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By Frank Firmstone

In a paper read at the meeting in Cleveland, Ohio, in 1875,* I showed that as a result of changing from open-topped to close-topped furnaces at the Glendon Iron Works, there had been a decided falling off in regularity of working, which we attributed to the very different distribution of the materials in the new method of filling. Subsequent experience has, on the whole, confirmed the opinions then expressed, and in 1881 we decided to try the modification of the Langen charger, shown on the accompanying drawings, thinking by its use to approximate to the distribution obtained by dumping the barrows at six equidistant points in the circumference of the open-topped furnaces. The top of the furnace is closed by a ring-shaped " bell," as we still call it, the outside of which is cylindrical and rests by the turned lower edge on the bored seat of a " loose ring," supported by the lower part of the hopper. The inside of the bell is an inverted frustrum of a cone, the central opening in which is closed by a cylindrical plug, which is prolonged into a pipe to carry off the gas.? This center-plug is connected by rods and chains to sectors on the ends of a forked lever, to the other end of which is attached, by a wire rope, the piston-rod of the blast-cylinder used in opening the top. The rods connected to the center-plug pass loosely through the apexes of triangular frames, to the other angles of which the bell is attached; it thus being suspended by four points when the top is open. When the materials are dumped out of the barrows into the hopper, a part is thrown over the crest of the bell into the space between it

Jan 1, 1885

By Franklin H. Allison

The influence of cobalt and nickel on the properties of steel might be readily expected to be very similar. The two elements occupy close and somewhat unusual positions in the periodic table, their chemical behavior and compounds are so completely analogous and their various physical properties, including the ferro-magnetic characteristic, show such 3 remarkable correspondence, that there is no doubt of a strong resemblance existing between these two metals. However, the variety of properties that are obtained from steel is due largely to the fact that the element iron possesses allotropic forms. Alloying elements that affect these allot ropic forms, or alter the nature of the allotropic changes, exert a profound influence on the resulting steel. In the case of nickel and cobalt, although these elements are very similar chemically and physically, it is found that they differ distinctly in their individual effects on the critical points of iron. Both nickel and cobalt form a series of homogeneous solid solutions with iron at temperatures above 1500" F. The difference in their behavior does not occur until changes begin to take place in the solid state below this temperature. An inspection of the respective thermal equilibrium diagrams at the lower temperatures makes the opposite effects of nickel and cobalt clearly evident. Effect of Nickel and Cobalt in Binary Alloys with Iron The binary diagram of iron-nickel has been investigated by a number of workers. The lower temperature portion in Fig. 1 is reconstructed from the data of D. and H, Hanson.1 The diagram of iron-cobalt, shown in Fig. 2, is taken from the work of Ruer and Kaneko.2 Masumoto3 has recently discovered a lower critical point in cobalt and this has been added to the diagram. In both diagrams the space lattice structures as determined by Andrews4 have been included. It is interesting to note

Jan 1, 1927

By Harry Seltz, J. C. DeHaven

InteRmetallic compounds are formed in many binary metal systems. Some compounds are stable to their melting points, and others decompose at lower transition temperatures. Even those of the first class are dissociated in the liquid state, as indicated by the continuous form of their solubility curves at their melting points1. While the lattice structures of some of these compounds have been determined, their thermodynamic properties have not been investigated. In this paper is described the determination of the free energy and heat of formation of the compound CdSb, which is of the first class mentioned above, melting congruently at 455' C. This compound shows a rhombic structure, and the lengths of the edges of the elementary cell containing four molecules are: a = 6.52, b = 8.60, c = 4.16 A.' There are three possible methods of determining the free energy of formation of a compound of this type. The first method, applying the third law of thermodynamics, requires the measurement of its heat capacity preferably to liquid hydrogen temperatures, and a calorimetric determination of its heat of formation. The second method involves the study of the equilibrium of the compound in some gas reaction, such as: CdSb + CO² = CdO + CO + Sb From the known free energies of formation of CdO, CO² and CO the free energy of formation of CdSb could be calculated. The third method measures the electromotive force of a galvanic cell in which the cell reaction is the reversible formation of the compound from the elements. The first method is generally applicable, but requires elaborate experimental equipment. The second method can not be used for compounds melting at low temperatures, owing to the difficulty in establishing equilibrium. The electromotive force method, therefore, seemed to offer

Jan 1, 1935

By J. C. DeHaven, Harry Seltz

InteRmetallic compounds are formed in many binary metal systems. Some compounds are stable to their melting points, and others decompose at lower transition temperatures. Even those of the first class are dissociated in the liquid state, as indicated by the continuous form of their solubility curves at their melting points1. While the lattice structures of some of these compounds have been determined, their thermodynamic properties have not been investigated. In this paper is described the determination of the free energy and heat of formation of the compound CdSb, which is of the first class mentioned above, melting congruently at 455' C. This compound shows a rhombic structure, and the lengths of the edges of the elementary cell containing four molecules are: a = 6.52, b = 8.60, c = 4.16 A.' There are three possible methods of determining the free energy of formation of a compound of this type. The first method, applying the third law of thermodynamics, requires the measurement of its heat capacity preferably to liquid hydrogen temperatures, and a calorimetric determination of its heat of formation. The second method involves the study of the equilibrium of the compound in some gas reaction, such as: CdSb + CO² = CdO + CO + Sb From the known free energies of formation of CdO, CO² and CO the free energy of formation of CdSb could be calculated. The third method measures the electromotive force of a galvanic cell in which the cell reaction is the reversible formation of the compound from the elements. The first method is generally applicable, but requires elaborate experimental equipment. The second method can not be used for compounds melting at low temperatures, owing to the difficulty in establishing equilibrium. The electromotive force method, therefore, seemed to offer

Jan 1, 1935

By George A. Bell

THE mine and milling plant of Demonstration Gold Mines, Ltd., is near the city limits of Baguio, Mt. Province, P. I. The mine road connects with the main highway to Manila. The nearest railway point is near sea level, approximately 40 miles distant. The Baguio district is very mountainous and has one of the heaviest rainfalls in the world. It is therefore difficult to maintain roads or to impound tailings and mine dumps. All supplies are trucked into the district direct from Manila or the nearest railway point, which means uncertain deliveries and high freight rates. Installation of equipment is difficult and costly. The average elevation at the mine is 4000 ft. and the climatic conditions are ideal except for a three months rainy season. The company generates its own power for mining and milling operations with three 400-hp. Ruston Diesel engines direct connected to 250-kw. General Electric alternating current generators. Labor conditions have been excellent, although at present social security laws are causing some unrest. Labor receives a higher average wage rate in this district than other labor in the Islands. The company also furnishes free living quarters, hospitalization and work- men's compensation. Taxation has been reasonable up to the present time, but some of the new mining legislation may make it difficult to operate and pay dividends. The future depends largely upon the continuation of $35 gold and the political outcome in the Islands. HISTORY The Demonstration ore body was worked by the Igorots for many years, as evidenced by old stopes and fill encountered in present operations. Attention of Americans was first attracted soon after the Spanish- American war. During the building of the Benguet road to Baguio, the engineers and foreman became interested in the geology of the district.

Jan 1, 1939

By John J. Reed

This paper was prepared as a supplement to the general review by Dr. N. G. W. Cook. His analysis of the problem in terms of the strain energy involved in making the excavation is excellent. It will contribute much towards a clearer understanding of rock behavior and control. Several of the practical applications described herein can be directly related to Dr. Cook's theories and conclusions, and are based on the very same principles. CONTROLLED BLASTING IN ROCK EXCAVATION Generally speaking, the natural rock is a relatively strong and competent structural material, if we conserve its inherent good properties and perhaps reinforce its weak spots. The difficulty often lies in blasting out the tunnel or chamber without damaging the walls and roof we wish to have remain afterwards. Much progress has been made in the last five years in better understanding the controlled excavation of rock. The specialized techniques known as smooth wall blasting and presplit blasting have now developed from the status of curiosities of rock excavation to the point where these techniques are specified in contracts drawn up for such rock excavation projects as tunnels, underground pourer houses, etc. These techniques have been well described and discussed in previous publications; there is no need to reiterate here. It might be well to point out that recent research has demonstrated the effect that inherent rock stress may have on presplitting in certain directions. Material can be presplit most readily parallel to the direction of maximum compressive stress, and this may not always be in the direction desired. Inherent rock stress measurements by stress relief over coring, etc., may have important value in deciding how to best presplit proposed excavations. In addition, recent work at the Colorado School of Mines has demonstrated the feasibility of con-

Jan 1, 1967

By F. Weinberg

INTEREST is currently being directed toward grain boundary morphologies in zinc in terms of grain boundary facetingl and grain boundary energies.' Some years ago the present author attempted to measure grain boundary energies in 99.999 pct purity Zn as a function of boundary angle, using the standard procedure of measuring equilibrium angles of the boundary traces at triple points. This followed an investigation he carried out on preferential melting of |H (112) Fig. 1—Electron transmission micrograph of a stacking fault, grain boundary intersection in copper. GRAIN BOUNDARY STACKING FAULT Fig. 2—Schematic representation of the intersection of Fig. 1, indicating inclination angles 0 and trace angles $. specimens were prepared by the Bollman technique in an electrolyte of 70 pct methanol, 30 pct HNO3 main-tained at -30°C. The interfacial free energy of the high angle grain boundary and of the stacking fault is assumed to be thermodynamically equivalent to the corresponding in-terfacial tensions. In terms of the true dihedral angles & between the intersecting interfaces, the equilibrium of interfacial tensions in the direction parallel to the stacking fault yields: ysF = -ygb(cos F1+ cos ±cosF2) Here, ysF is the stacking fault free energy and ygb is the grain boundary free energy, assumed equal on both sides of the intersection. Forces acting normal to the grain boundary, of the form ??gb/?F,l are assumed negligible as the grain boundary remains straight for a considerable distance on either side of the intersection. The micrograph of Fig. 1 may actually consist of several closely spaced stacking faults on the same slip plane. The actual point of intersection between the grain boundary and the first stacking fault, and the equilibrium configuration of the intersection, should not be affected by the presence of the other faults, as

Jan 1, 1970

By Wilbur E. Sanders

At some period during the operation of metalliferous and other commercially valuable mineral-deposits in connection with their underground mining, when the developments therein have become so extensive that their description is tedious and confusing, some scheme for naming or numbering the various workings and their parts is necessary for convenience of reference. A simple and symmetrical yet expansive system of classification must be devised, one that is capable of being extended to cover all possible exigencies and conditions of future operations within the property. Such a scheme, properly arranged, greatly simplifies communication between the various departments of the mining business, as, for instance, between the administrative and the operating departments of the concern, and is of the greatest assistance to the officers of the mine in enabling them to locate and describe particular points and parts of workings and specific kinds of work. Again, in the proper segregation and differentiation of mine-accounts, when they are carried out with that detail which will furnish ready information concerning the cost of a particular piece of work, or the various items and totals of expense connected with the development, operation and repair of each or all of the mine-workings, some such method of clesignatioi~ becomes a necessity. Moreover, such a plan is acl- mirably adapted to the needs of the mining engineer, who, in connection with his reports upon mining-properties, is sometimes required, in his descriptions of certain blocks of ore, to locate lists of assays of samples taken from many and various places, and to designate workings and parts of workings that are located in different parts of the mine, sometimes at points wide apart. To write out in full a sufficient description of any particular

Jan 1, 1907

By R. L. Brown, A. C. Fieldner

Committee it supports pioneering research on the development of a coal-burning gas turbine and through the Mining Development Committee it promotes research on a new type of continuous mining machine that operates without using explosives. Other organizations have contributed major publications on fundamental and applied coal research in the last two decades, including the Minerals Industries Experiment Station of Pennsylvania State College, the Illinois Geological Survey and University of Illinois, the University of West Virginia, the University of Michigan, the University of Alabama, the University of North Dakota, the Massachusetts Institute of Technology, the Koppers Company, the U. S. Bureau of Mines, and, in recent years, the Institute of Gas Technology. Engineering development work, which is included in the overall estimate of $20,000,000, is conducted largely by manufacturers of equipment, and this portion of the estimate is difficult to gage. It represents a large proportion of the estimate and probably is too small rather than too large. For example, the development of mobile coal-loading machines and continuous mining machines, outstanding in recent mining research, undoubtedly involved a high cost. Coal Mining From an economic point of view, the greatest research development in the coal industry obviously has been the growing degree of mechanization in mining. The percentage of underground-mined bituminous-coal output mechanically loaded has risen from 3 pct in 1926 to 67 pct in 1949. Coal operators and equipment , manufacturers have united in designing machinery. Loading machines of large capacity and astonishing flexibility are in common use. Shaking conveyors transport coal from producing faces to transfer points from which it may be carried long distances underground and on the surface; and in many mines rubber-tired shuttle cars carry the coal from the loader to the

Jan 1, 1952

By Frederick Tickell

PETROLEUM engineers are displaying considerable interest in those fundamental properties of matter and energy that control the phenomena of oil and gas production. The subject is a difficult one to investigate by laboratory experiments for two reasons: (1) it is impossible to reproduce in the laboratory the scale of forces and dimensions that exist in the underground reservoir; (2) if we attempt to scale down the dimensions we are unable to reduce all proportionally. It is as if we tried to construct a model blast furnace for the reduction of iron ore, and reduced all lineal dimensions. We should find that the interstices between the miniature chunks of ore would not .permit rapid transfer of gases, that combustion and heat transfer would not take place as in the full size furnace and that, in short, the contraption would not work. Just so, when we attempt to make a reduced scale oil field we find we must have, not only miniature reservoir and miniature wells, but "miniature" sand, oil, gas, etc. Much valuable work, however, has been done along these experimental lines and more will no doubt follow, but investigators should bear this point in mind and strive to attain dimensional homogeneity and dynamical similarity in order that their conclusions may be translated into terms applying to the oil reservoir. As Gibson says,1 "These conditions are attained when all terms of the physical equation have the same dimensions, . . . when all corresponding particles of the two systems trace out similar paths and when the velocities are such as to make all corresponding forces acting on two such particles in the same ratio. It is the purpose of this paper to discuss the mechanics of fluid movement as it pertains to the oil pool and to point out the complexity of the laws of fluid delivery under the conditions often found.

Jan 1, 1928

mean to say that these explosions are mechanical, but that the ejectment of the stock, throwing out of tops, etc., are mechanical. I see no reason at present, although I have had almost no experience in the use of large quantities of Mesabi ore, to change my ideas on the subject. That these explosions should follow irregular working or slipping in the furnace, I think can be explained. I have noticed that immediately following slips there is little or no settling of the stock on top, although there is no lessening of the volume of gas passing into the stoves and boilers. Supposing that, after a slip of 3 or 4 feet, the filling continues, but for some distance from the 'top the stock fails to move: there would be a much better chance for the deposited carbon to clog interstices in the stock, and for the additional effect in the same direction of the fine ore in the charge, than if the stock were properly settling. Under such conditions it is easily supposable that the openings would be entirely closed, or closed so tightly that the pressure below the obstruction would be raised to a point approaching the blast-pressure, or to a point high enough to force a passage or an enlargement of the small passages which may remain. When this occurs, gas from below under pressure carries with it large quantities of deposited carbon and fine ore; if the case is aggravated, coke, stone, bell, etc. As soon as the red-hot deposited carbon meets the air there are perfect conditions for a dust explosion, which naturally follows, the same as in a coal-mine or flour-mill.

Jan 1, 1899

Edward Keller, Baltimore, Md. (communication to the Secretary*) :—The authors of this paper are to be commended for their industry and congratulated upon the many interesting results which were the fruit of their researches. While thoroughness has marked their work in general, yet on a few points in particular they have touched but lightly, for which reason, it would appear to me, they have hit wide of the mark in their respective conclusions. The work alluded to pertains chiefly to the occurrence of magnetic iron oxide (ferroseferric oxide) in copper-mattes. Because the authors find that the magnetic residue, left by the dissolved sulphides, varies largely in quantity according to the strength of nitric acid used (with potassium chlorate) in dissolving the mattes, they conclude :— "It appears, therefore, that the ferroso-ferric oxide is the result of precipitation by the oxidizing agent, rather than an original constituent of the matte." In this part of their investigation, Messrs. Gibb and Philp have ignored some well-established data,. In the first place, they have overlooked the fact that there are mattes which are strongly magnetic and others which scarcely show any magnetic property. There is nothing in their work tending to explain this variation. They Seem to have tested none of their products for magnetism. Secondly, they have overlooked the fact that magnetic iron oxide probably exists in all ore-charges in the copper-matting furnaces, and, under the given conditions, that this oxide is very difficult to reduce and to combine with silica to form slag. Thirdly, they pay no attention to the varying specific gravity of the several grades of copper-matte, which may exceed, equal, or fall below that of the magnetic oxide. These are .essential points which, I believe, clearly in-

Jan 1, 1906

THE man who forgot to mail the letters his wife gave him was for once justified at Tulsa, for envelopes, scratch paper and tablecloths were all in demand and through the two days of the meeting of the Petroleum Division, pencils were busy everywhere sketching out diagrams, drawing curves, figuring, or just taking notes. Those attending took the serious papers seriously, and discussion was wide-ranging but pointed. Despite the highly technical character of the papers presented, the chairmen had never to call for discussion; it was only necessary to say the paper was open for it. Both days the meetings lasted until after five in the afternoon, and it was enthusiastically voted to advance the meeting hour on Friday, in order to give more time. In all, ten papers, abstracts of which appeared in MINING AND METALLURGY for October, and copies of all but two of which were available in print, were presented in the two days, and no more could have been handled to advantage in that time. All but one of these dealt with problems of production engineering. That, the opening paper, was a general review of demand, supply and price in 1928, by Campbell Osborn, in which he argued for the price control of production and showed how the economic conditions determined development. J. Elmer Thomas presented a carefully prepared review of the same data, but came to somewhat different conclusions as to trend, and J. E. Pogue pointed out that in recent years it has been the manufacturing rather than the producing industries that have been notably profitable. These and other discussions were too long to be reported here, but will be printed in full later.

Jan 1, 1928

By Y. C. Kim, S. L. Barua

M. Armstrong's paper is very interesting and can be regarded as a pioneering work of applying geostatistics on washed coal. The density levels used in her study are uniformly spaced, which facilitated curve fitting through a proper experimental design. Most of the existing coal washing plants in the US, however, gather washability data at non-uniform intervals which, in turn, affects the goodness of curve fitting. We would like to emphasize the importance of having a proper experimental design, if a similar geostatistical application is to be conducted on washed coal. We, at the University of Arizona, tried the variogram on recovery (Kim, Barua, and Baafi, 1982, SME preprint 82-143) which showed a similar pattern as Fig. 4 of Armstrong's paper. In both cases, the first experimental variogram value is invariably and inexplicably higher than the second variogram value. Although Armstrong ignores the first point because of "small number of sample points," we did not do so because there were 17 sample pairs. As a consequence, we concluded that the obtained experimental variogram was unsatisfactory and that further research is warranted. In other words, this disagreement in variogram interpretation between M. Armstrong and the University of Arizona begs the question whether the experimental variogram of Fig. 4 truly reflects the spatial correlation in washed coal, assuming there is such a correlation. Finally, we wish that Armstrong could have done a similar study on clean sulfur, which is a vital interest to the coal mines in the US. Her implied remark on sulfur in the concluding section of the paper may turn out to be incorrect because our experimental variograms on clean sulfur at different density levels were even less satisfactory than those on recovery. ?

Jan 1, 1986

THE Section on Aerial Geologizing of the American Institute of Mining and Metallurgical Engineers convened on Monday afternoon, Feb. 17, 1936, during the Annual Meeting of the Institute. Mr. Theodore Marvin presided. CHAIRMAN MARVIN.-We hope to get through with the papers on the program in time so that you can examine the instruments that are dis-played here, and also the photographs and air views brought by the Fairchild people. This is what we might call the first bread and butter session "of the Aviation Committee. The group, as many of you know, was started at the request of the Board of Directors two years ago. We have had two sessions since then, both of them of a somewhat general nature, their pur-pose being to point out the reasons why mining and petroleum engineers should be more interested in the facilities of aviation. Today we have two papers. The first is one by Mr. Eliel, of the Fairchild Company's California branch. In Mr. Eliel's absence, Mr. Gale, of the Fairchild Company, will read it. C. H. GALE.-Before I begin to read Mr. Eliel's paper, I would like to point out two instruments that he mentions. One is what he calls the solar-navigator, a new type of aerial navigating device which he has developed for use in flying cameras in aerial surveys. Flying a camera at high altitudes over unfamiliar territory is a very difficult procedure and only a few pilots in this country can do it. So far as I know, this is the first time this device has been discussed in public. Another facility I want to refer to in advance is the use of the stereoplanigraph in making contour maps from photographs. This is an extremely interesting procedure, which we are appreciating more than ever at the present time.

Jan 1, 1936

The Section on Aerial Geologizing of the American Institute of Mining and Metallurgical Engineers convened on Monday afternoon, Feb. 17, 1936, during the Annual Meeting of the Institute. Mr. Theodore Marvin presided. Chairman Marvin.—We hope to get through with the papers on the program in time so that you can examine the instruments that are displayed here, and also the photographs and air views brought by the Fairchild people. This is what we might call the first bread and butter session of the Aviation Committee. The group, as many of you know, was started at the request of the Board of Directors two years ago. We have had two sessions since then, both of them of a somewhat general nature, their purpose being to point out the reasons why mining and petroleum engineers should be more interested in the facilities of aviation. Today we have two papers. The first is one by Mr. Eliel, of the Fairchild Company's California branch. In Mr. Eliel's absence, Mr. Gale, of the Fairchild Company, will read it. C. H. Gale.—Before I begin to read Mr. Eliel's paper, I would like to point out two instruments that he mentions- One is what he calls the solar-navigator, a new type of aerial navigating device which he has developed for use in flying cameras in aerial surveys. Flying a camera at high altitudes over unfamiliar territory is a very difficult procedure and only a few pilots in this country can do it. So far as I know, this is the first time this device has been discussed in public. Another facility I want to refer to in advance is the use of the stereoplanigraph in making contour maps from photographs. This is an extremely interesting procedure, which we are appreciating more than ever at the present time.

Jan 1, 1937

By K. R. Grube, D. N. Williams

It is often desirable to perform fatigue studies at relatively high strains and at low strain rates. A low-cost fatigue machine has been constructed for this purpose which has proven quite versatile. This machine is based on the principle of repeated bending of a strip sample over a shaped mandrel. A photograph of a group of fatigue tests in progress is shown in Fig. 1. The test sample is held in place between two shaped mandrels having a flat at their base to grip the sample firmly. A cam-driven loading frame is used to bend the sample alternately over each mandrel. The sample slides freely in this frame and is held in place by a light spring to accommodate increases in sample length. The pivot point for the loading frame is selected so as to minimize movement at the loading point during operation. The number of cycles to failure is recorded by a rachet counter which is kept in operation by a series electrical connection through the sample and is operated by the drive cam. The maximum strain imposed at the sample surface on bending from one mandrel to the other is readily calculated from the relationship, where t is the sample thickness and r is the radius of curvature of the mandrels. The rate of straining can be controlled by control of the cam speed. The device as shown in Fig. 1 is set up to run six samples at ambient temperature. A much larger number of samples can be run at one time without difficulty. ALSO-, by slight realignment of the components the mandrel unit can be enclosed in a separate chamber permitting control of test temperature and environment. This permits a variety of fatigue and corrosion fatigue problems to be studied.

Jan 1, 1963

By NONE N/A

THE Section on Aerial Geologizing of the American Institute of Mining and Metallurgical Engineers convened on Monday afternoon, Feb. 17, 1936, during the Annual Meeting of the Institute. Mr. Theodore Marvin presided. CHAIRMAN MARVIN.-We hope to get through with the papers on the program in time so that you can examine the instruments that are dis-played here, and also the photographs and air views brought by the Fairchild people. This is what we might call the first bread and butter session of the Aviation Committee. The group, as many of you know, was started at the request of the Board of Directors two years ago. We have had two sessions since then, both of them of a somewhat general nature, their pur-pose being to point out the reasons why mining and petroleum engineers should be more interested in the facilities of aviation. Today we have two papers. The first is one by Mr. Eliel, of the Fairchild Company's California branch. In Mr. Eliel's absence, Mr. Gale, of the Fairchild Company, will read it. C. H. GALE.-Before I begin to read Mr. Eliel's paper, I would like to point out two instruments that he mentions. One is what he calls the solar-navigator, a new type of aerial navigating device which he has developed for use in flying cameras in aerial surveys. Flying a camera at high altitudes over unfamiliar territory is a very difficult procedure and only a few pilots in this country can do it. So far as I know, this is the first time this device has been discussed in public. Another facility I want to refer to in advance is the use of the stereoplanigraph in making contour maps from photographs. This is an extremely interesting procedure, which we are appreciating more than ever at the present time.

Jan 1, 1936

By G. Campbell

The paper by M. Lonoff looks at the importance of byproduct prices on copper production. The paper develops several interesting points on this topic, but there are some points in the theoretical discussion that could use further development. A couple of these theoretical topics will be considered here using the paper's framework of assumptions without concern about how realistic the assumptions are for the copper industry. Lonoff’s theoretical model is based on a static, homogenous world where all copper/byproduct deposits are identical, and these deposits are the main source of these metals. Due to the importance of the byproducts to the production decision, the term coproducts will be substituted for the term byproducts to reflect more accurately this condition. The conclusion is drawn that a rise in coproduct prices necessitates a decrease in copper prices because copper production is increased as a consequence of increased coproduct production. The observation that real world behavior does not always follow this pattern is dismissed as "speculation." However, it can be easily shown that within this simple framework market forces might create the observed behavior. The key question to be answered is what causes coproduct prices to rise. Three possible cases will be used as illustrations. The first case is the one implicity assumed by Lonoff. Here, the demand for coproducts increases at all prices (an outward parallel shift of the demand curve) with the demand for copper remaining constant. As reported in the paper, the results are higher coproduct prices, an increase in coproduct production, and lower copper prices due to the resulting increase in copper production. The second case is when the supply of coproducts are constrained-leading to higher market prices. Copper production, as required by the simple model, is also reduced which

Jan 1, 1984

By HOWARD I. YOUNG

F. W. SPERR, Houghton, Mich.-Why does 10 to 20 per cent. of the ore formation have to he lost? It is not clear to me why it should not all be taken out, from the conditions as I saw them underground this afternoon. H. I. YOUNG.-The grade of our ore is so low that we cannot stand the expense of timbering to support the roof, which, in a sheet-ground mine, would be from 25 to 50 per cent. of our total mining cost at present. After the orebody is mined out, we can often recover 10 to 20 per cent. of the material that is left. F. W. SPERR.-I think it should be a very simple mining engineering problem to mine all of that mineral without the use of a stick of timber. Similar work has been done in the mines of Grand Rapids Plaster Co. The usual operation in deposits of this kind is to open up and excavate as far as the roof will stand; when it caves, start in and dig somewhere else. But in the case I referred to they learned that by working the ground more systematically and leaving in a sufficient amount of pillar, they could later draw those pillars and get them all, and avoid uncon¬trolled breakages which would be likely to occur if they tried to hold up the overburden permanently. From the point of view of safety and also from the financial point of view, I contend that it is better to keep the caving under control and make it do what you want it to do, rather than to take out what you can conveniently for the time being and after a while be compelled to let the overburden do what it pleases.

Jan 1, 1918