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By W. C. Hittinger, J. McGlassan, J. W. Peterson

THIS paper describes the result of an investigation of the production of thin alloyed layers on a thicker substrate of pure germanium as one step in the manufacture of transistors.' The technique of alloying materials with semiconductors is a means of introducing small amounts of impurity elements in the alloyed regions of the crystal lattice of the semiconductor, the presence of which make possible the junction type transistor.2 Impurity elements are added which will produce regions having differing electrical resistivities and means of carrying current. Impurities are of two types: those which produce an excess of electrons (negative or n-type), and those which produce a deficiency of electrons (positive or p-type) in comparison to the pure semiconductor. The boundary between two such regions is designated a p-n junction. Elements in Group V of the periodic table, having five valence electrons, give rise to an excess of electrons when present substitutionally in the semiconductor lattice (usually germanium or silicon from Group IV). Similarly, elements in Group III create a deficiency of electrons. Germanium and silicon which are substantially free of impurities of either p or n-type are designated intrinsic (i-type) semiconductors. The usual junction ----trarnsistor has

Jan 1, 1958

NEW MEMBERS The following list comprises the names of those persons who became members during the period Mar. 10, 1916 to Apr. 10, 1916. ALLEN, P. R., Pres., McAlester Coal & Coke Co., Knight Templar Bldg., McAlester, Okla. BERNARD, CLINTON PERCIVAL, Min. Engr., Care Forminiere Mission Kasai, Tschikapa, Congo Belge, W. Africa. CARPENTER, GEORGE 0., Vice-Pres National Lead Co. St. Louis Mo. CLARK, WILLIAM ANDREWS, JR., Min. Engr., Pres., Elm Orlu Mining Co., Butte, Mont. CLAYTON, CHARLES YANCEY, Asst. PrOf. of Metallurgy and Ore Dressing, Missouri School of Mines, Rolla, Mo. COHEN, JULIUS MILTON, Mgr. Croesus Gold Mines, Ltd., Matheson, Ont., Canada. CRAMER, WILLIAM BRONSON, Met. at Concentrator, Old Dominion Copper Min. & Smelt. Co., Globe, Ariz. DAHL, SIMEON H., Mill Supt., Messina Transvaal Dev. Co., Messina, Transvaal S. Africa.

Jan 5, 1916

Gentlemen:-I herewith present a report on some of the more important activities of the Institute for the year 1921. The present incumbent took. over the active management of the Secretary's office on the first of July and his, work was facilitated, while becoming acquainted with the routine of the office, by the constant and., kindly assistance of the former, Secretary, Mr. Stoughton, during the following three months, and that no interruption occurred inn its regular and smooth operation is due to him and to the Assistant Secretary, who has always been ready to give the benefit of his experience and assistance. MINING AND METALLURGY Through the efforts of President Ludlow and the generous assistance of one of our members, coupled with the excellent work of Major Barbour, MINING AND METALLURGY has, during recent months, shown constant improvement, which could not have taken place, however, had it not been, for the support given by a number of our contributing members. We have every reason to feel encouraged with respect to the quality of the publication and its cost of production. For the year 1921, the net cost of MINING AND METALLURGY was about fifty cents per member, per annum. Occasional letters are received criticizing the Board for producing this publication, but they are more than offset by letters of approval. When the, full purpose of the publication is appreciated, criticism ceases. The elimination of MINING AND METALLURGY and reversion to free distribution of all papers to all members, whether desired or not, would mean such a heavy additional expense that the number of papers would have to be much curtailed. The generous cooperation of members in sending for only such papers as they particularly desired has saved, the Institute thousands of dollars. A plan is being worked out that will materially assist in securing a prompt distribution to members of all pamphlets dealing with subjects in which they are especially interested.

Jan 2, 1922

By Luis Emylnn Salas

If the ordinary wet method be attempted for silver-bullion containing tin, much trouble is experienced, varying with the amount of tin present. Even with a percentage as low as 0.05, the end-point is masked by a persistent turbidity, while with amounts ranging from 0.5 per cent. upward, the determination of the exact end-point is impossible, owing to the finely divided or colloidal metastannic acid resisting all efforts to cause it to settle, or to give a clear supernatant liquid. The object of the following experiments was to seek a remedy for these difficulties, and to find the conditions whereby the Gay Lussac method might be applied directly to these bullions. Material containing tin is met with frequently in bullion from Mexico or Bolivia; and tin is carried (sometimes in large quantities) in jewelers' sweeps. 1. A bullion was prepared containing Ag, 74; Cu, 25; and Sn, 1 per cent. A weighed amount was treated by the humid assay-method as if it were an ordinary bullion free from tin. Ten cc. of HNO, (1.21) was added, and the bottle was heated until all traces of

Jan 1, 1913

By Charles M. Means

A thoroughly modern coal-handling system has been installed at the Pittsburgh Terminal H. H. &. Coal Co.'s new No. 8 shaft, or Cover-dale mine, about 11 mi. (17.7 km.) from Pittsburgh on a spur of the Montour R. R. The Pittsburgh scam, which is the one worked, is reached at a depth of 342 ft. (104 m.). Power is delivered to the mine at 22,000 volts over a transmission line of the bow-arrow type of construction. A private telephone line connecting the various mines and the main office in Pittsburgh is carried on the same poles. The high-tension line is brought to an outdoor, step-down, transformer substation, where three 833-kv.-a., single-phase, 60-cycle, oil-insulated, self-cooled transformers reduce the potential to 2300 volts. The transformers are protected by electrolytic, aluminum-cell lightning arresters, horn gaps, and choke coils. High and low-tension busses, together with fuses, choke coils and air-break horn-gap switches with thcir remote-control operating mechanism are mounted on a substantial structural-steel tower 25 ft. (7.6 m.) in height. Mine Substation The transformer substation is adjacent to a. pressed-brick building that houses direct-current substation equipment together with switchboards, etc., for the control and distribution of power. This building also contains the hoist for the men and supplies. Main Switchboard The 2300-volt circuit is carried underground in a conduit from the transformer substation to an oil switch in the substation and supply hoist building. This is the main switch controlling the 2300-volt busbars mounted back to a twelve-panel black-slate switchboard. From the switchboard, 2300-volt circuits are carried to transformers feeding the street and house lighting systems and to other transformers furnishing power for the elevator and lighting circuits in the store building. Other 2300-volt circuits run from this switchboard to the main hoist building, fan house and auxiliary or man-and-supply hoist. High-tension wiring,

Jan 1, 1922

By Emile Gyss

THE speed of drilling rock has become an impor-tant factor in mining operations, while the place-ment of holes, kind, and quantity of explosive used. are equally important. These are a function of the rock hardness and toughness. Both of these fac-tors must be considered in compiling a table that will enable a mine operator or engineer to estimate drilling speeds in a given rock, knowing its hardness, and from its toughness, the dynamite required. The hardness of a homogeneous rock may be defined as its resistance to a penetrating medium, such as a drill-steel bit, and toughness, its resistance to with-stand rupture by the tearing apart of its minerals or parts of the same mineral. Rock hardness, as it has here been defined, is a function of the hardness of the component grains composing it, as well as grain size, shape, arrangement, and binding minerals. Rock tough-ness depends on substantially the same factors, but is measured by a totally different method. The units in which rock hardness is usually ex-pressed are either relative values or alphabetical desig-nations which carry no definite quantitative meaning. R. M. Raymond has suggested the measurement of com-posite rock hardness, based on mineral hardness as ob-tained by the Moh scale. This is done by multiplying the percentage of each mineral in a rock by the Moh mineral hardness and dividing by 100. These values convey a clearer conception in the minds of men in-terested in rock work -and are the basis of the units used in Tables 1 and 2. The hardness of rocks as it has been variously de-fined may be determined by different methods. The first method is one in which the proportionate average of the hardness of minerals making up a rock is the basis for classification. The other factors of grain size, shape, arrangement, and binding power are not considered.

Jan 6, 1927

By T. R. Cass

THE renewed interest in titanium, resulting from its increasing application as a structural material, has stimulated basic deformation studies on this metal. In the course of our work, we have developed a dislocation etchant and applied it to a perfection study of melt-grown single crystals as well as to a preliminary investigation of plastic deformation in titanium. The etchant, Keller's etch (21 cu cm HF, 64 cu cm HC1, 106 cu cm HNO3, and 160 cu cm H20), reveals the emergence of both grown-in and fresh dislocations on pure titanium and a-phase Ti-Al single crystals. Pits are produced only on surfaces within a few degrees of the basal plane; the more exactly parallel to a basal plane the surface is, the more distinct are the pits. The observed pit density, however, does not appear to depend on the surface orientation; the pits simul- taneously become less distinct as the misorientation from a basal plane increases. Etch times are short, a few seconds, for pure titanium; longer times are necessary for alloy crystals.

Jan 1, 1968

NEW MEMBERS The following list comprises the names of those persons who became members during the period Nov. 10, 1916 to Dec.10, 1916. BARNSDALL, THEODORE N., Treas. & Mgr., Highland Gas Co., 24 West Corydon. St., Bradford, Pa. BEASLEY, FRED E., Asst. Supt., Copper Refinery, Consolidated Mining & Smelting Co., Trail, B. C., Canada., BREWSTER, THOMAS T., Vice Pres., Gen. Mgr., Mt. Olive & Staunton Coal CO., 1012 Federal Reserve Bldg.,-St. Louis, Mo. BRINDLE ARTHUR ST. C.... Mining Recorder's Office, Trout Lake, B. C., Canada. BULLOCK, Harry E., Pres Kentucky-Jewel Coal Co., Lothair, Ky. BUTLER, PERCY BENNETT, Mine Operator :..P. 0. Box 335, Joplin, Mo. BUTLER, ROBERT S Supt., Three Johns Mining CO., ,Joplin,.Mo. CABOT, Godfrey, L., Carbon Black Maker, Gas Engr., 940 Old South Building Boston Mass.

Jan 1, 1917

By H. M. Strong

Nickel and carbon form a metastable nickel-nickel carbide eutectic system which was ohsen)able by freezing latent-heat arvests at pressures 210 khars. The eutectic freezing temperature Is pressure had a slope of -0.9°Cper kbar. At 50 khars, the nickel-nickel carbide eutectic was at 1297° * 5°C and 0.34 mole fraction Ni3C. The composition of the eutectic increased at an initial rate of 0.004 mol fraction per kbar. The carbon content of the a phase also increased with pressure. Seveval illustrations of nickel carbide microstruc-tures are given and data on the lattice expansion of nickel in terms of carbon content are included. IRON, cobalt, and nickel form a variety of carbides with compositions varying between MeC and MC. Of the three, the carbides of iron are most easily recovered. The nickel carbides are so unstable at temperatures above 900°C that their occurrence in Ni-C alloys is unusual. Under sufficient pressure, however, the temperature range for the stability of the ferrous metal carbides is likely to be increased, or their decomposition suppressed (e.g., see Hilliard' on FesC), providing an opportunity to study the unstable carbides more closely. This was found to be true for nickel carbide which, under pressure, formed a eutectic with nickel. This paper describes the conditions of formation of nickel-nickel carbide eutectic compositions and their subsequent recovery. Despite the comparative instability of the nickel carbides, something is already known about them through various chemical reactions at temperatures not exceeding a few hundred degrees, and from their recovery by the very rapid quenching of molten Ni-C alloys from temperatures of about 1450°C or above. At least four carbides of nickel have been reported: A discussion of the state of knowledge about Ni3C is given by ansen.' The studies of Morrogh and williams7 who obtained Widmanstatten nickel carbide structures and of sidorenko8 who first obtained nickel carbide eutectic structures are also of interest. Sidorenko used short heating times for molten nickel in a graphite crucible followed by very rapid quenching to obtain the eutectic structures. Long heating times produced only the nickel-graphite eutectic probably due to the presence of graphite crystals in the melt which nucleated graphite crystallization. According to the early work summarized by anssen,' nickel carbide may form at temperatures far above the melting point and may be recovered by very rapid quenching. More recently, Giardini and Tydings, working on diamond synthesis, found evidence for "free nickel carbide'' in high-pressure reactions carried to temperatures far in excess of the limit for diamond growth, followed by rapid thermal quench. They stated that nickel carbide was not found in association with diamond growth. In the present work, observations were made on the melting and solidification temperatures of Ni-C alloys as a function of composition, temperature, and pressure. The nickel-nickel carbide eutectic was found at pressures above 10 kbar and its variation with pressure followed up to 60 kbar. Nickel-nickel carbide microstructures were recovered by quenching under pressure from temperatures of about 1400°C and higher. The formation of nickel carbide structures under ordinary diamond-growing conditions was usually observed but the role of carbide formation as an intermediate step in diamond growth needs more study. EXPERIMENTAL METHODS The melting and solidification temperatures of various nickel-graphite compositions were observed by latent-heat arrests in the sample holder illustrated in Fig. 1. The samples were composed of mixtures of carbonyl nickel powder and National Carbon Co.'s SP-1 graphite packed to densities of about 6.4 g per cu cm. They were contained within

Jan 1, 1965

NEW MEMBERS The following list comprises the names of those persons who became members during the period of Apr. 10, 1918, to May 10, 1918. BALLARD, JOHN I Supt., Cable Mining Corpn., Cable, Mont. BURKMAN, JOHN M. F., Constr. Engr., U. S. Smelt. Refin. & Min. Co., Care -University Club, Mexico City, D. F. CALLEN, ALFRED COPELAND, Head, Mining Engineering Dept., West Virginia University Morgantown, W. Va. CHADWICK, LAWRENCE, Chem., Mt. Elliott Copper Co., Ltd., Selwyn, via Townsville, North Queensland, Australia. CODY, FRANK W., Skimmer, Reverberatory Furnace, Arizona Copper Co., Clifton, Ariz. COOLBAUGH, MELVILLE F., Prof. of Chem., Colorado School of Mines, Golden, Colo. DODGE, ALLAN WAYNE The Dodge Agency, 104 East Iron Ave., Salina, bans. DONNELLY, LEONARD G., Pet. Geol., Sinclair Oil & Gas Co., Sinclair Bldg., Tulsa, Okla.

Jan 6, 1918

By J. P. Savely, D. E. Nicholas, R. D. Call

Progress in the technology of slope design over the past 15 years now permits the selection of rational slope angles if suitable data on geology, hydrology, and rock properties are available for a specified project. Although a full-scale slope design study remains the best course of action, there are situations where an extensive study is not feasible due to time or budget constraints. Two typical examples are: (a) selecting pit slope angles for a preliminary feasibility study at the exploration stage; and (b) coping with a slope failure in an operating mine. In both instances, slope angles must often be chosen on the basis of data that are currently available or can be readily obtained. All too often during exploration programs, a feasibility study is initiated shortly before the decision deadline to drop the property or proceed to purchase. If the only existing data at this point are a few cross-sections at odd angles showing ore and waste contacts or a dog-eared map of the surface geology, there may not be time to collect and organize sufficient information for the design of slope angles. On the other hand, if during the drilling program geologic cross-sections were constructed and the structural data compiled in tabular form, rational slope angles could be computed within the allotted time.

Jan 4, 1977

By W. A. Ver Wiebe, E. G. Dahlgren

The year 1937 must be considered the most eventful one ever experienced in the development of oil and gas activity. Out of a total of 57 new pools discovered, 18 are apportioned to eastern Kansas and 39 to western Kansas. (For statistical purposes Kansas is divided along the meridian that separates ranges 3 E. and 4 E.) In addition to numerous longdistance extensions of the large Hugoton gas field of southwestern Kansas, two other gas pools were discovered in the area lying west of range 3 E. The 37 new oil pools in that area are to be found in 13 different counties, among which Rice heads the list with a total of seven oil pools and one gas pool. Ellis and Barton Counties both added six new oil pools, while Russell County follows in fourth place with four. Among eastern counties Butler heads the list with four new pools. Cowley arid Chautauqua each accounted for three new discoveries. The number of wells necessary to accomplish this result totals 2657, of which 1915 are oil wells and 128 gas wells. The initial production of the oil wells amounted to 2½ million barrels. Although most of the wells were drilled in proven territory, there was a good deal of wildcatting. The fact that 614 dry holes were completed emphasizes the ever-present risk attendant upon the efforts of pioneers. Some of the more venturesome spirits reached out to the counties farthest west in the state. An indication of the feverish excitement reached at times is recorded in the fact that no less than 600 drilling operations were in progress during one week in May, or the fact that over 100 new locations were staked during the second week in July. During one week in May, 65 successful oil wells were completed for an initial production of 68,000 barrels. Many drilling obligations came due during the year, and this perhaps accounts for the fact that one company had as many as 59 active operations at one time during September. Another evidence of great interest in oil possibilities in Kansas is furnished by the record of sales of oil properties, which in one case reached the high figure of about $3000 per acre.

Jan 1, 1938

By H. G. Warren, E. W. Hough

Correlation of interfacial tension of the methane-n-pentane and methane-n-decane systems was made by Hough and Stegemeier by the use of the Weinaug and Katz equation. The methane-n-heptane and ethylene-n-heptane systems were investigated by the authors. Additional systems taken from the literature were the me thane-propane system by Weinaug. and Katz, the methane-n-butane system by Pennington and Hough, and the n- butane -carbon dioxide system by Brauer and Hough. These systems were analyzed by the Weinaug-Katz equation and the Sugden equation on the IBM 1620 11 computer using a regression analysis program. Parachor and exponent values for each component and system were determined. The experimental work was close to the critical point of the light component in the n-butane-carbon dioxide and ethylene-n-heptane systems, between the critical points of the light and heavy components in the methane-n-pentane, methane-n-heptane and methane-n-decane systems, and close to the critical point of the heavy component in the methane-pmpane and methane-n-butane systems. An empirical formula was developed to find a value of the constant B in the Sugden equation for binary hydrocarbon systems from the parachor values of the two components. Interfacial tension for binary hydrocarbon systems was found to be a direct function of liquid-vapor phase density difference in the same manner as a single-component system. DISCUSSION Interfacial tension may be defined as the measure of the specific free surface energy between two phases having different compositions.1 The interfacial tension (IFT) for a binary system may be predicted for any temperature and pressure if the

Jan 1, 1967

By Leon O. Hart

The nickel-chromium alloys of importance are those containing iron and those free from iron. The most important alloys containing iron, with regard to high tonnage, are the nickel-chromium steels. Straight nickel steel was introduced about the year 1889, but it was not until 1895, when it was found that the addition of chromium greatly increased the strength and resistance to shock, that nickel-chromium steels came into use. The three types of nickel-chromium steels developed at this time were: Type 1, containing 3.,50 per cent. nickel and 1.50 per cent. chromium; type 2, containing 2.00 per cent. nickel and 1.00 per cent. chromium; and type 3, containing 1.50 per cent. nickel and 0.50 per cent. chromium.

Jan 1, 1921

ARIZONA Tucson University of AriZona, Mining Engineering Society. B CALIFORNIA Berkeley University of California, Mining Asso. B University of California, Library. B & T Los Angeles Chamber of Mines and Oil. B Southern California Local Section. T Public Library. B & T Oakland Oakland Free Library. T San Francisco California State Mining Bureau. T Mechanic's Merchantile Library. B Mining and Scientific Press. B Stanford University Stanford University Geological and Mining Society. B San Diego Public Library. B COLORADO Boulder University of Colorado, Library. T Denver Bureau of Mines. B Colorado Scientific Society. B Mining American. B Denver Public Library. B & T Golden Colorado School of Mines Magazine. B Colorado School of Mines Library. T Colorado School of Mines Scientific Society. B

Jan 1, 1923

By W. P. Haynes

No wildcat operations are recorded from France during the past year, and no new discoveries have been made. In northern Africa, in Morocco, some prospecting continued in the Gharb and Tselfat regions. Only very small production or shows were found. At the close of the year one cable-tool well (depth 400 meters) was drilling in the Tselfat district, and one rotary well in the Gharb. In Tunisia one well was drilling at Sloughia. Refinery building has been active under the new petroleum law, no less than six plants now being under construction. At Pechelbronn, it is estimated 130 wells were drilled, of which 73 wells, or 56 per cent, were productive. Total drilling was 45,000 m. One new Jurassic horizon was discovered. In the mining area approximately 17,500 m. of new gallery were driven. Production at Pechelbronn for the first nine months was as follows: From wells, 233,013 bbl.; from mines, 164,815 bb1.—a total estimated production for the year of 532,000 bbl. Production at Gabian was 3780 bbl. for the year. In Algeria production from Tliouanet was small, being estimated at 6510 bbl. This production is from Helvetian sands (Miocene) around a salt plug. Italy Production for the year was 211,500 bbl., an increase of 62 per cent over that of last year. Drilling to the extent of 97,000 ft. was done mainly by the A. G. I. P., the government company in the Province of Emilia. More locations are being tested in this area, where geophysical results have shown indications of buried uplifts. Oil has been encountered on two of these structures, at Fontevivo and Podenzano, but the wells have given trouble with salt water. The chief producer is the Societa Petrolifera Italiana at Salsomaggiore and Valezza. The production is from sand lenses at relatively shallow depths. New concessions of 2000 hectares were granted at several points in the Po Valley, and geophysical work is being carried on. The A. G. I. P. is working on a five-year program of exploration to test new areas.

Jan 1, 1933

By T. E. Leontis

Several publications1-7 during the past few years have demonstrated the markedly greater effect of cerium, as compared to all other alloying elements, in enhancing the strength and creep resistance of magnesium at elevated temperature either with or without the presence of other elements. In the work reported in Ref. 1-6, the cerium was added in the form of Mischmetal, which contains all the rare earth elements in essentially the same proportions as they occur in monazite sand, the principal ore of these metals. Mellor and Ridley7 have presented the creep characteristics at 200°C of magnesium alloys prepared both with pure cerium and with Mischmetal. Up to the present time, however, no comprehensive study of the effect of the various component elements of Mischmetal on the properties of sand-cast magnesium has been made. This hiatus in magnesium technology undoubtedly is associated with the difficulty in obtaining the rare earth metals separately. This investigation provides such a survey, the object of which was to determine which of the elements present in Mischmetal contributes the greatest effect in developing high strength and high resistance to creep at elevated temperatures. Toward this end the compositional variation of these properties has been determined as a function of temperature in the following alloy systems: 1. Magnesium-Mischmetal 2. Magnesium-cerium-free Misch- metal 3. Magnesium-didymiuin 4. Magnesium-praseodymium- lanthanum 5. Magnesium-cerium 6. Magnesium-lanthanum This designation, based on the names of the metals as furnished by the producer, is used throughout the paper in order to avoid the complicated system of listing all the elements present in the more complex alloys. The composition of the metals and the alloys is discussed in detail below. Preparation of Alloys ALLOYING INGREDIENTS The chemical composition of each of the six alloying ingredients used to prepare the alloys reported in this paper is given in Table 1. In each case, the percent total rare earths, percent cerium, percent neodymium, percent praseodymium, and percent thorium were determined in addition to the listed impurities. The percent lanthanum was determined by difference from the total rare earth content and consequently includes the other elements (samarium, terbium, yttrium, etc.) present in Mischmetal. These additional elements, however, seldom amount to more than 1 to 2 pet of the total rare earth content of Mischmetal. The iron content of the Mischmetal is considerably lower than that of the other metals. This grade of Mischmetal is now readily available. The metals are listed in the order of decreasing complexity. Elimination of the cerium from Mischmetal results in what the trade calls "Cerium-free Mischmetal." Carrying the separation a step further by eliminating the lantha-

Jan 1, 1950

By S. H. Chauvenet

THE binding of the boshes and in walls of blast furnaces has always been an expensive piece of work. When the old stone stack was replaced by the iron shell, the brickwork was kept at a thickness of five feet or more. These five-foot walls were still too thick, and the practice now is to have as thin walls as possible and to have a free circulation of air about the brickwork of the furnace. The "basket," or lattice-work binding, accomplishes this object, but it is expensive, as to first cost, and, if any change in the diameter of a furnace has to be made, it necessitates an alteration of the binding or of the thickness of the walls.

Jan 1, 1882

By S. H. Chauvenet

The binding of the boshes and inwalls of blast furnaces has always been an expensive piece of work. When the old stone stack was replaced by the iron shell, the brickwork was kept at a thickness of five feet or more. These five-foot walls were still too thick, and the practice now is to have as thin walls as possible and to have a free circulation of air about the brickwork of the furnace. The " basket," or lattice-work biuding, accomplishes this object, but it is expensive, m to first cost, and, if any change in the diameter of a furnace has to be made, it necessitates an alteration of the binding or of the thickness of the walls.

Jan 1, 1882

A general discussion on the subject of Crushing and Grinding was held on August 24, 1927, during the meeting of the Institute at Salt, Lake City. G. H. Clevenger, Chairman of the Milling Methods Committee of the Institute, made the following introductory remarks "Several years ago, a number of us felt that the time was ripe for a fundamental investigation of crushing and grinding. At the outset, it appeared that the first thing we needed was a yardstick whereby grinding efficiency could be measured. "The U. S. Bureau of Mines has been most generous in cooperating with the Milling Methods Committee in getting this work well undrr way. John Gross, who served the committee for a year as secretary, was placed in charge of the investigation and has been ably assisted by S. R. Zimmerley. "Messrs. Gross and Zimmerley will now present the Progrcss Report covering their work to date." Progress Report J. Gross, Salt Lake City, Utah.—-This has not been a simple problem, and when I tell you that me can give you a verbal report of what we have done during three years in five or ten minutes you will realize that we have necessarily done a great deal of work that dors riot appear in the final results. We have been in a virtually new field. Therefore, we have had to feel our way at each step so as to be fairly sure we were correet. The first thing that was realized in this problem ass that unless we had some method of measuring what happened when we crushed an ore, we might as well quit and not go further. we realized that if we tried to measure the results of crushing or grinding by the ordiuary sizing test we would not get anywhere. We could sieve down to say 200 mesh fairly accurately; we could even go one sieve size further with a little less accuracy, and then we were absolutely lost, unless we went into microscopic measurement. Even this latter method would not have been satisfactory. The question was: what were we going to measure? If we were going to measure size, we might measure one particular dimension of a particle and be off 200 per cent. or more. If we tried to measure surfaee, we would have something tangible; the surface of a particle, no matter how irregular, is something definite, far more definite than any linear dimension would be. Moreover, if we could measure surface, we would immediately have a method of checking the Rittinger law as to whether it was or was not correct. So the first thing that we sought. was a method whereby we could measure surface on crushed particles or, we will sag., on particles; it would not make any difference whether crushed or not. It then became a question of what kind of particles we were going to use in obtaining a method for surface measurement. We realizcd that it would be rather a corn-

Jan 1, 1928