Newark, N. J. David F. McFarland, Urbana, Ill. George L. Clark, Council Bluffs, Iowa. James F. Magee, Lancaster, Pa. Capt. Frederick S. Cook, Portland, Ore. A. G. McGregor, Warren, Ariz. John J. Croston, Atlanta, Ga. Emory M. Marshall, Santa Fe, N. M. Thomas Davis, Seattle, Wash. Benjamin L. Miller, Bethlehem, Pa. J. C. Dick, Salt Lake Cite, Utah. 2d Lieut. C. 0. Noble, U. S. Army. Chris. G. Dobson, Vancouver, B. C. Irving Perrine, Hutchinson, Kans. H. S. Emlaw, Grand Rapids, Mich. Fred S. Porter, Seattle, Washington. F. A. Fahrenwald, Cleveland, Ohio. Capt. H. R. Robbins, Peking, China Lieut. James L. Head, St. Louis, Mo. Joseph P. Ruth, Jr., Denver, Colo. A. A. Holland, Napanu, Canada. William A. Simkins, San Francisco, Calif. W. E. Hopper, Washington, D. C. T .V. Smirnoff, Siberia. Harry Hotchkin, Chicago, Ill. Harrison Souder, Cornwall, Pa. L. L. Hutchison, Tulsa., Okla. F. J. Sur, Denver, Colo. Paul S. King, Wilmington, Del. Harry Wolf, Denver, Colo. George K. Anderson, Jr., lies accepted a position as manager for Wight & Co., producers of air-cooled blast-furnace slag, at Longdale, Va. J. M. Armstrong, with the Caribbean Petroleum Co., has been transferred from Philadelphia to Maracaibo, Venezuela. Fred Sherman Baker, who has been with the Oriental Consolidated Mining Co., at Unsankinko, Chosen, Korea, is now at Columbia City, Ind. Ray J. Barber has removed from Roxbury, Mass., to New York City, and is now consulting engineer for the Roxbury Cold Mines, Inc.

Jan 9, 1919

Jan 1, 1923

Jan 1, 1923

By J. P. Hammond, C. J. McHargue

THERE have been no publications on the wire texture, on the cold-rolled sheet texture, nor on the recrystallized sheet texture of vanadium. Since it has a body-centered cubic structure, it would be expected to show strongly preferred orientations such as are found in iron' and molybdenum.' The wire textures of body-centered cubic iron,3 tungsten," molybdenum,5 antalum,6 iobium,6 and brass6 have been found to have [110] directions lying parallel to the wire axis. Wires of iron,' containing 1.95 pct V or 1.95 pct Si,7 and steel8 retain their texture upon recrystallization. Molybdenum9 and tungsttln' wires retain their texture after recrystallization at low temperatures. A [loo] recrystallization texture has been reported for mo1ybdenum9 and for a Fe-Ni alloy (53 atomic pct Ni).10 The cold-rolled sheet texture for iron,' mild steel," and molybdenum chiefly one in which the [110] directions lie parallel to the rolling direction and the (100) planes lie parallel to the rolling plane with a deviation from this position chiefly about the rolling direction as an axis. This paper presents the cold-rolled and the re-crystallized wire textures, and the cold-rolled and the recrystallized sheet textures for vanadium. The results show that the textures in vanadium are not significantly different from those reported for other body-centered cubic metals. The vanadium used in this investigation was the so-called "ductile" vanadium which has a nominal composition within the following limits:12 0, 0.05 to 0.12 pct; H, 0.001 to 0.004; N, 0.02 to 0.04; C, 0.03 to 0.07; and V, 99.8 to 99.9. The wires were formed by rolling annealed rods of 0.280 in. diam to 0.028 in., a reduction in diameter of 90 pct. The wires were then electrolytically etched to 0.005 in. diam and used as such for specimens. Annealed sheet was reduced 95 pct in thickness from 0.100 to 0.005 in. with a two-high, 4-in. diam mill using reductions no greater than 10 pct per pass. In order to avoid temperature effects, the sheet was allowed to cool between passes. X-ray specimens were made in the form of posts from the sheet. The sheet was mounted in a fixture and the edges were polished using metallographic technique. Each edge was alternately polished and etched during the last stages in order that all worked material would be removed. These post specimens were approximately square in cross-section. The specimens to be recrystallized were wrapped in tantalum foil, sealed in evacuated quartz tubes, and annealed at 1600°F. The X-ray data were obtained from transmission shots made with a 0.030 in. pinhole camera, and molybdenum radiation with a zirconium filter inserted between the specimen and film. The grain size was sufficiently small in both the cold-worked and recrystallized material to give satisfactory results with the specimens stationary. In order for the wire texture to be determined, transmission X-ray patterns were taken with the

Jan 1, 1953

Edward Halse, Puerto Berrio, Colombia, So. Amer. (communication to the Secretary*): The Taviche mining-district is generally known as " Taviches," being named from the two villages called respectively San Pedro Taviche and San Jero-nimo Taviche. It is so called by Jose G. Aguilera, in his paper on the Geographical and Geological Distribution of the Mineral Deposits of Mexico;' and in published reports by the late N. W. Rudston Read ;2 and by Juan de Dios Villarello3 The region is a large one, measuring about 24 miles long and 7 miles wide. Dr. Chance, in his interesting paper, tells us very little about the nature of the ores, and, with regard to the geology of the district, contents himself with observing that " the country, as a rule, consists of eruptive rocks; and no evidences of sedimentary strata appear near the mines." The latter part of the above statement is hardly correct. The formation is mainly

Jan 1, 1906

By AIME AIME

PRESIDENT BASSETT'S gavel called the Annual Business Meeting to order shortly after 10 a. m. on Tuesday. On motion of Eugene McAuliffe, reading of the minutes was dispensed with and Mr. Bassett read his annual report of the year's activities as follows : During the year I have visited eighteen of the twenty- seven sections, making an average of GG 2/3 per cent. The invitation to come again has always been extended, but in only one case have I been able to visit the same section twice. Chicago entertained the president twice during 1930. Mrs. Bassett accompanied me on visits to ten sections. Everywhere we have found the most cordial hospitality and a gratifying enthusiasm for the Institute. If anyone had fault to find with the management or felt dissatisfied with what was being done, it was carefully concealed. I am happy to report to you an agreeable, helpful and progressive spirit in each of the sections visited.

Jan 1, 1931

By Robert E. Sorenson

EXPLORATION for deep-seated orebodies in the Silver Belt area of the Coeur d'Alene mining district is complicated by meager surface expressions of diagnostic criteria, lack of knowledge of the significance of specific alteration phenomena, and the great expense involved in the exploration for ore shoots, the tops of which often occur near sea level elevation or below and as much as 4000 ft or more below the surface. Except for the early studies of Ransome and Calkins in 1903 and 1904,' little geological work was done in the Coeur d'Alene district for many years, and it is only during the last 15 to 20 years that complete and careful geological mapping has been applied to most of the mines in the area. Much early information, which now would prove invaluable, is lost in hundreds of miles of caved and inaccessible mine openings not mapped by mining geologists. In more recent years mining geology has become a tool of greater use in the district, and some measurable progress is being made in the accumulation of observations that are adding gradually to the knowledge of ore deposits in the district. The recognition of alteration phenomena and related features by Hoyt S. Gale3 in 1935, followed by the work of Shenon and McConnel in 1936-37,4 changed many of the concepts formerly held and opened the way for more critical study and mapping of alteration effects. Mapping of these effects has been in progress for several years but no well-organized, careful, and complete laboratory study of the alteration has been made by mining companies or by government agencies. Recently, Thomas Mitcham of Columbia University has been occupied in the collection and study of specimens carefully selected from several producing mines in the Silver Belt as well as from several prospects exhibiting alteration effects. Mr. Mitcham and the writer have discussed some of the preliminary results of his investigations, which indicate that definite and interesting material is forthcoming from his studies. Work of this kind, aided by careful observation by district geologists, should advance the knowledge of the environment of Silver Belt ore shoots and establish additional criteria for recognizing meager shallow expressions of deep-lying orebodies. Structural details in the Silver Belt area are extremely difficult to decipher on the surface because the area is almost completely covered by a deep mantle of surface debris and soil. A dense growth of small trees and buck brush adds to a geologist's difficulties. Often large areas reveal only scattered small outcrops with great intervening areas where the underlying formations must be deduced from small altered rock fragments. Some considerable success in obtaining surface information has come from bulldozer roads and cuts in selected areas. As this type of work receives more attention, knowledge of the surface expressions of formations, alterations, faulting, and veining is expanding and giving more reliable information to guide deeper development. Lack of diagnostic marker beds in the district contributes to a geologist's difficulties in determining fault displacements. In the Silver Belt, known commercally important sulphide orebodies commonly are associated with siderite and quartz gangue. Some of the veins at shallow horizons above productive ore shoots are composed of quartz with light-colored carbonate minerals such as calcite, ferrocalcite, ferrodolomite, ankerite, and carbonates with variable amounts of manganese. The relation of these carbonates to commercial orebodies is a problem offering possibilities for research. Shallow exposures of veins composed of quartz and the light-colored carbonates, often with some associated barite, grade into quartz and siderite veins at deeper horizons. The vertical range of these carbonates has been partially established for some veins, but no reliable method has been devised for predicting where the change in a vein may take place. Careful observation and analysis of carbonates may make it possible to predict more closely where the change to siderite may be expected. In 1926 Shannon5 pointed out some of the characteristics of the carbonate veins of the district and included a few chemical analyses. Some of the Silver Belt ore shoots have small commercial outcrops, and very shallow development of some properties has led to the opening of small ore shoots." Several small ore shoots developed at shallow depths have not been explored at deep horizons, and some important ore shoots with no commercially significant exposures at shallow horizons have been developed. The greatest problem of the mining geologist working in the Silver Belt area is to find the all-important link between the very meager shallow expressions of mineralization and the rich ore shoots that may be found below. To develop criteria for use in the recognition of the weak upper expression of ore shoots, the experience of past development programs must be relied upon heavily. The investment of more than a million dollars in the exploration for such ore shoots requires some reliable criteria if these ore shoots are to be found. Management needs some assurance that the risk involved is justified by well-developed and acceptable geological inference. The richness of some of the ore shoots found thus far has contributed greatly to the justification for a bold approach, but many negative results of blind exploration programs would lead eventually to extreme caution on the part of management. Fortunately, recent experiences of development programs have been quite successful. It is hoped that added knowledge. of the environment of Silver Belt ore shoots will contribute greatly to the sureness of approach toward their development. The Coeur d'Alene mining district is located in the panhandle of Idaho in Shoshone County. The population of the county is either employed in the

Jan 1, 1952

By Charles R. Keyes

I. Introductory,.......... 185 II. Hypotheses oF the Origin of OzaRk Ores..... 186 1. General Considerations........ 186 2. Schmidt-Leonhard and Gage View...... 187 3. Jenney Opinion.......... 187 4. Posepny Idea,.......... 188 5. Winslow-Robertson Hypothesis....... 188 6. Branner Proposition......... 189 7. Keyes Statement.......... 189 8. Van Hise-Bain Theory........ 190 III. Requirements of an Adequate WoRking-Hypothesis,... 190 IV. GeneRal Geotectonics of the OzaRk Region.... 192 1. Salient Aspects.......... 192 2. Geologic Formations......... 192 3. Character of Faulting...192 4. Extent of Flexing......... 193 5. Unconformity Inequalities....195 6. Warping of Strata...195 V. Classes of Ore-Deposits... 196 VI. Vadose ORe-ConcentRation,........ 197 VII. GeogRaphic DistRibution of the Ore-Bodies,... 199 VIII. Relation of ORe-Deposit to Geologic Structure... 201 1. General Occurrence of Ore-Bodies in Basins.... 201 2. Deposits of the Central Missouri District..... 203 3. Deposits of the Southwestern Missouri District.... 203 4. Deposits of the Northern Arkansas District... 305 5. Deposits of the Southeastern Missouri District.... 206 6. Synclinal Ore-Deposits of Other Districts.....207 7. Significance of Ore-Troughs in Prospecting... 209 8. Origin of the so-called Synclines,...210 9. Significance of the Cross-Bars of Joplin..... 213 10. Relation of Ore-Run to Ancient Relief-Features,... 215 IX. Direction of GRound-Water Circulation..... 216 X. VeRtical Range of Workable Ore-Bodies,... 218 XI. Oscillation of Ground-WateR Level...... 219 XII. Relations of Ore-Bodies to Lithoclasic Features,.. 220 XIII. PRimaRy Source of Ore-Materials,...... 220 XIV. Zone of Ore-Enrichment,......... 222

Jan 1, 1910

By Cornelius F. Kelley

EVERY man connected with the mining industry should take a significant pride in the fact that he belongs to an industry and to a profession that, from the beginning, has been constructive. The miner digs his ore and he gives the metal to art, to industry, and to commerce. The nature of our business is destructive only in that we deal with a wasting asset. That should be a source of great pride to those who belong to the profession. But unfortunately, the product of our mines, our smelters, and our re- fineries does not always go to constructive purposes. There are times when, in the administration of the affairs of men, our product chiefly goes to purposes which are destructive. When we look upon the panorama of horror that is being enacted throughout the world today, we wonder whether any effort toward the development of civilization and culture and education and well-being has been worthwhile. We are appalled to see the things that have been developed, through the application of science, toward progress and efficiency, now used for the catastrophic destruction of those things which are the most valuable that man has built. We must find hope that this is but an episodic thing; that it must, in the infinite wisdom of the Almighty, usher in a period of peace and progress, of civilization and development that will make man's existence upon earth worthwhile.

Jan 1, 1941

By R. E. Holmes, T. W. Leland

The solution to the unsteady-state mass- and heat-transfer equations describing the adsorption of a dilute component from a gas stream flowing through a packed bed is readily applicable to the design of hydrocarbon recovery units. The solution to these equations depends on the assumption of a linear equilibrium equation to relate concentrations on the surface to concentrations in the gas. This assumption is shown to be justifiable for components which are very dilute in the gas stream. This approach permits the prediction of the effects of bed shape and size, cycle time, and gas mass velocity on the recovery of each component. It also allows the time and gas flow rate needed for regeneration to be determined. The equations involve a constant for each component and another constant characterized by the type of adsorbent. These constants must be evaluated from operating data. Values of these constants determined for silica gel are presented. This paper points out the type of experitrrental data needed for a thorough design of hydrocarbon adsorption units. INTRODUCTION The growing importance of adsorption processes to recover hydrocarbons from natural-gas streams has created an urgent need for better methods to design and predict the performance of these processes. Since the original use of solid adsorbents in natural-gas processing was for dehydration, most of the current design methods for hydrocarbon recovery re extensions of those developed earlier for dehydration. These methods are based on an adsorptivity or bed loading factor defined as the amount of a particular component adsorbed per unit weight or per unit volume of the packed bed. The recovery of a given component is then expressed as an empirical function of its adsorptivity on a given adsorbent. In spite of the simplicity and initial utility of these methods, they are not completely satisfactory in that they do not predict the effect of the dimensions of the bed in relation to flow rate and cycle time, and do not predict the distribution of various components along the length of the bed. It is possible, however, to make a considerable improvement in the design of these processes by applying the basic equations of mass and heat transfer applicable to gases containing small concentrations of adsorbing components flowing through granular beds. These equations have been developed and solved by Anzelius,' Furnas,% nd Hougen and Marshall." where G = mass velocity of the inert constituents (assumed to be methane), lb/hr-sq ft, y = weight of an adsorbing component in the gas per unit weight of inert, lb of a given constituent per lb of methane, x = bed length, ft, p, = packed bed density, lb/cu ft, P, = gas density, Ib/cu ft, f = void fraction in the bed, t = time, hours, and w = weight of a given component adsorbed per unit weight of adsorbate free solid, Ib/lb pure adsorbent. The term on the left side of Eq. 1 represents the flow rate per unit bed volume of a component entering less the flow rate per unit bed volume of that component leaving the differential bed length. The terms on the right side represent, respectively, the accumulation rates per unit bed volume on the solid and in the gas phase within the differential bed section. The last term is negligible for this application since pgfv is quite small in comparison with p, and G. The partial differential is determined by the mass-transfer rate between gas and solid in the differential section.

By Meissner, C. A.

THE tendency all over Europe, just as it is with us, is to go to the use of turbines for new construction or replacement of old steam or even gas engines. 'The lower construction cost and the lower operating cost, when they can have high steam temperatures and pressures, together with their efficiency, is the cause of this change to turbines, both high and low pressure. The present trend is to equip plants with modern, efficient steam boilers, turbines, etc., and gradually work into high-pressure superheated steam equipment to accomplish a saving. One company has just completed a 375 to 400 lb., 700 deg. superheated steam installation and turbo-blowers with this end in view. Some of our new steam plants are using 350 lb. working pressure.

Jan 1, 1928

By EDWARHD HALSE

Discussion of the Paper of Dr. H. M. Chance, presented at the Lake Superior Meeting, September, 1904. EDWARD HALSE, Puerto Berrio, Colombia, So. Amer. (communication to the Secretary*) : The Taviche mining-district is generally known as a Taviches," being named from the two villages called respectively San Pedro Taviche and San Jeronimo Taviche. It is so called by José G. Aguilera, in his paper on the Geographical and Geological Distribution of the Mineral Deposits of Mexico;' and in published reports by the late N. W. Rudston Read ;2 and by Juan de Dios Villarello.3 The region is a large one, measuring about 24 miles long and 7 miles wide. Dr. Chance, in his interesting paper, tells us very little about the nature of the ores, and, with regard to the geology of the district, contents himself with observing that ? the country, as a rule, consists of eruptive rocks; and no evidences of sedimentary strata appear near the mines.? The latter part of the above statement is hardly correct. The formation is mainly eruptive, being hornblende-audesite of Tertiary age, which is limited on the east by the calcareous (Cretaceous) formation, and on the west by the Huronian rocks of Ocotlan. Limestone is seen close to the Santa Càtarina mine, at the northern end of the region. In the surface-working known as La Cueva, a little northeast of San Pedro, limestone forms the eastern wall of the deposit which consists of spots (moscas) of pyrargyrite in white opaque or transparent quartz. Ill one place the ore is associated with stibnite, and the quartz frequently exhibts a

Sep 1, 1905

By IRVING H. WENTIVORTII

(New York Meeting, February, 1912.) THE little town of San Nicolás, Tamaulipas, Mexico, lies approximately 60 miles east of Linares, situated in the State of Nuevo Leon, and 150 miles SE. of Monterey, as shown in the sketch-map. Fig. 1. The place is reached from Monterey by the Tampico train as far as Linares, a distance of 92 miles, and then by coach the rest of the way. It is situated in a narrow valley between low hills, the houses forming one main street and a plaza. It is peopled by about 500 inhabitants. The climate is temperate, the thermometer ranging from 90° in summer to a few degrees below freezing-point in winter; but this severe weather only lasts a day or two at a time, when the " northers " blow. There are no streams in the vicinity, but water sufficient for the use of the people is obtained from wells. The rainfall is about the same as that in the rest of NE. Mexico. The rainy months are July, August, and September. The rest of the year is practically dry, with an occasional showery day or two during the winter, when a " norther " is blowing. Timber is abundant in many localities. There are two varieties of oak, besides mesquite, ebony, "maguira," "patol," and a number of other kinds of trees indigenous to this region. I. HISTORY. On the discovery of the silver-lead hearing veins occurring in this district, the mining-camp of San Nicolás was founded in 1767 by the Spaniards, and numerous mines were opened and worked for a distance of abort 3 miles east and 5 miles west of the town. At the western extremity and near the Carrolena mine, a small town called San Pedro was built. The ruined walls of the houses form a single street, and all is over-

Aug 1, 1912

By William P. Blake

(Canal Zone Meeting, November, 1910.) A DEPOSIT of manganese-ore near Tucson, Ariz., merits notice by reason of the peculiar form in which it occurs, and as a striking. example of ore-deposition by vadose upward capillary flow of metal-bearing solutions with concentration at the surface of the country-rock. This deposit occurs at the northern end of the Coyote mountains, about 40 miles west of Tucson, upon the outcropping beds of porphyritic rock, which appear to be partly-metamorphosed strata of volcanic tufa, probably of late Secondary or of Tertiary age. The strata dip northward at a low angle, and present a series of basset-edges in parallel lines of outcrop, east and west, facing the south and extending over many acres. Successive groups of these outcrops, from 5 to 20 ft. in breadth, are coated with oxides of manganese in lustrous black films and crusts, shining in the sunlight like polished ebony, and covering the whole surface of the rock above the soil. Seen at a little distance, these croppings look like solid ledges of massive and pure ore; but closer inspection and a few blows of the hammer reveal their true nature as a superficial coating allied in origin to the blackened shining surface of rocks exposed in desert-regions, familiarly known as " desert paint" or "desert varnish,"' similar to the phenomena described by me in a former paper, but much thicker and heavier. * By reason of the death of the distinguished author, this communication, probably his last communication to technical literature, is published without revision of the proofs by him. A term first given y G. K. Gilbert. See Rocks, Rock-Weathering, and Soil; by George P. Merrill, p. 256 (New York, 1897). Superficial Blackening and Discoloration of Rocks, Especially in Desert Regions, Trans., xxxv., 371 (1905).

Sep 1, 1910

By J. W. Mills

This paper's aim is to demonstrate, by reviewing findings and conclusions of earlier authors and through recording and interpreting the outcome of recent laboratory study of the ores, that the ores around the Gem stocks are metamorphosed equivalents of common siderite-sulfide ores far from the stocks, as was first proposed by Hershey (1912, 1913). That is, all the ores probably have the Precambrian age of 1250 million years reported by Long et al. (1960). Those near the Gem stocks, however, were extensively metamorphosed in Cretaceous time during the emplacement of stocks so their resemblance and relation to other veins in the district are camouflaged.

Jan 1, 1985

By Ralph Hultgren, Bernard York, David W. Mitchell

It is a well-known fact that magnesium-alloy castings are apt to be coarse grained if the melt is not superheated several hundred degrees above the melting point before casting. (The casting temperature varies according to the shape of the mold. A typical casting temperature is perhaps 1400°F.) British practice is to heat to 900°C. (1650°F.) for 15 min., cool rapidly to casting temperature, and cast.' In Germany superheating is carried out at 850' to 900°C. (1560° to I650°F.) depending on the amount of scrap used. It is stated that further refinement will be obtained by prolonging the period of superheating or by increasing the superheat temperature to 950°C. (I740°F.).2 In the United States superheating is carried out at 1600' to 1700°F. (871' to 927°C.), perhaps even higher in some places. It is stated that superheating effects are found as low as 1500°F. (816°C.), but several hours are required.3 These commercial treatments lead to grain sizes in sand castings that may vary from 4 to 8 grains per sq. mm.! in heavy sections and from 60 to IOO in 1/2-in. sections to perhaps 380 in thin sections. It is also generally known that the refining effect of superheating is lost if the melt is held for some time at lower temperatures before casting. Aside from these very qualitative statements, there is little to be found in the literature as to the effect of temperature and time of superheat on the final grain size. Because of the uncertainty of these factors, the Office of Production Research and Development of the War Production Board placed a research contract with the University of California, supervised by the War Metallurgy Committee. This research, which was done under the "Restricted" Project NRC-550, is the basis of this paper, which has been released for publication by the O.P.R.D. The material studied was an alloy prepared from carbothermic magnesium. The temperatures required for grain refinement proved to be widely different from those used in practice, as described in the statements in the first paragraph. This difference is attributed to the fact that the magnesium in the specimens was of carbothermic origin instead of the electrolytic magnesium in common use. Materials and Methods The magnesium alloy studied was one of the most popular sand-casting alloys, with a nominal composition of 9 Per cent aluminum, 2 per cent zinc, and 0.1 per cent (minimum) manganese and the balance magnesium. This is designated

Jan 1, 1945

By A. M. Gaudin, F. W. Bowdish

MINERAL dressing is an industrial art concerned with the treatment and separation of solids suspended in fluids. Knowledge and evaluation of the area of solid-fluid interface is important in all cases except those involving only large pieces of solid. In fact, many problems relating to comminution, to flotation, to thickening and classification, could be dealt with more rationally if the interfacial area were known. A number of methods have been proposed for the measurement of the surface of certain finely divided solids. Among them are methods using rate of dissolution of the solid,7 its magnetic remanence,3 the turbidity of its suspension,8 and the character of the size distribution of the material.9 The first two are limited to one mineralogical species per sample; the third has certain optical limitations, especially for mineral mixtures, and the fourth is based on an extrapolation of uncertain validity. The need of a better and more general method of surface determination has long been felt, therefore. The method of P. H. Emmett,4 based upon the low-temperature adsorption of vapors, appears to fulfill this need. This method consists in determining the amount of nitrogen that is adsorbed by a given sample of solid at the temperature of boiling nitrogen. The more surface there is on the solid-both internal and external-the more nitrogen is abstracted. In actual operation, the method is somewhat less simple than has been stated so far, in that the nitrogen is adsorbed in an incomplete layer, the completeness and thickness of the layer being related to the pressure of the nitrogen in contact with the sample .2 This circumstance makes it necessary to determine the nitrogen adsorption for three or more values of the nitrogen pressure. APPARATUS In the Richards Mineral Dressing Laboratories an Emmett apparatus has been built and tested (Figs. 1 and 2). A mechanical vacuum pump B and a mercury diffusion pump A work in series to give a high vacuum. The sample, placed in bulb D, can be evacuated by this pump train by suitable operation of the stopcocks in the glass tubing that connects the various parts of the apparatus. C is a McLeod gauge, used to ascertain the order of magnitude of the vacuum obtained, and not for accurate pressure measurements. Pressure measurements are made in the mercury manometer F and gas-volume measurements in the gas burette E. Gases are stored in flasks L (nitrogen) and K (helium), arranged so that definite quantities of these gases can be introduced into

Jan 1, 1944