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By B. S. Lement

No appreciable stabilization of the austenite-martensite reaction occurs in a 15 pct Cr-0.7 pct C steel unless some martensite is initially present. Stabilization is induced by interrupting the subcool below M,; however, disappearance of the stabilization effect as manifest by burst formation of martensite may occur on continued holding at the final subzero reaction temperature. The higher the temperature of intermediate cycling after the initial subcool, the more permanent is the stabilization effect at the final reaction temperature. Appreciable conditioning of retained austenite occurs on reheating to about 500°C. These phenomena are explainable on the basis of the reaction-path theory. A RECENT investigation' carried out by the authors has shown that isothermal transformation of austenite to martensite definitely takes place in a 15 pct Cr-0.7 pct C steel and that appreciable amounts of martensite can form in this fashion. Investigations2-" arried out on other steels and iron alloys make it seem probable that isothermal formation of martensite is a phenomenon of fairly general occurrence. The reaction-path theory of Cohen, Machlin, and Paranjpe5,7 explains isothermal transformation on the basis of thermal activation of strain embryos which generate martensite plates with a velocity approaching that of sound. On the other hand, the nucleation and growth theory of Fisher, Hollo-mon, and Turnbull8 egards isothermal transformation as due to growth of athermally formed martensite nuclei. The experimental evidence obtained thus far favors the reaction-path theory in that the martensite reaction seems to be nu-cleation-controlled rather than growth-controlled. Stabilization is another phenomenon of importance with respect to the austenite-martensite reaction. According to the reaction-path theory, stabilization is a result of relaxation of strain embryos. It is postulated that strain embryos are present at the austenitizing temperature in the form of dislocations or lattice imperfections in the austenite which vary in the extent to which the lattice is displaced along the strain reaction path leading to martensite. On quenching from the austenitizing temperature, athermal martensite starts to form as soon as the M. is reached, because the activation energy of the transformation which decreases with decreasing temperature is lowered to below the level of the highest energy strain embryos. Martensite plates are generated during the cooling below M, from embryos possessing energies above the activation energy corresponding to the temperature at which the cooling is stopped. The distribution of lower energy embryos is changed because of the elastic and plastic strains produced in the remaining austenite as a result of the transformation. This effectively increases the number of strain embryos at all levels of energy below the activation energy and tends to stimulate further martensite formation either iso-thermally or on subsequent cooling. However, if the temperature at which the cooling is stopped is high enough for relaxation of strain embryos to occur, some degree of stabilization against further transformation may be induced. Whether stabilization will be observed on subsequent cooling will depend on the extent of decrease of activation energy with temperature. If the activation energy decreases sharply with temperature, it is possible that transformation will appear to continue with decrease in temperature in spite of the loss of embryos by relaxation. However, with a more gradual decrease in activation energy, stabilization will be manifest by no further transformation on cooling over a measurable temperature range until the

Jan 1, 1954

By Charles H. Thurman

THE data given herein were first included in a paper read before San Francisco Section, A.I.M.E., in October 1940, and are applicable to conditions existing until the gold-dredging industry was temporarily suspended by Order L-208 of the War Production Board in the fall of 1942. There is no doubt that gold dredging will be resumed at some future time, and on a scale equivalent to that of the recent past, but the cost data given herein will be affected to some extent by conditions existing at that time, and by labor rates and prices for materials then prevailing. DRAGLINE VS. BUCKET-LINE Dragline dredges should not be considered for mining large areas of low-grade placer gravel. In such deposits a dragline operator with a 5-cu. yd. dragline would be doing well to maintain an operating cost of 6¢ per cu. yd., while a bucket-line dredge with buckets no smaller than 7 cu. ft. each could be operated for less than 4¢ per cu. yd. By operating costs, I mean only field charges such as direct operating and overhead, which includes pay roll, power or fuel, repairs and maintenance, insurance, land clearing and general expenses, but not including such items as prospecting, depletion, depreciation of equipment, State Franchise Tax, or Federal Income Tax. It is not to be inferred that a dragline dredge cannot make a profit in small low-grade deposits, where the extent of a given property is too small to justify the use of the more costly bucket-line dredge. Consider small deposits of 10¢ gravel. It is obvious that a deposit of 5,000,000 cu. yd. of such gravel could not be mined profitably with a new, 7-cu. ft. bucket-line dredge, costing upward of $250,000, and with operation costs at 4¢ per cu. yd., paying for land or royalties out of earnings; nor could a new combination 5-cu. yd. dragline and washing plant, worth upward of $125,000 and working at 6¢ per cu. yd., make a profit. These comparisons are made because the hourly capacity of both types of dredges is nearly the same. The bucket-line dredge averages 93 per cent operating time in 24 hr., as against about 80 per cent or less for the dragline dredge. These percentages of operating time are important factors in making a comparison of this kind. The bucket-line dredge has greater efficiency in cleaning soft bedrock, usually characteristic of dredging deposits, and a 7-cu. ft. bucket-line dredge can be efficient to a total digging depth of 80 ft. (65 ft. below water, 15 ft. above). A 5-cu. yd. dragline dredge is limited to about 30 ft. of efficient digging depth, 5 ft. of which could be above water. In small areas of gravel not over 30 ft. deep, a 5-cu. yd. dragline dredge could make a profit where a bucket-line dredge could not do so. As an example: compare the dredging of 3,000,000 cu. yd. of 10¢ gravel 28 ft. deep with bucket line, costing 4¢ per cu. yd., and with a 5-cu. yd. dragline dredge operating at 6¢ per cu. yd. Because of small yardage, new equipment is not warranted, therefore we can assume that the dredges of both types are used equipment, fully depreciated. Dismantling, mov-

Jan 1, 1945

By H. N. Thomson

(Butte Meeting, August, 1913.) GENERAL. THE Tooele plant. off the International Smelting & Refining Co. is situated at the mouth of Pine canyon, Tooele county, Utah. It is connected with the main line of the San Pedro, Los Angeles & Salt Lake railroad by the Tooele Valley. railway, and is about 7 miles from Tooele Junction. Fig,. 1 is a general view of the plant. The copper plant has been in operation since July, 1910, and the first blast furnace it the lead plant was blown in on Feb. 29, 1912. The location of the plant was selected on sloping ground with the idea of using gravity to the fullest extent and thus keeping labor at a minimum. Practically the entire plant is constructed of steel, reinforced concrete, and. brick.

Jan 7, 1913

By Rossiter W. Raymond

The formal outline of Mr. Hague's life and work is embraced in the following statement, chiefly based upon data furnished by him, at my request, shortly before his death. At that time the probability that I would survive to record his death was apparently small; but I urged upon him the duty of providing, whether for me or for my successor as Secretary of the Institute, trustworthy material for the notice which somebody would some day have to write—and which might otherwise be incomplete or incorrect. Mr. Hague, with characteristic promptness and freedom from affectation, did what I asked of him; and I am therefore able to present an authoritative sketch—concerning the details of which I shall add my own comments, and some particulars obtained from friends. James Duncan Hague was born Feb. 24, 1836, at Boston, Maes., where his father, Rev. William Hague, D.D.,an eminent clergyman, then resided. After a preliminary education in private schools, he studied in 1854 at the Lawrence Scientific School of Harvard University; in 1855 and 1856 at the University of Göttingen, Hanover; and from 1856 to 1858 at the Royal Mining Academy of Freiberg, Saxony. In 1859-1861 he was attached as chemist to a South Sea exploring expedition, sent by W. H. Webb, of New York, to examine Jarvis, Baker, and other islands for phosphate-deposits. After the outbreak of the Civil War, he entered the U. 5. Navy, serving for a year as Judge Advocate to the fleet stationed at Port Royal, S. C. In 1863 he became Superintendent of the Albany and Boston copper-mine, in the Lake Superior region, where he was also connected with the earliest development of the Calumet and Hecla property. In 1867 he became the First Assistant Geologist in Clarence King's famous Exploration of

Jan 1, 1909

By Simon D. Strauss

The world appetite for minerals in the, third quarter of this century grew at a higher rate than had been anticipated. To illustrate, consider the experience of four, commodities. Excluding the Communist bloc, sometimes referred to as the centrally planned economies, demand for aluminum increased at a compound rate of 8.6% between 1950 and 1975,; copper rose by 4.4%; iron ore by 5.5%; and tin, the laggard in the group, by 2%. Except for tin, the figures are substantially greater than growth rates anticipated in 1950 in the Paley Commission report and other studies. The growth rate was not evenly distributed in geographical areas. Professor Wilfred Malenbaum of the University of Pennsylvania did an interesting study breaking these figures down as among three principal sources of demand -- the United States, other industrialized nations (which he referred to as the "rich lands"), and the developing world (which he referred to as the "poor lands").

Jan 1, 1982

Mine Taxation On Monday morning, Sept. 22, a session on- Mine Taxation was held in cooperation with the Internal Revenue Dept., U. S. Treasury, Mr. R. C. Allen presiding. This was followed by two adjourned sessions, at which Mr. R. C. Allen and Mr. A.D. Brokaw presided. The following paper was presented: Federal Taxation of Mines. By L. C. Graton. (Presented by the author; dis¬cussed by R. V. Norris, W. O. Hotchkiss, W. P. Beldon, Paul Armitage, R. C. Allen, E. F. Brown, William Belly, A. D. Brokaw, F. W. Sperr, C. H. Benedict, E. P. Griffitts, W. E. Forsythe, and the author). Coal and Gas The first session on Coal and Gas was held on Monday morning, Sept. 22; the second, on the afternoon of the same day. Mr. Curl Scholz presided at both sessions. The following papers were presented: Research on the Coal-mining Industry. By E. A. Holbrook. (Presented by the author.) Some Factors that Affect the Washability of a Coal. By Thomas Fraser and H. F. Yancey. (Presented by the author.) A Use Classification of Coal. By George H. Ashley. (Presented by title.) Distribution of Anthracite. By A; S. Learoyd. (Presented by title.) Height of the Gas Cap in the Safety Lamp. By C. M. Young. (Presented by the author.) Engineering Features of Modern Large Coal Mines in Illinois and Indiana. By C. A. Herbert and C. M. Young. (Presented by the authors.) Gas-producer Practice. By G. S. Brooks and C. C. Nitchie. (Presented by the authors.) Testing of Coals for Byproduct Coking and Gas Manufacture. By Horace C. Porter. (Presented by the author.) Coals of Ohio and their Limitations for Byproduct Coke. By Wilber. Stout. (Presented by the author.) Outdoor Substations in Connection with Coal-mining Installations. By H. W. Young. (Presented by the author.)

Jan 11, 1919

By Charles H. Thurman

The data given herein were first included in a paper read before San Francisco Section, A.I.M.E., in October 1940, and are applicable to conditions existing until the gold-dredging industry was temporarily suspended by Order L-208 of the War Production Board in the fall of 1942. There is no doubt that gold dredging will be resumed at some future time, and on a scale equivalent to that of the recent past, but the cost data given herein will be affected to some extent by conditions existing at that time, and by labor rates and prices for materials then prevailing. Dragline vs. Bucket-line Dragline dredges should not be considered for mining large areas of low-grade placer gravel. In such deposits a dragline operator with a 5-cu. yd. dragline would be doing well to maintain an operating cost of 6¢ per cu. yd., while a bucket-line dredge with buckets no smaller than 7 cu. ft. each could be operated for less than 4¢ per cu. yd. By operating costs, I mean only field charges such as direct operating and overhead, which includes pay roll, power or fuel, repairs and maintenance, insurance, land clearing and general expenses, but not including such items as prospecting, depletion, depreciation of equipment, State Franchise Tax, or Federal Income Tax. It is not to be inferred that a dragline dredge cannot make a profit in small low-grade deposits, where the extent of a given property is too small to justify the use of the more costly bucket-line dredge. Consider small deposits of 106 gravel. It is obvious that a deposit of 5,000,000 cu. yd. of such gravel could not be mined profitably with a new 7-cu. ft, bucket-line dredge, costing upward of $250,000, and in operation costs at 4¢ per cu. yd., paying for land or royalties out of earnings; nor could a new combination 5-cu. yd. dragline and washing plant, worth upward of $125,000 and working at 6¢ Per cu. yd., make a profit. These comparisons are made because the hourly capacity of both types of dredges is nearly the same. The bucket-line dredge averages 93 per cent operating time in 24 hr., as against about 80 per cent or less for the dragline dredge. These Percentages of operating time are important factors in making a comparison of this kind- The bucket-line dredge has greater efficiency in cleaning soft bedrock, usually characteristic of dredging deposits, and a 7-cu. ft. bucket-line dredge can be efficient to a total digging depth of 80 ft- (65 ft. below water, 15 ft. above). A 5-cu. Yd. dragline dredge is limited to about 30 ft. of efficient digging depth, 5 ft. of which could be above water. In small areas of gravel not over 30 ft. deep, a 5-cu. yd. dragline dredge could make a profit where a bucket-line dredge could not do so. As an example: compare the dredging of 3,000,000 cu. yd. of 10 gravel 28 ft. deep with bucket line, costin 4¢ Per cu. yd., and with a 5-cu. yd. dragline dredge operating at 6¢ Per cu. yd. Because of small yardage, new equipment is not warranted, therefore we can assume that the dredges of both types are used equip-ment, fully depreciated. Dismantling, mov-

Jan 1, 1946

By W. Rostoker

LAVES and Wallbaum1 and more recently Duwez and Taylor' have reported on the occurrence of a family of intermediate phases having the composition Ti2X, where X may be Cu, Ni, Co, Fe, or Mn.

Jan 1, 1953

By AIME AIME

THE stage is set for the 1930 Annual Meeting. It will take place in the Engineering Societies Building. Feb. 17, 18, 19 and 20, and an unusual pro- gram of technical papers, symposia, lectures and addresses, interspersed with luncheons, dinners, excursions and worthwhile entertainment for the four days has been arranged. The curtain rises on Monday morning and the first act is by the entire company-registration. Then the meeting hits its stride, for there are ten technical sessions on Monday, and the range of subjects includes most of the Institute membership. The Committee on Coal and Coal Products, which is about to become the Coal Division, presents a symposium of a dozen or more papers on Coal Classification, concluding its afternoon session with several papers on general subjects. At its luncheon between sessions, C. E. Bockus, president of the National Coal Association, will be the honored guest. Papers of theoretical character will be discussed at the morning session of the Committee on Geophysical Prospecting; at its afternoon session there will be presented summaries of results obtained at various properties by methods described at previous meetings of this group and permanently recorded in "Geophysical Prospecting," published by the Institute early in 1929. Members of the Petroleum Division should not overlook the paper by Theodor Zuschlag, on this Committee's program. It is entitled, "Oil Structure Mapping by the Sundberg Method." Members of the Iron and Steel and Institute of Metals divisions will find it profitable to attend the session on Engineering Education on Monday afternoon. E. A. Holbrook has arranged a program of ten-minute talks on Metallurgical Education which are designed to get down to "brass tacks." and the practical man may, in discussion, contribute as well as learn. At 5 p. m. Thomas T. Read will lecture+ at Columbia University, on "Recent Progress in Economics of the Mineral Industries."

Jan 1, 1930

By John M. Lovejoy

CURRENT production of petroleum on such a vast scale presents many interesting problems- the solutions of which are important not only to those directly interested in the business, but to the nation as a whole. The industry is relatively young. Until the discovers of the Lucas gusher at Spindletop in 1901 petroleum production had not exceeded 60,000,000 bbl. per year compared with 1,100,000,000 bbl. in 1936. In 36 years then, the modern oil business, production, transportation, refining, and marketing has developed. I will first present a brief history. of oil production as a background for consideration of the present situation.

Jan 1, 1937

By Charles H. Morgan

THE case of Henry Cort comprises: (1) the nature of Cort's inventions;, (2) their value to England and to mankind,; (3) the remuneration received therefor by him or his family; and (4) the suitable permanent record and recognition of his services by the representatives of the art lie founded-a debt long over-due, and still unpaid. I. CORT'S INVENTIONS. Under this head, it is unnecessary here to enter into details. The facts have been repeatedly published, and a brief outline of them will be sufficient for my present purpose. . Henry Cort, born in 1740 at Lancaster, England, became a navy broker in. London about 1765, and gained from that business in about ten years. something more than £20,000, which lie devoted to perfecting the manufacture of iron, building a mill at Fontley, near Portsmouth, and prosecuting, between 1777 and 1783, the experiments which culminated in .his two patents, one for puddling iron and the other for shaping it by rolling between grooved rolls.: Careful study of the contemporary evidence, including Cort's specifications, the testimony (in act as well as word) of his business rivals, the public declarations of eminent authorities, and the history of the times, leaves no possible doubt that Cort was the real inventor, of

Mar 1, 1905

By H. M. Chance

Jan 1, 1887

By E. D. Gardner

Apparently the widespread agitation for the codification of our mining laws has had its effect, and it is quite possible that Congress will take up the question during this present session. The greatest objection to our present statutes pertaining to metalliferous deposits seems to be directed against the law of the apex. Those who are not in favor of changing this law are very far in the minority and they apparently realize that it is useless to urge its retention. Next in importance to the repeal of the law of the apex, seems to be a widespread advocacy for the repeal of the law requiring discovery of mineral before a valid location of a mining claim can be made. To a lesser extent there appears to be a desire to have the law changed so as to allow patent for claims without mineral discoveries. The purpose of this article is to review the arguments in favor of the proposed change of the discovery requirement, to show some of the evils that may be expected to result therefrom, and to consider whether a system may be devised to correct the undesirable features of the present law in this respect and at the same time not expose the mining fraternity and the general public to the evils which would result from the repeal of this fundamental requirement. Under the law as at present framed, the validity of a mining location is dependent upon the fact of discovery of mineral within the boundaries of the land claimed. " * * * but no location of a mining claim shall be made until the discovery of the vein or lode within the limits of the claim located" (Sec. 2,320, U. S. Rev. Stat.). All authorities agree that discovery is the source of the miners' title. Lindley, in his valuable work on Mines (3d Ed., Sec. 335), lays down the rule in part as follows: "Discovery is the initial fact. Without that no right can be acquired. * * * Such discovery must precede the location, or be in advance of intervening rights. The proof of recording and marking a claim will not authorize the court to presume a discovery." As is well stated by the U. S. Supreme Court in Erhard v. Boaro (113 U.S. 536):

Jan 1, 1917

By A. K. Mukherjee, John E. Dorn

The effects of strain rate and temperature on the critical resolved shear stress for (321)[111] slip were determined for the silver-rich CsCl type of intermetallic compound AgMg. The flow stress increased only slightly as the test temperature was first decreased below room temperature; a rapid increase in the flow stress was obtained with yet further decrease in temperature from about 250' to 4OK. The effect of both the temperature and strain rate on the flow stress over the low-temperature range could be rationalized satisfactorily in terms of the Peiwls mechanism when the deformation was controlled by rate of nucleation of pairs of kinks. IN spite of the well-documented interest of metallurgists and engineers concerning the mechanical behavior of intermediate phases and intermetallic compounds, very little definitive information is available on this important subject. As recently summarized by westbrook,1 only limited and modest progress has been made thus far in elucidating the details of the mechanism of plastic deformation for the intermetallic compounds; the available information largely concerns phenom-enological descriptions of empirical observations and experimental facts, principally with reference to poly crystalline aggregates. The present report on the elucidation of the rate-controlling mechanism for slip in the bcc structure of AgMg is part of the comprehensive program of a systematic investigation on the mechanical behavior of intermetallic compounds. The intermetallic compound AgMg has a CsCl type of lattice structureZ and is completely ordered up to its melting point of 820c3 This material was selected for our present investigation because of its simple crystal structure, moderate and congruent melting point, ordered structure persisting up to the melting point, and some solubilities of the constituent elements, which could be expected to help in the growing of single-crystal specimens. Whereas previous investigations on the properties of AgMg include hardness,*"6 slip systems,7 tensile flow stress of polycrystalline specimens,' and electrical resistivity,4 the current investigation will be directed principally at elucidating the rate-controlling dislocation mechanism responsible for slip in single crystals at low temperatures. It will be shown that the strain rate is consistent with a model involving the rate of nucleation of pairs of kinks by the Peierls mechanism for plastic deformation. EXPERIMENTAL TECHNIQUES Single-crystal specimens of the AgMg intermetallic compound were prepared and tested as follows: 1) A master alloy ingot of AgMg was produced by melting and chill casting the high-purity silver (99.995 wt pct) and high-purity magnesium (99.997 wt pct) in an induction furnace under a helium atmosphere. 2) Sections of the above-mentioned ingot were placed in a graphite mold containing a spherical cavity in which a single-crystal sphere of 1 in. diam was grown under helium by the Bridgman technique. 3) The operative slip systems were investigated at room temperature on a singlecrystal of AgMg, from measurements of the angles made by the slip traces on the two surfaces of the specimen, which were at 90 deg to each other. The investigation confirmed that the AgMg compound undergoes slip primarily in the (321) plane and in the [Ill] direction, but a small amount of secondary slip was also noticed in the (112) (111) system. No slip was observed in the (110) planes. 4) The single-crystal sphere, mentioned earlier, was oriented in a graphite mold containing a cylindrical cavity of 3/8 in. diam above the spherical receptable to give the angle xo = 45 deg between the axis of the cylindrical bar and the normal to the slip plane (321), and the angle AO = 45 deg between the slip direction [Ill] and the axis of the bar. Oriented single-crystal bar seeds were produced by melting, under a helium atmosphere, a polycrystalline bar in the cylindrical cavity above the oriented spherical seed and by growing an oriented single-crystal bar from the seed. 5) Finally, oriented single-crystal specimens were grown from these cylindrical seeds. 6) The cylindrical specimens were machined in a High-Tension Spark Cutting unit to give a 2-in. gage length. The spark-machined gage section was elec-tropolished in a bath containing 200 ml of H3PO4,

Jan 1, 1964

By G. H. BUCHANAN

ALTHOUGH the nomenclature of the chemical tools of flotation is probably familiar to you, it will do no harm to review it; . In order to make the terms more real I have employed an illustration which likens flotation to an old-fashioned balloon ascension, such as we witnessed in boyhood at the county fair. The mineral to be floated is the aeronaut, conspicuous in his gilt-spangled tights, who is to be separated from you and me and the other small boys who are standing about, said boys being the g-a-n-g-u-e, or g-a-n-g, as we would have spelled it. The oil film surrounding the bubble is the counterpart of the silken fabric of the balloon, and bubble and balloon will rise for. the same reason, namely. that the fluid outside it is heavier than the fluid within. In flotation reagent nomenclature the material of which the bubble is made is called the "frother.",

Jan 1, 1930

By AIME AIME

ON April 7 the twentieth national Open-hearth Conference of the A.I.M.E. will be held in Birming¬ham, Ala., in conjunction with a meeting of the Committee on Blast Furnaces and Raw Materials. At least 300 engineers and operators are expected to attend. Birmingham, the industrial city and iron, and steel center of the South, has been called the "Magic City." Men actively engaged in business in Birmingham today have seen practically every building in the business district erected, have witnessed the establishment of every existing industry, and have hunted birds cm the site now one of the busiest corners of the business district. Incorporated as a town in 1871, the city today has a population of more than 380,000 in its metropolitan area. It is

Jan 1, 1937

By Gerard Matthes

ONLY in recent years has any practical headway been made in the application of aerial photography to geological problems, and up to the present time its principal value to the geologist and mining engineer has been in "areal geology;" i. e., the study of formations as revealed at the surface. The object of this paper is to set forth briefly the principal advantages that may be derived from aerial photographic data in geological work and to serve in a measure as a guide to those who may be con-templating its use. Geophysical prospecting has for object the locating of mineral under the surface. Inasmuch as the geologist's chief complaint in life is a dual one-inability to see under the surface and inability to visualize comprehensively what he does see on top of the ground-geophysical prospecting coupled with aerial photography should do much to lessen his burdens. To what extent aerial photography can be made a useful adjunct to geophysical prospecting remains to be proved, but the inference drawn here is that it holds many alluring possibilities. To avoid disappointments, it should be stated at the outset that to the :geologist or mining engineer an aerial photograph or mosaic is only a tool, the effecient use of which he must set out to master. Upon his skill and ingenuity in applying it to particular problems will depend largely the value of the results that he will obtain. Under the most favorable conditions an aerial mosaic or even a few loose photographs, because of the exceptionally comprehensive oversight which they afford of field data, such as dips and strike observations at isolated outcrops, local indications of faulting, mineral and fossil finds, greatly facilitate study and correlation, save much tedious foot work, and may repay their cost many times. Even so, types of country may be found where the most, skillful use of the best of pictures will produce results so meager as to render the cost of aerial photography entirely unwarranted.

Jan 1, 1928

By E. H. Crabtree

IN an ideal mill, with perfect milling operations, the mineral extraction would be 100 per cent, the, concentrate would be 100 per cent mineral, the tailing would assay zer.0 mineral and the milling cost would be zero dollars. Such an operation can, of course, never be attained. We can only strive to approach it as nearly as possible and in doing so most recognize .the fact that the three primary factors in milling: assay of concentrate, assay of tailing, and cost of operation bear a definite economic relationship to each other. This relation will change from time to time and will be different for different mills, depending on milling equipment, character and quality of feed, market conditions, and other factors. It is granted that for a given operation there is an economic point, but the location of this point is difficult. It is for the purpose of making some of these economic points a little more tangible that this paper has been prepared.

Jan 1, 1930

By George S. Rice

MECHANIZATION in coal mining is a phrase which has attracted world-wide attention, and those persons not engaged on the practical side of coal-mine operations seem to regard mechanization as a panacea for many difficulties of the industry. The term "mechanization" as now employed by experienced mining men is restricted to mean mechanical loading of coal at the face. In a broader sense mechanization in coal mining was begun nearly half a century ago with the introduction of compressed-air undercutting machines and locomotives and, later, of electrically operated locomotives, undercutting and shearing machines, and drills. The use of coal-cutting machines, which has increased until now about three- fourths of the bituminous coal produced is being mechanically cut, first displaced hand-picking except in a few long-wall mines, and later gradually displaced the dangerous and coal-smashing method of blasting-off- the-solid.

Jan 1, 1929

By R. A., Pallanch

SO many variations of lead-zinc ores occur in nature that it is impossible to state any rules that will apply to the concentration of ores of this type. Some have lead and zinc in approximately equal amounts; others may have pre- dominant amounts of one or the other metal. There are gradations from all sulfide to completely oxidized minerals. Some such ores carry little pyrite, others contain much more pyrite than they do lead and zinc combined. The behavior of ores in flotation is largely a function of their lead-zinc ratios. their content of pyrite or pyrhotite, the nature of existing soluble salt conditions, the character of the gangue constituents: and the speed with which the minerals float. For the purposes of this paper only those lead-zinc ores handled commonly in present-day flotation practice will be considered. These are practically all-sulfide ores with relatively minor degrees of sulphatization or oxidation.

Jan 1, 1936