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By Theodore Marvin

FOLLOWING the receipt of questionnaires from many parts of the world, the Aviation Committee is completing a review of the use of aviation in mining and petroleum operations. The summary of this study should be available at the 1937 Annual Meeting in New York City, at which time several papers will be presented on specific application of aerial geologizing. From the reports received, there is little question that this air branch of mining is here to stay. Of course, the transportation of personnel arid material continues to merit attention but it is in the division of aerial geologizing that flying is finding its widest, most technical application.

Jan 1, 1937

By B. W. Roberts, V. A. Phillips

A copper alloy containing- 25.5 at, pct Zn and 19.0 at. pct Ni, which was previously found to show an anoma1old.s hardening effect on quenching- from 600 "C and aging- at 400oc, has now been examined by neutron diffraction. No evidence of long-range order was found. The aged sample showed diffuse scattering- consistent with clustering. The anomalous hardening effect is now attributed to lattice strains caused by clustering rather than (long-range) order hardening. SOLID-solution Cu-Ni-Zn alloys (the commercial 'nickel silvers") have been reported to show anomalies in: change of resistivity on cold working,1-6 temperature coefficient of resistance,2-12 resistivity at low temperatures,13,14 parameter (vs temperature),2"4 calorimetric data,2,4 specific heat,15,16 dilation,2-4 and elastic modulus.17 The structure responsible for the anomalies is produced by annealing typically near 400°C and is rather loosely referred to as the ('K-Zustands" (K state), a term coined by Thomas1' who apparently meant simply that the arrangement of atoms on the sites deviated from that expected statistically. Thomas proposed that the K state occurred in a variety of (solid-solution) alloys such as Cu-Ni-Zn, Ni-Cr, Ni-A1, Ni-Cu, Fe-A1, and Fe-Si and is recognized because its formation is strongly temperature-dependent and results in an increase in electrical resistance which can then be decreased by cold working. Later workers on ('nickel silver" have interpreted the K state variously as short-range order, long-range order. or a combination. The present work was prompted by the discovery by Phillips and Jones19 of a substantial hardening effect when an 18 pct "nickel silver" alloy which is fairly close to the Cu2NiZn composition, was reheated in the range 150" to 450 C after previously quenching from 600°C or, alternatively. was slow-cooled from 600°C or above. The phenomenon was attributed to (long-range) order hardening. Due to the similarity in the atomic scattering factors of copper. nickel, and zinc atoms, the ''nickel silvers" are unfavorable for X-ray diffraction studies aimed at detecting ordering. Nevertheless Bialas et a1.,20 using a powder sample containing 47.96 wt pct Cu, 24.03 wt pct Ni, and 27.98 wt pct Zn, slow-cooled from 400" to 200°C taking 500 hr, observed weak super lattice lines. Further unpublished work" using an anomalous dispersion X-ray technique indicates that zinc atoms are regularly ordered at the corner points of the lattice cell, while the nickel and copper atoms are statistically distributed on the remaining sites. Köster 17 also observed X-ray superlattice lines, for example, in an alloy containing 43.5 wt pct Cu, 28.6 wt pct Ni, and 27.9 wt pct Zn superimposed on the basic fcc cell with a = 3.62 kX. He proposed a Cu3Au-type superlattice with the Ll2 structure in which the A sites were statistically occupied by copper and nickel atoms and the B sites by zinc. He adds that substitution must be possible so that zinc atoms partly occupy A sites. Below about 35 pct Cu, Koster had some evidence for a CuAu-type superlattice with the Llo tetragonal fcc structure with a = 3.82 kX, c/a = 0.88 which could be preserved by quenching. This is suggested17722 to correspond to CuNiZn. While the present work was in progress Hirabaya-shi et a1.23 made an independent comprehensive neutron-diffraction study of a single crystal containing 50.05 at. pct Cu, 26.57 at. pct Ni, 0.25 at. pct Mn, 0.13 at. pct Fe, balance zinc. The presence of manganese and iron is surprising since the crystal was supposedly grown from high-purity metals. The homogenized crystal showed evidence of long-range ordering after an anneal of 5 months at about 300°C. Three possible crystal models were proposed. A curious feature of their results23 is that they could not find any neutron-diffraction evidence of ordering in a powdered polycrystalline near-stoichiometric Cu2NiZn alloy. There appears to be some essential difference between a near-stoichiometric Cu2NiZn alloy and one somewhat further off stoichiometry as used by the present authors. Thus Sato14 was able to reproduce the low-temperature resistivity anomaly reported by one of the authors13 on the present alloy if he used a similar composition, but found the normal behavior of the residual resistivity in a near-stoichiometric alloy. satol2 found that the resistivity of a cold-drawn slightly off-stoichiometric alloy increased to a maximum on isothermally annealing at 300°C and then decreased ("over-aged"). Since he could not explain this on the basis of ordering phenomenon, he proposed that zinc atoms were segregating to stacking faults (Suzuki effect) and found etching bands on the surface by replication which were attributed to the widening of faults. Sato suggested14 that the hardening effect observed by Phillips and Jones19 is partly due to the Suzuki effect. EXPERIMENTAL The starting material was 1/4-in.-diam hard-drawn rod of a commercial 18 pct "nickel silver" alloy identical with that used in a previous study by Phillips

Jan 1, 1967

By G. W. Josephson

JUDGING by the progressive atmosphere prevailing in the nonmetallic mineral industries during the past year, postwar conditions were healthful though inflationary. Demand for most industrial mineral products has been exceptionally high and many new production records were attained. Severe shortages of some commodities existed, especially building materials and fertilizers. Production costs and prices increased and profitable operation was general. Under these conditions expansion programs were the order of the day. Ample funds were available to finance the purchase of good equipment; and, as wages and other operating costs were increasing, primary emphasis was placed on attaining maximum efficiency in new installations. These efforts were hampered by shortages and slow delivery of desirable equipment, so compromises in design were often necessary. However, on the whole, production practice improved.

Jan 1, 1948

By E. W. Rouse

THE year 1936 has seen rehabilitation of many plants which had been closed or severely curtailed. The Steptoe smelter of the Nevada Consolidated Copper Co. has been transformed by a rearrangement of the flow of material and utilization of mechanical handling to a maximum. The Phelps Dodge Corp. reports the construction of newer and better reverberatories at the Copper Queen smelter, and of particular interest, a single high-pressure waste-heat boiler placed directly over the uptake. There has also been a complete reconstruction of the smelter at the Laurel Hill plant of the Nichols Copper Co.

Jan 1, 1937

By W. W. Krech, T. E. Perkins

As fractures are propagated through rocks, energy is absorbed near the extending crack tip. Apparent surface energies for several rocks have been measured by cleavage under dynamic con-ditions. At nominal crack velocities from 0.5 to 500 in (min, measurements showed that fractures propagated in discrete jumps. Calculated surface energies and moduli were relatively insensitive to nominal rate of cleavage. in another set of experiments, rocks were cleaved under high confining stresses. The rocks were submerged in low leak-off fluids which formed a filter cake on the freshly cleaved surfaces (similar to the hydraulic lracturing process). Apparent surface energies were increased substantially as the surrounding fluid pressure was increased. Moduli in bending increased significantly upon application of the first 1,000 psi but were insensitive to stress level at greater pressures. INTRODUCTION For almost 20 years, hydraulic fracturing processes have been utilized effectively to stimulate oil and gas wells. During this period, some process improvements have resulted from studies of fracture orientation, mechanics of fracturing, areas generated, conductivities of cracks, etc. Yet many questions remain concerning the conditions and pressures needed during fracture propagation. In this paper we will report additional studies of the mechanics of fracture extension. It was shown previously3 that large rock samples could be cleaved under controlled conditions so as to measure the apparent surface energy (that amount of energy absorbed per unit area of new surface created). In this paper we consider the effects of two additional factors on surface energies, viz.: (1) effect of cleavage rate and (2) effect of confining stress level. THEORY Cleavage experiments were conducted on rock samples similar to that illustrated in Fig. 1. Blocks of rock several inches wide, 2- to 3-in. thick, and up to 3 ft in length were grooved longitudinally with shallow guide slots. A crack was initiated and allowed to extend along the web as the top of the rock specimen was pulled (or pushed) apart. Auxiliary equipment permits the measurement of (1) force applied at the top, (2) separation at the top and (3) crack length. (Further experimental details will be given in the next section.) The rock beams created by the crack are considered ton be cantilever beams. The deflection (or separation of the rock beams) at any point is calculated 4,5 by the beam Eq. 1.

Jan 1, 1967

By AIME AIME

WAR undoubtedly accelerates metallurgical progress, although its most obvious effect is a tremendous waste of materials. The necessity for restrictions in normal uses of metals results in a search for substitutes or for enhanced properties that will make a limited supply last longer. An insatiable demand for more metal to be produced more quickly favors trial of new processes, new metallurgical tools, and new methods of fabrication. Greatest advance is made, of course, in practical physical and process metallurgy. Theoretical or fundamental research necessarily must take a secondary position, and is so regarded in this review. It is not that developments in theoretical physical metallurgy are lacking entirely, but, following the same trend noted in other countries as they entered war activities, attention in the U.S.A. has been shifted strongly to those developments having an immediate practical application.

Jan 1, 1943

By B. M. Larsen, J. W. Campbell

Several articles have recently been published discussing the conditions necessary for accurate measurements of temperatures in the open-hearth steel furnace. In the course of a study of refractories service conditions in steel furnaces, the present writers have taken temperatures in several open-hearth shops in the Pittsburgh district. The conclusions, as to conditions necessary for accurate measurements of temperature, are somewhat at variance with those of other investigators. The subject is closely connected both with the close control of steel-making and the prevention of overheating of the silica refractories used in roofs and walls. It is becoming more and more important to obtain furnace temperatures of fairly definitely known accuracy. At present, the most useful instrument for such measurements is the disappearing-filament type of optical pyrometer. This method of measurement has formed the basis of most other discussions on the subject and was also used by the writers. Previous Investigations In 1916, Burgess' made perhaps the first systematic series of measurements in steel furnaces. The emissivity figures of 0.40 for liquid steel and of 0.53 to 0.65 for liquid slags had been determined by the Bureau of Standards and were used by Burgess in this work. These correction factors are still being used and are regarded as fairly accurate, so that the tapping and teeming temperatures on metal streams given by Burgess should be very nearly correct. Most of his temperatures of furnace roofs and slag surfaces were taken while flames were present in the furnaces and include a few roof temperatures above 1700' C. (3100' F.).

Jan 1, 1927

By R. W. Raymond

THE sudden death of Dr. Drown, on Nov. 17, 1904, brought to multitudes the pang of personal loss. Of all those who, as students at Lafayette College, the Massachusetts Institute of Technology and Lehigh University, were brought under his influence, not one can have forgotten him, and all will now acknowledge, with an unfading gratitude, what they owe in professional equipment to his wise, clear, skillful guidance, and in character to his sympathetic, stimulating personality. Outside of this wide circle, the experts of both hemispheres will lament the departure of one who, in his department of scientific inves¬tigation, both knew what work was needed, and how to do it so that it needed not to be done again. The older members of the American Institute of Mining Engineers will remember with gratitude the part he took, as Secretary from 1873 to 1884, in promoting the interest of that organization, and in shaping the plan and policy which it has followed with such noteworthy success. And, in addition to all these (though partly included among them), there are a host of friends; who can scarcely think of the public loss by reason of their own. Thomas Messenger Drown was born March 19, 1842, at Phil¬adelphia, Pa. His parents were natives of New England; and. he was the youngest of their three sons. He received his preliminary education in the public schools and the High School of Philadelphia, from which he was graduated in 1859. Be-

Jul 1, 1905

SME's Annual Membership Report - 1961 Membership Directory

Jan 7, 1961

By R. J. Brison, W. C. Bleimeister

The International Salt Company has long been interested in finding an efficient process for the removal of impurities from rock salt, and particularly from the rock salt produced at the Detroit mine. Methods which have been used previously at the Detroit mine included both hand sorting and differential crushing in a Bradford breaker with rejection of the oversize. Neither of these methods was adequately effective. The development of a new process for removal of impurities from rock salt has been described in the preceding article." Basically, the process consists of exposure of crude rock salt to radiant heating which selectively heats the impure particles. Subsequently the heated particles are removed by adhesion to a heat sensitive-coating on a conveyor belt. This method was found to be effective in improving both the quality and appearance of rock salt by the rejection of the dark, impure particles. The first commercial unit employing the new thermoadhesive method of dry separation of minerals was installed at the Detroit mine of International Salt Company in Detroit, Mich. (Fig. l). This unit was first put into operation in March 1957. The purpose of the Detroit installation was 1) to serve as a pilot plant for evaluating the process on a commercial scale and 2) to produce marketable quantities of rock salt of improved quality and ap- pearance. The design of this plant was based on the results and information obtained from a 1-tph pilot plant at Battelle Memorial Institute. DESCRIPTION OF PLANT Location: The separation plant was installed underground near the crushing and screening plant, for this was the most suitable location from the standpoint of material handling. Furthermore, ample space was availabe at this location. Because the process requires a relatively constant temperature, the uniform year-around temperature of the mine (57°F) gave an added advantage to an underground operation. Feeding: The rock salt is conveyed to a surge bin, from which it is fed to the heating unit by a conveyor. The feed-rate control consists simply of an adjustable gate at the bottom of the surge bin. The plant may be fed either No. 1 grade of rock salt (0.279 to 0.375 in.) or No. 2 grade (0.375 to 0.500 in.) with a maximum input capacity of 500 tons per 15-hour day. Heating Unit: The heating unit (Fig. 2) consists of a panel of infrared lamps suspended inside a low-speed revolving screen. The radiant-heat panel, which is curved for most effective utilization of the heat, holds 240 infrared lamps of standard industrial type, each rated at 500 watts. The position of the panel is adjustable so that it can be placed centrally over and to within 6 in. of the salt bed on the screen. The entire heat panel is suspended by rollers in ¦ R. J. Brison and O. F. Tangel: Development of a Thermo-adhesive Method for Dry Separation of Minerals.

Jan 1, 1961

By Sydney H., Ball

ONE of the important mineral discoveries of the eighteenth century was , that of the Minas Geraes, Brazil; diamond fields. The production of this and of .other diamond discoveries in neighboring states made Brazil the premier producer of diamonds, succeeding India; its 140 years of supremacy finally passed to- South Africa- 60 years ago. Three times have diamonds contributed heavily to Portugal's somewhat checkered financial history; first in the sixteenth and seventeenth- centuries when the diamond trade of India was controlled by its citizens residing in ,Goa, later in the late eighteenth and the first 75 years of the nineteenth century when the Brazilian fields were the world's source of diamonds, and now, when the Angola diamond mines are the principal source of revenue of its colony, Portuguese West Africa. Certain phases in the history of the administration of the Brazilian field are sufficiently curious to warrant description.

Jan 1, 1929

By F. R. Hensel

The present paper describes a number of experiments with fine silver, coin silver, silver-cadmium oxide and silver-nickei-copper compacts, prepared by powder metallurgical methods. The test data are of a preliminary nature, since most of the work was exploratory. Fine Silver Eject of Compacting Pressure on Hardness and Density during Cold and Hot Pressing The cold-welding properties of silver have received considerable attention and the welding characteristics are functions of such variables as: cleanliness of metal particles (impurities and adsorbed gases), chemical nobility of particles, plasticity and hardness, particle assortment, particle shape, particle porosity, apparent density, temperature, pressure, time, recrystalliza-tion characteristics. Chemical nobility, plasticity and low temperature of recrystallization after work-hardening are responsible for the excellent low-temperature bonding properties of silver. Several series of compacts were pressed at pressures of 5, 10, 20, 30, 40, 50, 60 70 and 80 tons per square inch, at temperatures of 32°C. (room temperature), l00°, 2000, 300°, 400°, and 450°C. Silver powder of minus 325-mesh, produced by displacing silver from a nitrate solution by means of copper, was used. The density was calcuiated from accurately measured and weighed compacts. The hardness was measured on the Rockwell F scale. The investigation shows that an increase in pressure promotes a higher density and hardness regardless of pressing temperature, up to a temperature of 400° C. The pressure-density curves at various pressing temperatures are shown in Fig. I, the pressure-hardness curves at various pressing temperatures, in Fig. z. The greatest increase in both hardness and density was obtained in the pressure range of 5 to 20 tons per square inch. A compact from each series was annealed at 300°C. in air, for various lengths of time. The hardness values after annealing are shown in Table I. A minimum hardness was obtained after one hour of annealing. No change in density occurred during annealing. The maximum density was obtained at 80 tons per sq. in., and at this pressure the hardness is equal to that of hard-drawn wrought

Jan 1, 1945

By J. T. Ryan

FIGURES for the first 11 months of 1935 indicate that the total coal production of the United States for 1935 will be approximately 416,000,000 tons, or almost identical with the production figures for 1934. Bituminous production will show a gain of about six million tons, and anthracite production a loss of about the same tonnage, compared with the previous year. This does not take into account so-called "bootleg" anthracite coal amounting to approximately 5,000,000 tons. Twenty-nine years ago, in 1906, the production of coal was almost identical with this year's production. At that time, 626,000 men were employed in producing this tonnage, which took a toll of 2138 lives from accidents. In 1935, approximately 540,000 men were required to produce the same tonnage with an estimated loss of 1155 lives. This shows definite safety advancement in the industry, but even so accidents are still costing an average of 3c. a ton more than they should.

Jan 1, 1936

By HARRINCTON EMERSON

UNEMPLOYMENT is the most ominous shadow ahead of the industrial nations today. Only two great industrial countries are free from unemployment, France and the Soviet Commonwealth. In France the social unit is the family, not the individual. This has saved France. In the Soviet Commonwealth, development is proceeding so rapidly from agricultural to industrial that there is still a dearth of muscle workers in the non-agricultural enterprises. In the other industrial countries unemployment results both from acute temporary recession in industrial activities and from the rapidly increasing substitution of the machine for the man. Temporary recessions can be mitigated, alleviated by makeshifts, often ill considered. Secular recessions due to a fundamental change in the way of accomplishing physical, chemical results cannot be cured by any makeshift. There must be a period of transition. There is therefore before us the three- fold problem, immediate, prosimate and ultimate.

Jan 1, 1930

By J. J. Gilman

The dependence of ortho kink-band formation on crystal orientation, on temperature, and on the conditions at the ends of a specimen is described. Load-compression curves for crystals that kink are presented. The reversibility of ortho kinking is demonstrated, and motion of kink planes through crystals is shown. Finally, a phenomenological explanation of ortho kink-band formation is given. ORTHO compressive kink bands (Fig. la) were discovered for the case of metals by Orowan,1 and they have been discussed by Jillson2 and in some detail by Hess and Barrett." However, their history in nonmetallic crystals is considerably older. It is not known when they were first observed in mineral crystals, but descriptions of them may be found as early as 1885.* They were sometimes mistaken for twins.6 Mügge seems to have been first to realize their true nature and importance. He reviewed the knowledge of them for a wide variety of crystals: anhydrite, antimonite, kyanite, vivianite, gypsum, mica, graphite, molybdenite, barium bromide, cal-cite, sodium nitrate, and barite. Also, the "twins" observed by Bridgman7 in sapphire crystals resemble kink bands more than twins. The terms ortho and para kink bands have been coined in order to distinguish between two types of kink bands which seem to represent the same geometrical configurations, but which have different origins and sizes. Ortho kink bands are the usual type that form at low loads when zinc crystals are compressed parallel to the basal plane. Para kink bands form at much higher loads in highly deformed crystals. These terms refer to compression phenomena and are not to be confused with analogous tension phenomena such as tensile kink bands and deformation bands. Mügge described the geometry of ortho kink bands quite completely for kyanite crystals, Fig. lc. The geometry observed for cadmium by Orowan1 and for zinc by Hess and Barrett3 is very similar to that described by Mügge. (See Hess and Barrett for a complete discussion.) Mügge associated kinking with bending combined with basal slip. He pointed out that the kink angles

Jan 1, 1955

By Robert Leach

THIS paper gives a brief summary of the process of manufacture of sterling silver, and some of its more important physical properties, as observed in commercial production of rolled sheet and wire. Although papers have been published by Turner and Smith,1 Rose,2 Sperry3 and Jordan,4 there are few technical data available, and unfortunately the time allowed for the preparation of this paper has not been sufficient to make it as comprehensive as the title might indicate. ANALYSIS OF STERLING SILVER Fine or pure silver is too soft for coinage and the manufacture of articles in which strength and resistance to wear are desired. From the earliest times of which we have record, copper has been the metal generally used to harden silver. Analyses of coins and silver articles from ancient tombs show varying amounts of copper, and old Roman silver objects in the British Museum have approximately the same analysis as our sterling. The first authentic record of the establishment of a standard alloy is during the reign of Henry II in England. During the twelfth and thirteenth centuries, the people in the Eastern Provinces of Germany had a reputation for the standard and purity of their silver coinage, and it is said that Henry II employed some of these Easterlings, as they were called, to improve and standardize the English coinage, which had become debased. The peculiar standard adopted is probably accounted for by the system of weights used. A troy pound contains

Jan 1, 1928

By Basil B. Zavoico

The production of all Russian fields incressed from approsimatctly 74,000,000 bbl. during 1926-27, to approximately 83,000,000 bbl. during 1927-28. Of this amount Baku was responsible for 54,.500,000 bbl., Grozny for 25,800,000 bbl., and Emba for 1,200,000 bbl. Accordingly, the proportional importance of the Grozny oil field has been considerably increased, the present production being twice that of 1913. The most notable factor of production during 1927-28 was the importance of gushers; 40.8 per cent. of the total was thus obtained. In the Baku fields 26 per cent. of the total, and in Grozny 74.2 percent'. of the total were produced by naturally flowing wells. This may be explained by the reduction in authorizations for drilling by the central authorities, and, accordingly, the local trusts increased the production to the planned figures at the expense of the proved prolific reserves. In Baku region, the Surnkany oil field produced 36.1 per cent. of the total Baku production, or an equivalent of 53,800 bbl. per clay, the largest percentage coining from the fifth horizon. Nest year's plans call for continual development of that horizon as well as of the sixteenth horizon in the Bibi-Eibat field, which was opened lately. In the Grozny fields the New Area (Bellik) WAS responsible for 79.4 per cent. of the total production. The authorized plan for 1928-29 production calls for 92,200,000 bid., and a reasonably accurate estimate for 1932--33 production is placed at. 156,000,000 bbl., with Baku contributing 101,800,000 bbl., Grozny 44,100,000 bbl., Emba 6,200,000 bbl., Kuban 2,100,000 bbl., Saghalien Island 1,400,000 bbl., and Russian Turkestan 400,000 bbl. In connection with recent discoverices in the Baku area these figures art. quite conservative. The average production per well per day in the Baku oil fields was 49.2 bbl., in Grozny 175 bbl.; in detail, Surakany oil field averaged 250 bbl., and the New Area in Grozny 514 bbl. per day. New completions in all Baku fields averaged 264 bbl. per day, and in Grozny 970 bbl. pel. day. These figures show a considerable progress in the technical developnlent of all fields, compared even with the prerevolution figures, since all the mprovements are noted in the fields that arc over 30 years old.

Jan 1, 1929

By H. H. Moss

OXYACETYLENE .cutting has experienced rapid development in the last few years and greater advances and expansion and broader application may be expected in the immediate future. Marked changes in cutting practice may be expected as a result of the advances in metallurgical science that have produced special alloy steels with properties requiring different cutting techniques than for ordinary low-carbon steels. Much current attention is being directed to those problems of modified cutting practices. Cutting has thus ceased to be merely a shaping problem. It is rapidly coming to have a predominantly metallurgical aspect. The problem is no longer how to cut a given shape, but how to cut a given steel. The answer

Jan 1, 1936

By Herbert Clark Hoover, Lou Henry Hoover

SINCE the Sixth Book has described the iron tools, the vessels and the machines used in mink, this Book will describe the methods of assaying1 ores; because it is desirable to first test them in order that the material mined may be advantageously smelted, or that the dross may be purged away and the metal made pure. Although writers have mentioned such tests, yet none of them have set down the directions for performing them, wherefore it is no wonder that those who come later have written nothing on the subject. By tests of this kind miners can determine with certainty whether ores contain any metal in them or not ; or if it has already been indicated that the ore contains one or more metals, the tests show whether it is much or little ; the miners also ascertain by such tests the method by which the metal can be separated from that part of the ore devoid of it ; and further, by these tests, they determine that part in which there is much metal from that part in which there is little. Unless these tests have been carefully applied before the metals are melted out, the ore cannot be smelted without great loss to the owners, for the parts which do not easily melt in the fire carry the metals off with them or consume them. In the last case, they pass off with the fumes ; in the other case they are mixed with the slag and furnace accretions, and in such event the owners lose the labour which they have spent in preparing the furnaces and the crucibles, and further, it is necessary for them to incur fresh expenditure for fluxes and other things. Metals, when they have been melted out, are usually assayed in order that we may ascertain what pro- portion of silver is in a centumpondium of copper or lead, or what quantity of gold is in one libra of silver ; and, on the other hand, what proportion of copper or lead is contained in a centumpondium of silver, or what quantity of silver is contained in one libra of gold. And from this we can calculate whether it will be worth while to separate the precious metals from the base metals, or not. Further, a test of this kind shows whether coins are good or are debased ; and readily detects silver, if the coiners have mixed more than is lawful with the gold ; or copper, if the coiners have alloyed with the gold or silver more of it than is allowable. I will explain all these methods with the utmost care that I can.

Jan 1, 1950

By R. Schuhmann

Distribution of material in the fine sizes of a comminution product generally is well represented by the empirical equation' y = 100 (x/k)a [1] in which y — cumulative percent finer, x = particle size, a -= distribution modulus, and k = size modulus. Charles3 found that the energy consumption in comminution is usefully expressed by another empirical relation, E = Ak(1-D) [2] in which E = energy input per unit volume of material, A = a constant, k = size modulus based on Eq. 1, and n = a constant; (1-n) is the slope of a plot of log E vs log k. Holmes3 has presented energy equations similar to Eq. 2. The constants a and n in Eqs. 1 and 2 have been shown to depend both on the nature of the material and on the comminuting device. Moreover, Charles showed that within experimental error a and n are a — n+1 = 0 [3] Combining Eqs. 2 and 3, E = A k-a [4] In the first sections of this article it is shown that the energy equation, Eq. 4, can be derived directly from the size distribution equation for the fine sizes, Eq. 1. The derivations are made without assuming any of the specific relationships between energy and particle size which have been common in previous literature. For comminution processes in which Eqs. 1 and 4 adequately represent the experimental data, the constant A in Eq. 4 is found to be a simple and useful inverse measure of grindability. That is, A is the energy consumption per unit volume of comminution product finer than unit size as determined from the straight line portion of the log-log plot of the size distribution. These considerations all lead to a unifying hypothesis of comminution mechanism from which both Eq. 1 and Eq. 4 can be derived. Finally, it is pointed out that this hypothesis raises serious questions as to the significance of the Rittinger hypothesis, the Kick hypothesis, and other theories in which energy numbers are systematically assigned to various size fractions of comminution products in order to calculate theoretical energy consumptions. Derivation of the Energy Equation from the Size Distribution Equation: For simplicity, consider the comminution of 100 volumes of a feed material of relatively uniform particle size. The comminution process may be considered as the summation of many individual and independent comminution events. The extent of comminution is most easily expressed as the number of comminution events, z. In the first derivation, the key assumption is that the characteristics of the comminution events in a given crushing or grinding process are substantially constant and do not vary with the progress of the comminution process. Accordingly the characteristics of an average comminution event may be defined. In one such event, a quantity of energy $E is applied to a single particle of size f and volume $v. The crushing of this particle produces fine particles with a size distribution similar to that given by Eq. 1: yw=100(x/ka)a0 [51 In this equation yo, a0, and k0 are used to characterize the product of an individual comminution event rather than the product of the comminution process as a whole. In using Eq. 5, we will not be concerned with values of x close to the feed size f and will therefore assume only that the equation is applicable to the finest sizes of the material. In 100 volumes of total product, the actual volume of product finer than x from a single comminution event, or dy, is given by The total volume of material below size x, resulting from z events, is then given by y = z(dy) =z(dv) (x/ka)a0 =" Eq. 7 reduces to Eq. 1 when we let a, = a and [8a] z =100/dv (ka/k )1 or k = ka (zdv/100)-1/a [8b] Eq. 8a shows that the distribution modulus of the comminution product is the same as for the product of an individual comminution event. Eq. 8b shows how the size modulus of the comminution product k varies with the extent of comminution as measured by the number of events, z, or as measured by the fraction of the feed actually subjected to com- minution1 zdv/100. The energy input to 100 volumes of total feed, or 100E, is the sum of the energy inputs for all the comminution events: 100E =z (dE) [9]

Jan 1, 1961