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By William Campbell

(Cleveland Meeting, October, 1912.) THE structure of iron and steel, though the object of so much study and research for the past 25 years, is by no means thoroughly understood. In the first place, we have three or more distinct iron-carbon thermal diagrams, each with its own supporters, and each representing a theory of the structure and constitution of cast-iron. In the second place, by reason of the fact that austenite, the solid solution of carbon in iron, decomposes in the solid state into ferrite, or pure iron, and cementite (Fe3C), and that quenching from above this transition-range, no matter how rapid, cannot entirely prevent the change and thus preserve the austenite by itself at ordinary temperatures, it happens that under the microscope we find, in addition to the ferrite, Fe3C, and austenite, which the thermal diagram of steel requires, it series of transition-products with distinctive structures, to which have ,been given the names martensite, troostite, sorbite, etc. Now these transition-products, in addition to the solid solution, austenite, have been the source of much controversy, at times very bitter. One side would insist that, say, troostite was an entity, which the other side would deny, pointing out that it must be a transition-mixture, with a particular structure. That austenite was a solid solution of carbon in iron has been denied by one school ; we have been told that Fe24C dissolved both Fe3C and Fe, and thus gave rise to a whole series of quenching-products-all this in spite of the fact that no matter how the thermal diagrams differ in regard to cast-iron, they all agree in regard to the solid solution, austenite, for Fe24C finds no place on the diagram. Thus it happens that while the authorities fight both in regard to the iron-carbon diagram and the structures met with in hard- * Associate Professor of Metallurgy, Columbia University in the City of New York.

Dec 1, 1912

By Kim Beattie

IN spite of the fact that in 1944 Canada experienced a decline in production of all her leading base metals-nickel, zinc, lead, and copper; despite uncured headaches in the coal-mining industry; and cheerfully ignoring a still further drop in gold, the most valuable product of her mines, which had the lowest output of any year since 1931, the Canadian miner retains the traditional optimism of miners everywhere as he looks forward to the postwar period. Some factors should keep the Canadian mining industry from being too optimistic of the coming era of peace, but the fraternity generally holds that its confident attitude towards the future is based on sound reasons. The decline in production in the Canadian mining industry last year can be almost wholly attributed to the serious shortage of labor and the difficulty in obtaining transport and supplies in remote areas. Some falling off occurred in the demand for certain strategic metals, but the diversion of gold miners, especially, without replacements being obtainable, to direct war work or allied pursuits, was certainly the principal cause of the reduced output in 1944. But that is a situation which will right itself at the close of the conflict.

Jan 1, 1945

By H. M. Wilten

THIS article presets a view of a problem encountered in petroleum refining in the deterioration of equipment used in condensation of vapors and cooling of liquids. Discussion is limited to the problems of shell- and tube-type exchangers and condensers. In this service shell- and .tube-type equipment is gradually displacing other types and, for this reason, its economic importance ill oil-refining practice is also increasing. Considering oil - refinery practice during the last two decades one can readily see many important improvements in the apparatus used. Briefly, the present equipment is safer, more efficient, and Ignore economical. Improvement in apparatus used for the condensation of distillates has, in my opinion, been less than that in other essential distilling apparatus. So it is hoped that this discussion will stimulate research among the producers as well as among the consumers of this equipment with a view to ameliorating this condition.

Jan 1, 1937

By William B. Plank

AGAIN the records show an unprecedented enrollment of students in the mineral technology schools of the United States and Canada. In the current year, 1938-'39, 9619 students were resident in the 53 schools of the United States arid 1014 in the six schools of Canada. These data are from my fifth study of the mineral technology schools of the United States and Canada. the last previous study having been made for the year 1936-'37. The undertaking as previously was made under the auspices of the Mineral Industry Education Division of the A. I. M. E. The data or, the various schools were collected in the same way as for former studies.

Jan 1, 1939

By William M. Baldwin

Jan 1, 1946

By William M. Baldwin

Jan 1, 1946

By J. J. Tietjen, D. Richman

Single-crystal Gap lms been epitaxially grow from the vapor phase at a rate oJ 3 p per nzin without encountering a7Zy low-ang-le grain boundaries or debwading- the electrical properties of the material. This growth rate exceeds any value previol~sly reported for the vapor phase growth of Gap. In pure material, mObilities ns high as 175 sq cm per U-sec at room tenzperature and 1450 sq cm per v-sec at 77°K have been obtained. These values are anLong the highest that have been attai)led for this material. For the first time, Gap possesses a number of important properties which make it well-suited for use in electro-optic modulators. First, the transverse electro-optic effect is operable in this material, which makes it possible to increase the path length of the modulated iron doping of Gap has been achieved; this results i?z resistivities of approximately 10" ohm-cm. The problelrls of residual strain and isolated shorting paths in these crystals have been partially solved. Electro-optic modulation of visible radiation has been demonstrated with this material. It is anticipated that further improvement with regard to the probleins of strain and shorting paths will result in a practical Gap electro-optic modulator. radiation without increasing the applied voltage. In addition, this permits the use of thin crystals so that relatively small voltages are needed to provide the requisite high electric fields. Second, GaP is a cubic crystal and therefore does not introduce critical optical-alignment problems associated with birefrin-gent crystals, such as ammonium dihydrogen phosphate (ADP), and potassium dihydrogen phosphate

Jan 1, 1968

By Lauren A. Wright

SINCE the early nineteen-thirties the production of talc* in California has increased five-fold to a yield in 1947 of about 76,000 tons (fig. 1); conse- .' Unless otherwise qualified, the term "talc" in this paper will imply a mixture of the pure talc with such related minerals as commonly occur in the commercial material. quently the state is now one of the nation's three principal talc producers. The 1947 output, which represented about one-sixth of the national total for that year, was approximately equal to production from Vermont, and was second in value to that from New York. New York has an annual output of about 130,000 tons. Three factors have been mainly responsible for the expansion of talc production in California. (1) Technical advances and innovations, particularly in the ceramic industry, have increased the demand for certain California talcs. The nation's high-qual- LAUREN A. WRIGHT, Junior Member AIME, is Associate Geologist, California Division of Mines, San Francisco, Calif. Los Angeles Meeting, October 1948. San Francisco Meeting, February 1949. TP 2622 H. Discussion of this paper (2 copies) may be sent to Transactions AIME before Feb. 28, 1950. Manuscripts received Dec. 7, 1948; revision received Aug. 29, 1949. This paper is Contribution No. 508 of the Division of Geological Sciences, California Institute of Technology, Pasadena, Calif. the industry, mainly through demand for the urgently needed steatite. Fibrous talc, used as a paint extender by the armed forces, also was produced in quantity. (3) Expanding western industry has continued to draw heavily on California talc deposits, and has extended the upward production trend into the postwar period. Considerably more than half of California's current talc output is used as ceramic raw material. The paint, rubber, paper, and textile industries are the more important consumers of the remainder. Smaller amounts are used as insecticide carriers, and in cosmetics, and various minor industrial applications. During World War I1 the principal steatite deposits were studied in detail by members of the U. S. Geological Survey; other sources of commercial talc in the state have in the past received but scant geologic attention. The following discussion is essentially a preliminary report based on research currently in progress by the California Division of Mines, and includes a brief outline of previous steatite studies by the U. S. Geological Survey. Distribution of California Talc Deposits: The principal talc resources of both California and Nevada are confined to an elongate belt that extends from the vicinity of Baker, in north-central San Bernardino County, northwestward to include the southern Death Valley region, the Inyo Range, and the Palmetto-Oasis district of western Nevada (fig. 2). This belt, of which all but the northernmost tip lies in California, is approximately 200 miles long and 30 miles in average width. Included in the belt are four contrasting areas. The deposits within each area are geologically similar and yield talcs that have characteristic properties and applications. Three of these local "talc provinces" lie within California's portion of the talc-

Jan 1, 1951

By Lauren A. Wright

SINCE the early nineteen-thirties the production of talc* in California has increased five-fold to a yield in 1947 of about 76,000 tons (fig. 1); conse- .' Unless otherwise qualified, the term "talc" in this paper will imply a mixture of the pure talc with such related minerals as commonly occur in the commercial material. quently the state is now one of the nation's three principal talc producers. The 1947 output, which represented about one-sixth of the national total for that year, was approximately equal to production from Vermont, and was second in value to that from New York. New York has an annual output of about 130,000 tons. Three factors have been mainly responsible for the expansion of talc production in California. (1) Technical advances and innovations, particularly in the ceramic industry, have increased the demand for certain California talcs. The nation's high-qual- LAUREN A. WRIGHT, Junior Member AIME, is Associate Geologist, California Division of Mines, San Francisco, Calif. Los Angeles Meeting, October 1948. San Francisco Meeting, February 1949. TP 2622 H. Discussion of this paper (2 copies) may be sent to Transactions AIME before Feb. 28, 1950. Manuscripts received Dec. 7, 1948; revision received Aug. 29, 1949. This paper is Contribution No. 508 of the Division of Geological Sciences, California Institute of Technology, Pasadena, Calif. the industry, mainly through demand for the urgently needed steatite. Fibrous talc, used as a paint extender by the armed forces, also was produced in quantity. (3) Expanding western industry has continued to draw heavily on California talc deposits, and has extended the upward production trend into the postwar period. Considerably more than half of California's current talc output is used as ceramic raw material. The paint, rubber, paper, and textile industries are the more important consumers of the remainder. Smaller amounts are used as insecticide carriers, and in cosmetics, and various minor industrial applications. During World War I1 the principal steatite deposits were studied in detail by members of the U. S. Geological Survey; other sources of commercial talc in the state have in the past received but scant geologic attention. The following discussion is essentially a preliminary report based on research currently in progress by the California Division of Mines, and includes a brief outline of previous steatite studies by the U. S. Geological Survey. Distribution of California Talc Deposits: The principal talc resources of both California and Nevada are confined to an elongate belt that extends from the vicinity of Baker, in north-central San Bernardino County, northwestward to include the southern Death Valley region, the Inyo Range, and the Palmetto-Oasis district of western Nevada (fig. 2). This belt, of which all but the northernmost tip lies in California, is approximately 200 miles long and 30 miles in average width. Included in the belt are four contrasting areas. The deposits within each area are geologically similar and yield talcs that have characteristic properties and applications. Three of these local "talc provinces" lie within California's portion of the talc-

Jan 1, 1951

By Ed Van Eeckhout

As part of a U.S. Bureau of Mines-sponsored project on the utilization of "stiff" backfill to minimize potential rock burst hazards, a finite element study was undertaken to predict stresses and displacements around a stope mined up from the 5400 level of the Sunshine mine, Kellogg, Idaho. This stope was to be backfilled using a high-modulus fill. In preparation for that configuration, certain instrumentation was installed near the 5400 level to monitor stress changes. Due to untenable economics, only 2 cuts of the stope were ever made. This paper presents the results of the instrument readings taken during the first cut and compares them with the numerical predictions, as well as presents the modeling results of closure and fill stresses in the stope if it had been mined.

Jan 1, 1984

By JOHN R. SUMAN

IT appears now that the conflict with the totalitarian states will be a long-drawn-out struggle. The course of this war up to now indicates that this may well be the first major conflict where man power has not been the vital and determining factor. Mechanized warfare has made it possible for relatively small, well-equipped groups to outmaneuver and defeat large armies which lack the necessary modern equipment. Under these circumstances, ultimate victory becomes a matter of resources and productive ability. The important question is not how many soldiers can he put into the field, but the volume and speed in producing the armaments essential to ensure a victory. The resources available to the opposing nations and the efficiency of their systems of enterprise and production will be primary factors in determining the ultimate outcome. Germany had a head start of eight years in the armament race, and it is not easy to overcome such an advantage overnight.

Jan 1, 1942

By GLENVILTE A. COLLINS

(Presented at a Meeting of the Spokane Local Section of the Institute, Feb. 17, 1912, and accepted for publication in the Bulletin. ) WHILE I am not at the present time engaged in active mine-management, my duties permit of extensive study and examination of many mines, mills, and reduction-works in various places throughout the United States. Being much interested in efficiency-work in general, and an ardent reader of writings on this subject by Frederick W. Taylor and others, as applied to manufacturing-plants, and having served my apprenticeship from mucking to the engineering design of ore-dressing and underground plants, I hope that this paper will lead others to investigate the field more fully, to the improvement of general mine- and mill-operations, as well as the advancement, intellectually, physically, and financially, of the employee and his relations with the employer. If a man who is prepared to look closely and observe broadly starts in Canada and zig-zags from camp to camp to southern Mexico, taking time casually to inspect mines, mills, and smelters, he will be pitifully impressed by the great difference in customs, and the general waste of labor, time, and money throughout the country. He will so seldom observe a dollar's worth of results given in exchange for a dollar spent that he will form a poor opinion of operating-efficiency and management. This highly-scientific department, requiring an amount of skill and executive ability equaled in few, if any, of the professions, certainly falls short of the standard established in our greater manufacturing industries. It is easily said that this is due to the diversity of conditions in mining, milling, and smelting. But on second view it must be admitted that there is room for tremendous improvements in nearly every mining-organization. The proposal of such improvements is often met by the argument that any mine

Sep 1, 1912

By C. H. Mathewson, E. M. Thalheimer

In planning the present experiments, we have made a particular effort to secure that adjustment of working conditions which would render the forthcoming tests most serviceable by way of indicating the comparative properties of the three different commercial grades of copper used. More specifically, we have endeavored to obtain certain definite information with respect to the relative behavior under test of ordinary electrolytic copper and furnace-refined lake copper containing (a) a moderate percentage of arsenic and (b) a rather large percentage of arsenic, in addition to the usual content of silver and other impurities. These comparisons were made systematic and comprehensive by testing throughout a series of (eight) reductions running from 0 to 70 per cent. in the case of cold-rolled metal, and throughout a series of (15) temperatures running from 100' C. to 1,000" C. in the case of annealed metal. In other words, a survey of properties similar to that made by Grard,' in the case of electrolytic copper, was here repeated (with modifications) and extended to two other commercial varieties of copper. The great importance of copper both as a material of construction and as the base of our most important alloys (aside from steel) has led to innumerable investigations of its properties, particularly in commercial forms. Naturally, the merits of furnace-refined lake coppers us. those of the very pure electrolytic product have furnished the subject of much experimental work and animated discussion, wherein the effect of arsenic has by no means been overlooked. In the literature of the past 10 years,

Jan 1, 1917

By Bunting S. Crocker

EBBLE grinding at Lake Shore is not a temporary BlE wartime substitute. The tube milling plant, with a 1000 ton per day capacity, grinds a hard siliceous ore to 90 pct — 325 mesh. The plant, prior to using pebbles, was consuming 4.3 lb of 11/4-in. grinding balls per ton of ore, which amounted to 785 tons of balls per year. At September 1951 prices, $132.60 per ton, this steel cost amounted to $104,400 per year, or $0.285 per ton milled. By the Lake Shore method of substituting screened rock for this steel, all of this cost is saved. This is one of the major economies in Lake Shore mill practice. Regardless of the ultimate price of grinding balls, a change back to steel balls is not considered. The present pebble plant is more flexible than a steel ball plant and equally efficient. For example, if it is desired to change the size of grinding media, the pebble charge in any mill can be changed completely in 4 to 5 days, as against 76 days to change completely a 1-in. steel ball charge. To change pebble size it is necessary only to change two sets of screens and clean out the rock feed storage bin. This will take 8 to 10 days as against 3 to 4 months to clean out the customary supply of grinding balls kept on hand. Also it has not always been possible to purchase all desired sizes of balls at any price. In an analysis of savings effected by the use of the pebble mills, the flexibility of the Lake Shore grinding plant should be discussed, as it has a direct bearing on these savings. The plant has always used several units to handle tonnage rather than sending all the tonnage through a single unit. This principle may result in using small diameter mills, but no objection to that is seen. At no time has any advantage been found in cost per ton ground in large diameter mills. Both the capacity and the power of any mill varies as the diameter raised to the 2.6th power. Consequently large or small mills are equally efficient, and a plant, should be designed to use as many units or combination of units as is consistent with reasonable operating practice. Mills under 5 ft diam are harder to reline, etc. To define the case at Lake Shore, 2600 tons per day formerly were milled in seven 7x6-ft ball mills and twelve 5x16-ft (and two 6x16-ft) tube mills.* This gave an excellent test plant and an extremely efficient one. In this plant the ratio of ball mills to tube mills was 1:2. When the much cheaper pebble mills were substituted for the tube mills, this ratio was changed to one ball mill to four pebble mills to take the greatest possible advantage of the cheaper operating mill, i.e., the pebble mill. This flexibility without loss in efficiency has been an important item in the cost savings. It is interesting to note that the use of pebbles for fine grinding was proved first in the laboratory in a 12-in. ball mill. In fact, since 1934 all testing on — 8 mesh material has been done in this 12-in. mill. Scope of the Tests A paper on fine grinding at Lake Shore Mines was published in July 1940.' This paper covered 7 years of intensive research on fine grinding as well as sizing methods and equipment, plant scale grinding tests on 5x16-ft tube mills with and without grate discharges both with 1-in. and -in. balls, the use of laboratory mills to evaluate plant changes, and several reports on classifiers and classification. In the following July the addendum report2 was added in which the idea of series-circuit grinding was introduced, and the results of running five stages of tube mills and bowl classifiers were shown. Since 1940, the ball milling end of the plant has been altered extensively as a result of tests on the use of 3-in. rods in 7x6-ft mills and the use of the Tyler repulping screen with from 7 to 14 mesh screens. These tests are lengthy and may be covered in a separate report later. The scope of this report is confined to ore ground by rod milling and ball milling until it passed through an 8 mesh Tyler Ty-rod screen. The —8 mesh screen undersize then was pumped to a primary bowl classifier in open circuit and the sands from the bowl sent to the primary pebble mills, see Fig. 1. In the pebble mill circuit the ore is ground to 90 pct —325 mesh (24 pct + 28 microns). In studying the flowsheet, attention should be paid to the efficiency of the classification equipment used. The Tyler repulping screen is an efficient machine on the 8 to 10 mesh separation, and the bowl classifier is equally efficient at the 325 mesh separation. Efficient classification is a necessity for series-circuit stage grinding. The ore is hard siliceous porphyry, 60 pct SiO,, 80 pct insoluble. Its grindability at different meshes has been shown near the top of the list in F. C. Bond's grindability tests.' Lake Shore is not shown, but an adjacent mine with identical ore, Wright-Hargreaves, is. Reasons for the Changeover Since 1936 grinding balls have been rising steadily in price with no sign of stopping. For a mill that used 4.5 to 5.2 lb of grinding balls for every ton of ore ground this rise represented an alarming increase in grinding costs. In many cases the quality of the grinding balls fell off as the scrap steel became more difficult to obtain. The ratio of tube mills to ball mills increased with the use of the Tyler repulping screen in the ball mill circuit. Originally only 3.0 lb of balls per ton were used in the tube mills, and this

Jan 1, 1953

By Bunting S. Crocker

EBBLE grinding at Lake Shore is not a temporary BlE wartime substitute. The tube milling plant, with a 1000 ton per day capacity, grinds a hard siliceous ore to 90 pct — 325 mesh. The plant, prior to using pebbles, was consuming 4.3 lb of 11/4-in. grinding balls per ton of ore, which amounted to 785 tons of balls per year. At September 1951 prices, $132.60 per ton, this steel cost amounted to $104,400 per year, or $0.285 per ton milled. By the Lake Shore method of substituting screened rock for this steel, all of this cost is saved. This is one of the major economies in Lake Shore mill practice. Regardless of the ultimate price of grinding balls, a change back to steel balls is not considered. The present pebble plant is more flexible than a steel ball plant and equally efficient. For example, if it is desired to change the size of grinding media, the pebble charge in any mill can be changed completely in 4 to 5 days, as against 76 days to change completely a 1-in. steel ball charge. To change pebble size it is necessary only to change two sets of screens and clean out the rock feed storage bin. This will take 8 to 10 days as against 3 to 4 months to clean out the customary supply of grinding balls kept on hand. Also it has not always been possible to purchase all desired sizes of balls at any price. In an analysis of savings effected by the use of the pebble mills, the flexibility of the Lake Shore grinding plant should be discussed, as it has a direct bearing on these savings. The plant has always used several units to handle tonnage rather than sending all the tonnage through a single unit. This principle may result in using small diameter mills, but no objection to that is seen. At no time has any advantage been found in cost per ton ground in large diameter mills. Both the capacity and the power of any mill varies as the diameter raised to the 2.6th power. Consequently large or small mills are equally efficient, and a plant, should be designed to use as many units or combination of units as is consistent with reasonable operating practice. Mills under 5 ft diam are harder to reline, etc. To define the case at Lake Shore, 2600 tons per day formerly were milled in seven 7x6-ft ball mills and twelve 5x16-ft (and two 6x16-ft) tube mills.* This gave an excellent test plant and an extremely efficient one. In this plant the ratio of ball mills to tube mills was 1:2. When the much cheaper pebble mills were substituted for the tube mills, this ratio was changed to one ball mill to four pebble mills to take the greatest possible advantage of the cheaper operating mill, i.e., the pebble mill. This flexibility without loss in efficiency has been an important item in the cost savings. It is interesting to note that the use of pebbles for fine grinding was proved first in the laboratory in a 12-in. ball mill. In fact, since 1934 all testing on — 8 mesh material has been done in this 12-in. mill. Scope of the Tests A paper on fine grinding at Lake Shore Mines was published in July 1940.' This paper covered 7 years of intensive research on fine grinding as well as sizing methods and equipment, plant scale grinding tests on 5x16-ft tube mills with and without grate discharges both with 1-in. and -in. balls, the use of laboratory mills to evaluate plant changes, and several reports on classifiers and classification. In the following July the addendum report2 was added in which the idea of series-circuit grinding was introduced, and the results of running five stages of tube mills and bowl classifiers were shown. Since 1940, the ball milling end of the plant has been altered extensively as a result of tests on the use of 3-in. rods in 7x6-ft mills and the use of the Tyler repulping screen with from 7 to 14 mesh screens. These tests are lengthy and may be covered in a separate report later. The scope of this report is confined to ore ground by rod milling and ball milling until it passed through an 8 mesh Tyler Ty-rod screen. The —8 mesh screen undersize then was pumped to a primary bowl classifier in open circuit and the sands from the bowl sent to the primary pebble mills, see Fig. 1. In the pebble mill circuit the ore is ground to 90 pct —325 mesh (24 pct + 28 microns). In studying the flowsheet, attention should be paid to the efficiency of the classification equipment used. The Tyler repulping screen is an efficient machine on the 8 to 10 mesh separation, and the bowl classifier is equally efficient at the 325 mesh separation. Efficient classification is a necessity for series-circuit stage grinding. The ore is hard siliceous porphyry, 60 pct SiO,, 80 pct insoluble. Its grindability at different meshes has been shown near the top of the list in F. C. Bond's grindability tests.' Lake Shore is not shown, but an adjacent mine with identical ore, Wright-Hargreaves, is. Reasons for the Changeover Since 1936 grinding balls have been rising steadily in price with no sign of stopping. For a mill that used 4.5 to 5.2 lb of grinding balls for every ton of ore ground this rise represented an alarming increase in grinding costs. In many cases the quality of the grinding balls fell off as the scrap steel became more difficult to obtain. The ratio of tube mills to ball mills increased with the use of the Tyler repulping screen in the ball mill circuit. Originally only 3.0 lb of balls per ton were used in the tube mills, and this

Jan 1, 1953

By Bunting S. Crocker

PEBBLE grinding at Lake Shore is not a temporary wartime substitute. The tube milling plant, with a 1000 ton per day capacity, grinds a hard siliceous ore to 90 pct - 325 mesh. The plant, prior to using pebbles, was consuming 4.3 lb of 1 1/4-in. grinding balls per ton of ore, which amounted to 785 tons of balls per year. At September 1951 prices, $132.60 per ton, this steel cost amounted to, $104,400 per year, or $0.285 per ton milled. By the Lake Shore method of substituting screened rock for this steel, all of this cost is saved. This is one of the major economies in Lake Shore mill practice. Regardless of the ultimate price of grinding balls, a change, back to steel balls is not considered. The present pebble plant is more flexible than a steel ball plant and equally efficient. For example, if it is desired to change the size of grinding media, the pebble charge in any mill can be changed completely in 4 to 5 days, as against 76 days to change completely a 1 1/4-in. steel ball charge. To change pebble size it is necessary only to change two sets-of screens and clean out the rock feed storage bin. This will take 8 to 10 days as against 3 to 4 months to clean. out the customary supply of grinding balls kept on hand. Also it has not always been ' possible to purchase all desired sizes of balls at any price. In an analysis of savings effected by the use of the pebble mills, the flexibility of the Lake Shore grinding plant should be discussed, as it has a direct bearing on these savings. The plant has always used several units to handle tonnage rather than sending all the tonnage through a single unit. This principle may result in using small diameter mills, but no objection to that is seen. At no time has any advantage been found in cost per ton ground in large diameter mills. Both the capacity and the power of any mill varies as the diameter raised to the 2.6th power. Consequently large or small mills are equally efficient, and a plant should be designed to use as many units-or combination of units as is consistent with reasonable operating practice. Mills under 5 ft diam are harder to reline, etc. To define the case at Lake Shore, .2600 tons per day formerly were milled in seven 7x6-ft ball mills and twelve 5x16-ft (and two 6x16-ft) tube mills.* This gave an excellent test plant. and an extremely efficient-one. In this plant the ratio of ball mills to tube mills was 1: 2. When the much cheaper pebble mills were substituted for the tube mills, this. ratio -was changed to one ball mill to four pebble mills to take the greatest possible advantage of the cheaper operating mill, i.e., the pebble mill. This flexibility without loss in efficiency has been an important item in the cost savings. It is interesting to note that the use of pebbles for fine grinding was. proved first in the laboratory in a 12-in. ball mill. In fact, since 1934 all testing on -.8 mesh material has been done in this 12-in. mill. Scope of the Tests A paper on fine grinding at Lake Shore Mines was published in July 1940.1 This paper covered 7 years of intensive research on fine grinding as well as sizing methods and equipment, plant scale grinding tests on 5x16-ft tube mills with and without .grate discharges-both with 1 1/4-in. and 3/4-in. balls, the use of laboratory mills to evaluate plant changes, and several reports on classifiers and classification. In the following July the addendum report' was added in which the idea of series-circuit grinding was introduced, and the results of running five stages of tube mills and bowl classifiers were shown. Since 1940, the ball milling end of the plant has been altered extensively as a result of tests on the use of 3 1/2-in. rods in 7x6-ft mills and the use of the Tyler repulping screen with from 7 to 14 mesh screens. These tests are, lengthy and may be covered in a separate 'report later. The scope of this report is confined to ore ground by rod milling and ball milling until it passed through an 8 mesh Tyler Ty-rod screen. The -8 mesh screen undersize then was pumped to a primary bowl classifier in open circuit and the sands .from the bowl sent to the primary pebble mills, see Fig: 1. In the pebble mill circuit the ore is ground to 90 pct -325 mesh (24 pct + 28 microns) In studying the flowsheet, attention should be paid to the efficiency of the classification equipment used. The Tyler repulping screen is an efficient machine on the 8 to 10 mesh separation, and the bowl classifier is equally efficient at the 325 mesh separation. Efficient classification is a necessity for series-circuit stage grinding. The ore is hard siliceous porphyry, 60 pct SiO2, 80 pct insoluble. Its grindability at different. meshes has been shown near the top of 'the list in F. C. Bond's grindability tests' Lake Shore is not shown, but an adjacent-mine with identical ore, Wright-Hargreaves, is. Reasons for the-Changeover Since 1936 grinding balls have been rising steadily in price with no sign of stopping. For a mill that used 4.5 to 5.2 lb of grinding balls for every ton of ore ground this rise represented an alarming increase in grinding costs. In many cases the quality of the grinding balls fell off as the scrap steel became more difficult to obtain. The ratio of tube mills to ball mills increased with the use of the Tyler repulping screen in the ball mill circuit. Originally only 3.0 lb of balls per ton were used in the tube mills, and this

Jan 1, 1952

By F. Twyman, D. M. Smith

THOSE chemists (they are still greatly in the minority) who use the spectroscope, use it very often, and find it almost indispensable. As a means of detecting minute quantities of the metals it is unrivalled. A metal can be readily distinguished in the presence of any other element, compound, or mixture without the necessity of separation. The qualitative analysis of the metallic constituents of a substance, which the spectroscope gives so easily, is a sure basis for planning a chemical analysis. As the determination of each element proceeds the purity of precipitates may be checked as often as desired. If, possessing these advantages, the spectroscope has been neglected in general chemistry, it is not surprising that it was neglected in metallurgical chemistry; for many of the impurities which are of industrial interest, even when they are present in a metal or alloy in small quantities, are not then always easily detected by the examination of their visible spectrum. The history of the development of the art has been given in Bureau of Standards Scientific Paper No. 444.

Jan 1, 1928

By Charles Fettke

IN 1914, the officials of the Brundred Oil Corpn., faced with the problem of introducing new methods to increase production in the old and nearly depleted pools of Venango County, became interested in the Smith-Dunn (Marietta) process which was at that time being tried out in southeastern Ohio and which was already yielding very encouraging results. A license to use the process in Pennsylvania was secured from the owners of the patents. These patents were later declared invalid. The method was first used in Pennsylvania on a property consisting of about 434 acres, of which 300 are productive, at Hamilton Corners, 15 miles northeast of Oil City, in Cherry Tree and Oakland Townships, Venango County. The producing horizon is the First Sand of the Venango Group. A small oil pool was opened up in this vicinity in 1904. By July, 1916, when the compressed air was first introduced to restore pressure, the production had dropped to a point where it was no longer possible to continue profitable operation. From that time until March, 1927, over 100,000 bbl. of oil have been recovered from the tract. The property is being operated at present by the Brundred Oil Corpn. and Lux. The 1926 production, amounting to 10,650 bbl., was only 400 bbl. short of the maximum reached during any year of the 10-year period that the process has been in operation. Inasmuch as the Hamilton Corners pool is the first one in Pennsylvania in which the Marietta process was tried out, and the one in which it has been longest in continuous operation, considerable interest attaches to the results obtained. Through the courtesy of H. D. Brown and W. J: Brundred, officials of the Brundred Oil Corpn., all their data on this operation were made available to the writer in connection with an investigation of rejuvenation methods in the State for the Pennsylvania Geological Survey.

Jan 1, 1928

By Vincent P. Gi. ccnella

GOLD was discovered in Gold Canyon on May 15, 1849. Following this discovery placer miners worked the gravels in the canyon for-ten years, finally discovering the outcrop of the Comstock lode at Gold Hill in May, 1859, and in Ophir ravine on June 12 of the same year. Before long large quantities of gold and silver, were taken from the lode and one of the West's most spectacular mining booms drew thousands of fortune seekers to Nevada. After a long period of production activity waned and in late years little mining was done. The recent reopening of the old mines and the discovery of ore in other parts of the vein, and in other veins of the district, has led to a revival of interest in the Comstock. Virginia City, Gold Hill, and Silver City, situated along the great vein system, are enjoying a period of prosperity and a large influx of people.

Jan 1, 1934

By AIME AIME

MOST of the copper mines in Canada are favored by nature in having other metals besides, copper in their ore, which puts them in a most satisfactory competitive position. Noranda ore has an important gold content, Flin Flon gold and zinc, and International Nickel of course has nickel. All of the larger copper companies in Canada operated during 1.933 and the total production of copper exceeded that of the year before. The Britannia Mining and Smelting Co. worked out to succcessful conclusion a three-product flotation process for separating the copper, zinc and iron from its low-grade ore. Although the method and equipment is different from that used at the Flin Flon mine, the object is the same, that

Jan 1, 1934