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By George B. Clark

THE geological data emphasized so successfully in prospecting for new deposits, that is, structural controls, strength of solutions, and type of mineralization, are basically those required for successful exploitation. In the mining of newly discovered deposits the most economical methods should be employed as early as possible to keep the overall cost per unit produced at a minimum and to permit maximum extraction of valuable minerals. A crucial question is: How can geological data be translated into useful quantitative results which will aid in achieving this end? H. E. McKinistry1 has suggested that a solution may be reached in one of two ways: 1-the usual approach, use of judgment based on experience; or 2-mathematical calculations and tests on models, both subject to certain limitations. He also suggests that in addition to better use of geology more case data and theoretical data are needed on which to base sound judgment. Further research, therefore, is necessary. Perhaps in this field the emphasis should be on more specialization in mining methods and ground movement by men with thorough training in physics, engineering, geology, and underground mining. These specialists would be equipped to point out the most economical and scientific methods of exploitation.

Jan 8, 1954

By T. R. Scott

The acid pressure leaching of zinc-lead flotation concentrates from the McArthur River deposit, Northern Territory, Australia, has been studied in a three-stage, continuous, co-current system, using titanium reactors of 6 gal capacity. The starting pulp contained 2.7 lb solids per gal of synthetic spent electrolyte and the final liquors contained 120-125 gpl Zn. Parameters investigated included temperature (95-120°C), oxygen pressure (30-100 psi), acid addition (80-130% of theoretical), and leaching time (35-65 min per stage). Technical factors studied included mixing and pumping of feed, agitation, settling and washing and control mechanisms. The chemistry of liquor impurities, of scale formation in autoclaves and of lead jarosites in residues was studied in some detail. Results indicated that 90-93% zinc recovery could be obtained with a "low- acid" process, using 113°C and 70 psig with oxygen as the favored operating conditions. Residues contained 16-18% elemental sulphur and 15% lead, together with unreacted pyrite and gangue minerals. Pelletizing of residues was impracticable, and alternative suggestions for the recovery of lead, sulphur and silver are discussed. Preliminary estimates for plant and operating costs are given and enable some comparison to be made with conventional procedures.

Jan 1, 1973

By T. Wasson

Midland and Isabella counties have been the centers of activities for the year 1932. The major part of the 6,967,000 bbl. produced during the year was obtained from the old Mt. Pleasant field and the Eastern Extension field. The total production to the end of 1932 for Michigan, from all fields since discovery, is 20,679,600 bbl. Production in the Eastern Extension field was obtained from Dundee limestone of Devonian age, at a depth of about 3600 ft. As a result of the year's activity in this area, the limits of the Eastern Extension have been defined. No new fields have been discovered. A number of prospective areas have been drilled and condemned by dry holes. Probably the most outstanding development of the year was the discovery of oil on the Yost farm, in sec. 35 of Greendale Township, Midland County, by the Pure Oil Co., in the early part of December. Production is from the Dundee limestone similar to that in the Eastern Extension but is 4 miles south of that area. The first well has averaged about 500 bbl. per day since completion. It is near the center of a solid block held by the Pure Oil Co., so that rapid development due to competitive drilling is not expected. During the early part of the year the Midland-Isabella area was under proration, but on May 17 proration restrictions were discontinued and remained so until the end of the year. While the Eastern Extension saw the principal activity, some work was done in other fields of Midland and Isabella counties, but very little new production was added. The Vernon field on the north showed a slight increase in production over 1931. The Leaton field decreased. The well in Porter Township, Midland County, is still kept in the production ranks but very little drilling was done in that area. The old Saginaw field, Saginaw County, still remains the only spot in the state where commercial production is obtained from the Berea sand. It showed a slight decline over 1931 with no new producers for the year. The Muskegon field on the west side of the state showed a considerable decline over 1931, but owing to the rejuvenation of some wells by the use of acid this drop was not as great as might have been expected. Only two new producers were drilled in that area.

Jan 1, 1933

(Members are urged to send in for this column any notes of interest concerning themselves or their fellow-members.) Members and guests who called at Institute headquarters during the period June 10, 1916 to July 10, 1916: Arthur Adams, Miami, Ariz. John M. Lovejoy, New Rochelle, N. Y. J. H. Batcheller, Mattapoisitt, Mass. J. F. Manning, Seoul, Korea. R. S. Bonsib, Low Moor, Va. E. P. Mathewson, Anaconda, Mont. E. L. Booth, New York, N. Y. Edwin W. Mills, Seoul, Korea. C. L. Bryden, Scranton, Pa. Arthur Notman, Bisbee, Ariz. F. Crabtree, Pittsburgh, Pa. L. B. Reifsneider, Daiquiri, Cuba. L. B. Eames, Pueblo, Colo. W. S. Schuyler, Berkeley, Cal. S. J. Gormly, Guayacan, Chile. 0. N. Scott, Toronto, Ont., Canada. Ernest A. Hersam, Berkeley, Cal. Arthur F. Taggart, New Haven, Conn. A. W. Hudson, Douglas, Aria. Warren D. Thompson, Boston, Mass. Chas. W. Johnston, West Norfolk, Va. Thor. Warner, IGngman, Ariz. Rodolphe L. Agassiz has been chosen president of the Calumet & Hecla Mining Co., an office which has been vacant for over a year. Percy E. Barbour, Managing Editor of the Engineering and Mining Journal, resigned his commission as 2d Lieutenant in the Main Coast.

Jan 8, 1916

ENGINEERS AVAILABLE (Under this heading will be published notes sent to the Secretary of the Institute of members or other persons introduced by members.) Member, Cornell M. E., graduate, aged 31, married. Will soon complete 2 years' engagement in the Russian oil fields. Eight years' practical experience in drilling for and producing oil. Can speak Russian fluently and some French and German. Open for engagement. Interview after August 15, in the United States. No. 299. Metallurgist, four years' experience in electric furnace operation on steel, ferro-alloys and smelting of ores, both practical and research, desires position as metallurgist or superintendent. No. 314. Member, technical mining graduate. 5 years' experience in coal and metal mines and construction work. Married. Aged 27. Employed at present. Interview in Salt Lake City or Denver. No. 316. Member, American, aged 39, married, desires position as superintendent or mine superintendent. 14 years' experience in opencut and underground work. 12 years' Spanish, Portugese, Cuban and Mexican labor. Fluent Spanish. Good training in first aid and safety first. Specialty of high explosives and steam-shovel work. Good costs. Go anywhere, but tropics preferred. References. Interview, New York or Philadelphia, No. 318.

Jan 10, 1916

By H. N. Eavenson

The eleven mines of the United States Coal and Coke Co. in the Pocahontas coal field are situated in McDowell County, W. Va., which is a mountainous region. The valleys rarely exceed 200 ft. (60 m.) in width, the hillsides slope from 25°to 33°, and the tops, from 600 to 900 ft. above the valleys, carry practically no level land. At least 80 per cent. of the area is covered with timber. All the workings are drift mines; and while the average grades of the seams worked are ample for drainage, local dips and swamps necessitate the use of a large number of local pumps or of numerous drainage ditches to keep the mines free from water during heavy rains. The water handled in any mine is not great, compared with the coal output, and usually causes little trouble except during extremely wet periods. In new workings, the water encountered, except in rare cases, is trifling; it is only after rib drawing has started and the surface has been broken that water troubles begin. The strata overlying the coal are sandstone, shales, and slates; as the soil is thin and sandy, it does not tend to puddle and stop the cracks, which remain open for a long time. As mining progresses and the robbed area increases, the broken area becomes larger, increasing the openings into the mined territory. The cover over the robbed portions of the mines varies from 30 to 750 ft. (9 to 228 m.). When the ground is saturated, considerable water finds its way into the mines the day after a heavy rainfall and for three or four days it tends to fill the low places, wash the tracks, etc. and unless from three to four times as many pumps are installed as are normally needed, considerable output is lost. In most cases the water will flow from the mines, and the obvious solution is to provide drainage ditches of ample size to carry the maximum flow expected, so that the inflow will have no opportunity to flood the working places. Laying out the drainage headings on the proper average grades was an easy matter but where blasting was necessary to provide uniform grades, as was frequently the case, it was important that the maximum flow to be expected and the size of ditches to be provided should be known so that only rock work necessary to provide proper drainage

Jan 1, 1922

By H. T. Byck

THE plastering properties of six representative California drilling muds were studied over a temperature range of 70° to 175° F. at several mud weights, using a high-pressure circulating filter press with full size consolidated cores. In all tests, with untreated as well as with chemically treated muds, the filtration rates at elevated temperature were higher than at low temperatures and in nearly every case this increased filtration rate was notably larger than could be attributed alone to the decreased viscosity of water-the flowing medium-at elevated temperatures. It is concluded that no existing method will permit even an approxi-mate determination of the filtration rate at high temperature from data at room temperature. It is necessary to measure filtration at the tem-perature actually anticipated in the well, or to make a sufficient number of tests at various lower temperatures so that a small extrapolation of these data to the anticipated well temperature may be applied. Such tests should be carried out on the mud as actually used in the well. The viscosity of each of the muds was determined over the same temperature range. While no relationship was observed between mud viscosity and plastering properties, it was found that chemical treatment of the muds for viscosity reduction shifted the temperature of minimum viscosity to appreciably higher values than for untreated muds.

Jan 1, 1939

By T. J. Hudson, P. B. Queneau, J. D. Prater

The process parameters for effective utilization of nitric acid as an oxidant for copper-iron sulfides have been developed. Leaching variables found to be important were acid concentration, temperature, time, atmosphere, pressure, mineral type, particle size, and percent solids. Particular attention was devoted to analysis and control of fumes evolving during the oxidation. Data were recorded on metal extraction, elemental sulfur formation and oxidation, product gas composition and evolution rate, reagent consumption, and residue flotation response. The study was concluded by laboratory testing a flowsheet based on the foregoing observations. Ninety-eight percent of the copper contained in a chalcopyrite-bornite concentrate was recovered, requiring 1.6 lb of nitric acid to be regenerated externally per pound of copper extracted. Iron remained in the leach residue as hydrogen jarosite and was ultimately rejected from the system by froth flotation. Sixty percent of the sulfur contained in the copper concentrate reported in the elemental form; the remainder was oxidized to sulfate and eliminated with the hydrogen jarosite in the flotation tails or by neutralization of the solvent extraction raffinate with lime. Nitrogen was evolved primarily as NO and NOD; up to 3% N2O also was present. Gases containing sulfur were absent except when pyrrhotite was solubilized in the absence of soluble copper. In this case, HAS was evolved.

Jan 1, 1974

By Donald F. Taylor

TANTALUM and columbium are newcomers in the world of metals. Many of the metals described in this volume had been known and used for centuries before either tantalum or columbium was known to exist. The scarcity of the ores and the comparative difficulty of extraction delayed their technology until specialized methods of processing could be developed. HISTORY Early in the nineteenth century, 1801, Hatchett discovered a new oxide, which he called columbium oxide, and a year later, Ekeberg announced that he had found a new element, which he named tantalum. The preparation of the metal tantalum in impure form was first announced by Berzelius in 1824, but the actual production of ductile metal did not occur until 1903, when von Bolton, of Siemens and Halske, developed a process for the production of tantalum pure enough to be drawn into electric-lamp filament wire. The use of tantalum as a filament wire began to decline when ductile tungsten was introduced in 1909. In 1921, C. W. sake, of Fansteel Metallurgical Corporation, produced the first ingot of tantalum metal in America. The first ingot of columbium was produced in 1927 in the laboratory of the same company. There are several good reasons why tantalum and columbium are often mentioned together. They occur together in their important minerals, are similar in many of their properties, and are

Jan 1, 1953

C. W. GOODALE, Butte, ,Mont.-While there are many points in Mr. Read's, paper which I am not prepared to discuss thoroughly, I am inclined to believe that difficulties are involved in the establishment of all employment bureau, which shall have exclusive control over the employment and discharge of workmen. I suppose you .have heard a great deal: about the so-called "rustling card? at the works of the Anaconda company. That is a very innocent sort of card, although the I. W. W. organization has made a great deal of noise about it. An applicant for a job is handed a blank on which he tells his nationality, his age, whether married or single, and the place of his last employment. The company then writes to the place where he says he was last employed to find out whether he is telling the truth; we do not ask the previous employer whether the man is blacklisted or has anything; against his record; but simply, "Was this man formerly in your employ?" A great hullabaloo has been made, about this practice by some of the men in Montana who are afraid, of their own records; but out of 53,000 applications for employment received by the Anaconda company since the employment bureau was formed, only 647 were rejected, which does

Jan 1, 1918

By R. Jr. Schuhmann

PROBLEMS in expressing, interpreting, and using size-distribution data recur in many phases of mineral dressing; therefore it is desirable that size analyses be ex-pressed in such a form, either numerically or graphically, that comparisons can be made readily. The size distribution of comminuted material is a result of a specific physical operation on the material and therefore should be governed by some definite physical principle, or cause-effect relation. Although this principle has not been dis-covered, it has been found that the size distribution of comminuted, homogeneous solids may be expressed by relatively simple mathematical equations. Two equa-tions in particular, proposed by Gaudin1 and by Rosin and Rammler,2 respectively, have stood out, both having wide demon-strated ranges of application. The form and the method of application of the two appear almost irreconcilably different on the surface, but, as will be shown, they are asymptotic in the fine sizes when expressed in the same units. This paper gives the results of a further study of the Gaudin and Rosin-Rammler relations, made with the object of develop-ing a form of size-distribution equation that will be more usable and more signifi-cant-particularly in comminution studies, both for interpreting the nature of size distribution and for evaluating surface. The work is summarized in the following:

Jan 1, 1940

By S. B. Lement

THE nature of the carbides that form during the tempering of martensite is a subject of continuing controversy. The only direct methods of identification available are X-ray and electron diffraction. These methods are subject to several difficulties. Only a relatively few diffraction lines of appreciable intensity emanate from carbide phases that are formed at low tempering temperatures. Furthermore, some overlapping of carbide and matrix lines occurs. There is also the problem that numerous lines in the patterns of possible carbide phases that may be present have about the same d-spacings. Increasing the number of carbide lines and eliminating the matrix lines can be accomplished by extraction techniques. However, there is always the possibility that a change in carbide structure will occur as a result of removal from the parent matrix. Therefore, such techniques as electrolytic extraction and making extraction replicas should be checked by other methods. For identifying small amounts of carbide in a tempered martensitic matrix, electron diffraction carried out in reflection is more advantageous than X-ray diffraction. To properly prepare a specimen for reflection electron diffraction, an etchant that will selectively attack the matrix and thereby cause the carbide particles to stand in relief should be used. With an electron beam directed at a grazing angle to the specimen surface, the major contribution

Jan 1, 1960

By W. F. Hosford, E. W. Kelley

Deformation studies have been conducted at room temperature on single crystals of magnesium and magnesium alloys with thorium and with lithium. Single crystals oriented to suppress shear on the easily activated basal slip systems were deformed by plane-strain compression. Compression along the C axis was accommodated by {1011} banding. Compression perpendicular to the unconstrained c axis activated {1012} twinning, and, after virtually complete twinning, deformation continued by {1011) banding in the twinned material. Compression perpendicular to the constrained c axis was accommodated by the simultaneous operation of (1012) twinning against the constraint and (1011 ) banding. Although this orientation was favorable for {1010)(1210) prism and {1011}(1~10) pyramidal slip, these modes were not observed in pure magnesium or in Mg-0.5 pct Th. However, {10i0)(1~10) prism slip was observed in crystals of Mg-4 pct Li during compression perpendicular to the constrained c axis. Fracture in all materials occurred parallel to (1124) or {l~il) depending on the orientation and composition of the specimen. THE mechanical behavior of the hcp metals is strongly anisotropic. Although several slip systems have been reported the slip is cpmmonly in the directions of closest packing, the (1210),' and this does not produce strains parallel to the c axis. Hence the inherent anisotropy. The deformation mode most easily activated in magnesium at room temperature is (0001)(1210)- basal slip. Also {1010}(1~10) prism slip and {1011)(1210) pyramidal slip have been reported, primarily at elevated temperatures.2"4 However, at room temperature the shear stresses to activate the prism and pyramidal modes are roughly a hundredfold greater than that required for basal slip.'j4 Thus prism and pyramidal slip may be expected only under special conditions of loading. Strains normal to the basal plane can be produced by twinning, however. Many twinning modes have been reported for magnesium,' with (1012) twinning the most common and relatively easy to activate. Magnesium can deform by (1012) twinning when stressed along the c axis jn tension, but not in compression. In contrast, (1011) twinning is activated by compression along the c axis and not by tension. In addition to primary twinning, secondary twinning or slip can occur within the reoriented material of primary twins.' In general at least five independent shear systems must be active to bring about an arbitrary shape change such as that in the individual grains of a deforming polycrystalline material.' Because basal slip can_ provide only two independent shear systems and (1012) twinning can only accommodate an extension of the c axis, other deformation modes must be active in magnesium for an arbitrary shape change to occur. The purpose of this investigation has therefore been to study the various deformation modes in magnesium at room temperature, with special emphasis on those modes that are less easily activated. The effect of the alloying elements, thorium and lithium, has also been investigated. In polycrystalline aggregates, unambiguous identification of deformation modes is extremely difficult and the direct evaluation of the resolved shear stresses to activate them is not feasible. On the other hand, uni-axial tension and compression experiments on single crystals may not activate some of the- deformation modes because basal slip and/or {1012) twinning cannot be suppressed in most orientations. However, it should be possible to activate all possible deformation modes using oriented single crystals and plane-strain compression. Identification of active deformation systems and evaluation of the resolved shear stresses required to activate them should be facilitated. Wonsiewicz and Backofen have recently completed an investigation of the plasticity of pure magnesium crystals at various temperatures utilizing plane-strain compression and selected crystal orientations. This technique has also been used in the present work. The seven orientations selected for study are indicated in Table I. Plane-strain compression along the c axis (orientations A and B) should activate some deformation mode _other than basal, prism, or pyramidal slip, or (1012) twinning. In orientations C and D, prism or pyramidal slip would be expected to take place. When the compressive load is applied perpendicular to an unconstrained c axis (orientations E and F) the three slip modes should be suppressed but not (10i2) twinning. In orientation G, basal slip should occur.

Jan 1, 1969

By John C. Smock

THE question of the proper valuation of mines of iron ore was suggested to me by the difficulties experienced in getting answers for the United States Census Office, while I was engaged in the work of collecting the statistics of mines in New Jersey and New York The answers to the questions relating to values of real estate of mine properties varied so greatly that it was necessary to revise them according to some general principles of valuation. Generally the returns of mine proprietors Seemed to be too low. There were, however, examples of what would be termed excessive valuation. The Subject appeared to be of practical importance, and led to the paper here presented. The following table of selected mine statistics is given, prefacing the discussion of the principles of valuation. It is in part made up of census returns and partly of data obtained directly from mine owners and managers. The mines which were Selected for the Several groups and mining districts include nearly all of those from Which the more full and carefully filled returns were received, and are also representative of their respective districts. Hence the averages obtained from them become good types of these groups or districts. The mines of New Jersey appear in Six groups, each containing from three to eleven mines, or, in all, thirty-four mines. The magnetic iron ores of New York are in four well-marked groups, and there are twenty-six mines in them. Then follow the red hematite mines of St. Lawrence and Jefferson counties; and, lastly, the brown hematite groups of Dutchess and Columbia counties, and those of the adjacent parts of Connecticut and Massachusetts. The whole number of mines represented by the table is eighty-eight, of which twenty-eight are hematite mines. The first column gives the value of the real estate; the second that of the plant; the third is the sum of these two, or the capital invested. Then follow the number of men employed, the amount of wages paid during the census year, and the value of materials used in mining and preparing the ores for market.* The seventh column gives the total expendi- * The value of materials is somewhat uncertain in many cases, as royalties are included under this head. Likewise, under wages, the cost of explosives and light is often included. Hence it is impossible to draw the line sharply between these items of expenditure.

Jan 1, 1882

Discussion of the paper of Robert H. Richards, presented at the Butte meeting, August, 1913, and printed in Bulletin No. 81, September, 1913, pp. 2299 to 2303. C. D. DEMOND, Anaconda, Mont. (communication to the Secretary*) :-Any one who has observed the increased efficiency of the Wilfley tables in a mill when fed from a reasonably good hydraulic classifier, as compared with tables fed from a spitzkasten., which is a very poor classifier, will agree to the advantage of ? better classification." It must be gratifying to Dr. Richards to know that, directly or indirectly, maim mill men are responding to his persistent advocacy of correct principles of ore dressing and are accepting the results of his investigations. As he says, these principles mean much for both the conservation of resources and the profit of operators. When Dr. Richards gives us accurate figures as to the maximum size of free mineral grains in the tailings of the Wilfley table and of the vanner, they will be of a good deal of practical value in delimiting the proper fields for the Wilfley, the vanner, and the round table. He has coined the terms ? free settling" and "hindered settling."' The series may be completed by adding "crowded settling," the main principle of action on both the vanner and the Wilfley table, which is the principle of separation in a mass of grains crowded as closely together as they can be and yet continue free to move between one another; and the occurrence of larger mineral particles in the Wilfley tailing than in that from the vanner is apparently caused by the more violent agitation, due chiefly to the purposely sudden reversal of the stroke. It seems likely that the agitation caused by the wash water dropping directly upon the concentrate on the vanner is more harmful than that due to the shake. For the very finest material that can be concentrated by usual methods, the round table is superior to the vanner because it does not, have even, the gentle agitation of the latter. The action on round tables is, not crowded settling," but "film sizing," 2 but agitation is harmful in the latter action. George Gates proved this harm 20 years ago : in slaking the first successful large-scale application of canvas tables in California gold mills he abandoned all shaking motion, although he had patented canvas tables to which such motion was applied.

Jan 11, 1913

By John Brownson

Ge-Si N-N heterodiodes hare been built recently which show promise as high-speed logic devices. Low-resistivity germanium is deposited on silicon substrates held at temperatures above the germanium melting point and an alloyed heterojunction formed. The diodes are fabricated from this material using conventional mesa techniques. Over-all device qualify has been greatly improved by the use of epitaxial silicon substrates, that is, a subsirale consisting of a film of thin, high -resistivity silicon on a thicker Piece of low-resistirily silicon crystal. A semimpirical device design equation has been devised which predicts switching performance fairly well within the range of resistivitics and geometries employed. Switching times 01 0.9 ns and PIV 's of —20 v are typical of the better 10-ma diodes. Switching times as low as 0.5 ns have been observed for 10-ma diodes and as low as 2.8 ns for 200-ma diodes. With further development it should be possible to improve switching speed by a factor of four. IN our laboratory, Ge-Si heterodiodes have been built recently which show promise as high-speed logic devices. The diodes have been built using a process reported in some detail in an earlier publication.' The process in short involves alloying a thin film of low-resistivity germanium into a silicon substrate. the germanium having been transported and deposited by the well-known Theuerer halide reduction process.2 This process contrasts with that reported earlier by Oldham who used an essentially conventional direct epitaxial deposition technique.3 Oldham's process, unlike ours, requires cleavage of the silicon sample inside the reactor furnace the instant prior to deposition. Our process has the advantage of yielding large-area macro-scopically plane heterojunctions. Heterodiodes in general have several interesting properties. Without attempting to summarize the theory of heterojunctions.4 two of these properties which have direct relevance should be mentioned. First, N-.V and P-P heterojunction diodes rectify alternating current. Provided that either the band gap or the electron affinity of the two materials is different (which in general is the case), electronic barriers will exist in the junction band structure. When the device is sufficiently forward-biased, the barriers shift so as to permit current flow, and when it is reverse-biased. the barriers block current flow. Second, for N-N and P-P heterodiodes. the foward-conduction process involves majority carriers only. Consequently. when such a device is turned off. there is no minority-carrier storage and hence the diodes switch on and off quite rapidly. As we have reported earlier. N-P and N-N Ge-Si heterodiodes have been built in this laboratory. As one would predict from theory, the N-P heterodiodes were rather slow in turning off while the N-N's were quite fast. Similarly, the turn-off time of the N-P's increased rapidly with forward current while that of the N-N's was independent of forward current. Both N-N's and N-P's were moderately photosensitive. Photocurrents resulting from normal room illumination were as high as 1 µa at 1 v for small-area devices. The most disappointing parameter of the early N-N devices was reverse leakage.' The reverse characteristic was invariably "soft" and leakage at only several volts reverse bias was intolerable. The reverse characteristic was greatly improved by using higher-resistivity silicon substrates. Leakage becomes large at voltages about one third of the avalanche voltage one would expect of a P-N homo-junction formed on silicon of the same resistivity. Thus leakage could be reduced to reasonable limits by using unconventionally high-resistivity silicon. Medium-power diodes formed on 30 ohm-cm substrates leaked typically 15 to 50 µa at 100 v reverse bias. The use of high-resistivity silicon substrate material, however, created a new problem. In order to have an acceptable forward-conductance characteristic. the area of the diodes had to be increased. With this increase in area, the capacitance increased. Switching time for N-N heterodiodes is essentially a linear function of capacitance. Thus when the resistivity was raised. so was the switching time. A SEMIEMPIRICAL HETERODIODE DESIGN EQUATION As a result of our experiments with a limited range of diode geometries and resistivities. a semi-

Jan 1, 1965

For the benefit of those of our members who are considerable holders of securities, but owing to their isolated situations are not in-close touch with the metropolitan market and current quotations, we are publishing two very interesting graphs, showing the course of the bond and stock markets in New York over a long period. These graphs are furnished through the courtesy of the financial department of the New York Tribune.

Jan 5, 1919

For the benefit of those of our members who are considerable holders of securities, but owing to their isolated situations are not in close touch with the metropolitan market and current quotations, we are publishing two very interesting graphs, showing the course of the bond and stock markets in New York over a long period. These graphs are furnished through the courtesy of the financial department of the New York Tribune.

Jan 7, 1919

For the benefit of those of our members who are considerable holders of securities, but owing to their isolated situations are not in close touch with the metropolitan market and current quotations, we are publishing two very interesting graphs, showing the course of the bond and stock markets in New York over a long period. These graphs are furnished through the courtesy of the financial department of the New York Tribune.

Jan 12, 1919

For the benefit of those of our members who are considerable holders of securities, but owing to their isolated situations are not in close touch with the metropolitan market and current quotations, we are publishing two very interesting graphs, showing the course of the bond and stock markets in New York over a long period. These graphs are furnished through the courtesy of the financial department of the New York Tribune.

Jan 6, 1919