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Mr. Brown : .That part of the Standard Company's plant which has been added since the publication of Mr. Leggett's paper, and is described in mine, renders the single-phase, alternating system, which Mr. Hale has called " unelastic," much more elastic than it had been. The original plant at Bodie was substantially the same as the Telluride plant mentioned in his paper. The machines came from the same shops, and were practically the same; but while the Telluride Company has changed completely to a polyphase system, the Standard Company has retained its original plant, but has belted on a directcurrent generator at the receiving end, thereby converting the water-power into electricity, electricity into power, the power into electricity, and finally again electricity into power for use in the mines. This is a roundabout course, to be sure, but it shows that there are possibilities even in the out-of-date single-phase system. The only point perhaps, that deserves particular notice with respect to the hoist is the fact that the rheostat, or starting-resistance, was not built originally

Jan 1, 1897

By E. S. Bardwell

THE reverberatory copper-refining furnaces at the Great Falls Reduction Dept. of the Anaconda Copper Mining Co. have used successively, as fuel, lump coal on grates, pulverized coal, oil and natural gas. In no other plant, so far as can be ascertained, has such a variety of fuels been used. This fact affords a unique opportunity for comparing the relative efficiency obtained with these several fuels under nearly identical conditions. FURNACES The present furnace refinery at Great Falls was placed in operation in April, 1916. The original installation consisted of two furnaces, each with hearths 36 by 14 ft. and provided with fire boxes 10 by 12 ft. for firing lump coal on grates. These furnaces had air-cooled sand bottoms and chrome-brick side walls both above and below the metal line. The roofs were of 12-in. silica brick. Each furnace was provided with a waste-heat boiler of approximately 400 boiler-hp. capacity. We soon found that chrome brick was very unsatisfactory as sidewall material because of its excessive spalling. At the first opportunity the furnaces were rebuilt, using magnesite brick below the metal line and silica brick from the metal line to the roof. At the same time the thickness of the side walls was increased, thus decreasing the width of the hearth to 13 ft. At about this time also, the thickness of the furnace roofs was increased from 12 to 15 in. No further changes occurred in furnace design until 1922, when the use of lump coal on grates was abandoned in favor of pulverized coal.

Jan 1, 1932

By E. DeGolyer

THE petroleum production of the world for 1924 again passed the billion-barrel mark, as it did in 1923. A preliminary estimate of production is 1,016,000,000 bbl., a decrease of 1,100,000 bbl., or less than 1 per cent. from the 1,017,100,000 bbl. produced in 1923, the year of greatest production. FIG. 1.-TOTAL WORLD AND UNITED STATES PRODUCTION. Production in the United States decreased 18,500,000 bbl., the. first decrease in yearly production since 1906. Mexican production decreased almost 10,000,000 bbl. Russia, Persia, Roumania, Venezuela, and Peru increased their production by an amount almost great enough to offset the decline in the United States and Mexico. The decline in the production in the United States and Mexico was considerably less than anticipated by leading geologists, economists, and statisticians; nor did the increase in consumption entirely meet the expectations of estimators. Early in the year, the statistical department of one of the most important oil companies forecast a draft on stocks, from an excess of demand over supply, of about 80,000,000 bbl. Instead of decreasing our stocks, they were increased by about 33,000,000 barrels.

Jan 3, 1925

By Rudolf Kudlich

The problem of eliminating the hazards of hoisting in mines has been with us since the industry passed its earliest stages, when coal and ore could be won from surface working and tunnels. At first, safety devices were introduced as means of decreasing the amount of labor necessary to produce the mineral, or to increase the amount that could be obtained from a certain opening. For example, crude ladders replaced winding footpaths or steps cut into the walls of the pit or shaft, decreasing the distance it was necessary to carry the product to the surface and eliminating, to some extent, the hazard introduced by the precarious footing afforded by such paths and steps. Latcr, instead of being carried from the pit on the backs of men, the product was hoisted in buckets or baskets on a rope passing over a pulley or around a windlass. Thus the capacity of the pit was considerably increased, and the hazard due to making many trips up and down the shaft was eliminated. From such beginnings accident prevention in mine hoisting advanced with the importance of the industry, until at present hoisting compares favorably with other branches of the mining industry with reference to safe practices. As in the other branches, this progress has been accomplished along two general lines—by legislation, rules, and education, and by the installation of safety devices. Though due credit must be given the former, it is not so satisfactory as the latter. Legislation, to be effective, requires a policing and inspection system to guarantee enforcement, such as we cannot hope to inaugurate. Rules may be satisfactory so long as the employer controls the labor market, and dismissal or some other form of discipline is an effective means of insuring obedience to the rules; but where labor demand is in excess of the supply, or where labor organizations are in control, such measures are not effective. An educational campaign will draw attention to hazards and may awaken a desire to avoid accidents by exercising the proper care. It is necessary, therefore, to place our reliance mainly on mechanical devices to prevent accidents, and to depend as little as possible on laws,

Jan 1, 1923

By Paul L. Goddard, Alfred G. Hoyl, William R. Sirola

A good place to look for elephants is in elephant country, and old mining districts are certainly elephant country as far as minerals are concerned. In many areas probably more ore is still in the ground than has been taken out. The old timers were good miners and hard workers and when they left ore behind, it was usually for good reason; but many an old mining district has been revived by new approaches to old problems, taking advantage of new techniques and new equipment. One of these is the Front Range mineral belt of Colorado, which has produced minerals for the past 100 years through the ups and downs of mineral prices and the general economy. Gold, silver, copper, lead, and zinc have been found in abundance in the complex sulfide veins of the area. Between Idaho Springs and Central City lie several strong veins which have been mined successfully in the past. The two strongest of these veins, striking northeast-southwest, (Lake-Bald Eagle), and northwest-southeast, (Crown Point-Belman) , and dipping northeast and northwest, respectively, intersect in a flat X near the head of Virginia Canyon. From the lowest drainage of the area, Clear Creek Canyon, the old timers drove the Central, or Big Five, haulage-drainage tunnel due north. It intersects the two veins 8460 ft from the portal and 1670 ft below the surface. The two veins were mined successfully at the surface and at the tunnel level. Without an opening to the surface at the in- side end of the tunnel, ventilating became very difficult as the stopes were opened up, and mining ceased in 1929. Vertically, 1200 to 1600 ft of virgin ground remains in the veins.

Jan 6, 1959

By J. Donovan Jacobs

An underground excavation project usually is a highly organized complex of different but interrelated construction activities. It is the whole effort, including the necessary tools, which will be referred to as the System. Tunnel-driving and shaft-sinking operations are among the most systematic of construction efforts. Systems are not new in the performance of construction. It is the Systems Concept which seems only recently to have been discovered and made the subject of much study and discussion. HISTORICAL From the seventeenth century, when explosives were first utilized for rock excavation, until the successful application of the rotary-head continuous tunneler in this decade, the cyclical drill-blast-muck-support method has been standard tunnel-driving procedure throughout the world. Whatever improvements occurred were the result of development of better tools for performing the various operations of the cycle. The electric locomotive replaced the mule and permitted the use of larger muck cars. The steam drill, which ended the day of the double jack, was itself quickly made obsolete when compressed air replaced steam as the source of drilling energy. Power shovels were introduced to save the time and money involved in the hand-loading of excavated materials. A cubic yard of rock tunnel muck can be excavated today for just half the man-hours of labor required in 1948. Developments over 20 years which cumulatively have resulted in this economy include: drifter drills mounted on hydraulically controlled booms and positioners; tungsten-car- bide-tipped bits; long feed shells on the drifters, making it possible to drill the full depth of a round without changing steel; better designed,

Jan 1, 1970

By Persifor Frazer

A classification of natural objects is usually based either upon some fundamental and permanent attribute of the thing itself (as in the case of scientific classifications), or it embraces one or more generalizations convenient for use in ordinary life. Thus, it suffices for the statistician to know that so many tons of fish are annually taken by our fishermen, and that they realize so many thousands of dollars, whereas to the student of natural history the anatomy, habits, and relationships of the animals are of chief interest, as settling their respective places in the scale of animate nature. Many different classifications of coals have been attempted, as one would naturally anticipate from the immense extent of the coal trade, and the different localities whence the supply was derived. The English divisions were prevalent up to the date of the publication of the last geological survey of the State, except so far as they were modified by local designations. Indeed, Rogers' classifications made very little alteration in the English nomenclature, as may be seen by comparing the tables given below. To commence with the different kinds mentioned in Ure's Dictionary of Arts, Manufactures and Mines of 1845 : " 1. Cubical Coal.—Black, shining, compact, moderately hard and easily frangible. Comes out in rectangular masses, of which the

Jan 1, 1879

By Rudolf Kudlich

The problem of eliminating the hazards of hoisting in mines has been with us since the industry passed its earliest stages, when coal and ore could be won from surface working and tunnels. At first, safety devices were introduced as means of decreasing the amount of labor necessary to produce the mineral, or to increase the amount that could be obtained from a certain opening. For example, crude ladders replaced winding footpaths or steps cut into the walls of the pit or shaft, decreasing the distance it was necessary to carry the product to the surface and eliminating, to some extent, the hazard introduced by the precarious footing afforded by such paths and steps. Latcr, instead of being carried from the pit on the backs of men, the product was hoisted in buckets or baskets on a rope passing over a pulley or around a windlass. Thus the capacity of the pit was considerably increased, and the hazard due to making many trips up and down the shaft was eliminated. From such beginnings accident prevention in mine hoisting advanced with the importance of the industry, until at present hoisting compares favorably with other branches of the mining industry with reference to safe practices. As in the other branches, this progress has been accomplished along two general lines—by legislation, rules, and education, and by the installation of safety devices. Though due credit must be given the former, it is not so satisfactory as the latter. Legislation, to be effective, requires a policing and inspection system to guarantee enforcement, such as we cannot hope to inaugurate. Rules may be satisfactory so long as the employer controls the labor market, and dismissal or some other form of discipline is an effective means of insuring obedience to the rules; but where labor demand is in excess of the supply, or where labor organizations are in control, such measures are not effective. An educational campaign will draw attention to hazards and may awaken a desire to avoid accidents by exercising the proper care. It is necessary, therefore, to place our reliance mainly on mechanical devices to prevent accidents, and to depend as little as possible on laws,

Jan 1, 1923

By C. DeWitt Smith

"It just looks like everything is doing fine but humans," wrote Will Rogers fifty years ago. "Animals are having a great year, grass was never higher, flowers were never more in bloom, trees are throwing out an abundance of shade for us to loaf under. Everything the Lord has a hand in is going great, but the minute you notice anything that is in any way under the supervision of man, why, it's cockeyed." Do these words from two generations ago apply to oil shale? The United States has been blessed with deposits that can yield synthetic crude oil at a cost competitive with natural crude oil-under present economic conditions and with existing technology. Yet, the oil shale program is cockeyed because of the artificial obstacles that have been placed in its path "under the supervision of man." But more about this later. For the moment, let's focus on...

Jan 10, 1974

By R. E. Barnes

An overall view of the perlite industry is concisely presented. The geology, mining, milling, processing, and applications of perlite, as well as the present status of the perlite industry are treated. Perlite, in strict petrological usage, describes a specific variety of volcanic glass in which strain, incident to cooling, yielded a concentric structure of fracturing which may be visible either to the naked eye or under a microscope. In commercial usage, the term perlite includes any naturally occurring acidic glass of volcanic origin that will expand when heated to a suitable temperature. The name perlite is a derivation of perlstein which originally defined "certain glassy rocks (hyaloliparites, hyalo-rhyolites) with numerous concentric cracks, from the fancied resemblance of broken out fragments to pearls."1 While perlite has been known to geologists for many years, it was not until 1941, while investigating perlite for use in enamel, that an assayer in Superior, Ariz., noted the unusual expansion characteristics of the ore. Further investigations were delayed until following World War II when many small plants were built and experimentation in the treatment and uses of perlite began. The Perlite Inst. was organized in 1949 to promote the development of the new industry, establish commercial standards through research, and to explore new uses and markets. The Institute, located in New York, represents some 50 producers in the U.S., Canada, Australia, England, France, Germany, Greece, Japan, Mexico, and New Zealand. In 1949, 71,l002 short tons of crude perlite were produced, sold or used by U. S. producers, and this figure increased to 325,0003 short tons by 1959. Such a rate of increase indicates the rapid and continuing growth of the perlite industry. GEOLOGY Perlite ore in its crude form has been found in seven of the mountainous western states, since un-devitrified siliceous volcanic rocks are limited to this section of the U. S. Commercially operated perlite deposits are normally of Eocene and Oli-gocene age.4 These deposits are often several hundred feet thick and may extend over hundreds of acres. In 1959, 13 companies in six states produced crude perlite, although the output in New Mexico comprised 79 pct of the total domestic crude output. Other states in order of their production were: Nevada, Arizona, California, Colorado, and Utah.5 Foreign deposits of perlite which are either producing or under exploration are Australia, Canada, Greece, Hungary,6 Iceland, Ireland, Japan, Mexico, New Zealand, and Sardinia. The ore may exhibit a variety of characteristics depending partially on its water content and eruption history and may range through many shades from black to white. While these characteristics may vary slightly among deposits, perlite ore from a particular source is normally quite uniform. Available chemical analyses of perlites from a large sampling of domestic deposits were recently assembled by the Technical Committee of Perlite Institute and are presented in Table I. While the ranges given do not apply to a particular perlite, they are an indication of the chemical analysis which may be expected from any presently commercially operated deposit. The specific gravity of the perlite ore ranges between 2.2 and 2.4, and its bulk density when crushed and sized is 75 to 90 Ib per cu ft. MINING AND MILLING Perlite ore is quarried from open pits by conventional power equipment, although blasting has been occasionally employed. The rock is then stock-piled until needed. While the milling of perlite may seem a simple process compared to that required for basic metals, or even other nonmetals, the need for accurate control of particle size becomes extremely important in further processing. The first step in this operation is the primary crusher, which is normally a jaw crusher. Following crushing, the material is dried, if necessary, in a rotary dryer and conveyed to a secondary grinder which may be a rod mill, hammer-mill, or cone crusher. However, the crushing characteristics of the perlite, caused by incipient cooling fractures, requires it be removed from the grinding operation once it is reduced to the required size so as to prevent overgrinding. Following the grinding operations, various size screens are used to separate the ore according to particle sizes required for particular uses. Most plants use two or more stages of crushing with perhaps four stages of screening.

Jan 1, 1961

By John L. Boardman

The Anaconda company has never indulged in any employee activities at Butte which might be termed paternalistic, but it has exerted a vast amount of effort in care of its employees during working hours. The reason for this policy is not lack of interest or that the company does not feel the effect of employees' activities while they are "off the job"; it is that the company and the city of Butte have grown up together and each has been adequate in its own sphere, the company in providing employment at the highest possible wage and the city in providing housing, sanitation, commercial services, medical services, schools, churches, amusements and entertainments. The one exception to this independence between the company and the community is the Butte Water Co., which is a wholly owned subsidiary of the Anaconda Copper Mining Co. Mention of this relationship is made here because the water supply of such a city as Butte is one of the principal factors in determining the health of the people. Very early in the development of the Anaconda company an adequate and dependable water supply for the operations became necessary, therefore the company took over this important community function. So well has this activity worked out that during the whole period of time covered, in which the company has expanded to become practically the sole mine operator and the community has grown from a small mining camp to the status of a modern city, there has been no shortage of water or any outbreak of water-borne, epidemic disease. Conditions Leading to Organized Safety Effort A brief sketch of conditions in Butte prior to 1912 is necessary to an understanding of the reasons for placing accident prevention on an organized basis. As early as the year 1884 there were a large number of small independent mining operations depending principally upon the production of silver, although even then copper was becoming prominent in the value of total production for the district. The Butte camp was then just emerging from the log cabin stage to that of a modern city.

Jan 1, 1940

By W. M. Weigel

The rapid advance, during recent years, in the manufacture of articles that have been in common use for generations and the development of new materials entering into appliances and devices unheard of fifty years ago have created a demand for some of the more common non-metallic minerals. To supply this demand there has quietly developed a branch of the mining industry of which little is known by most mining engineers —the mineral-filler industry. In this paper, and generally in the trade, the term mineral filler is applied to a mineral used in its natural state after mechanical preparation only (such as grinding, milling and washing), without undergoing any chemical change and without exerting any chemical action on the substance with which it is incorporated. The consumption of mineral fillers is confined chiefly to large manufacturing centers in the Eastern and Northern Statcs. Where available, materials originating near the place of consumption are used, as most fillers bring a comparatively low price and, frequently, the freight may equal the cost of the finished filler at the mine. The Southern States have abundant deposits of non-metallic minerals suitable for fillers, which supply the manufacturing industries in adjacent states. Many of these deposits are equal to, or superior, in quality to those mined in the North, but they can not compete with them because of the freight rates. The mineral-filler industry has felt the present depression, but it has suffered less than most mining industries, for as a rule the mills are simple, the overhead expenses are low, and the labor is entirely local and can revert to farm work when the plant closes down. Many other deposits in the southern district will undoubtedly be developed when business revives and freight rates are adjusted. Most of the non-metallic mines are small and the tonnage handled is low in comparison with the tonnage involved in modern large-scale mining of coal, iron, copper, etc. On the other hand, at nearly all non-metallic

Jan 1, 1923

By J. B. Austin, R. L. Rickett

Measurements of the rate of decomposition of austenite at constant temperature are commonly represented by plotting the percentage transformed on linear coordinates against time on either a linear or a logarithmic scale, a method that yields a curve that in shape resembles an integral sign (Fig. 1). A graph of this kind is not always convenient because extrapolation to the beginning or end of the transformation, or even intebrpolation, may be uncertain unless there are a large number of observations, which seldom happens; furthermore, the degree of consistency of a set of measurements is difficult to judge from such a curve. It is desirable therefore to find some mode of plotting, or even better to find a standard variety of graph paper, that gives a straight line instead of the integral shape. The straight line has many advantages; the number of readings required to fix the position of the curve is greatly reduced, interpolatiorr is easy and rapid, extrapolation can be carried out with greater confidence and, finally, the consistency of the measurements is readily estimated from the scatter of the points. The last advantage is particularly valuable when the data are obtained by direct microscopic examination alone, because they are influenced by the skill of the observer in estimating the relative size of areas, possibly also by undetected inhomogeneity of the specimen. A search for ways of representing the observations as a straight line yielded two methods which are described in this paper. The paper also includes an account of some interesting relations brought to light in applying these methods to the available experimental data. Usually the best way to derive such a method of plotting is to base it on established principles of chemistry and physics, as has been done, for example, for the temperature variation of the equilibrium constant of a chemical reaction. But so little is known of the mechanism of the decomposition of austenite, and so little is available in the way of well established background for changes of this kind, that it is simpler to rely upon purely empirical means. The general plan therefore is to study existing data with a view to finding some function of the direct observations that will

Jan 1, 1939

By A. E. Outerbridge

I had the honor to present to the American Institute of Mining Engineers at the Pittsburg meeting, February, 1896, a paper having the foregoing title, in which I said : " It has generally been accepted as a fact that cast-iron, under the influence of repeated shocks, becomes brittle, and will finally break under a blow which otherwise it would have withstood. It will probably surprise metallurgists, therefore, to learn that experiment disproves the supposed fact, and establishes exactly its opposite. " The result of about a thousand tests of bars of cast-iron of all grades, from the softest foundry mixtures to the strongest car-wheel metal, enables me to assert with confidence that, within limits, cast-iron is materially strengthened by subjection to repeated shocks or blows." Three tables were appended showing increase of strength

Jan 1, 1905

By W. M. Weigel

The rapid advance, during recent years, in the manufacture of articles that have been in common use for generations and the development of new materials entering into appliances and devices unheard of fifty years ago have created a demand for some of the more common non-metallic minerals. To supply this demand there has quietly developed a branch of the mining industry of which little is known by most mining engineers —the mineral-filler industry. In this paper, and generally in the trade, the term mineral filler is applied to a mineral used in its natural state after mechanical preparation only (such as grinding, milling and washing), without undergoing any chemical change and without exerting any chemical action on the substance with which it is incorporated. The consumption of mineral fillers is confined chiefly to large manufacturing centers in the Eastern and Northern Statcs. Where available, materials originating near the place of consumption are used, as most fillers bring a comparatively low price and, frequently, the freight may equal the cost of the finished filler at the mine. The Southern States have abundant deposits of non-metallic minerals suitable for fillers, which supply the manufacturing industries in adjacent states. Many of these deposits are equal to, or superior, in quality to those mined in the North, but they can not compete with them because of the freight rates. The mineral-filler industry has felt the present depression, but it has suffered less than most mining industries, for as a rule the mills are simple, the overhead expenses are low, and the labor is entirely local and can revert to farm work when the plant closes down. Many other deposits in the southern district will undoubtedly be developed when business revives and freight rates are adjusted. Most of the non-metallic mines are small and the tonnage handled is low in comparison with the tonnage involved in modern large-scale mining of coal, iron, copper, etc. On the other hand, at nearly all non-metallic

Jan 1, 1923

By J. B. Austin, R. L. Rickett

Measurements of the rate of decomposition of austenite at constant temperature are commonly represented by plotting the percentage transformed on linear coordinates against time on either a linear or a logarithmic scale, a method that yields a curve that in shape resembles an integral sign (Fig. 1). A graph of this kind is not always convenient because extrapolation to the beginning or end of the transformation, or even intebrpolation, may be uncertain unless there are a large number of observations, which seldom happens; furthermore, the degree of consistency of a set of measurements is difficult to judge from such a curve. It is desirable therefore to find some mode of plotting, or even better to find a standard variety of graph paper, that gives a straight line instead of the integral shape. The straight line has many advantages; the number of readings required to fix the position of the curve is greatly reduced, interpolatiorr is easy and rapid, extrapolation can be carried out with greater confidence and, finally, the consistency of the measurements is readily estimated from the scatter of the points. The last advantage is particularly valuable when the data are obtained by direct microscopic examination alone, because they are influenced by the skill of the observer in estimating the relative size of areas, possibly also by undetected inhomogeneity of the specimen. A search for ways of representing the observations as a straight line yielded two methods which are described in this paper. The paper also includes an account of some interesting relations brought to light in applying these methods to the available experimental data. Usually the best way to derive such a method of plotting is to base it on established principles of chemistry and physics, as has been done, for example, for the temperature variation of the equilibrium constant of a chemical reaction. But so little is known of the mechanism of the decomposition of austenite, and so little is available in the way of well established background for changes of this kind, that it is simpler to rely upon purely empirical means. The general plan therefore is to study existing data with a view to finding some function of the direct observations that will

Jan 1, 1939

By John L. Boardman

The Anaconda company has never indulged in any employee activities at Butte which might be termed paternalistic, but it has exerted a vast amount of effort in care of its employees during working hours. The reason for this policy is not lack of interest or that the company does not feel the effect of employees' activities while they are "off the job"; it is that the company and the city of Butte have grown up together and each has been adequate in its own sphere, the company in providing employment at the highest possible wage and the city in providing housing, sanitation, commercial services, medical services, schools, churches, amusements and entertainments. The one exception to this independence between the company and the community is the Butte Water Co., which is a wholly owned subsidiary of the Anaconda Copper Mining Co. Mention of this relationship is made here because the water supply of such a city as Butte is one of the principal factors in determining the health of the people. Very early in the development of the Anaconda company an adequate and dependable water supply for the operations became necessary, therefore the company took over this important community function. So well has this activity worked out that during the whole period of time covered, in which the company has expanded to become practically the sole mine operator and the community has grown from a small mining camp to the status of a modern city, there has been no shortage of water or any outbreak of water-borne, epidemic disease. Conditions Leading to Organized Safety Effort A brief sketch of conditions in Butte prior to 1912 is necessary to an understanding of the reasons for placing accident prevention on an organized basis. As early as the year 1884 there were a large number of small independent mining operations depending principally upon the production of silver, although even then copper was becoming prominent in the value of total production for the district. The Butte camp was then just emerging from the log cabin stage to that of a modern city.

Jan 1, 1940

By H. S. Munroe

AN elaborate discussion under this heading formed a chapter in one of the reports made by Professor Raymond as Commissioner of Mining Statistics.* In a subsequent report- was printed a paper, by Mr. William Main, Jr., of Columbia, South Carolina, containing a theoretical investigation into the effect of the velocity of impact on the effective ditty of stamps. A visit to the Lake Superior copper region last summer suggested an inquiry into the relative efficiency and economy of the enormous steam stamps of the copper-mills, as compared with the results obtained with the cant and tappet stamps commonly used in the West. The atmospheric stamp used at the Phoenix Mill promised to add interest to the inquiry, as giving an example of unusually high speed, this stamp making 160 drops per minute. In introducing his subject Dr. Raymond makes the following remarks, which are quite apropos of the present investigation : "In considering the economical application of stamping machinery, we meet, at- the beginning, with serious difficulties in obtaining accurate data for comparison. The weight and fall of stamps vary as the shoes and dies wear out; and this may lead to a change of speed also. Moreover, defects in engines, boilers, or machinery for the transmission of power, may occasion serious losses, which cannot fairly be charged to the arrangements of the stamps proper. Again, the capacity of stamp-mills is directly dependent, in some degree, upon the nature and extent of discharge, fineness of screens, and other peculiarities of the battery. Finally the hardness and tenacity of the rock crushed varies so much that comparisons between different localities cannot be implicitly trusted. The safest experiments are those made in the same mill, by changing first one and then another condition of working; but this is seldom possible for such * Mineral Resources West of the Rocky Mountains, 1871, p. 380. †- Mineral Resources West of the Rocky Mountains,, 1873, p. 345.

Jan 1, 1881

By Arthur Tauber, Horst Kedesdy

FERRITES are sintered metallic oxides of the spinel structure type1 and belong to the class of soft ferromagnetic materials. Similar to a ceramic, they can be formed and fired to a dense body, exhibiting a high electrical volume resistivity ranging from 10 90 10' ohm-cm as compared with 10-6 hm-cm for some of the metallic magnetic materials. This high resistivity, with resulting low eddy current losses, finds special application at high frequencies. The dispersive susceptibility of ferrites at microwave frequencies has also led to many applications in this field. Where high resistivity with high permeability is desirable, ferrites are used in low frequency applications. During the last few years ferrites exhibiting rectangular hysteresis loops have been developed for computer and magnetic memory systems. The general formula for ferrites is MeFe2O4 where Me is a divalent metal ion such as Ni, Zn, Mg, Mn, Cu, Cd, and Fe. Only two of these ferrites are nonferromagnetic, namely, those with Zn and Cd. Solid solutions can be formed between different ferrites, and it is of interest to note that solid solutions of a ferromagnetic ferrite with a nonferromagnetic ferrite yield much better magnetic materials than the basic ferrite body. In general, it can be said that the solid solution formation between ferrites has widened the field of ferrite synthesis and has led to methods of preparing materials with a large variety of magnetic properties. During the last two decades the synthesis of ferromagnetic oxides has been the object of extensive research, but commercial production has been started only within the last ten years. Along with more fundamental studies, there remains the never- ending task of developing ways to realize the optimum characteristics of materials in large-scale production. Ordinarily, to produce a ferrite material it is necessary for the constituent oxides to be mixed intimately, pressed, and then fired at temperatures above 1000°C. Ferrite Synthesis: Formation of a basic ferrite by solid state reaction from Fe,O, and a monoxide such as NiO, under normal atmospheric conditions, is governed by a progressive diffusion of cations between adjacent particles of the constituents. Firing temperature, furnace atmosphere, and cooling can vary the magnetic properties, however. If, for example, a dioxide, a sesquioxide, or an oxide of the Me0 type is substituted for the monoxide, the reaction mechanism becomes more complex and extremely dependent on atmospheric conditions and firing cycles. For this reason reproduction often

Jan 1, 1958

By H. S. Munroe

As elaborate discussion under this heading formed a chapter in one of the reports made by Professor Raymond as Commissioner of Mining Statistics." In a subsequent report? was printed a paper., by Mr. William Main, Jr., of Columbia, South Carolina, containing a theoretical investigation into the effect of the velocity of impact on the effective ditty of stamps. A visit to the Lake Superior copper region last summer suggested an inquiry into the relative efficiency and economy of the enormous steam stamps of the copper-mills, as compared with the results obtained with the cam and tappet stamps commonly used in the West. The atmospheric stomp used at the Phoenix Mill promised to add interest to the inquiry, as giving an example of unusually high speed, this stamp making 160 drops per minute. In introducing his subject Dr. Raymond makes the following remarks, which are quite apropos of the present investigation: "In considering the economical application of stamping machinery, we meet, at the beginning, with serious difficulties in obtaining accurate data for comparison. The weight and fall of stamps vary as the shoes and dies wear out; and this may lead to a change of speed also. Moreover, defects in engines, boilers, or machinery for the transmission of power, may occasion serious losses, which cannot fairly be charged to the arrangements of the stamps proper. Again, the capacity of stamp-mills is directly dependent, in some degree, upon the nature and extent of discharge, fineness of screens, and other peculiarities of the battery. Finally the hardness and tenacity of the rock crushed varies so much that comparisons between different localities cannot be implicitly trusted. The safest experiments are those made in the same mill, by changing first one arid then another condition of working; but this is seldom possible for such

Jan 1, 1881